Green Synthesis of 2,2'-Bibenzazole and Its Polymers by Using Hexachloroacetone as C2 Synthon

A novel cyclization reaction by using hexachloroacetone as C2 synthon has been studied. The optimal condition was obtained by synthesis of bibenzothiazole in the presence hexachloroacetone in water. Experimental results showed that the nucleophilicity of substrates played a key role in the cyclization reaction, and catalytical amount of oxygen in reactions was also vital to trigger ring fusion in the formation of target compounds. Accordingly, the mechanism of cyclization reaction was proposed: the thiazole ring is formed in the first place by a nucleophillic attack of 2-aminobenzenethiol, followed by CCl3 cleavage from hexachloroacetone. Then the second 2-aminobenzenethiol launches another nucleophilic attack, and three chloride ions leave to form the second thiazole ring. The method was applied to the substrates of 2,5-diaminobenzene-1,4-dithiol and benzene-1,2,4,5-tetraamine, respectively and two polymers of polyphenylene dithiazole and polyphenylene diimidazole were successfully prepared. The experimental conditions were mild, the yield was high and the application value was high.