Reactions of N-Acyloxy-2-nitrobenzenamines. I. Thermolysis in Benzene or Bromobenzene

N-Acyloxy-2-nitro- and N-acyloxy-2,4-dinitro-benzenamines have been pyrolysed at 140� in benzene or bromobenzene solution. Homolysis (to form RCO2 and ArNH ) is ruled out since virtually all the carboxylate is isolated as carboxylic acid. This acid might arise via a concerted elimination process (the other product being a benzofurazan 1-oxide), or via heterolysis to ArNH+, RCO2- with subsequent transfer of proton, and cyclization of the singlet 2-nitrophenylnitrene. These simple reactions compete with bimolecuiar reactions of products with substrate, in which the corresponding amine, azoxy compound and acid anhydride are generated. Attempts to synthesize N-tosyloxy derivatives of nitrobenzenamines gave only thermal decomposition products. N-Trifluoroacetoxy-2,4-dinitrobenzenamine was isolated as a crude product which detonated violently.

On the involvement of diazonium ions in the photorearrangement of azoxybenzene

Photolysis of aromatic azoxy compounds in non-basic solvents in the presence of 2-naphthol leads quite generally to azonaphthols in addition to the normal photorearrangement product. Free diazonium ions are implicated as the precursors of the azonaphthols, both the latter and the usual photorearrangement product being derived from the same excited state of the azoxy compound. Variation of the solvent, light intensity, substrate concentration, and percent reaction all cause changes in the product distribution. Such changes can be accommodated by postulating an intermediate which can either afford the normal rearrangement product by loss of a proton to a weak base, or expel a diazonium ion when no base is present.

ORGANIC SULFUR COMPOUNDS: PART I. BENZOTHIAZINE HYDROXAMIC ACIDS AND RELATED COMPOUNDS

2H-1,4-Benzothiazine hydroxamic acids of type V (see Table I) are readily prepared by reducing suitably substituted (o-nitrophenylthio)acetates (II, R″ = Me or Et) by means of sodium borohydride and palladium–charcoal. The ester precursors can be prepared by the interaction of o-nitrothiophenols and α-bromoesters, but such a method is limited in scope. Diethyl bromomalonate, for example, reacts atypically with o-nitrothiophenol. The ester precursors are better prepared by Fischer–Speier esterification of the corresponding acids (II, R″ = H) which, in turn, are the products of nucleophilic attack by α-mercaptoacids on suitable o-chloro- (or bromo-) nitrobenzenes. This general preparative method failed in two instances. When o-chloronitrobenzene or 4-chloro-3-nitrotoluene was reacted with α-mercaptoisobutyric acid, the only acidic product obtained was α.,α′-dithiodiisobutyric acid.Reduction of methyl 2-(o-nitrophenylthio)benzoate (VI) with sodium borohydride and palladium–charcoal gave an azoxy compound, namely 2,2'-bis((o-methoxycarbonyl)phenylthio)azoxybenzene (VII).

THE IDENTIFICATION OF AZOXY COMPOUNDS

An azoxy compound can be treated with concentrated sulphuric acid to produce a nydroxyazo product consisting chiefly of the para isomer. This reaction, the Wallach rearrangement, is the basis for a suggested generic test for an azoxy compound. For the identification of a given azoxy compound, two derivatives are suggested: the hydrazo compound produced by the reduction of the azoxy compound by zinc dust, and the azo compound produced by the oxidation of the hydrazo compound. These compounds are described for the first time: 2,2′-dichloro-4-hydroxyazobenzene, 2,5′,2,5′-tetrachloro-4-hydroxyazobenzene, 2,2′-dimethoxy-5,5′-dichloroazobenzene, 3,3′,4,4′-tetrachlorohydrazobenzene, 2,2′-dimethyl-3,3′-dichlorohydrazobenzene, and 2,2′-dimethoxy-5,5′-dichlorohydrazo-benzene.