| abstract |
A process is described for isomerizing the cis,cis- and cis,trans-isomers of di-(p-aminocyclohexyl)methane to the corresponding trans,trans-isomer. The starting isomer, or mixture of isomers, is converted to the corresponding bis-benzaldimine by reaction with benzaldehyde (or benzaldehyde containing 1 to 3 inert substituents), the bis-benzaldimine is isomerized in the presence of a basic catalyst (potassium t-butoxide, potassium hydroxide preferred) to give predominantly the trans,trans-isomer of the bis-benzaldimine, and the latter is subjected to acid hydrolysis to yield the trans,trans-isomer of the free diamine. The process can be applied to the individual cis,cis- and cis,trans-isomers of the diamine as well as to admixtures of these isomers with the trans,trans-isomer, such as the mixtures of these stereoisomers obtained by catalytic hydrogenation of di-(p-aminophenyl)methane. |