PART 1 DIPOSITIVE CARBONIUM IONS PART 11 SYNTHESIS AND REACTIONS or ; TETRAMETHYLBENZOCYCLOBUTENE_ DERIVATIVES T3931: "for “10 Damn of DI}, D; MICHIGAN STATE UNIVERSITY Richard Wayne Fish 1960 THEb‘ta 1.1 BRA R Y Michigan Sm: ”,3 Unirfrsity Z<grozz .0252”: Hmfi '8 iamflis; ”Saw “29:05 PART I DIPOSITIVE CARBONIUM IONS PART II SYNTHESIS AND REACTIONS OF TETRAMETHYLBENZOCYCLOBUTENE DERIVATIVES BY Richard Wayne Fish AN ABSTRACT Submitted to the School of Advanced Graduate Studies of Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 1960 Approved ABSTRACT The primary purpose of this investigation was to determine the structure of the speciesre3ponsib1e for the intense red color observed when trichloromethylpentamethylbenzene was added to 100% sulfuric acid. Cryosc0pic measurements showed that five particles were pro- duced in the reaction. _ Two of these, swept from the solution with dry nitrogen, were hydrogen chloride. Conductance measurements on the original and the hydrogen chloride-free solutions showed that two bisulfate ions were produced. Hydrolysis of the original solution gave a nearly quantitative yield of pentamethylbenzoic acid. The hydrogen chloride-free solution gave a nearly quantitative yield of pentamethyl- benzoic acid and approximately one mole of chloride ion per mole of trichloromethylpentamethylbenzene when hydrolyzed. The best explana- tion for these data is that the fifth particle must be a stable dipositively charged carboniuxn ion (11). CH3 CH3 CH3 H3 (1) CH3 cc13 + 2sto4——> CH Q é-c1 + mm + ZHSO4' CH3 H3 CH3 CH3 I 11 This is believed to be the first reported example of a dipositive carboniurn ion. The structure of the dipositive ion was investigated by ultraviolet, visible and proton magnetic resonance spectroscopy. These spectra are compared with spectra of compounds with similar structures. ii The dication was also produced when trichloromethylpentamethyl- benzene was dissolved in trifluoroacetic acid which had been saturated with boron trifluoride. Evaporation of the solvent from the solution gave a dark red, almost crystalline residue. A colorless liquid, formed when this residue was heated under reduced pressure, was ultimately converted to pentamethylbenzoic anhydride. The mechanism of this reaction is discussed. The aluminum chloride-catalyzed reaction of.carbon tetrachloride with pentamethylbenzene, which gave excellent yields of trichloromethyl- pentamethylbenzene, was extended to the preparation of trichloromethyl- 2, 3, 4, 5-tetramethy1benzene and trichloromethyl-Z, 4, 6-trimethylbenzene. These compounds also form dipositive carbonium ions in 100%. sulfuric acid and in trifluoroacetic acid saturated with boron trifluoride. , An investigation of the thermal stability of trichloromethylpenta- -methylbenzene showed that when it is heated at 110-1250, it undergoes an intramolecular cyclization with a loss of one mole of hydrogen chloride. The product is 0., a-dichlorotetramethylbenzocyclobutene, isolated in 89% yield. Hydrolysis Of the dichloro compound gave a quantitative yield of tetramethylbenzocyclobutenone. Tetramethylbenzocyclobutenone was refluxed with deuteroethanol to determine its ability to enolize to a tetramethylbenzocyclobutadienolate anion. Although two experiments gave a ketone with the same melting point, and an infrared spectrum showing a carbon-deuterium absorption, attempts to repeat the exchange were not successful. By means of a variety of reduction procedures, it was possible to convert tetramethylbenzocyclobutenone to the corresponding. alcohol, hydrocarbon, or hexarnethylbenzene, each in good yield. Refluxing with alcoholic sodium hydroxide converted tetramethylbenzocyclobutenone to pentamethylbenzoic acid. iii PART I DIPOSITIVE CARBONIUM IONS PART II SYNTHESIS AND REACTIONS OF TETRAMETHYLBENZOCYCLOBUTENE DERIVATIVES BY Richard Wayne Fish A THESIS Submitted to the School of Advanced Graduate Studies of Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 1960 ACKNOWLEDGMENT The author wishes to express his sincere appreciation and gratitude to Professor Harold Hart for his inspiration, guidance and understanding during the course of this investigation. Grateful acknowledgment is due to Dr.. J.. L. Dye for the use of his conductance equipment and helpful suggestions on cryoscoPic and conductance measurements, and to Dr.. J.. C. Woodbrey and Mr. J.. D- Graham for determining the proton magnetic resonance spectra. ‘ i . Appreciation is extended to Dr.. E. K. Fields and Dr.. R. J. Rolih,. Standard Oil Company (Indiana), for the generous supply of pentamethylbenzene and to the Shell Chemical Corporation for the samples of durene. Appreciation is also extended to the Petroleum Research Fund of the American Chemical Society whose fellowship program pro- vided personal financial assistance from June, 1958 through June, 1960. >€<>.'<****>}<**>i<***** TABLE OF CONTENTS Page PART I DIPOSITIVE CARBONIUM IONS INTRODUCTION ........................ RESULTS AND DISCUSSION . , ................ Cryoscopic Measurements ............... Stoichiometry ....... .............. Conductance Measurements ............... 12 Interpretation . ..................... 14 DrivingForces for the Formation of Dipositive Ions. 18 Other Trichloromethylpolymethylbenzenes ....... 25 Ultraviolet and Visible Spectra ............. = 32 Proton Magnetic Resonance Spectra ...... 42 Miscellaneous Experiments ............... 50 EXPERIMENTAL ........... ........... 59 A. Syntheses ........... .......... 59 Trichloromethylpentamethylbenzene ....... 59 Trichloromethyl-2, 3, 4,, 5-tetramethylbenzene . 60 Trichloromethyl-12,4,6-trimethy1benzene.x . 64 Bromodurene................. .. 65 Durenecarboxylic acid . .I ...... 67 Prehnitene (1,2, 3,4-tetramethylbenzene). 68 (a) Decarboxylation of 2,3,4, 5—tetra- methylbenzoic acid. ......... 68 (b) Jacobson rearrangement of durene . 70 Methyl 2., 3, 5, 6-tetraxnethylbenzoate ..... 71 Methyl 2,3,4,5-tetramethylbenzoate. 73 Methyl 2, 4, 6-trimethylbenzoate . ....... 75 Pentamethylbenzoic anhydride . I. ...... 75 (a) Mixed anhydride intermediate ..... 78 (b) Reduction of pentamethylbenzoic anhydride . ....... 79 Z, 3, 4, 5, 6- PentamethylbenzoPhenone ....... 79 Pentamethylbenzophenone dichloride . ...... 82 Pentamethylbenzaldehyde ..... ...... 85 0., c-Dichloromethylpentamethylbenzene ..... 86 Chloromethylpentamethylbenzene. ...... 89 B. Structure Proof of the Trichloromethyl Compounds. 90 vi TABLE OF CONTENTS - Continued Page Reaction of trichloromethylpentarnethylbenzene- 100% sulfuric acid. ............ 90 (a) With water ................ 90 (b) With methanol . ........ 90 Solvolysis of trichloromethylpentamethylbenzene . 93 (a) With aqueous acetone. 93 (b) With methanol. .......... 93 Reaction of trichloromethyl-Z, 3, 4, 5atetramethy1- benzene-100% sulfuric acid. 95 (a)Withwater................95 (b)Withmethanol.............. 95 Solvolysis of trichloromethyltetramethylbenzene . 97 (a) With aqueous acetone . 97 (b) Withmethanol . 97 Reaction of trichloromethyl- 2, 4, 6-trimethy1- benzene-100% sulfuric acid . ....... .. 99 (a) With water . ......... 99 (b) With methanol . 99 Solvolysis of trichloromethyl- Z, 4, 6- -trimethyl— benzene............. ...... ..101 (a) With aqueous acetone . ....... 101 (b) Withmethanol . 101 C. Reaction of trichloromethylpentamethvlbenzene with trifluoroacetic acid saturated with boron tri- fluoride.......................103 D. Reaction of benzoyl chloride with phOSph -orus penta- chloride.......................105 E. Reaction of benzotrichloride with 100% sulfuric acid in the presence of several aromatic hydrocarbons 106 F. Cryoscopic Measurements . .; . .. 107 Apparatus . ...... ............ 107 Procedure........... ......... .108 Stock sulfuric acid. ....... 110 G. Conductance Measurements ............ 110 Apparatus............. ........ .110 Procedure.....................111 H. Quantitative Determination of Hydrogen Chloride from Dissolution of Trichloromethyl Compounds inSulfuricAcid..................lll Apparatus.....................lll Procedure.....................114 vii TABLE OF CONTENTS - Continued , Page I- Spectra ........................ 116 Ultraviolet and visible .............. 116 Proton Magnetic Resonance ........... 116 Infrared . .................. 116 SUMMARY ........................... 117 PART II SYNTHESIS AND REACTIONS OF TETRAMETHYL- BENZOCYCLOBUTENE DERIVATIVES INTRODUCTION ........................ 119 RESULTS AND DISCUSSION. .. ....... ......... 122 EXPERIMENTAL ....................... 137 A. Syntheses . ..... ............... 137 a,a-Dichlorotetramethylbenzocyclobutene. 137 Tetramethylbenzocyclobutenone . 139 Tetramethylbenzocyclobutenol ...... 141 a. Reduction of tetramethylbenzocyclo- butenone . ....... 141 l. Attempted reduction with lithium aluminum hydride in tetrahydrofuran . 141 2. Sodium borohydride- aluminum chloride in diglyme . 141 3. Sodium borohydride in diglyme 142 Tetramethylbenzocyclobutene ...... 143 B. Attempt to trap the intermediate (in the trans- formation of trichloromethylpentamethylbenzene to a, a.-dichlorotetramethylbenzocyclobutene) with maleic anhydride. 145 C. Stability of Tetramethylbenzocyclobutenone . 147 1. To ethanolic 1 N hydrochloric acid . 147 2.. To ethanolic 0.1 N sodium hydroxide . 148 3.-To 0.1Msodiummethoxide. .... 149 D. Reactions of Tetramethylbenzocyclobutenone . 149 Deuterium exchange studies . 149 viii TABLE OF CONTENTS - Continued