Mechanistic study of the reactions of 1,2-disubstituted alkenes with hydrogen bromide in acetic acid

Journal Article · Fri Mar 01 04:00:00 EDT 1974 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00813a035· OSTI ID:4333899

Pasto, Daniel J.; Meyer, G. Richard; Lepeska, Bohumir

The stereochemistry and kinetics of the addition reactions of hydrogen bromide and acetic acid to cis- and trans-2-butene and 3-hexene and cyclopentene in hydrogen bromide-acetic acid have been studied. The stereochemistry of the addition of deuterium bromide and acetic acid-O-d to cis- and trans-2-butene occurs 84 plus or minus 2% anti, is invariant over a 100-fold concentration range of deuterium bromide, and is unaffected by the presence of added lithium bromide or lithium perchlorate. The stereochemistry of the addition reactions to cis- and trans-3-hexene is 84-85% anti. The stereochemistry of the addition reactions to cyclopentene is 96 plus or minus 4% anti (no syn addition product detected by ir techniques) and is not altered on change in the concentration of deuterium bromide or by the presence of added lithium bromide or perchlorate. The kinetics of the reaction of cyclopentene with hydrogen bromide in acetic acid appear to obey the kinetic expression -d[alkene]/dt = k_RBr [alkene Br]² + k_ROAc[alkene] [HBr] in which alkyl bromide is derived only from the third-order term and alkyl acetate is derived only from the second-order term. k_RBr and k_ROAc, vary slightly with change in the initial concentration of hydrogen bromide, the rate constants decreasing with decreasing hydrogen bromide and cyclopentene concentration; however, the rate expression appears to remain the same. This phenomenon is attributed to changes in the reaction medium with change in hydrogen bromide concentration. The hydrogen-deuterium kinetic isotope effect is found to be 0.48 plus or minus 0.02 for cyclopenotyl bromide formation and 0.63 plus or minus 0.07 for cyclopentyl acetaote formation. The effect of added lithium bromide and lithium perchlorate on the rate of reaction has been determined and is discussed. A mechanism for the addition reactions is proposed involving syn and anti AdE3 transition states in which the hydrogen ion is delivered to the carbon by undissociated hydrogen bromide as the nucleophilic portion of the addends is delivered to the BETA carbon.

• Research Organization: Univ. of Notre Dame, IN
• Sponsoring Organization: USDOE
• NSA Number: NSA-29-024016
• OSTI ID: 4333899
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 6 Vol. 96; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

*DEUTERIUM-- ISOTOPE EFFECTS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ACETIC ACID
ALKENES
CHEMICAL REACTION KINETICS
DEUTERIUM COMPOUNDS
HYDROBROMIC ACID
STEREOCHEMISTRY