Alkanethiols, oxidation

Alkanethiols. Oxidation of alkanethiols to alkanesulfonic acids with concentrated HNO3 may cause ignition of the thiol.15... 

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 ... 

The fdr studies reveal that the alkyl chains in SAMs of thiolates on Au(lll) usually are tilted 26-28° from the surface normal, and display 52-55° rotation about the molecular axis. This tilt is a result of the chains reestabUshing VDW contact in an assembly with - 0.5 nm S—S distance, larger than the distance of - 0.46 nm, usually quoted for perpendicular alkyl chains in a close-packed layer. On the other hand, thiolate monolayers on Ag(lll) are more densely packed owing to the shorter S—S distance. There were a number of different reports on chain tilt in SAMs on Ag(lll), probably owing to different amounts of oxide, formed on the clean metallic surface (229,230,296,297). In carefully prepared SAMs of alkanethiolates on a clean Ag(lll) surface, the alkyl chains are practically perpendicular to the surface. 

Autoclave reactions involving ethylene oxide with alkanethiols or an (unspecified) alcohol went out of control and exploded violently. Similar previous reactions had been uneventful [1], An arenethiol was being reacted with ethylene oxide under catalysis by a fraction of a percent of sodium hydroxide (solid) dissolved in the thiol to which the oxirane was slowly charged. After an initial exotherm a white solid precipitated, the exotherm died away and later resumed, with dissolution of the solid, the reaction then running out of control from the backlog of charged oxirane [2],... 

Oxidation of alkanethiols to alkanesulfonic acids with excess cone, acid as usually described is potentially hazardous, the exotherm often causing ignition of the thiol. A modified method involving oxidation under nitrogen and at temperatures 1-2 C above the m.p. of the thiol is safer and gives purer products [1]. Technical butanethiol (containing 28% of propane- and 7% of pentane-thiols) is hypergolic with 96% acid [2], Oxidation of several thiols to the sulfonic acids by addition to stirred cone, acid had been effected normally, but when 2 new... 

Related (diisopropoxyphosphoryl)- and (diisobutoxyphosphoryl)formonitrile oxides (114), generated in basic media from the corresponding oximes react in situ with alcohols, phenols, alkanethiols, thiophenols, aliphatic and aromatic primary amines, hydrazines and hydrazides as well as 4-aminoantipyryne to give hydroxymates, thiohydroxymates, and amidoximes, respectively. It is important to note that the addition is stereoselective and gives E-adducts with the exception of (i-Pr0)2P(0)C( N0H)0Me, which is formed as a 1 1 mixture of E and Z isomers. 

The high tendency of thiols to form sulfur-gold bonds upon oxidation on a gold electrode was used in numerous investigations to modify gold electrodes for different analytical and synthetic purposes. Nonanethiol [29], butanethiol and octanethiol [30], hexadecanethiols [31], oc-tadecanethiol [32], ferrocene-terminated alkanethiol (FCCO2C11H22SH) [33], 2-... 

Based on cp-AFM evidence for the simple case of an n-alkanethiolate/Au SAM, the M structures show no evidence for penetration of metal to form conducting filaments that can cause shorts. The resultant junctions, however, do show extensive formation of reaction product layers with complex chemical compositions which may lead to unfavorable characteristics for molecular device operation. Indeed, in recent reports the use of Ti deposition on LB films, which contain water and inorganic salts at the bottom Pt electrode/LB film interface, leads to formation of inorganic titanium oxide type species in the junction but these complex inorganic layers have also been reported to impart fortuitously quite useful device... 

Lu P, Demirkan K, Opila RL, Walker AV (2008) Room-temperature chemical vapor deposition of aluminum and aluminum oxides on alkanethiolate self-assembled monolayers. J Phys Chem C 112(6) 2091-2098... 

This le electrode reaction implies the loss of the thiol hydrogen and the oxidation of the S to a formal oxidation state of —1 upon adsorption of -alkanethiol (RSH) at Au. 

Widrig et al. [196] have studied voltam-metrically, the SAMs of several -alkanethiols formed on pc-Ag electrodes. Analysis of data showed that during adsorption, the hydrogen of thiol group is lost and the sulfur is oxidized by one electron. Based on the charge required for the reductive desorption of the mono-layer, the surface coverage was found to be 7.0 X 10-10 j -2... 

Pyridine 1-oxide and a series of its methyl analogues undergo thioalkylation at the a-and y-positions when heated with an alkanethiol in acetic anhydride at 95 °C for 3 h (Table 13). Under these conditions, attack by thiol at 2- or 4-methyl groups does not seriously compete with ring substitution. j8 -Substitution does not occur at C-3 in 2-methylpyridine, but it does so at C-5 where the adjacent a-position is vacant. Notice that again a 3-methyl substituent tends to direct substitution to C-2 rather than C-6. This is also true for 3,4-dimethylpyridine. Increasing the size of the 4-substituent does reduce the relative... 

Self assembly of monolayers on gold electrodes provided a viable approach to sensor construction (see below), as well as permitted electrochemical characterization of the mechanism involved in chemisorption [233,236-239]. Electrochemical investigation of the spontaneous adsorption of n-alkanethiols onto a gold electrode and the subsequent desorption of the monolayer were rationalized in terms of oxidation and reduction of the sulfur atom [233]. More intimate details concerning the chemical fate of all species involved in the chemisorption process have not yet been elucidated. 

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