EFFECTS OF ALKYL CHAIN-LENGTH ON THE ADSORPTION OF N-ALKYL ISOCYANIDES (R-N-C) ON GOLD POWDER

The chemisorption of the alkyl isocyanides n-butyl (C4H9NC), n-hexyl ( C6H13NC), n-octyl (C8K17NC), n-dodecyl (C12H25NC), and n-octadecyl iso cyanide (C18H37NC) On Au powder from 1,2-dichloroethane (DCE) was exam ined using both solution (FTIR) and surface (diffuse reflectance infra red fourier transform or DRIFT) spectroscopic techniques. For the isoc yanides with fewer than 12 carbon units in their alkyl tails, equilibr ium binding constants (K-1), surface coverages (n(1s) and n(a) mol/g(A u)) and qualitative rates of solution-surface equilibria in DCE solven t are the same. Competition studies between C-13-labeled C18H37NC and nonlabeled C4H9NC show that the ratio of adsorbed isocyanides at equil ibrium, (C18H37NC)-C-13/C4H9NC, is 4.1. Adsorption studies show that i socyanides are bound strongly to the surface at low coverages (less th an 70% of saturation coverage), but binding affinity is significantly lower at higher coverages. Studies of C18H37NC and C4H9NC in n-decane, DCE, and nitromethane (MeNO2) solvents show that solvent polarity aff ects the rate of monolayer formation, surface coverage, and equilibriu m binding constants.