Tanning agents prepared from ammonium bisulphite and phenol-formaldehyde condensates

• Main Authors: MAUTHE GUSTAV, KOMAREK ERNST
• Format: Patent
• Language: English
• Published: 29.03.1961
• Subjects: APPARATUS THEREFOR; CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING,IMPREGNATING, FINISHING; CHEMISTRY; COMPOSITIONS FOR TANNING; HIDES; LEATHER; METALLURGY; PELTS; SKINS

864,079. Tanning leather. FARBENFABRIKEN BAYER A.G. Nov. 26, 1958, No. 38199/58. Class 76. [Also in Group IV (a)] Synthetic tanning agents, which are practically free from ash and have a purity number greater than 90, are prepared by reacting a phenol or a polyphenol with a molar excess of formaldehyde in the presence of a small amount of an alkali metal hydroxide, neutralizing the mixture and, after separation of the low molecular weight salt-containing resin, further reacting it with ammonium bisulphite. Phenols and polyphenols specified are phenol itself, o-, m- and p-cresols, o-, m- and p-chlorophenols; dihydroxydiphenylmethane, dihydroxydiphenyl-dimethylmethane, dihydroxydiphenylsulphone and the corresponding dihydroxydiphenyl compounds obtained from the other above-specified phenols; empyreumatic oil; and low molecular weight novolacs. The ammonium bisulphite is preferably formed during the reaction by first adding ammonia and then introducing gaseous sulphur dioxide. The tanning agents can be used not only for the manufacture of white leather but also as pretannins, re-tannins and exchange tannins; they are especially useful for continuous use in the pit systems. In Example 2, a cow-hide, limed, split to 3 mm., delimed and mordanted in the usual manner, is drum tanned with a tannin mixture consisting of 250% water, 7% pure tannin Quebracho sulph., 7% pure tannin Mimosa sulph. and 7% pure tannin prepared by reacting ammonium bisulphite with a low molecular weight novolac which has been further reacted with formaldehyde in the presence of sodium hydroxide; the leather is then fatliquored and finished in the usual manner. Another example describes the pre-tanning of a cow-hide with a tanning agent of the invention followed by treatment with vegetable tanning agents. Other examples describe the treatment of goat-hides and cow-necks.