Consecutive acid-base reactions

A. (a) Each ion below has two consecutive acid-base reactions (called stepwise acid-base reactions) when placed in water. Write the reactions and the correct symbol (for example, K2 or for the equilibrium constant for each. Use Appendix B to find the numerical value of each equilibrium constant. 

Simultaneous or Consecutive Acid-Base Reactions A General Approach 761... 

The reactions taking place in the vicinity of the electrode surface can be classified as acid-base reactions, hydration-dehydration equilibria, interactions of negatively charged species with metal cations, and ringopening reactions. Some of these reactions precede the electrode process proper, some are interposed between two electrode processes and some are consecutive to the electrochemical step. 

Beside consecutive-competing reactions, instantaneous (generally acid-base) reactions are also used as an indicator of segregation, especially in multijet tubular reactors. Ottino (102) deduced the relationship t (t) between nwarpedn and real time from the comparison between experimental conversion X(t) along the axis of a tube and the theoretical expression X(tw). ay was then calculated by (7-10) and the efficiency eff(t) by ... 

We have seen in the last chapter that many catalysed reactions are determined kinetically by a single acid-base reaction between the catalyst and the substrate, and when this is so /c or k in Equation (105) is just the second-order velocity constant for this reaction. The interpretation is not quite so simple when the reaction involves two consecutive proton transfers, of which the first is effectively at equilibrium. Thus for acid catalysis we may have... 

This argument can be extended to consecutive reactions having a rate-determining step. - P The composition of the transition state of the rds is given by the rate equation. This composition includes reactants prior to the rds, but nothing following the rds. Thus, the rate equation may not correspond to the stoichiometric equation. We will consider several examples. In Scheme IV a fast acid-base equilibrium precedes the slow rds. 

Dermatan sulfate, also termed chondroitin sulfate B, a related glycosaminoglycan constituent of connective tissue, was known to be composed of galactosamine and a uronic acid, originally believed to be glucuronic acid but then claimed to be iduronic acid based largely on color reactions and paper chromatography. However, the d or L-enantiomer status of the latter monosaccharide was not clear. Jeanloz and Stoffyn unequivocally characterized the monosaccharide as L-iduronic acid by consecutive desulfation, reduction, and hydrolysis of the polysaccharide, followed by isolation of the crystalline 2,3,4-tri-0-acetyl-l,6-anhydro-/ -L-idopyranose, which was shown to be identical to an authentic specimen synthesized from 1,2-0-isopropylidene-/ -L-idofuranose.34... 

A part of the evidence for the mechanisms given in equations (40) and (42) is provided by the work of Lowry and co-workers (Lowry and Richards, 113 Lowry and Faulkner, 24) on the mutarotation of tetra methylglucose. In water the reaction proceeds at a measurable rate, and it is clearly catalyzed by both acids and bases. In aqueous solution pyridine is a powerful catalyst but in pure dry pyridine no reaction occurs, and likewise in pure dry re-cresol there is no reaction. Upon investigating the reaction in a mixture of pyridine and n-cresol, Lowry and Faulkner (24) found it to take place very rapidly. From these experiments Lowry drew the important conclusion that a proton cannot by itself wander from one part of the molecule to another. The transformation can occur only if the medium in which the molecule is placed has both acidic and basic properties, so that a proton can be removed from the molecule at one place and a proton added to the molecule at another place. Now these experiments furnish strong support to the mechanism of reactions (40) and (42) whereby both members of the conjugate acid-base pair play a part in the reaction. Instead of representing this mutual dependence by means of consecutive bimolecular reactions, Lowry chose to represent it by means of one trimolecular reaction... 

Recently, it has been observed that the selectivity to C -olefins in the ODH of n-butane on vanadium supported catalysts decrease with the acid character of the support [3]. In this way, it has been proposed that the acid-base character of the catalysts could Influence the rates of the selectivity determining step, i.e. the desorption of olefinic intemediates and/or the consecutive reactions of the desorbed olefins. 

For j3-morpholinopropiophenone at pH <9 the consecutive reaction of the a,j8-unsaturated ketone need not be considered. For the rate v ( = d[Ke]/dt= — d[MB]/di) of the studied system, corresponding to opposed first- and second-order reactions, accompanied by two acid-base... 

It has been suggested that the Incorporation of alkali metals on Ti02-vanadia catalysts decreases both the V=0 stretching frequencies and their polarizing power, while the incorporation of acid anions produces an opposite trend [20]. In addition, the presence of alkali ions decreases the heat of the propylene adsorption [17,18, 21]. Thus the different catalytic behavior of doped alumina supported vanadia catalysts, could be explained on the bases of the influence of the acid-base character of catalysts on the adsorption/desorption of propane and propene. In any case, the redox properties must be also considered. In this way, it will be interesting to study if, realy, a lower reducibility of the active sites could favor a lower rate of the consecutive reactions, as it has been observed in the case of K-doped catalysts. 

Thus, after the termination of the intensive gas evolution from the acidic melts corresponding to the pseudo-equilibrium state of the system, the investigators performed the potentiometric titration of the products formed in the nitrate melt. Consecutive additions of the base-titrant Na202 into the formed solution give rise to two sequential acid-base processes, which we shall now discuss. The first stage is the formation of pyro-salts according to the reaction... 

Dehydration of alcohols over solid catalysts can yield alkenes by intramolecular dehydration, whereas ethers are the product of an intermolecular process. The catalysts used can be acidic or basic solids or bifunctional acid-base materials. Although selective synthesis of any desired product is possible, complications can arise as a result of side-reactions-dehydrogenation and decomposition of the starting alcohol, decomposition and consecutive transformations of intermediates and products (j9-cleavage of carbocations, oligomerization of alkenes). 

Mulhaupt and coworkers have reported the details of several studies related to the preparation of block copolymers from thiol, maleic acid and hydroxy-functional polypropylene prepared by a metallocene catalyst [157, 158]. The same group also reported the transformation of metallocene-mediated olefin polymerization to anionic polymerization by a novel consecutive chain-transfer reaction for the preparation of polypropylene-based block copolymers [159]. The latter were also... 

The consecutive reactions of N-glycosides partially correspond to those already outlined for acid/base catalyzed conversions of monosaccharides. However, starting with N-containing intermediates, which with the nitrogen function possess a catalyst within the molecule, these reactions proceed at a high rate under substantially milder conditions, which are present in many foods. 

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