R1???C6???H4???NH???C6H4???R2 wherein R1 is an alkyl group (preferably a branched alkyl group) having 6 to 12 carbon atoms and preferably 8 or 9 carbon atoms; and R2 is a hydrogen atom or an alkyl group (preferably a branched alkyl group) having 6 to 12 carbon atoms and preferably 8 or 9 carbon atoms.