Quarternisation of Benzothiazoles and 1,2,3 - Benzothiadiazoles
The chemistry of 1,2,3-benzothiadiazola is briefly reviewed. The early work on the preparation and properties of methyl- and ethyl-1,2,3-benzothiadiazolium salts is described, and more recent work on 2-aryl-l,2,5-benzothiadiazolium salts is summarised. The limitations of methyl and ethyl iodides as quaternising agents for 1,2, 3-benzothiadiarzole are discussed. Alternative methods of quaternisation using the more reactive dimethyl and diethyl sul-phates, methyl toluene-p-sulphonate, and methyl and ethyl 2,4-dinitro- benzenesulphorates to give new quaternary salts are described and discussed. Ion-exchange methods were employed to obtain the halides of these quaternary salts. Alkyl-1,2,3-benzothiadiasolium salts were previously thought to be sulphonium salts. From the results of reductive fission of these salts, it now seems probable that the alkyl group is attached to N-3. Other evidence is also presented in support of this view. The results obtained for the preparation of methyl- and ethyl - 1,2,3-benzothiadiazolium salts indicated that esters of nitro-substituted benzenesulphonic acids (particularly 2,4-dinitrobenzene-sulphonates) would be most suitable for preparing higher alkyl- 1,2,3-benzothiadia7olium salts . The methods which have been used to prepare alkyl esters of aromatic sulphonic acids are reviewed. These techniques were then applied to the synthesis of alkyl, subsbitutod alkyl, and polymethylene bis 2,4-dinitrobenzGnesulphonates. The methods which were used to prepare the few alkyl 2,4-dinitrobenzonnaulphonatee previously recorded have been re-examined and the yields considerably improved. The quaternisation of 1,2,3-benzothiadiazole with higher alkyl, substituted alkyl, and polymethylene bis 2,4-dinitrobenzeoGsulphonat«s has been studied. A brief review of the quaternisation of benzothiaziole and some of its derivatives is given. Experiments on the quaternisation of benzothiazole using the esters of 2,4~dinitrobenzenesulphonic acid mentioned earlier were carried out to obtain a qualitative comparison of their reactivity*
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