Organic synthesis at high pressures

Only a brief outline of the effects of pressure on rates and equilibria is given here since the subject is amply documented elsewhere. It has long been appreciated that the position of a chemical equilibrium may be shifted by the application of external pressure in reactions in both the liquid and the gaseous phase. This shift in equilibrium favours the direction of the reaction which results in the smaller volume this is an application of the Le Chatelier s principle. In gas-phase reactions the term volume denotes the total volume of the system in dilute solutions the term volume denotes the algebraic sum of the partial molar volumes of the individual reagents and products. The thermodynamic relationship which summarizes this effect is 

For solutions, the V are partial molar volumes, that is, the volume change brought about by the dissolution of 1 mol of solute in an infinite volume of solvent. 

Equation (7.1.3) indicates that a reaction with a negative volume of activation is accelerated by pressure, whereas a reaction with a positive value of Ayt is retarded. The magnitude and the sign of the volume of activation contains information about the mechanism of the reaction, as discussed in ref. 2, Chapter 4. The following generalizations can be made. 

Positive contributions to the volumes of activation result from dissociative processes, from bond breaking, and from the relaxation of solvation due to charge neutralization. 

For multistep reactions, the measured volume of activation is the sum of the activation volume for the rate-determining step and the volumes of reaction for any pre-equilibria occurring prior to the slow step. 

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Matsumoto K, Acheson R (eds) (1991) Organic synthesis at high pressures. Wiley, New York... 

K. Matsumoto and R. M. Acheson, eds., Organic Synthesis at High Pressures. Wiley, New York, 1991. 

Monographs (a) N. S. Isaacs, Liquid High Pressure Chemistry, WUey, New York 1991 (b) W. J. le Noble (Ed.), Organic High Pressure Chemistry, Elsevier, Amsterdam 1988 (c) R. M. Acheson, E. K. Matsumoto, Organic Synthesis at High Pressure, Wiley, New... 

K. Matsumoto, R. Mohrin Acheson, Organic Synthesis At High Pressures, John Wiley Sons, New York 1991. 

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