THE SYNTHESIS AND CHARACTERIZATION OF A SILICA-IMMOBILIZED CROWN ETHER: CHARACTERIZATION OF CHEMICALLY MODIFIED ADSORBENTS.

Persistent Link:
http://hdl.handle.net/10150/187616
Title:
THE SYNTHESIS AND CHARACTERIZATION OF A SILICA-IMMOBILIZED CROWN ETHER: CHARACTERIZATION OF CHEMICALLY MODIFIED ADSORBENTS.
Author:
ELHASSAN, AHMED MOHAMED.
Issue Date:
1983
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The effect of the physical state and chemical composition on molecular interactions has been studied for a number of chemically modified adsorbents. During the course of the study a reaction scheme was put together for the synthesis of a particular substituted crown ether. The synthesized allyl-benzo-15crown-5, which is not reported in the literature to date, was silylated and immobilized on a silica surface. The bonded phase was characterized by UV spectroscopy and by chromatography under both "normal" and "reverse" phase conditions. UV spectroscopy was also used to elucidate the physical state of several other phenyl alkyl bonded phases. Chromatographically, the bonded crown ether phase was found to be more polar than a C₈ stationary phase. A comparison of the selectivity of the two phases revealed that the former has a better selectivity towards a homologous series of alkyl benzenes under different reverse phase conditions. The selectivity of the crown ether phase was found to be dependent on the nature of the organic modifier in the mobile phase. This dependence was considered to be added evidence for the universality of the dynamic solvated stationary phase model. Both normal and reverse phase chromatographic conditions indicated an acid-base type of interaction between the crown ether and a number of substituted phenols. This was reflected in an increase in the retention of these probes as a function of their increasing acidity. A dramatic temperature effect observed on the crown ether stationary phase under aqueous THF mobile phase, but not under aqueous MeOH, was attributed to a temperature and/or solvent-induced phase change. A hysteresis effect, also seen only with aqueous THF, indicated that the crown ether phase undergoes a solvent-assisted conformational change. Further evidences for such a change was found spectroscopically in the abrupt break in the UV absorbance of these molecules as a function of temperature, as well as the irreversibility of the absorbance of the n- π* band on cooling. UV spectroscopy of bonded phenyl alkyls showed that there are about two monolayers of water molecule strongly adsorbed to the surface and totally impermeable to lypophilic species. Evidence for the existence of a solvated crystal, or liquid crystal, like clusters was rationalized with a cooperative sorption effect which may be dependent on the reaction conditions during immobilization. Despite a significant increase in the liquid character observed as the chain length is increased to 4-7 methylene groups, the bonded clusters still appear to preserve a fairly ordered environment. The physical state of the immobilized species was found to change with the experimental conditions and the change was reflected on the selectivity of the system.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Ether -- Absorption and adsorption.; Sorbents.; Liquid chromatography.; Chromatographic analysis.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemistry; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Burke, Michael F.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleTHE SYNTHESIS AND CHARACTERIZATION OF A SILICA-IMMOBILIZED CROWN ETHER: CHARACTERIZATION OF CHEMICALLY MODIFIED ADSORBENTS.en_US
dc.creatorELHASSAN, AHMED MOHAMED.en_US
dc.contributor.authorELHASSAN, AHMED MOHAMED.en_US
dc.date.issued1983en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe effect of the physical state and chemical composition on molecular interactions has been studied for a number of chemically modified adsorbents. During the course of the study a reaction scheme was put together for the synthesis of a particular substituted crown ether. The synthesized allyl-benzo-15crown-5, which is not reported in the literature to date, was silylated and immobilized on a silica surface. The bonded phase was characterized by UV spectroscopy and by chromatography under both "normal" and "reverse" phase conditions. UV spectroscopy was also used to elucidate the physical state of several other phenyl alkyl bonded phases. Chromatographically, the bonded crown ether phase was found to be more polar than a C₈ stationary phase. A comparison of the selectivity of the two phases revealed that the former has a better selectivity towards a homologous series of alkyl benzenes under different reverse phase conditions. The selectivity of the crown ether phase was found to be dependent on the nature of the organic modifier in the mobile phase. This dependence was considered to be added evidence for the universality of the dynamic solvated stationary phase model. Both normal and reverse phase chromatographic conditions indicated an acid-base type of interaction between the crown ether and a number of substituted phenols. This was reflected in an increase in the retention of these probes as a function of their increasing acidity. A dramatic temperature effect observed on the crown ether stationary phase under aqueous THF mobile phase, but not under aqueous MeOH, was attributed to a temperature and/or solvent-induced phase change. A hysteresis effect, also seen only with aqueous THF, indicated that the crown ether phase undergoes a solvent-assisted conformational change. Further evidences for such a change was found spectroscopically in the abrupt break in the UV absorbance of these molecules as a function of temperature, as well as the irreversibility of the absorbance of the n- π* band on cooling. UV spectroscopy of bonded phenyl alkyls showed that there are about two monolayers of water molecule strongly adsorbed to the surface and totally impermeable to lypophilic species. Evidence for the existence of a solvated crystal, or liquid crystal, like clusters was rationalized with a cooperative sorption effect which may be dependent on the reaction conditions during immobilization. Despite a significant increase in the liquid character observed as the chain length is increased to 4-7 methylene groups, the bonded clusters still appear to preserve a fairly ordered environment. The physical state of the immobilized species was found to change with the experimental conditions and the change was reflected on the selectivity of the system.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectEther -- Absorption and adsorption.en_US
dc.subjectSorbents.en_US
dc.subjectLiquid chromatography.en_US
dc.subjectChromatographic analysis.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorBurke, Michael F.en_US
dc.identifier.proquest8405495en_US
dc.identifier.oclc690664790en_US
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