Formation of monocarboxylic acids and polyols on a graphite surface


A heterocatalytic model involving the graphite surface, which has been previously used for the surface formation of chemisorbed amino acids, is consistently extended to the synthesis of monocarboxylic acids and polyhydroxylated compounds. Extensive computations with semi-empirical and ab initio quantum chemical methods have been carried out to analyze reaction pathways on surface models of different sizes. The model assumes surface recombinations involving small functional groups. Polymerization is initiated by either a carboxyl (COOH) or a formyl (HCO) group that is anchored to the graphite surface through two chemisorption sites, and proceeds by the addition of mobile diffusors of the type CHn (1 <= n <= 3) and CHn’OH (0 <= n’ <= 2). Polymer length is determined by the competition between surface diffusion and hydrogenation. Some of the features observed in the laboratory regarding the surface self-assembly of monocarboxylic chains, in the organic inventory of star-forming regions and in carbonaceous meteorites can be addressed with the present approach. (c) 2007 Elsevier B.V. All rights reserved.

SURFACE SCIENCE 602, 1053-1060