Carbon Sulfur Ring Structure

The sulfides are chemically neutral they can have a linear or ring structure. For molecules of equal carbon number, their boiling points are higher than those of mercaptans they constitute the majority of sulfur containing hydrocarbons in the middie distillates (kerosene and gas oil). 

The n-d-M correlation is an ASTM (D-3238) method that uses refractive index (n), density (d), average molecular weight (MW), and sulfur (S) to estimate the percentage of total carbon distribution in the aromatic ring structure (% C ), naphthenic ring structure (Cj,), and paraffin chains (% Cp). Both refractive index and density are either measured or estimated at 20°C (68°F). Appendix 4 shows formulas used to calculate carbon distribution. Note that the n-d-M method calculates, for example, the percent of carbon in the aromatic ring... 

Two strains were isolated and purified, Pseudomonas sp. CDT-4, and Nocardia aster-oides, CDT-4b (ATCC 202160 and 202161, respectively). The microbes were passed through a multiple screen, first to allow growth on dibenzothiophene (DBT) as a sole source of sulfur, and then on fossil fuels, to identify organisms capable of desulfurization without metabolizing the DBT phenyl ring structures. N. asteroides sp. CDT-4b was found to metabolize DBT. The Pseudomonas species was found to utilize trace levels of sulfate from media and was found to be incapable of growth on DBT as a sole source of sulfur. However, the co-culture could remove more than 20% sulfur, with supplementation of a second sulfur-free carbon source. 

The presence of high-molecular weight p-sulfur with chain structure seemed improbable since the sulfur was not extractable with boiling toluene. The p-sulfur is known to convert to the soluble ring structure (Sg) rather rapidly at 115°. Wibaut (119) thought the formation of a carbon-sulfur complex similar to the surface oxide formed with oxygen very likely. He was not able, however, to analyze definite surface groups. Hofmann and Nobbe (123) established that the sulfur content was dependent on the specific surface area. Enoksson and Wetterholm (124) confirmed by X-ray diffraction that no crystalline sulfur was present in exhaustively extracted charcoal with 13% sulfur content. 

Heterocyclic. A closed-ring structure in which one or more of the atoms making up the ring (that usually has a five or six members) is something other than carbon such as nitrogen, oxygen, or sulfur. 

Thus by analogy it is anticipated that the molecular dimensions for thiepin (44) will be almost identical to those of thiepin 1,1-dioxide (45). Bond localization in the thiepin ring is evident from the X-ray structural data where both carbon-carbon single and double bonds and carbon-sulfur single bonds showed little change from normal values. 

We did not mention polar hydrocarbons in the crash course on organic nomenclature (Box 10.1). This term refers to compounds containing one or more nitrogen, oxygen, or sulfur atoms replacing carbon atoms in ring structures or sometimes attached to them. These... 

Upon soHdification of molten sulfur, S7T rapidly changes into S t, which is converted into SX, although at a much slower rate. The molecular structure of S7T is that of an octatomic sulfur chain (1,2). The symbol S t designates long, polymerized chains of elemental sulfur. SL is perhaps the most characteristic molecular form of sulfur, namely, that of a crown-shaped, octatomic sulfur ring designated in more recent literature as (3). The allotropes have different solubility in carbon disulfide. S7T and SX are soluble in carbon disulfide, whereas S X does not dissolve in this solvent. 

It can be seen in Fig. 3 that the saturate fraction consists primarily of linear paraffins having between 12 and 25 carbons. The monoaromatic fraction is much more complicated as is the diaromatic fraction. Almost no sulfur species are found in the saturates or monoaromatic fractions. Thus, the sulfur species that must be removed from these fuels are found in multiring aromatic structures. The sulfur-free aromatic fraction was shown to be composed primarily of five classes of alkyl-substituted aromatic ring structures. These are illustrated in Fig. 4, and the individual components are enumerated in Table II. 

Petroleums also contain compounds in which sulfur, oxygen, and/or nitrogen atoms are combined with carbon and hydrogen. These elements usually are combined with the complex ring structures that make up the larger molecules of petroleums. These larger nonhydrocarbon compounds form a class of chemicals generally called resins and asphal-tanes. The quantity of these compounds in petroleum is often very small however, as much as 50% of the total molecules in some heavy crude oils are resins and asphaltines. 

Sulfur can also be present in complex ring structures found in crude oils. The sulfur atoms can either be part of the ring or be attached to the ring. These molecules are usually very large, containing 30 or more carbon atoms. However, some simple examples will illustrate the types of sulfur compounds found in crude oils. 

Kreulen reported that Rasa coal was a humic coal and contained no sapropelites, waxes, or resins (4). He noted that Rasa coal exhibits dual character, i.e., it exhibits both low- and high-rank characteristics. Chemical tests indicated that a small amount of the sulfur present is in side chains, and a large amount occurs in ring structures. Using a statistical structural analysis method based on density, van Krevelen computed that 59% of the carbon in Rasa coal is aromatic (4). 

Recently, series of carbon-sulfur [n]helicenes substituted with w-octyl groups at the a-positions of the terminal thiophene rings were prepared (Fig. 15.16) [64, 87]. The helical structures of [7]helicene 44 and [ll]helicene 45 were confirmed by X-ray crystallography. Multiple short S-S contacts were found, especially for racemic [ll]helicene 45. Asymmetric synthesis of [ll]helicene 45 provided enantiomeric excess of either the (-)- or the (+)-enantiomer for the monoannelation or, unprecedented, triannelation approach (Fig. 15.16). Also, selective diannelation of octathiophene 47, followed by monoannelation of decathiophene 46, provided an efficient synthetic route to (-)-[ll]helicene 45, avoiding protection/deprotection steps [64],... 

As expected from the electronic structure, the 1,2,5-thiadiazoles readily undergo nucleophilic attack (see also Section 4.02.1.6). The site of attack, however, is variable and can take place either at carbon, sulfur or a ring proton (Scheme 1 also see Section 4.26.3.3.6). 

A phenothiazine has a three-ring structure, in which a sulfur atom and a nitrogen atom link two benzene rings. If a carbon atom replaces the nitrogen atom at position 10 with a double bond to the side chain, the compound becomes a thioxanthene. Phenothiazines are classified into three groups. 

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