Mercapto-groups

The interesting reactions where a free mercapto group is linked to the nitrogen atom of the thiazole (63), after the cleavage of a fused ring, is another illustration of the additive properties of the carbocation (Scheme 40). 

Another possible route to 2-unsubstituted thiazoles is replacement of a mercapto group by a hydrogen. Various methods have been used hydrogen peroxide in acid medium (17-19) dilute nitric acid (17), and metallic catalysts (20-22). 

Tertiary structure also refers to the overall shape of a molecule, especially to structures stabilized by disulfide bridges (cystine) formed by the oxidation of cysteine mercapto groups. 

The solubility in alkali sulfide solutions stems from the presence of disulfide groups —S—S— in ortho position to the terminal amino groups. These disulfide groups are reduced to the mercapto groups —SH, which are soluble in alkaU. 

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. 

Thioglycohc acid is recommended as a cocatalyst with strong mineral acid in the manufacture of bisphenol A by the condensation of phenol and acetone. The effect of the mercapto group (mercaptocarboxyhc acid) is attributed to the formation of a more stable carbanion intermediate of the ketone that can alkylate the phenol ring faster. The total amount of the by-products is considerably reduced (52). 

When thiourea or thiosemicarbazide are used for substitution of a chlorine atom with a mercapto group, thiouronium salts are formed first, and they are hydrolysed by aqueous base. Other groups, such as alkoxy, alkyl, amino and cyano, if present, are usually not... 

The versatility of pyrimidine substituted chloroquinazolines as intermediates is due to the ready replacement of the halogen atoms by hydrogen, alkyl, alkoxyl, amino, and mercapto groups (see Section VI, A). 

Fusion of 4-hydroxyquinazoIine with phosphorus pentasulfide yields 4-mercaptoquinazoline and, similarly, substituted 2,4-dimercapto-quinazolines have been obtained from the corresponding dihydroxy compounds. The greater reactivity of the 4-mercapto as compared with the 2-mercapto group has permitted the preparation of 4-amino-2-mercaptoquinazolines (see 7a). 

F. Quinolines Carrying a Mercapto Group on the Benzo Ring, 400... 

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. 

Only 4-amination of 2,4-dimercaptopyrimidine occurs with ammonia, methylamine, or dimethylamine, but both mercapto groups can be displaced in its 5-nitro derivative. 

Disubstitution of 2,4-dichloropyrimidine with thiourea proceeds more readily than with hydrosulfide ion, principally because the former intermediate (229) contains the activating, cationic acylated thio group compared to the highly anionized mercapto group in the latter reaction. 

Schwefelwasserstoff, m. hydrogen sulfide, -rest, m. mercapto group, sulfhydryl, SH. -saure, /. hydrosulfuric acid (H2S). -Strom,... 

Menthyl chloride, El reaction of, 392 E2 reaction of, 390 Mercapto group, 667 Mercuric trifluoroacetate. 

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