Simultaneous acid-base reactions

Clearly the two reactions are analogous and demonstrate that the reaction between hydroxide ion and hydrogen bromide is simultaneously a Brpnsted acid-base reaction and a Lewis acid Lewis base reaction Br0nsted acid-base reactions constitute a sub category of Lewis acid Lewis base reactions... 

In an early work by Mertz and Pettitt, an open system was devised, in which an extended variable, representing the extent of protonation, was used to couple the system to a chemical potential reservoir [67], This method was demonstrated in the simulation of the acid-base reaction of acetic acid with water [67], Recently, PHMD methods based on continuous protonation states have been developed, in which a set of continuous titration coordinates, A, bound between 0 and 1, is propagated simultaneously with the conformational degrees of freedom in explicit or continuum solvent MD simulations. In the acidostat method developed by Borjesson and Hiinenberger for explicit solvent simulations [13], A. is relaxed towards the equilibrium value via a first-order coupling scheme in analogy to Berendsen s thermostat [10]. However, the theoretical basis for the equilibrium condition used in the derivation seems unclear [3], A test using the pKa calculation for several small amines did not yield HH titration behavior [13],... 

However, this simple picture only applies to gases that do not undergo reactions in the boundary layers. For gases that do react, for example through hydration and acid-base reactions, the net flux depends on the simultaneous movement of all the solutes involved, and the flux will not be the simple function of concentration expressed in Equation (3.25). An example is CO2, which reacts with water to form carbonic acid and carbonate species-H2C03, HCOs and COs . The situation is complicated because the exchange of H+ ions in the carbonate equilibria results in a pH gradient across the still layer, and it is therefore necessary to account for the movement of H+ ions across the still layer as well as the movement of carbonate species. The situation is further complicated in the case of CO2 by the kinetics of hydration and dehydration, which may be slow in comparison with transport. 

An important practical problem in ricefields is the loss of N fertilizer through volatilization of NH3 from the floodwater. Loss of NH3 is sensitive to the pH of the floodwater, and hence is intimately linked to the dynamics of dissolved CO2 (Bouldin and Alimago, 1976). To quantify this it is necessary to consider the simultaneous transfers of CO2 and NH3 across the air-water interface and their coupling through acid-base reactions. There is an equation of type (3.33) for the flux of NH3 across the still air layer and, as for the dissolved CO2 and carbonate species, the flux across the still water layer is... 

Kirk GJD, Rachhpal-Singh. 1992. Simultaneous transfer across an air-water interface of gases that interact through acid-base reactions. Atmospheric Environment 26A 1651-1660. 

Forward and reverse acid-base reactions proceed simultaneously and can therefore be represented as occurring at the same time by using two oppositely facing arrows ... 

The characteristic features of parameter estimation in a molecular model of adsorption are illustrated in Table 9.9, taking the simple example of the constant-capacitance model as applied to the acid-base reactions on a hydroxylated mineral surface. (It is instructive to work out the correspondence between equation (9.2) and the two reactions in Table 9.9.) Given the assumption of an average surface hydroxyl, there are just two chemical reactions involved (the background electrolyte is not considered). The constraint equations prescribe mass and charge balance (in terms of mole fractions, x) and two complex stability constants. Parameter estimation then requires the determination of the two equilibrium constants and the capacitance density simultaneously from experimental data on the species mole fractions as functions of pH. 

Because the enolate ion is the preferred resonance structure so a better mechanism for the acid base reaction shows the enolate ion being formed simultaneously as the acidic proton is lost (Following fig.). As the hydroxide ion forms its bond to the acidic proton, the C-H bond breaks, and the electrons in that bond form a rbond to the carbonyl carbon atom. Simultaneously, the carbonyl n bond breaks in such a way that both electrons move onto the oxygen. The electronegative oxygen is responsible for making the a proton acidic. 

This plasma also contains other ions. The advantage derives from the simultaneous presence of thermal electrons, allowing the capture of electrons, and of a basic ion, OH, which reacts with acidic compounds in the most classical acid-base reaction. Because of the presence of the methane, the same mixture is also suitable for positive ion production. 

An acid and a base always work together in the transfer of a proton. In other words, one species behaves as an acid only if another species simultaneously behaves as a base, and vice versa. Even when an acid or a base merely dissolves in water, an acid-base reaction occurs because water acts as the other partner. Consider two typical acidic and basic solutions ... 

Oxidation-reduction reactions or redox reactions are defined as a family of reactions in which electrons are transferred between species. The species that receives electrons is reduced and that donates electrons is oxidized. Similar to acid-base reactions, redox reactions are always a matched pair of half-reactions. An oxidation reaction cannot occur without a reduction reaction occurring simultaneously. 

Johannes Nicolaus Brensted (1879-1947) was a Danish physical chemist who, simultaneous with Thomas Lowry, introduced the protic theory of acid-base reactions in 1923. 

Bronsted, Johannes Nicolaus (1879-1947) Danish physical chemist in 1923 he introduced the protonic theory of acid-base reactions, simultaneously with the English chemist Thomas Martin Lowry. 

Amine plus alkoxysilane, from modification at one end of the polymer chain only, opens the way to modification at both ends, by the amine and alkoxysilane respectively, so achieving an acid/base reaction and alkoxy reaction with silica simultaneously and with the same polymer. An improvement of nearly twofold in tensile strength, wear resistance and heat emission can be achieved. 

Thus in a mixture of pyridine and cresol, tetra-O-methylglucose was found to mutarotate, whereas in either pyridine or cresol, mutarotation was insignificant 54h). Lowry, therefore, proposed that the mutarotation of sugars is basically a ternary reaction involving simultaneous acid-base catalysis. The ternary reaction involves the simultaneous transfer of a proton from the acid catalyst to the sugar in the same step that a proton is trans-... 

From this perspective, an acid-base reaction occurs when one species donates a proton and another species simultaneously accepts it an acid-base reaction is thus a proton-tranter process. Acid-base reactions can occur between gases, in nonaqueous solutions, and in heterogeneous mixtures, as well as in aqueous solutions. 

Two important reactions involving coenzyme A are worthy of mention the first is the oxidative decarboxylation of pyruvate to acetyl-coenzyme A, which is catalyzed by the multienzyme complex, pyruvate dehydrogenase. This reaction involves a series of steps mediated by five coenzymes, during which a series of acid-base reactions and nucleophilic displacements take place, with pyruvate being oxidized and converted to acetyl-CoA. Another essential series of reactions involving acetyl-CoA is that of fatty acid synthesis. Here acetyl-CoA is converted to malonyl-CoA through condensation of the enzyme-bound thioester, with the occurrence of simultaneous decarboxylation. 

For simplicity of presentation individual mechanisms have been emphasized until now. However, in practice, various different defect states occur simultaneously. Their distribution, i.e. their concentration, can be obtained from solution of the overall reaction scheme. This will be treated systematically in Chapter 5. Here we just mention that oxygen vacancies cannot only be destroyed by redox reactions but also by pure acid-base reactions. Thus, H2O can be dissolved in many oxides with the formation of internal OH groups (OH" on 0 positions). According to... 

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

The reversible reaction between a solid solute and its ions in aqueous solution is never the sole process occurring. At the very least, the self-ionization of water also occurs, although we can generally ignore it. Other equilibrium processes that may occur include reactions between solute ions and other solution species. Two possibilities are acid-base reactions (Section 18-7) and complex-ion formation (Section 18-8). Calculations based on the Ksp expression may be in error if we fail to take into account other equilibrium processes that occur simultaneously with solution equilibrium. We have encountered the dissolution of Pbl2(s) several times already in this chapter. However, the dissolution process is, in fact, a lot more complex than we ve shown. As suggested below, there are many competing processes ... 

There are two philosophies regarding how to best slow a runaway reaction. One view holds that simple water deluge is the best method as it provides immediate cooling and dilution. The anti position is that the batch should be deluged and neutralized simultaneously. Kumpinsky reports that minimum self-heat rates occur between pH 4 and 7 [78]. Since neutralization involves production of additional heat, because the pH of a runaway batch is rarely known, and since the phenolic reactions are catalyzed by acid, base, and salt it seems likely that simple deluge is the surest method. 

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