Desulfurization procedure

Thioketals, unlike ordinary ketals, are formed readily from ketones and thiols (RSH) in the presence of acid catalysts. The desulfurization procedure usually goes well, but the product is rather difficult to separate by extraction from the large excess of Raney nickel required for optimum yields. 

Removal of the mercapto (or thione) function is most commonly achieved using Raney nickel, although concentrated HCl at high temperatures or nickel boride have been employed. Thiohydantoins are transformed into imidazolidin-4-ones by sodium in amyl alcohol (70JHC439). Oxidative desulfurization procedures too are often used the reactions probably proceed through the unstable sulfinic acid species which very readily eliminates sulfur dioxide. The high resistance of sulfonic acids to acid hydrolysis renders unlikely the possibility that they are reaction intermediates. 

With selenium, there are only a few hundred references to reductive deselenation compared with several thousands for the reductive cleavage of the C—S bond. Since the chemistries of selenium and sulfur are so similar, it is not surprising that the main deselenation procedures were borrowed from the desulfurization procedures. However, from the practical point of view, appreciable differences will be encountered due to the weaker C—Se bond and to the greater sensitivity of Se towards nucleophilic attack. 

Alkylthio groups are readily removed by the well-known, Raney niclml desulfurization procedure, which is particularly valuable in cases in which the initial presence of the alkylthio group is necessary in order to direct the entering glycosyl moiety to the desired imidazole nitrogen atom (N-9).i < i -> i- - ... 

The tricyclic adduct (15e R = CH2CH20Bn,Me) closely resembling (15a) (Table 2) could be cleaved by t-BuOK in t-BuOH followed by treatment with Mel to afford dihydropyrroles (105 R = CH2CH2Bn,Me). The tricyclic adduct (15e R = H) also gave the pyrrolidine derivative (106) on treatment with tetrabutyltinhydride followed by acid hydrolysis. The relative stereochemistry of the ethoxycarbonyl functions is not lost during this particular desulfurization procedure <85T3537>. 

Radian Corp., 1977, Evaluation of Regenerable Flue Gas Desulfurization Procedures, Vol. 1, EPRI FP-272, Electric Power Research Institute, Palo Alto, CA, January. 

In Summary The Wolff-Kishner reduction is the decomposition of a hydrazone by base, the second part of a method of deoxygenating aldehydes and ketones. It complements Clemmensen and thioacetal desulfurization procedures. 

Diallylsulfonium salts undergo intramolecular allylic rearrangement with strong bases to yield 1,5-dienes after reductive desulfurization. The straight-chain 1,5-dienes may be obtained by double sulfur extrusion with concomitant allylic rearrangements from diallyl disulfides. The first step is achieved with phosphines or phosphites, the second with benzyne. This procedure is especially suitable for the synthesis of acid sensitive olefins and has been used in oligoisoprene synthesis (G.M. Blackburn, 1969). 

One method for using sodium alumiaate to desulfurize flue gas containing sulfur dioxide is described (45). This procedure led to a process where aluminum sulfate [10043-01-3] could be generated as a by-product of flue gas desulfurization (46). 

Two techniques, electrochemical reduction (section IIl-C) and Clem-mensen reduction (section ITI-D), have previously been recommended for the direct reduction of isolated ketones to hydrocarbons. Since the applicability of these methods is limited to compounds which can withstand strongly acidic reaction conditions or to cases where isotope scrambling is not a problem, it is desirable to provide milder alternative procedures. Two of the methods discussed in this section, desulfurization of mercaptal derivatives with deuterated Raney nickel (section IV-A) and metal deuteride reduction of tosylhydrazone derivatives (section IV-B), permit the replacement of a carbonyl oxygen by deuterium under neutral or alkaline conditions. 

An alternative preparation of deuterio-Raney nickel is described using a more elaborate purification procedure. There is no evidence however, that the use of this nickel results in a better yield or higher isotopic purity of products from the desulfurization reactions. 

In the course of synthesis of B-homo-progesterone (66) Himizu and Schichita utilized the Ringold procedure to convert 3j5,20 -dihydroxy-5a-pregnan-7-one diacetate (63) to 3/3,20yS-dihydroxy-B-homo-5a-pregnan-7-one diacetate (64). The latter is desulfurized with Raney nickel after prior... 

The low reactivity of alkyl and/or phenyl substituted organosilanes in reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols. The reaction mechanism is reported in Scheme 5 and shows that alkyl radicals abstract hydrogen from thiols and the resulting thiyl radical abstracts hydrogen from the silane. This procedure, which was coined polarity-reversal catalysis, has been applied to dehalogenation, deoxygenation, and desulfurization reactions.For example, 1-bromoadamantane is quantitatively reduced with 2 equiv of triethylsilane in the presence of a catalytic amount of ferf-dodecanethiol. 

Desulfurization of organic compounds over Ra-Ni is a well-known procedure.364-369 Ra-Ni exists in different forms (W1 to W8), differing in the preparation procedure and sometimes symbolized as Ni(H). Ra-Ni is sometimes called a catalyst however, it is used usually in large excess and the reaction is stoichiometric. Ra-Ni can desulfurize every C—S bond containing compound but it can also hydrogenate a lot of other functional groups. Unwanted side reactions are sometimes suppressed by using deactivated Ra-Ni. 

Since the chemistry of the C-Se bond is very similar to the chemistry of the C-S bond, the deselenation procedures are also very similar to the desulfurization methods. Thus, Ra-Ni is an efficient reagent in hydrogenolytic desel-enations, but the outcome of the reaction depends on the preparation of the catalyst.426 28... 

A procedure for immobilization of a P. stutzeri UP-1 strain using sodium alginate was reported [133], This strain does not perform sulfur-specific desulfurization, but degrades DBT via the Kodama pathway. Nevertheless, the report discussed immobilization of the biocatalyst cells in alginate beads with successful biocatalyst recovery and regeneration for a period of 600 h. However, the immobilized biocatalyst did decrease in specific activity, although the extent of loss was not discussed. The biocatalyst was separated after every 100 h of treatment, washed with saline and a boric acid solution and reused in subsequent experiment. The non-immobilized cells were shown to loose activity gradually with complete loss of activity after four repeat runs of 20 hour each. The report does not mention any control runs, which leaves the question of DBT disappearance via adsorption on immobilized beads unanswered and likewise the claim of a better immobilized biocatalyst. 

The procedure begins by converting the R. rhodochrous (1), ATCC 53968, into mutant-/ , rhodochrous strains (2) incapable of breaking C—S bonds, by the action of a mutagen. Then, the desulfurization active colonies are separated from the desulfurization inactive colonies via screening for BDS activity and classified as CS+ or CS-, respectively. Following this, DNA is extracted from CS+ R. rhodochrous (1) and cut into... 

Harmata and co-workers introduced a procedure for the reductive desulfurization of selected 2,1-benzothiazines with sodium amalgam, leading to the formation of the 2-alkylanilines in high yields <94S142>. This method is regioselective and general. As an example, alkylation of 187 followed by treatment with Na/Hg resulted in the formation of the aniline 188 in 68% overall yield (Scheme 50). 

This procedure for the preparation of l-ethyl-3-(3-dimethyl-amino)propylcarbodiimide and its salts is a modification of one that has been published.4 Unsymmetrical carbodiimides have also been prepared by desulfurization of the corresponding thioureas with mercuric oxide3 or by dehydration of the corresponding ureas with -toluenesulfonyl chloride in pyridine.4 Unsymmetrical 1,3-disubstituted ureas are best prepared by the reaction... 

The present procedure2 describes the conversion of resin-bound, primary aliphatic amines into isothiocyanates and the conversion of the latter into 3-aminothiophenes. The generation of isothiocyanates is related to known procedures,3 in which amines are first treated with carbon disulfide and the resulting dithiocarba-mates are desulfurized by treatment with a condensing agent (alkyl chloroformates, carbodiimides, lead or mercury salts, etc.). The presence of resin-bound isothiocyanates on the polystyrene support could be qualitatively ascertained by infrared spectroscopy (KBr-pellet strong absorption at 2091 cm-1). 

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