Reversing the selectivity: radical substitution of Br by H
المؤلف:
Jonathan Clayden , Nick Greeves , Stuart Warren
المصدر:
ORGANIC CHEMISTRY
الجزء والصفحة:
ص990-991
2025-07-29
535
Reversing the selectivity: radical substitution of Br by H
Radical substitution reactions can also be used to remove functional groups from molecules. A useful reagent for this (and, as you will see, for other radical reactions too) is tributylti hydride, Bu3SnH. The Sn–H bond is weak and Bu3SnH will react with alkyl halides to replace the halogen atom with H, producing Bu3SnHal as a by-product.
Clearly, for this reaction to be energetically favourable, the new bonds formed (Sn–Br and C–H) must be stronger than the old bonds broken (Sn–H and C–halogen). Look at this table of average bond energies and you will see that this is indeed so. The use of a tin hydride is crucial to this reaction: Sn–H bonds are weaker than Sn–Br bonds, while, for carbon, C–H bonds are stronger. Bu3SnH is therefore an effective source of Bu3Sn• radicals, and the Bu3Sn• radical will abstract halogens, particularly I or Br, but also Cl, from organic halides, breaking a weak C–halogen (C–Hal) bond and forming a strong Sn–Hal bond. The complete mechanism of the reaction reveals a chain reaction.
الاكثر قراءة في مواضيع عامة في الكيمياء العضوية
اخر الاخبار
اخبار العتبة العباسية المقدسة
