Thioxanthene oxide

Fig. 2.15. Structure of thioxanthene oxides (9, 9 a, 9b) separated by RLCC (269) enantiomers with (R, R )-5-nonyltartrate...

The thioxanthene ligand is oxidized to thioxanthone and sulfone ligands, the ratio of which depends on the amount of KMn04 Eq. (37) ... 

Ternay and coworkers examined the conformations of thioxanthene-10-oxide (186) and related compounds. They found that oxygen preferred the pseudoequatorial position, 186e, but that the amount of pseudoaxial conformer, 186a, increased when the oxygen was complexed with iodine monochloride or trifluoroacetic acid171. 

The ESR spectrum of the thioxanthene S, S-dioxide radical anion itself shows that the two possible conformers coexist, since the two methylene protons are not equivalent. In the case of the 9-monoalkyl derivatives, the large coupling constant observed for the 9-proton leads to the conclusion that the 9-substituent is in the boat equatorial position as in II1 F Thus the radical anions and the neutral molecule display different conformations. The protons in the 9-position of the radical anions of cis-9-methylthioxanthene S-oxides (2, n — 1, R1 = H, R2 = CH3) have an appreciable coupling constant10 which suggests that these radical anions have the substituent in the pseudo-axial position. Furthermore, in the radical anions the S—O bond is pseudo-axial. These situations are exactly the opposite of that observed for the neutral compound. 

The DszC enzyme was able to convert the following compounds other than DBT thioxanthen-9-one, 2,8-dimethyl DBT, 4,6-dimethyl DBT, and 3,4-benzo DBT. Non-organosulfur compounds such as biphenyl, carbazole, and dibenzofuran did not show any activity. This indicates that dszC specifically recognizes sulfur atom [151]. One study specifically examined the DszC enzyme for oxidation of aryl sulfides [179] and reported oxidation of many sulfides including, naphthyl methyl sulfide, phenyl methyl sulfide, and its alkyl derivatives. 

Kargi, F., Biological Oxidation of Thianthrene, Thioxanthene and Dibenzothiophene by the Thermophilic Organism Sulfolobus Acidocaldarius. Biotechnol. Letters, 1987. 9 pp. 478-482. 

In a search of jr-donor systems for the preparation of compounds having a metallic conductivity, the bis-thioxanthene cumulene 56 was obtained. It was oxidized by cone. H2SO4 to the acetylenic dication 57 rather than undergoing the expected protonation of the multiple bonds (equation 22)36. 

Thianthrene radical ion(l+) perchlorate was employed to effect one-electron oxidation of Cu(TPP) (TPP, tetraphenylporphyrinate) to [Cu (Tpp )]+[sbcy (82JA6791). It was also used to dehydrogenate thio-xanthene (44)(R = H), forming perchlorate 43 or, in the presence of an electron-rich aromatic, the 9-Ar-substituted-thioxanthene 44 (R = Ar) (80MI4 82MI4) or, in the presence of a phosphine, phosphonium salts 44 (R = P-"R (81MI7). 

Isolation of Oxidation Products. After oxygen absorption had ceased, or reached the desired value, the oxidates were poured into water. In many cases the reaction product could be removed by filtration in high yield. In this manner xanthone (m.p. 172-174°C.), was isolated from oxidations of xanthene or xanthen-9-ol thioxanthone (m.p. 208-210°C.), from thioxanthene acridine (m.p. 107-109°C.), from acridan anthracene (m.p. 216-217°C.), from 9,10-dihydroanthracene phenanthrene (m.p. 95-99°C.), from 9,10-dihydrophenanthrene pyrene (m.p. 151-152.5°C.) (recrystallized from benzene) from 1,2-dihydropyrene and 4-phenan-throic acid (m.p. 169-171 °C.) (recrystallized from ethanol) by chloroform extraction of the hydrolyzed and acidified oxidate of 4,5-methyl-enephenanthrene. 

Oxidation of sulfur to the oxide or dioxide is not generally useful in simple thiopyrans and though the annelated compounds do readily afford the sulfones under a variety of conditions, it is more common to build in the oxidized sulfur from the beginning. Regeneration of the sulfide from the sulfoxide in thioxanthenes has been demonstrated with dichlorocarbene under phase transfer conditions (80JOC5350). 

Other Organosulfur Compounds. There have been reports of the microbial metabolism of other OSC. However, few of these studies have given the identities of intermediates or organic endproducts of the OSC. For example, aerobic cultures have been reported to remove sulfur from phenyl sulfide (62). Thioxanthene and thianthrene were transformed to water-soluble products by a dibenzothiophene-oxidizing bacterium (48). In addition, thianthrene and thioxanthene served as sole carbon sources for the aerobic thermophile S. acidocaldarius (69) which released sulfate from these compounds. 

Changes are observed in the UV-visible absorption spectrum of 9-(4,5-dimethyl-l,3-dithiol-2-ylidene)thioxanthene during electrochemical oxidation. The absorption of the neutral molecule at 384 nm gradually decreases as oxidation to the dication occurs and new peaks appear at 325 and 408 nm (Equation 10). The oxidation potential for the single two-electron process as derived by cyclic voltametry is +0.23 V <2006CEJ3389>. 

Transient radicals and radical cations generated by the 7- and photo-irradiative oxidation of thioxanthene in the presence of an electron scavenger have been characterized spectroscopically and kinetically (Scheme 57) <1996JPC13539>. 

Both thioxanthene and thioxanthone give a ca. 1 1 mixture of sulfoxide and sulfone in high overall conversion in a Ti02-mediated photocatalytic oxidation (Scheme 62) <1998JPH(114)213>. Thioxanthone is oxidized to either its sulfoxide or sulfone in high yields and with excellent selectivity by stoichiometric quantities of perfluoro-rfr-2,3-dialkyloxaziridines 324 at —40 °C (Equation 57) <1994JOC2762>. 

Naphthoquinone and 2-acylbenzenethiols react by sequential conjugate addition, aldol reaction, and atmospheric oxidation to produce 1277-benzo[3]thioxanthene quinones 423. The exact conditions required depend on the nature of the thiol, but are quite mild (Equation 123) <2004BCJ2095>. 

Diaryl-3//-2,l-benzoxathiole 1-oxides react with hydrazine to give high yields of 9-aryl-9//-thioxanthene 10,10-dioxides. It is proposed that the role of the hydrazine is to initiate cleavage of the O-C bond which is followed by attack of S on the adjacent aromatic ring (Equation 124) <1998H(49)143>. 

An example of the application of chronopotentiometry is the oxidation of tropy-lidene [235,236] and thioxanthene [236]. 

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