Catalysis by hydrogen ions

Reaction (7) is the source of free radicals. It is similar to the reaction 

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For suitable substances the average life-time of the hydrated or unhydrated species can be deduced from the broadening of nuclear magnetic resonance lines. This has recently been applied to acetaldehyde (Evans et al., 1965 Ahrens and Strehlow, 1965) and to isobuty-raldehyde (Hine and Houston, 1965) the velocities deduced for catalysis by hydrogen ions are in fair agreement with those obtained by other methods. 

Catalysis by transition metals in liquid-phase oxidation has been thor- oughly investigated. The roles of other ions have not been sufficiently studied. This paper is concerned with catalysis by hydrogen ions and some anions, in the chain oxidation of secondary alcohols such as cyclohexanol and 2-propanol. Secondary alcohols, because of their polarity, are convenient for studying ionic homolytic reactions and their role in chain oxidation. 

The decomposition of the intermediate in the catechol oxidation is first-order and is subject to catalysis by hydrogen ions, viz. 

In a biochemical context, superacid catalysis is sometimes used to denote catalysis by metal ions, analogous to catalysis by hydrogen ions. 

Another reactive system is based on the diepoxides. In the case of l,2 3,4-dianhydroerythritol, it has been shown that the rate of the alkali-catalyzed reaction at room temperature is proportional to the product of the concentrations of the hydroxyl ion, the diepoxide, and the cellulose. Catalysis by hydrogen ion is very slow and, for efficient reaction, zinc fluoborate at elevated temperatures has been used. 

If we find experimentally kD > kH in a catalyzed reaction, then an acid-base equilibrium must always be involved in the kinetic scheme. If the reaction involves only one proton transfer, then the converse is also true for catalysis by hydrogen ions, i.e., if kB > fcD, then there is no pre-equilibrium. On the other hand, in a reaction involving two successive proton transfers the pre-equilibrium and the subsequent proton... 

There are two instances in which the value of kD/kH depends upon the conditions under which a reaction is carried out. In the acid-catalyzed hydrolysis of ethyl orthocarbonate Wynne-Jones (110) finds fcD/fcH > 1 for catalysis by hydrogen ions, but kD/kK < 1 for catalysis by acetic acid. 

The correlation between rates and acid strengths was noted by Snethlage when it had become evident that acid catalysis could be separated into a catalysis by hydrogen ion and one by the undissociated acid. This correlation was expressed quantitatively by... 

It follows from eq. (2.4) that at high acid concentrations, catalysis by hydroxide ions is minor, while at high base concentrations, catalysis by hydrogen ions is minor. 

The observation of specific catalysis by hydrogen ions in both aqueous and ethanolic solution suggests that for ethyl diazoacetate the first step in Equation (88) is at equilibrium, and the second step rate-determining. This is confirmed by several other observations. In the first place, the reaction takes place about three times faster in D2O than in The subject... 

As our third example of reactions of diazo-compounds we shall consider the decomposition of the diazoacetate ion, which is extremely sensitive to catalysis by hydrogen ions and other acidic species. It was first studied kinetically by King and Bolinger, but their results show certain anomalies which remained unexplained for many years. In the solutions studied, the only detectable process is N2CHCO2 +H2O -> CH2OHCO2 +N2, and the reaction can be followed conveniently by measuring the nitrogen evolved. Diazoacetates are fairly stable in concentrated alkalis, but... 

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