Premium
Mechanism of Homogeneously and Heterogeneously Catalysed Meerwein–Ponndorf–Verley–Oppenauer Reactions for the Racemisation of Secondary Alcohols
Author(s) -
Klomp Dirk,
Maschmeyer Thomas,
Hanefeld Ulf,
Peters Joop A.
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305460
Subject(s) - chemistry , acetophenone , catalysis , lanthanide , cyclohexanone , hydrogen , reaction mechanism , substrate (aquarium) , organic chemistry , medicinal chemistry , ion , oceanography , geology
The mechanism of hydrogen transfer from alcohols to ketones, catalysed by lanthanide( III ) isopropoxides or zeolite Beta has been studied. For the lanthanide catalysed reactions, ( S )‐1‐phenyl‐(1‐ 2 H 1 )ethanol and acetophenone were used as case studies to determine the reaction pathway for the hydrogen transfer. Upon complete racemisation all deuterium was present at the 1‐position, indicating that the reaction exclusively takes place via a carbon‐to‐carbon hydrogen transfer. Zeolite Beta with different Si/Al ratios was applied in the racemisation of ( S )‐1‐phenylethanol. In this case the racemisation does not proceed via an oxidation/reduction pathway but via elimination of the hydroxy group and its re‐addition. This mechanism, however, is not characteristic for all racemisation reactions with zeolite Beta. When 4‐ tert ‐butyl cyclohexanone is reduced with this catalyst, a classical MPV reaction takes place exclusively. This demonstrates that zeolite Beta has a substrate dependent reaction pathway.