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1. Introduction

As can be inspected from the literature, there were rising concerns in the mid-s, regarding the plentiful of the waste being produced by the chemical industry [1, 2]. A paradigm change was undoubtedly desirable, from the old-fashioned perceptions of reaction selectivity, and efficiency which emphasis fundamentally on the chemical yields, to one that allocates the value to the enlargement of the bulk raw materials exploitation, avoidance of the utilization of the hazardous chemicals/reagents/solvents and also preventation of the waste being formed within the boundaries of environmental awareness. To this context, in , the term sustainable development was coined by Brundtland, in his report; he mainly focused on the emergence of the societal and industrial development to afford an escalating global population with a suitable value of life in such a way that it should be sustainable over a long period of time [3]. Therefore, complete balance necessities to be found among the three Ps-planet, people, profit i.e. environmental impact, societal equity and economic development. More specifically, in sharp contrast to the green chemistry, sustainable development also comprises an economic factor and if a technology is not economically viable, it could not be sustainable for a long time. Remarkably, a tremendous curiosity in sustainable and green progress, united with a cultivating concern for the climate change, has engrossed attention on resource competence and also driving the shift from a conventional linear flow of bulk materials in a “take−make−use−dispose”economy, towards the greener and even more sustainable globular economy. Interestingly, since the 12 principles of green chemistry (Prevention of waste; Atom economy; Less hazardous chemical syntheses; Designing safer chemicals with fewer hazards; Safer solvents and auxiliaries; Design for energy efficiency; Use of renewable feedstocks; Reduce derivatives during synthesis; Catalysis; Design for degradation; Real-time analysis for pollution prevention; Inherently safer chemistry for accident prevention), postulated by Anastas & Warner in [4], scientists around the world are trying to reduce the volatile organic solvents (VOCs) which generally are the major portion (approx. 80% of the total content) of the reaction vessel as compare to the reactants/reagents, and also has the tendency to escape into the environment, which in turns contribute to ozone depletion as well as smog in urban areas, and hence extremely dangerous for mankind [5]. Therefore, great efforts are being put forward to reduce these hazardous VOCs, and the corrosive acid catalysts, participating in the reaction to make the chemical processes even more sustainable and environmentally friendlier [6]. To this context, over the past few decades, several surrogates for instance water, ionic liquids, supercritical fluids, and switchable solvents in addition to many green strategies such as ultrasound, flow chemistry, biocatalysis, microwaves, and multi-component etc., have successfully been developed [7, 8, 9]. Generally, water is thought to be an archetype solvent as it enjoy many classical properties, nonetheless it not only suffer from insolubility issues with the majority of organic compounds but also has a difficulty of removing it after the completion of the reaction because of its high boiling point, and even in many cases compounds gets decompose into the water in addition, some reactions for example amidations and transesterifications, can not be performed in water because of competing product hydrolysis [10]. On the other hand, supercritical fluids which possess low vapor pressure along with the advantages of easy disposal/removal, and recycling, are thought to be the best eco-friendly substitutes of VOCs, but, they requires more sophisticated equipment to perform the reaction. To this context, researchers turn their attention towards the ionic liquids due to their remarkable physiochemical properties but owing to their high cost as well as involvement of the non-renewable resources besides purification before their usage make them of bit doubt from green perception [11]. Consequently, bearing in mind, the urgency of the suitable alternative green solvents in place of conventional solvents to carry out the crucial synthetic transformations for sustainable development in R and D and also for the chemical industry, Abbott’s discovery of the deep eutectic solvents (DESs), also known as low transition temperature mixtures (LTTMs), or low-melting mixtures (LMMs) or deep eutectic ionic liquids (DEILs), has become one of the strongest pillars to the modern synthetic community. Generally, in DES, two/three components are mixed in an appropriate amount to generate a eutectic mixture with lower melting point as compare to the individual components being used [12, 13, 14, 15]. As a consequence, an infinite number of melts involving different compositions/components with distinctive properties like price of the raw materials, melting point, polarity, dissolving ability etc., can be accomplished effortlessly. Interestingly, because of the involvement of non-covalent interactions including hydrogen bonds, it has been noticed that the melting points of the DESs are generally below 100°C, even some of them are liquid at room temperature, and they have been the role model among the greener solvents over the past two decades to both academic as well as industrial community because of their remarkable properties and benefits such as biodegradability, low cost and low vapor pressure in addition to non-toxicity and good thermal stability. Among the DESs, a low melting mixture of DMU/TA can be regarded as the solvent of the 21st century, as it hold the following features: (i) Generally, it does not require tedious work-up after the reaction is being completed, rather, just filtration after addition of the water to the reaction mixture while hot, furnishes the analytically pure compounds and most of the time no need of chromatographic purification but simple recrystallization provides the pure form of the required products; (ii) the melting mixture can willingly be recovered and recycled several times without any substantial loss in the activity; (iii) the reaction cleanly underwent towards the product formation at faster rate as compare to the known procedure, and mostly better yields are obtained under operationally simple reaction conditions; (iv) No additional catalyst and solvents are needed in this method, as in conventional procedure, generally both, the corrosive catalysts as well as hazardous, flammable, and volatile organic solvents are being employed; (v) No inert atmosphere is required for a reaction to be successfully completed in parallel yields; (vi) This method also provide good selectivity and also exhibit excellent functional group tolerance; (vii) Easy preparation of the melt from the bulk renewable resources and no further purification before its utilization is needed; (viii) improved safety and very simple handling as comparison to the conventional practices.

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Bearing all the above mentioned applications and peculiar physiochemical properties of the DMU/TA melt in mind, which we still feel is immature, although employed for a variety of successful reactions for instance Diels-Alder reaction, Stille, Sonogashira, Suzuki, and Heck coupling reactions, Biginelli reaction, 1,3-dipolar reaction, in addition to its applicability for the synthesis of quinolines, arylhomophthalimides, prymidopyrimidinediones, tetrahydropyrimidinones, hydantoins, dihydropyrimidinones, quinazolines, and a variety of functionalized indole systems with excellent selectivity in decent yields. Interestingly, the beauty of this method is its double and triple role in the reaction vessel to facilitate the accomplishment of the reactions in a clean and smooth fashion without the involvement of any catalyst/additives or solvent. In short, after a brief introduction related to the sustainability and green synthetic approaches, herewith, we have tried to display a deep survey of what has already been done in this field, and open the opportunities to the young researches to find out the new advances by employing this DES and also medium engineering might be utilized to optimize the synthetic utility of various other combinations of the DESs. Green chemistry 12 principles as well as the achievements made by employing a low melting mixture of DMU/TA in the domain of synthetic organic chemistry are displayed in the Figure 1.

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2. Construction of indole systems under a low melting mixture of DMU/TA

The name indole was originated from portmanteau, a combination of both the words, indigo and oleum which was first isolated from the indigo dye, while treating it with oleum [16, 17]. As can be inspected from the literature, indole scaffold, a notable privileged lead bicyclic aromatic system (10π-electrons), formally known as benzopyrrole, have immeasurable potential applications ranging from the broad-spectrum biological (e.g. anti-HIV, antiviral, antimicrobial, antidiabetic, antimalarial, anti-cholinesterase, anticancer, anti-inflammatory, antioxidant, anti-tubercular, anti-hypertensive, anti-convulsant, anti-analgesic, and anti-depressant activities etc.), agrochemical and clinical applications to the novel therapeutic agents in addition to their usage as dyes, and smart functional materials as well [18, 19, 20]. Interestingly, this venerable heterocyclic moiety is not only a part of several important drug molecules and remarkable receptors in host-guest chemistry but also reside in a variety of medicinally active natural products for instance strychnine, reserpine, alstonine etc.; widespread in diverse species of animals, plants, marine organisms, and the part of lysergic acid diethylamide (LSD) as well [21]. More interestingly, they have inimitable property of mimicking the structure of peptides and nicely bind to the enzymes, in addition to exhibit the momentous pharmacological, physiological, synthetic and industrial applications [22]. A list of some important biologically active molecules (1–12) containing the indole moiety is depicted in the Figure 2 [23, 24].

The typical Fischer indolization (FI) reaction involving arylhydrazine (13) and aldehyde/ketone (14) in the presence of appropriate acid or acid catalyst along with its systematic mechanistic pathway is displayed in the Figure 3. Although, a number of pathways were anticipated for the FI, but the one proposed in by G.M. Robinson and R. Robinson was the most accepted by the scientific community as it was established by both kinetic as well as the spectroscopic means (Figure 3) [25]. The mechanism for this particular reaction commence with the activation of the carbonyl carbon of 14 through the protonation with acid/acid catalyst, employed in the operation, which on further reaction with 13 provide the N-arylhydrazone intermediate (17). Next, the intermediate (17) afforded the ene-hydrazine intermediate (18) by means of tautomerization, which upon subsequent [3,3]-sigmatropic rearrangement, distracting the aromaticity of aryl ring system, followed by rearomatization deliver another intermediate (20) through the bis-iminobenzyl ketone (19). Latter furnishes the required indole derivatives (15) by virtue of cyclization followed by the loss of ammonia molecule via21 (Figure 3). Interestingly, it has been observed that the reaction conditions as well as the nature of the substrate decide the rate determining step (rds). Generally, ene-hydrazine intermediate (18) formation or the [3,3]-sigmatropic rearrangement step has been noticed as the rate-limiting step depending on the situation, as discussed further below. The [3,3]-sigmatropic rearrangement has been observed as rate determining step, in a specific case of α-N-acyl hydrazones in addition to weak acidic solutions as well as when ammonia elimination is prevented due to steric effects [25]. Whileas, in most of the cases including the strong acidic condition favors the ene-hydrazine (18) formation as the rds-step of the reaction. More specifically, unsymmetrical 1,l-diarylhydrazines under strong acidic condition provide the indolization at most activated ring (i.e. most susceptible to the protonation), whileas under neutral reaction conditions almost equal amount of isomers are generally being formed.

Accordingly, synthetic chemists have long sought approaches for the construction of indole architectures, and a plethora of methods continue to be reported in this trend [26]. Hardly surprising, to date, a myriad of methods involving both intra- and intermolecular transformations for the construction of indole derivatives, particularly the usage of named reactions such as, Gassman, Bartoli, Thyagarajan, Julia, Schmid, Wender, Couture, Kihara, Nenitzescu, Engler, Saegusa, Liebeskind, Sundberg, Hemetsberger, Magnus, Feldman, Reissert, Makosza, Leimgruber–Batcho, Watanabe, Larock, Yamanaka–Sakamoto, Hegedus–Mori–Heck, Fürstner, Castro, Natsume, Nordlander, and so on, have successfully been employed [27]. But, to our best knowledge, despite its numerous complications, rearrangements, and also mechanistic mysteries, Fischer indole protocol, an old yet effective procedure which involve a pericyclic tool namely, [3,3]-sigmatropic rearrangement, remains the epitome for the scientific community around the globe to assemble diverse indole and its congeners [28]. Although, a variety of acid catalysts for example HCl, AcOH, PPA, TiCl4, ZnCl2, SOCl2, PCl3, TsOH, H2SO4, mont-morilloniteclay zeolite etc., have been employed to synthesize the indole framework using FI protocol, but simple, and eco-friendly methods which involve non-hazardous, inexpensive and easily accessible chemicals as well as reagents utilizing the environmentally benign practices are always of particular interest. In this regard, König’s group in , first time reported a green approach by employing the FI strategy under a low melting mixture of dimethyl urea (DMU):L-(+)-tartaric acid (TA) in (7:3) ratio to yield a range of indole derivatives in good-to-excellent yields [24]. The beauty of this particular green method relies on the fact that, a clean low melting mixture is generated just by heating the two components in appropriate amount at much lower temperature than its individual components, and can be used without further purification. Herewith, the low melting mixture, acts as mild acidic catalyst (pH 3.7) as well as solvent to furnish the required indoles with great functional group compatibility and selectivity. As can be seen from an inspection of the Figure 4, these authors prepared a range of functionalized indole systems (22–47) in decent yields using acyclic and cyclicketones in addition to cyclic enol ethers for instance dihydrofuran and dihydropyran. Fascinatingly, optically active ketone deliver the indole with retention of the configuration. Moreover, indolenines (31), was also prepared through this powerful technique in respectable yields under mild reaction conditions (Figure 4). Besides, hormone melatonin (25) and dimebon (26) were also obtained by utilizing this wonderful green approach as a crucial step (Figure 4). Inspiring form this simple yet powerful procedure and also from the applications of the indole moiety containing molecules, two years later to this report, in , Kotha and his teammates have successfully employed this strategy for the synthesis of C2-and Cs-symmetric bis-indole systems (52, 53, 58, 60–62) from bicyclo-3,7-diones and 1-methyl-1-phenylhydrazine under DMU/TA (7:3) reaction conditions (Figure 5) [29]. Later on, Kotha’s team nicely expanded this delightful method for the generation of a variety of carbazole derivatives (32–35) including pyrano-carbazole (36) and aza-cyclophane based carbazoles (37 and 38) as depicted Figure 4 [30, 31, 32] in Figure 4. Interestingly, utilizing this tactic, they have also prepared carbazole-based natural products such as tijapinazole D (32) and tijapinazole I (33) in addition to the crown-based indolocarbazole (47). Moreover, in the laboratory of Kotha’s group, diverse hetero-polycyclic compounds (39–43) in addition to the propellane derivatives (44) have been assembled by using ring-closing metathesis (RCM) and Fischer indolization in a low melting mixture of DMU/TA as crucial steps, (Figure 4) [33, 34, 35]. Keeping the importance of C3-symmetric molecules in medicinal and bioorganic chemistry besides their vital role in material science and technology, the same group has also prepared star-shaped C3-symmetric compounds 45 and 46 involving cyclotrimerization and DMU/TA mediated indolization approach (Figure 4) [36]. Furthermore, as can be inspected from the Figure 5, they design and constructed varied cyclophane derivatives (48, 49, 54, 55 and 59) through the involvement of the Grignard reaction, RCM and a low melting mixture mediated indolization sequences in respectable yields because of their applicability in supramolecular chemistry [37, 38, 39, 40, 41]. In addition to these, Kotha’s group has also prepared diverse polycyclic mono- (50, 56, 63) and bis-indole derivatives (51, 57, 58, 64) by means of a deep eutectic mixture of DMU/TA (70:30) under operationally simple reaction conditions [42, 43, 44, 45].

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3. Synthesis of bis-(indolyl)methane, indenylindoles and 2,2-disubstituted indolin-3-ones

In recent past, bis-(indolyl)methanes (BIMs) have attracted a tremendous attention of the research community due to their potential applications both in pharmaceuticals and agrochemicals besides their activity in breast tumor cells, bladder cancer and also inhibits proliferation practice as well. Moreover, they display antitumorgenic, antibiotic, antimicrobial activity and anti-inflammatory activities etc., and are mostly found in marine natural sources. Fascinatingly, getting inspired from the above applications and also other, if any, the group of Nagarajan constructed the diverse BIMs (67) including the natural products arsindoline A and B via a green protocol in the presence of DMU:TA (70:30) (Figure 6) [46]. Surprisingly, the BIMs were not formed when instead of aldehydes (66); cyclicketones (68) were treated with indole derivatives in the Kotha’s laboratory, rather they received indenylindoles (dienes) 69 under parallel reaction conditions (Figure 6) [30]. On the other hand, it has been found that, numerous medicinally active natural and non-natural products possess 2,2-disubstituted indolin-3-one scaffold in addition to their usage as the key building blocks in the total synthesis of diverse indole alkaloids. In this regard, Xie’s group involved a deep eutectic mixture of DMU/TA to furnish a range of 2,2-disubstituted indolin-3-one derivatives (72) as displayed in the Figure 6 [47].

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Synthesis of heterocyclic compounds has always been of prime importance to the research community because of their vital role in a numerous areas ranging from material sciences and technology to the pharmaceutical and agrochemical industries. To the best of our knowledge, to date, a choice of drugs containing heterocyclic scaffolds are available in the world market, and many hundred are under clinical trials around the globe. Therefore, there are always high demands to develop novel strategies for the generation of heterocyclic systems particularly involving milder reaction conditions in an environmentally friendlier manner from easily assessable bulk materials. To this context, although a number of methods having several advantages and disadvantages are available in the literature but in recent years, the deep eutectic solvents have changed the scenario of modern synthetic chemistry by providing a plethora of green approaches towards the construction of these valuable molecules. Among the heterocyclic systems, quinoline scaffold has received a considerable amount of interest because of its availability in a plethora of bioactive molecules. A very simple yet effective green procedure for the synthesis of a variety of quinoline derivatives (75) have been developed by Zhang and his co-workers with the involvement of a low melting mixture of DMU:TA (70:30) in moderate-to-excellent yields in a Friedländer fashion (Figure 7) [48]. On the other hand, the Biginelli procedure, a multi-component reaction, has been employed for assembling the dihydropyrimidinones (DHPMs) under a green reaction conditions by Köenig’s team because of their utility in calcium channel blockers and also as HIV inhibitors and anticancer agent (Figure 7) [49]. Captivatingly, this procedure works equally well with masked aldehydes to furnish the required DHPMs in reasonable yields. In another study, the same group has utilized this powerful green methodology for assembling diverse functionalized pyrimidopyrimidinedione derivatives (85) with the help of Biginelli reaction in which the low melting mixture play a triple role such as solvent/catalyst/reagent (Figure 7) [50]. In this study, although, they have tried several low melting mixtures but DMU/TA in a ratio of 7:3 provided the best results.

In a separate study, Krishnakumar et al., has reported a green chemical procedure for the construction of N-arylhomophthalimides (83) by employing the Michael addition reaction of the Michael-donor (homophthalimides) 82 with Michael-acceptor (chalcones) 81 in DMU:TA low melting mixture (Figure 7) [51]. In this report, the authors have screened various reaction conditions but the mention conditions provided the good results for both electron withdrawing as well as electron donating groups containing contestants.

The hydantoin and its congeners are the key scaffolds from biological point of view as they are the part of various molecules which exhibit a range of activities for instance antidepressants, antiulcer, antidiabetic agents, anticonvulsant, antiarrhythmic, and antiviral etc. Moreover, this moiety also play a significant role in agrochemistry, cosmetic industry, dye-sensitized solar cells, chiral auxiliaries and also used as the intermediates for the generation of enantiomerically pure natural and non-natural α-amino acids by means of the dynamic kinetic resolution. Therefore, keeping the consequence of these molecules in mind, König’s group in developed a simple and eco-friendly method for the synthesis of 1,3,5-trisubstituted hydantoin derivatives (93/94) in excellent yields by means of DMU/TA melt-mediated green approach (Figure 7) [52]. Interestingly, during their experimentation, they noted down good diastereoselectivity in which anti-isomers were isolated in major amount whileas syn-diastereomers were obtained as minor products, confirmed by nuclear overhauser effect (NOE) and X-ray analysis means. On another front, quite recently, Kotha’s team has reported mono-hydantoins as well as thiohydantoins by means of three component reaction under low melting mixture of DMU/TA with electron neutral, electron donating, and electron withdrawing groups possessing aniline derivatives (Figure 7) [53]. Finally, the tetrahydropyrimidinones (80) and quinazoline derivatives (88) have been reported, by the groups of Baskaran and Zhang, respectively by employing the same low melting mixture of DMU/TA under similar reaction conditions as can be inspected from the Figure 7 [54, 55].

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4. Conclusions and outlook

In summary, a novel method involving DMU/TA as a low melting mixture has comprehensively been revealed in this chapter, depicting its pivotal role in the heart of modern synthetic organic chemistry particularly for the generation of a variety of valuable heterocyclic systems. Herein, we have disclosed, a decade advancements made in this field since its inspection (). As discussed above in detail, this simple, environmentally benign, cost effective, and productive method has already been shown its impact in the domain of modern preparative chemistry in general, and green chemistry in particular. We assure that this chapter based on greener transformations, will not only help the readers for complete understanding of a low melting mixture of DMU/TA, and its contribution towards the vital synthetic organic transformations, but also would inspire the motivated researchers to exploit the masked opportunities. More importantly, this method might provide a new way to the chiral catalyst mediated reaction since herewith, chiral tartaric acid is part of the melt, and may act as a valuable handle for the generation of chirality in a molecule under the operation.

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Acknowledgments

Dr. Rashid Ali is grateful to DST-SERB New Delhi for financial support (Project File no. ECR//). In addition, he also thanks Jamia Millia Islamia, New Delhi, India, for providing the necessary research facilities.

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This application is a division of prior U.S. application Ser. No. 761,511 filing date Aug. 1, , now U.S. Pat. No. 5,039,759. FIELD OF THE INVENTION This invention pertains to the preparation of high solids coating compositions and more particularly to the use of substituted ureas as reactive cosolvents and/or reactive diluents together with water to form the liquid vehicle for the application of film forming polymers. The resultant water borne high solids coating compositions can be either solutions or dispersions depending upon the particular polymer and substituted urea chosen as the reactive cosolvent or reactive diluent. Water borne high solids coating compositions as used herein are coatings in which the principal application medium is a mixture of water and an essentially non-volatile organic material capable of reacting with the base film forming polymer and/or crosslinking agent. They may be of two types (1) dispersions of organic polymers (latex) to which the co-reactive organic (reactive diluent) materials may also serve as filming aids, antifreeze agents, defoamers, etc.; and (2) solutions of organic polymers in which the thinner is a mixture of an organic co-reactive material (reactive cosolvent) and water. It is the intent of this invention to disclose the preparation of water borne high solids coating compositions in which the reactive organic material is also a solvent or dispersant as well as essentially non-volatile and as a consequence may of the problems associated with the prior art "organic solvent borne" and "water borne coatings" are circumvented. BACKGROUND ART The employment of solutions or dispersions of organic polymers dissolved or dispersed in volatile organic liquids to formulate organic polymer coating compositions and their subsequent application onto various substrates as coatings thereon requires the handling and evaporation of large quantities of organic solvents. Because of the undesirable ecological and environmental problems and problems associated with the exposure of workers in the coatings industry to the organic solvents, alternate coating methods have become a necessity. Consequently there has been a shift to coating techniques where water is substituted for much of the volatile organic solvent or diluent in the coating compositions. These are often referred to as "water borne" coating compositions even where water is not the sole dispersing or dissolving vehicle for the organic polymer. The rise in the use of water borne coatings has introduced problems peculiar to systems containing a mixture of water and organic cosolvent or dispersant. These problems arise form the fact that the evaporation of water is dependent upon the ambient humidity conditions, and the relative rates of evaporation of the organic solvent vis a vis water. Polymers which were developed for water borne coatings systems were often based on the chemistry of the polymers used in existing solvent systems. Thus alkyds, epoxy esters, and oil modified polyurethanes originally developed for nonaqueous formulations were modified for aqueous formulations by the incorporation of acid moieties. One of the earliest techniques for the incorporation of acid groups was to maleinize a long oil alkyd or epoxy ester. In this process the alkyd or polyester is reacted at 200°-260° C. for 30-60 minutes with maleic anhydride in the presence of an excess of drying acid. The excess drying acid serves as a reactive chain transfer agent to prevent premature gelation. Accelerators, commonly iodine or sulfur dioxide, were often employed in this thermal polymerization process. The maleic anhydride moiety (now a succinate) is hydrolyzed and neutralized with volatile and/or fixed bases to render the polymer soluble in the water/cosolvent mixture. Enough unsaturation is left in the resin for siccative cross-linking of the final film. Another early technique was to use dimethylol propionic acid (derived by condensation of propanal with formaldehyde followed by oxidation). This unique acid-diol along with the monoglyceride is reacted with phthalic anhydride or isophthalic acid to form a polyester/alkyd having free acid groups. The carboxyl moiety of the dimethylol propionic acid is sterically hindered and does not esterify during the polymerization but reacts subsequently with the neutralizing base thus solubilizing the polymer. Oil modified urethanes are produced by substitution of a diisocyanate for the phthalic anhydride. The urethane reaction is carried out at moderate temperatures (50°-100° C.). These types of polymers form the basis of water born coating materials used today in low cost product and consumer finishes. The next innovation was the development of resins that could be cross-linked by reaction with aminoplasts. These resins contained available hydroxyl functionality as well as an ionizable moiety. The acid containing polymers were used early in electro-coating, and were synthesized by partially esterifying an epoxy resin with a drying fatty acid followed by reaction with trimellitic anhydride. The carboxyl groups incorporated were neutralized in the usual manner. Esterification of the partial epoxy ester with para-aminobenzoic acid in place of trimellitic anhydride yielded early cationic polymers. The cationic polymers are, commonly neutralized with acetic, lactic and other volatile organic acids to attain solubility. Today the resins are highly specialized for their intended applications. Techniques for the incorporation of the ionic moieties include graft polymerization of carboxylic vinyl monomers to the base epoxy and polyester backbones as well as the development of functionalized telechelic polymers from readily available monomers. As the coatings industry moves, because of environmental and health regulations, from the more conventional solvent coatings to water borne and high solids systems, there has developed a need for new water borne reactive diluents and reactive cosolvents to serve this emerging technology. At the present time many of these end use needs are being addressed by solvents and reactive materials already in commerce. However, none of these materials ere designed for these applications; rather the industry adapted what was available. Today the state of the art has advanced to the point where the real needs are apparent and further improvement in the coating systems requires improved reactive co-solvents and reactive diluents as well as polymers. For example many of the prior art resin solvents used in water borne coating systems led to degraded polymer properties in the final coatings. Water borne coatings as used herein are coatings in which the principal application medium is water. They may be of two types: (1) dispersions in which organic materials are added at low levels as filming acids, antifreeze additives, defoamers, etc.; (2) solutions in which part of the application medium is an organic solvent. Performance requirements demand that coatings resist the adverse effects of water in the environment and yet in water born solution coatings technology they are applied from a solution which contains a large fraction of water. This requires that the coatings are not truly water soluble; rather, a number of techniques are employed to maintain solubility throughout application and film formation. The techniques commonly employed are: (a) Ionic groups are incorporated into the polymer, (b) A means of crosslinking the film after application is employed, (c) A cosolvent is used to maintain solubility of the polymer throughout the film forming process. In the case of solution coatings, it is imperative that during the drying stage, after a particular substrate has been covered with a layer of coating composition that a single phase be maintained until the water and cosolvent components have evaporated away leaving the now insoluble organic polymer deposit. It is also necessary that the cosolvent be miscible with the water and that the organic polymer coatings be soluble in the cosolvent. The relative volatility of the cosolvent with respect to water involves vapor pressure, molecular weight and the relative humidity during the drying operation. Under high humidity conditions the rate of water evaporation becomes very slow while the evaporation of the volatile organic co-solvent remains relatively constant. Consequently under conditions of high humidity, imperfections develop during film formation which are detrimental to the overall performance of the coating. These imperfections which form under high humidity conditions are related to the limited solubility of the film forming polymers in the resulting water rich composition. The problem becomes understandable when it is cast in terms of the phase chemistry of a water borne coating. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a phase diagram of a hypothetical water born system containing water, a cosolvent and a film forming polymer. FIG. 2 is a phase diagram of a hypothetical water borne high solids dispersions coating composition containing water, a reactive diluent, and a polymer. FIG. 3 is a phase diagram of a water borne high solids solution coatings composition containing water, a reactive cosolvent and a polymer. A simplified phase diagram of a hypothetical water borne system is illustrated in FIG. 1. FIG. 1 is a phase diagram representing water as A, the cosolvent as C and the film forming polymer as B. The area of a single phase, 2, is separated from the area of two phases, 4, by the curved line A-A'-B. The point E represents the application composition of the water born system. In the case of a volatile cosolvent under ideal conditions (low humidity) the straight line E-B represents the changing composition during film formation. Under conditions of high humidity the dotted line E-S-B illustrates that the film formation pathway has taken an excursion into the two phase region which causes premature coagulation of the film forming polymer and results in coating imperfections. The points illustrated by FIG. 1 are: (i) The cosolvent is miscible with water; line AC is in the one phase region in its entirety. (ii) The coatings polymer is soluble in the cosolvent; line CB is in the one phase region in its entirety. (iii) Film formation must take place in such a manner that the phase boundary, A-A'-B, is not crossed. (iv) Lastly, it is often desired to clean the application equipment with water along, which means the phase boundary, A-A'-B, must be avoided during cleaning; line EA. In real systems the phase diagrams are more complicated than illustrated. The shape of the two phase region is more irregular and is not as predictable as indicated. The model does, however, provide a framework for understanding solubility relationships and provides a common basis for understanding the objectives of the present invention. It is an object of this invention to provide non-volatile, reactive organic materials which are also solvents or diluents suitable for the preparation of water borne high solids coating compositions. It is another object to provide reactive solvents/reactive diluents which serve to provide high solids coating compositions in the form of either solutions or aqueous dispersions. It is still another object to provide reactive solvents/reactive diluents which will not degrade the polymers used in the coatings compositions or the properties of the finished coating. Other objects will become apparent to those skilled in the art upon a further reading of the specification. Water borne high solids coatings avoid many of the problems referred to earlier. Again the advantage of water borne high solids coating compositions can be illustrated by use of phase diagrams. Since water borne high solids coatings may be either of the dispersion type or the solution type, two different phase diagrams will be required to understand the phase relationships. FIG. 2 is a simplified, hypothetical phase diagram of a water borne high solids dispersion coating composition, representing water as A, the reactive diluent as C, and the polymer including the crosslinker as B. The area of single phase, 2, is separated from the area of two phases, 4, by the curved line A-A'-B. The point E represents the application composition of the water borne high solids dispersion coating. The straight line E-D represents the changing composition during film formation; the dashed line E-B is the film forming pathway that the water borne coating of the prior art would take. The salient features of the phase diagram area: (i) The reactive diluent need not be totally soluble in water, but rather is distributed between the aqueous phase and the polymer phase. (ii) The reactive diluent is essentially non-volatile and becomes a part of the final coating and consequently the total non-volatiles (total solids) in the composition in the final film, point D, is equal to the sum of the polymer including the crosslinker and the reactive diluent. (iii) The film forming pathway proceeds from a homogeneous, stable two phase composition to a single phase and therefore the reactive diluent must be compatible (soluble in) with the polymer phase. FIG. 3 is a phase diagram of a water borne high solids solution coating composition representing water as A, the reactive cosolvent as C, and the polymer including the crosslinking agent as B. The area of single phase, 2, is separated from the area of two phases, 4, by the curved line A-A'-B. The point E represents the application composition of the water borne high solids solution coating. The straight line E-D represents the changing compositions during the film formation process. The notable features of FIG. 3 are: (i) The reactive cosolvent is generally miscible with water, line A-C is in the one phase region in its entirety. (ii) The coatings polymer is soluble in the reactive cosolvent; line CB is in the one phase region in its entirety. (iii) Film formation can result only from the removal of water (evaporation) and hence the film formation remains in the single phase region thus avoiding the high humidity film defects of the prior art. (iv) The reactive cosolvent is essentially non-volatile and becomes a part of the final coating and consequently, the total non-volatiles (total solids), in the film composition, point D, is equal to the sum of the polymer including the crosslinker and the reactive cosolvent. In both cases the reactive diluent and/or reactive cosolvent becomes a part of the final coating and as such must contribute to, not detract from, the overall performance of the coating. The reaction product of polymer, reactive diluent and/or reactive cosolvent with the crosslinking agent must have suitable properties such as toughness, adhesion, impact resistance, abrasion resistance, scratch resistance, resistance to solvents, chemicals, acids, bases, and have good color, gloss and stability as is required according to the end use application. This is well understood by those skilled in the art. SUMMARY OF THE INVENTION Water borne high solids coating compositions meeting the objects above can be prepared by blending; (1) at least one water dispersible, crosslinkable organic polymer free of amide groups; (2) water; (3) at least one reactive urea derivative having the generic formula: ##STR1## wherein each of R1, R2, R3 and R4 is a monovalent radical selected from the class consisting of hydrogen, alkyl groups having 1 to about 10 carbon atoms, hydroxyalkyl groups having 2 to about 4 carbon atoms and one or more hydroxyl groups, and hydroxypolyalkyleneoxy groups having one or more hydroxyl groups and with the provisos that: (i) said urea contains at least one --NH and one --OH group or at least two OH groups or at least two --NH groups; (ii) R1 and R2 or R1 and R3 can be linked to form a ring structure; and (iii) R1, R2, R3 and R4 are never all hydrogen at the same time; (4) A crosslinking amount of a crosslinking agent; and (5) Optionally, a catalytic amount of a crosslinking catalyst. Except for hydrogen, the monovalent radicals may be substituted with ether, halogen, quaternary ammonium, sulfonium, phosphonium and like substituents. Suitable water dispersible organic polymers for use in the present invention include anionically, cationically, and entropically stabilized polymers which contain a plurality of reactive --OH and/or --NHCOO-- groups. The prior art contains a plentitude of routes for incorporation of the entities required to impart homogeneous water dispersibility into various organic polymers. The following list is by no means complete, but will serve to illustrate some of the more important routes to obtain operable polymers. Anionically stabilized polymers were probably the earliest water borne polymers. Hoy et al. (U.S. Pat. No. 3,392,129) teach the use of carboxylation of unsaturated fatty acid esters of polyether polyols and their subsequent neutralization with organic amine bases to render the polymers soluble in a water/cosolvent blend. Hoy and Payne (U.S. Pat. No. 3,440,192) describe the preparation of water borne fatty acid polyesters by the introduction of carboxyl groups. Milligan and Hoy (U.S. Pat. No. 3,412,054) demonstrate the synthesis of water borne polyurethanes via the reaction of dimethyolpropionic acid and subsequent neutralization. Schurmann (U.S. Pat. No. 4,096,127) describes the use of tertiary ammonium dimethyolpropionate to prepare polyurethanes thus avoiding the subsequent neutralization step. Shell Chemical Co. in their trade publication of describe water borne coatings from partial fatty acid epoxy esters and their subsequent reaction with trimelitic anhydride. Jerabek (U.S. Pat. No. 3,984,299) shows the reaction of primary and secondary amines with an epoxy resin to produce a polymer which when neutralized with acetic or lactic acid provides a water borne cationically stabilized polymer. In a like manner Bosso and Wismer (U.S. Pat. Nos. 3,962,165 and 4,959,106) show the reaction of sulfides and phosphines to give products which could be converted to sulfonium and phosphonium water dispersible salts with organic acids. Kempter et al, Fatipec Congress (), describe the preparation of a Mannich base polyamine from bis phenol-A, formaldehyde and a lower alkyl secondary amine; the resultant Mannich base was reacted with an epoxy resin to form a pendant amine containing polymer, which was soluble when acid neutralized in a water/cosolvent blend. Spoor et al (U.S. Pat. No. 3,455,806) show the polymerization of dialkylaminoethyl methacrylate with methyl methacrylate, and hydroxyethyl methacrylate to make a cationically stabilized acrylic polymer. This is the cationic analogue of an anionic acrylate made from methacrylic or acrylic acid and neutralized with amines as described typically by Finn et al. (U.S. Pat. No. 4,136,075). Graetz, et al. (U.S. Pat. No. 4,322,328) describe entropically stabilized water borne latexes from acrylate monomers using the methacrylic acid ester of the monomethyl ether of polyethyleneglycol, mole wt. , as the key generator of the entropic barrier. It describes the use of these sterically stabilized dispersions in water borne coatings. The common feature of all of these methods is that homogeneous water dispersible polymers are obtained each of which is capable of having a plurality of reactive --OH and/or --NHCOO-- groups which provide for inter polymerization with the subject ureas and the cross linking agent. Preferred water dispersible, crosslinkable organic polymers for use in this invention include: Polyester alkyd resins Carboxylated hydroxyl-containing epoxy fatty acid esters Carboxylated polyesters Carboxylated alkyd resins Carboxylated acrylic interpolymers free of amide groups Carboxylated vinyl interpolymers, such as styrene/acrylic copolymers. The ratio of the amounts of water and reactive diluent or cosolvent used to prepare the coating compositions is dictated by the type of water borne coating desired. Thus in the aqueous dispersion type, the amount of reactive diluent is usually determined by the film properties desired. Usually these can be attained by ratios of reactive diluent/water in the range of about 5/95 to about 30/70. On the other hand in the solution type the ratio of reactive cosolvent to water is limited by the solubility characteristics of the water dispersible polymer. Thus a hydrophilic polymer would require less reactive cosolvent while a more hydrophobic polymer would require more. Generally, polymers of these types are soluble in a blend of reactive cosolvent/water of about 20/80 to about 60/40. In practice the base coating may be formulated at rather high ratios of reactive cosolvent/water i.e., about 60/40 to about 90/10 and then let down with water to attain application viscosities. One skilled in the art can easily establish the optimum ratios for a particular coating composition with a minimum of experimentation. The amount of organic polymer used in these compositions is not narrowly critical. However a practical range for the solution type is about 15 to about 45% by weight of polymer with the amount of reactive solvent being about 10 to about 20% by weight, the amount of crosslinker being about 10 to about 30% by weight and the amount of water being about 60 to about 5% by weight. A practical range of organic polymer used for the dispersion type of coating composition is about 35 to about 50% by weight, with the amount of reactive diluent being about 5 to about 20% by weight, the amount of crosslinker being about 5 to about 20% by weight and the amount of water being about 55 and about 10% by weight. The reactive urea derivatives in the coating composition claimed herein can be designated as either reactive cosolvents or reactive diluents depending on the type of coatings formed. In the case of coating compositions which are dispersions, the ureas function as reactant. diluents. In the case of coatings compositions which are solutions, the ureas function as reactive cosolvents. The term reactive is used herein to mean that the urea derivatives can be incorporated into the finished coating by crosslinking agents which cure through NH and/or OH groups. The reactive ureas used in this invention may be represented by the following: N-(2-hydroxyethyl)-N,N'-ethylene urea N-(2-hydroxyethyl)-N'-butyl urea N,N-bis-(2-hydroxyethyl)-N'-butyl urea N,N-bis-(2-hydroxyethyl) urea N,N'-bis-(2-hydroxyethyl) urea N-(2-hydroxy-1-propyl)-N'-butyl urea N,N'bis-(3-hydroxy-2,2-dimethyl-1-propyl) urea N,N'-dimethyl urea tetrakis-(2-hydroxyethyl) urea tris-(2-hydroxyethyl) urea N,N'-bis-(2-hydroxyethyl)-N,N'-ethylene urea N-(2-hydroxyethyl)-N'-methyl urea N,N'-bis-(2-hydroxyethyl)-N-ethyl urea N,N'-bis-(2-hydroxyethyl)-N,N'-diethyl urea N,N'-bis-(2-hydroxyethyl)-N,N'-dimethyl urea N,N,N'-tris-(2-hydroxyethyl)-N'-methyl urea N,N'-diethyl urea N-butyl-N'-(2-ethyl-1-hexyl) urea N-butyl-N'-propyl urea N-methyl-N'-butyl urea N-methyl-N'-2-propyl urea Illustrative of suitable crosslinking agents for the water borne high solids coating compositions described herein are water soluble or water dispersible polyepoxides, such as the glycidyl epoxides or cycloaliphatic epoxides (Arladite® 297, Epon® 582, etc.) and the water dispersible aminoplasts such as the reaction product of an aldehyde (e.g. formaldehyde, acetaldehyde, paraformaldehyde, trioxane etc.) with urea, thiourea, melamine, benzoguanamine, acetoguanamine, dicyandiamine and the like. The aminoplasts may be etherified with a lower alcohol such as methyl, ethyl, butyl, isobutyl, propyl or isopropyl alcohol. Aminoplasts which are of particular value in anionically stabilized water borne high solids coating compositions are the methylated urea-formaldehyde resins, the alkylated benzoguanamines and methylated melamine-formaldehyde resins with the latter being the most desirable. The choice of catalyst suitable for the practice of this invention is dictated by the choice of crosslinking reaction. Thus if aminoplasts are employed to crosslink the organic polymer and reactive urea, an acidic catalyst is preferred. Illustrative of the acidic catalysts of the invention are one or more of the following: alkysulfonic acids such as methane sulfonic acid, ethane sulfonic acid and the like, arylsulfonic acids such as p-toluene sulfonic acid, alkylaryl sulfonic acid, acids such as a C10 to C18 alkylbenzene sulfonic acid, sulfamic acid, dialkyl hydrogen phosphates such as diamyl hydrogen phosphate, aryl hydrogen phosphates such as diphenyl hydrogen phosphate and phosphoric acid itself. Often these catalysts are rendered water dispersible by neutralization with lower alkyl amines. When cationically stabilized water dispersible organic polymers are employed, the basic character of the base resin retards the reaction with an aminoplast and extremely high temperatures must be employed. To circumvent this problem the blocked isocyanates are often employed to crosslink these polymers. The polymer isocyanates have been extensively reviewed by Wicks (Prog. Org. Chem., 3, 73 ()). a blocked isocyanate is an isocyanate adduct which is stable at ambient conditions but dissociates to regenerate isocyanate functionality under the influence of heat. Temperatures of 120° to about 250° C. are necessary to release the blocking groups which are usually volatilized from the coating. The dissociation temperature of blocked isocynates based on commercially utilized blocking agents decrease in the order: epsilon-caprolatam, phenols, methyl ethyl ketoxime, and active methylene compounds. Blocked isocyanates which are stable and water dispersible have been described by Rosthauser and Williams (Proceedings Polymeric Materials Science and Engineering; Vol. 50, pg. 344 ()). Catalysts which promote the urethane reaction are well known to the art and are illustrated by tertiary amines such as triethyl amine, bis(dimethylaminoethyl) ether and the like, organometallic salts of tin, mercury, zinc, bismuth and the like such as dibutyl tin diacetate, zinc octoate, phenyl mercuric acetate and bismuth octoate. The amount of catalyst required to promote the reaction is dependent upon the curing conditions required in the coating process. Those skilled in the art may readily determine the catalyst level with a minimum of experimentation. In practice if a catalyst is desired it is usually in the level of 0.02 to about 1% based on the weight of the water dispersible organic polymer. Background of the curing relations of hexamethoxymethylmelamine may be found in an article by R. Saxon et al. in J. Appl. Poly. Sci. 8, 475 (). In the practice of this invention, one may also employ a mixture of at least one reactive urea derivative and at least one reactive carbamate derivative, the latter having the generic formula: ##STR2## wherein each of R1 and R2 is a monovalent radical selected form the class consisting of hydrogen, alkyl groups having 1 to about 10 carbon atoms, hydroxyalkyl groups having 2 to about 4 carbon atoms and one or more hydroxyls, hydroxalkyleneoxy groups having one or more hydroxyl groups, and hydroxypolyalkyleneoxy groups having one or more hydroxyl groups, and R3 is a monovalent radical selected from the class consisting of alkyl groups having 1 to about 10 carbon atoms, hydroxyalkyl groups having about 4 carbon atoms and one or more hydroxyl groups, hydroxyalkyleneoxy groups having one or more hydroxyl groups and hydroxypolyalkylenoxy groups having one or more hydroxyl groups, with the provisos that said carbamate contains at least one --NH and one --OH group or at least two --OH groups, and that R1 and R2 or R1 and R3 can be linked to form a ring structure. The reactive carbamates used in this invention may be represented by the following: 2-hydroxyethyl 1-butylcarbamate 1-hydroxy-2-propyl 1-propylcarbamate 2-hydroxy-1-propyl 1-propylcarbamate 1-hydroxy-2-propyl 1-butylcarbamae 2-hydroxy-1-propyl 1-butylcarbamate 2-methyl-1-propyl 2-hydroxyethylcarbamate 2-propyl bis (2-hydroxyethyl) carbamate 2-hydroxyethyl 2-hydroxyethylcarbamate 2-hydroxyethyl (2-hydroxyethyl) (ethyl) carbamate 2,3-dihydroxy-1-propyl dimethylcarbamate 2,3-dihydroxy-1-propyl ethylcarbamate 1,3-dihydroxy-2-propyl 1-butylcarbamate 2,3-dihydroxy-1-propyl tetramethylenecarbamate 2-hydroxyethyl bis-(2-hydroxyethyl) carbamate 3-(2,3-dihydroxy-1-propyl) oxazolidone 5-(hydroxymethylene) oxazolidone 3-(2-hydroxyethyl)-5-(hydroxymethylene) oxazolidone 4-(hydroxymethylene) oxazolidone 2-hydroxyethyl carbamate 1-butyl 2,3-dihydroxy-1-propylcarbamate The invention is further described in the examples which follow. All parts and percentages are by weight unless otherwise specified. EXAMPLE 1 Preparation of N-(2-Hydroxyethyl)-N,N'-Ethylene Urea Grams (34.2 moles) of aminoethylethanolamine and grams (34.8 moles) of dimethyl carbonate were charged to a 12-liter, 5-necked flask equipped with stirrer, heating mantle, water cooled condenser, distillation head, thermometer and nitrogen purge. The flask contents were heated to 80° C. and stirred for 3 hours before being allowed to stand overnight. The mixture was heated again while removing methanol and other volatile materials up to 195° C. kettle temperature and 140° C. vapor temperature. A total of grams of condensate was collected. The rest of the material in the flask was subjected to vacuum distillation giving material boiling 210° C. @ 1 mm Hg. A total of g of distillate and 412 g residue resulted from the distillation. The distilled product could be further purified by recrystallization from 2-butanone. EXAMPLE 2 Preparation of N-Hydroxyethyl-N'-Butyl Urea 61.7 Grams (1 mole @ 99% purity) of ethanolamine and 170 grams of dichloromethane were charged to a flask equipped with stirrer, thermometer, feed tank, distillation head and condenser. 101 Grams (1 mole @ 98% purity) of butyl isocynate were fed dropwise with stirring and cooling (dry ice bath) during 1.5 hrs. such that the temperature of the reaction mixture was maintained at about 30° C. At this time some solid had been formed and it was redissolved by heating to 46° C. The mixture was stirred at 46° C. for an additional two hours and then freed of volatile materials by stripping at 90° C. and 2 mm Hg leaving 181 g of solid product. This material could be recrystallized from 2-butanone giving tiny white crystals melting at 67° C. EXAMPLE 3 Preparation of N-Hydroxypropyl-N'-Butyl Urea 75.1 Grams (1 mole) of 1-amino-2-propanol and 180 grams of dichloromethane were charged to a flask equipped as in Example 2. To the resulting mixture was added 101 grams (1 mole @ 98% purity) of butyl isocyanate dropwise with cooling and stirring during 1 hr. 10 min. and at a temperature of about 35° C. The resulting mixture was stirred another 2 hrs. @ 40° C. and then stripped 2 hrs. @ 80° C. and 2 mm Hg pressure leaving 178.4 g crude product which was a liquid. This material was 87 area % one component by gas chromatography. EXAMPLE 4 N-(2-Hydroxyethyl)-N,N'-Ethylene Urea/Cargill- Resin Crosslinked by Cymel 323 A water borne high solids coating composition was prepared by dissolving 16.22 parts of a carboxylated water dispersible organic polymer (Cargill®-) in 10.06 parts of hydroxyethyl ethylene urea. To the resulting solution was added 1.09 parts of triethylamine and the resulting mixture was then diluted with 47.11 parts of water. To this solution was then added 25.52 parts of aminoplast (Cymel™-323, American Cyanamid) to make a total of 100 parts. The resultant coating composition contained 46.7% non-volatiles and was cast (wet film thickness 1.2 mils) on a steel panel and cured at 250° F. for 40 minutes resulting in a hard, tough, glossy coating. A similar coating was prepared on aluminum foil and by extraction was found to be over 94% insoluble in boiling toluene. EXAMPLE 5 Hydroxyethyl Ethylene Urea+Hydroxyethyl Butylcarbamate/Cargill- Resin Crosslinked by Cymel-323 A water borne high solids coating composition was prepared by dissolving 16.20 parts of a carboxylated water dispersible organic polymer (Cargill®-) in 5.03 parts of hydroxyethyl butyl carbamate and 5.03 parts of hydroxyethyl ethylene urea. To the resulting solution was added 1.10 parts of triethylamine and the resulting mixture was then diluted with 47.10 parts of water. To this solution was then added 25.53 parts of aminoplast (Cymel®-323, American Cyanamid) to make a total of 100 parts. The resultant coating composition contained 46.7% non-volatiles and was cast (wet film thickness 1.2 mils) on a steel panel and cured at 225° F. for 40 minutes resulting in a hard, tough, glossy coating. A similar coating was prepared on aluminum foil and by extraction was found to be over 82% insoluble in boiling toluene. EXAMPLE 6 Comparative Water Borne Coatings Composition Crosslinked by Cymel-323 A comparative coating composition of the prior art was prepared by dissolving 20.46 parts of the carboxylated water dispersible organic polymer (Cargill®-) in 12.69 parts of butoxyethanol. To the resulting solution was added 1.38 parts of triethylamine and the resulting mixture was then diluted with 59.48 parts of water. To this solution was then added 5.99 parts of aminoplast (Cymel®-323 American Cyanamid) to make a total of 100 parts. The resultant coating composition contained 25.3% non-volatiles, was cast (wet film thickness 1.2 mils) on a steel panel and cured at 250° F. for 15 minutes resulting in a hard, tough, glossy coating. A similar coating was prepared on aluminum foil and by extraction was found to be over 79% insoluble in boiling toluene. EXAMPLE 7 Preparation of N,N'-bis-(2-Hydroxyethyl) Urea Using this method of Example 1 excepting that each mole of aminoethyl ethanolamine is replaced by two moles of ethanolamine, a mixture containing N,N'-bis(2-hydroxyethyl) urea is obtained. EXAMPLE 8 Preparation of N,N-bis-(2-Hydroxyethyl) Urea Using the method of Example 1 excepting that each mole of aminoethyl ethanolamine is replaced by one mole of diethanolamine plus one mole of ammonia, a mixture containing N,N-bis-(2-hydroxyethyl) urea is obtained. EXAMPLE 9 Preparation of Tetrakis-(2-Hydroxyethyl) Urea Using the method of Example 1 excepting that each mole of aminoethyl ethanolamine is replaced by two moles of diethanolamine, a mixture containing tetrakis-(2-hydroxyethyl) urea is obtained. EXAMPLE 10 Preparation of N,N'-bis-(3-Hydroxy-2,2-Dimethyl-1-Propyl) Urea Using the method of Example 1 excepting that each mole of aminoethyl ethanolamine is replaced by two moles of 3-amino-2,2-dimethyl-1-propanol, a mixture containing N,N'-bis-(3-hydroxy-2,2-dimethyl-1-propanol) urea was obtained. EXAMPLE 11 Preparation of N,N'-bis-(2-hydroxyethyl)-N,N'-Dimethyl Urea Using the method of Example 1 excepting that each mole of aminoethyl ethanolamine is replaced by two moles of N-methyl ethanolamine, a mixture containing N,N'-bis-(2-hydroxyethyl)-N,N'-dimethyl urea is obtained. EXAMPLE 12 When Example 4 is followed except that a chemically equivalent amount of N,N'-dimethyl urea is substituted for N-(2-hydroxyethyl)-N,N'-ethylene urea, a hard, tough, glossy coating is obtained. EXAMPLE 13 When Example 4 is followed except that a chemically equivalent amount of N-butyl-N'-(2-hydroxy-1-propyl) urea is substituted for N-(2-hydroxyethyl)-N,N'-ethylene urea, a hard, tough, glossy coating is obtained. EXAMPLE 14 When Example 4 is followed except that a chemically equivalent amount of N,N'-(2-hydroxyethyl)-N,N'-dimethyl urea is substituted for N-(2-hydroxyethyl)-N,N'-ethylene urea, a hard, tough, glossy coating is obtained. EXAMPLE 15 Preparation of N-Methyl-N'-Butyl Urea 280.32 Grams (3.84 moles) of butylamine and 300 ml of dichloromethane were charged to a round bottom flask equipped with stirrer, cold bath, thermometer, addition funnel and reflux condenser. 229.8 Grams (4.03 Moles, a 5% excess) of methyl isocyanate were charged to the addition funnel and added to the flask contents over four hours keeping the contents between 0° and 35° C. After an additional hour of stirring the exothermic reaction subsided and the mixture was allowed to stand overnight. The mixture was freed of solvent and lights in a vacuum rotary evaporator leaving a white solid. Further drying in a vacuum desiccator gave material melting at 65°-68° C. The proposed structure of the product is in agreement with its proton NMR spectrum and infrared spectrum. EXAMPLE 16 Preparation of N-Methyl-N'-Isopropyl Urea 284.9 Grams (4.81 moles) of isopropylamine were placed in a round bottom flask equipped with stirrer, thermometer, reflux condenser and addition funnel. 250.3 Grams (4.39 moles) of methyl isocyanate were charged to the addition funnel and added slowly to the flask with stirring. During the course of the reaction, solids began to precipitate and approximately 300 ml of toluene were added to maintain fluidity. After all of the methyl isocyanate had been added and the exothermic reaction had subsided, the heterogeneous mixture was heated to reflux and solids dissolved for transfer to a stripping flask. The mixture was freed of solvent and lights under vacuum on a rotary evaporator and with a hot water bath for heat input. The crude product (484.6 g, 95% crude yield) was 90.4 area % pure by gas chromatography and melted at 91°-97° C. Mixtures of this material with 1-propyl-3-butyl urea exhibited significant melting range depressions. Addition of small amounts of liquid carbamates to these mixtures resulted in further melting range depressions such that the resulting mixtures were partly liquid at ambient temperature. Differential scanning calorimetry of several binary mixtures of this material with N-propyl-N'-butyl urea indicated that a eutectic mixture of about 65% N-propyl-N'butyl urea and 35% N-methyl-N'-isopropyl urea existed and that its melting point was about 30° C. This is about a 40° to 60° C. melting point depression from that of the individual components. EXAMPLE 17 N-Propyl-N'-Butyl Urea Preparation 205.76 Grams (3.48 moles) of n-propylamine were charged to a 1-1., round bottom flask equipped with stirrer, thermometer, reflux condenser and addition funnel. 313.7 Grams (3.16 moles) of butyl isocyanate were charged to the addition funnel and added to the flask with stirring at a rate which maintained the contents at about 60°-65° C. Toluene was added to dissolve the solid product for transfer to a stripping vessel. The crude product solution was about 92 area % ureas on a solvent-free basis by gas chromatography. The crude product solution was freed of most of the solvent and lights under vacuum with a rotary evaporator leaving 480.6 g of pale yellow solid melting from 68°-70° C. Infrared analysis showed a clean spectrum in agreement with the proposed structure's functionality. The gas chromatograph showed three, major peaks in a 1:2:1 ratio indicating possible `scrambling` of alkyl groups and a statistically determined ratio of products. EXAMPLE 18 N-Propyl-N'-Butyl Urea Preparation at Low Temperature 205.8 Grams (3.48 moles) of n-propylamine and 250 ml of dichloromethane were charged to a round bottom flask equipped with stirrer, thermometer, reflux condenser and dropping funnel. 313.7 Grams (3.16 moles) of butyl isocyanate were added to the dropping funnel and then metered into the flask with stirring and strong external cooling (solid CO2 bath) at a rate slow enough to maintain the contents generally below 0° C. except for brief excursions to higher temperatures. The resulting mixture was left to stand overnight and then freed of solvent and lights under vacuum with a rotary evaporator leaving 462.3 g of crude product (92.6% crude yield). After further drying of a portion under vacuum a 97.6 area % purity was recorded by gas chromatography. The product contained substantially only one compound by gas chromatography. It melted at 70°-72° C. As noted in Example 16, evidence for the existence of a eutectic between this compound and N-methyl-N'-isopropyl urea was obtained by differential scanning calorimetry. EXAMPLE 19 Preparation of N-butyl-N'-(2-Ethyl-1-Hexyl) Urea 128.98 Grams (1 mole) of 2-ethyl-1-hexylamine and 500 ml of toluene were charged to a flask equipped with dropping funnel, thermometer, condenser, stirrer, Dean & Stark trap and condenser. The contents of the flask were refluxed for 3 hours to remove water, then cooled to 0° C. 99.6 Grams (1 mole) of butyl isocyanate were charged to the dropping funnel and added during 1 hr. 5 min. to the stirred flask contents. The flask contents remained at 30° C. or less during the addition. The resulting crude reaction product was freed of the bulk of volatiles by stripping (final conditions 204° C. @ 1 atmos.). A small sample was distilled with the bulk of the material distilling 157°-164° C. @ 0.001 mm Hg. A sample of distilled material was analyzed by GC showing three major product peaks in the approximate area ratio of 2:5:1 in order of decreasing volatility. Although the invention has been described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes can be made without departing from the spirit and the scope of the invention.