GB861431A - Improvements in or relating to the production of benzimidazole derivatives - Google Patents

Abstract

Compounds of the general formula I <FORM:0861431/IV (b)/1> in which R and R1 are the same or different and are hydrogen or substituent groups and either or both of the benzene rings may carry substituents, are prepared by heating a compound of general formula II <FORM:0861431/IV (b)/2> or a mixture of a diamine of formula III <FORM:0861431/IV (b)/3> and malic acid or a functional derivative thereof, with orthophosphoric acid, pyrophosphoric acid or a polyphosphoric acid. R and R1 may be, for example, alkyl, hydroxyalkyl or alkenyl groups having 1-3 carbon atoms, or an aralkyl group. The benzene groups may carry as additional substituents, for example, halogen, methyl or methoxy groups. In the preparation of compounds of the formula given above in which R and R1 are other than hydrogen it is advantageous to introduce these substituents initially into the compounds of formula IV <FORM:0861431/IV (b)/4> by treatment with an alkyl, hydroxyalkyl, alkenyl or aralkyl halide or a dialkyl sulphate. Thus, for example, alkyl, allyl, hydroxyethyl, dihydroxypropyl or benzyl radicals may be introduced. The reaction of a diamine of formula <FORM:0861431/IV (b)/5> with malic acid or a functional derivative thereof to produce initially a compound of formula (II) <FORM:0861431/IV (b)/6> is preferably effected at 130-200 DEG C. in the presence of an inert solvent and an inert gaseous diluent. Alternatively, compounds of formula II <FORM:0861431/IV (b)/7> may be obtained by reacting a nitroamine instead of a diamine with malic acid or a functional derivative thereof and subsequently reducing the nitro groups with ring closure. In treating the compounds of formula II <FORM:0861431/IV (b)/8> with phosphoric acid it is advantageous to use an excess of phosphoric acid and to carry out the reaction at 130-200 DEG C. Specification 814,249 is referred to.