To a cooled, well-stirred solution of 2 gm (0.0115 mole) of 1-chloro-l-nitrosocyclohexane dissolved in a mixture of 20 ml of ethanol and 10 ml of distilled water is added, in small increments, enough sodium borohydride until the color has been discharged. The reaction mixture, which is neutral, is acidified slightly to pH 4. The product is separated by exhaustive extraction with ether. The ether extract is dried over sodium sulfate, filtered, and freed of ether by evaporation. The colorless crystal mass is pressed dry on a clay plate and recrystallized from petroleum ether to afford 0.94 gm (61%), m.p. 89-90°C.
The partial reduction of aliphatic nitro compounds was mentioned as early as the turn of this century. However, only with the commercialization of nitroalkanes did these reactions achieve any real significance. Among the chemical reducing agents, zinc dust and acetic acid have been recommended.
Hydrogenation of nitrocyclohexane on a silver dichromate catalyst has recently been patented. In this procedure, it is said to be important to control the hydrogen take-up to prevent hydrogenation of the oxime to the hydroxylamine. This is accomplished by venting hydrogen off as soon as the theoretical quantity of hydrogen has been used up to convert the nitro compound to the oxime.
Olefinic nitro compounds have been reduced to the saturated oxime with hydrogen and a palladium-on-carbon catalyst. To maximize the yield of oxime, 0.5-1.0 mole of hydrogen chloride per mole of nitroolefin must be present. Since the by-products contain crude ketones also, a posttreatment with hydroxylamine hydrochloride and sodium acetate has been recommended. By this means, 1-nitrocyclooctene has been converted to cyclooctanone oxime [b.p. 63°C (0.08 mm Hg), m.p. 41.7-42.7°C] and 1-nitro-l-octadecene has been converted to stearaldoxime (m.p. 88-89.8°C). Whether this method is confined to 1-olefin derivatives is not clear.
Nitro olefins have also been reduced with zinc dust and acetic acid, to produce oximinoalkanes. The preparation of 5-ethyl-3-nonanone oxime gives the necessary details. To be noted is that the carbon bearing nitro group in the starting material also bears the double bond. Whether this structural feature is essential if the reduction is to stop at the oxime stage may need further elucidation.
