Sulfur compounds thiols

Orthoesters, RC(OR )2 (1), thioesters, RCSOR ( A) Sulfur compounds Thiols), and carbamates, H2NCOOR, are not covered in this review. 

Food, flavors consist of numerous compounds, none of which alone is characteristic of specific food. Classes of compounds which emcompass food flavors are - hydrocarbons (aliphatic, ali-cyclic, aromatic) carbonyls (aldehydes, ketones) carboxylic acids, esters, imides, anhydrides alcohols, phenols, ethers alkylamines, alkylimines aliphatic sulfur compounds (thiols, mono-, di- and tri-sulfides) nitrogen heterocyclics (pyrroles, pyrazines, pyridines) sulfur heterocylics (thiophenes, thiazoles, trithiolane, thialidine) and oxygen-heterocyclics (lactone, pyrone, furan). Discussion will be limited to striking developments in heterocyclics. 

The azeotrope formation between sulfur compounds, thiols, alkane disulfides, and thiophenes, and petroleum hydrocarbons have been extensively studied by the Anglo-Iranian Oil Co. the results have been published in several papers (87, 88). Research workers of this company have also secured data on vapor-temperature relationships of sulfur compounds (110). 

The majorify of sulfur compounds (thioles and sulfides) have been successfully removed from liquid fuel using a hydrodesulfurization process where high temperature and high pressure are required [7-9, 159]. As mentioned in section 2.5 some sulfur species are very resistant to hydrodesulfurization and those include thiophenic compounds, especially dibenzothiophene and 4,6 dimethyldibenzothiophene [148]. Various methods based on extraction and adsorption have been proposed to remove these compounds [7, 8, 13,145, 147-149, 151-158]. In the extraction route, sulfiir species are first oxidized and then extracted using organic solvents as, for instance acetonitrille [13, 149]. On the other hand, an adsorption process is usually tailored to enhance either adsorption forces, selectivity, or to impose a chemical reaction. So fer the enhancement in the removal of thiophenic compounds was reported on materials where n-complexation can occur as on Cu-Y zeolites [151, 153], or on alumina with highly dispersed sodium [147]. In the latter case, mono- and disodium thiophene metallates are formed. Another desulfurization methods use formation and subsequent precipitation of S-alkylsulfonium salts [148]. 

I H2S reacts in another way with the olefinic hydrocarbons producing thiols and sulfur compounds (Equation 8.3 and 8.4) ... 

Of the general formula, R - S — H, where R represents an aliphatic or cyclic radical, the thiols —also known as mercaptans— are acidic in behavior owing to their S—H functional group they are corrosive and malodorous. Their concentration in crude oils is very low if not zero, but they are created from other sulfur compounds during refining operations and show up in the light cuts, as illustrated in Table 8.6. 

Interpreting the mass spectra of sulfur compounds is aided by the observation of an M+2 peak because of the presence of the mass 34 isotope of sulfur The major cleav age pathway of thiols is analogous to that of alcohols... 

A problem associated with the use of abrasive metal poHshes is that the fresh metal, which has been exposed by the cleaning, rapidly oxidizes or tarnishes. Thus, many modem poHshes contain inhibitors. Sulfur compounds, eg, alkyl benzyl thiols, commonly are used, as are mercapto esters such as lauryl thioglycolate [3746-39-2] and dialkyldisulfides (52—54). 

The chemistry of organic sulfur compounds is very rich and organosulfur compounds are incorporated into many molecules. Thiols, or mercaptans as they were originally called, are essential as feedstocks in the manufacture of many types of mbber (qv) and plastics (qv). They are utilized as intermediates in agricultural chemicals, pharmaceuticals (qv), ia flavors and fragrances, and as animal feed supplements. Many reviews have been undertaken on the chemistry of the thiols, regarding both their preparation and their reactions (1 7). 

Another area in which sulfur compounds have long found use is in the area of agricultural chemicals. Many of these materials had been produced by the manufacturer of the agricultural chemicals, but difficulties in containing odor and the use of hydrogen sulfide in heavily populated areas again pushed toward specialization by several companies. A Hst of agricultural chemicals, and the thiol that is used or has been used in production, follows ... 

The System described in the previous section has been extended with a sulfur chemiluminescence detector (SCO) for the detection of Sulfur compounds (32). The separated fractions were thiols + sulfides + thiophenes (as one group), benzothio-phenes, dibenzothiophenes and benzonaphtho-thiophenes. These four groups have been subsequently injected on-line into and separated by the GC unit. Again, no overlap between these groups has been detected, as can be seen from Figure 14.20, in which the total sulfur compounds are shown and from Figure 14.21 in which the separated dibenzothiophenes fraction is presented. The lower limit of detection of this method proved to be 1 ppm (mg kg ) sulfur per compound. 

Sulfur in crude oils is mainly present in the form of organosulfur compounds. Hydrogen sulfide is the only important inorganic sulfur compound found in crude oil. Its presence, however, is harmful because of its corrosive nature. Organosulfur compounds may generally be classified as acidic and non-acidic. Acidic sulfur compounds are the thiols (mercap-tans). Thiophene, sulfides, and disulfides are examples of non-acidic sulfur compounds found in crude fractions. Extensive research has been carried out to identify some sulfur compounds in a narrow light petroleum fraction.Examples of some sulfur compounds from the two types are ... 

Lithium aluminum hydride reduces most sulfur compounds with cleavage of the C—S bond, including thiols. " Thioesters can be reduced with Ni2B (from NiBr2/... 

Because of their inherent penetrating smell, certain organic sulfur compounds are used for odorization. Repellents from the skunk contain compounds such as trans-2-butene-l-thiol and 3-methyl-1-butanethiol. Ethylmercaptan, because of its extremely low odor threshold, is the favorite compound used as an odorant in natural gas and liquid propane for leak detection. Tetrahydro-thiophene is also often used. Common odorization reagents are summarized in Table 15-1 and Figures 15-1 to 15-3. 

Contact of the sohd oxidant with organic thiols or sulfides may cause a violent reaction and flash fire [1]. This procedure was recommended formerly for treating spills of sulfur compounds [2,3], but is now withdrawn as potentially hazardous. Use of an aqueous solution of up to 15% concentration, or of 5% sodium hypochlorite solution is recommended [1]. Addition of 10 g of oxidant to 5 ml portions of... 

Certain reduced sulfur compounds such as thiols, sulfides, disulfides, and trisulfides, specifically those having the functionality... 

The chemiluminescent reaction with chlorine dioxide provides a highly sensitive and highly selective method for only two sulfur compounds, hydrogen sulfide and methane thiol [81]. As in the flame photometric detector (FPD), discussed below, atomic sulfur emission, S2(B3S -> ) is monitored in the wave-... 

It is more than likely that when sulfur occurs in a crude oil or in coal (other than the pyrites), it is organically bound in one of the three forms listed in Table 8.3—the thiols, sulfides, or disulfides. The combustion of these compounds is very much different from that of other sulfur compounds in that... 

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