12. Gas-phase reactions of aliphatic alcohols with 'bare' FeO+

Article abstract of DOI:10.1002/hlca.19960790113

Ion/molecule reactions of 'bare' FeO^- with linear and branched aliphatic alcohols have been examined by Fourier -transform ion-cyclotron resonance mass spectrometry. Depending on the chain length of the alcohol, three different types of reactions can be distinguished: i) Oxidation of the alcohols in the α-positions, to yield the corresponding carbonl-Fe⁺ complexes, involves an initial O-H bond activation of the alcohol resulting in the formation of RO-Fe⁺-OH as the central intermediate. ii) The formation of Fe(OH)⁺₂, concomitant by loss of the corresponding neutral alkenes, competes with the generation of neutral OFeOH and a carbocation R⁺ These couples point to the existence of an intracomplex acid-base equilibrium and are connected with each other by a proton transfer from either acid to the other, e.g. i-C₃H⁺₇ + OFeOH?C₃H₆ + Fe(OH)⁺₂. The process is driven by the Lewis acidity of FeO⁺ and starts with the abstraction of a hydroxide anion from the alcohol. iii) For longer alcohols, e.g. pentanol, functionalization of non-activated C-H bonds which are remote from the O functionality is observed. Here, the OH group of the alcohol serves as an anchor, which directs the reactive metal-oxide cation toward a particular site of the hydrocarbon chain.