Preparing alpha hydroxy aliphatic sulphonates continuously - free of bisulphite, from sulphur dioxide, aldehyde and alkali hydroxide

摘要

An alkali metal or ammonium salt of an alpha-hydroxy aliphatic sulphonic acid is continuously prepd. by introducing an alkali metal or ammonium hydroxide and an aldehyde into a reactor, maintaining a hydroxy/aldehyde mol. ratio of at most 1, and introducing SO2 gas into the aq. phase regulating the pH to at most 7.0. The cpds. are used as hardeners in photographic development baths. The solns. of these cpds. must be stable to storage and free from HSO3 ions (max. 0.05%). The above process provides such solns. other possible methods using ion exchangers are too complicated.