Benzimidazole derivatives and precursors

With a view to the relationship between the structure and action of glyodin, the research in the benzimidazole series was first centred on active substances containing long alkyl chains. Of these, l-methyl-2-phenyl-3-dodecylbenzimidazolium ion has been used in plant protection in the form of its insoluble salts. These salts such as the 

The most important derivatives used in agriculture are 2-substituted benzimidazoles (17) and 2-substituted aminobenzimidazoles (18). 

The derivatives of the above two parent compounds also substituted in position 1 represent a further group of compounds (19, 20). 

The alkyl esters of N-benzimidazol-2-yl-carbamic acid (22) can be prepared by the methylation of thiourea with dimethyl sulfate and the subsequent N-acylation in alkaline medium of the S-methyl-isothiourea formed (23) with the alkyl ester of chloroformic acid. Finally, N,N -bis(alkoxycarbonyl)-S-methylthiourea (24), obtained as an intermediate product is condensed with o-phenylene diamine in glacial acetic acid. 

The product can be filtered off as a dark brown crystalline substance (Harvey, 19S9 Klopping, 1960 Littrell et al., 1967). They can also be synthesised by the reaction of calcium cyanamide with chloroformic acid alkyl ester and o-phenylene diamine (Adams and Schlatter, 1966 Toth et al., 1972 Burmakin et al., 1974), or by the reaction of alkyl cyano carbamates (25), produced by the treatment of cyanamide with chloroformic acid alkyl ester, with o-phenylene diamine (Adams and Schlatter, 1969), or by the reaction of cyanamide with alkyl mercaptan, chloroformic acid alkyl ester and o-phenylene diamine (Schlatter, 1970)  

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