Environmentally friendly organic synthesis in supercritical carbon dioxide /
Synthesis of many specialty chemicals are carried out in organic solvents. These organic solvents are coming under close scrutiny because of their toxicity and/or their persistence in the environment. Therefore, there is a great push in the industry today to replace these organic solvents with envir...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731990231&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Synthesis of many specialty chemicals are carried out in organic solvents. These organic solvents are coming under close scrutiny because of their toxicity and/or their persistence in the environment. Therefore, there is a great push in the industry today to replace these organic solvents with environmental benign solvents, such as supercritical fluids. In this study, supercritical carbon dioxide (scCO₂) was used as the reaction medium to replace the conventional organic solvents. Our objective is to answer the fundamental question "is it feasible and perhaps even more advantageous to carry organic synthesis reactions in supercritical fluids?" Specifically, (1) Diels-Alder reaction between isoprene and methyl acrylate was carried out in scCO₂ in the temperature range 110-140 °C and pressure range 96.4-179.2 bar in a 300 mL autoclave. It was observed that in the vicinity of the reaction mixture critical loci, the reaction rate constant decreases with increasing pressure, while the selectivity remains unchanged. Transition-state theory was used to explain the effects of pressure on reaction rate and selectivity. (2) Asymmetric homogeneous catalytic hydroformylation of styrene was then carried out in scCO₂ at the temperature range 65-80 °C and the pressure range 144.8-199.9 bar. Catalyst used in this reaction is {[(COD)Rh(Et-DuPHOS)]+BARF-}. A mechanism cycle was proposed for this reaction and a kinetic model was developed based on this mechanism cycle. SIMUSOLV was used to fit the experimental data to obtain the best fit model parameters. The kinetic model was found to be consistent with the general trends of the reaction conversion profile. The styrene hydroformylation reaction rate was found to increase with pressure while reaction regioselectivity was decreased at constant temperature. Partial molar volumes of reactants and transition-state compounds were related to pressure effects on reaction rate and regioselectivity based on transition-state theory. Simulated regioselectivity was compared to experimental data using infinite solution model, real mixture model, and real mixture model with regressed interaction coefficients respectively. Through these model simulations, an understanding of reaction rate and selectivity control by adjustments of pressure was developed in this study. |
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| Item Description: | Vita. "Major Subject: Chemical Engineering". |
| Physical Description: | xiii, 126 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 107-110). |