Reduction of Nitroalkanes

The combination PMHS/Pd/C reduces nitrobenzenes to anilines in high yields (Eq. 329),316 as does Et3SiH/RhCl(PPh3)3 (Eq. 330).554 This latter combination can also reduce both nitro and enone functionalities.554 

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Scheme 7.5. BusSnH-catalyzed reduction of nitroalkanes to alkanes...

Table 7.2. Bu3SnH-catalyzed reduction of nitroalkane to alkanes...

Supplemental Reference for Table 25. Organosilane Reduction of Nitroalkanes... 

Use of copper and silver salts in ethylenediamine solution provides a method for catalytic H2 reduction of nitroalkanes to oximes (541) ... 

Reduction of nitroalkanes RNO2 with samarium(II) iodide, obtained from samarium and 1,2-diiodoethane, yields either alkylhydroxylamines RNHOH or alkylamines RNH2, depending on the amount of the reagent434. The base-catalysed reaction of nitroalkanes with phenyl(vinyl) sulphoxide (399) yields the conjugate adducts 400, which fragment to allylic nitro compounds 401 on thermolysis435. 

Oximes RCH=NOH are produced in the reduction of nitroalkanes RCH2NO2 by carbon disulphide in the presence of triethylamine461 or wet potassium carbonate and... 

Knifton reported that solutions of cuprous salts in amine solvents are excellent catalysts for the selective reduction of nitroalkanes to the corresponding oximes. 

Fig. I4J Tafel plots for the reduction of nitroalkanes at the dropping mercury electrode. pH 6.65.

The reduction of nitroalkanes to A -monosubstituted hydroxylamines has not been extensively explored. The classical approach involves electrolytic reduction of primary and secondary nitroalkanes. Catalytic hydrogenation and hydride reductions of nitroalkenes also yield hydroxylamine derivatives. 

Primary and secondary nitroalkanes are reducible in acid and neutral solutions, whereas the formation of the anion of the aci form in alkaline solution generally prevents their reduction in this medium. Electrolysis of nitroalkanes in acid solution at low temperature yields as main product the corresponding alkylhydroxylamine [4-7], which is further reducible only in a rather narrow pH region, around pH 7. The electrolytic reduction of nitroalkanes in hydrochloric acid is probably the method of choice for the preparation of alkylhydroxylamines evaporation of the catholyte after reduction yields the alkylhydroxylamine hydrochloride in a rather pure form [6]. In Table 1 the yields of alkylhydroxylamines and amines from the reduction of some nitroalkanes are given. 

Table 1 Results from Electrolytic Reduction of Nitroalkanes at 20 C...

The cathodic reduction of nitroalkanes (primary and secondary) affords [50] (four-electron reduction in acidic or neutral media) the corresponding hydroxylamines that are often quite difficult to be converted into amines. 

Fu and co-workers have recently used tin catalysts to reduce thionocarbonates in which the turnover step is the reaction of BusSnOPh with PMHS (cf. Eq. 10) [38]. The same group has established Bu3SnH-catalyzed reductions of nitroalkanes to alkanes and azides to amines using PhSiH3 as the reagent for the regeneration of the tin catalyst [39, 40]. 

Synthesis of oximes and amines. Copper salts solubilized in aqueous alkyl polyamines solvents have been found to promote the homogeneous reduction of nitroalkanes to oximes by CO at atmospheric pressure and 85 C in good yields and conversion(9. Catalysis is favoured by the use of copper salts of weak acids solubilized in alkylpolyamlnes solvents of pKa > 9.2. The suggested reaction path involves the formation of a solvated cuprous carbonyl complex, which by combination with the nitroalkane anion gives a copper-nitroalkane complex ... 

Microperoxidase 8 is a heme octapeptide, obtained by enzymatic hydrolysis of heart Cytochrome c, in which a histidine is axially co-ordinated to the heme iron, and acts as a fifth ligand. It exhibits two kinds of activities a peroxidase-like activity and a cytochrome P45o-like activity. Ricoux et al. (2000) have shown that microperoxidase 8 is not only able to oxidise various aliphatic and aromatic hydroxyl-amines with the formation of microperoxidase 8-Fe(II)-nitrosoalkane or -arene complexes absorbing around 414 nm, but also that these complexes can be obtained by reduction of nitroalkanes. 

It will be recalled that methane (CH4) can be converted to nitromethane (H3CNO2) by the action of nitric acid on methane at high temperature (Chapter 6, Equation 6.10). The nitration of other alkanes by the same process can also be effected, but separation of the multitude of isomers that can be formed (from all but the simplest alkanes) can be difficult. Nitroalkanes, R-NO2 (sometimes accompanied by their corresponding nitrite isomers, R-ONO), can also be prepared (as shown in Chapter 7, Table 7.5e) by treatment of alkyl halides with nitrite anion (ONO ). Reduction of nitroalkanes (R-NO2) with hydrogen (H2) in the presence of a platinum (Pt) catalyst or lithium aluminum hydride (LiAIlT,) in ether produces the corresponding amine (Equation 10.18). 

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