Kinetic analysis of the asymmetric amplification exhibited byB-chlorodiisopinocampheylborane

Autor: Charles W. Moeder, John R. Sowa
Rok vydání: 2004
Předmět:
Zdroj: Journal of Physical Organic Chemistry. 17:317-324
ISSN: 1099-1395
0894-3230
Popis: A quantitative investigation was undertaken to determine experimentally the relative reaction rates of the heterochiral and homochiral species of B-chlorodiisopinocampheylborane (Dip-Cl), a reagent that exhibits asymmetric amplification. Using the method of flooding to reduce the apparent second-order reaction to pseudo-first-order conditions, rate constants of 3.8 (±1.0) × 10−4 and 1.7 (±0.8) × 10−5 m−1 s−1 (at −15°C) were found for the homochiral and heterochiral species, respectively. The resulting relative reaction rate, the value of g in Kagan and co-workers' model, was 0.04 ± 0.03. Additional experiments were conducted to confirm this value. The deterioration of the chiral purity of the final product was simulated throughout reaction conversion and compared with actual values. Through minimization, a relative reaction rate (g) of 0.08 ± 0.04 was determined. Finally, using 8-hydroxyquinoline complexation, the change in isomeric ratio of the Dip-Cl remaining in the reaction solution was measured. The relative reaction rate (g) required to consume the isomers at the observed rate was determined as 0.08 ± 0.01. Thus, three independent methods have been used to determine the relative reaction rate (g) of the heterochiral to homochiral species with good agreement to give an average value of 0.07 ± 0.03. Copyright © 2004 John Wiley & Sons, Ltd.
Databáze: OpenAIRE
Externí odkaz: