Study On The Synthesis Of Thiabendazole

Thiabendazole is an efficient,broad-spectrum fungicide,with characteristic of lo ng-lasting effect,which is used for disease control of a variety of crops fungal and preservation of fruits and vegetables,even for industrial fungicides and insectifuge of human and animal gut.So,it is essential for a wide range of pesticides,pharma ceuticals and industrial area.The key production techniques of thiabendazole have n ot in the hands of domestic,which result in productioncapacity not yet meeting do mestic market demand,hence,the development and optimization of thiabendazole pr ocess is important to promote a broad market of thiabendazole.In this paper,firstly,2-?1-hydroxyethyl?benzimidazole was obtained by conden sation of o-phenylenediamine with lactic acid under acidic conditions,thenoxidized a lso catalyzed by H₂O₂ in the presence of phosphotungstic acid to give 2-acetyl benz ene imidazole,which halogenated by bromine to give 1-?1H-benzimidazol-2-yl?-2-bro moethanone,one finally cyclizated with thiocarboxamide to give 2-?4-thiazolyl?-1H-benzimidazole,namely thiabendazole.The effect of operation conditions on the rea ction was investigated through single factor experiment toobtain optimal synthetic co nditions.The results showed that:in the preparation of 2-?1-hydroxyethyl?benzimidazol e,the best results was obtained that yield was 96.7%and purity was 99.2%when t he reaction was carried out at 100 for 4 h with dosage of material n?o-phenylenedia mine?:n?lactic acid?:n?HCl?=1:1.2:1.2 and 20%hydrochloric acid chosen.O xidation reaction,the yield of 2-acetyl benzimidazole was 93.6%when n?catalyst?:n?2-?1-hydroxyethyl?benzimidazole?was 0.5:100 and temperature was 91?.Then the yield of 1-?1H-benzimidazol-2-yl?-2-bromoethanone was 88.8%when the ratio of n?2-acetylbenzyl and imidazole?:n?bromine?was 1:1.2 and the reaction temperature w as 10?.Finally the yield of thiabendazole was 81.7%and HPLC purity was 98.8%when the reaction was carried out at 45?with the ratio of n?1-?1H-benzimidazo l-2-yl?-2-bromoethanone?:n?thiocarboxamide?:n?phosphorus pentasulfide?=1:2.5:3.2.In summary,total yield of thiabendazole was 65.7%with 2-?1-hydroxyethyl?benzimi dazole as calculation basis.