Acid-base exchange

As an adjective applied to metals base represents the opposite of noble, i.e. a base metal would be attacked by mineral acids, base exchange An old term used to describe the capacity of soils, zeolites, clays, etc. to exchange their cations (Na, K, Ca ) for an equivalent of other cations without undergoing structural change. An example of the general process of ion exchange. ... 

The second method often employed for the preparation of peroxo complexes involves the use of the late transition metals76 and exploits the mild acidic properties of hydrogen peroxide, i.e. the reaction is an acid-base exchange (Figure 2.23). 

To overcome the problem with the charges on acids and bases, we can be less ambitious, and make more restricted comparisons of acidity and basicity.233 To obtain a useful quantitative measure of the hardness of acids and bases, we apply the concept in Equation 3.1 to the acid base exchange reaction in Equation 3.7, which will take place from left to right if A1 and B1 are the harder acids and bases relative to A2 and B2. 

Translation of the Hard and Soft Acids and Bases principle into a readily applicable formal expression has never been achieved. Huheey suggested, that the driving force to the HSAB rule is a strong hard-hard interaction only, in a set of an acid/base exchange reaction [18]. Nalewajski presented a thorough discussion of that topic [57] and summarized older concepts. Soft-soft interaction is predominantly covalent, whereas hard-hard interaction occurs through ionic forces. The classical formula for energy (Eq. 17) explains why a soft-soft interaction is favored over a soft-hard one the favorable hard-hard situation cannot be accounted for by Eq. 17. 

Let us consider the generalized acid-base exchange reaction as follows ... 

We have already applied this formula for the correlation of the reaction surface of a number of well known acid-base exchange reactions involving diatomic molecules using the global hardness data of the corresponding diatomic molecules computed through our algorithm. 

A look at the Eqs. 13.23 and 13.29 reveals that the hardness difference is directly related to the reaction energy of the acid/base exchange reactions. It may be represented by ... 

For colloids that undergo acid-base exchanges in aqueous media (as the vast majority of soil colloids do), there is a contribution to the surface charge given by Equations 5.3 and 5.4, which can be determined rather easily by means of acid-base titrations. Figure 5.18 shows an example of the procedure a titration of the colloidal suspension in an appropriate supporting electrolyte (one which does not show specific adsorption onto the colloidal particles) is compared with the same electrolyte alone. The... 

The third section is devoted to various aspects of biosynthesis, turnover, and function of lipids in the central nervous system, such as metabolism of polyenoic fatty acids, base-exchange reactions, biosynthesis of complex lipids, and the latest progress in phos-phatidylinositol biochemistry. In addition papers on the implications of lipids in transmitter release and in receptors are included. 

To assert that the decomposition of the Meisenheimer intermediate 2 (step 2) is the rds in the case of o-toluidine requires being more precise, as fliis step is a little more complicated than what has been described in Scheme 33.3. The decomposition of 2 can follow two alternative pathways that are indicated in Scheme 33.4. The first alternative (path a) is a base-catalyzed decomposition process, which consists of the fast deprotonation of intermediate 2 by the amine to form intermediate 3, followed by slow departure of die fluorine ion. The other, is an uncatalyzed decomposition pathway (pafli b) that consists of the initial elimination of fluorine ion leading to aromatic ammonium salt 4, that is subsequently deproto-nated by the base present in die medium in a fast acid-base exchange (Scheme 33.4). 

A new dimension to acid-base systems has been developed with the use of zeolites. As illustrated in Fig. XVIII-21, the alumino-silicate faujasite has an open structure of interconnected cavities. By exchanging for alkali metal (or NH4 and then driving off ammonia), acid zeolites can be obtained whose acidity is comparable to that of sulfuric acid and having excellent catalytic properties (see Section XVIII-9D). Using spectral shifts, zeolites can be put on a relative acidity scale [195]. An important added feature is that the size of the channels and cavities, which can be controlled, gives selectivity in that only... 

Bio-Rex 70 2.4 0.70 Weakly acidic cation exchanger with car-boxylate groups on a macroreticular acrylic matrix for separation and fractionation of proteins, peptides, enzymes, and amines, particularly high molecular weight solutes. Does not denature proteins as do styrene-based resins. 

Three techniques, one of which is ion chromatography, are used to determine the concentrations of three ions in solution. The combined concentrations of Na+ and K+ are determined by an ion exchange with H+, the concentration of which is subsequently determined by an acid-base... 

Weak acid cation exchangers have essentially no abiUty to spHt neutral salts such as sodium chloride [7647-14-5]. On the other hand, an exchange is favorable when the electrolyte is a salt of a strong base and a weak acid. 

Wea.kA.cid Cation Exchangers. The syathesis of weak acid catioa exchangers is a one-step process when acryHc acid or methacrylic acid is copolymetized with DVB. If an acryHc ester is used as the monomer iastead of an acryHc acid, the ester groups must be hydrolyzed after polymerization usiag either an acid or base (NaOH) to give the carboxyHc acid functionaHty, or the sodium salt (4) of it. 

The acryHc weak base resias are syathesized from copolymers similar to those used for the manufacture of weak acid cation-exchange resias. For example, uader appropriate temperature and pressure conditions, a weak acid resia reacts with a polyfuactioaal amine, such as dimethylaminopropylamine [109-55-7] (7) to give a weak base resia with a tertiary amine fuactioaaHty. 

Eig. 5. Pressure drop as affected by resin type, flow rate, and temperature, where A, B, and C, correspond respectively to acryUc strong base anion exchanger (Amberlite IRA-458), styrenic strong base anion exchanger (Amberlite IRA-402), and styrenic strong acid cation exchanger (Amberlite IR-120), all at 4°C. D represents styrenic strong acid cation resin (Amberlite IR-120) at 50°C (14). To convert kg/(cm -m) to lb/(in. -ft), multiply by 4.33 to convert... 

When strong acid cation exchangers are used in the Na" form and strong base anion exchangers are used in the CL form, they are regenerated with a 10% sodium chloride [7647-14-5], NaCl, solution. Other concentrations may be used, perhaps with some adjustment in flow rate. 

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