Effect of Photostability of 2-Pyrazoline Fluorescent Whitening Agents on the Rate of Yellowing of Whitened Wool

Sulfonated 2-pyrazolines containing two, three, and four phenyl groups have been synthesized and examined as fluorescent whitening agents for wool. Although the photostability of these whiteners increases as the number of phenyl substituents is increased, the rate of photoyellowing of wool containing these whiteners has been found to be independent of the whitener used. The rate of photoyellowing of wool treated with the diaryl-2-pyrazoline (Ha) increases with increasing whitener concentration up to 0.4% owf and then remains constant up to a concentration of 1.6% owf—the highest level studied.