Leaving Group Dependence of the Rates of Halogen-Magnesium Exchange Reactions

Relative reactivities and absolute rate constants of the reactions of haloarenes with i-PrMgCl center dot LiCl were investigated in THF at 0 degrees C. The rate of the halogen-magnesium exchange decreases in the series Arl > ArBr > ArCl (relative reactivities: 10(11):10(6):1). Preliminary experiments show that the p-tolylsulfinyl group is exchanged slightly faster than iodide, while a tosyl group is exchanged at least 10(4) times more slowly than a bromide.