Sulfur-containing aromatic heterocycles

Figure 1.41 A selection of five-membered oxygen and sulfur-containing aromatic heterocycles.

Laboratory studies with petroleum and petroleum fractions. The first report of microbial oxidation of sulfur heterocycles was published by Walker et al. (28). Using computerized mass spectrometry (MS) to analyze the residual oil extracted from aerobically-grown mixed cultures, they observed losses of 40% of the dibenzothiophenes and 50% of the naphthobenzothiophenes. They concluded that the sulfur-containing aromatics were approximately twice as resistant to microbial degradation as their hydrocarbon analogues. 

Thiophene, a sulfur-containing heterocycle, undergoes typical aromatic substitution reactions rather than addition reactions. Why is thiophene aromatic ... 

A viscosity reducing method based on the selective cleavage of carbon sulfur bonds of aromatic heterocyclic molecules containing a sulfur heteroatom. The physicochemical properties of these heterocycles contribute to the liquid viscosity. The method comprises contacting the liquid with an effective amount of a biocatalytic agent. 

In any event, 02SbFg and 02AsFg act as very effective one-electron oxidants with regard to aromatic amines, nitrogen- and sulfur-containing heterocyclic compounds (Dinnocenzo and Banach 1986, 1988,1989) as well as to perfluorobenzene, benzotrifiuoride, and perfluoronaphthalene (Richardson et al. 1986). The oxidation proceeds in Freon (CHCIF2) at temperatures from -115 to -145°C, and the formation of the organic cation-radicals has been firmly established. 

A mammal may emit many volatile compounds. Humans, for instance, give off hundreds of volatiles, many of them chemically identified (Ellin etal., 1974). The volatiles include many classes of compound such as acids (gerbil), ketones, lactones, sulfides (golden hamster), phenolics (beaver, elephant), acetates (mouse), terpenes (elephant), butyrate esters (tamarins), among others. The human samples mentioned before contained hydrocarbons, unsaturated hydrocarbons, alcohols, acids, ketones, aldehydes, esters, nitriles, aromatics, heterocyclics, sulfur compounds, ethers, and halogenated hydrocarbons. Sulfur compounds are found in carnivores, such as foxes, coyotes, or mustelids. The major volatile compound in urine of female coyotes, Canis latrans, is methyl 3-methylhut-3-enyl sulfide, which accounts for at least 50% of all urinary volatiles (Schultz etal, 1988). 

Mercaptoacids were successfully applied in the MRCs with aminozoles on the way to the novel sulfur containing seven-membered heterocycles [145-147], Thus, condensation of 5-aminopyrazoles with mercaptoacetoacid and aromatic ketones or aldehydes resulted in the formation of pyrazolothiazepines 107 (Scheme 50). 

Photodimerizations have been observed in a variety of sulfur-containing heterocycles notable examples include the photodimerization of 2- and 3-ary lbenzo[b]thiophens,287 benzo[h]thiophen 1-oxide,288 benzo[h]thiophen 1,1-dioxide,289 and its 2-bromo289 and 2-methyl derivatives.290 All four possible dimers were obtained on irradiation of thio-chromone in aromatic solvents,291 and 1-thiauracil (345) is converted into... 

Catalytic hydrodesulfurization (HDS) is a very important industrial process that involves removal of sulfur from crude oils by high-temperature ( 400°C) treatment with hydrogen over Co- or Ni-promoted Mo or W catalysts supported on alumina. In an attempt to determine the mechanism of this process, many transition metal complexes of thiophene, a sulfur-containing heterocycle that is particularly difficult to desulfurize, have been prepared and their reactivities studied in order to compare their behavior with those of the free thiophenes that give H2S and C4 hydrocarbons under HDS conditions (88ACR387). Thiophene can conceivably bind to the catalyst surface by either cr-donation via a sulfur electron pair or through a variety of -coordination modes involving the aromatic system... 

Keywords aromaticity, indane, indene, nitrogen-containing heterocycles, oxygen-containing heterocycles, sulfur-containing heterocycles, thermochemistry... 

The resonance energy per electron for the sulfur-containing heterocycles (13)-(15) (X = Y = S) have been determined. The values are —0.005/1, —0.008/1, and — 0.012/S, respectively. These values, when compared with thiophene (0.032/1), indicate these isomers (13)-(15) are not aromatic (73JA3907). 

---