High pressure reactions, review

Applications of photochemical techniques to reactions between coordination compounds in solution and gases at high pressures are reviewed. The main result of increasing the pressure in gas-liquid phase systems is to increase the solubility of the gas in the liquid. The high pressure photolysis technique has been used (1) to synthesize complexes containing N > CO, or... 

An excellent review on vibrational spectroscopy in supercritical fluids was published in 1995 by Poliakoff et al. [6]. In the late 1990s, Kessler et al. [7] developed IR and Raman spectroscopy for the investigation of rapid high-pressure reactions in optical cells. Raman was preferred to IR for the determination of the decomposition rate of peroxides under high pressure. They studied the decomposition of tert-butyl peroxypivalate at pressure up to 180 MPa and temperatures of 90-160 °C. A typical Raman spectrum is presented in Fig. 5.3. 

For a review on high-pressure reactions in glass microreactors, see Verboom, W. (2009) Chem. Eng. Technd., 32,1695-1701. 

Hydration of Ethylene Usings Dilute Acids. A review of the early work on the hydration of ethylene using dilute acids, the weak acid process, has been given (48). The reaction is favored by the use of low temperatures and high pressures. Temperatures in the range of 150—250°C are the most frequendy quoted (132—137), although temperatures as low as 80°C have been reported (138). 

For a detailed treatment of the kinetics of reactions at high pressures, consult the review article by Eckert (14). 

Solvent exchange reactions have been reviewed several times in the last 10 years. A comprehensive review by Lincoln and Merbach was published in this series in 1995 (6). More recent reviews focused more on high pressure techniques for the assignment of reaction mechanisms (7-9) or on water exchange (10). This review is a follow up of the exhaustive Lincoln and Merbach review (6). The main features of solvent exchange on metal ions will be pointed out, taking into account developments and new results from the last 10 years. 

This section reviews the criteria for hazards testing of reactions on a small scale, particularly whether the experiments should be run in an open laboratory or in a high-pressure cell. 

Reviews on the activation of dioxygen by transition-metal complexes have appeared recently 9497 ). Details of the underlying reaction mechanisms could in some cases be resolved from kinetic studies employing rapid-scan and low-temperature kinetic techniques in order to detect possible reaction intermediates and to analyze complex reaction sequences. In many cases, however, detailed mechanistic insight was not available, and high-pressure experiments coupled to the construction of volume profiles were performed in efforts to fulfill this need. 

In the following sections the effect of pressure on different types of electron-transfer processes is discussed systematically. Some of our work in this area was reviewed as part of a special symposium devoted to the complementarity of various experimental techniques in the study of electron-transfer reactions (124). Swaddle and Tregloan recently reviewed electrode reactions of metal complexes in solution at high pressure (125). The main emphasis in this section is on some of the most recent work that we have been involved in, dealing with long-distance electron-transfer processes involving cytochrome c. However, by way of introduction, a short discussion on the effect of pressure on self-exchange (symmetrical) and nonsymmetrical electron-transfer reactions between transition metal complexes that have been reported in the literature, is presented. 

Recent reviews by Ertl and Engel have summarized most of the chemisorption and low pressure catalytic findings . In general, the reaction proceeds through a Langmuir-Hinshelwood mechanism involving adsorbed CO and O atoms. Under reaction conditions typical in most high pressure, supported catalyst studies, and most low pressure UHV studies, the surface is almost entirely covered by CO, and the reaction rate is determined by the rate of... 

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