Solvent-Free and Liquid-Phase Iodination of Thiophene Derivatives with Potassium Dichloroiodate Monohydrate

Iodination of a series of benzene and thiophene derivatives by potassium dichloroiodate monohydrate was studied with and without a solvent. The liquid substrates tend to be more reactive in water while the solid substrates afford better yields in dichloromethane or under the solvent-free conditions. The 2-substituted thiophenes show good to excellent yields whereas the yield for 3-substituted and 3,4- or 2,4-disubstituted thiophenes and benzene derivatives are significantly lower. The mechanochemical reaction of 5-carbaldehyde-2,2′-bithiophene shows excellent yields, while 2,2′-bithiophene gives practical yields only in dichloromethane. In the case of thiophene and N-acetyl-p-toluidine, electrophilic iodination is accompanied by a small extent of chlorination.