Abstract
The sulfonation of 1‐ and 2‐phenylnaphthalene, 1,1′‐ and 2,2′‐binaphthyl, and that of the 2,2′‐dihydroxy, 2,2′‐dimethoxy and 2,2′‐dimesyloxy derivatives of 1,1′‐binaphthyl with SO~3~ in dichloromethane as solvent was studied at 22 ± 2°C. Sulfonation of 1‐phenylnaphthalene and 1,1′‐binaphthyl leads to substitution at (each of) the α‐naphthyl moieties, initially at the 4‐position and subsequently at the 6‐ and 7‐position, in a ratio of approximately 8:92 and 14:86, respectively. Upon sulfonation the more planar 2‐phenylnaphthalene and 2,2′‐binaphthyl both give initially the 8‐sulfonic acid derivative (8‐S) and subsequently a mixture of 8,4′‐S~2~ and 8,8′‐S~2~, respectively; their further sulfonation affords mixtures of the 4,8,4′‐S~3~ + 6,8,4′‐S~3~ and of the 4,8,8′‐S~3~ + 6,8,8′‐S~3~, respectively, both in an isomer ratio of approximately 19:81.
Sulfonation of 2,2′‐dimethoxy‐1,1′‐binaphthyl gives initially the 3‐S and 6‐S derivatives in an isomer ratio of approximately 13:87 subsequently the 3,6′‐S~2~ and 6,6′‐S~2~ derivatives and eventually the 3,6,4′,6′‐S~4~ and 4,6,4′,6′‐S~4~ derivatives. Monosulfonation of 2,2′‐dimesyloxy‐1,1′‐binaphthyl gives the 5‐S and 6‐S in a ratio of 58:42. With a large excess of SO~3~, 4,6,4′,6′‐S~4~, 4,6,5′,7′‐S~4~ and 5,7,5′,7′‐S~4~ are eventually formed. Sulfonation of 2,2′‐dihydroxy‐1,1′‐binaphthyl gives initially the 5‐S and 6‐S, the ratio of which increases upon increasing the amount of SO~3~ employed from approximately 35:65 on using ≤ 1.0 mol‐equiv. of SO~3~ to approximately 62:38 on using > 6.0 mol‐equiv. of SO~3~. Under the latter conditions the substrate species undergoing sulfonation is proposed to be the di‐sulfated species 3.