High Pressure Chemistry

Abstract

The technology associated with application of hydrostatic pressure in chemistry is presented. Apparatus and equipment range from a straightforward autoclave‐type arrangement to more sophisticated techniques of subjecting materials or chemical reactions in solution to pressure, and monitoring events caused by pressure application while the system is under pressure (ie, in situ ). Spectroscopic detection is the principal monitoring technique in in situ methods. The wide span of time ranges of changes taking place during a pressure cycle requires different types of technologies and these are described. The type of system under investigation directs the choice of method and the range of pressure applied. For synthetic and preparative solution chemistry, pressures up to a few thousand megapascals (MPa) have been used. For processing of materials to bring about a change in properties, pressures up to 600 MPa are usually adequate, whereas for most mechanistic studies pressures > 200 MPa are rarely used (1 atm = 1.01325 × 10 5 Pa; 1 Pa = 1 N/m 2 ). Examples of systems studied from organic chemistry, inorganic chemistry, bioinorganic chemistry, and colloid chemistry are provided. These clearly illustrate the value of applying hydrostatic pressure and demonstrate insight into understanding physicochemical and chemical changes that occur. Such insight is not normally achievable by other experimental approaches and highlights the unique value and success of high pressure technology in chemistry.

Application of High Pressure in the Elucidation of Inorganic and Bioinorganic Reaction Mechanisms

“…[48][49][50][51][52][64][65][66][67][68][69][70][71][72][73] Technical development recently has revolved mostly around improvements, often incremental, in aspects such as sensitivity, detection range, resolution, and particularly in data acquisition and processing. Hence, a total survey of all the variations of pressure cells, their incorporation into appropriate instruments, and their method of operation will not be repeated here.…”

“…Surveys have been reported several times in recent years. [64][65][66][67][68][69][70][71][72][73] However, some of the guiding principles and general approach in successful practice in high-pressure kinetics measurements, independent of the particular method or instrument, will be covered. Consideration of various properties, many of them obvious, and conditions of reactants and solvents for suitable design of experiments will also be noted.…”

“…The properties at issue are rates of ligand substitution and electron exchange, and the acid-base characteristics. The rate of water exchange on the Mo72 Fe 30 cluster possessing the stoichiometry, [Mo 72 Fe 30 O 252 (CH 3 COO) 12 [Mo 2 O 7 (H 2 O)] 2 [H 2 Mo 2 O 8 (H 2 O)] (H 2 O) 91 $150H 2 O has been determined by 17 O NMR experiments 237 (Scheme 7.2).…”