Cyclization and related reactions of iodoethanol on Ag(110)

The adsorption and reaction of 2-iodoethanol (IEtOH) on a clean Ag(110) surface were studied under ultrahigh vacuum conditions using temperature programmed deposition (TPD). Under these conditions alcohols are typically unreactive on the clean Ag(110) surface. Replacement of one of the beta hydrogens with a weakly bound (53 kcal/mol) iodine atom, however, opens a channel for IEtOH decomposition by initial carbon-iodine scission. TPD results indicate that there are two major reaction channels at 263 and 340 K for IEtOH decomposition on the clean Ag(110) surface. The reaction intermediates that give rise to these two pathways were deduced based upon the products observed, the overall produce stoichiometry, and the desorption temperatures of the products. The 263 K reaction channel has an overall stoichiometry of C2H5O, corresponding to a hydroxyethyl intermediate. The hydroxyethyl intermediate undergoes a beta-hydride elimination and C-O scission, ultimately yielding volatile acetaldehyde, ethylene, water, ethanol, and another surface intermediate that decomposes at 340 K. Unlike unsubstituted alkyl groups on clean Ag(111) and AE(110) which couple to form alkanes, there is no evidence for hydroxyethyl coupling to give butanediol. Thus, the hydroxyethyl cannot be treated simply as a substituted alkyl group; that is probably due to interactions between oxygen and the surface. The stoichiometry of the products released at 340 K, C2H4O, is suggestive of an oxametallacycle intermediate. The products of this reaction channel are the same as the 263 K channel with the addition of a cyclic eater product, gamma-butyrolactone. This species has not previously been synthesized from a C-2 precursor in ultrahigh vacuum, and its observation suggests that surface oxametallacycle chemistry may be richer than previously recognized. (C) 1997 American Vacuum Society.