Active sulfur

The diffusion process has not been designed to ensure sterility, although temperatures above 65°C significantly retard microbial activity. Sulfur dioxide, thiocarbamates, glutaraldehyde, sodium bisulfite, and chlorine dioxide are all used, occasionally disregarding their redox incompatibilities, to knock down or control infections. The most common addition point is to the water from the pulp presses as it is returned to the diffuser. Surfactants ate almost... 

Photochemical reaction of the ester 114 afforded the alkene 115 and three products derived from 115. A mechanism, involving dimerization of 114 leading to a dithietane intermediate 116, was proposed. Trapping of active sulfur species, generated from 116, with dienes was also described (75CB630). 

A. Nudelman, The Chemistry of Optically Active Sulfur Compounds, Gordon and Breach, New York, 1984. 

Jupiter s moon lo on which a number of very active sulfur volcanoes have been discovered [64]. These volcanoes are powered by SO2 gas which forces the hquid sulfur from its underground deposits to the surface. 

Aside from the sulfur, the sulfur bearing compounds that can liberate sulfur at the vulcanization temperature can be used as vulcanizing agents. A few sulfur donors are given in Table 14.5, which include some compounds like dithiodimorpholine (DTDM), which can directly substitute sulfur. Others, like tetramethylthiuramdisulhde (TMTD), can act simultaneously as vulcanization accelerators. The amount of active sulfur, as shown in Table 14.5, is also different for each compound. Sulfur donors may be used when high amount of sulfur is not tolerated in the... 

The polysulfidic moieties of the silanes are unstable, and cleavage of the sulfur groups results in active sulfur species. A notorious problem with this kind of coupling agents is the balance between its reactivity towards the silica, requiring a temperature of at least 130°C to obtain an acceptable speed, and its eagerness to react with the rubber polymer, which starts to become noticeable at temperamres above 145°C. Furthermore, the primary and secondary reactions are chemical... 

Oxidative desulfuration releases active sulfur that binds to, and deactivates, P450 Selective inhibitors Specific inhibitor of lAl Specific inhibitor of 1A2 Specific inhibitor of 2A6 Specific inhibitor of 2C9 Specific inhibitor of 2D1 Specific inhibitor of 2E1... 

Fragments C-N-N-C and S Diazenes and hydrazines with a sulfur source The reaction of 2,3-diazabuta-l,3-dienes with sources of active sulfur to prepare 1,3,4-thiadiazoles has been reviewed in CHEC(1984) <1984CHEC(6)545>, CHEC-II(1996) <1996CHEC-II(4)379> and Chapter 13.12 in the Houben-Weyl Science of Synthesis <2004HOU(13)349>. 

Optically Active Sulfur Compounds Absolute Configuration at Sulfur Determined by X-Ray Analysis... 

In the last two decades optically active sulfur compounds have found wide application in asymmetric synthesis. This is mainly because organic sulfur compounds are quite readily available in optically active form. Moreover, the chiral sulfur groupings that induce optical activity can be removed from the molecule easily, under fairly mild conditions, thus presenting an additional advantage in the asymmetric synthesis of chiral compounds. This section deals with reactions in which asymmetric induction in transfer of chirality from sulfur to other centers was observed. This subject has been treated only in a cursory manner in recent reviews on asymmetric synthesis (290-292). 

Procedures 1 and 2 yield new organosulfur compounds whose chirality is due to the presence of the newly formed chiral carbon atom or heteroatom procedure 3 affords optically active sulfur-free compounds. The third procedure is most attractive from the preparative point of view. 

The Doctor test measures the amount of sulfur available to react with metallic surfaces at the temperature of the test. The rates of reaction depend on metal type, temperature, and time. In the test, a sample is treated with copper powder at 149°C or 300°F. The copper powder is filtered from the mixture. Active sulfur is calculated from the difference between the sulfur contents of the sample (ASTM D129) before and after treatment with copper. 

Interchange with the original complex leads to the formation of a mixture of polysulfidic complexes, which are considered to be the active sulfurating species. 

There is much concern about the emissions which result when fuel sulfur combusts (i.e., sulfur oxides). These gaseous products further react to form environmental pollutants such as sulfuric acid and metal sulfates. Active sulfur and certain sulfur compounds can corrode injection systems and contribute to combustion chamber deposits. Under low-temperature operating conditions, moisture can condense within the engine. Sulfur compounds can then combine with water to form corrosive acidic compounds. 

Elemental sulfur is sometimes termed active sulfur because of its highly aggressive and corrosive nature toward metal, especially copper, bronze, and brass. Copper sulfide readily forms when in contact with elemental sulfur. 

Some bacteria specifically utilize oxygen bound in the sulfate complex of a compound. As a result of this metabolic activity, sulfur is reduced to H2S. For this reason, these microbes are called sulfate-reducing bacteria (SRB). They can tolerate temperatures as high as 80°C (176°F) and environments from about pH 5 to pH 9. Species such as Desulfivibrio and Desulfomonas are examples of SRB. 

Fuel Contains Hydrogen Sulfide or Active Sulfur... 

The delay period exhibited with sulfenamide cures is explained in terms of the formation of intermediates by reaction with activated sulfur (Scheme 5) (80MI11508). The 2-mercap-tobenzothiazole (31) produced reacts rapidly with the sulfenamide providing a more facile pathway for vulcanization (equation 11). The amine (38) produced also acts as a catalyst, so that the cure, once started, becomes autocatalytic (64MI11503). 

A number of attempts have been made to use optically active sulfur ylides to transfer the chirality of sulfur to carbon in the formation of epoxides and cyclopropanes. The results were somewhat disappointing. Thus, virtually no asymmetric induction was observed with the ylide (1) [475]. With the stabilized ylides (2), e.e. values in the range 7-43% were reported [476]. Better results were obtained with sulfonium ylides derived from Eliel oxathiane [477]. Optically active diaryl epoxides could be prepared under PTC in high yields and good e.e. values. 

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