One Sulphur Atom

One Sulphur Atom.— The synthesis of the 2,3- and 2,7-dihydrothiepins (96) and (98) by cycloaddition of DMADC to (95) and (97), respectively, has been described, reaction occurring via isolable cyclobutene intermediates. Unlike the parent compoiind (99 X = lone pair) which ring-contracts rather than give the 1-benzothiepin, the sulphone (99 X = Og) may be dehydrated on acid treatment to the corresponding 1-benzothiepin dioxide. The sul-phoxide (99 X = O) undergoes SO-elimination under the same conditions, consistent with the 1-benzothiepin monoxide as an intermediate however, this compound could not be isolated. A successful route to substituted 1-benzothiepins is enol-acetylation of keto-precursors such as (100). In the 

3-benzothiepin system, substituted derivatives are well known but attempts to synthesize (101), a potential precursor to 3-benzothiepin itself, by SClg addition to o-vinylstyrene were unsuccessful. A number of acid-catalysed cyclization reactions have been examined as routes to thiacycloheptane 

Analogous systems (106) ° and (107) have also been prepared and transformations of the carbonyl group of (106) examined.  

The system (108) (in effect a masked di-t-butyl diketone) and its derivatives have received attention this year. Photolysis of (108 = O), for example, 

Sv tek, R. Zahnadnik, and M. Protwa, Coil. Czech. Chem. Comm., 1972, 

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In addition to the simple acids discussed above, sulphur forms two peroxosulphuric acids containing the —O—O— linkage and a number of thionic acids containing more than one sulphur atom. 

The oxidation of disulphide species with at least one sulphur atom at the sulphoxide oxidation level will also be covered briefly. 

In low or sulphurless systems, thiurams containing more than one sulphur atom act as sulphur donors. They also confer low tendency to reversion, and good heat stability. 

In the crystal structure of pyrite, which is modelled on the periclase structure (fig. 5.1), Fe2+ ions occupy Mg24- positions and the mid-points of (S-S)2- dimeric anions are located at the O2- positions. Each Fe2+ ion is in octahedral coordination with one sulphur atom belonging to six different (S-S)2- dimers, and the... 

A SFe molecule consists of one sulphur atom and six fluor atoms. We wish to write down the Lewis structure for this molecule in order to know something about the internal atomic arrangement and the positions of the lone pairs in this molecule. Thus the 3-step procedure given hy (2- 2) on page 59 is used again ... 

Heterocycles containing One Sulphur Atom Thiopyrans. - A convenient synthesis of 2-phenylthiopyran-4-one (217) has been developed from methyl styryl ketone and ethyl formate. The enolate... 

Systems containing Two Sulphur Atoms or One Sulphur Atom and... 

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... 

The reactions of bis(phosphoryl) disulphides with a variety of tervalent phosphorus acid derivatives or triphenylphosphine have been studied by means of low-temperature n.m.r. Intermediates were detected which indicated initial attack on one sulphur atom followed by substitution reactions at one of the phosphorus atoms, Arbuzov dealkylations, or phosphorane formation. An example is shown for the reaction of tributyl phosphite with bis(diethoxyphosphoryl) disulphide (25). In order to obtain solely thiophosphate products it is necessary to use bis(thiophosphoryl) disulphides, and one such compound (26) has been proposed as a highly effective reagent for the oxidation of oligonucleoside phosphites to phosphorothioates. A comparison of the efficiency of (26) with that of four other sulphurizing agents for use in... 

It appears that radicals containing more than one sulphur atom are resonance stabilized, perhaps by formation of a three-electron bond [2], e.g. ... 

The use of sulphur donors in place of elemental sulphur has been practised since the early 1920s when it was found that the accelerators tetramethyl thiuram disulphide and tetraethyl thiuram disulphide in conjunction with zinc oxide gave vulcanizates with improved ageing properties when compared with conventional accelerated sulphur systems. For many years it was believed that vulcanization was brought about by the abstraction of one sulphur atom from the disulphide to yield the corresponding monosulphide... 

Other Reactions of Inorganic Ligands Triphenylphosphine removes one sulphur atom from the thiocumato-complex (12), giving triphenylphosphine sulphide, SPPhg. The reaction is second-order, with an activation energy of 7.8 1.0 kcal mol-. ... 

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