Abstract
The reaction of three isomeric iodoanisoles with an excess of 80∼96% sulfuric acid at temperatures 20∼100°C has been investigated by the H NMR analysis of the sulfonation products. Both o- and p-iodoanisoles, [1] and [2], readily underwent disproportionation, giving 2, 4-diiodoanisole [4] and a mixture of four sulfonic acids, anisole-2- and 4-sulfonic acids, [5] and [6], 4-iodoanisole-2-sulfonic acid [7], and 2-iodoanisole-4-sulfonic acid [8].
With increasing temperatures, the relative yields of [4] and [6] decreased in favor of [8], while the relative yield of [7] did not change significantly (Table 2 and 3). Iodoanisoles recovered from the reaction mixture was found to consist both of [1] and [2], the latter being predominant. Interconversion between [1] and [2] occurred slowly even in 80% sulfuric acid at 20∼60°C, but under these conditions no disproportionation took place and the yields of [7] and [8] were quite small.
m-Iodoanisole [3] was readily sulfonated to give a mixture of 5-iodoanisole-2-sulfonic acid [9] and 3-iodoanisole-4-sulfonic acid [10], neither disproportionation nor isomerization being observed to occur.
A mechanistic analogy to the Reverdin rearrangement has been suggested for the sulfonation of [2] to [8].
