Kinetics in Acid Media

Abstract

Catalysts f o r the condensation of obenzoylbenzoic acid to anthraquinone in the presence of concentrated and .fuming sulfuric acid have been sought by kinetic measurements; flasks were held at constant temperature in an oil thermostai and other conditions were varied systematically. The only added substance which promoted the reaction velocity was sulfur trioxide. A study of this reaction in fuming acids of various concentration established that the reaction is unimolecular, practically quantitative, inhibited by the water and t o a greater extent by the anthraquinone formed during the reaction. These lastphe-LTHOUGH catalysis was recognized more than EI hundred years ago, our knowledge of catalytic phenomena is for the most part still uncoordinated.Reactions of organic materials in sulfuric acid media disclose widely varying effects and useful products obtainable in achieving esterification (63), dehydration (69), hydration(1, $3, 68, 64), alkylation (4, 6, 28, 35, 36, 37, 40, 57), condensation (20, 34, %), polymerization (3, 32, 39, 41, @, 62) and molecular rearrangement (9, H), but no comprehensive explanation of the kinetics has been advanced.Changing solvents for reactions have been noted to change rates sixfold (7), two thousand fold (@), and one and a half million fold (84, 25). To explain these phenomena, investigators have used different properties of the solvent to account for the results: cohesion (66), refraction (11), viscosity (29), solvent power (IQ), and dielectric constant (31,43, 67). No general interpretation, therefore, exists to explain the retarding or accelerating action of solvents. The tendency for catalysis may be less a function of the general factors in experimental conditions than of temperature, time, pressure (when phase is gaseous and order is higher than unimolecular) , and solvent factors.Kinetic studies of the decomposition of organic acids by sulfuric acid were initiated in 1906 by Bredig and Lichty (5). The unusual effects noted in the sulfuric acid decomposition of oxalic acid led Taylor (60) to develop his theory of negative catalysis. Wiig (72) summarized the work in this field to 1930, discussing in detail the double retarder theory. Schierz (51) studied the effects of various nitrogen compounds on the decomposition of formic acid, and in 1938 two Russians (47) noted the inhibitory effects of sulfur dioxide, hydrogen sulfide, phosphorus pentoxide, and arsenic pentoxide. Work on the decomposition of malic acid (l5,16, 68) showed the effects of fourteen inhibitors. A 1 Present address, Colgste-Palmolive-Peet Company, Jersey City, N. J. nomena are contrary to results previously reported in the literature. Various reaction mechanisms are discussed. The energy of activation as measured in the fuming sulfuric acid media is 26,100 calories. The temperature coeflcient for a 10' C. rise is approximately 3. The commercial implications and engineering values of the above data are: to indicate methods of determining desirable operating conditions, to suggest means f o r continuous ...