Alkanethiolate

Alkanethiols and other sulfur-bearing hydrocarbons covalently attach to metal surfaces alkanethiol onto gold is the most widely studied of these systems [27-29,31,32,45]. These SAMs are ordered provided the alkane chain contains nine or more carbons [32]. Binary solutions of two alkanethiols also appear... 

The self-assembly of alkanethiols on gold has been an important topic in surface chemistry over die last few years [39] and STM has contributed significantly to our understanding of these systems. In particular, the... 

Liu G-Y and Salmeron M B 1994 Reversible displacements of chemisorbed n-alkanethiol molecules on Au(111) surface an atomic force microscopy study Langmuir 10 367... 

Apart from domain boimdaries, some of the defects in alkanethiol monolayers (pitholes) are created by the thiol itself 159] by etching processes. It was found that the solvent used for preparation also has some effect on the resulting defect density. 

The lubricant properties of alkanethiols and fluorinated alkanes have been studied extensively by scanning probe techniques [163]. In agreement with experiments on LB monolayers it was found that the fluorocarbon monolayers show considerably higher friction than the corresponding hydrocarbon monolayers [164, 165 and 166] even though the fluorocarbons are known to have the lowest surface free energy of all organic materials. 

Laibinis P E, Flickman J J, Wrighton M S and Whitesides G M 1989 Orthogonal self-assembled monolayers— alkanethiols on gold and alkane carboxylic-acids on alumina Science 245 845-7... 

Flahner G, Wdll C, Buok M and Grunze M 1993 Investigation of intermediate steps in the self-assembly of n-alkanethiols on gold surfaoes by soft-x-ray speotrosoopy Langmuirs 1955-8... 

Dannenberger O, Buok M and Grunze M 1999 Self-assembly of/ -alkanethiols A kinetio study by seoond harmonio generation J. Phys. Chem. B 103 2202-13... 

Liedberg B and Tengvall P 1995 Moleoular gradients of -substituted alkanethiols on gold preparation and oharaoterization Langmuir 3821-7... 

Atre S V, Liedberg B and Allara D L 1995 Chain length dependenoe of the struoture and wetting properties in binary oomposition monolayers of OH and CHj-terminated alkanethiolates on gold Langmuir 3882-93... 

DiMilla P A, Folkers J P, Biebuyck H A, Harter R, Lopez G P and Whitesides G M 1994 Wetting and protein adsorption of the self-assembled monolayers of alkanethiolates which are supported on transparent films of gold J. Am. Chem. Soc. 116 2225-6... 

Li W, Virtanen J A and Penner R M 1995 Self-assembly of n-alkanethiolate monolayers on silver nanostructures protective encapsulations Langmu/r 11 4361... 

Terril R H ef a/1995 Monolayers in three dimensions NMR, SAXS, thermal and eleotron hopping studies of alkanethiol stabilized gold olusters J. Am. Chem. Soc. 117 12 537... 

Hosteler M J ef a/1996 Monolayers in three dimensions synthesis and eleotroohemistry of w-funotionalized alkanethiolate stabilized gold oluster oompounds J. Am. Chem. Soc. 118 4212... 

Hostetler M J, Stokes J J and Murray R W 1996 Infrared speotrosoopy of three-dimensional self-assembled monolayers n-alkanethiolate monolayers on gold oluster oompounds Langmuir M 3604... 

In spite of S—H bonds being less polar than O—H bonds thiols are stronger acids than alcohols This is largely because S—H bonds are weaker than O—H bonds We have seen that most alcohols have pA s of 16-18 The corresponding value for a thiol IS about 10 The significance of this difference is that a thiol can be quantitatively con verted to its conjugate base (RS ) called an alkanethiolate, by hydroxide Conse quently thiols dissolve m aqueous base... 

Alkanethiolate ions (RS ) are weaker bases than alkoxide ions (RO ) and undergo synthetically useful 8 2 reactions even with secondary alkyl halides... 

Sulfides compounds of the type RSR are prepared by nucleophilic substitution reac tions Treatment of a primary or secondary alkyl halide with an alkanethiolate ion (RS ) gives a sulfide... 

It IS not necessary to prepare and isolate the sodium alkanethiolate m a separate opera tion Because thiols are more acidic than water they are quantitatively converted to their alkanethiolate anions by sodium hydroxide Thus all that is normally done is to add a thiol to sodium hydroxide m a suitable solvent (water or an alcohol) followed by the alkyl halide... 

Section 16 15 Sulfides are prepared by nucleophilic substitution (8 2) m which an alkanethiolate ion attacks an alkyl halide... 

Fluorinated and Ghlorfluorinated Sulfonic Acids. The synthesis of chlorinated and fluorinated sulfonic acids has been extensively reviewed (91,92). The Hterature discusses the reaction of dialkyl sulfides and disulfides, sulfoxides and sulfones, alkanesulfonyl haHdes, alkanesulfonic acids and alkanethiols with oxygen, hydrogen chloride, hydrogen fluoride, and oxygen—chloride—hydrogen fluoride mixtures over metal haHde catalysts, such as... 

Organosulfur Adsorbates on Metal and Semiconductor Surfaces. Sulfur compounds (qv) and selenium compounds (qv) have a strong affinity for transition metal surfaces (206—211). The number of reported surface-active organosulfur compounds that form monolayers on gold includes di- -alkyl sulfide (212,213), di- -alkyl disulfides (108), thiophenols (214,215), mercaptopyridines (216), mercaptoanilines (217), thiophenes (217), cysteines (218,219), xanthates (220), thiocarbaminates (220), thiocarbamates (221), thioureas (222), mercaptoimidazoles (223—225), and alkaneselenoles (226) (Fig. 11). However, the most studied, and probably most understood, SAM is that of alkanethiolates on Au(lll) surfaces. 

Fig. 11. Surface-active organosulfur compounds that form monolayers on gold (a) alkanethiol (b) dialkyl disulfide (c) dialkyl sulfide (d) alkyl xanthate ...

Chemisorption of alkanethiols as well as of di- -alkyl disulfides on clean gold gives indistinguishable monolayers (251) probably forming the Au(l) thiolate species. A simple oxidative addition of the S—S bond to the gold surface is possibly the mechanism in the formation of SAMs from disulfides ... 

In the alkanethiol case, the reaction may be considered formally as an oxidative addition of the S—H bond to the gold surface, followed by a reductive elimination of the hydrogen. When a clean gold surface is used, the proton probably ends as a molecule. Monolayers can be formed from the gas phase (241,255,256), in the complete absence of oxygen ... 

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