Cation exchanger, hydrolysis

Deamidation of soy and other seed meal proteins by hydrolysis of the amide bond, and minimization of the hydrolysis of peptide bonds, improves functional properties of these products. For example, treatment of soy protein with dilute (0.05 A/) HCl, with or without a cation-exchange resin (Dowex 50) as a catalyst (133), with anions such as bicarbonate, phosphate, or chloride at pH 8.0 (134), or with peptide glutaminase at pH 7.0 (135), improved solubiHty, whipabiHty, water binding, and emulsifying properties. 

Acidic Cation-Exchange Resins. Brmnsted acid catalytic activity is responsible for the successful use of acidic cation-exchange resins, which are also soHd acids. Cation-exchange catalysts are used in esterification, acetal synthesis, ester alcoholysis, acetal alcoholysis, alcohol dehydration, ester hydrolysis, and sucrose inversion. The soHd acid type permits simplified procedures when high boiling and viscous compounds are involved because the catalyst can be separated from the products by simple filtration. Unsaturated acids and alcohols that can polymerise in the presence of proton acids can thus be esterified directiy and without polymerisation. 

Although catalytic hydration of ethylene oxide to maximize ethylene glycol production has been studied by a number of companies with numerous materials patented as catalysts, there has been no reported industrial manufacture of ethylene glycol via catalytic ethylene oxide hydrolysis. Studied catalysts include sulfonic acids, carboxyUc acids and salts, cation-exchange resins, acidic zeoHtes, haUdes, anion-exchange resins, metals, metal oxides, and metal salts (21—26). Carbon dioxide as a cocatalyst with many of the same materials has also received extensive study. 

SG sols were synthesized by hydrolysis of tetraethyloxysilane in the presence of polyelectrolyte and surfactant. Poly (vinylsulfonic acid) (PVSA) or poly (styrenesulfonic acid) (PSSA) were used as cation exchangers, Tween-20 or Triton X-100 were used as non- ionic surfactants. Obtained sol was dropped onto the surface of glass slide and dried over night. Template extraction from the composite film was performed in water- ethanol medium. The ion-exchange properties of the films were studied spectrophotometrically using adsorption of cationic dye Rhodamine 6G or Fe(Phen) and potentiometrically by sorption of protons. 

The slower rate of hydrolysis of alkyl substituted esters in the presence of the cation exchange resin can be explained by the assumption that the alkyl groups interfere more in the formation of the intermediate complex on the resin surface than in the homogeneous system. The efficiency of the resin q was less than unity... 

J mol ). This is additional evidence in favor of rate limitation by inner diffusion. However, the same reaction in the presence of Dowex-50, which has a more open three-dimensional network, gave an activation energy of 44800 J mol , and closely similar values were obtained for the hydrolysis of ethyl acetate [29] and dimethyl seb-acate [30]. The activation energy for the hydrolysis of ethyl acetate on a macroreticular sulphonated cationic exchanger [93] is 3566 J mol . For the hydrolysis of ethyl formate in a binary system, the isocomposition activation energy (Ec) [28,92] tends to decrease as the solvent content increases, while for solutions of the same dielectric constant, the iso-dielectric activation energy (Ed) increases as the dielectric constant of the solvent increases (Table 6). 

The rate of hydrolysis of sarin on Dowex-50 cation exchange resin is insensitive to the stirring rate. However, with a more active catalyst (Amberlite-IRA 400), the rate constant at 20°C was 5.3, 7.5, and 8.5 h at 60,800 and 1000 revolutions/min , respectively, suggesting that film diffusion was the rate-limiting. step. Thus, the mechanism of the rate-limiting step depends on the nature of the catalyst [34]. 

Studies by Deathrage ef a/.137 139 revealed that most of dipeptides were hydrolyzed 100 times faster with cation exchange resins (Dowex-50) than with HC1. Deathrage etal.139 also found that the entropy of activation was significantly less than in the case of hydrolysis of the same compounds by HC1, while the enthalpies of activation for the two cases were practically the same. While the entropy changes associated with catalysis by the cationic exchange resins remain obscure, presumably the mechanism of the catalysis follows that for homogeneous acids as described here later. 

Hammet and collaborators140, 141 studied in more detail the hydrolysis of aliphatic esters with a cation-exchange resins as catalyst. They found that replacement of 70% of the hydrogen ions in a crosslinked polystyrenesulfonic add by cetyl-trimethylammonium ions had a specifically favorable effect on the effectiveness of the remaining hydrogen ions for the hydrolysis of ethyl-n-hexanoate. From these findings, the important contributions of the hydrophobic forces, in addition to the electrostatic forces, is clearly demonstrated. 

The diacetylated ethane-1-hydrox-1,1-diphosphonic acid is prepared by dissolving the diphosphonic acid in acetic acid and adding acetic anhydride [114]. The sodium salt can be directly converted to the free acid form by passing it through an hydrogen cation exchanger. The bicyclic dimer is prepared by basic hydrolysis of diacetylated cyclic dimer, as shown in Eq. (70) ... 

E. Kenndler, K. Schmidt Beiwl, F. Mairinger, M. Pohm, Identification of Proteinaceous Binding Media of Easel Paintings by Gas Chromatography of the Amino Acid Derivatives after Catalytic Hydrolysis by a Protonated Cation Exchanger, Fresenius Journal of Anaytical. Chemistry, 342, 135 141 (1992). 

U. Schneider, E. Kenndler, Identification of Plant and Animal Glues in Museum Objects by GC MS, After Catalytic Hydrolysis of the Proteins by the Use of a Cation Exchanger, with Simultaneous Separation from the Carbohydrates, Fresenius Journal of Analytical Chemistry, 371,81 87 (2001). 

The hydrolysis of sucrose catalyzed by the strongly acidic cation-exchange resin Amberlite 200C in RH form was chosen as a model reaction to compare the use of stirred tank and continuous-flow reactors [47-49], Scheme 10.6. 

Cation-exchange resins are used as catalysts in the produdion of MTBE (methyl tertiary-butyl ether, 2-methoxy-2-methylpropane) and various other oxygenates and, lately, also in the dimerization of isobutene [30]. Other commercial applications of the cation-exchange resins indude dehydration of alcohols, alkylation of phenols, condensation readions, alkene hydration, purification of phenol, ester hydrolysis and other reactions [31]. The major producers of ion-exchange resins are Sybron Chemicals Incorporated [32] (Lewatit resins), Dow Chemical Company [33] (DOWEX resins), Purolite [28] (Purolite resins), and Rohm and Haas Company [27] (Amberlyst resins). 

In order to study further the favorable aspects of in situ acid catalyzed hydrolysis, experiments were performed at different temperatures so as to evaluate the dependence of rate on temperature. Solutions of aldlcarb were passed through a jacketed column around which water at 30, 40, or 50°C was circulating. The ion exchange bed (5 cm x 0.70 cm) contained 2.0 g of Bio-Rad AG MP-50 strong acid cation exchange resin (iT ", 100-200 mesh), and the solution flow rate was approximately 1.0 ml/mln. The percent of Initial aldlcarb remaining at the end of the column for each temperature decreased from 76% at 30 C to 56% at 40 C and 35% at 50°C. Future temperature studies will be done in order to evaluate the practicality of temperature control in a detoxification filter unit. 

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