Sulfur dehydrogenation with

An elegant synthesis of 1,3,7,9-tetramethyldibenzothiophene has been recorded as shown in Eq. (2). Cyclization of the diene (34) to the octahydrodibenzothiophene was accomplished with either aluminum chloride or a mixture of acetic acid and sulfuric acid (90%). Subsequent dehydrogenation with palladium on carbon gave the tetramethyl compound. The NMR spectrum of this compound has been discussed earlier... 

Dibenzofuranols are available by Michael addition of l-morpholino-1-cyclohexenes (198) to 1,4-benzoquinones (197, Scheme 50). Treatment of the intermediate adducts 199 with acid affords 6,7,8,9-tetrahydro-2-dibenzofuranols (200), which on dehydrogenation with sulfur or palladized charcoal afford the dibenzofuranols 201 in good yield. 

A2-Pyrazolines are converted into pyrazoles by oxidation with bromine or Pb(OAc)4 and they can also be dehydrogenated with sulfur. 3,5-Diphenylpyrazoline (419) on heating with platinum disproportionates to the pyrazole (420) and the pyrazolidine (421) (66AHC(6)347). 

Peter H. Given Whereas Tschamler and Fuks, and Peover studied more or less pure vitrinites, Mazumdar apparently worked with whole coals. Moreover, Indian coals, being from Gondwanaland strata, are most probably of very different petrographic composition compared with European and North American coals (rich in exinites and inert macerals See p. 284). Quite apart from the question whether sulfur dehydrogenation really is free of side reactions, there may well be a spread of data at any level or rank because of petrographic differences. 

In another set of experiments the effect of prior dehydrogenation on the yields of gases (especially that of methane) was studied. As shown earlier, dehydrogenation with either sulfur (17, 18) or iodine (22) leads to the complete inhibition of tar formation and fixation of the corresponding carbon (alicyclic) in char. It is thus possible to study the contribution, if any, of the hydroaromatic structure towards gas formation by partial or complete fixation of the hydroaromatic carbon in char. 

The reaction of phenols with alicyclic 1,3-dicarbonyl compounds in phosphorus oxychloride or sulfuric acid also leads to 3,4-fused coumarins (40JA2405). Dehydrogenation to the dibenzopyranone occurs on heating with sulfur or with palladium-charcoal (73CB62). 

Dihydrobenzo[6]thiophene 426 and its 2-methyl derivative182 are readily dehydrogenated with sulfur to the corresponding benzo[ ]-thiophene. 2,3-Dihydrobenzo[6]thiophenes are oxidized by peracetic acid to the corresponding sulfones (Section VI, P, 2), and give crystalline complexes with mercuric chloride. 

C-Dihydrotoxiferine I chloride, C-tolKsN +Cl, [a]D —600° (1 1 aqueous alcohol), has two N-methyl groups attached at the quaternary Nb nitrogen atoms (39). Molecular distillation of the alkaloid chloride gives nordihydrotoxiferine with loss of methyl chloride this ditertiary base can be converted back into the bisquatemary alkaloid, as the diiodide, by methylation with methyl iodide (39). Dehydrogenation of C-dihydrotoxiferine I with sulfur or with zinc dust gives isoquinoline... 

When diethylamine reacts with acetonitrile and sulfur in the presence of zinc powder, 2-methylimidazoline is formed126 and may be dehydrogenated with nickel to 2-methylimidazole. Using the same method, 2-ethyl-, 2,4-dimethyl-, and 2-ethyl-4-methylimidazoles have been synthesized in yields of about 10%.126... 

Problem 30.5 Cadinene C15H24, is found in oil of cubebs. Dehydrogenation with sulfur converts cadinene into cadaiene, CisHig, which can be synthesized from carvone by the following sequence ... 

Cocker et al found the tetralin derivative (1) to be dehydrogenated normally by sulfur at 230-240° but to lose the n-buty1 group to give (3) on reaction with selenium at 330-350°. Dehydrogenation with palladium charcoal at 260-280° gave a mixture of (2) and (3). 

Pimaric acid (6) and isopimaric acid (7) differ in carbon skeleton from abietic acid, and the amounts initially present in rosin are lost in the process described for the preparation of dehydroabietic acid. In the step of dehydrogenation with palladium the two acids act as hydrogen acceptors and are converted into a mixture of dihydro-pimaric and dihydroisopimaric acids. Note that pimaric acid and isopimaric acid have been shown to be rearranged to abietic acid by concentrated sulfuric acid. 

There are three reported processes in which another heteroatom (O, Rh, or Ir) in a five-membered ring is replaced by sulfur. Along with dehydrogenation of 139 by means of sulfur was the formation of140(25%, m.p. 112°C)... 

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