Carbamic acid azides

Carbamyl Azide in Vol 2, p C40-L, under Carbamic Acid and Derivatives... 

Azidomethylcarbamyl Azide. See under Methyl carbamic Acid and Beil 3, (17)... 

Carbamic acid and derivs 2 C40—C42 carbamic acid esters 2 C40 carbamic acid ethyl esters 2 C40-C41 carbamic acid methyl ester 2 C41 carbamic azide 2 C40... 

Azidoocrylic Acid. See Acryloylazide under Acrylic Acid and Derivatives, p A97 Azidoomide (Carbamyl Azide). See under Carbamic Acid and Derivatives and Beil 3, 129, (59) [102]... 

Reaction of carboxylic acids gives acyl azides, which rearrange to isocyanates, and these may be hydrolyzed to carbamic acid or solvolysed to carbamates. Decarboxylation leads to amines. 

The isocyanate can he isolated if the Curtius degradation is carried out in an inert solvent. The isocyanate also can be reacted with a heteroatom-nucleophile either subsequently or in situ. The heteroatom nucleophile adds to the C=N double bond of the isocyanate via the mechanism of Figure 8.12. In this way, the addition of water initially results in a carbamic acid. However, all carbamic acids are unstable and immediately decarboxylate to give amines (see Figure 8.5). Because of this consecutive reaction, the Curtius rearrangement represents a valuable amine synthesis. The amines formed contain one C atom less than the acyl azide substrates. It is due to this feature that one almost often refers to this reaction as Curtius degradation, not as Curtius rearrangement. 

An ester group at C-3 or C-5 is not different in function from any ester in aliphatic or aromatic compounds. The ester can be converted into an amide or a hydrazide, or it may be hydrolyzed. The hydrazide can be converted into an acid azide and rearranged to an isocyanate which in turn will form a carbamate or can be hydrolyzed to an amine. However, the amine group can be replaced with chlorine by diazotization in hydrochloric acid, not an ordinary pattern of behavior (76AHC(20)65) although similar reactions do occur in the 1,2,4-triazole ring system. 

Conversion of the corresponding isocyanates, resulting from the heating of the azides in benzene, with alcohols of general formula R OH, yielded the carbamic acid esters LXXVIb (150), and with amines R"R" NH, the urea derivatives LXXVIc and LXXVIIc (151, 152). 

It is now possible to polymerize isobutylene to butyl rubber in toluene instead of the usual chloromethane.215 A new titanium sandwich catalyst does the trick. European manufacturers are phasing out some chloroparaffin lubricants.216 In Japan, rubber is being chlorinated in water instead of carbon tetrachloride.217 This still involves chlorine, but does get rid of the solvent. 1,2-Dimethoxyethane is being used as an alternative to chlorinated solvents for the Schmidt Reaction for conversion of an ester to an amine through an acid azide and a carbamate (3.6).218 This eliminated accidents from polyazides made in situ from methylene chloride or chloroform. 

In order to build up chains containing the carbamic acid radical, NH. CO, just as Curtius and his co-workers have built up chains containing glycyl, NH.CHj.CO, alanyl and asparagyl radicals, Curtius and Lenhard, in 1904, proposed to make use of the azide of hippuryl-carbamic acid,... 

Carbonyl azides react with alcoholic hydroxy compounds to form the corresponding urethanes. In the same manner, ferrocenoyl azide, and 3-fe-rrocenylpropionyl azide can derivatized, hydroxy-steroids and the resultant derivatives are determined electrochemically by LC with the detection limits at subpicomole levels. 2-[2-(Azidocarbonyl)ethyl]-3-methyl-1,4-naphthoquinone (AMQ) reacts with primary and secondary alcohols to produce carbamic acid derivatives and is used in LC with BCD and FL detections. 7-Methoxycoumarin-4-carbonyl azide (7-MC-4-CON3) and 3,4-dihydro-6,7-dimethoxy-4-methyl-3-oxoquinoxaline-2-carbonyl azide (DMEQ-CON3) are also applied to LC with FL detection as precolumn reagents. 

Carbamic Acids. The esters of carbamic add or substituted carbamic acids (urethans) do not react readily with hydrazine, but the corresponding carbamyl chlorides do. The semicarbazide or substituted semi-carbazides that result yield carbamyl azides with nitrous acid. Most carbamyl azides are prepared more conveniently from the carbamyl chlorides and sodium azide. Monosubstituted carbamyl azides can also be synthesized from isocyanates and hydrazoic acid. -... 

The azide of carbamic acid, NH2CPN3, rearranges only with difficulty among the products only a trace of a hydrazine compound was... 

The reactions of HN3 with cyclic alcohols to yield mixtures of ketones, amines, and products with an enlarged ring are catalyzed by H2SO4 [1]. Tertiary alcohols are converted to azides in the presence of acid [12] or TiCU [13]. Aldehydes and ketones with HN3 undergo a Schmidt-type reaction by liberating N2 and inserting NH In the presence of H or Lewis acids [14]. Ketones yield secondary amides and, in the case of cyclic ketones, lactames. Aldehydes are converted to nitriles or N-formylamines. Tetrazole derivatives result with excess HN3 [1, 15]. However, a-azido ethers are obtained from aldehydes and HN3 in the presence of alcohols by catalysis of TiC [16]. Carboxylic acids and anhydrides form amines, N2, and CO2 in Schmidt reactions with HN3. Intermediates are carbamic acids which form by insertion of NH into the R-COOH bond [1, 14]. High yields result for acids of arenes [17]. 

Nitrogen nucleophiles used to diplace the 3 -acetoxy group include substituted pyridines, quinolines, pyrimidines, triazoles, pyrazoles, azide, and even aniline and methylaniline if the pH is controlled at 7.5. Sulfur nucleophiles include aLkylthiols, thiosulfate, thio and dithio acids, carbamates and carbonates, thioureas, thioamides, and most importandy, from a biological viewpoint, heterocycHc thiols. The yields of the displacement reactions vary widely. Two general approaches for improving 3 -acetoxy displacement have been reported. One approach involves initial, or in situ conversion of the acetoxy moiety to a more facile leaving group. The other approach utilizes Lewis or Brmnsted acid activation (87). 

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