Sulfuration Reactions

Extensive research has been conducted on catalysts that promote the methane—sulfur reaction to carbon disulfide. Data are pubhshed for sihca gel (49), alurnina-based materials (50—59), magnesia (60,61), charcoal (62), various metal compounds (63,64), and metal salts, oxides, or sulfides (65—71). Eor a sihca gel catalyst the rate constant for temperatures of 500—700°C and various space velocities is (72)... 

Of the several syntheses available for the phenothiazine ring system, perhaps the simplest is the sulfuration reaction. This consists of treating the corresponding diphenylamine with a mixture of sulfur and iodine to afford directly the desired heterocycle. Since the proton on the nitrogen of the resultant molecule is but weakly acidic, strong bases are required to form the corresponding anion in order to carry out subsequent alkylation reactions. In practice such diverse bases as ethylmagnesium bromide, sodium amide, and sodium hydride have all been used. Alkylation with (chloroethyl)diethylamine affords diethazine (1), a compound that exhibits both antihista-minic and antiParkinsonian activity. Substitution of w-(2-chloroethyl)pyrrolidine in this sequence leads to pyrathiazine (2), an antihistamine of moderate potency. 

Chlorpromazine (33) can probably be considered the prototype of the phenothiazine major tranquilizers. The antipsychotic potential of the phenothiazines was in fact discovered in the course of research with this agent. It is of note that, despite the great number of alternate analogs now available to clinicians, the original agent still finds considerable use. The first recorded preparation of this compound relies on the sulfuration reaction. Thus, heating 3-chlorodiphenylamine (30) with sulfur and iodine affords the desired phenothiazine (31) as well as a lesser amount of the isomeric product (32) produced by reaction at the 2 position. The predominance of reaction at 6 is perhaps due to the sterically hindered nature of the 2 position. Alkylation with w-C3-chloropropyl)dimethylamine by means of sodium amide affords chlorpromazine (33). ... 

The various boiler sulfur reactions are shown here ... 

We suggest that the ejected thiyl radical undergoes a fast 1,2-migration of silyl group from silicon to sulfur (Reaction 85), affording a new silyl radical that either reacts with (TMSlsSiH (Reaction 86) which completes the reaction cycle, or replaces the (TMSlsSi radical in the above described reaction sequence. 

Purple photosynthetic bacteria using the sulfide to sulfur reaction... 

The P2N4S2 ring in 111 is readily susceptible to nucleophilic attack at sulfur. Reactions with organolithium reagents give monolithium derivatives... 

Sulfonium, cyclopropyldiphenyl tetrafluoroborate, 54, 28 Sulfonium salts, acetylenic, furans from, 53, 3 Sulfonium ylides, 54, 32 Sulfur, reaction with organo-lithium compounds, 50, 105 Sulfuryl chloride, with 1,1-cyclobutanedicarboxylic acid to give 3-chloro-l,1-cyclobutanedicarboxylic acid, 51, 73... 

Reaction of a sulfinyl sulfone with a nucleophile in the manner shown in (139) is, of course, an example of a nucleophilic substitution at sulfinyl sulfur. Reactions of this general type occur frequently and are of great importance in the chemistry of most kinds of sulfinic acid derivatives. At this point it would seem desirable to discuss what is known about such key aspects of their mechansim as stereochemistry and the timing of the bond-making and bond-breaking processes necessary in such a substitution. In doing this we will call upon results obtained from the study of such reactions using a variety of different types of sulfinic acid derivatives. 

Carbon reacts also with other sulfur-containing compounds with resulting fixation of sulfur. Reaction of various forms of carbon with hydrogen sulfide was reported by Baraniecky, Riley, and Streeter (126) and by Polansky, Knapp, and Kinney (128). The reaction of carbon blacks with hydrogen sulfide and with sulfur was studied extensively by Studebaker (86). At 150°, the increase in sulfur content was proportional to the quinone content as measured by catalytic hydrogenation using Adams catalyst (see page 203). 

Synthetic FT diesel fuels can have excellent autoignition characteristics. The FT diesel is composed of only straight-chain hydrocarbons and has no aromatics or sulfur. Reaction parameters are temperature, pressure and H/CO ratio. FT product composition is strongly influenced by catalyst composition the yield of paraffins is higher with cobalt catalytic ran and the yield of olefins and oxygenates is higher with ironcatalytic ran. 

Zaback DA, Pratt LM (1992) Isotopic composition and speciation of sulfur in the Miocene Monterey Formation reevaluation of sulfur reactions during early diagenesis in marine environments. Geochim Cosmochim Acta 56 763-774... 

The black sulfide may also be made by other methods such as adding sodium thiosulfate, Na2S203 in excess to a dilute solution of sodium mercurichlo-ride, Na2HgCl4 and treating mercury with molten or powdered sulfur. Reactions... 

The ratio of oxidizer to fuel will also affect the amount of heat and gas that are produced. A stoichiometric mixture of KCIO 3 and sulfur (equation 8.1) contains a 2.55 1 ratio of oxidizer to fuel, by weight. Colored smoke mixtures in use today contain ratios very close to this stoichiometric amount. The chlorate /sulfur reaction is not strongly exothermic, and a stoichiometric mixture is needed to generate the heat necessary to volatilize the dye. 

In delineating the scope of the bromination-nucleophilic sulfur reaction, two difficulties have been encountered. Bromination with bromine is not successful with tertiary hydrogens such as those present in prolyl derivatives (72CB625). Bromination can be accomplished by means of N-bromosuccinimide in presence of 2,2 -azobisisobutyronitrile however, in this case, 3,6-dialkylpiperazine-2,5-diones yield tetrabromo derivatives. These could be successfully utilized for the required purpose, as shown in Scheme 37. The trick consisted of displacing the bromine atoms attached to the ring by methoxy groups, followed by debromination and thiolation (75BCJ605). 

An alternate and more controlled approach to the synthesis of phenothiazines involves sequential aromatic nucleophilic displacement reactions. This alternate scheme avoids the formation of the isomeric products that are sometimes observed to form from the sulfuration reaction when using substituted aryl rings. The first step in this sequence consists of the displacement of the activated chlorine in nitrobenzene (30-1) by the salt from orf/io-bromothiophenol (30-2) to give the thioether (30-3). The nitro group is then reduced to form aniline (30-4). Heating that compound in a solvent such as DMF leads to the internal displacement of bromine by amino nitrogen and the formation of the chlorophenothiazine (30-4). Alkylation of the anion from that intermediate with 3-chloro-l-dimethylaminopropane affords chlorpromazine (30-5) [31]. 

The preparation of a diarylamine required for the synthesis of a phenothiazine via the sulfuration reaction requires the use of an activated chlorobenzene. 

W. A. Pryor, Mechanisms of Sulfur Reactions, McGraw-Hill Book Co., Inc., New York, 1962. 

Derive the general Nemst equation for expressing the EH value of a hydrogen sulfide solution as a function of pH and H2S tol by assuming that H2S is oxidized to elemental sulfur [reaction 10 in Table 14.2], Calculate the EH for a 10-4 M H2Stot solution at pH 8 and 25°C. 

Fig. 29. Correlation between relative hydrogenolysis reactivity and the electron densities on sulfur. ( ) Reaction conditions 300°C, 71 atm, sulfided CoO-Mo03/A1203 (5). (1) DBT (2) benzo[fo]naphtho[2,3-4]thiophene (3) 7,8,9,10-tetrahydrobenzo[b]naphtho[2,3-rf]thio-phene (4) 5b,6,ll,lla-tetrahydrobenzo[fc]naphtho[2,3-d]thiophene. (O) Reaction conditions 450°C, 1 atm, sulfided CoO-Mo03/A1203(6). (5) Thiophene (6) tetrahydrothiophene (7) benzothiophene (8) 2,3-dihydrobenzothiophene. ( + ) Reaction conditions 360°C, 2.9 MPa, sulfided NiO-Mo03/Al203(3). (9) 1-Methyl-DBT (10) 2- or 3-methyl-DBT (11) 4-methyl-DBT (12) 4,6-dimethyl-DBT. (A) Reaction conditions 300°C, 102 atm, sulfided CoO-Mo03/ Al203(8). (13) 2,8-Dimethyl-DBT (14) 3,7-dimethyl-DBT (15) 4-methyl-DBT (16) 4,6-di-methyl-DBT. Reprinted with permission from Ref. 38, Ma et al. (1995). Copyright 1995 American Chemical Society.

It appears that the discrepancy in the results reported above is caused chiefly by the difference in the method of conducting the coal-sulfur reaction. If coal and sulfur are mixed intimately (in 2 1 proportion) and heated in a Gray-King assay retort from room temperature to 360°C. for one hour and maintained at this temperature for another hour (as was done by Mazumdar et al. (17, 18) in their initial studies on coal dehydrogenation), followed by... 

---