The Role of Sulfur

Ca.ta.lysts for Acetylation. Sulfuric acid is the preferred catalyst for esterifying cellulose and is the only known catalyst used commercially for this function. The role of sulfuric acid during acetylation has been discussed (77,78). In the presence of acetic anhydride, sulfuric acid rapidly and almost quantitatively forms the cellulose sulfate acid ester (77). Even in the absence of anhydride, the sulfuric acid is physically or mechanically retained (sorbed) on the cellulose. The degree of absorption is a measure of the reactivity or accessibiUty of different celluloses. 

The use of mixed acid (mixt of nitric and sulfuric acids) as a nitrating agent was first described in 1846 by Muspratt Hoffman (Ref 1). The sulfuric acid in their mixt was considered to be a dehydrating agent , a view first advanced by Spindler (Ref 4) and developed further by Markovnikov (Ref 7) Sapozhnikov (Ref 8). The modern concept of the role of sulfuric acid in mixed... 

Harkins, I., and S. W. Nkksic. Studies on the role of sulfur dioxide in visibility reduction. J. Air Pollut. Control Assoc. 15 218-221, 1%5. 

The role of sulfur in these vents is complex and often obscured by its multiple redox states and by uncertainties in the degree of equilibration. Studies by Styrt et al. (1981), Arnold and Sheppard (1981), Skirrow and Coleman (1982), Kerridge et al.(1983), Zierenberg et al. (1984), and others have shown that the sulfur in these deposits is enriched in S relative to a mantle source (typical 5 " S ranges are between 1 and 5%c), implying small additions of sulfide derived from sea water. 

A special case represents acid sulfate waters released from mines where metal sulfide ores and lignite have been exploited. S- and 0-isotope data may define the conditions and processes of pyrite oxidation, such as the presence or absence of dissolved oxygen and the role of sulfur-oxidizing bacteria (i.e. Taylor and Wheeler 1994). 

Karcher, B and D. W. Fahey, The Role of Sulfur Emission in Volatile Particle Formation in Jet Aircraft Exhaust Plumes, Geophys. Res. Lett, 24, 389-392 (1997). 

The role of sulfur functionalities in such processes has received much attention in the recent general literature [482-484] as well as in a number of reviews inter alia [120, 485]). The tt bond of a thiocarbonyl group can be directly involved in (2 + 2), (3 + 2) and (4 + 2) cycloadditions (see [120] and references therein). 

Bonzel and Ku performed a detailed study on the influence of sulfur on the adsorption of CO (208) as well as on the catalytic C02 formation (209) on a Pt(lll) surface. It was found that preadsorbed sulfur affected both the adsorption energy of CO as well as the total amount of CO adsorbed. A Pt surface saturated with sulfur (6S x 0.75) was no longer able to adsorb any CO. Consequently, the rate of C02 formation also decreased continuously with increasing sulfur content of the surface and became practically zero for 6S x 0.28. These results demonstrate the role of sulfur as a rather effective catalyst poison. 

Much has been written about the role of sulfuric acid as an index of national prosperity. Since this acid is generally considered to be one of the most important heavy chemicals and is used in so many of the industries, it is possible to evaluate trends in economic conditions by following the trends in the consumption of sulfuric acid. This applies not only to industry but also to agriculture because of the use of sulfuric acid in the manufacture of fertilizers. 

So, on palladium catalysts, the role of Pd-S (presulfiding) is different from the role of sulfur-containing molecules in competition for adsorption with the unsaturated hydrocarbon. 

Sulfur is generally considered to be a poison of hydrogenation reactions. However, in commercial hydrogenation and dehydrogenation reactions, sulfur is also used as a modifier, and in some cases as activator of catalytic hydrogenation reactions. Barbier and co-authors review the Role of Sulfur in Catalytic Hydrogenation Reactions. ... 

J. A. Maga, The role of sulfur compounds in food flavor. Part II thiophens, CRC Crit. Rev. Food Technol., 1975, 6, 241-270. 

In order to investigate the role of sulfur, benzonaphthothiophene was selected as a PNA molecule containing heteroaromatic sulfur. 

Comment on the role of sulfur in the steps in this synthesis of the turmeric flavour compound ar-turmerone. 

The fate of sulfuric acid in the upper stratosphere and mesosphere is key to understanding the role of sulfur in the upper atmosphere [10]. In this regard the photolysis of sulfuric acid (H2SO4) via the reaction... 

Maw, G. A. (1965). The role of sulfur in yeast growth and in brewing. Wallerstein Laboratory Communications, XXVIII, N° 95, April, 49-70. 

Maga, J. A. The role of sulfur compounds In food flavor. 

The chapter is divided into four main parts Sec. 2 Thiols , Sec. 3 Thioethers , Sec. 4 Disulfides , and Sec. 5 Sulfoxides and Sulfonyls . They describe how sophisticated radiation-chemical techniques have been applied to address the role of sulfur-free radicals derived from these three classes of sulfur-containing compounds, in particular, in the biological environment. Important outputs from these studies are new directions for improving our knowledge of how sulfur-centered radicals interact with major cellular targets during oxidative stress, i.e. proteins, DNA, and lipids. 

The role of sulfur functionalities in activating alkenic and alkynic dienophiles, and directing their cycloadditions to 1,3-dienes, has been recently reviewed and only some essential points are outlined here. Depending on the oxidation state of sulfur, its vinyl derivatives range from strongly or weakly electron-deficient (sulfones or sulfoxides) to electron-rich (sulfides) dienophiles. 

Sasaki K., Tsunekawa M., Ohtsuka T., and Konno H. (1998) The role of sulfur oxidizing bacteria Thiobacillus thioox-idans in pyrite weathering. Coll. Surf. 133, 269 - 278. 

Write a mechanism for the formation of anthraquinone from 2-ben-zoylbenzoic acid, indicating clearly the role of sulfuric acid. What is the name commonly given to this type of reaction ... 

---