Synthesis of Urethane

Urethane is required in large quantities for the manufacture of polyurethanes, a class of important polymers which are used for a number of commercial applications. 

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Waste PETP was depolymerised by glycolysis to give hydroxyl-terminated oligomers(DPET), which were used in the synthesis of urethane oils. The effect of depolymerisation temps., the type of glycol and the amount of catalyst on the yield and composition of the depolymerisation products was studied. The physical properties of the urethane oils were compared with those of a commercially-available product. The reaction of DPET with isocyanates produced random linkage between different molecules with or without terephthaloyl groups. 15 refs. 

Y-F Zhu, WD Fuller. Rapid, one-pot synthesis of urethane-protected tripeptides. Tetrahedron Lett 36, 807, 1995. 

Synthesis of Urethane Modified Acrylics and Acrylic Modified Urethanes. 1) Synthesis of PBH. Into a reaction kettle equipped with a nitrogen inlet, stirrer, reflux condenser, and an addition funnel charged 500g of xylene. The xylene was heated to reflux and a mixture of 375g butyImethacrylate (BMA), 125g of 2-... 

Scheme 9 Synthesis of Urethane-Protected TV-Alkyl Amino Acids via Oxazolidin-5-ones199"101 ...

The use of heterogeneous catalysts in the synthesis of urethanes from aliphatic and aromatic amines, C02 and alkyl halides has been explored only recently. Titanosilicate molecular sieves [60a], metal phthalocyanine complexes encapsulated in zeolite-Y [60a], beta-zeolites and mesoporous silica (MCM-41) containing ammonium cations as the templates [60b, c], and adenine-modified Ti-SBA-15 [60d, e] each function as effective catalysts, even without any additional base. 

The acylation of ammonia or primary and secondary amines by chloro-formic esters (chlorocarbonates) is the most general method for the synthesis of urethanes. Chlotoformates are obtained by the action of phosgene on alcohols (method 289) and, without purification, are converted to carbamates by cold concentrated ammonium hydroxide. Over-all yields from primary and secondary alcohols range from 55% to 94%. N-sub-stituted carbamates result in similar yields when primary" or secondary" amines are substituted from ammonia in the reaction. Aqueous sodium hydroxide is sometimes used to neutralize the acid formed. ... 

Peptide synthesis. In the above-mentioned synthesis of urethanes the carboxylic acid azide may be the intermediate, and this possibility prompted the Japanese chemists to investigate the usefulness of diphcnylphosphoryl azide in peptide synthesis. Indeed the reagent allows coupling of acylamino acids or peptides with amino acid esters or peptide esters in the presence of a base in high yield and with practically no racemiza-tion. The new method is compatible with various functional groups. 

Another interesting bromide ion-catalyzed reaction is the anodic oxidation (undivided cell) of secondary formamides in methanol leading to urethanes [232]. This reaction proceeds via the intermediate A-bromo amide, which under elimination of HBr forms the isocyanate, which is attacked by methanol. Thus, a phosgene-free technical synthesis of urethanes is made possible. Urethanes can be used as stable isocyanate equivalents [Eq. (42)]. 

Urethanes. The ability of the tin dicarboxylates to promote addition of alcohols to isocyanates suits well for the synthesis of urethanes and in polyurethane technology. ... 

Urethane-modified alkyds are similar to simple alkyds except that dibasic acid is replaced with a difunctional isocyanate such as toluene diisocyanate or hexamethylene diisocyanate. The process is also similar to simple alkyds. Coatings made with urethane-modified alkyds dry faster and harder than alkyds, yet retain flexibility. These systems have better water-, chemical- and abrasion-resistance than alkyd resins, and cost is also relatively low (Wicks et al., 1998). These are used in clear finishes for wood floors, cabinets, OEM, maintenance, and architectural coatings. The aliphatic-based systems are excellent for exterior use, or where UV exposure is possible, while aromatic-based systems usually have better abrasion-resistance. Chemo-enzymatic synthesis of urethane-based systems produces better control of stereochemistry and can impart unique properties (Athawale Bhabhe, 1998 Athawale Gaonkar, 1999 Athawale Joshi, 2000, 2004 Bhabhe Athawale, 1998). 

Bhabhe, M.D. V.D. Athawale. Chemoenzymatic synthesis of urethane oil based on special functional group oil./. Appl. Polym. Sci. 1998, 69, 1451-1458. 

For the synthesis of urethane-acrylate prepolymer, hexamethylene diisocyanate (HDI, 0.178 moles,) was placed in a reaction vessel, then 2-hydroxyethyl-acrylate (HEA, 0.178 moles) was added. The reaction temperature was kept at 45°C for 30 min., to avoid thermal polymerization through the vinyl groups, then a stoichiometric quantity of dry polypropylene glycol (PPG) (MW 725, hydroxyl number 147 mg of KOH/g (67.4 ml.)) was added along with dibutyl-tin-dilaurate as a catalyst... 

Poly(Amino Acids) 210 12.6.1 Synthesis of Urethane-Based "Pseudo" ... 

A direct synthesis of urethans from halides has been published Sym. sulfonylureas can be prepared from the corresponding sulfonamides by pressure carbonation... 

Synthesis of Urethanes, Isocyanates, and Ureas, Conventional Method... 

Monsanto company has developed a method for the synthesis of urethanes, eliminating the use of phosgene" (Scheme 10). 

Scheme 10. New synthesis of urethane without using phosgene...

A new route to urethanes avoids phosgene and isocyanates by reacting amines and alcohols directly with CO over a catalyst in the presence of an acid. The urethanes 332 hitherto prepared in this way have been designed to be cracked to isocyanates 333, and a new BASF patent application covers both the synthesis of urethanes and their thermolysis to isocyanates [215]. The catalyst consists of a cationic Group VIII metal (e.g. Pd) with weakly coordinating counterions and methylene-bis-phosphine ligands. 

Diphenylphosphoryl azide (DPPA) and triethylamine were formerly employed by Yamada and co-workers in a simple one-pot synthesis of urethanes from carboxylic adds [250]. This procedure involved treatment of a carboxylic acid with triethylamine to produce the triethylammonium carboxylate salt, followed by heating in the presence of DPPA to yield the isocyanate via a Curtius-type rearrangement of the acyl azide. An alcohol was then introduced, functionalizing the isocyanate in situ to yield the urethane. 

The first promoter to be discovered [42] for the synthesis of urethanes and the one for which more modifications have been later proposed is FeCU. A molar ratio FeCls/Pd = 20 was initially used [42] at a relatively high CO pressure (189 Kg/cm ) and 190 °C. The alcohol was not a requisite for the reaction to proceed and, by carbonilating nitrobenzene employing Pd/ALOj-FeClj and a gas mixture... 

Recently, a different catalytic system has been reported for the synthesis of urethanes, based on orthometallated ruthenium complexes of the kind [RuL(CO)2C1]2 (best ligand LH = 2-phenylpyridine) in the presence of a base (best NaOMe) [186], The initial rate is first order in catalyst concentration and second order in CO pressure, but is independent on nitrobenzene concentration. If aniline was used as a substrate in place of nitrobenzene, no carbonylation was observed and this was said to represent an evidence that aniline is not an intermediate in the catalytic cycle. However this experiment is inconclusive, since carbonylation of aniline may require the previous oxidation of the starting complex by nitrobenzene, analogously to what found for the Ru(C0)3(DPPE) and Ru3(CO)i2 based systems (vide supra). No experiment was attempted using a nitro compound in the presence of a fferently substituted aniline, analogous to the ones describes for the aforementioned catalytic systems. 

Figure 2.66 A simplified reaction scheme for synthesis of urethane alkyds...

Others. The seed oil was used by the ancient Egyptians for embalming in mummification however, by far the largest use of castor oil is as its dehydrated or partially dehydrated form in industrial lubricants, coatings, paints, varnishes, and others also in synthesis of urethanes, foams, plastics, and certain perfume chemicals, among others.Sulfonat-ed castor oil (Tfrrkey red oil) is widely used in the textile and printing industry as a surfactant. ... 

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