Selective Free Radical Reactions using Supercritical Carbon Dioxide

2014 ◽  
Vol 136 (6) ◽  
pp. 2200-2203 ◽  
Author(s):  
Philip J. Cormier ◽  
Ryan M. Clarke ◽  
Ryan M. L. McFadden ◽  
Khashayar Ghandi
Keyword(s):  
Carbon Dioxide ◽  
Free Radical ◽  
Supercritical Carbon Dioxide ◽  
Radical Reactions ◽  
Free Radical Reactions ◽  
Supercritical Carbon

Free-Radical Chemistry in Supercritical Carbon Dioxide

2004 ◽  
Author(s):  
J. M. Tanko
Keyword(s):  
Carbon Dioxide ◽  
Free Radical ◽  
Supercritical Carbon Dioxide ◽  
Green Chemistry ◽  
Chemical Reactions ◽  
Environmentally Benign ◽  
Supercritical State ◽  
Liquid Phases ◽  
Temperature And Pressure ◽  
Supercritical Carbon

During the 1990s, the chemical industry has focused on ways to reduce and prevent pollution caused by chemical synthesis and manufacturing. The goal of this approach is to modify existing reaction conditions and/or to develop new chemistries that do not require the use of toxic reagents or solvents, or that do not produce toxic by-products. The terms “environmentally benign synthesis and processing” and “green chemistry” have been coined to describe this approach where the environmental impact of a process is as important an issue as reaction yield, efficiency, or cost. Most chemical reactions require the use of a solvent that may serve several functions in a reaction: for example, ensuring homogeneity of the reactants, facilitating heat transfer, extraction of a product (or by-product), or product purification via chromatography. However, because the solvent is only indirectly involved in a reaction (i.e., it is not consumed), its disposal becomes an important issue. Thus, one obvious approach to “green chemistry” is to identify alternative solvents that are nontoxic and/or environmentally benign. Supercritical carbon dioxide (sc CO2) has been identified as a solvent that may be a viable alternative to solvents such as CCl4, benzene, and chloroflurocarbons (CFCs), which are either toxic or damaging to the environment. The critical state is achieved when a substance is taken above its critical temperature and pressure (Tc, Pc). Above this point on a phase diagram, the gas and liquid phases become indistinguishable. The physical properties of the supercritical state (e.g., density, viscosity, solubility parameter, etc.) are intermediate between those of a gas and a liquid, and vary considerably as a function of temperature and pressure. The interest in sc CO2 specifically is related to the fact that CO2 is nontoxic and naturally occurring. The critical parameters of CO2 are moderate (Tc = 31 °C, Pc = 74 bar), which means that the supercritical state can be achieved without a disproportionate expenditure of energy. For these two reasons, there is a great deal of interest in sc CO2 as a solvent for chemical reactions. This chapter reviews the literature pertaining to free-radical reactions in sc CO2 solvent.

THE THERMAL CIS–TRANS ISOMERIZATION AND DECOMPOSITION OF METHYL CROTONATE

1963 ◽  
Vol 41 (10) ◽  
pp. 2492-2499 ◽  
Author(s):  
James N. Butler ◽  
Gerald J. Small
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Free Radical ◽  
Gas Phase ◽  
Rate Constant ◽  
Radical Reactions ◽  
Side Reactions ◽  
Free Radical Reactions ◽  
Trans Isomerization

Methyl crotonate undergoes a homogeneous, unimolecular cis–trans isomerization in the gas phase at temperatures from 400 °C to 560 °C. The rate constant for the cis → trans reaction was found to be [Formula: see text]independent of pressure in the range from 0.1 mm to 10 mm. The equilibrium trans/cis ratio is approximately 4.5, independent of temperature, from 200 °C to 500 °C. Simultaneous free-radical reactions also occur, the most important of which are the isomerization to methyl vinylacetate, and the decomposition to give carbon dioxide and the various butene isomers. Side reactions gave carbon monoxide, methane, propylene, numerous other hydrocarbons, and various ethers.

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