ox OUR PRESENT KNOWLEDGE OF AROMATIC DIAZO-COiMPOUNDS. 185 



diazonium salt with an alkali xanthate and hydrolysed the resulting 

 aromatic xanthate, thus obtaining either the thiophenol or the disulphide 

 produced by oxidation. Either of these products yields the correspond- 

 ing sulphonic acid on treatment with alkaline permanganate solution.' 



The production of sulphinic acids by the direct action of sulphurous 

 acid on diazonium salts appears to have been first observed by Miiller and 

 Wiesinger." A simple process, due to Gattermann,^ was accidentally 

 discovered during an investigation of o-methoxybenzenediazonium chloride, 

 when it was found that this salt on treatment with sulphurous acid yielded 

 a diazonium sulphite which, on mixing with copper powder, evolved 

 nitrogen giving rise to the corresponding sulphinic acid, this product 

 being subsequently oxidised by means of permanganate solution. 



In general, the reaction takes place most readily with the diazonium 

 sulphate, a cold solution of this salt in a large excess of dilute sulphuric 

 acid being saturated with sulphur dioxide and finally treated with copper 

 powder, 



RN2HSO4 -> RN2SO3H -^ N2 + RSO2H. 



In the case of the diazotised naphthylamines it is better to add their 

 solutions to the mixture of reduced copper and sulphurous acid. 



These processes for the production of sulphonic acids have not, how- 

 ever, been successfully applied to the diazonium salts derived from the 

 nitrated aromatic amines. 



5. Rejilacement of the Diazo-7'adicle by Hydrogen. — The method 

 originally employed for the elimination of the diazo-radicle consisted in 

 boiling the diazonium chloride with absolute alcohol ; this operation does 

 not, however, invariably give the requiied result, and Hantzsch ■* has 

 accumulated evidence in support of the view that the normal decomposi- 

 tion of a diazonium salt by an alcohol leads to the production of an alkyl 

 phenoxide. Benzenediazonium chloride or sulphate when boiled with 

 methyl alcohol yields anisole unaccompanied by benzene. Increase in 

 the molecular weight of the alcohol or the accumulation of negative 

 substituents in the aromatic nucleus diminishes the yield of ether and 

 augments that of the hydrocarbon. The benzenediazonium salts, when 

 treated with ethyl alcohol, yield phenetole and a trace of benzene ; their 

 chloro- and bromo-derivatives, when boiled with this reagent, give 

 halogenated benzenes but no substituted ethers, whereas methyl alcohol 

 converts them into mixtures consisting chiefly of the substituted phenoxide 

 and a small quantity of the halogenated hydrocarbon. Numerous 

 examples of this reaction will be found in the work of Remsen and his 

 pupils.'' 



In the case of diphenyltetrazonium chloride the elimination of the 

 diazonium radicle takes place in two stages, 



ClN2.CeH,.C,H,N.,Cl -> CoHs.CeH.N^Cl -> CeH,.C,H5.6 



The reversion to the parent hydrocarbon is more readily effected by 

 the process introduced by Baeyer and Pfitzinger,^ which consists in 

 reducing the diazonium salt to the hydrazine with stannous chloride, and 



' F. Baver & Co., D.R-P., 70286 ; W.ynne and Bruce, Trans., 1898, 78, 738. 



- Ber., 1879, 12, 1848. » Her., 1899, 32, 113C. 



* Bcr., 1901, 34, 3337. "■ Amer. C'/iem. J., 16, 105 ; 19, 581, 647, 561. 



' Ber., 1898, 31, 479. 



•» Ber 1885, 18, 90, 786 (compare Wynne and Bruce, he. cit.). 



