Hydrogen chloride with nitro compounds

Both aliphatic and aromatic nitro-compounds can be readily reduced in acid solution to the corresponding primary amine. Thus when a mixture of nitrobenzene and tin is treated with hydrochloric acid, the tin dissolves to give stannous chloride, SnCh, which in these circumstances then reacts with more acid to give stannic chloride, SnCl, and the nascent hydrogen produced from... 

An equihbrium mixture of the isomers usually contains a much higher proportion of the tme nitro compound. The equiUbrium for each isomeric system is influenced by the dielectric strength and the hydrogen-acceptor characteristics of the solvent medium. The aci form is dissolved and neutralized rapidly by strong bases, and gives characteristic color reactions with ferric chloride. 

These may be prepared by reduction of appropriate nitro compounds. The free amines are unstable, but can be isolated as the tin(IV) chloride double salts, and give stable acetyl derivatives. 2-Acetamidothiophene has been prepared by a Beckmann rearrangement of the oxime of 2-acetylthiophene (63AHC(l)l). 2-Aminothiophene hydrochloride was isolated in 84% yield when cw-4-benzhydrylthiocrotononitrile was treated with hydrogen chloride gas in dry ether (equation 46) (69JHC147). 

In this section, consideration will be given to the actual processes of acetal- or ketal-formation and not to the more indirect methods by which acetals and ketals of the polyhydric alcohols may be synthesized from compounds (e.g. derivatives of the monosaccharides) containing preformed alkylidene or arylidene groupings. The condensation of a carbonyl compound with a glycol is facilitated by acidic catalysts, and, since the reaction is reversible, by dehydration. The catalysts most frequently employed are concentrated sulfuric, hydrochloric and hydro-bromic acids, gaseous hydrogen chloride, zinc chloride and cupric sulfate others are phosphorus pentoxide, sulfosalicylic acid, and anhydrous sodium sulfate. The formation of benzylidene compounds is promoted less efficiently by phosphorus pentoxide than by either concentrated sulfuric acid or concentrated hydrochloric acid 1" the reaction is assisted by chloro- and nitro-substituents on the aromatic nucleus, but hindered by methyl- and methoxy-groups.18... 

The air-sensitive Cp-substituted hydridovanadium complex is obtained by hydrogenolysis of the corresponding methyl derivative. The corresponding anionic compound is obtained by reduction of CpV(CO)4 with sodium and protonation with water (Scheme 64). Thus obtained [CpVH(CO)3] (106) is a useful one-electron reductant to reduce bromo- and iodoalkanes, bromoalkenes, and arylbromides in THF. Furthermore, acid chlorides are reduced to the aldehydes. A similar reduction with (106) is performed by using phase-transfer conditions in the presence of tetrabutylammonium hydrogen sulfate. Nitro compounds and organic halides are reduced under these conditions. 

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