From Other Sulphur Heterocycles

From Other Sulphur Heterocycles. The diazo-ketone (24), prepared from 27f-thiopyran-3(6//) Oi c and phenyl azide, yields (25) upon heating, which apparently is the stable tautomer of 3-hydroxy-4-phenylaminomethylthiophen, and (26). The structures of both compounds were proven by 2f-ray crystallography. The thermal and photochemical reactions of 1,4-dithiin sulphoxides 

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From Other Sulphur Heterocycles. The reaction of (46) with 2 eq. of bromine in CHjC gave (47), except for, (46d), which directly gave (48a). Further bromination of (47a) gave (48b). The formation of (47) from (46) has been assumed to proceed via (49) to (53).15 The reaction of (54) with chloroacetone under basic conditions unexpectedly yielded (55) in 44% yield.16 Photolysis of (56) gave tetraphenylthiophen, tetraphenyl-1,4-dithiine, diphenyl-acetylene and sulphur. The products are assumed to be formed via the dimer (57) and (58), which were isolable under appropriate conditions. Photolysis of (56) in the presence of dimethyl acetylenedicarboxylate gave a 17% yield of dimethyl 2,5-dif)henyl-thiophen-3,4-dicarboxylate.17 The reaction of (59) with diphenyl-acetylene at 300°C gave tetraphenylthiophen.1 ... 

In addition to benzenoid diazo components, diazotised heterocyclic amines in which the amino group is attached to a nitrogen- or sulphur-containing ring figure prominently in the preparation of disperse dyes [87,88], since these can produce marked bathochromic shifts. The most commonly used of these are the 6-substituted 2-aminobenzothiazoles, prepared by the reaction of a suitable arylamine with bromine and potassium thiocyanate (Scheme 4.31). Intermediates of this type, such as the 6-nitro derivative (4.79), are the source of red dyes, as in Cl Disperse Red 145 (4.80). It has been found that dichloroacetic acid is an effective solvent for the diazotisation of 2-amino-6-nitrobenzothiazole [89]. Subsequent coupling reactions can be carried out in the same solvent system. Monoazo disperse dyes have also been synthesised from other isomeric nitro derivatives of 2-aminobenzothiazole [90]. Various dichloronitro derivatives of this amine can be used to generate reddish blue dyes for polyester [91]. 

Isolation of the hydrocarbons from other lipids The total lipid extract may be subjected to removal of elemental sulphur by passage through an activated copper column (Blumer, 1957) and then to chromatographic separation on adsorbent columns or thin layer plates. For column chromatography, silic el is used with a short alumina bed on the top of the silic el. Both adsorbents should be partially deactivated by the addition of water (2—5%) to prevent the formation of artifacts (Blumer, 1970). Elution with a non-polar solvent such as hexane or pentane and subsequently with mixtures of non-polar and polar solvents, e.g. benzene and methanol, permits the isolation of several fractions containing saturated, unsaturated, aromatic hydrocarbons and more polar compounds (methyl esters, alcohols, acids, phenols and heterocyclic compounds). The interference from esters encountered in the isolation of aromatic hydrocarbons can be avoided prior to separation by saponification of the esters of fatty acids, which are easily removed. 

Preparative uses of thiolates, quite apart from syntheses of other sulphur functional groups discussed elsewhere in this Volume, include the demethyl-ation of aryl methyl ethers with EtS in hot DMF, and a similar use of thiophenol for demethylating aza-heterocyclic O-methyl ethers, of type =N—C(OMe)=. 2-Methylthio-l-methylbenzimidazole does not react with thiophenol, though an alternative reaction path is available for certain hetero-aryl methyl sulphides (17). ... 

Hydrogen sulphide is a key intermediate in the formation of many heterocyclic sulphur compounds. It is produced from cysteine by hydrolysis or by Strecker degradation ammonia, acetaldehyde and mercaptoacetaldehyde are also formed (Scheme 12.4). All of these are reactive compounds, providing an important source of reactants for a wide range of flavour compounds. Scheme 12.6 summarises the reactions between hydrogen sulphide and other simple intermediates formed in other parts of the Maillard reaction. 

Heterocyclic This designates a closed-ring structure, usually 5-membered or 6-membered, in which one or more of the atoms in the ring is an element other than carbon (e.g. sulphur, nitrogen, etc.). Homopolymerisation The process of formation of synthetic high polymers from a single monomer. 

Other work on four-membered heterocycles containing one sulphur atom includes a study of the vacuum-u.v. photodecomposition of thietan 1,1-dioxide and the formation of a thietanone from a xanthate and diphenylketen, and reports of several thiets. There is evidence that photolysis of (107) in a matrix at 77 K leads to the o-thiobenzoquinone (108), which is interconvertible with the... 

As distinct from benzene and other ring systems which contain carbon as the only ring constituent are a number of heterocyclic ring compounds in which one or more of the carbons is replaced by an oxygen, nitrogen or sulphur atom. These too may be either saturated or unsaturated. 

Dithiins and Related Compounds.—Diacetylenic sulphides react with Na2X (X = S, Se, or Te) to give the mono- and di-substituted heterocycles (24). Other syntheses of 1,4-dithiins from acetylenes are the reactions of amidines of phenylpropiolic acid with sulphur (or selenium) in DMF, and of dimethyl acetylenedicarboxylate with hydrogen bromide in liquid sulphur dioxide. In the latter reaction, sulphuric acid is formed by disproportionation. 

With respect to the organization of reviewing the material, the present Chapter follows quite closely Chapter 16 in Volume 2 of these Reports. Aspects of the chemistry of 1,3-thiazines arising from work on the cephalosporins and related compounds are reviewed in Chapter 3, and those concerning 2-azathiabenzenes are discussed in Chapter 6 in connection with other heterocyclic systems containing sexivalent sulphur. 

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