Eastern Illinois University The Keep Masters Theses Student Theses & Publications 2001 The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces Jeannine M. Christensen Eastern Illinois University This research is a product of the graduate program in Chemistry at Eastern Illinois University. Find out more about the program. Recommended Citation Christensen, Jeannine M., "The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces" (2001). Masters Theses. 1569. https://thekeep.eiu.edu/theses/1569 This is brought to you for free and open access by the Student Theses & Publications at The Keep. It has been accepted for inclusion in Masters Theses by an authorized administrator of The Keep. For more information, please contact [email protected]. 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PLEASE SIGN ONE OF THE FOLLOWING STATEMENTS: Booth Library of Eastern Illinois University has my permission to lend my thesis to a repu~ college or university for the purpose of copying it for inclusion in that instifutiqh's library or research holdings. asfo~/o/ Date 1 respectfully request Booth Library of Eastern Illinois University NOT allow my thesis to be reproduced because: Author's Signature Date thesis4_form The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces (title) BY Jeannine M. Christensen THESIS SUBMITIED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Masters of Science in Chemistry IN THE GRADUATE SCHOOL, EASTERN ILLINOIS UNIVERSITY CHARLESTON, ILLINOIS 2001 YEAR I HEREBY RECOMMEND THIS THESIS BE ACCEPTED AS FULFILLING THIS PART OF THE GRADUATE DEGREE CITED ABOVE ,:;/~ /01 r I DATE DATE The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces Jeannine M. Christensen Eastern Illinois University January 11, 2001 The Reactivity of Boron and Aluminum Compounds with Silica Gel Surfaces By: Jeannine M. Christensen Advisor: Dr. Jonathan P. Blitz Co-Advisor: Dr. Carol A. Deakyne Date Submitted: January 11, 2001 Approved by the thesis committee: Date I I I I . • I . 11 /()I ·Date Date ABSTRACT The unmodified silica gel surface contains isolated silanols, vicinal silanols, and siloxane species. Silica gels can be thermally and/or chemically treated to obtain a desired surface. Hexamethyldisilazane (HMDS) was used to chemically modify the silica gel to obtain a surface that contains vicinal silanol groups and siloxane species. The silica gel was thermally treated at 600°C to create a surface that contains isolated silanols and siloxane species. Four types of silica gels (unmodified, 600°C, HMDS and 600°C/HMDS) were reacted with three boron compounds. The boron compounds used were boron trichloride (BCb), triethyl borane (B(CH2CH3)3) and triethyl borate (B(OCH2CH3)3). To determine the behavior of the surface species with the boron compound used, infrared spectroscopy and elemental analysis techniques were used. Infrared spectroscopy studies showed that BCb reacted with isolated silanol groups, vicinal silanols and siloxanes on the silica gel surfaces. The reactions of B(CH2CH3h and B(OCH2CH3)3 with the silica gel surfaces were found to have an effect on isolated silanols and siloxane species, but not on vicinal silanol groups. The spectra of B(CH2CH3)3 modified silca gels were compared to Al(CH2CH3)3 modified silica gels and very little difference was found. With both Al(CH2CH3)3 and B(CH2CH3)3, residual vicinal silanol bands were found in the spectra of the unmodified and HMDS silica gel. Elemental analysis of the modified silica gels was used to determine the amount of boron chemisorbed on the silica gel surface. The reactivity trend of boron compounds was found to be BCb >B(OCH2CH3)3 >B(CH2CH3)3. The reaction of BCb with the silica gel surfaces was shown to have a reactivity trend of unmodified> 600°C > HMDS > 600°C/HMDS. The reactivity trend for the reaction of B(CH2CH3)3 and B(OCH2CH3) with the silica gel was as follows: unmodified > 600°C > 600°/HMDS > HMDS. The reactivity trend of B(CH2CH3)3 and B(OCH2CH3)3 differed from BCb due to the fact that vicinal silanol species are not reactive with these boron compounds. The elemental analysis of B(CH2CH3)3 modified silca gel was compared to Al(CH2CH3)3 silica gel and it was found that there was a larger amount of aluminum being adsorbed to the silica gel surface. Ab initio calculations were performed to understand the difference in reactivity between the aluminum (AICb and Al(CH2CH3)3) and boron (BCb and B(CH2CH3)3) compounds with an isolated silanol group. Molecular geometries were optimized completely at both the HF/6-31G(d,p) and MP2/6-31(d,p) levels of calculation. The optimum geometries were then used to compute the single­ point energies that were used to evaluate reaction enthalpies and free energies. For the overall reactions, the changes in enthalpy and free energy are negative. Complete reaction pathways were determined for the AICb and BCb reactions with an isolated silanol. Locating the transition states for Al(CH2CH3)3 and B(CH2CH3)3 reaction pathways has proven difficult. ii DEDICATIONS I would like to dedicate this work to my family, especially to my wonderful parents, Wesley and Kathleen Christensen. They have given me the love, support and encouragement I needed to complete this study. To my Dad, thank you for all of your supportive phrases, including "TCB-it". To my Mom, thank you for always knowing how to take my stress away. My sisters, Kristine and Kathy, for their comedic abilities in making me laugh when I didn't think I could. And a great big thank you to everyone who helped me in the process. I couldn't have done it without you. "You were always there to help me You were always there . to guide me You-were always there to laugh with me You were always there to cry with me But most important you were always there to love me and I want to assure you that I am always here to love you" Susan Polis Schutz iii ACKNOWLEDGMENTS I would like to thank both Dr. Jonathan P. Blitz and Dr. Carol A. Deakyne for allowing me to be a part of this research project and for their never-ending patience and guidance throughout. My professional discipline and understanding of chemistry has grown enormously as the result of the enriching time spent with these outstanding educators. My effort spent working on this thesis has provided a quality educational experience and has given me the research capability to continue to grow professionally. Also, I would like to thank the educators and staff within the Chemistry Department for their valuable assistance during my time at Eastern Illinois University. My experience at Eastern Illinois University has been both valuable and rewarding. Thank you, all; for helping me achieve my goals. iv TABLE OF CONTENTS Abstract Dedications iii Acknowledgments iv Table of Contents v List of Tables vii List of Figures viii Chapter I: Introduction and Background A. Introduction 1 B. Silica Gel Surfaces 1 C. Modified Silica Surfaces 3 D. Boron Compounds 4 E. Aluminum Compounds 9 F. Computational Chemistry 12 G. Schrodinger Equation 14 H. Born-Oppenheimer Approximation 14 I. Linear Combination of Atomic Orbitals (LCAO) 15 J. Hartree-Fock Theory 16 K. M011er-Plesset Perturbation Theory 16 L. Basis Sets 17 M. Types of Basis Sets 18 N. Notations Used in Basis Sets 19 0. Reaction Enthalpies and Free Energies 20 v Chapter II: Experimental Section A. Materials 24 B. Methods 24 C. IR Analysis Preparation 25 D. Liquid IR Preparation 26 E. Quantitative Data Analysis 27 F. Computational Methods 28 Chapter Ill: Results and Discussion A. Infrared Studies of the Silica Gel Surface 29 B. Infrared Studies of Silica Gels Reacted with Boron Compounds 30 1. Boron Trichloride (BCb) 31 2. Triethyl borane (B(Et)3) 34 3. Triethyl borate ·(B(OEth) 36 C. Elemental Analysis 39 D. B(Eth versus Al(Eth 42 E. Computational Results and Discussion 44 F. Geometrical Parameters 44 G. Reaction Thermochemistry 48 Chapter IV: Conclusion A. Conclusion 51 References 54 Appendix A 57 vi List of Tables: Table 1: Elemental Analysis for Statistical Calculations Table 2: Summary of Band Assignments Table 3: Isolated Silanol/Siloxane Ratio Table 4: Elemental Analysis of Boron Compound Reactions Table 5: Elemental Analysis of B(Eth versus Al(Eth Table 6: Optimized Bond Lengths and Angles for Reactants Table 7: Optimized Bond Lengths and Angles for Complex 1 Table 8: Optimized Bond Lengths and Angles for Transition States Table 9: Optimized Bond Lengths and Angles for Complex 2 Table 10: Optimized Bond Lengths and Angles for Products Table 11: Single-Point Energies and Enthalpies (in hartrees) Corrected to 298 K for the HF/6-31G(d,p) Geometeries. Table 12: Single-Point Energies and Free Energies Corrected to 298 K for the HF/6-3.1.G(d,p) Geometeries Table 13: Single-Point Energies and Enthalpies (in hartrees) Corrected to 898 K for the HF/6-31G(d,p) Geometeries Table 14: Single-Point Energies and Free Energies Corrected to 898 K for the HF/6-31G(d,p) Geometeries Table 15: Single-Point Energies and Enthalpies (in hartrees) Corrected to 298 K for the MP2/6-31G(d,p) Geometeries. Table 16: Single-Point