Scholars' Mine Masters Theses Student Theses and Dissertations 1966 Kinetics and mechanisms of base-catalysed reactions Rohit Panalal Sheth Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses Part of the Chemical Engineering Commons Department: Recommended Citation Sheth, Rohit Panalal, "Kinetics and mechanisms of base-catalysed reactions" (1966). Masters Theses. 5735. https://scholarsmine.mst.edu/masters_theses/5735 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. KINETICS AND MECHANISMS OF BASE·CATALYSED REACTIONS By ROHIT PANALAL SHETH A THESIS submitted to the faculty of THE UNIVERSITY OF MISSOURI AT ·roLLA in partial fulfillment of the requirements for the degree· of MASTER OF SCIENCE IN CHEMICAL ENGINEERING Rolla, Missouri 1966 ~... ii TABLE OF CONTENTS Page TITLE PAGE • • • • • • • • • • • • • • • • • • • • • • • • • i TABLE OF CONTENTS • • • • • • • • • • • • • • • • • • • • .ii LIST OF FIGURES • • • • • • • • I I I I I I I I I • • • • • iv LIST OF TABLES • • • • • • • • • • • • • • • • • • • • • • • v GLOSSARY OF TERMS • • • • • • • • •• • • • • • • • • • • • • vi QIAPTER I. Introduction • • • • • • • • • • • • • • • • • • 1 CHAPTER II. Literature Review • • • • • • • • • • • • • • • 4 CHAPTER III. Theory •••• • • • • • • • • • • • • • • • • 27 CHAPTER IV. Experimental • • • • • • • • • • • • • • • • • 31 A. Purpose of Investigation •• • • • • • • • • • • • • 31 B. Plan of Experimentation • • • • • • • • • • • • • • 32 c. Experimental Set-Up • • • • • • • • • • • • • • • • 32 D. Analytical Techniques • • • •• • • • • • • . .· . • • 33 1. Gas Chromatography • • •• • • • • • • • • • • 33 (; 2. Operating Conditions • • • • • • • • • • • • • 34 3. Sampling • • • • • • • • • • • • • • • • • • • 34 E. Preparation of calibration Curve • • • • • • • • • 34 F. Experimentation • • • • • • • • • • • • • • • • • • 35 G. Data and Results • • • • • • • • • • • • • • • • • 35 CHAPTER V. Discussion • • • • • • • • • • • • • • • • • • • • 48 A. Discussion of Data and Results • • • • • • • • • • 48 B. Discussion of Michael Mechanism ••••• • • • • • 51 c. Signifi.cance of the Rate Constants for the Reverse Process and of the Principle of Microscopic Reversibility • • • • • • • • • • • • • • • • • • • 58 D. Objections (Reservations) • • • • • • • • • • • • • 61 iii Page CHAPTER VI. Conclusions • • • • • • • • • • • • • • • • • • 66 QIAPTER VI I. Summary • • • • • • • • • • • • • • • • • • • 68 APPENDIX A. List of Computer Programs • • • • • • • • • • • 70 1. A Program for the Calculations of Adduct Concentrations • • • • • • • • • • • • • • • • • • 70 2. A Program for the Calculations of Rate and Equilibrium Constants • • • • • • • • • • • • • • • 71 3. A Program for the Calculations of Activation Energies • • • • • • • • • • • • • • • • • • • • • 73 APPENDIX B. List of Computer Programs (Error Calculations). 75 1. A Program for Computing the Effect of Error in Temperature on Activation Energies •••••••• 75 2. A Program for Correcting Equilibrium Rate Constants •••••••••••••. •••••••• 78 APPENDIX c. List of Equipment and Materials ' • • • • • • • • 81 BIBLIOGRAPHY • • • • • • • • • • • • • • • • • • • • • • • • .83 ACKNOWLEDGEMENTS • •• • • • • • • • • • • • . .. ........ 86 • 87 VITA • • • • • •• • • • • • • • • • • • • • • • • • • • • • iv LIST OF FIGURES Figure Page 1. Standard Curve of Area-Ratio as a Function of ~1ole-Ratio • • • • • • • • • • • 36 2. Concentration of Adduct as a Function of Time (Run 1) • • • • • • • • • • 43 3. Concentration of Adduct as a Ftmction of Time (Run 2) •• • • • • • • • • 44 4. Concentration of Adduct as a Function of Time (Run 3) •• • • • • • • • • 45 S. Concentration of Adduct as a Function of Time (Rtm 4) • • • • • • • • • • 46 6. Concentration of Adduct as a Function of Time (Run 5) •• • • • • • • • • 47 v LIST OF TABLES Table Page I Reported Equilibrium Yield of Adduct at Various Temperatures • • • • •• • • • • • 9 II Experirental Data for Run 1 • • • • • • • • • 38 III Experiroontal Data for Run 2 • • • • • • • • • 39 IV Experimental Data for Run 3 • • • • • • • • • 40 v Experimental Data for Run 4 • • • • • • • • • 41 VI Experimental Data for Run 5 • • • • • • • • • 42 VII Dependence of Rate Constants on Temperature • 49 VIII Equilibrium Yields at Various Reaction .Temperatures • • , • • • • • • • • • • • • • 50 IX Activation Parameters • • • • • • • • • • • • 52 X Entropies of Activation of Some Well Studied Reactions • • • • • • • • • • • • • • 53 XI Acidities of Reaction Components • • • • • • 60 XII Rate Constants and Entropies of Activation as Functions of Ionization Constants ••••• 60 XIII Theoretical Values for ~S~Reaction • • • • • 62 vi GLOSSARY OF TERMS Ea Arrhenius activation energy 6F* Free energy of activation 6H* Heat of activation h Plank's constant Boltzman constant Rate constant Ke Equilibrium constant Ka Dissociation constant for adduct Kb Dissociation constant for base (~·Buok) Km Dissociation constant for malonic ester R Gas constant 6S* Entropy of activation T Absolute reaction temperatu~ SUBSCRIPTS f Forward process r Reverse process 1 Olapter I INTRODUCfiON Base-catalysed reactions normally involve complex series of transformations. Their kinetics is usually governed by a variety of equilibria, participating in the overall and con­ current processes as well as by competitive side-reactions that interfere with the normal course of such reactions. :-.Iechanisms which have been proposed• by and large, are primarily based on product, by-product and intermediate analyses together \vith some scattered kinetic and isotopic evidence. In the cases where kinetic studies have been attempted, highly complex mechanisms have usually been proposed due to the frequent necessity of using heterogeneous media or employing involved mathematical treatments to describe the kinetics of the base-catalysed reactions. One of the most common and the least thoroughly studied class of reactions in this general area is the "Michael Reaction". It is the name commonly assigned to the base~catalysed addition of an activated methylene compound, the addendum, to a suitably activated :olefin, the acceptor, to yield normal or abnormal and retrogression Michael adducts as illustrated below: 2 y R R y I I I I CIIR + CH CH CR I II I I (1) z Ol 0!2 z I I X X Normal Adduct R R R X I I I I CH CH •., CH + CH2 I I II I CH z CR z I X/" y y Abnormal Adduct Retrogression Ad ducts where, Y and Z may be COOR, COR, CONH2, N02, S02R, CN or OIO•Y and X may be the same or different than z. Even though the l--lichae 1 reaction has been known since 1887, there are no thorough kinetic studies reported of typical systems in any abstracted publication. In the late 1940's studies were begtm by Shafer, Loeb and Johnson (43) on the abnormal Michael reaction. Later studies by Korst (25) and by Wulfman (52) indicated the need for thorough kinetic studies of both abnormal and normal Michael Reactions before any definitive mechanism could be proposed for these reactions. Wulfrnan (52), in his original studies, observed initial pseudo "first-order" followed by pseudo zero-order kinetic paths for the normal Michael reaction. These observations were taken to imply a change from homogeneous to heterogeneous media as the reaction proceeds coupled with fortuitous relationships between the various terms required to describe reaction kinetics. 3 ~1ehta (31) avoided these problems by using dilute solutions and by deriving an improved mathematical model for the rate law, which took into account the acidity of the product and sol vent as we 11 as that of the starting material. The study by Mehta (31) of a typical Michael reaction - ethyl crotonate, dimethyl malonate, t-butyl alcohol (solvent) and potassium tertiary butoxide (catalyst) with various initial co~ cent rations of reactants indicated that the kinetics of the system was consistent with the generally accepted Michael mechanism. The work presented here was undertaken to test the validity of the existing Michael mechanism through the use of thermodynamic interpretation of the experimentally obtained kinetic data. The investigation involved the study of the effect of temperature variations on the rate of the Michael reaction. Activation energies and entropies of activation were determined by conventional methods and their magnitudes were applied to furnish valuable clues to the true mechanism of the Michael reaction. 4 Chapter II LITERATURE REVIEW The ~tichael reaction or addition, in its original scope, is the addition of an addendum or donor containing an active n~thylene group to a conjugated carbon-carbon double bond (4). It can be adequately described by the reversible and .base­ catalysed addition of diethyl malonate (I), an addendum containing an activated methylene group, to methyl crotonate (II), an acceptor \"i th an activated double bond, to yield 1,1 - dicarbethoxy - 3 - carbomethoxy - 2 - methyl -propane (III) (Chart 1). Product (III) is referred to as the normal Hichael adduct, and the reaction sequence leading to (III) is known as the normal ~1ichael reaction or addition. The scope of the Hichael Reaction has been surveyed by Conner and ~1cClellan (7) and there have been more recent extensions of their review. Some of the numerous variations of the Michael Reaction are