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Oxidative Cleavage of Cyclopropanes Witpi Mercuric Acetate

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Oxidative Cleavage of Cyclopropanes Witpi Mercuric Acetate This dissertation has been microfilmed exactly as received 69 -11,697 ROBINS, Richard Dean, 1942- OXIDATIVE CLEAVAGE OF CYCLOPROPANES WITPI MERCURIC ACETATE. Tlie Ohio State University, Ph.D., 1968 Chemistry, organic University Microfilms, Inc., Ann Arbor, Michigan OXIDATIVE CLEAVAGE OF CYCLOPROPAKES WITH MERCURIC ACETATE DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University By Richard Dean Rotins, B.A., M.S. The Ohio State University 1968 Approved ty Adviser Department of Chemistry DEDICATION To life. ii ACKNOWLEDGMENT To Professor Robert J. Ouellette I extend my gratitude for the origination of this problem, his invaluable assistance during the course of this investigation, and above all for his sincere effort in aiding me to become a competent chemist. I would also like to extend a special note of thanks to Dr. Aubrey South. Ill VITA November 19; 1942 Born - N. Manchester, Indiana 1964............. B.A.; Manchester College, N. Manchester, Indiana 1966 ............. M.S., The Ohio State University, Columbus, Ohio 1964-1965 ....... Teaching Assistant, Department of Chemistry, The Ohio State University, Columbus, Ohio 1965-1968 ....... Research Associate, Department of Chemistry, The Ohio State University, Columbus, Ohio PUBLICATIONS ''Oxidative Cleavage of Cyclopropanes. IV. Kinetics of the Cleavage of Arylcyclopropanes by Merciuric Acetate,'' J. Am. Chem. Soc., 90, 1619 (1968). ''1 ,3-Acetoxyl Participation in the Solvolysis of Organomercury Compounds (l),'' Tetrahedron Letters, 397 (1968). FIEKDS OF STUDY Major: Organic Chemistry Studies in Organic Chemistry. Professors Melvin Newman, Harold Shechter, Leo Paquette, Gideon Fraenkel and Robert J. Ouellette Studies in Physical Chemistry. Professors Frank Verhoek and George MacWood Studies in Inorganic Chemistry. Professors Daryl Busch and Andrew Wojcicki iv CONTENTS Page ACKNOWLEDGMENT..................................... iii VITA .............................................. iv TABLES............................................ vi ILLUSTRATIONS..................................... vii INTRODUCTION ...................................... 1 KINETICS OF THE REACTION OF MERCURIC ACETATE WITH PHENYLCYCLOPROPANES.......................... 6 COMPARISONS OF SELECTED HEAVY METAL ACETATES......... 24 1,5-ACETOXYL PARTICIPATION IN TÎIE SOLVOLYSIS OF ORGANOMERCURY C O M P O U N D S.......................... 59 THE CLEAVAGE OF OTHER CYCLOPROPANES BY MERCURIC ACETATE....................... 43 EXPERIMENTAL...................................... 49 APPENDIX.......................................... 68 REFERENCES CIT E D ................................... 69 V TABLES Table Page 1. Decomposition of Mercuric Acetate ................... 10 2. Rate of Cleavage of Substituted Arylcyclopropanes . 15 5 . Activation Parameters for the Cleavage of Arylcyclopropanes ............................... 15 k. Effect of Addends on Rate at 5 0 ° ................... I8 5 . Rate Constants for Cleavage by Ion Pair at 25° .... 35 6 . Lead Tetraacetate Decomposition at 2 5 ° ............. 55 7. Solvolysis of Organomercury Compounds ............... 4l 8. Rate of Bicyclic Cleavage by Mercuric Acetate ........ 45 9* Bicyclic Type Cleavage from Thallium Triacetate .... 44 10. Relative Rates of Cleavage by Cleavage T y p e .......... 45 11. Relative Rates of Tosylate Solvolysis ............... 46 12. Activation Parameters for the Cleavage of Selected Bicyclics ............................. 47 1 5 . Visible Spectroscopy D a t a ........................... 67 VI ILLUSTRATIONS Figui'e Page 1. Typical Second Order Plot at 50*1° for the Reaction of p-methylphenylcyclopropane with Mercuric Acetate ........................... 9 2. Kinetic Plot for Mercuric Acetate Decomposition at 75° Assuming 0.33 Order Reaction............... 11 3. Hammett a"*" Plot at 50.1°........................ 17 h. Ultraviolet Spectrum of Phenylcyclopropane and Mercuric Acetate in Methanol .................. 23 5- Free Perchloric Acid Dependence on ZPb^^ at O.O6 I F [HClO^lo and 0.02 M[Pb+4]o.................. 30 6 . Graphical Determination of k for p-Methylphenylcyclo- propane at 24 . 9 ° ................................ 32 7. Hammett Plot of log k'*' versus at 2 4 . 9 ° ....... 35 VI1 INTRODUCTION The chemistry of cyclopropanes has been extensively investigated in recent years. This study deals with the reaction of electrophiles with highly strained substituted cyclopropanes. Most electrophilic reagents that react with olefins also attack cyclopropane bonds to give products resulting from ring cleavage. Many such reactions are summerized in Lukina's^ review on the structure and reactivity of cyclopropanes. Physical and theoretical chemists became interested in cyclopro- panes and suggested models to explain their reactivity.^ Coulson and Moffitt^ revised previous theories by considering that the hybridization of the carbon-carbon bonds is different than that of the carbon-hydrogen bonds, and that neither is sp^ nor spS. Using this model Ingraham® calculated that the bent endo-ring orbitals are sp^'i® and the exo-ring orbitals, sp®‘®®. Ingraham suggested that these p-weighted internal cyclopropyl bonds are well placed for conjugation with unsaturated groups. Conjugation between cyclopropane rings and unsaturated substi­ tuents was first observed by Kizhner^ in I915 a,nd later by Robinson^ in 1916. The review by Lukina^ presents several examples of cyclopropyl conjugation effects. Cyclopropane rings have also been shown to act as proton-acceptor groups in hydrogen bonding.® Other physical evidence has been presented demonstrating that cyclopropanes are more similar to olefins than alkanes. Linnett^ found 1 the force constant for carbon-hydrogen stretching in cyclopropane is 5 .0 X 10^ dynes/cm as compared to those of methane and ethylene, being H .79 X 10^ and 5 .I x 10^ dynes/cm, respectively.® The C^®-H coupling constants are a measure, of hybridization of that bond.® Muller^® and coworkers found a coupling constant of 16 I cps for cyclopropane, com­ pared to 125 and 156 cps found for methane and ethylene, respectively. Roberts^^ and coworkers reported that based on carbon-carbon coupling constants the hybridization of the orbitals used in forming the internal bonds is sp® and that for the external bonds is sp^. An elementary molecular orbital treatment of cyclopropane by Handler^® also suggests that the external bonds are close to sp^ hybridization. A recent sum­ mary of the description of bonding in cyclopropanes was given by Bernett.^® The strain of the small ring is the ultimate reason for all the above anomalies relative to most cycloalkanes. Based on strain free cyclohexane, Seubold^'^' found the strain energy to be 2J.k kcal/mole. The direction of cyclopropane ring opening in substituted cyclo- propanes by electrophilic reagents is of interest. The ring cleavage can be considered to involve initial electrophilic attack to give an intermediate carbonium ion. Therefore, the stability of the generated charge should determine which bond is attacked and the direction of 1 opening. The cleavage of a carbon-carbon single bond as the result of a direct bimolecud.ar reaction with an electrophile is fundamentally a simple reaction. Such an attack is designated, 8^2 in the Hughes-Ingold 3 terminology. In this type of reaction the electrophilic reagent may be thought to displace a carbonium ion. I I + I I — Ç— C— + E -> — Ç+ + — C— E Of the many possible combinations of electrophiles and leaving groups that can be envisaged as participants in Sg2 processes, only electro­ philic attack on carbon-metal bonds has been examined in any detail. The only case where carbon-carbon single bonds have been shown to be cleaved by electrophilic reagents is in compounds containing a cyclopro­ pane ring. Cyclopropane ring cleavage by reagents, now classified as electro­ philes, to yield adducts has been known since the 19th century.The cleavage process can be interpreted in terms of initial electrophilic attack to produce an intermediate of carbonium ion-like character fol­ lowed by addition of a nucleophile. The degree of synchronization of“ attack by the electrophile and the nucleophile is a subject of some interest. In general the direction of cyclopropane ring cleavage is thought to reflect the stability of the incipient carbonium ion.® Most early investigations dealt with the problem of position of ring cleavage as a function of substitution. It has been generalized that Markovnikov's rule can be applied to the reactions of cyclopropanes as well as of olefins. However, the generalization clearly has to be modi­ fied to include the effect of other factors, such as ring strain and steric accessibility to the reagent. Of these two factors only ring strain has heen examined in detail. In a thorough study of the acid- catalyzed addition of acetic acid to hicyclo[n. 1.0]alkanes LaLonde^”^ and covorkers observed that the extent of internal "bond cleavage increases with decreasing values of n. In a similar manner the cleavage of the same class of compounds hy thallium triacetate and lead tetraacetate has heen observed to exhibit the same trends.Levina^® has cleaved the hicyclo[n.1 .0 ]alkanes with mercuric acetate, hut the details of this reaction have not heen examined as extensively as with acid, thallium triacetate and lead tetraacetate. The stereochemistry of the ring cleavage of cyclopropanes has heen examined only recently. LaLonde and coworkers have shown that
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