Ethyl nitrite, nitrosation

Zingiberene also forms a nitrosate, C,5H24. N2O4, when the sesquiterpene dissolved in an equal volume of glacial acetic acid, is cooled to 0°, and ethyl nitrite, and then nitric acid added. The nitrosate is dissolved in acetic ether and precipitated with alcohol. It forms a yellow powder, melting with decomposition at 86°. 

The preparation of oximes from olefins is a valuable approach for the synthesis of nitrogen-containing compounds such as amino acids and heterocycles. Okamoto and colleagues have reported that a catalytic reduction-nitrosation of styrenes 31 with ethyl nitrite and tetrahydroborate anion by the use of bis(dimethylglyoximato)cobalt(II) complex afford the corresponding acetophenone oximes 32 (Scheme 23). 

A mechanistically intriguing transformation resulted when 9-aminocarbazole formed salt 137 via the reaction of its Grignard derivative with dibromo-triphenylphosphorane. Reaction of the salt 137 with ethyl nitrite gave 3-bromocarbazole the authors speculate that nitrosation followed by nitrogen loss generates the carbazol-9-yl cation, attacked in a nucleophilic sense by bromide at C-3. ... 

A variation of this procedure is the nitrosation of a phenol such as thymol in an alcohol solution with hydrochloric acid and sodium nitrite. This procedure is said to avoid the evolution of oxides of nitrogen, since it may involve the intermediate formation of ethyl nitrite as the nitrosating agent [31]. However, from the safety standpoint, the oxides of nitrogen and nitrite esters must be considered hazardous. 

Alkylmalonic esters are especially suitable starting materials for the preparation of -(hydroxyimino) esters. Shivers and Hauser261 obtained high yields in such cases by means of ethyl nitrite and an equimolar amount of sodium ethoxide. Barry and Hartung recommend carrying out the nitrosation in ethereal solution with sodium nitrite and hydrogen chloride.262... 

Carbazoles normally react with electrophiles to yield the 3-monosubstituted and 3,6-disubstituted derivatives. Further reaction may occur at the 1- and the 8-positions. There is evidence that the initial reaction occurs at the 9-position. Thus, nitrosation of carbazole with sodium nitrite in acetic acid yields 9-nitrosocarbazole which, when treated with nitric acid, is converted into 3-nitrocarbazole (09CB3797) and 3,6-dinitrocarbazoIe (46USP2392067). Direct nitration of carbazole with nitric acid (02GEP128853) or with ethyl nitrate also yields the 3-nitro and 3,6-dinitro derivatives, together with 1,3,6,8-tetranitrocarbazole (27CB738). 

Until relatively recently no kinetic studies on the nitrosation of alcohols had been reported, presumably since the reactions are very rapid and require special techniques. Some kinetic measurements on the reverse reaction, the hydrolysis of alkyl nitrites have been reported here conventional kinetic methods were used. Early workers examined the reactions of the series methyl, ethyl, i-propyl and t-butyl nitrites in an acetic acid-acetate buffer and found a small increase in rate constant along the series (Skrabal et a ., 1939). Later Allen measured the rate constants for the hydrolysis of a number of alkyl nitrites in aqueous dioxan solvent for both acid- and base-catalysed reactions (Allen, 1954). The rate constants for the O-nitrosation of alcohols were determined indirectly by measurement of the overall equilibrium constant for the process, by noting the change in the rate constant for the nitrosation of phenol in the presence of added alcohols. These, combined with the known data for the reverse hydrolysis reaction, enabled the rate constants for the forward reaction to be obtained (Schmid and Riedl, 1967). The reactivity sequence MeOH > EtOH > i-PrOH > t-BuOH was deduced, and attributed to a steric effect. 

The nitrosation of substituted ethylbenzenes was carried out by Kovendi and Kirez350 with ethyl or methyl nitrite the resulting benzophenone oxime was hydrolysed by boiling for 3-4 h with 20% hydrochloric acid and the acetophenone produced was extracted with benzene. 

The work began with the condensation of urea with ethyl cyanoacetate. The product, cyanoacetylurea on treatment with dilute, warm sodium hydroxide (NaOH) generated 4-aminouracil (4-amino-2,6-dioxypyrimidine). Nitrosation of the sulfate salt with sodium nitrite produced the corresponding isonitroso derivative, which underwent easy reduction (with ammonium sulfide) to the corresponding 5,6-diaminouracil (4,5-diamino-2,6-dioxypyrimidine). 

Amines can be determined in explosives after nitrosation,< ) as mentioned in Chapter VI. Thus diphenylamine in the presence of centralite (N,N -diphenyl N,N -diethylurea) can be determined either after saponification and distillation with successive nitrosa-tion of the distillate, or after dissolving the propellant in ethyl-acetate-methanol (1 1), followed by the addition of acetic acid and nitrite. After nitrosation (10 min), sulphamic acid is added to destroy the excess of nitrite, and precipitated cotton powder is filtered off. Polarographic electrolysis is carried out in a solution containing about 40 per cent ethanol. 

Nitro- and nitroso-pyrroles are markedly acidic. The former are pale yellow compounds which give yellow solutions in alkali. The simple nitroso compounds, lacking aryl or alkoxycarbonyl substituents, are only stable as their yellow salts. The sodium salts of nitro- and nitroso-pyrroles result from nitrations and nitrosations effected, respectively, by means of ethyl nitrate or amyl nitrite in presence of sodium or sodium ethoxide (see below). These... 

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