The New Method Study On The Synthesis Of Benzonthiazole Derivatives By Disulfides

Benzothiazole derivatives are an important class of heterocyclic compounds, which havebeen widely used in agriculture, industry, medicine fields and so on. Since benzothiazolederivatives were found, the synthetic method had become a research focus in organicchemistry.Benzothiazole derivatives were mainly synthesized by o-aminobenzenethiol,2-haloaniline, thiourea or thioamides. However, o-aminobenzenethiol was not stable andwas oxidized into disulfides easily, while thiourea compounds suffered from complexsynthetic process and high cost. Herein, some new synthetic methods of benzothiazolederivatives prepared by the stable starting material disulfides have been appeared in recentyears.This dissertation is a first successful example to synthesize substituted benzothiazlesfrom stable and readily available materials disulfides and carboxylic acids mediated byphosphorus trichloride in one-pot tandem reactions. The synthetic method has theadvantages of simple operation, short synthetic steps, short reaction time, which is a newmethod for synthesis of benzothiazole derivatives.The main content of this dissertation show as follows:1. The novel synthetic method to prepare2-substituted benzothiazole derivatives wasproduced by the reaction of disulfides and carboxylic acids. Through the optimization ofthe reaction conditions, the highest yield of2-substituted benzothiazole derivatives wasobtained when the disulfides reacted with carboxylic acids mediated by phosphorustrichloride in the ratio of1:2.0:2.4(disulfides/carboxylic acids/PCl3) under an inertatmosphere of Ar in anhydrous toluene at100℃.2. Under the best reaction condition,18benzothiazole compounds (two new compounds)were synthesized by the recation of aromatic disulfides with different substituted aromaticcarboxylic acids and aliphatic carboxylic acids, which show this synthetic method couldmake various carboxylic acids react with different disulfides effectively. Furthermore, thestructure of the synthetic compounds were characterized by mass spectrometry, nuclearmagnetic resonance and so on. 3. A variety of carboxylic acids were examined under the optimized reaction conditionsto explore the scope of the substrates. During the experimentation, the aromatic carboxylicacids or aliphatic carboxylic acids all could react with the disulfides to synthesize thecorresponding benzothiazole derivatives. In the absence of DBU, the benzothiazolederivatives were obtained in a higher yield when the aromatic carboxylic acids containingelectron-donating groups than electron-withdrawing groups. However, in the presence ofDBU, the aromatic carboxylic acids containing electron-withdrawing groups could offer ahigher yield of aim product than the aromatic carboxylic acids containingelectron-donating groups. After adding DBU into the reaction solution of aliphaticcarboxylic acids, all the yield of aim product decreased obviously. Furthermore, differentdisulfides could react with carboxylic acids to produce the corresponding benzothiazolederivatives.4. The possible reaction mechanism could be speculated through experiments.Benzothiazole derivatives were synthesized via the reaction of the disulfides andcarboxylic acids mediated by PCl3through two routes containing the preferential cleavageof the S-S bond and subsequent cleavage of the S-S bond. The preferential cleavage of theS-S bond mechanism was the main route to prepare benzothiazole from the disulfides. PCl3was not only used to prepare acyl chloride from carboxylic acids, but also to break the S-Sbond of the disulfides.