Mercaptans, alkylation preparation

Mercaptans (or thio-alcohols or thiols), the sulphur analogues of the alcohols, were formerly prepared by the interaction of an alkyl halide and sodium hydrosulphide in alcoholic solution ... 

Peptides typically are prepared for this ligation process using a-alkyl thioesters, because they are simple to make at the time of peptide synthesis. However, due to the relatively slow reaction kinetics of alkyl thioesters, most native chemical ligation processes have been catalyzed through the use of thiol compound additives, such as benzyl mercaptan or thiophenol (Dawson et al., 1997). These compounds react with the initial a-alkyl thioester to form another intermediate, an aryl thioester, which is more reactive toward the N-terminal cysteine on the other peptide to be coupled. A study... 

In abroad sense, the model developed for the cobaloxime(II)-catalyzed reactions seems to be valid also for the autoxidation of the alkyl mercaptan to disulfides in the presence of cobalt(II) phthalocyanine tetra-sodium sulfonate in reverse micelles (142). It was assumed that the rate-determining electron transfer within the catalyst-substrate-dioxygen complex leads to the formation of the final products via the RS and O - radicals. The yield of the disulfide product was higher in water-oil microemulsions prepared from a cationic surfactant than in the presence of an anionic surfactant. This difference is probably due to the stabilization of the monomeric form of the catalyst in the former environment. 

The preparation of thiols by S ,2 attack of nucleophilic HS on an alkyl halide gives poor yields because the mercaptan loses a proton to form an anion, RS, which reacts with a second molecule of alkyl halide to form a thioether. 

Improvements in feed preparation and pretreatment have made important contributions to the advances in alkylation technology (12, 17). The ability to design better fractionators has made higher quality feedstocks available, and feed pretreatment facilities have been developed to remove water, mercaptans, sulfides, and diolefins effectively. The benefits of these advances have been realized as higher alkylate yields and octanes, lower acid consumption, and reduced corrosion. 

Reaction of Resin-Bound Iron Complex (54) with Alkyl Mercaptans, Thiophenols, and Phenols (Fig. 9)31. Sodium thiolates are prepared analogously to the alkoxides from thiol and sodium hydride, except that dry DMF is used as a solvent. The substitution on the polymer-bound arene (54) is performed at 70° in DMF within 16 h. The resin is filtered and washed with DMF (2 x 50 ml), MeOH (2 x 50 ml), H20 (2 x 50 ml), MeOH (2 x 50 ml), and CH2CI2 (3 x 50 ml) and then dried in vacuo at 40° to yield a red resin. 

The Leuckart Thiophenol Reaction allows the preparation of thiophenols and corresponding thioethers from anilines or their corresponding diazonium salts. The first step is the reaction of an aryl diazonium salt with a potassium alkyl xanthate to give an aryl xanthate, which affords an aryl mercaptan upon basic hydrolysis or an aryl thioether upon warming. 

Although the compounds in which R" is alkyl can be prepared more readily by the simple Mannich reaction, this sequence is useful for nitrogen compounds such as aromatic amines, hydrazines, and hydroxylamine which do not ordinarily enter into the Mannich reaction. These intermediates react cleanly with mercaptans (21) and with dimercaptans (17) to produce compounds of the type XVI and XVII. 

Thermal decomposition of methyl xanthates is similar to the pyrolysis of acetates for the formation of the double bond. Olefins are obtained from primary, secondary, and tertiary alcohols without extensive isomerization or structural rearrangement. The other products of the pyrolysis of the methyl xanthates are methyl mercaptan and carbon oxy-sulfide. The xanthates prepared from primary alcohols are more difficult to decompose than those prepared from secondary and tertiary alcohols. Over-all yields of 22-51% have been obtained for a number of tertiary alkyl derivatives of ethylene. Originally the xanthates were made by successive treatment of the alcohol with sodium or potassium, carbon disulfide, and methyl iodide. In a modification of this procedure sodium... 

This reaction is analogous to similar methods for the preparation of ethers (methods 113 and 116), Both simple and mixed sulfides may be made from aliphatic mercaptans or thiophenols. The sodium mercaptides are formed from the mercaptans and aqueous or alcoholic solutions of sodium hydroxide or alcoholic sodium ethoxide. Alkylation is effected by halides, alkyl sulfates, or esters of sulfonic acids. The over-all yields of sulfides are usually above 70%. r-Butyl mercaptan is alkylated directly by /-butyl alcohol in strong sulfuric acid to give /-butyl sulfide in 87% yield. ... 

Sodium sulfhydride (NaSH) is a much better reagent for the formation of thiols (mercaptans) from alkyl halides than H2S and is used much more often. It is easily prepared by bubbling H2S into an alkaline solution, but hydrosulfide on a supported polymer resin has also been used. " The reaction is most useful for primary halides. Secondary substrates give much lower yields, and the reaction fails completely for tertiary halides because elimination predominates. Sulfuric and sulfonic esters can be used instead of halides. Thioethers (RSR) are often side products. The conversion can also be accomplished under neutral conditions by treatment of a primary halide with F and a tin sulfide, such as PhsSnSSnPhs. An indirect method for the preparation of a thiol is the reaction of an alkyl halide with thiourea to give an isothiuronium salt (119), and subsequent treatment with alkali or a... 

It is possible to prepare compounds of the general formula Sn(SR )R3 from reactions of a mercaptan (R SH) and either Sn(hal)R3 (hal = Cl, Br, I), Sn(OH)R3, or (R3Sn)20 (R,R = alkyl, aryl groups).The example given here uses x-oxo-bis(tributyltin) as the organotin precursor because this is one of the least expensive tin compounds available. 

Synthesis of mercaptans.1 Mercaptans can be obtained in 30-75 % yield by heating (I) with an alkyl halide in ethanol for 24 hr. Acetylurea (3) is the other product. An intermediate l-acetyl-2-alkyl-2-thiopseudourea hydrohalidc (a) is involved. These thiopseudoureas can be isolated if prepared in acetonitrile solution. Yields of mercaptans are high when primary halides are used but rather low in the case of secondary... 

Preparation of mercaptans (thiols). An alkyl halide, for example lauryl bromide, reacts with thiourea to give the isothiourea hydrobromide, which on alkaline hydrolysis affords the mercaptan. In the preparation of lauryl mercaptan the... 

From 94, several compounds were generated such as the 3-thioalkyl compounds 96 (40-67%) by reaction with alkyl bromides. Intermediate 94 was also treated with HCl, iodine, 1,3-dibromopropane or with ethyl chlorocar-bonate affording the mercaptane 97 (68%), the disulfide 98 (45%, n = 0), compound 99 (37%, = 3) and the thiocarbonate 100 (67%), respectively. By a partial hydrolysis of the nitrile group with H2SO4 at reflux, carboxamides lOla-b (92%) were prepared from 96. The same reagents 96 can be transformed into methyl esters 102 (Scheme 26). 

Detergents can also be prepared from other organic substrates, such as alcohols, mercaptans, amines and alkyl-phosphonic or -thiophosphonic acids, but these are much less commercially significant than the three main types mentioned above. 

R. Adams, W. Reifschneider, A. Ferret-ti, Org. Synthesis Coll. Vol. 5, Wiley Sons, New York, 1973, pp. 107-110. Alternatively, the acyl chloride could either be reacted with mercaptan and co-balt(II) chloride [37] or thioacetamide followed by alkyl bromide [38] to produce the corresponding thioester. While these avoid the inconvenient preparation of the copper salt, yields were lower due to side-product formation. 

According to the process of Campbell and Klingmann (1961) thiolcarbamic acid esters can be prepared with a good yield (90%) by the reaction of carbamoyl chlorides with alkyl mercaptans in solvent-free m ium, in the presence of anhydrous zinc chloride as catalyst. The reaction is the following ... 

For the determination of alkyl- and arylmercaptans, reaction with acrylonitrile followed by analysis of unreacted excess has been recommended [135]. Atkinson and Natoli [171] proposed an indirect catalytic method. The determination of tertiary and secondary thiols has been discussed [172]. Kawahara [173] proposes to detect trace amounts of mercaptans in the form of pentafluorobenzyl esters prepared from a-bromo-... 

Alkylation plays an important role in the production of synthetic rubber of the GR-S type, this unit process being employed for the preparation of ethylbenzene from which styrene is derived. Much lauryl mercaptan has been manufactured for use as a modifier in making synthetic rubber. 

A series of alkyl and aryl mercaptan-tail porphyrins has been prepared by Collman and Groh (Scheme 28) The Cs alkyl chain may be prepared directly by treating mono-(o-aminophenyl)triphenylporphyrin (57) with S-acetyl or S-tritylthiohexanoyl chloride... 

The use of mejo-(o-aminophenyl)triphenylporphyrin 57 to prepare a series of alkyl and aryl mercaptan-tail porphyrins as cytochrome P450 models has been described in Sect. 3.B. A similar series of compounds has been prepared by acylation of the tripivalamide-p-aminophenylporphyrin 147 to give the alkyl mercaptan tailed picket-fence porphyrins 154 (Scheme 45) . A similar compound 155 with an appended thioether chain has also been prepared and is reportedly capable of reversibly binding dioxygen ... 

Marvel and co-workers [7] were one of the first groups to study in detail the preparation and polymerization of alkyl thioacrylates. Mikeska [8] earlier prepared thioacrylic esters by the reaction of chloropropionyl chloride and the mercaptan followed by dehydrohalogenation with diethylaniline. Marvel prepared alkyl thioacrylates by the reaction of a,yS-dibromopropionyl chloride with mercaptan followed by the reaction with sodium iodide to eliminate the bromine atoms to give the acrylate ester. 

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