Sulphur compounds, disulphides

Sulphur compounds, (a) Disulphides can be purified by extracting acidic and basic impurities with aqueous base or acid, respectively. However, they are somewhat sensitive to strong alkali which slowly cleaves the disulphide bond. The lower-melting members can be fractionally distilled under vacuum. The high members can be recrystallised from alcohol, toluene or glacial acetic acid. 

Handbook of Preparative Inorganic Chemistry, 2nd edn, Vol 1 (1963) and vol 2 (1965), Academic Press, NY. 

CRC - Handbook of Chemistry and Physics, 76th edn, CRC Press Inc., Boca Raton, Florida, 1995-1996. N.D.Cheronis and J.B.Entrikin, Identification of Organic Compounds, Interscience, NY, 1963. 

F Feigl and V. Auger, Spot Tests in Organic Analysis, 7th edn, Elsevier, Amsterdam, 1989. 

Fieser and L.Fieser, Reagents for Organic Synthesis, J.Wiley Sons, Inc., NY, vol 1 1967 to vol 

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Group 20 is a nice collection of wonderful sulphur compounds. Disulphides such as diallyl disulphide (Flavis 12.008, FEMA 2028) with onion- and garlic-like notes are followed by extremely powerful mercaptans like the grapefruit compound p-l-men-thene-thiol (Flavis 12.085, FEMA 3700). In addition, thiols with tropical sulphury notes complete the picture of interesting molecules. 

The following classes of sulphur compounds occur in Solubility Groups II, III and VII sulphonic acids and derivatives, ArSO,OR sulphinic acids and derivatives, ArSOOR mercaptans, RSH thiophenols, ArSH sulphides or thioethers, RSR disulphides, RSSR sulphoxides, RR S->0 ... 

In some cases chain transfer agents are added to reaction mixture or to control the Molecular weight of the polymers. Mercaptans are used for this purpose. The modifying action of sulphur compounds is much greater than most of the solvents. The modifying action of diisopropylxanthate disulphide in the synthesis of SBR (styrene butadiene rubber) can be shown as under ... 

In a method described by Bates and Carpenter [8] for the characterization of organosulphur compounds in the lipophilic extracts of marine sediments these workers showed that the main interference is elemental sulphur (S8). Techniques for its elimination are discussed. Saponification of the initial extract is shown to create organosulphur compounds. Activated copper removes S8 from an extract and appears neither to create nor to alter organosulphur compounds. However, mercaptans and most disulphides are removed by the copper column. The extraction efficiency of several other classes of sulphur compounds is 80-90%. Extracts are analyzed with a glass capillary gas chromatograph equipped with a flame photometric detector. Detection limit is lg S and precision 10%. 

Tris trifluoromethyl phosphine bums in air, but, unlike its methyl analogue, has not so far been found to form addition compounds with sulphur, carbon disulphide or silver iodide. With chlorine it forms the addition compound P(CF3)3Cl2 (b.p. 94°), and there is some indication that an addition compound of lower stability may be formed with bromine. With either of these halogens at higher temperatures, partial replacement of CF3 by halogen occurs and a similar reaction occurs with iodine, yielding some P(CF3)2l and P(CF3)l2. 

Since sulphur compounds are important in the off-flavour of UHT milk, attempts to improve its flavour have focused on reducing the concentration of these, e.g. by adding thiosulphonates, thiosulphates or cystine (which react with mercaptans) or sulphydryl oxidase, an indigenous milk enzyme (which oxidizes sulphydryls to disulphides Chapter 8). 

Many cheeses contain the same or similar compounds but at different concentrations and proportions chromatograms of some cheese varieties are shown in Figure 10.25. The principal classes of components present are aldehydes, ketones, acids, amines, lactones, esters, hydrocarbons and sulphur compounds the latter, e.g. H2S, methanethiol (CH3SH), dimethyl sulphide (H3C-S-CH3) and dimethyl disulphide (H3C-S-S-CH3), are considered to be particularly important in Cheddar cheese. The biogenesis of flavour compounds has been reviewed by Fox et al. (1993, 1996a) and Fox, Singh and McSweeney (1995). 

The neutral sulphur compounds include sulphides or thioethers, disulphides, sulphoxides and sulphones, sulphate and sulphonate esters, and isothiocyanates. Acidic sulphur compounds, i.e. sulphonic and sulphinic acids, thiols and thio-phenols, and the primary sulphonamides have already been discussed. The sulphates of amines are converted by aqueous sodium hydroxide into the free bases the sulphate anion can be detected in the resulting aqueous solution as barium sulphate in the usual manner. 

Polarography has been successfully applied to the investigation of structural problems involving sulphur compounds. The presence of a disulphide bond has been established by means of the polarographic reduction waves of cytochrome C (156) and lipoic acid (757), and in cyclic disulphides of the oxytocine and vasopressine type (158). The elucidation of the process responsible for the reduction wave of lipoic acid was carried out by comparison with reduction waves of cyclic disulphides, where the disulphide bond was incorporated into rings of various size. The similarity indicated that in lipoic acid an S—S bond which is a part of a larger cyclic system is reduced. 

Vitenberg et al. [623] have described a gas chromatographic method for the determination of traces (down to l-10pg kg ) of sulphur compounds, such as hydrogen sulphide, mercaptans, sulphides and disulphides, in industrial waste waters (kraft paper mill effluents) by a combination of headspace analysis and microcoulometiy. This method increases the analytical sensitivity 102-103 times without any preliminary concentration of the sample. 

Leek and Bagander [342] determined reduced sulphur compounds (hydrogen sulphide, methyl mercaptan, carbon disulphide and dimethyl sulphide) in seawater by gas chromatography using flame detection. Detection limits ranged from 0.2ng L 1 for carbon disulphide to 0.6ng L 1 for methyl mercaptan. Hydrogen sulphide was determined at the... 

In a modern refinery the different hydrocarbon streams contain a variety of sulphur compounds, including hydrogen sulphide, mercaptans, sulphides, disulphides, and thiophenes. The amount and the type of the sulphur compounds depends highly on the used crude oil type, but even the most sweet (low sulphur) crudes contain considerable amounts of sulphur. For different reasons the sulphur concentration of the product streams of the crude destination train must be reduced ... 

Direct syntheses of fluorocarbon-sulphur compounds from non-fluorinated starting materials are limited, but bis(trifluoromethyl) disulphide may be obtained from carbon... 

Similar tests were then carried out with a variety of metal sulphides on six different metal substrates, and the results are shown in Table 6.2. Again they showed that the lives were consistently better with molybdenum substrates, for all the sulphides tested. This strongly suggested that some chemical interaction was taking place, possibly between free sulphur or sulphur compounds and the molybdenum in the substrate. Where the original sulphide under test was itself molybdenum disulphide, this reaction would represent a re-supply mechanism. Where some other sulphide was under test, the reaction would again enable molybdenum disulphide to be formed which would supplement the life of the original sulphide. 

Considerable doubt and controversy exist about the mechanism of action of a number of other molybdenum compounds or mixtures in lubrication, and in particular about whether their action involves in situ formation of molybdenum disulphide. Braithwaite has stated that one of the reasons for the development of soluble molybdenum compounds was that it "was thought by some (erroneously) that Organo-molybdenum sulphur compounds would decompose to M0S2 which would then provide lubrication." Nevertheless Braithwaite goes on to refer to several other authors, such as Feng et al , Isoyama and Sakurai , and Yamamoto et al , all of whom maintain that they have shown the formation of molybdenum disulphide from organo-molybdenum sulphur compounds. Similar results have been reported by... 

Several publications have reported that composites of molybdenum disulphide with a high nickel content were not satisfactory , and nickel alloys are recognised to be susceptible to attack by sulphur or sulphur compounds at elevated temperatures. Al tman et al found that certain alloying elements, especially molybdenum, can stabilise the composite structures. However, the adverse reports of composites in nickel are not universal, and a few successful examples will be described later. 

The first group of sulphur compounds mentioned above can be defined as common fermentative sulphur volatiles (CFSV) and includes in our presentation ethylmercaptan (EtSH), dimethyl sulphide (DMS), diethyl sulphide (DES), dimethyl disulphide (DMDS), diethyl disulphide (DEDS), methyl thioacetate (MTA), ethyl thioacetate (ETA), 2-mercaptoethanol (ME), 2-(methylthio)-l-ethanol (MTE), 3-(methylthio)-l-propanol (MTP), 4-(methylthio)-l-butanol (MTB), benzothiazole (BT) and 5-(2-hydroxyethyl)-4-methylthiazole (HMT) (see Table 5.6). 

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