Nitro compounds, aliphatic nitroalkanes

In the course of the last two decades the chemistry of aliphatic nitro compounds— both nitroalkanes and nitroaJkenes has received particular attention. A variety of compounds have been obtained and their properties examined. 

Nitroalkane can be used as a convenient reagent for alkyl anion synthesis. Aliphatic nitro compounds can also be considered as versatile building blocks and intermediates in organic synthesis. They are readily available, and there are a wide variety of methods for converting the nitro group to other functional groups. 

Aliphatic and alicyclic ketones condense with primary nitroalkanes under the influence of A,A-dimethylethylenediamine to yield ally lie nitro compounds as mixtures of geometrical isomers, e.g. equation 125408. 

IV. PHOTOCHEMISTRY OF ALIPHATIC NITRO COMPOUNDS A. Simple Nitroalkanes... 

Aliphatic nitro compounds with the nitro group on a tertiary carbon were reduced to amines with aluminum amalgam [146 or iron [559]. 2-Nitro-2-methylpropane afforded ferf-butylamine in 65-75% yield [146. Even some secondary nitroalkanes were hydrogenated to amines. fra s-l,4-Dinitrocy-clohexane was converted to frans-l,4-diaminocyclohexane with retention of configuration. This may be considered as an evidence that the intermediate nitroso compound is reduced directly and not after tautomerization to the isonitroso compound [560] (see Scheme 54). 

Aliphatic nitro compounds are versatile building blocks and intermediates in organic synthesis,14 15 cf. the overview given in the Organic Syntheses preparation of nitroacetaldehyde diethyl acetal.16 For example, Henry and Michael additions, respectively, lead to 1,2- and 1,4-difunctionalized derivatives.14 18 1,3-Difunctional compounds, such as amino alcohols or aldols are accessible from primary nitroalkanes by dehydration/1,3-dipolar nitrile oxide cycloaddition with olefins (Mukaiyama reaction),19 followed by ring cleavage of intermediate isoxazolines by reduction or reduction/hydrolysis.20 21... 

MCPBA has been regarded as the reagent of choice for the conversion of primary aliphatic amines into the corresponding nitro compounds. The peroxy acid must be used in excess to minimize formation of dimers of the intermediate nitroso compounds, llie yield of nitroalkane is also increased if the reaction is carried out at elevated temperature, since this favors the monomeric rather than the dimeric foim of the intermediate nitrosoalkane and allows it to be oxidized further. For example, cyclohexylamine gave the dimer of nitrosocyclohexane (43%) when oxidized by MCPBA at 23 C, but at 83 C (in boiling 1,2-di-chloroethane) the only product was nitrocyclohexane (86%). 

When aliphatic nitro compounds are used instead of aldehydes or ketones, no reduction occurs, and the reaction has been referred to as a Tollens reaction (see 16-43). However, the classical condensation of an aliphatic nitro compound with an aldehyde or ketone is usually called the Henry reaction or the Kamlet reaction, and is essentially a nitro aldol reaction. A variety of conditions have been reported, including the use of a silica catalyst, Mg—A1 hydrotalcite, a tetraalkylam-monium hydroxide,proazaphosphatranes, " or an ionic liquid.A solvent free Henry reaction was reported in which a nitroalkane and an aldehyde were reacted on KOH powder. Potassium phosphate has been used with nitromethane and aryl aldehydes. The Henry reaction has been done using ZnEt2 and 20%... 

Evidence of the increasing interest in the field were Symposia on Nitro Aliphatic Chemistry in 1961 [I ] on Nitro Compounds in 1963 [2], and in 1968 13. Then a few excellent review articles appeared by Dolel el (4). Noble. Borgardt and Reed (5), Shechier 6aj, Shechter and R. B. Kaplan (6b], a review on nucleophilic substitution Sg 1 of aliphatic nitro compounds by Beletskaya and Drozd 245]. collective volumes edited by H. Feuer [7]. monographs by. Perekalin and Sopova 8). Novikov and co-workers (9. See also (1 20. Some books exist where the chemistry of nitroalkanes form important chapters, viz. by Asinger [lO], Matasdand Maiasd [ 1J. Sosnovsky 1 2. ... 

Photofragmentation is the principal primary process of excited aliphatic nitro compounds subsequently producing N02 and the corresponding radicals (entry 8), which may recombine to form nitrites. The excited nitroalkanes or nitroarenes can also be photoreduced in the presence of a hydrogen-atom donor (entry 9). 

Similarly, complexes NLL4 L = tertiary phosphine) react with aliphatic and aromatic nitro compounds RNO2 to yield the complex Ni(RNO)L2 and phosphine oxide (46). The ligand RNO is kinetically labile and readily displaced by phosphine L(47), thereby making it possible to design a catalytic oxidation cycle. For aliphatic nitroalkanes, oxygen transfer is retarded both... 

Mechanical sensitivity of the liquid aromatic nitro compounds is very lower and increased with the increase of the number nitro mechanical sensitivily of liquid nitro aliphatic compound is decreased with the increase of carbon atoms, and the mechanical sensitivity is dramatically increased with the increase of nitro group number on the same carbon atom for example, in nitromethane, its explosion limit is 7.3 % (volume) and its impact sensitivity is 0-8 % (hammer is 10 kg and characteristic drop height is 50 cm) mechanical sensitivity of nitro alcohol is lower than that of nitroalkane and aromatic nitro compounds. 

The simplest aliphatic nitro compound is nitromethane. Liquid aliphatic nitro compounds also include nitroalkanes including multi nitro groups and carbon atoms. 

Aliphatic nitro-compounds, as their nitronate anions, react with molybdenum peroxide, MoO5.py.HMPA, to give carbonyl compounds. Primary nitroalkanes give the carboxylic acid. A re-appraisal of potassium permanganate as oxidant for primary nitroalkane salts indicates this can be an excellent reagent for the preparation of aldehydes, particularly quaternary aldehydes. ... 

Interestingly enough, no reduction of aliphatic, unactivated nitro compounds seems to occur although the reduction of aromatic nitro compounds by BY is well documented [47,161,162] a few examples for the reduction of ketones containing an additional nitro moiety have been reported. However, these reactions gave only low yields of the desired hydroxy nitroalkanes [163,164]. Better results have been obtained using the masked amino ketones 122 (Fig. 34) to afford the (5 )-configurated alcohols 123. a,P-Unsaturated nitroal-kenes 124 were reduced with moderate to excellent e.e. to afford nitroalkanes 125. 

Since many aliphatic primary amines are usually prepared by methods not involving the reduction of a nitroalkane (cf. aromatic amines), their oxidation may provide a useful route to this class of compound. For amines which lead to tertiary nitroalkanes, potassium permanganate appears to be the most satisfactory reagent198 (the preparation of 2-nitro-2-methylpropane, Expt 5.191). In the case of amines which lead to primary or secondary nitroalkanes the oxidant of choice is m-chloroperbenzoic acid, and Expt 5.191 includes a general procedure for this reaction.199... 

Nitro groups can be introduced into aliphatic compounds by way of an aldol reaction between the anion of a nitroalkane and an aldehyde or a ketone. The a-hydrogens of nitroalkanes are sufficiently acidic that they are removed by bases such as aqueous NaOH and KOH. The of nitromethane, for example, is 10.2. The... 

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