Processing stabilizer, effect

The substances typically used are sulfides, dialkyl dithiocarbonates or thiodipro-pionates, such as dilauryl thiodipropionate (DLTDP) and distearyl thiodipropionate (DSTDP) as well as disulfides. These products develop their effect mainly in the range of long-term service temperatures, i. e., at moderate temperatures, and they exhibit few process stabilizing effects (with the exception of disulfides). 

The higher strain energy in thiirene dioxides (19) compared to thiirane dioxides (17) is obvious. Yet, the elimination of sulfur dioxide from the latter is significantly faster than one would expect for a thermally allowed concerted process. Consequently, either aromatic-type conjugative stabilization effects are operative in thiirene dioxides2,12 or the relative ease of S02 elimination reflects the relative thermodynamic stability of the (diradical )99 intermediates involved in the nonconcerted stepwise elimination process. 

Full accounts have appeared of the exchange of trimethylsilyl for chlorosilyl groups on treatment of trimethylsilylylides with chlorosilanes and of the stabilizing effects of the simple silyl (SiHa) group on ylides. The exchange process involves nucleophilic attack of the ylide on the silicon of the chlorosilane, e.g. 

E is one of several elasticity numbers characterizing the stabilizing effect which adsorbed surfactant molecules have on an interface during mass-transfer processes (22). Note that E is inversely proportional to the capillary radius so that the effect of soluble surfactants on the bubble-flow resistance is larger for smaller capillary radii. 

However, a comparison made by Carlsson of the experimentally obtained protection effects and those calculated on the basis of reaction (3) showed that process (3) cannot be alone responsible for the observed stabilizing effect. ... 

However, an important problem arises during the peroxidative removal of phenols from aqueous solutions PX is inactivated by free radicals, as well as by oligomeric and polymeric products formed in the reaction, which attach themselves to the enzyme (Nazari and others 2007). This suicide peroxide inactivation has been shown to reduce the sensitivity and efficiency of PX. Several techniques have been introduced to reduce the extent of suicide inactivation and to improve the lifetime of the active enzyme, such as immobilization. Moreover, Nazari and others (2007) reported a mechanism to prevent and control the suicide peroxide inactivation of horseradish PX by means of the activation and stabilization effects of Ni2+ ion, which was found to be useful in processes such as phenol removal and peroxidative conversion of reducing substrates, in which a high concentration of hydrogen peroxide may lead to irreversible enzyme inactivation. 

Ab initio SCRF/MO methods have been applied to the hydrolysis and methanol-ysis of methanesulfonyl chloride (334). ° The aminolysis by aromatic amines of sulfonyl and acyl chlorides has been examined in terms of solvent parameters, the former being the more solvent-dependent process.Solvent effects on the reactions of dansyl chloride (335) with substituted pyridines in MeOH-MeCN were studied using two parameters of Taft s solvatochromatic correlation and four parameters of the Kirkwood-Onsager, Parker, Marcus and Hildebrand equations. MeCN solvent molecules accelerate charge separation of the reactants and stabilize the transition... 

In summary, the space strain is indicative of the stability of electron-transfer products. Electrode reactions fail to reveal such an effect. In liquid-phase processes, this effect, however, plays a decisive role. As Baizer and Lund s book (1983, p. 907) underlines... 

This is observed in the case of the secondary alcohol illustrated, where a secondary carbocation would be generated. A methyl migration would merely lead to another secondary carbocation, and this serves no stabilizing effect. However, a hydride migration produces a tertiary carbocation, so this process will stabilize the system. This is what actually happens, and the major product is a bromide where the halogen appears to have attacked the wrong position. 

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