The Influence of Fluorination on Boundary-Layer Surface Chemistry

Parker, Bryan; Zhang, Ruiming; Dai, Qing; Gellman, Andrew J.

doi:10.1021/bk-1992-0485.ch011

Cited by 4 publications

(4 citation statements)

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“…The adsorbed oxygen atom acts as a Bronsted base and deprotonates the acid to produce acetate, CH 3 CO 2 . During heating the CH 3 CO 2 decomposes to produce CO 2 , CH 4 , and other species at temperatures on the order of 600 K. We have also observed that CH 3 CO 2 H is deprotonated on the oxidized Ag(110) surface and decomposes to produce CO 2 at high temperatures …”

Section: Resultsmentioning

confidence: 99%

Carboxylic Acid Deprotonation on the Ag(110) and Ag(111) Surfaces

2001

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The surface chemistry of hydrocarbon carboxylic acids has been compared with that of perfluorinated carboxylic acids on the Ag(110) and Ag(111) surfaces. The hydrocarbon acids adsorb reversibly on the clean silver surfaces. On Ag(110) their desorption energies increase linearly with increasing alkyl chain length (n) and are given by the expression ∆Edes ) 10.6 + 0.9n kcal/mol. The surface chemistry of the perfluorinated acids is quite different from that of the hydrocarbon acids in the sense that they deprotonate to form perfluorocarboxylate species on both Ag(110) and Ag(111) surfaces. The perfluorocarboxylates are stable until the surface temperature reaches ∼620 K, at which point they decompose yielding desorption of CO2 and other decomposition fragments. On both Ag surfaces 2,2,2-trifluoroacetate (CF3CO2) generated by deprotonation of 2,2,2-trifluoroacetic acid (CF3CO2H) has been identified by its vibrational spectrum. The fact that fluorinated acids deprotonate on the Ag surfaces while the hydrocarbon acids desorb during heating indicates that fluorination lowers the deprotonation barrier, ∆E ‡ dep, to the point that it is lower than the desorption energy, ∆Edes.

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Section: Resultsmentioning

confidence: 99%

Carboxylic Acid Deprotonation on the Ag(110) and Ag(111) Surfaces

2001

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“…For their tribochemical properties, then, alcohols, fluorinated alcohols, and the corresponding alkoxides have been studied in order to determine their structure, the orientation of the alkyl chains with respect to the surface, and their thermal stability. [2][3][4] The chemistry of ethanol on clean and preoxidized Ag and Cu surfaces is well-understood. 5,6 On the preoxidized surfaces ethanol deprotonates to form water, which desorbs below room temperature, and ethoxide, which is stable to 350 K. The ethoxide is a stable intermediate bound to the surface through the oxygen atom, until it decomposes by -hydride elimination (the -carbon is adjacent to the oxygen atom) to form acetaldehyde.…”

Section: Introductionmentioning

confidence: 99%

“…The fluorinated analogues of these alcohols can in turn be used as models for possible boundary layer additives for use with high-temperature perfluoropoly(alkyl ether) lubricant fluids. For their tribochemical properties, then, alcohols, fluorinated alcohols, and the corresponding alkoxides have been studied in order to determine their structure, the orientation of the alkyl chains with respect to the surface, and their thermal stability. − …”

Section: Introductionmentioning

confidence: 99%

FT-IRAS of Adsorbed Alkoxides: Fluorinated Ethoxides on Cu(111)

Street

Gellman

1996

J. Phys. Chem.

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Fourier transform infrared reflection absorption spectra (FT-IRAS) of a set of fluorinated ethoxides (CF n H 3-n CH 2 OH, n ) 0-3) on the Cu(111) surface have been obtained. The decomposition reactions of adsorbed mono-, di-, and trifluoroethoxide to gaseous fluoroaldehydes exhibit different reaction kinetics, as previously reported, and the reaction of trifluoroethoxide-d 2 (CF 3 CD 2 O-Cu(111)) exhibits a primary isotope effect. Quantitative measurements of the absorption intensities of CF 3 CH 2 O (ad) and CF 3 CH 2 OH allowed determination of the orientation of the adsorbed trifluoroethoxide. FT-IRAS results indicate that the orientation of trifluoroethoxide is different than that of ethoxide. Ethoxide on the Cu(111) surface has the C-C bond tilted 70 ( 2°from the surface normal while in trifluoroethoxide the C-C bond is oriented 50 ( 5°from the surface normal. In both species the plane of the molecule defined by the C-C-O atoms is tilted toward the surface. This tilt between the plane of the molecule and the plane of the surface normal is 17 ( 2°for ethoxide and 20 ( 11°for trifluorethoxide. These results indicate that the effect of fluorination of the methyl end group is to tilt it away from the surface.

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“…Besides examining the SEF's, this study also represents a continuation of our recent efforts 5 on examining the role of fluorine in modifying the dynamic behavior of fluorocarbons versus hydrocarbons. These experiments should be of relevance to the lubrication process, as designers take advantage of the high thermal stability and chemical inertness of fluorocarbons but still need information regarding potential additives soluble in fluorocarbons. − Alcohols represent boundary-layer lubricant additives, − intended to interact with an oxide-coated surface and form a molecular layer film, thereby preventing contact between engine parts. In spite of the fact that we deal with a silica surface in the absence of shear, we also hoped this study could provide some insight into the surface-layer dynamics relevant for boundary-layer lubrication.…”

Section: Introductionmentioning

confidence: 99%

NMR Study of the Molecular Dynamics of Ethanol and 2,2,2-Trifluoroethanol Liquids Confined to Nanopores of Porous Silica Glasses

Ballard

Jonáš

1996

Langmuir

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A dynamic nuclear magnetic resonance (NMR) study of the polar fluids ethanol (EtOH) and 2,2,2trifluoroethanol (TFE) confined to porous silica sol-gel glasses is reported. The 13 C NMR spin-lattice relaxation times, T1, were measured in glasses with pore radii ranging from 18.9 to 54.8 Å, over a temperature range from -13.6 to 30.5 °C. The data were analyzed in terms of the two-state, fast exchange model, and surface layer relaxation times, T1s, were calculated. On the basis of surface enhancement factors, T1b/T1s, where T1b is the relaxation time of the bulk liquid, it was concluded that the more acidic TFE has a weaker hydrogen bond interaction with silica, due to the fact that the alcohols serve as hydrogen bond acceptors. The experiment shows that EtOH and TFE have nearly identical surface layer viscosities, originating from the differences in hydrogen bonding with the silica surface. Confinement was found to have little effect on the internal rotation of terminal CF 3 or CH3 groups.

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The Influence of Fluorination on Boundary-Layer Surface Chemistry

Cited by 4 publications

References 0 publications

Carboxylic Acid Deprotonation on the Ag(110) and Ag(111) Surfaces

Carboxylic Acid Deprotonation on the Ag(110) and Ag(111) Surfaces

FT-IRAS of Adsorbed Alkoxides: Fluorinated Ethoxides on Cu(111)

NMR Study of the Molecular Dynamics of Ethanol and 2,2,2-Trifluoroethanol Liquids Confined to Nanopores of Porous Silica Glasses

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