Carbazates

Phenyl-3,6-dihydro-l,3,4-oxadiazin-2-one (50) is a high temperature blowing agent used primarily for polycarbonates (qv). It is prepared by the reaction of a-hydroxyacetophenone and methyl carbazate (52), made from hydrazine and dimethyl carbonate (175) ... 

A third approach to 3-amino-/3-lactams is by Curtius rearrangement of the corresponding acyl azides. These are readily prepared from r-butyl carbazides, available via photochemical ring contraction of 3-diazopyrrolidine-2,4-diones in the presence of f-butyl carbazate (c/. Section 5.09.3.3.2). Thus treatment of (201) with trifluoroacetic acid followed by diazotiz-ation gives the acyl azide (202) which, in thermolysis in benzene and subsequent interception of the resulting isocyanate with r-butanol, yields the protected 3-amino-/3-lactam (203) (73JCS(P1)2907). 

C3H7NO2 51-79-6) see Carisoprodol Felbamate Mebutamate Tybamate ethyl carbazate... 

Methyl 2-butynoate, 55, 76 Methyl carbazate, 58, 102, 103, 106 METHYL (CARBOXYSULFAMOYL)-... 

The rate of decomposition of hydrazine in stainless steel vessels (which is accompanied by corrosion) is directly proportional to carbon dioxide concentration over 20 ppm and below 250 ppm. The species responsible for the catalytic decomposition is not one of the expected corrosion products, iron(II) carbazate or its nickel or chromium(II) analogues. 

ETHYL HYDRAZINECARBOXYLATE (Carbazic acid, ethyl ester)... 

Dihydropyrrole a-ketoester 423 when reacted with 2,2,2-trichloroethyl carbazate in refluxing xylene underwent smooth cycloaddition to afford cycloadduct 48 in 86% yield. Reaction of 423 with thiosemicarbazide in acetic acid yielded a product mixture to give the tetracycle 48. Its benzyloxycarbonyl group was cleaved by reaction with HBr to give crystalline 424 <2002JOG7880> (Scheme 94). 

The hydrochloride of 3-amino-4-hydrazinopyridine 65 was prepared by reaction of the 4-chloro-3-nitropyridine derivative with ethoxycarbonyl-hydrazine in phenol to give the hydrochloride of ethyl 3-(3-nitro-4-pyridyl)carbazate 64 (R2 = OEt), which on successive heating in concentrated hydrochloric acid and hydrogenation over Pd/C gave 65. Its reaction with phenylacetic acid or with phenoxyacetic acid gave the hydrochloride... 

A facile route to l,3,4-oxadiazepin-2-ones has been developed by Komatsu et al. involving acid-catalysed cyclisation of carbazate derivatives derived from the reaction of N, A -di-tert-butyldiaziridinone and a-hydroxy ketones with BF3.Et20 catalysis <00H(52)541>. 

Methylbutyl iso valerate, ml 77 Methyl tert-butyl ketone, h70 Methyl caprate, m226 Methyl caproate, m270 Methyl caprylate, m349 Methyl carbazate, m275... 

The carbazate is sufficiently pure for most applications and is conveniently handled as a liquid. When the product is cooled in an ice box, it crystallizes as a waxy mass such samples remain tacky after several recrystallizations from petroleum ether, however. A pure sample may be obtained by extracting an ether solution of the carbazate with dilute sodium hydroxide to remove any phenol, followed by distillation and recrystallization of the product from petroleum ether (b.p. 30-60°). White needles are obtained which melt at 41-42°. 

Butyl carbazate has been prepared by reaction of hydrazine... 

Butyl carbazate, conversion to /-butyl hydrazodiformate, 44,18 /-Butyl chloride, 44, 102 ree-Butyl cinnamate, 41, 62 rec-Butyl crotonate, 41, 60 reaction with n-butyl Grignard reagent, 41, 61... 

In a 1-1. round-bottomed flask fitted with a mechanical stirrer are placed 82 g. (0.62 mole) of /-butyl carbazate,2 72 g. of glacial acetic acid, and 100 ml. of water. The solution is cooled in an ice bath, and 47.0 g. (0.68 mole) of solid sodium nitrite is added over a period of 40-50 minutes, the temperature being kept at 10-15° (Note 1). The mixture is allowed to stand in the ice bath for 30 minutes, 100 ml. of water is added, and the floating oil is extracted into four 40-ml. portions of ether. The combined ether extracts are washed twice with 50-ml. portions of water and with 40-ml. portions of lAf sodium bicarbonate solution until no longer acidic (about three washings are required). The solution is dried over magnesium sulfate, and the ether is removed by distillation from a water bath maintained at 40-45° water aspirator pressure of 140-150 mm. is used. The pressure is then... 

Butyl azidoformate has been prepared only from /-butyl carbazate.8 6... 

Butyl hydrazodiformate has been prepared by acylation of /-butyl carbazate by means of /-butyl azidoformate 3 4 or /-butyl cyanoformate.5 /-Butyl azodiformate has been prepared only by oxidation of the hydrazo compound. ... 

B. t-Bulyl carbazate. In a 1-1. Erlenmeyer flask are placed 388.4 g. (2.0 moles) of phenyl <-butyl carbonate and 120.2 g. (2.4 moles) of a 64% hydrazine solution (Note 6). The mixture is swirled by hand and heated on a hot plate. When the internal temperature reaches 75-80°, it then rises rapidly and spontaneously to 104—110°, the two layers forming a dear solution. The solution is allowed to cool overnight. The mixture is then diluted with 500 ml. of ether and transferred to a separatory funnel in which it is shaken vigorously for about 10 minutes with a solution prepared from 160 g. (4.0 moles) of sodium hydroxide and 1.2 1. of water. The resulting two layers are placed in a 2-1. continuous extractor and extracted for 48 hours with ether. The ether solution is dried over magnesium sulfate, and the ether is removed by distillation from a water bath. The last portions of ether are removed with the aid of a water aspirator. The residual oil is then distilled using a Claisen flask with an air bath maintained at 115-125°. After 1 or 2 drops of fore-run the carbazate is collected at 61-65° (1.2 mm.), 24d 1.4518. The yield is 235-256 g. (89-97%) (Note 7). 

Butyl carbazate is also a key intermediate in the synthesis of /-butyl azidoformate,5 6 12 /-butyl hydrazodiformate, /-butyl azo-diformate,18 and /-butyl N-hydroxycarbamate,12 14 all of winch are valuable synthetic intermediates. 

Dehydrative condensation of pyrrole-2-carboxaldehyde 77 and ethyl carbazate afforded carbethoxyhydrazone 78 in quantitative yield. Cyclization of 78 in the presence of a catalytic amount of sodium hydride (10mol%) in dimethyl-formamide (DMF) at 100°C led to the formation of pyrrolo[l,2-tf][l,2,4]triazin-4-one 27 in 75% yield (Scheme 8) <1999T13703>. 

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