Patent ID: 7354457

Claim:
A process for pretanning, tanning or retanning an animal hide, comprising: obtaining a tanning agent prepared by reacting at least one aldehyde according to formula (I) where Z is an unsubstituted or substituted C 1 -C 12 -alkylene, unsubstituted or substituted C 5 -C 12 -cycloalkylene or unsubstituted or substituted C 6 -C 14 -arylene, with at least one further identical or different aldehyde according to formula (I), the reaction being carried out in the presence of an acidic catalyst and at least one further carbonyl compound according to formula (II) where each of R 1 to R 4 , independently of one another, is hydrogen, unsubstituted C 1 -C 12 -alkyl, unsubstituted C 3 -C 12 -cycloalkyl, unsubstituted or substituted C 7 -C 13 -aralkyl or unsubstituted or substituted C 6 -C 14 -aryl; and applying the obtained tanning agent to the animal hide.