Examples of reactions catalysed by acids and bases

The observation that the decomposition of isotopically labelled NH2 N02 produces only the species is in accord with this 

Turning to the kinetic studies, Bronsted and Pedersen found that in dilute solutions of strong acids the rate of decomposition at 15°C was independent of hydrogen ion concentration over a wide range (10 -0.4m). They attributed this rate to basic catalysis by water molecules, and concluded that there was no acid catalysis they also found that added neutral salts had little effect on the rate. Subsequent work in more 

Bronsted and Pedersen showed that Equation (86) is also obeyed in aniline buffers, and shortly afterwards the same was found to be the case for catalysis by seven substituted anilines. A little later the same behaviour was observed for seven cation bases, typified by [Co(NH3)50H] which can accept a proton to give [Co(NH3)5H20]. The parallel catalytic effect exerted by these bases of very different charges and chemical nature provided a firm foundation for the theory of general catalysis by acids and bases. 

In all the catalytic solutions so far considered, catalysis by hydroxide ion (or the kinetically equivalent decomposition of the nitramide anion) could be neglected, and Bronsted and Pedersen were unable to give a value for the catalytic constant of hydroxide ion. Measurements in more alkaline solutions were made at 25°C by Tong and Olson.Under these conditions the observed velocity constant is given by 

Catalysis by amines has also been investigated in a number of non-hydroxylic solvents. Thus Bell and Trotman-Dickenson studied catalysis by 21 primary, secondary, and tertiary amines in anisole at 25 C, and later work included the measurement of temperature coefficients and 

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We have established that the formation of enols is catalysed by acids and bases. The reverse of this reaction—the formation of ketone, from enol—must therefore also be catalysed by the same acids and bases. If you prepare simple enols in the strict absence of acid or base they have a reasonable lifetime. A famous example is the preparation of the simplest enol, vinyl alcohol, by heating ethane-1,2-diol (glycol—antifreeze) to very high temperatures (900 °C) at low pressure. Water is lost and the enol of acetaldehyde is formed. It survives long enough for its proton NMR spectrum to be run, but gives acetaldehyde slowly. 

A general route to 3-substituted butenolides (72), which could have considerable potential, is the cyclization of phosphonium salts (71), simply by treatment with triethylamine in methylene chloride. The salts are easily obtained from a-bromo-ketones and bromoacetic acid and, in the examples quoted in this preliminary study, overall yields are high except when 2-bromocyclohexanone was used as the ketonic component (c/. 3, 133). The 3-substituted butenolide group present in naturally occurring cardenolides can be built up from an a-methylthioketone residue by a Reformatsky reaction, followed by acid- and base-catalysed rearrangements. ... 

The early study of catalysis by acids and bases was concerned chiefly with the use of catalysed reactions for investigating general problems of physical chemistry. For example, the first correct formulation of the kinetic laws of a first-order reaction was made by Wilhelmy in 1850 in connection with his measurements of the catalytic inversion of cane sugar by acids. Catalytic reactions also played an important part in the foundation of the classical theory of electrolytic dissociation towards the end of the nineteenth century, and kinetic measurements (notably on the... 

The most widely used homogeneous catalysts are simple acids and bases which catalyse well-known reactions such as ester and amide hydrolysis, and esterification. Such catalysts are inexpensive enough that they can be neutralized, easily separated fi om organic materials, and disposed of. This, of course, is not a good example of green chemistry and contributes to the huge quantity of aqueous salt waste generated by industry. 

The term hydrolysis comes from the word hydro meaning water and lysis meaning breakdown. A hydrolysis reaction is one in which a a bond is cleaved by the addition of the elements of water to the fragments formed in the cleavage. A hydrolysis reaction is catalysed by acid, base or hydrolysing enzyme. For example, the analgesic drug aspirin (acetyl salicyhc acid) is easily hydrolysed in the presence of acid, moisture and heat to form salicylic acid. 

Overall second-order kinetics have been observed for catalysis by bases, alcohols or acids, and in the base-catalysed reactions the formation of ether groups is relatively insignificant46147). The base catalysis can be further activated by an acid co-catalyst, HA. For example any resident hydroxyl groups can act as internal co-catalysts. Tanaka and Kakiuchi48) proposed the following scheme for the reaction catalysed by base (B) with acid co-catalyst ... 

Enolisation is an example of a reaction which is catalysed both by acids and by bases. Studies in buffered solutions have shown that eqn (3) (Bell, 1959, 1973)... 

A few more vinyl halides can be made stereospecifically by halogenation and base-catalysed elimination. One example is the vinyl bromide E-28 available by stereospecific lruns bromination of crotyl alcohol 26 followed by stereospecific elimination.4 Various regioselectivities are available in the elimination reaction so the formation of that particular alkene is in a way more surprising than the stereopecificity of the reaction. Presumably the bromine atoms increase the acidity of nearby Hs (H-2 and H-3 in anti-21) so that one or other of the vinyl bromides will be formed. One explanation is an intramolecular elimination through an anti-peri-pimsa transition state in a chair like conformation using OLi as an internal base 26. It can reach H-3 in a five-membered cyclic array. 

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