Nitrocyclohexane reduction

The only other nitroparaffin manufactured on a large scale was nitrocyclohexane [1122-60-7] made by Hquid-phase nitration of cyclohexane. Nitrocyclohexane was the starting material for S-caprolactam via reduction to cyclohexanone oxime. This process has been superseded by other, more efficient processes (see Caprolactam). Nitrocyclohexane is not being produced ia large quantities for either captive use or sale. 

In addition to the present method,2 1-amino-1-methylcyclo-hexane has been synthesized by the following procedures Ritter reaction, e.g., with 1-methylcyclohexanol (76%, 67%)3i 4 or 1-methylcyclohexene (35%,) 4 5 Hofmann reaction with 1-methyl-cyclohexanecarboxamide (80% as hydrochloride) 6 reduction of 1-methyl-l-nitrocyclohexane (63%) 6 Schmidt reaction with 1-methylcyclohexanecarboxylic acid (42%).6... 

Various procedures have been developed for the production of oximes from nitroparaffins. Direct reduction with zinc dust and acetic acid has been proposed, but the yields are poor because of the simultaneous formation of amines. A synthesis for cyclohexanone oxime has been demonstrated which involves the formation and selective hydrogenation of 1-chloro-l-nitrocyclohexane. The halogenated intermediate is prepared in quantitative yield by chlorination of the sodium salt of acz -nitrocyclo-hexane, and subsequent hydrogenation is performed in an 80% yield over palladium-on-charcoal, ... 

A novel dehydrogenation-reduction of nitrocyclohexane at 420°C over PdO-Al Oj catalysts yields aniline ... 

Titanium(II) reagents have also been used to reduce aliphatic nitro compounds to amines halo, cyano and ester groups are not reduced. Sodium borohydride, in the presence of catalytic amounts of nickel(II) chloride, reduces a variety of aliphatic nitro compounds to amines. Nickel boride (Ni2B) is an active catalyst for reductions of primary, secondary and tertiary nitro aliphatic compounds to amines. The reduction of nitrocyclohexane (45) yields cyclohexylamine (47) as well as small amounts of dicyclohexylamine (49), the latter being formed via reaction of intermediates (46) and (48 equation 28). 

Other complex metal hydrides can only rarely be applied to reduction of C=C bonds. Sodium borohydride, which can be used in aqueous-alcoholic solution, seems not normally to attack ethylenic bonds. A few cases only of partial reduction of cyclic iminum salts96 and of selective reduction of unusually activated ethylenic bonds97 have been reported. However, some polynitro aromatic compounds, e.g., 1,3,5-trinitrobenzene, can be converted in high yield with saturation of the aromatic system into nitrocyclohexanes or nitro-cyclohexenes.98 Sodium hydridotrimethoxyborate has proved valuable as a mild reducing agent for preparation of a series of nitroparaffins from nitro-alkenes."... 

Under suitable conditions it is possible to isolate the A-substituted hydroxylamines that are formed as intermediates in the reduction of nitro compounds. For this purpose it is essential in the reduction of aromatic nitro compounds to work with neutral or nearly neutral solutions suitable reducing agents are hydrogen and platinum oxide catalysts in glacial acetic acid,82,83 zinc dust in ammonium chloride solution,84 aluminum amalgam,85 and ammonium sulfide.86 Aliphatic nitro compounds may be reduced as their alkali salts (nitronates) by diborane in tetrahydrofuran, then giving A-alkylhydroxyl-amines 87 for instance, A-cyclohexylhydroxylamine is thus obtained from nitrocyclohexane in 53% yield. However, aliphatic nitro compounds are converted into A-alkylhydroxylamines more simply by catalytic hydrogenation in the presence of palladium-barium sulfate unlike aromatic nitro compounds, aliphatic nitro compounds require an acid medium for reduction to hydroxylamines an oxalic acid medium has proved the most suitable. 

When a mixed catalyst containing silver is used, the hydrogenation of nitroalkanes can be conducted so that reduction stops at the oxime stage this has been studied in detail for nitrocyclohexane.74... 

In a process developed to commercial maturity by DuPont, and industrially practiced by this company from about 1963 to 1967 [121], cyclohexanone oxime is obtained by a route that encompasses the nitration of cyclohexane to nitrocyclohexane and the reduction of the latter to the oxime, which is converted to caprolactam by the Beckmann rearrangement. According to U.S. Patent 2,634,269, nitrocyclohexane can be converted directly to caprolactam in the gas phase at 25(F450°C using a polyborophosphate catalyst. 

Cydohexylamine is generally produced by catalytic liquid-phase hydrogenation of aniline under high pressure (60 bar) at 230 ""C on cobalt catalysts. Alternative methods of synthesis are the ammonolysis of cyclohexanol at 200 bar and 220 °C on a calcium silicate catalyst, the catalytic ammonolysis of cyclohexyl chloride and the reduction of nitrocyclohexane. 

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