Carbamates, nitro

Attempts have been made to develop methods for the production of aromatic isocyanates without the use of phosgene. None of these processes is currently in commercial use. Processes based on the reaction of carbon monoxide with aromatic nitro compounds have been examined extensively (23,27,76). The reductive carbonylation of 2,4-dinitrotoluene [121 -14-2] to toluene 2,4-diaLkylcarbamates is reported to occur in high yield at reaction temperatures of 140—180°C under 6900 kPa (1000 psi) of carbon monoxide. The resultant carbamate product distribution is noted to be a strong function of the alcohol used. Mitsui-Toatsu and Arco have disclosed a two-step reductive carbonylation process based on a cost effective selenium catalyst (22,23). 

The common impurities found in amines are nitro compounds (if prepared by reduction), the corresponding halides (if prepared from them) and the corresponding carbamate salts. Amines are dissolved in aqueous acid, the pH of the solution being at least three units below the pKg value of the base to ensure almost complete formation of the cation. They are extracted with diethyl ether to remove neutral impurities and to decompose the carbamate salts. The solution is then made strongly alkaline and the amines that separate are extracted into a suitable solvent (ether or toluene) or steam distilled. The latter process removes coloured impurities. Note that chloroform cannot be used as a solvent for primary amines because, in the presence of alkali, poisonous carbylamines (isocyanides) are formed. However, chloroform is a useful solvent for the extraction of heterocyclic bases. In this case it has the added advantage that while the extract is being freed from the chloroform most of the moisture is removed with the solvent. 

CjHjNjO 17687-24-0) see Dipyridamole S-nitro-l-pentanamine (CjHjjNjOj) see Deferoxamine (S-nifropentyl)carbamic acid benzyl ester (C13HUN2O4 92034-20-3) see Deferoxamine 4-nitrophenethylamine hydrocbloride (C H iCINjO 29968-78-3) see Dofetilide 4-nitrophenetole... 

Sometimes it is useful to be able to remove a protecting group by photolysis. 2-Nitrobenzyl carbamates meet this requirement. The photoexcited nitro group abstracts a hydrogen from the benzylic position, which is then converted to a a-hydroxybenzyl carbamate that readily hydrolyzes232... 

Some examples for the introduction of amino protecting groups such as 2-(4-nitro-phenyl)ethoxycarbonyl (npeoc) or benzyloxycarbonyl (Z) were already given in the compilation of carbamates produced with imidazolium caiboxylates in Section 4.6.1. 

Arenecarbonitrile oxides react with alkyl (p-nitrophenyl)carbamates at the nitro group, the nitrogen atom of the latter being the nucleophilic center. Tautomeric N-hydroxybenzimidazole N-oxides 382 and 383 form as the final products (430). 

Reisch and Niemeyer photolysed sulphanilamide (40) in ethanol and obtained the nitro derivative (41), carbamate (42), azobenzene (43) and 2-methylqui-... 

CARBAMIC acid, krt-BUTYL ESTER, 48, 32 Carbazole, 2-nitro-, 46, 85 Carbazoles, from o-azidobiphenyls,46,SS from o-nitrobiphenyls and triethyl phosphite, 48, 115 2-Carbethoxycyclodecanone, 47, 22 2-Carbethoxycyclododecanone, 47, 22 2-Carbethoxycyclohexanone, 45, 82 2-Carbethoxycyclononanone, 47, 22 2-Carbethoxycyclooctanone, 47, 20 t-Carbinamines, see /-Alkylamines Carbodiimide, [3-(dimethylamino)-propyl]ethyl-, hydrochloride, 48, 83... 

Reduction is used for carbonyl functionalities [71, 230] such as thioesters [231], amides [232], and carbamates [233], as well as for sulfur [234] and selenium [122] compounds. Recently, the synthesis of a potential carbohydrate vaccine is described via an reduction-oxidation sequence [235]. An efficient solid-phase synthesis of pyrimidine derivatives that involved reduction of the corresponding nitro derivatives was developed by Makara et al. in 2001 (Scheme 3.9) [236]. 

Chemical/Physical Forms water-soluble salts (Hartley and Kidd, 1987). When heated to 75 °C, asulam decomposed to sulfanilic acid, carbamic acid, and sulfanilamide. At 90 °C, 4-nitro- and 4-nitrosobenzene sulfonic acids were released (Rajagopal et al., 1984). 

A solution of fuming or absolute nitric acid in acetic anhydride is another commonly used reagent for the V-nitration of V-alkylamides. Curry and Mason used this reagent to synthesize a series of aliphatic and alicyclic V-nitro-V-alkylcarbamates from the corresponding V-alkylcarbamates. Aromatic ring nitration is observed if aryl groups are present in the carbamate substrate. 

Nitro-l/f-p5rrazole-l-[A/, 7V-bis(tert-butoxycarbonyl)]carboxamidine (1) has been developed as a new reagent for the rapid and efficient solid and solution phase synthesis of bis(carbamate)-protected guanidines from primary and secondary amines <99TL53>. 

Further substitution on this compound leads to a somewhat more potent antinema-todal drug. Nitration of (53-6) under the usual conditions leads to the corresponding nitro derivative (54-1). The nitro group is then reduced to the corresponding amine (54-2). Acylation with isopropyl chloroformate forms the corresponding carbamate and thus cambendazole (54-3) [57]. 

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