Mercapto group, replacement with

Further work elucidated the stmcture of the dyes in this group by synthesizing trichioroarylthiazinones (18) from an o-aminoaryl mercaptan (19) and chloranil (20) treatment with sodium disulfide replaced the halogens by mercapto groups. 

The reactivity of halogens in pyridazine N- oxides towards nucleophilic substitution is in the order 5 > 3 > 6 > 4. This is supported by kinetic studies of the reaction between the corresponding chloropyridazine 1-oxides and piperidine. In general, the chlorine atoms in pyridazine A-oxides undergo replacement with alkoxy, aryloxy, piperidino, hydrazino, azido, hydroxylamino, mercapto, alkylmercapto, methylsulfonyl and other groups. 

An intramolecular 8 Ar2 mechanism (19) is possible in the replacement of 0X0 substituents with chloro or mercapto groups by means of phosphorus oxychloride or pentasulfide, respectively, via the intermediates shown. In the former, an intermolecular mechanism (20) is perhaps more likely. Frequently a base is not added in such reactions. 

The action of aniline on 3-phenyl-5-mercapto-l,2,4-thiadiazole under restrained conditions is reported to remove the mercapto group as hydrogen sulfide, with formation of the corresponding 5-anilino compound.75,200 This replacement, normally difficult in aromatic systems, may be due to the unusual reactivity of the thiol grouping in this particular structural environment. 

Mercapto-l,2,4-thiadiazoles are oxidized, by 2N nitric acid at 50-60°, by chromic acid mixture, chlorine, or potassium permanganate to the disulfides, which are reconvertible to the thiols by reduction with sodium amalgam and alcohol.71,72,91 168 Use of excess chlorine in aqueous acetic acid results in replacement of the mercapto group by the halogen.168... 

The dye C.I. Solubilised Sulphur Red 11 [90218-69-2] (25) contains neither thiolate groups nor their precursors. It is prepared by treating perylenetetracarboxylic dianhydride with l,4-diaminobenzene-2-sulfonic acid, then with cyanuric chloride and with NH3. It is not known whether the chlorine of the monochloro-triazine groups of the precursor is replaced by a mercapto group in dyeing. 

The replacement of an amino group by a mercapto group on an aromatic nucleus is effected by treating the diazotized amine with potassium ethyl xanthate and hydrolyzing the resulting aryl ethyl xanthate (Leuckart). Yields of 40-80% are reported for thiophenols containing methyl, halo, and methoxyl groups. Potassium ethyl xanthate is readily prepared from alcoholic potassium hydroxide and carbon disulfide. ... 

In 2-mercaptobenzothiazole, energetic oxidation with hydrogen peroxide leads to the replacement of the mercapto group by hydrogen, probably via oxidation to sulfinic acid (equation 550) [1197]. 

If the hydroxy group of a 2-amino alcohol is replaced by a mercapto group (XCIX) the reaction with carbon disulfide yields thiazolidine-2-thiones (C) with liberation of hydrogen sulfide. This method though is practically never used since thiazolidine-2-thiones are more simply obtained from 2-halo amines (see further under Section IV.l) which are themselves starting materials for the 2-amine thiols. 

Dunbrook and Zimmermann 113) report still higher yields, even with short reaction times, when sodium polysulfide and carbon disulfide are used (method C ). The essential appears to be the replacement of the chlorine atom by a mercapto group and the reduction of the nitro group to an amino group, followed by ring closure of the resulting o-aminothiophenol with carbon disulfide to the benzothiazoline-2-thione (method A). 

Thiamine anhydride (77) is a useful source of sulphur analogues of thiamine. Thus, it reacts with thioacetic acid to give the thiazolinethione (78), which on successive desulphurization by the action of hydrogen peroxide and treatment with barium chloride affords acetylthioethylthiamine (79) hydrolysis finally produces mercaptoethylthiamine (80), the sulphur analogue of thiamine. This is convertible into further derivatives, particularly by replacement of the mercapto-group of the 5-side-chain by amino-, sul-phenyl-, sulphinyl-, and sulphonyl-residues [e.g. (81), (82)]. ... 

Hydroxy and mercapto substituents at the 3- and 5-positions can also exist in tautomeric forms (see Section 4.01.5.2) and can be alkylated at either the substituent or the ring nitrogen atom. 3-Methoxy groups are not replaced by nucleophiles, but both 3- and 5-alkylthio groups react readily, as does 3-methoxy-l,2-benzisothiazole. Alkylthio compounds can be oxidized to sulfoxides and sulfones, and the latter readily undergo nucleophilic replacement. All the hydroxy compounds react with phosphorus pentachloride to give the chloro derivatives. 

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