Urethans acid esters

The reaction of uiea with alcohols yields caibamic acid esters, commonly called urethanes (see Urethane polymers) ... 

It yields a diphenyl-urethane, which melts at 99° to 100°, and is very useful for identification purposes. The phenyl-urethane, melting at 80° is less useful for this purpose, since its melting-point is almost identical with those of benzyl and nonyl alcohols. It combines with phthalic acid to form a phthalic acid ester, melting at 188° to 189°. 

Benzaldehyde dimethyl acetal 121 reacts, for example, with the silylated allylic alcohol 645, in the presence of SnCl2-MeCOCl, via an intermediate analogous to 641, to the 3-methylenetetrahydrofuran 646 and methoxytrimethylsilane 13 a [182], whereas benzaldehyde dimethyl acetal 121 reacts with the silylated homoallylalco-hol 640 in the presence of TMSOTf 20 to afford exclusively the ds 4-vinyltetrahy-drofuran 647 and 13 a [183]. A related cyclization of an a-acetoxy urethane 648 containing an allyltrimethylsilane moiety gives the 3-vinylpyrrohdine 649 in 88% yield and trimethylsilyl acetate 142 [184, 185]. Likewise, methyl 2-formylamido-2-trimethylsilyloxypropionate reacts with allyltrimethylsilane 82 or other allyltri-methylsilanes to give methyl 2-formamido-2-aUyl-propionate and some d -unsatu-rated amino acid esters and HMDSO 7 [186] (Scheme 5.56). 

The linker group is immobilized as a urethane to the amino-functionalized carrier (59). It facilitates the attachment of a variety of molecules such as alkyl halides, alcohols or amines bound as carboxylic acid esters and amides. 

Amide urethane, and ester groups in the polymer chain, such as those present in nylons and polyesters may be hydrolyzed by acids to produce lower-molecular-weight products. Polyacetals are also degraded by acid hydrolysis, but ethers, such as polyphenylene oxide (PPO), are resistant to attack by acids. 

At a slightly elevated temperature, alcohols add to the C=N double bond of isocyanates according to the same mechanism. The addition products are called carbamic acid esters or urethanes ... 

Methods for the capillary gas chromatographic separation of optical isomers of chiral compounds after formation of diastereoisomeric derivatives were developed. Analytical aspects of the GC-separation of diastereoisomeric esters and urethanes derived from chiral secondary alcohols, 2-, 3-, 4- and 5-hydroxy-acid esters, and the corresponding jf- and -lactones were investigated. The methods were used to follow the formation of optically active compounds during microbiological processes, such as reduction of keto-precursors and asymmetric hydrolysis of racemic acetates on a micro-scale. The enantiomeric composition of chiral aroma constituents in tropical fruits, such as passion fruit, mango and pineapple, was determined and possible pathways for their biosynthesis were formulated. 

An acrylic oligomer is a higher molecular weight functional acry-lated molecule which may be, for example, polyesters of acrylic acid and methacrylic acid. Other examples of acrylic oligomers are the classes of urethane acrylates and urethane methacrylates. Urethane acrylates are manufactured from aliphatic or aromatic or cycloaliphatic diisocyanates or polyisocyanates and hydroxyl-containing acrylic acid esters. 

Thioanalogs of ketones, acetals, carboxylic acids, esters, amides, ° isocyanates, " urethanes, and ureas are often prepared by reactions similar to those used for... 

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. 

A 2- or 6-hydroxy-substituted purine can be prepared from the corresponding 4,5-diamino-pyrimidinol by cyclization with an acid, ester, ortho ester, or amide. If the ring closure is performed with reagents such as urea, alkyl chloroformates, urethanes, phosgene, and alkyl isocyanates, the 8-hydroxypurines are formed. Various xanthine and uric acid derivatives have been prepared by the condensation of 5,6-diaminopyrimidine-2,4-diols with formic acid. Purin-2-ol (1) was prepared by this route from 4,5-diaminopyrimidin-2-ol and ethyl orthoformate. ... 

The non-urethane type A -Trt amino acid fluorides have been synthesized and were shown to undergo clean reaction with amino acid esters without loss of configuration. 

Pyridines by Enamines. Like 6-aminouracil (243) 3-aminocrotonitrile (245a) and 3-aminocrotonic acid esters (245 b, c), vinylogues of cyanamide or urethane represent stable but acyclic members of enamines with a free amino group. Vinamidinium salts (7) in the presence of sodium methoxide or the related 3,3-diethoxy-... 

Dithiazines, urethanes, or iminocarboxylic acid esters result from the reaction of ethyl azidoformate with l,2-dithiole-3-thiones.232... 

Urethanes or dithiocarbonic acid amides are cyclization agents which, with sodium hydride as a base, convert 2-aminonicotinic acid esters into pyrido[2,3-[Pg.98]

Friesen reported as early as 1929 on the herbicidal activity of an N-arylcarbamic acid ester, phenyl urethane, however, its action causing abnormal growth on wheat and oats was utilised for practical purposes only IS years later. 

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