The sodium salt ('Indicator R-Na') (I; X=Na) is ob- tained by dissolving the acid in water (1700 ml.), at 600, containing a slight excess of Na2CO3, salting out with NaCl (50 g.) and filtering when cold. Traces of impurity may be removed, if desired, by extraction of the dry salt with petroleum ether, b.p. 80-100o. Yield: 43 g.
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Channon et al. (1944) studied this question.
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