Desulphurization Reactions

The desulphurization of benzylic sulphides by irradiating them in the presence of tervalent phosphorus compounds has again been used in the synthesis of paracyclophanes. A particularly elegant use of this reaction was made in the synthesis of (71), a compound which exhibits an intramolecular charge-transfer absorption band. There have been several reports of the synthesis of 

The reductive cleavage of several aryl disulphides to thiols by their reaction with triphenylphosphine in aqueous dioxan has been reported. Several examples have been reported of the cleavage by phosphines and phosphites of S—SandS—N bonds contained in heterocyclic ring systems. Examples include (73) and (74).  

Other desulphurization reactions which probably involve ionic intermediates include those of (75) and /S-ketosulphides. The reaction of the latter type of compounds is thought to involve enolate carbanions, and this 

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The use of Raney nickel for desulphurization reactions has been well known for a considerable time144. Some work has been carried out on sulphones, the most notable... 

Roberts had reported that the low reactivity of alkyl and/or phenyl substituted organosilanes in the reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols (vide supra)49. The general reaction mechanism (Scheme 11) shows that alkyl radicals abstract hydrogen atom from thiols and the resulting thiyl radicals abstract hydrogen from the silane. This procedure has been applied in dehalogenation, deoxygenation and desulphurization reactions. This approach has also been extended by the same... 

Schemes Benzothiophen desulphurization. Reaction network ref. 196). For the mer-capto intermediate X, Y = H, SH X = Y...

Earlier, attention was drawn to a novel application of the oxidative desulphurization reaction which occurs between sulphoxides and phosphonothioic acid esters. When 1 mol of the thio acid is allowed to remain in contact with 2 mol of a racemic methyl alkyl sulphoxide for 2 weeks at room temperature, the unreacted sulphoxide is found to be optically active, a result which represents asymmetric deoxygenation of the sulphoxide. The chemical course of the reaction is consistent with Scheme 31. Since the appearance of the initial results, corrections have been made to the configurations of the phosphorus-containing substrates, and hence the stereochemical details and mechanistic arguments require reappraisal neverthless, the fact remains that (-t-)-sulphoxides are obtained by the use of the ( S)-(-)-acids, R (R O)P(S)OH , a feature which can be used to determine the chirality of other like acids. Dialkyl and alkyl aryl sulphoxides are also known to form diastereoisomeric complexes with (5)-(-)-/er butylphenylphosphinothioic acid, distinguishable by their NMR spectra, and through such complexation it is possible to assess the enantiomeric composition of the sulphoxide " ... 

Use of Caro s acid, H2SO5, generated in situ by electrolysis as the scrubbing reagent. The new desulphurization reaction may be written as ... 

Because of this, the flame smelting conditions (autogenous or with the use of extra fuel) are important. In the oxidation of sulphides, the relevant desulphurization reactions (PbS, ZnS, FeS), Aat are also major contributors of heat, are of the type ... 

Typically desulphurization reactions are carried out with a large excess of Raney nickel. The reaction is not truly catalytic in nature since the hydrogen used to replace the sulphur usually comes from hydrogen retained by the metal during its preparation. In addition the nickel is consumed by the combination with the sulphur to form nickel sulphide. In practice a minimum ratio of 2-6 1 for nickd atoms to sulphur atoms is necessary. ... 

Thus in both reversible reactions the absorption of H2S would be adversely affected by the presence of water vapour in the feed gas. Values of logio-fiT, for the two desulphurization reactions are given, and hence the equilibrium quantities of HaS (p.p.m. volume/volume) are tabulated, showing that ZnO is more efficient than Fe804 in the removal of HaS. A further potential disadvantage of iron oxide (compared with zinc oxide) is associated with the relative ease of reduction of the two sulphides according to the equation ... 

Desulphurization reactions on zinc oxide. The reaction of zinc oxide with H2S is a non-catal3dic chemical reaction in stoichiometry. 

Other molecules containing nitrogen and oxygen have a strong inhibition effect on desulphurization reactions.H2S, which is produced during HDS reactions, is also known to act as an inhibitor. 

Altering the desulphurization reaction pathways for hindered sulphur compounds by using zeolite-containing catalysts. 

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