COMPOUNDS CONTAINING SULPHUR

A wide variety of photoreactions have been reported in sulphur-containing compounds, with particular attention being paid to the photochemistry of thiones. Electrocyclic ring closure to the eyelobutabenzo[b]thiophenes (131) is the principal reaction observed on irradiation of the mono-substituted 1-benzo-thiepines (132). Photorearrangement of the 2-methyl-1,5-benzo-thiazepines (133) takes a different course and affords the isomeric 

Direct irradiation of 9-dimethylsulphonium fluorenylide (141) in acetonitrile or tetrahydrofuran yields primarily the Stevens rearrangement product 9-methyl-9-(methylthio)fluorene (142), and a 1,2-shift of a sulphonic acid group is thought to be involved in the photoisomerization of the sodium salt of metanilic acid (m-aminobenzenesulphonic acid). Photoinduced rearrangement of 4,5-(ethylenedithio)-1,3-dithiole-2-thione (143) to the 

Intramolecular [ 2 + 2] photoadditions in sulphur-containing systems have been employed in studies directed towards the total synthesis of dicyclopenta[a,d]cyclooctane terpenoids and in the conversion of the tetrathiadiene (145) into the propellane (146), a process in which the ease of reaction is 

Detailed studies of photoaddition of thiocarbonyl-containing compounds have been reported. A molecular orbital analysis of such additions has been undertaken and the results have proved useful in rationalizing observed regiochemistries. 

3-Trimethyl-2-thioxo-1,2-dihydronaphthalene adds to electron-rich alkenes such as 2,3-dihydrofuran, ethyl vinyl ether, vinyl 

Early studies (e.g. Weber, 1894) indicated that the empirical formula of the fully cross-linked material was C10H16S2CI2. However later studies by Meyer and Mark (1928) provided evidence that one atom of sulphur is subsequently liberated for every molecule of S2CI2 utilized. Using cyclohexene as a model compound Vidwans (1959) found that the initial reaction was almost quantitative and kinetically first order and for which the following mechanism was suggested  

It would therefore appear that, in outline, the following processes may occur during cold cure  

Whilst the Parkes Process has been in continual use for well over a century the Peachey-Skipsey Process (Peachey and Skipsey, 1921) was industrially short lived. Thin rubber sheets, or rubber-coated fabrics were treated with sulphur dioxide and then, after aeration, with hydrogen sulphide. The high activity of the system is usually ascribed to the formation of nascent sulphur in situ in the rubber according to the equation  

It is known that in spite of the general lack of commercial success with this process a variant of it was still in use in about 1950 in England by one company. 

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 

A wide variety of rearrangement reactions have again been reported in sulphur-containing compounds, cis - trans-isomerization is observed on irradiation of a series of higher polysulphur analogues (219) of l,2-dithiol-3-ylidene ketones in ethanol containing a catalytic amount of hydrogen chloride 178 the tram-photoproduct (220) rapidly reverts to the cis-isomer by a dark process which 

Not surprisingly, the thianaphthalene (223) is easily isomerized on irradiation to the thiopyran (224),182 and ejca-2,3-epithio-5-norbomene (225) has been reported to undergo ring-cleavage on irradiation in acetonitrile to give the isomer 

Kataoka, and H. Shimizu, Chem. and Pharm. Bull. (Japan), 1974, 22, 2485. 

The Dewar thiophen structure (232) of the photoproduct of tetrakis(trifluoro-methyl)thiophen (233) has been confirmed.188 The possible intermediacy of a 

Photochemical cyclodehydrogenation of l-(benzothien-3-yl)-2-(l-naphthyl-ethylene gave the expected pentacyclic product on irradiation in cyclohexane in the presence of iodine, whereas the isomer (249) was converted into the product (250).191 The latter result contrasts with known examples of j3-styrylnaphthalene 

There is, in the period covered by this report, an unusually high level of interest in the photochemistry of sulphur-containing compounds and in particular in the photoreactions of thiones. A 

The indolinespirobenzothiopyrans (173) show photochromic behaviour and yield the coloured isomers (174) on irradiation a dramatic red shift of 100 nm is observed in comparison with the oxygen analogue. 

Dewar thiophene (175) has been isolated and identified on argon matrix irradiation of thiophene (176) 

An analogous photoaddition of thiones to ketene acetals has been observed, but reaction with bromoketene acetals takes a different 

Type II photocyclization and cleavage pathways. This transformation is the first example of a y-hydrogen abstraction in a thioiraide and provides an attractive route to sulphur-containing 8-lactams. 3-Acyl-2-thiotetrahydro-1,3-thiazines (208) were similarly converted into the 6-lactam derivatives (209) by 

Reviews on the photochemistry of sulphonic acids and their derivatives and of sulphenic acids and their derivatives, and on the photochemical synthesis and transformations of organosulphur compounds, have been published. 

The photoreactions of thiones continue to attract attention. Matrix isolation studies of the phototautomerism of 2 (Iff)-pyridine-thione, 4(3H)-pyrimidinethione and 3(2H)-pyridazinethione have been described. Photoreactions involving intramolecular hydrogen abstraction by a thione have also been reported irradiation of the N,W-dialkyl-a,j3-unsaturated thioaraides (144) in benzene, for example, gave the azetidinethiones (145) in good 

Other miscellaneous reactions reported include the photosolvolysis of 2-alkoxy-2-phenyl-l,3-dithiolane in neutral aqueous solution and the photochemical generation of a-sulphur-substituted cyclopropylcarbinyl radicals.  

Most cooked foods contain thiazoles. Simple alkyl-substituted thiazoles generally have odour threshold values in the range 1-1,000 pg/kg. Odour descriptions include green, vegetable-like, cocoa, nutty, and some are claimed to have meaty characteristics [22]. Although most alkylthiazoles result from thermal 

12 The Maillard Reaction Source of Flavour in Thermally Processed Foods 

A number of furans with thiol, sulphide or disulphide substitution have been reported as aroma volatiles, and these are particularly important in meat and coffee. In the early 1970s, it was shown that furans and thiophenes with a thiol group in the 3-position possess strong meat-like aromas and exceptionally low odour threshold values [50] however, it was over 15 years before such compounds were reported in meat itself In 1986,2-methyl-3-(methylthio)furan was identified in cooked beef and it was reported to have a low odour threshold value (0.05 pg/kg) and a meaty aroma at levels below 1 pg/kg [51]. Gasser and Grosch [52] identified 2-methyl-3-furanthiol and the corresponding disulphide, bis(2-methyl-3-furanyl) disulphide, as major contributors to the meaty aroma of cooked beef. The odour threshold value of this disulphide has been reported as 0.02 ng/kg, one of the lowest known threshold values [53]. Other thiols which may contribute to meaty aromas include mercaptoketones, such as 2-mercapto-pentan-3-one. 2-Furylmethanethiol (2-furfurylmercaptan) has also been found in meat, but is more likely to contribute to roasted rather than meaty aromas. Disulphides have also been found, either as symmetrical disulphides derived from two molecules of the same thiol or as mixed disulphides from two different thiols [54]. 

Kawamura S (1983) In Waller GR, Feather MS (eds) The Maillard Reaction in Foods and Nutrition. ACS Symposium Series 215. American Chemical Society, Washington, p 3 Hodge JE (1967) In Schultz HW, Day EA, Libbey LM (eds) Chemistry and Physiology of Flavors. AVI, Westport, p 465 

Hurrell RE (1982) In Morton ID, MacLeod AJ (eds) Food Flavors. Elsevier, Amsterdam, p 399 

Photo-Fries rearrangements have been reported in 

Carbon-sulphur bond homolysis with the formation of biradicals (159) has been proposed to account for the photorearrangement of the allene thiiranes (160) to the thiiranes (161) and the thietane-3-thiones (162)low temperature matrix studies have established that photodecomposition of the 1,2,5-thiadiselenole (163) occurs via an initial photorearrangement to the novel spirothiaselenirane (164)whereas initial sulphur-sulphur bond homolysis is thought to account for the photochem- 

The regioselective radical addition of -toluene-sulphonyl cyanide to alkenes has been achieved photochemically Regioselective adducts have also been obtained on irradiation of Se-phenyl(selenothioperoxy)benzoate with terminal or cyclic alkenes. 

Ring cleavage initiated by carbon-sulphur bond homolysis 

The potential use of 4-thiouracil as a photochemical probe in nucleic acid studies has been investigated in 5 -0-(2 - 

Graziano, M. R. lesce, and R. Scarpati, J. Chem. Soc., Chem. Commun., 1981, 720 (c/. ref. 146a in last year s Report). 

Lundt and B. Skelbaek-Pederson, Acra Chem. Scand., Ser. B, 1981,35, 637. 

Miyashi, N. Suto, T. Yamaki, and T. Mukai, Tetrahedron Lett., 1981,22, 4421. 

1-Dimethylgermole has been prepared for the first time, and trapped as the maleic anhydride adduct dimethylgermylene, generated thermally from (152), behaves as a singlet species in its additions to conjugated dienes. 

Laporterie, G. Manuel, J. Dubac, P. Mazerolles, and H. lloughmane,/. Organomet. Chem., 1981,210, C33. 

HjCS is seen to dominate over vibrational and rotational relaxation, as the fluorescence spectra of 5, show that the species retain their memory of the initially excited rovibronic levels at relatively high pressures. Fluorescence excitation of jet-cooled thiophosgene, CljCS, has been reported.  

Kawasaki, K. Kasatani, and H. Sato, Chem. Phys. Lett., 1980, 75, 128. 

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The most important class of stabilisers are the lead compounds which form lead chloride on reaction with hydrogen chloride evolved during decomposition. As a class the lead compounds give rise to products of varying opacity, are toxic and turn black in the presence of certain sulphur-containing compounds but are good heat stabilisers. 

The early work of Kennerly and Patterson [16] on catalytic decomposition of hydroperoxides by sulphur-containing compounds formed the basis of the preventive (P) mechanism that complements the chain breaking (CB) process. Preventive antioxidants (sometimes referred to as secondary antioxidants), however, interrupt the second oxidative cycle by preventing or inhibiting the generation of free radicals [17]. The most important preventive mechanism is the nonradical hydroperoxide decomposition, PD. Phosphite esters and sulphur-containing compounds, e.g., AO 13-18, Table la are the most important classes of peroxide decomposers. 

Other compounds include the plant-derived sterols (phytosterols) and other sulphur-containing compounds found in onions and their relatives. Only a few of the more important examples will be discussed in the following sections. 

Our estimate is a compromise between the experimental values and Hilado s apparently slightly high value. This comparative analysis of the two approaches will be continued within the paragraph that deals with flashpoints since there will then be available better evaluation tools for both methods. The comparison between both tables shows that the range of values is higher than the author s. In particular, sulphur-containing compounds were not considered. The regression conducted for this substance was of mediocre quality because of the small amount of data, so an equation was not proposed. 

The preparation of the 1,3,2,4-dithiadiphosphetane 2,4-disulphi.des (110 R=Me, Et, Pr, or Ph) has been described. Some new sulphur-containing compounds including the oximino esters (111 isolable as their methyl esters) and the dihydro-... 

Another approach was developed by Scott in the 1970 s (7.8) which utilises the same mechanochemistry used previously by Watson to initiate the Kharacsh-type addition of substituted alkyl mercaptans and disulphides to olefinic double bonds in unsaturated polymers. More recently, this approach was used to react a variety of additives (both antioxidants and modifiers) other than sulphur-containing compounds with saturated hydrocarbon polymers in the melt. In this method, mechanochemically formed alkyl radicals during the processing operation are utilised to produce polymer-bound functions which can either improve the additive performance and/or modify polymer properties (Al-Malaika, S., Quinn, N., and Scott, 6 Al-Malaika, S., Ibrahim, A., and Scott, 6., Aston University, Birmingham, unpublished work). This has provided a potential solution to the problem of loss of antioxidants by volatilisation or extraction since such antioxidants can only be removed by breaking chemical bonds. It can also provide substantial improvement to polymer properties, for example, in composites, under aggresive environments. 

In 1977, a survey of low molecular weight sulphur-containing compounds in Nature ,4 noted that these secondary metabolites had little more in common than the possession of one or more sulfur atoms. The reader was left with a kaleidoscopic impression of almost 80 chemical structures. A comprehensive review today would require many hundreds of sulfur-containing chemical structures. 

This is a selective detector for phosphorus and sulphur-containing compounds which makes use of the... 

CH2F CH2 N-ftjX, chlorofluoroethane sulphur-containing compounds, e.g. CH2F CH2 Si2 esters of 1-alkylated fluoroacetic acids, CH-ft F C02iZ and CiZ iZ F C02B acetyl and chloroacetyl fluoride. 

In order to characterise the components further, mass spectral analysis was carried out. When head space volatiles from undigested cow slurry were analysed on a non-polar column the results (Figure 5) demonstrated the presence of several sulphur containing compounds—methanethiol, carbon disulphide, dimethyl sulphide, 2-propanethiol,... 

Table V summarises the data of the sulphur analysis of the hydrocracked liquids and the various bpt fractions for CoMo and NiMo catalysed experiments. The sulphur contents of neither the total hydrocracked liquids nor the individual bpt fractions showed any dependence on repeat contact or catalyst type. The values did show that the sulphur concentrated in the recycle solvent fraction (275-450°C), suggesting that, even under the relatively strong conditions used, certain sulphur-containing compounds will survive to be recycled in the solvent However, the sulphur content of the coal liquid feed was reduced by about 50% and the sulphur content of the likely upgradable product was low.

The Hydrogen Bond in Sulphur-Containing Compounds I. V. Zuika and Yu. A. Bankovskii, Russ. Chem. Rev. Engl. Transl.), 1973, 42, 22-36. 

C—S bonds, a process which is exploited in the desulphurisation of organic sulphur-containing compounds. 

Vulcanization by the traditional curing methods utilized in the rubber industry is based on sulfur or sulphur-containing compounds and is also the most widely applied technique for curing liquid rubbers containing macromolecules with double bonds. Chinons, peroxides, phenol formaldehyde resins, and other compounds are often used for curing liquid rubbers as an alternative sulfur vulcanization. 

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