Why are organotin hydride reductions of organic halides so frequently retarded? kinetic studies, analyses, and a few remedies

Download
  1. Get@NRC: Why are organotin hydride reductions of organic halides so frequently retarded? kinetic studies, analyses, and a few remedies (Opens in a new window)
DOIResolve DOI: http://doi.org/10.1021/jo502710a
AuthorSearch for: ; Search for:
TypeArticle
Journal titleJournal of Organic Chemistry
ISSN0022-3263
Volume80
Issue3
Pages13211331; # of pages: 11
SubjectIntegral equations; Kinetic theory; Kinetics; Organic solvents; Organometallics; Rate constants; Repair; Tin; Chain transfer rates; Hydride reduction; Model kinetic equations; Organic halides; Propagation step; Radical chain; Reaction conditions; Side reactions; Chains; anthracene; benzophenone; cyclohexane; organohalogen derivative; organotin compound; radical; addition reaction; Article; chemical analysis; chemical reaction kinetics; chemical structure; reduction
AbstractKinetic data for reduction of organic halides (RX) by tri-n-butylstannane (SnH) reveal a serious flaw in the current view of the kinetic radical chain: the tacit but unproven assumption that the speed of reaction is determined by the slowest propagation step. Our results show this is rarely true for reductive chains and that the observed rate is in fact controlled by unseen side-reactions of propagating R• and Sn• radicals with the solvent (notably, benzene!) or solvent impurities (e.g., trace benzophenone dryness indicator in THF) or, crucially, with allylic-CH and conjugated unsaturated groups in substrates and products. Most R• and/or Sn• radicals are therefore converted into relatively inert delocalized species A• and/or B• that inhibit the chain. Retardation in the degraded chain is given by a simple sum of terms, each being the ratio of the chain-transfer rate divided by the rate of chain-return. The model kinetic equation is linear and easy to ratify, interpret, and apply: to calculate retarding rate constants, optimize reaction conditions, and identify additives or "remedies" that repair the chain and accelerate reaction. The present work is thus expected to have a helpful impact on the practice and design of SnH radical chain based (and related) syntheses. © 2014 American Chemical Society.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21276502
Export citationExport as RIS
Report a correctionReport a correction
Record identifierdcb1e8a5-b43b-4338-9c28-be364784f2c7
Record created2015-10-13
Record modified2016-05-09
Bookmark and share
  • Share this page with Facebook (Opens in a new window)
  • Share this page with Twitter (Opens in a new window)
  • Share this page with Google+ (Opens in a new window)
  • Share this page with Delicious (Opens in a new window)