Tributyltin hydride (Bu3SnH) is used synthetically to reduce alkyl halides, replacing a halogen atom with hydrogen. Free-radical initiators promote this reaction, and free-radical inhibitors are known to slow it or stop it. Your job is to develop a mechanism, using the following reaction as the example.
Propose initiation and propagation steps to account for this reaction.Calculate values of for your proposed steps to show that they are energetically feasible. (Hint: A trace of Br2 and light suggests it’s there only as an initiator, to create Then decide which atom can be abstracted most favorably from the starting materials by the That should complete the initiation. Now decide what energetically favored propagation steps will accomplish the reaction.)
The bond-dissociation enthalpies:
Br- Br 192 kJ/mol
H- Br 368 kJ/mol
Bu3Sn-H 310 kJ/mol
Bu3Sn-Br 552 kJ/mol
In this step Br2 dissociate to form Br free radicals and this Br. will react with tributyltin hydride ( Bu3SnH ) and forms tributyltin free radical.
The propagation reaction involves two steps. In the 1st step the bromobenzene under goes free radical substitution reaction and forms cyclohexane free radical with Br-SnBu3
Again this cyclohexane free radical react with H-SnBu3 and the reaction is carried out as follows:-