Substituted Sulphides

Steric effects are not of major importance, as shown by the fact that f-butyl-substituted sulphides can be autoxidised in the presence of a catalyst. Rather, it is the inhibitory action of traces of f-butyl sulphoxide which is responsible for the overall lack of oxidation activity. This bears out the observed order of effectiveness of sulphide antioxidants added to oxidising hydrocarbons [97], where t-butyl substituents confer excellent antioxidant properties. 

The copper-catalysed thermolysis of toluene-/)-sulphonyl azide in the presence of various sulphides also affords the corresponding sulphimides. A kinetic study on the reactions of Chloramine-T with orrAo-substituted sulphides indicates a marked steric hindrance by or//ro-substituents, while the anchimeric effect of ortho-groups that have a carbonyl function decreases in the order CHjCOjH CH COjMe < CH COj- < COjMe COJti < COr-... 

The application of ly transition metal carbides as effective substitutes for the more expensive noble metals in a variety of reactions has hem demonstrated in several studies [ 1 -2]. Conventional pr aration route via high temperature (>1200K) oxide carburization using methane is, however, poorly understood. This study deals with the synthesis of supported tungsten carbide nanoparticles via the relatively low-tempoatine propane carburization of the precursor metal sulphide, hi order to optimize the carbide catalyst propertira at the molecular level, we have undertaken a detailed examination of hotii solid-state carburization conditions and gas phase kinetics so as to understand the connectivity between plmse kinetic parametera and catalytically-important intrinsic attributes of the nanoparticle catalyst system. 

A. Nucleophilic Reactions.—(/) Attack on Saturated Carbon. The Arbusov reaction has been used to prepare organosilicon-substituted phosphonates (1) and phosphorylated ethers (2a) and sulphides (2b). Bromo- and chloro-derivatives of the cyclic phosphite (3) do not react with ethyl halides... 

Much higher asymmetric induction was observed in the two-phase oxidation of simple alkyl aryl and diaryl sulphides , substituted alkyl aryl sulphides and dithioacetals of formaldehyde by sodium metaperiodate in the presence of proteins such as bovine serum y-globulin and egg albumin. Optical purities of the sulphoxides so formed ranged between 20 and 85%. 

This series of reagents is characterized by the use of metals under the appropriate conditions. In this regard, a mixture of zinc dust and titanium tetrachloride in ether provided a useful synthesis of vinyl sulphides, with the possibility of further substitution alpha to the sulphur atom, as outlined in equation (16). The reaction is easy to carry out and gave yields of 49 to 87%, although the authors do not provide much detail of their experimental procedure and of the purity (chemical or stereochemical) of their products. 

It is interesting to note that the oxidation of sulphoxides by peracids is faster in alkaline than in acidic solution. This is in contrast to the oxidation of sulphides and amines with the same reagents " . The oxidation rate of ortho-substituted aryl alkyl sulphoxides with aromatic peracids is less than the corresponding meta- and para-substituted species due to steric hindrance of the incoming peracid anion nucleophiles . Steric bulk in the alkyl group also has some effect . Such hindrance is not nearly so important in the oxidation reaction carried out under acidic conditions . 

Loss of catalytic activity resulting from internal displacements is not usually a serious problem below temperatures of about 100 C. However, highly active R-groups, such as benzyl, methyl and allyl, undergo internal displacement more readily, particularly in the presence of strong nucleopfiles. For instance, the presence phenolates and thiolates may lead to the formation of benzyl alcohol, ethers, or sulphides from benzyl-substituted quaternary ammonium salts. 

When o-Nitroaniline is treated by sodium nitrite in acid medium and then by an inorganic sulphide, it forms an explosive diazonium sulphide. Note that even though the presence of a nitrated group does not help, it certainly is not a factor that is vital to cause the explosion, since this is a property that is common to all these diazonium salts whatever the nature of the substitution on the ring. The situation is exactly the same with p-nitroaniline. 

Bis(trimethylsilyl)peroxide (1) can be used to produce phosphine oxides stereospecifically from either phosphines (with retention) or phosphine sulphides (with inversion).1 A variety of organoelement substituted pentadienes, including the phosphine oxides (2) and (3),... 

The electron impact induced ortho effects in 2-nitro-substituted aromatic sulphides containing e.g. 2-pyridyl, 2-(5-methylthio-l,3,4-thiadiazolyl) moieties have been studied105, the 2,6-bis(nitrophenylthio)pyridines being typical representatives for the compounds studied105. 

Substituted Phenyl 2,4,6-trinitrophenyl sulphides. By UV-VIS measurements of the reactions of 4 -substituted phenyl 2,4,6-trinitrophenyl sulphides with amines in DMSO, Crampton s group131 showed the presence of two well-separated processes which were interpreted by Scheme 7129. In each case a rapid reversible equilibrium was established leading to the 3-adduct (10). They also observed a second, much slower process resulting in formation of the N-substituted picramide derivatives, 13. The final spectra were identical to those of the independently prepared products, 13. Chamberlain and Crampton133 showed that the reaction products are in rapid equilibrium with anions derived from them by amine addition at the 3-position and/or loss of a side-chain proton, but they did not find evidence for the accumulation of spectroscopically observable concentrations of intermediates such as 12. 

Phenyl 2,6-dinitro-4-trifluoromethylphenyl sulphide. Chamberlain and Crampton130 studied also the reaction of phenyl 2,6-dinitro-4-trifluoromethylphenyl sulphide with amines in DMSO. They observed a single rate process with butylamine giving the expected substituted product again, the observed rate constant increased with [butylamine]. In the reaction with pyrrolidine a rapid reaction giving the 3-pyrrolidino adduct was observed, which could be suppressed by addition of pyrrolidinium perchlorate. Under these conditions the expected 1-substituted product was formed. 

In contrast with the reactions involving sulphide or hydrogen sulphide anions, aryl alkyl thioethers and unsymmetrical dialkyl thioethers (Table 4.3) are obtained conveniently by the analogous nucleophilic substitution reactions between haloalkanes and aryl or alkylthiols under mildly basic conditions in the presence of a quaternary ammonium salt [9-15] or polymer-supported quaternary ammonium salt [16]. Dimethyl carbonate is a very effective agent in the formation of methyl thioethers (4.1.4.B) [17]. 

As an alternative to the oxidation of sulphides and sulphoxides (see Chapter 10), sulphones can be prepared by the nucleophilic substitution reaction of the sulphinite anion on haloalkanes. In the absence of a phase-transfer catalyst, the reaction times are generally long and the yields are low, and undesirable O-alkylation of the sulphinite anion competes with S-alkylation. The stoichiometric reaction of the preformed tetra-n-butylammonium salt of 4-toluenesulphinic acid with haloalkanes produces 4-tolyl sulphones in high yield [1], but it has been demonstrated that equally good... 

The condensation of isocyanate esters with diguanides proceeds in an entirely comparable manner, providing a corresponding series of s-triazin-2-ones (i.e. substituted ammelines) 378). However, since loss of water from carbamoyl-intermediates [e.g. RNHCONH C( NH)NH C( NH) -NH2] occurs much less readily than loss of hydrogen sulphide from their thiocarbamoyl-analogues, melamines are not formed in this reaction 378). The production of adducts from phenyl isocyanate and tetra-. 

Ethyl phenyl sulphide is lithiated mainly in the ortho position, but with significant amounts of meta and para lithiation and substitution products. Superbases, on the other hand, prefer to deprotonate afkylthio benzenes at benzylic or a-positions, rather than on the ring ... 

With only a few exceptions, the CdS is deposited from a standard ammo-nia/thioureabath at ca. 70°C, with variations in the concentrations of reactants, the use of temperature programming, and some variation in pH (using an ammonium chloride buffer). It is notable that, in spite of many attempts to substitute CdS by another CD material (driven by the desire for a environmentally friendlier material), CdS remains the best material to date for this purpose, both for CIS and CdTe cells. Other materials deposited by CD include various Zn(OH,S), Zn(OH,Se), and ln(OH,S) compounds and ln(OH)3. The three first materials appear to be incompletely sulphided or selenided hydroxides, and it is not clear whether they are a mixed or a single phase. Also, it is usually unclear whether oxide or hydroxide also occurs [although one XPS study of ln(OH,S) has demonstrated the absence of either ln(OH)3 or ln2S3 in the film]. While some of these buffer layers approach CdS in terms of cell efficiency, they are invariably inferior. 

The driving force for Eq. (3.45) is the much lower value of K p for CdS (ca. 10 Table 1.1) than for Cd(OH)2 (2 X 10 " ), which reflects the more negative free energy of formation of the former. This means that sulphide will readily substitute for hydroxide in the case of Cd. An idea of the amount of sulphide needed to con-... 

Chemical deposition of ZnS has been the subject of considerable activity, the main reason for which is its hoped-for substitution for CdS in thin-film photovoltaic cells. Since the chemistries of Zn and Cd are similar in many ways, it might be expected that deposition of their chalcogenides is also similar. However, there is a dominant difference in their properties that results in the fact that ZnS is considerably more difficult to deposit by CD than CdS. This difference is manifested by the difference in solubility products between the respective hydroxides and chalcogenides. Considering, for example, the sulphides, the relevant values of K p are ... 

---