[36049-77-1] · C14H25IN2 · N-Methyl-N,N´-dicyclohexylcarbodiimidium Iodide · (MW 348.31)
(conversion of alcohols to iodides)
Physical Data: colorless hygroscopic crystals; mp 111-113 °C.
Preparative Method: 1,3-Dicyclohexylcarbodiimide (42 g, 0.204 mol) was dissolved in a large excess of Iodomethane (90 mL, 1.45 mol) and stirred at 70 °C for 3 days under a nitrogen atmosphere. The excess MeI was removed by distillation under reduced pressure and the residue was dissolved in dry toluene (150 mL) at 40 °C. The resulting crystalline mass was filtered off under an inert atmosphere and the crystals were washed with cold, dry toluene until colorless. The product was dried under vacuum (0.1 mmHg) at rt to provide 35 g (75%) of colorless crystals.
Handling, Storage, and Precautions: the compound should be stored under an inert atmosphere at refrigerator temperatures, where it is reputed to be stable for several months.
First reported in 1972, the sole reported use of N-methyl-N,N´-dicyclohexylcarbodiimidium idodide (1) is in the conversion of alcohols to iodides. The original article1 contains the first description of the preparation in bulk of a carbodiimidium salt and describes its use in the preparation of some primary and secondary iodides. In three of the examples, inversion of configuration was exclusive, (2) -> (4), hinting at a mechanism such as that shown in eq 1. The reagent was said to be good for the preparation of very hindered secondary iodides, but the yields are generally low (eqs 2 and 3). The reagent is, however, quite successful in preparing iodides from alcohols in multifunctional compounds (6),2 (7),3 and (8).4
Kim F. Albizati
University of California, San Diego, CA, USA