Sulfur naturally occurring compounds

Chemical Synthesis. If cholesterol is heated with elemental sulfur at 150°C for several days, a mixture of PCAH results (J2), the detailed composition of which is not known. Other dehydrogenation reagents, such as selenium, catalyze the production of alkyl naphthalenes and phenanthrenes from naturally occurring terpenes (J3). Thus, in principle, it is possible that the PCAH in an anoxic sediment could result from the chemical dehydrogenation of various naturally occurring compounds. These reactions may take place slowly over the years and may be catalyzed by trace elements, elemental sulfur, and clay minerals. 

Sulfur is plentiful in naturally occurring compounds. Inorganic sulfates can be reduced via the sulfide and incorporated into amino acids. Hydrogen sulfide is used as a source of sulfur by some microorganisms. Organic sulfur may represent an alternative sulfur-containing nutrient. 

Thiatriazines arc not naturally occurring compounds. The nomenclature of 1,2,4,6-thia-triazines is based on the IUPAC rules and Chemical Abstracts.1 2 The valence state of the sulfur atom is assigned with the Greek letter lambda (/.). In this section, the chemistry of the ring system of 124,2,4,6-thiatriazines with three-coordinated sulfur and of the l/4,2,4,6-thiatriazine 1-oxides or 1-imides with four-coordinated sulfur with maximum unsaturation is described. A review of the literature until 1990 is available3 and also a more recent review.82... 

Sulfur is one of the more common constituents of the earth s crust and can be ranked as the 16th or 17th most abundant element [68]. The mean sulfur content-of the rocks forming the crust of the earth is estimated to be about 400 ppmw. Sulfur naturally occurs as elemental sulfur, metal sulfides in coal and mineral ores, sulfates, hydrogen sulfide in natural gas, and complex organic sulfur compounds in crude oil and coal. All of these various forms of sulfur are used as sulfur sources, but the most important sources are elemental sulfur, hydrogen sulfide in natural gas, and iron pyrites. 

A variety of compounds have been reported to be important in meat flavors (25. 33). The most prominent naturally occurring compounds are amino acids, nucleotides and other phosphate compounds, and inorganic salts. Of lesser importance are various sugars and organic acids. Especially prominent are nitrogen-sulfur compounds such as cysteine and thiamin. Various other compounds that have been reported to be of importance in meat flavor include the peptides anserine, carnosine and glutathione. 

Sulfoxides are compounds that contain a sulfinyl group covalendy bonded at the sulfur atom to two carbon atoms. They have the general formula RS(0)R, ArS(0)Ar, and ArS(0)R, where Ar and Ar = aryl. Sulfoxides represent an intermediate oxidation level between sulfides and sulfones. The naturally occurring sulfoxides often are accompanied by the corresponding sulfides or sulfones. The only commercially important sulfoxide is the simplest member, dimethyl sulfoxide [67-68-5] (DMSO) or sulfinylbismethane. 

J. W. Eitzgerald, "Naturally Occurring Organosulfur Compounds in Soil," inJ. O. Ntiagu, ed.. Sulfur in the Environment, Part II Ecological Impacts, Wiley-lnterscience, New York, 1978, pp. 391—443. 

Sulfoxides (R1—SO—R2), which are tricoordinate sulfur compounds, are chiral when R1 and R2 are different, and a-sulfmyl carbanions derived from optically active sulfoxides are known to retain the chirality. Therefore, these chiral carbanions usually give products which are rich in one diastereomer upon treatment with some prochiral reagents. Thus, optically active sulfoxides have been used as versatile reagents for asymmetric syntheses of many naturally occurring products116, since optically active a-sulfinyl carbanions can cause asymmetric induction in the C—C bond formation due to their close vicinity. In the following four subsections various reactions of a-sulfinyl carbanions are described (A) alkylation and acylation, (B) addition to unsaturated bonds such as C=0, C=N or C= N, (C) nucleophilic addition to a, /5-unsaturated sulfoxides, and (D) reactions of allylic sulfoxides. 

Table 13-1 Some naturally occurring sulfur compounds... 

We have only recently understood the phenomena that control rainwater pH in the natural, unpolluted environment. As pointed out in Section 16.2, these appear to be mainly the cycles of sulfur and nitrogen compounds. A model of the unperturbed system is necessary in order to understand and predict the changes that occur when strong sulfur- and nitrogen-acids are... 

There are several naturally occurring variations on the lactam-thiazolidine or lactam-dihydrothiazine structures, leading to other useful antibiotics or to inhibitors of the (5-lactamases, enzymes that hydrolyze the (5-lactam unit. One group, termed carbapenems 5 has a five-membered ring in which the thiazolidine sulfur is replaced with CH2- Such compounds may still contain sulfur in a thioethylamine side chain (derived from L-cysteine) as in thienamycin 6, originally isolated from Streptomyces cattleya (Scheme 2). 

Naturally occurring alliin, the major precursor to the garlic aroma, is (RcSs)-( I )-,S -allyl-[.-cysteine sulfoxide 26 (Scheme 10) with both a chiral carbon and chiral sulfur - probably the first such compound (note that sulforaphene - see earlier - was isolated more or less simultaneously with alliin). Hence there are four possible stereoisomers. The alliin level in garlic is significant 5-14 mg g 1 fresh weight. 

This chapter covers only the chiral compounds that are cited in the literature by virtue of their optical activity. To keep the chapter to an acceptable length, a discussion of the stereochemical properties of sulfenamides showing axial chirality is omitted (17). Similarly, to limit the scope of the review, the chemistry of penicillin, cephalosporin sulfoxides and related compounds (14,18,19), steroidal sulfoxides (15,16), and other naturally occurring chiral sulfur compounds (4) is not discussed. For the same reason, only selected results are discussed and in some cases only references are given to recent papers and review articles on special topics. 

Put simply, petroleum is a naturally occurring mixture of hydrocarbons, generally in a liquid state, which may include compounds of sulfur, nitrogen, oxygen, metals, and other elements (ASTM, 2004). In more specific terms, petroleum has also been defined (ITAA, 1936) as ... 

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