Sulfur dehydrogenation

The figures of B. K. Mazumdar et al. shown in parentheses are the revised values computed by these authors after it had been pointed out that at temperatures above 200°C. the sulfur dehydrogenation method they used is capable of removing hydrogen from aromatic nuclei as well as alicyclic rings. The revised figure for a coal of 85% C was 0.16, not 0.23. 

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. 

Keywords aminal, sulfur, dehydrogenation, C-H activation, thiourea, carbenium thiocyanate... 

A Convenient method for obtaining pure 2-acylphenanthrene is the acylation of 9,10-dihydrophenanthrene followed by sulfur dehydrogenation. In this case, only the 2-position is attacked the over-all yield is about 48%. Anthracene is acylated in the 9-position (60%). The isomeric acetylacenaphthenes have been prepared from the hydrocarbon and acetic... 

The nuclear amino group is stable during the sulfur dehydrogenation of 2-amino-9,10-dihydrophenanthrene (cf. method 2). ° In another instance, it is protected by acetylation before dehydrogenation/ ... 

Dehydrogenation of the As-thiazoline in the presence of sulfur gives the thiazole (23-30, 853). 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

The composition of a reforming catalyst is dictated by the composition of the feedstock and the desired reformate. The catalysts used are principally platinum or platinum—rhenium on an alumina base. The purpose of platinum on the catalyst is to promote dehydrogenation and hydrogenation reactions. Nonplatinum catalysts are used in regenerative processes for feedstocks containing sulfur, although pretreatment (hydrodesulfurization) may permit platinum catalysts to be employed. 

Rhenium oxides have been studied as catalyst materials in oxidation reactions of sulfur dioxide to sulfur trioxide, sulfite to sulfate, and nitrite to nitrate. There has been no commercial development in this area. These compounds have also been used as catalysts for reductions, but appear not to have exceptional properties. Rhenium sulfide catalysts have been used for hydrogenations of organic compounds, including benzene and styrene, and for dehydrogenation of alcohols to give aldehydes (qv) and ketones (qv). The significant property of these catalyst systems is that they are not poisoned by sulfur compounds. 

Production of a-methylstyrene (AMS) from cumene by dehydrogenation was practiced commercially by Dow until 1977. It is now produced as a by-product in the production of phenol and acetone from cumene. Cumene is manufactured by alkylation of benzene with propylene. In the phenol—acetone process, cumene is oxidized in the Hquid phase thermally to cumene hydroperoxide. The hydroperoxide is spHt into phenol and acetone by a cleavage reaction catalyzed by sulfur dioxide. Up to 2% of the cumene is converted to a-methylstyrene. Phenol and acetone are large-volume chemicals and the supply of the by-product a-methylstyrene is weU in excess of its demand. Producers are forced to hydrogenate it back to cumene for recycle to the phenol—acetone plant. Estimated plant capacities of the U.S. producers of a-methylstyrene are Hsted in Table 13 (80). 

Most synthetic camphor (43) is produced from camphene (13) made from a-piuene. The conversion to isobomyl acetate followed by saponification produces isobomeol (42) ia good yield. Although chemical oxidations of isobomeol with sulfuric/nitric acid mixtures, chromic acid, and others have been developed, catalytic dehydrogenation methods are more suitable on an iadustrial scale. A copper chromite catalyst is usually used to dehydrogenate isobomeol to camphor (171). Dehydrogenation has also been performed over catalysts such as ziac, iadium, gallium, and thallium (172). 

Dehydrogenation of A -imidazolines (294 Z = NR) gives imidazoles, but requires quite high temperatures and a catalyst such as nickel or platinum. Alternatively, hydrogen acceptors such as sulfur or selenium can be used (70AHC(12)103). 

The synthesis of indazoles from their 4,5,6,7-tetrahydroderivatives (439) by means of sulfur or, better, by catalytic dehydrogenation over palladium on charcoal (67HC(22)l) can also be included here. 

Triphenylene has been prepared by self-condensation of cyclohexanone using sulfuric acid or polyphosphoric acid followed by dehydrogenation of the product, palladium-charcoal, or selenium by electrolytic oxidation of cycloliexanone from chlorobenzene and sodium or phenyllilhium from 2-cyclolu xyl-l-phenylcyelohexanol or... 

Before dehydrogenation of ethane became the dominant method, ethylene was prepared by heating ethyl alcohol with sulfuric acid. 

In a widely used industrial process, the mixture of ethylene and propene that is obtained by dehydrogenation of natural gas is passed into concentrated sulfuric acid. Water is added, and the solution is heated to hydrolyze the alkyl hydrogen sulfate. The product is almost exclusively a single alcohol. Is this alcohol ethanol, 1-propanol, or 2-propanol Why is this particular one formed almost exclusively ... 

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