GB893338A - Synthetic tanning agents - Google Patents

Abstract

A synthetic tanning agent comprises the condensation products of a diaryl sulphone having the formula <FORM:0893338/IV (a)/1> -wherein R and R1 may be the same or different and represent a hydrogen atom or a methyl radical-and a neutralized, partially disulphonated derivative of a bis-phenol of formula <FORM:0893338/IV (a)/2> -wherein R2 is a methyl or ethyl radical and R3 is as R and R1 above-the degree of sulphonation being an average of 75 to 85% of the theoretical amount for a disulphonated bis-phenol. The tanning agent is prepared by reacting 0,75 to 1 mole of the sulphone with 1 mole of the sulphonic acid salt and with 1,5 to 2 moles of formaldehyde in the three stages (1) using 0,5 to 0,7 mole of formaldehyde, a reaction time of 4 to 5 hours and a weakly acid or weakly basic medium, (2) using 0,5 to 0,7 mole of formaldehyde, a reaction time of 2 to 4 hours and a neutral medium and (3) using 0,5 to 0,7 moles of formaldehyde, a reaction time of 4 to 5 hours and a weakly acid or weakly basic medium, the pH of the medium for stage (3) being the opposite to that used in stage (1). The formaldehyde for the condensation may be provided by formalin, para formaldehyde, trioxane or monomethylol dimethyl hydantoin. In Example I the sulphone is prepared from phenol and 100% sulphuric acid and the sulphonated bis-phenol from 2,2 bis(p-hydroxyphenyl)propane and 98% sulphuric acid. The phenol used to prepare the sulphone in Example II is a mixture of phenol itself and a technical cresol containing 54% m-cresol, 29% p-cresol and the remainder other phenols containing o-cresol and phenol. Specifications 481,308 and 615,190 are referred to.