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Abstract
The sulfur trioxide sulfonation of diphenyl ether (1), diphenyl sulfide (2), and the related tricyclic dibenzo-[b, e][1, 4]dioxin (3) and xanthene (4) has been studied. The substrates 1 and 2 both yield initially the 4-sulfonic acid derivative (4-S) and subsequently the 4, 4′-S2. In a large excess of 104.5 wt-% H2SO4 the further sulfonation of 1-4, 4′-S2 gave the 1-2, 4, 4′-S3 and subsequently some 1-2, 4, 2′,4′-S4. Sulfonation of the dibenzodioxin 3 with 4.0 mol-equiv. of SO3 gave the 2-S derivative, whereas with 12.0 mol-equiv. of SO3 a mixture of the 2, 7-S2 and 2, 8-S2 was obtained in yields of 57 and 43%, respectively. Sulfonation of xanthene (4) with 4.0 mol-equiv. of SO3 yielded the 2, 7-S2 derivative.