Sulfur sources

The earliest reported reference describing the synthesis of phenylene sulfide stmctures is that of Friedel and Crafts in 1888 (6). The electrophilic reactions studied were based on reactions of benzene and various sulfur sources. These electrophilic substitution reactions were characterized by low yields (50—80%) of rather poorly characterized products by the standards of 1990s. Products contained many by-products, such as thianthrene. Results of self-condensation of thiophenol, catalyzed by aluminum chloride and sulfuric acid (7), were analogous to those of Friedel and Crafts. 

Equation 1 is an oversimplification of the actual process. The polymerizable sulfur source for the PPS polymerization consists of a dehydrated product of A/-meth5i-2-pyrrohdinone [872-50-4] (NMP) and aqueous sodium sulfide feedstocks. During the course of this dehydration, one equivalent of NMP is hydrolyzed to form sodium A/-methyl-4-aminobutanoate (SMAB) (eq. 3). 

The process implications of equation 3 go beyond the weU-known properties (27—29) of NMP to faciUtate S Ar processes. The function of the aminocarboxylate is also to help solubilize the sulfur source anhydrous sodium sulfide and anhydrous sodium hydrogen sulfide are virtually insoluble in NMP (26). It also provides a necessary proton acceptor to convert thiophenol intermediates into more nucleophilic thiophenoxides. A block diagram for the Phillips low molecular weight linear PPS process is shown in Eigure 1. 

Eig. 1. The key steps for the Phillips PPS process are (/) production of aqueous sodium sulfide from aqueous sodium hydrogen sulfide (or hydrogen sulfide) and aqueous sodium hydroxide 2) dehydration of the aqueous sodium sulfide and NMP feedstocks 5) polymerization of the dehydrated sulfur source with -dichlorobenzene to yield a slurry of PPS and by-product sodium chloride in the solvent (4) polymer recovery (5) polymer washing for the removal of by-product salt and residual solvent (6) polymer drying (7) optional curing, depending on the appHcation and (< ) packaging. 

Sulfur is produced from a variety of sources using many different techniques in many countries around the world. Worldwide changes have affected not only the sources of sulfur, but also the amounts consumed. Sulfur sources in the United States underwent significant changes during the 1980s. Voluntary sulfur from the Frasch process (mines) suppHed only 25% of the sulfur in the United States in 1995, compared to about 53% in 1980, whereas recovered or involuntary sulfur suppHed 63% of the sulfur in the United States in 1995, compared to 34% in 1980. About 12% is suppHed from other forms, primarily by metallurgy (21,33). 

Sulfuric acid is the most important sulfur-containing intermediate product. More than 85% of the sulfur consumed in the world is either converted to sulfuric acid or produced direcdy as such (see Sulfuric acid and sulfur trioxide). Worldwide, well over half of the sulfuric acid is used in the manufacture of phosphatic fertilizers and ammonium sulfate for fertilizers. The sulfur source may be voluntary elemental, such as from the Frasch process recovered elemental from natural gas or petroleum or sulfur dioxide from smelter operations. 

Table 9. U.S. Sulfuric Acid Production by Sulfur Source, t x 10 ...

Potential Processes. Sulfur vapor reacts with other hydrocarbon gases, such as acetjiene [74-86-2] (94) or ethylene [74-85-1] (95), to form carbon disulfide. Higher hydrocarbons can produce mercaptan, sulfide, and thiophene intermediates along with carbon disulfide, and the quantity of intermediates increases if insufficient sulfur is added (96). Light gas oil was reported to be successflil on a semiworks scale (97). In the reaction with hydrocarbons or carbon, pyrites can be the sulfur source. With methane and iron pyrite the reaction products are carbon disulfide, hydrogen sulfide, and iron or iron sulfide. Pyrite can be reduced with carbon monoxide to produce carbon disulfide. 

A variety of routes is available for the preparation of metal-thionitrosyl complexes. The most common of these are (a) reaction of nitride complexes with a sulfur source, e.g., elemental sulfur, propylene sulfide or sulfur halides, (b) reaction of (NSC1)3 with transition-metal complexes, and (c) reaction of [SN]" salts with transition-metal complexes. An example of each of these approaches is given in Eq. 7.1,... 

Metal-polysulfido complexes have been synthesized by a variety of methods using various reagents as sulfur sources, e.g., Ss, M2S (M=alkali metal), P2S5, H2S, organic polysulfanes, etc. The nature of the resulting polysulfido complexes often depends on the reaction conditions such as the ratio of starting materials, solvents, reaction temperature, and reaction time. In addition, the use of different ligands leads to the different results in most cases. This section shows typical synthetic methods for metal-polysulfido complexes based on recent reports on their syntheses. 

Reaction of Low-Valent Metal Compounds with Elemental Sulfur or Other Sulfur Sources... 

The cathodic approach has been investigated actively as a method for the production of thin film CdS, in particular for the fabrication of heterojunction cells. Photoactive CdS films could be grown in alkaline NH3/NH4Cl-buffered aqueous solutions containing thiosulfate as sulfur source and complexed Cd (EDTA+NH3), on Ti substrates [41]. The electroreduction of thiosulfate was considered to proceed as... 

Single-phase ZnS films of a fine grain size (no XRD shown) and a band gap of 3.7 eV were electrodeposited from aqueous alkaline (pH 8-10) solutions of zinc complexed with EDTA, and thiosulfate as a sulfur source [101]. The voltammet-ric data implied that deposition occurred either by S-induced UPD of Zn or by a pathway involving both Zn " and thiosulfate concurrently. 

Biedlingmeier JJ, A Schmidt (1983) Arylsulfonic acids and some 5-containing detergents as sulfur sources for growth of Chlorellafusca. Arch Microbiol 136 124-130. 

Cook AM, R Hiitter (1982) Ametryne and prometryne as sulfur sources for bacteria. Appl Environ Microbiol 43 781-786. 

The Cory neb acterium sp. that utilizes dibenzothiophene as a sulfur source produced... 

Bacteria selected for growth with bis-(3-pentflnorophenylpropy)-sulfide as sulfur source are able to use dimethyl sulfoxide, dibenzyl snlfide, and some long-chain disulfides as sources of sulfur (van Hamme et al. 2004). Degradation takes place by oxidation to the sulfone, scission of the C-S bond to an alkanol, and an alkyl sulfinate that is degraded with loss of the snlfnr, which is nsed for growth. 

Woodruff, L.G. and Shanks, W.C. Ill (1988) Sulfur isotope. study of chimney minerals and vent fluids from 21°N East Pacific Rise Hydrothermal sulfur sources and disequilibrium sulfate reduction. J. Geophys. Res., 93, 4562-4572,... 

The data reported identifies sulfur substrates tested for growth as sole sulfur source for the various strains. The strains may metabolize other sulfur compounds (not listed). A complete name of listed strains in Table 3 comprises Rhodococcus sp. SY1 Rhodococ-cus sp. H-2 Rhodococcus sp. D-l Rhodococcus ECRD-1 Gordona CYKS1 Nocar-dia sp. CYKS2 Paenibacillus All-2 Mycobacterium sp. WU-F1 Mycobacterium sp. WU-0103 Mycobacterium phlei sp. GTIS10 and Agrobacterium MC501. 

Chang and co-workers isolated strain Nocardia sp. CYKS2 from a dyeing industry wastewater using DBT as the sole sulfur source [27]. This strain also desulfurized DBT to the same product 2-HBP however, it had broader substrate specificity and was reported to desulfurize thiophenes, sulfides, and disulfides (Table 3) in addition to DBT. However, it did not desulfurize trithiane, thianthrene and 4,4 -thiodiphenol. The desulfurization experiments were conducted in batch with the rate reported as 0.279 mg-sulfur/L dispersion/h for DBT conversion. 

---