Chromium(VI) oxide dissolved in a mixture of acetic acid with concentrated hydrochloric acid converts, at or near room temperature, iodoarenes to (dichloroiodo)arenes, in a very simple and efficient procedure.
References
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KareleB. Ya., and NeilandO. Ya., Latv. PSR Zinat. Akad. Vestis, Kim. Ser., 1970, 587; Chem. Abstr. 1971, 74, 42033. They failed to chlorinate three iodonitrobenzenes, 4-iodobenzoic acid, and 2-iodoacetophenone; for ten appropriate iodobenzenes the crude yields for ArICl2 were 73–96%.
13.
Makhon'kovD. I., CheprakovA. V., and BeletskayaI. P., Zh. Org. Khim., 1986, 22, 681; Chem. Abstr., 1987, 106, 155951. Only iodobenzene was chlorinated there to give PhICl2 (75%; 94% purity).
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