Acid catalysis

About: Acid catalysis is a research topic. Over the lifetime, 4076 publications have been published within this topic receiving 96563 citations.

Rothemund and Adler-Longo reactions revisited: synthesis of tetraphenylporphyrins under equilibrium conditions

Abstract: We present a new synthetic strategy for preparing tetraphenylporphyrins that should greatly expand synthetic entries into porphyrin containing model systems. Pyrrole and the desired benzaldehyde react reversibly at room temperature with trace acid catalysis to form the cyclic tetraphenylporphyrinogen at thermodynamic equilibrium. An oxidant is then added to irreversibly convert the porphyrinogen to the porphyrin. The greater stability of the cyclic porphyrinogen over the open-chain polypyrrylmethanes occurs when the reaction is performed at moderate dilution (10-2 M). The reaction at high dilution or high concentration affords a negligible yield of the cyclic porphyrinogen. Porphyrinogen exchange reactions provide proof of equilibrium. This methodology is complementary to the Adler-Longo procedure, allowing small quantities of porphyrins to be prepared from sensitive aldehydes in 30-40% yield without difficult purification problems. This methodology is also extended to the preparation of meso-tetraalkylporphyrins and one hybrid porphyrin containing both aryl and alkyl substituents. The mild reaction conditions and convenience of this method permit consideration of new design strategies in preparing complex porphyrins.

Novel Brønsted Acidic Ionic Liquids and Their Use as Dual Solvent−Catalysts

Abstract: The reaction of triphenylphosphine or N-butylimidazole with cyclic sultones gives zwitterions that are subsequently converted into ionic liquids by reaction with trifluoromethane sulfonic acid or p-toluenesulfonic acid. The resulting ionic liquids have cations to which are tethered alkane sulfonic acid groups. These Bronsted acidic ionic liquids are useful solvent/catalysts for several organic reactions, including Fischer esterification, alcohol dehydrodimerization and the pinacol rearrangement. The new ionic liquids combine the low volatility and ease of separation from product normally associated with solid acid catalysts, with the higher activity and yields normally found using conventional liquid acids.

Industrial application of solid acid–base catalysts

Abstract: A statistical survey of industrial processes using solid acid–base catalysts is presented. The number of processes such as alkylation, isomerization, amination, cracking, etherification, etc., and the catalysts such as zeolites, oxides, complex oxides, phosphates, ion-exchange resins, clays, etc., are 127 and 180, respectively. The classification of the types of catalysts into solid acid, solid base, and solid acid–base bifunctional catalysts gives the numbers as 103, 10 and 14, respectively. Some significant examples are described more in detail. On the basis of the survey, the future trend of solid acid–base catalysis and the fundamental research promising for industrial success are discussed.

Heterogeneous Basic Catalysis

Abstract: Heterogeneous acid catalysis attracted much attention primarily because heterogeneous acidic catalysts act as catalysts in petroleum refinery and are known as a main catalyst in the cracking process which is the largest process among the industrial chemical processes. In contrast to these extensive studies of heterogeneous acidic catalysts, fewer efforts have been given to the study of heterogeneous basic catalysts. The types of heterogeneous basic catalysts are listed in Table 1. Except for non-oxide catalysts, the basic sites are believed to be surface O atoms. The studies of heterogeneous catalysis have been continuous and progressed steadily. They have never been reviewed in the chemical Reviews before. It is more useful and informative to describe the studies of heterogeneous basic catalysis performed for a long period. In the present article, therefore, the cited papers are not restricted to those published recently, but include those published for the last 25 years. The paper first describes the generation of basic sites before describing methods used in the characterization of basic surfaces. These are indicator methods, temperature programmed desorption (TPD) of CO{sub 2}, UV absorption and luminescence spectroscopies, TPD of H{sub 2}, XPS, IR of CO{sub 2}, IR of pyrrole, and oxygen exchange betweenmore » CO{sub 2} and the surface. The paper then discusses studies on the catalysis by heterogeneous basic catalysts. Some of these reactions are dehydration, dehydrogenation, hydrogenation, amination, alkylation, ring transformation, and reactions of organosilanes. Catalysts discussed are single component metal oxides, zeolites, non-oxide types, and superbasic catalysts. 141 refs.« less

Computer Modeling of Chemical Reactions in Enzymes and Solutions

Abstract: Basic Principles of Chemical Bonding. Chemical Reactions in the Gas Phase and in Simple Solvent Models. Chemical Reaction in All--Atom Solvent Models. Potential Surfaces and Simulations of Macromolecules. Modeling Reactions in Enzymes: An Introduction. General Acid Catalysis and Electrostatic Stabilization in the Catalytic Reaction of Lysozyme. Serine Proteases and the Examination of Different Mechanistic Options. Simulating Metalloenzymes. How Do Enzymes Really Work? Index.