Promoters acidic

The catalysts used in the industrial alkylation processes are strong Hquid acids, either sulfuric acid [7664-93-9] (H2SO or hydrofluoric acid [7664-39-3] (HE). Other strong acids have been shown to be capable of alkylation in the laboratory but have not been used commercially. Aluminum chloride [7446-70-0] (AlCl ) is suitable for the alkylation of isobutane with ethylene (12). Super acids, such as trifluoromethanesulfonic acid [1493-13-6] also produce alkylate (13). SoHd strong acid catalysts, such as Y-type zeoHte or BE -promoted acidic ion-exchange resin, have also been investigated (14—16). 

Hardly surprisingly the tendency of alkanes to lose proton and form carbanions is not marked, as they possess no structural features that either promote acidity in their H atoms, or are calculated to stabilise the carbanion with respect to the undissociated alkane (cf. carboxylic acids, p. 55). Thus CH4 has been estimated to have a pKa value of 43, compared with 4.76 for MeC02H. The usual methods for determining pKa do not, of course, work so far down the acidity scale as this, and these estimates have been obtained from measurements on the iodide/organo-metallic equilibria ... 

Acid drainage results from the reaction of sulfide minerals with oxygen in the presence of water. As we show in this section, water in the absence of a supply of oxygen gas becomes saturated with respect to a sulfide mineral after only a small amount of the mineral has dissolved. The dissolution reaction in this case (when oxygen gas is not available) causes little change in the water s pH or composition. In a separate effect, it is likely that atmospheric oxygen further promotes acid drainage because of its role in the metabolism of bacteria that catalyze both the dissolution of sulfide minerals and the oxidation of dissolved iron (Nordstrom, 1982). 

The presence of acidic centers in the catalyst promotes acid-catalyzed processes in addition to the above reactions. Of course, their rates may be much higher than those of metal catalyzed ones. 

The change in surface acidity with water content was also demonstrated by the ability of kaolinite to promote acid-catalyzed polymerization (236). Styrene, p-methylstyrene, and p-methoxymethylstyrene polymerized vigorously on kaolinite that was dried at 110°C. At 0.2% wt water content, p-methylstyrene and p-methoxystyrene polymerized and at 0.6% wt water content, only p-methoxystyrene polymerized. The polymerization results are consistent with lower acidity at higher water contents since the susceptibility of these monomers to acid-catalyzed polymerization is in the order p-methoxystyrene > p-methylstyrene > styrene. 

Fluorine is also used commercially as an additive in hydrotreating catalysts. Fluorine is added especially to hydrocracking catalysts because it increases the acidity of the catalyst and thus promotes acid-catalyzed cracking of hydrocarbons. Test reactions, such as the cracking of cumene to give benzene and propene, have demonstrated clearly that fluorine rather than... 

Tn Chapter 43 we mentioned the role of histamine in promoting acid secretion in the stomach, and its role in causing gastric ulcers. The drug cimetidine was designed to counteract the effect of histamine. Histamine is produced in the body by decarboxylation of histidine using the mechanism you have just seen. 

Acidity. For many years the pH of the paper has been considered an important characteristic affecting peramnence. Permanency specifications exist which call for paper with a pH of 6.5 or higher. Other specifications say that the pH should not be lower than 5.5. There is no disagreement, however, about the poor permanency of paper when it is under pH 5.5 (4). In this context, paper pH is determined by the extraction procedure already described. The acidity that is present in the paper will promote acid hydrolysis of the glucosidic bonds of cellulose. To prevent this type of degradation and to produce paper with a high extract pH, the paper machine process water system must be controlled at a neutral to alkaline pH with a minimum of total acidity, preferably with an excess of alkalinity. The term total acidity is used to describe the concentration of all dissolved ions and particles in the process water that contribute to acidity in the system and a low extract pH in the paper. For example, papermaker s alum dissociates to alumi-... 

An Al3+-exchanged montmorillonite, for example, is as active as concentrated sulfuric acid in promoting acid-catalyzed reactions. Sulfuric acid treatment of natural montmorillonite similarly affords the much more active and widely used acid catalyst known as K-10 or KSF (from Sud-Chemie or Fluka, respectively). 

Replacement of Diazo Sulfide Groups with Fluorine in the Silver(l) Ion Promoted Acid Decomposition of Aryl Diazo Sulfides... 

Fig. 23.5 Proposed mechanism by which thiol promotes acid-catalyzed bisphenol A production. Reprinted with permission from [16], Copyright 2006 Elsevier...

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