ALIPHATIC NITRO COMPOUNDS Nitromethane

Among aliphatic nitro compounds nitromethane was only recently recognized as an explosive. Tetranitromethane is not explosive but can form an explosive when mixed with combustible substances. Tetranitromethane possesses here a chMacter... 

The condensation of arylsulfonyl acetonitriles 369a-c with 22a proceeds via addition of the in-situ formed anion 370 to the arylsulfonyl acetonitriles 369 to afford the dimers 371, in 69-94% yield, and hexamethyldisiloxane 7 [136]. Furthermore, y9-dicarbonyl compounds such as ethyl acetoacetate 372 a or ethyl benzoyl-acetate 372b are O-silylated by 22 a or 22 c to rather stable alkyl 3-O-trimethylsilyl-oxycrotonoate 373a and alkyl 3-0-trimethylsilyloxy-3-phenyl acrylate 373b [130]. Aliphatic nitro compounds such as nitromethane are O-trimethylsilylated and further transformed into oligomers [132] (cf Section 7.6) and are thus unsuitable reactants for silylation-C-substitutions (Scheme 4.50). 

Many of the compounds that undergo ready base-catalysed keto i enol prototropic changes, e.g. / -keto esters, l,3-(/ -) diketones, aliphatic nitro compounds, etc., form relatively stable carbanions, e.g. (25), that can often be isolated. Thus it is possible to obtain carbanions from the keto forms of the /J-keto ester (23a) and nitromethane (24a) and, under suitable conditions, to protonate them so as to obtain the pure enol forms (23b) and (24i>), respectively. It thus seems extremely probable that their interconversion follows the intermolecular pathway (a). The more acidic the substrate, i.e. the more stable the carbanion to which it gives rise, the greater the chance that prototropic interconversion will involve the carbanion as an intermediate. 

Bowman has surveyed the reactions of cx-substituted aliphatic nitro compounds with nucleophiles, which undergo either S l substitution or polar reaction (Scheme 5.16).118 The reactions between a wide variety of nucleophiles and BrCH2N02 are shown in Scheme 5.17.119a b All the thiolates, PhS02 and I attack Br to liberate the anion of nitromethane. The hard nucleophiles, MeO , OH, and BH4 attack the hard H+ electrophilic center. Phosphorous nucleophiles attackthe oxygen electrophilic center, and only Me2S attacks the carbon electrophilic center. 

As in the case of other groups which activate adjacent CH6, the nitro group in aliphatic nitro compounds soon acquired importance in preparative organic chemistry, particularly for condensation reactions. The condensing agents are normally bases. Thus nitromethane will react with benzaldehyde to give first a nitro-alcohol and then a nitro-olefin (Priebs, 188425) ... 

Aliphatic nitro compounds are intermediates with considerable potential in orgarhc synthesis (cf. Section 9.6). Irhhally, ahyhc substitutions with nitromethane were investigated, but unfortunately complex mixtures of mono- and dialkylation products were formed. In contrast, good results were obtained with primary and... 

Besides solvation, a solvent can also participate in entrainment of ion-radical transformations. The reaction between tertiary aliphatic nitro compounds and the sodium derivative of nitromethane, NaCH2N02, is an example (Kornblum and Erickson 1981). To prepare NaCHjNOj, nitromethane is treated with sodium hydride. Then a tertiary aliphatic nitro compound is introduced into the solution formed. Several organic solvents were probed and CHjSOjCHj (DMSO) turned out to be the most effective. Kornblum and Erickson (1981) attributed this result to the formation of small amounts of NaCH2SOCH3 (sodium dimsyl) that was produced from DMSO as a result of its reaction with sodium hydride. Sodium dimsyl acts as a powerful one-electron reducer that induces the following chain anion-radical process ... 

Aliphatic nitro compounds nitroparaffins (e.g. nitromethane, nitroethane, etc.). 

The surface chemistry of the cyclic aliphatic nitro compound (nitrocyclohexane), shows some important similarities with that of nitromethane. 

This is an important method of preparing aliphatic nitro compounds. Preparation 239.—Nitromethane. 

In the case of simplest nitro compounds the absorption band produced by this group corresponds to the following values. For aliphatic nitro compounds, for example nitromethane, nitroethane, 1- and 2-nitropropanes, they are 260-270 mu at extinctions s = 40-120. (According to Ungnade said Smiley [1] the values for higher nitroparaffins are 274-278 mp, s = 24-41.) For aromatic nitro compounds, such as nitrobenzene the bands are 250-260 mp at extinctions s = 9000-10,000. When a primary or secondary nitro group takes an aci-form, the maximum disappears, as shown by earlier research work of Hantzsch and Voigt [2]. 

The largest group of organic molecular compounds, in which hydrogen bond formation plays no part, are the compounds, usually in the ratio 1 1, between on the one hand aliphatic and aromatic nitro compounds (nitromethane, tetranitro-methane, chloropicrin CC13N02, nitrobenzene, s-trinitrobenzene, picric acid), quinones, anhydrides (phthalic acid-and maleic acid anhydride) and ketones with on the other hand especially aliphatic and aromatic amines (aniline, pyridine), unsaturated aliphatic and aromatic hydrocarbons, ethers etc. 

Aliphatic nitro compounds are highly versatile building blocks in organic synthesis7 8 (see Scheme 1). For example, the nitroaldol addition (Henry reaction)9 leads to the formation of 1,2-nitro alcohols, 2, which are easily transformed into 1,2-amino alcohols, 3, by reduction, and into a-hydroxycarbonyl compounds, 4, by hydrolysis10 (Nef reaction). The former process, mostly using nitromethane, has been widely employed in carbohydrate chemistry.11... 

Aliphatic nitro compounds show a number of reactions which parallel those of carbonyl chemistry. Primary and secondary nitro compounds exhibit tautomerism paralleling keto-enol tautomerism (Scheme 3.94a). Aliphatic nitro compounds dissolve in aqueous sodium hydroxide with the formation of sodium salts. The resultant anions behave as carban-ions and will condense with aldehydes. An example involves the formation of m-nitrostyrene from nitromethane and benzaldehyde (Scheme 3.94b). 

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%... 

Because of their kinship to syntheses of nitro sugars, some syntheses of simpler, cyclic, aliphatic nitro compounds will be mentioned. Tetrahydropyran-2-ol, which is in tautomeric equilibrium with 5-hydroxypentanal (126), was found to undergo nitromethane addition catalyzed by sodium hydroxide to give120 tetrahydro-2-(nitromethyl)-pyran (128). Undoubtedly, the first reaction-product is the diol ni-tronate (127), which, under the conditions of processing (acidification and steam distillation), forms the cyclic ether 128. 

Aliphatic nitro compounds are characterized by another interesting and mechanistically important property. Based on tautomeric and protolytic equilibria the stable form of nitromethane in basic solution is that of a double bonded ac/-nitromethane anion, CH2=N02 , which becomes ready target for electrophilic radical additions. An example, studied by pulse radiolysis, is its reaction with hydroxyl radicals as formulated in eq. 3."... 

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

Mould producing fungi are more tolerant of trimethylol nitromethane than bacteria. However, trimethylol nitromethane and other methylolnitro-hydrocarbons cannot be ranked among the very effective formaldehyde releasing compounds, although in alkaline media there is a noticeable increase of the tendency, especially of trimethylol nitromethane, to release formaldehyde accompanied by a corresponding increase in efficacy. A report of Clark et al (1974) surveys the synthesis and antimicrobial activity of aliphatic nitro compounds. 

A significant improvement on the C-acylation of nitromethane anion (Vol. 3, p. 175) has been published, and the method extended to reaction with other aliphatic nitro-compounds. Thus, the generality of the reaction of acylimid-azoles with nitronate ions has been established and serves as a synthetic route to a variety of a-nitro-ketones and -esters (Scheme 38). Similarly, the C-carboxylation... 

Lundberg, P. (1989) Consensus report for nitromethane. Arbete och Halsa, 32, 86-91 Markofsky, S. (1991) Nitro compounds, aliphatic. In Elvers, B., Hawkins, S. Schulz, G, eds,... 

The above mentioned process of the transformation of compounds should also be possible for the other nitro compounds studied, nitromethane and nitrocyclohexane. However, no aliphatic nitroso compounds (or oximes obtained by isomerisation of the aliphatic nitroso compound) have been detected either in the gas or in the adsorbed phase. This is obviously caused by the easy migration of the a-hydrogen along... 

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 yields of nitro alcohols from simple nitroparaffins and aliphatic aldehydes or benzaldehyde are usually above 60%. The condensations are generally carried out with aqueous ethanolic sodium hydroxide, although weaker bases are sometimes desirable to prevent polymerization of the aldehyde. Sodium bisulfite addition compounds of the aldehydes are sometimes used. Better results are obtained with sodium methoxide than with alkali hydroxides in the condensation of nitroethane with formaldehyde. Sodium alkoxides are also used to effect the condensation of nitroethane with acetone and cyclohexanone. Condensation proceeds to the nitroalkanediol stage in certain cases with both nitromethane and with formaldehyde. ... 

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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