Tartaric acid surface conditions

The corrosion of tin by nitric acid and its inhibition by n-alkylamines has been reportedThe action of perchloric acid on tin has been studied " and sulphuric acid corrosion inhibition by aniline, pyridine and their derivatives as well as sulphones, sulphoxides and sulphides described. Attack of tin by oxalic, citric and tartaric acids was found to be under the anodic control of the Sn salts in solution in oxygen free conditions . In a study of tin contaminated by up to 1200 ppm Sb, it was demonstrated that the modified surface chemistry catalysed the hydrogen evolution reaction in deaerated citric acid solution. 

The enantioselective hydrogenation of prochiral substances bearing an activated group, such as an ester, an acid or an amide, is often an important step in the industrial synthesis of fine and pharmaceutical products. In addition to the hydrogenation of /5-ketoesters into optically pure products with Raney nickel modified by tartaric acid [117], the asymmetric reduction of a-ketoesters on heterogeneous platinum catalysts modified by cinchona alkaloids (cinchonidine and cinchonine) was reported for the first time by Orito and coworkers [118-121]. Asymmetric catalysis on solid surfaces remains a very important research area for a better mechanistic understanding of the interaction between the substrate, the modifier and the catalyst [122-125], although excellent results in terms of enantiomeric excesses (up to 97%) have been obtained in the reduction of ethyl pyruvate under optimum reaction conditions with these Pt/cinchona systems [126-128],... 

Surface modification of skeletal nickel with tartaric acid produced catalysts capable of enantiose-lective hydrogenation [85-89], The modification was carried out after the formation of the skeletal nickel catalyst and involved adsorption of tartaric acid on the surface of the nickel. Reaction conditions strongly influenced the enantioselectivity of the catalyst. Both Ni° and Ni2+ have been detected on the modified surface [89]. This technique has already been expanded to other modified skeletal catalysts for example, modification with oxazaborolidine compounds for reduction of ketones to chiral alcohols [90],... 

A Raney Ni catalyst modified by tartaric acid and NaBr is fairly effective for enantioselective hydrogenation of a series of (3-keto esters (Scheme 1.41) [203a,214,215]. The enantio-discrimi-nation ability of the catalyst is highly dependent on the preparation conditions such as pH (3—4), temperature (100°C), and concentration of the modifier (1%). Addition of NaBr as a second modifier is also crucial. Ultrasonic irradiation of the catalyst leads to even better activity and enantioselectivity up to 98% ee [214d-f. The Ni catalyst is considered to consist of a stable, selective and weak, nonselective surface area, while the latter is selectively removed by ultrasonication. 

In this section, we focus on the Ni(llO) surface, the metal most commonly modified by tartaric acid, to yield the successful enantioselective catalytic system for the hydrogenation of P-ketoesters [6, 7], A detailed study [22, 23] of the adsorption of (/ ,/ )-tartaric acid on Ni(llO) as a function of temperature and coverage again shows a polymorphic system, (Fig. 5.8) with the local nature of the chiral adsorbate changing dynamically as conditions change, echoing the findings on Cu(llO). 

Although this approach is the only example in which catalytic activity and stereochemical control are not separated, no synthetic application can yet be foreseen because the concentration of such chiral sites in practically useful polycrystalline metal catalysts is very low and surface restructuring is likely to occur under reaction conditions. A similar conclusion can be drawn about the importance of other chiral metal structures, such as a screw dislocation or a chiral surface produced by asymmetric corrosion. Interestingly, asymmetric leaching of Ni in the presence of tartaric acid has already been proposed as an explanation for the enantio-differentiation by the tartaric acid-modified Ni catalyst [5]. 

Acid cleaners based on sulfamic acid are used in a large variety of appHcations, eg, air-conditioning systems marine equipment, including salt water stills wells (water, oil, and gas) household equipment, eg, copper-ware, steam irons, humidifiers, dishwashers, toilet bowls, and brick and other masonry tartar removal of false teeth (50) dairy equipment, eg, pasteurizers, evaporators, preheaters, and storage tanks industrial boilers, condensers, heat exchangers, and preheaters food-processing equipment brewery equipment (see Beer) sugar evaporators and paper-mill equipment (see also Evaporation Metal surface treati nts Pulp). 

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