[Thet619]

Hello @ everyone.

Ive got a question concerning the synthesis of Tetracyanoquinodimethane. The reaction equation is as follows:



The first step was furnished in a schlenk-flask and stirred at -20 degrees. In the second step the pyridine solution was added dropwise. Ive got a question concerning the mechanism: While the second step is a dehydrohalogenation, im uncertain about the first step?! NBS is an indicator for a Wohl-Ziegler-Bromination. On the other hand i have no radical starter like AIBN or heat. Instead a temperature of -20 degrees is required! And all Wohl-Ziegler-Reactions ive done so far require a radical starter. I know that Wohl-Ziegler is possible without a radical starter, but then heat/reflux or UV radiation ist required.

I would appreciate your help, and especially why, if so, it is a Wohl-Ziegler-Reaction.
Greets,
Thet619

[orgopete]

I concur that this is probably not a free radical reaction based up the reaction conditions. That should not be too problematic in that NBS can be used for ionic brominations of alkenes, notably in a reaction of an alkene with NBS/H2O. I believe even the free radical mechanism remains unresolved as to whether it is NBS or low concentrations of Br2 in the bromination.

None the less, this remains an interesting mechanistic question.