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Selective Oxidation of Alkanes with Molecular Oxygen and Acetaldehyde in Compressed (Supercritical) Carbon Dioxide as Reaction Medium
Author(s) -
Theyssen Nils,
Hou Zhenshan,
Leitner Walter
Publication year - 2006
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.200501385
Subject(s) - acetaldehyde , chemistry , oxygenate , supercritical fluid , supercritical carbon dioxide , photochemistry , alkane , oxygen , carbon dioxide , catalysis , radical , carbon monoxide , carbon fibers , electrochemical reduction of carbon dioxide , inorganic chemistry , organic chemistry , ethanol , materials science , composite number , composite material
Abstract The oxidation of cycloalkanes or alkylarenes with molecular oxygen and acetaldehyde as sacrificial co‐reductant occurs efficiently in compressed (supercritical) carbon dioxide (scCO 2 ) under mild multiphase conditions. No catalyst is required and high‐pressure ATR‐FTIR online measurements show that a radical reaction pathway is heterogeneously initiated by the stainless steel of the reactor walls. For secondary carbon atoms, high ketone to alcohol ratios are observed (3.5–7.9), most probably due to fast consecutive oxidation of alcoholic intermediates. Since CC scission reactions are detected only to a very small extent, tertiary carbon atoms are transformed into the corresponding alcohols with high selectivity. Detailed analysis of the product distributions and other mechanistic evidence suggest that acetaldehyde acts not only as the sacrificial oxygen acceptor, but also as an efficient H‐atom donor for peroxo and oxo radicals and as a crucial reductant for hydroperoxo intermediates. In comparison to other inert gases such as compressed N 2 or Ar, the use of carbon dioxide was shown to increase the yields of alkane oxygenates under identical reaction conditions.