The invention comprises compounds of the general formula: <;FORM:0843692/IV(b)/1>; in which R1 is an alkyl group and R2 a hydrogen atom or an alkyl group, with the proviso that R1 and R2 may be similar or dissimilar alkyl groups, acid addition salts thereof and a process for the manufacture of the said compounds by condensing a compound of the general formula: <;FORM:0843692/IV(b)/2>; with a hydrazine derivative of the general formula: <;FORM:0843692/IV(b)/3>; or reacting a hydrazone of the general formula: <;FORM:0843692/IV(b)/4>; with a reactive carboxylic acid derivative of the general formula: <;FORM:0843692/IV(b)/5>; in which X is a halogen atom or an O-alkyl group. Specification 843,689 is referred to.;FORM:0843692/IV(b)/5>;FORM:0843692/IV(b)/4>;FORM:0843692/IV(b)/3>;FORM:0843692/IV(b)/2>;FORM:0843692/IV(b)/1>