Abstract
Chlorination of benzo-2,1,3-thiadiazole (I) in the presence of iron and paraform gives only 4-chlorobenzo-2,1,3-thiazole. Chlorination of 5,6-dimethylbenzo-2,1,3-thiadiazole (II) under exactly the same conditions gives only 5,6-dimethyl-4,7-dichlorobenzo-2,1,2-thiadiazole. Similarly chloromethylation of II in the presence of paraform gives only 5,6-dimethly-4,7-di(chloromethyl)benzo-2,1,3-thiadiazole. Chlorination and chloromethylation of I proceed through the intermediate formation of monosubstituted compounds which change into disubstimted ones.
It is known [2,3] that Chlorination of benzo-2,1,3-thiadiazole (I) and its 5,6-dimethyl derivative (II) with chlorine in the presence of iron gives mainly the 4,7-dichloro substitution products III and IV respectively.
It was previously shown [4] that chloromethylation of I with dichlorodimethyl ether in the presence of anhydrous aluminum chloride also gives mainly 4,7-di(chloromethyl)benzo-2,1,3-thiadiazole (V). Bases and pseudo-bases (paraform, urotropine. dimethylformamide) have a retarding effect on chloromethylation. When the reaction is run in the presence of these latter the products comprise besides V, 4-chloromethyl-2,1,3-thiadiazole (VI), or else, if enough base is added, there is no reaction.
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References
V. G. Pesin and S. A. D'yachenko, KhGS [Chemistry of Heterocyclic Compounds], 541, 1966.
V. G. Pesin, A. M. Khaletskii, and V. A. Sergeev, ZhOKh,33, 949, 1963.
V. G. Pesin, V. A. Sergeev, and A. M. Khaletskii, ZhOKh,34, 3028, 1964.
V. G. Pesin and E. K. D'yachenko, KhGS [Chemistry of Heterocyclic Compounds], 533, 1966.
V. G. Pesin, A. M. Khaletskii, and V. A. Sergeev, ZhOKh,33, 1759, 1963.
V. G. Pesin, A. M. Khaletskii, and Chao Chihchung, ZhOKh,27, 1570, 1957.
V. G. Pesin, V. A. Sergeev, and A. M. Khaletskii, ZhOKh,34, 1263, 1964.
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For Part XLII see [1].