The use of iodine in 20% oleum for the iodination of a range of aromatic nitro-compounds is described. The conditions necessary to achieve reaction and proof of the identities of the products are included. The system has been found to behave as an electrophilic reagent but it will not introduce an iodine atom ortho to a nitro-group.Technology, Romford Road, London E.15 THE direct iodination of aromatic molecules containing deactivating substituents has received little attention. Suitable reagents are those involving cationic iodine in concentrated sulphuric acid or oleum. Iodine in 50-65% oleum,2 in which the electrophile is probably3 12+, has frequently been used to polyiodinate singly and double deactivated molecules, but it is difficult to use for partial iodination under controlled conditions, as the reaction mixture usually has to be heated to remove the 1
Spectrophotometric, conductometric, cryoscopic, and magnetic studies of solutions of a wide range of iodine-containing compounds in sulphuric acid and in oleum provide evidence for the ions Ib+, 13+, and H,IO,+, in addition to I+. Some indication that IO+ is formed in 65% oleum is adduced, and it is suggested that white crystals obtained from such solutions are the ionic compound (IO)HS,O,.Various oxidation-reduction equilibria in these solutions have been elucidated.
PREVIOUS reports1 of the iodination of aromatic compounds with iodine in oleum have been concerned with iodine in 50-65% oleum in which the electrophile is probably2 the cation 1 :. This reagent will polyiodinate benzene derivatives containing two deactivating groups but partial iodination under controlled conditions is difficult, as the reaction mixture has to be heated to remove much of the sulphur trioxide before dilution and isolation.
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