The Preparation of the Pure cis-isomers of Four Fluorescent Whitening Agents of the Sulphonated Stilbene Type

Photoisomerisation of four purified stilbene-derived fluorescent whitening agents (FWA) in methanol solution, followed by removal of residual trans-isomer, has afforded the pure cis-isomers in good yield. Measurement of the u.v. absorption characteristics of the pure isomers has yielded data that now permit the determination, for any single FWA studied, of both the total concentration of FWA in solution and of the cis:trans isomer ratio