Patent GB-388989-A (GB)
Title: Improvements in making tanning materials
IPC: C14C3/20
Filed: 1932-07-07
Abstract: Synthetic tanning-materials are manufactured by condensing an aromatic sulphonic acid with an aldehyde in the presence of thiourea or substances which readily yield thiourea, e.g. ammonium thiocyanate.  The amount of thiourea or substance yielding it required is of the order of a catalytic amount but depends on the nature of the sulphonic acid employed.  Suitable starting materials are the simpler aromatic sulphonic acids or preferably the sulphonation products of phenolic compounds.  The sulphonation for the preparation of these compounds may be carried out by any standard method, e.g. by means of sulphuric acid, chloro-sulphonic acid or oleum, the nature of the finished product varying with the degree of sulphonation.  At the end of the reaction the mixture is diluted and partially neutralized, and may be used directly in tanning, alone or in conjunction with mineral and vegetable tanning materials.  The products are particularly suitable for the production of white leather.  They are also useful for securing even colouring with acid or direct dyes, and as mordants for basic dyestuffs.  In example: (1) phenol is sulphonated by means of sulphuric acid at 95-100 DEG  C. and the product condensed with formaldehyde in the presence of thiourea; the product, after neutralization of excess mineral acid, may be employed in the following processes: (a) in tanning pickled sheepskins in the presence of salt solution; (b) in supplementary tannage of chrome tanned kidskins; (c) in supplementary tannage of alum tanned pigskins; (d) in tanning pickled calfskins, in conjunction with Quebracho extract; (e) in tanning pickled snakeskins in the presence of brine; (f) in yard tannage for heavy leather, to replace part of the vegetable extracts used to make up the layers; (2) phenol is sulphonated with sulphuric acid at 40 DEG  C. and the product condensed with acetaldehyde in the presence of thiourea; (3) 4 : 4<1>-dihydroxydiphenyldimethylmethane is sulphonated by means of chlorosulphonic acid at 60 DEG  C. in the presence of glacial acetic acid and zinc, and the product is condensed with formaldehyde in the presence of thiourea; (4) 4 : 4<1>-dihydroxydiphenyldimethylmethane is sulphonated by means of sulphuric acid at 60 DEG  C. and the product condensed with formaldehyde in the presence of thiourea; (5) phenol is sulphonated by means of sulphuric acid at 95-100 DEG  C. and the product condensed with formaldehyde in the presence of ammonium thiocyanate; (6) naphthalene is sulphonated by means of sulphuric acid at 140 DEG  C. and the product condensed with paraformaldehyde in the presence of thiourea; (7) o-, m- or p-cresol is sulphonated by means of sulphuric acid at 70-80 DEG  C. and the product condensed with formaldehyde in the presence of thiourea; (8) p-tertiary butyl phenol is sulphonated by means of sulphuric acid at 95 DEG  C. and the product condensed with formaldehyde in the presence of thiourea; (9) the thiourea in (8) is replaced by the product of condensation of equimolecular quantities of thiourea and formaldehyde in dilute acid solution.  The products of examples 2 to 9 may, after neutralization, be directly employed in tanning as in example 1.