Reaction of dichloromethane with pyridine derivatives under ambient conditions.

Pyridine derivatives and dichloromethane (DCM) are commonly used together in a variety of different applications. However, DCM slowly reacts with pyridine and a variety of other representative pyridine derivatives to form methylenebispyridinium dichloride compounds under ambient conditions. The proposed mechanism (two consecutive S(N)2 reactions) was studied by evaluating the kinetics of the reaction between 4-(dimethylamino)pyridine and DCM. The second-order rate constants for the first (k(1)) and second (k(2)) substitutions were found to be 2.56(+/-0.06) x 10(-8) and 4.29(+/-0.01) x 10(-4) M(-1) s(-1), respectively. Because the second substitution is so much faster than the first, the monosubstitution product could not be isolated or detected during the reaction; it was synthesized independently in order to observe its kinetics.