Reaction of gaseous H(D) atoms with physisorbed i-propanol: Oxidation to acetone

Monolayers of i-propanol ((CH3)(2)CH-OH) were adsorbed at 125 K on graphite covered Pt(111) single crystal surfaces and subjected to fluxes of thermal H atoms. The mechanisms of the reactions of i-propanol (OH, OD) with H(D) atoms were investigated with thermal desorption spectroscopy (TDS). The initial reaction step is an Eley-Rideal-type H abstraction at the secondary CH group to form the i-propyl radical ((CH3)(2)C .-OH). This reaction proceeds with an apparent cross-section of about 1.5 Angstrom(2). Impact of a further H(D) atom can transfer the radical via a second H abstraction reaction at the OH group into acetone ((CH3)(2)C=0). Accordingly, the overall reaction consists of oxidation of i-propanol to acetone, Alternatively, i-propanol is restored from the radical via H addition to the radical carbon centre. Likewise, adsorbed acetone is transferred into i-propanol by H impact. The presence of the OH group in the target molecule i-propanol enhances the abstraction reaction cross-section at the CH group by a factor of about five as compared to abstraction from CH2,3 groups of physisorbed alkanes.