Though sulfonephthaleins are used widely, there are only a few reports about their synthesis. Harden and Drake [ 6 6. Harden , W. ; Drake , N. A new series of sulfonephthaleins . J. Am. Chem. Soc. 1929 , 51 , 562 . [CrossRef] View all references ] synthesized a number of sulfonephthaleins having four halogens in the o-sulfobenzoic acid part of the molecules. The sulfonephthaleins were prepared by the addition of halogenated o-sulfobenzoic ...