Adsorbed water excess acidity

In this context the lipase was immobilized on a support which also adsorbed water and propionic acid. During the reaction, the water caused a decrease of the reaction rate. While the water adsorption on the catalyst results in a reversible decrease of the enzyme activity, an excessive accumulation of water in the bulk mobile phase resulted in rapid irreversible deactivation of the enzyme. 

In serum replacement (6), the latex is confined in a cell with a semi-permeable membrane, e.g., Nuclepore filtration membrane, and water is pumped through the latex to literally replace the serum. The removal of adsorbed ions is quantitative provided the adsorption-desorption equilibrium is maintained. The Na+ and K+ ions are replaced by IT " ions by pumping dilute hydrochloric acid through the latex followed by water to remove the excess acid. Serum replacement takes longer than ion exchange, but avoids the arduous resin purification step moreover, the serum is recovered quantitatively in a form suitable for analysis. 

For serum replacement (6), the latex is confined in a cell with a uniform-pore-size Nuclepore filtration membrane. Distilled, deionized water is pumped through the latex until the conductance of the effluent stream is about the same as that of the distilled, deionized water. This serum replacement removes the adsorbed emulsifier and solute electrolyte quantitatively and allows recovery of the serum in a form suitable for further analysis however, it does not+replace the Na+ and K counterions of the surface groups with Vl ions. To do this, dilute hydrochloric acid (ca. 10 N) is pumped through the latex, followed by distilled, deionized water to remove the excess acid. The latex is then titrated conductometrically to determine the surface charge. 

Because amino groups act autocatalytically (15-17) in the presence of water, for acid catalysis an excess of HC1 was used to overcompensate the formation of -NH3+C1 . In these cases, the gels were washed with methanol and water until no Cl" could be detected in the filtrate. How far the incorporation of amino groups into silica could affect the adsorption of acid components was of interest. Lactic acid and a sulfonic acid (a commercially available dye named Telon Light Yellow) were chosen as test components (18). In Figure 7 the adsorption isotherm of lactic acid is shown. Unmodified Si02 does not have remarkable adsorption in aqueous solution under these circumstances. The result shows the effect of the amino modification quite clearly, because the lactic acid load of the adsorbent is remarkable, and it is difficult to adsorb small water-soluble molecules in an aqueous environment. 

When excess formic acid was brought over a Ni-sample at — 5°C the bands of the covalently bound acid were not observed (see Fig. 15, spectrum A), but strong bands were found at 1587 and 1351 cm-1, which indicated the presence of formate ions on the surface. The strong band at 1724 cm-1 was due to physically adsorbed acid and is also found on silica samples without Ni. Furthermore, narrow bands were present at 1639 cm-1, 2041 cm-1 and 1887 cm-1 these were due to adsorbed water and chemisorbed carbon monoxide. 

The color of benzidine adsorbed on bentonite is reversibly altered by adsorbed water vapor. Vedeneeva (80) found that the intense blue color observed in the presence of excess water changed to green, yellow and finally colorless as the adsorbed water was removed. This color sequence was reversed when moisture was added. More recently, Hase-gawa (14) reexamined this so-called benzidine reaction with both benzidine and tetramethylbenzidine, using benzene as a supporting solvent for the catalyst suspension. Adsorption of benzidine on natural or acid-treated clay produced a greenish-yellow color (curves A and B, Fig. 27) with absorption maxima at 4400 A, 7800 A, and 8800 A, in close... 

Suto et described the purification of an amide library with basic ion exchange resins. The reaction was performed using an excess of acid chloride as acylating agent (see Scheme 3.4.1). After completion of the reaction, addition of a small amount of water led to the hydrolysis of the excess acid chloride. Carboxylic acids as well as hydrochloric acid formed during the reaction were then adsorbed on the resin. The desired amides remained in solution and were isolated in excellent yields and HPLC purities >98%. 

Bibby and coworkers [664] reported on an interesting FTIR spectroscopic observation of an interaction between an excess of H2O and Bronsted acid OH groups of H-Y. They foimd that at temperatures as low as 298 and 353 K this interaction and subsequent water desorption resulted in a partial breaking of Al-framework bonds imder formation of Al-OH and Si-OH species and finally in a collapse of the framework (cf. [472]). In another series of experiments, Bibby and coworkers [665] found out by IR spectroscopy that HjO and DjO on D-ZSM-5 and H-ZSM-5 experienced at 353 K only a slow H/D exchange. Since approximately one water molecule was adsorbed per framework Al, the authors proposed that the adsorbed water was only partially protonated but also interacted with the zeolite framework. 

The reaction proceeds by heating the mixture to 150°C or higher with or without a catalyst . Catalysts such as p-toluenesulfonic acid or titaniimi(IV) isopropoxide, are typically used to facilitate reaction rates. The reaction is driven to completion by continuous removal of water from the reaction medium. Sometimes, one component is used in a slight excess to ensure complete conversion. The final product is purified over an adsorbent to remove trace water and acids, both of which are detrimental to base stock quality. Commercially, esters are generally produced by batch processes. 

Thorium oxide on activated carbon was prepared by absorption of thorium nitrate from its solution in anhydrous acetone on the activated carbon Supersorbon. The excess solution was decanted, the catalyst was dried at 80 °C, and the adsorbed thorium oxide was decomposed by excess 5% ammonium hydroxide solution. After repeated washing and decanta-nation with distilled water and acetone, the catalyst was dried at 180°C. It was then stabilized by heating to 360°C for 5 hr in a stream of nitrogen. The content of thorium oxide was 2.9% (wt.). The BET surface area was 870 m2/g. Prior to kinetic measurements, the catalyst was modified by passing over acetic acid vapors (100 g acid/1 g catalyst). 

Food samples are dissolved in water and acidified with acetic acid (135,157). According to Gilhooley et al. (157), excess methanol has to be removed from solutions before passing through polyamide because it impairs the adsorption of the dyes by the polyamide. The solution is stirred with polyamide powder, and the slurry is transferred to a microcolumn or it is passed through the column of polyamide. The latter is recommended since dyes are adsorbed as a narrow band at the top of the column. The column is washed with hot water to remove sugars, acids, and flavoring materials and with acetone to remove basic dyes, water-soluble carotenoids, and some antho-cyanins. The adsorbed acid dyes are eluted with methanol sodium hydroxide (164,172,175), with methanol ammonia (176), or with acetone ammonia (157). Acetone ammonia is preferred because it can be removed in a water bath and, on addition of acid, no salts are formed that interfere with the adsorption of the dyes by the polyamide (157). The eluate is evaporated to dryness and redissolved in the HPLC mobile phase (156). 

---