THE CHEMISTRY OF SOME DI- AND TRI-PHENYLMETHANIE DYES by Stephen Anthony GORMAN B.Sc. (Hons) being a thesis submitted to the University of Central Lancashire in partial fulfilment of the requirement for the degree of DOCTOR OF PHILOSOPHY November 1998 Department of Environmental Management University of Central Lancashire Preston ACKNOWLEDGEMENTS I would like to express my sincere gratitude to Dr. Don Mason, my Directot of Studies, and to Professor John D. Hepworth, Seèond Supervisor, for their constant• interest, support and guidance throughout the course of my work and during the writing of my thesis. My thanks are also due to Dr. B. M. Heron and Dr. C. D. Gabbutt for theft interest and help. I am also indebted to my employer, William Blythe Ltd., for allowing the time for my studies. S.A.G. DECLARATION I declare that, whilst registered with the University of Central Lancashire for the degree of Doctor of Philosophy, I have not been a registered candidate or enrolled student for another award of any other academic or professional institution during the research programme. No portion of the work referred to in this thesis has been submitted in support of any application for another degree or qualification of any other University or Institution of learning. Signed........................................... Stephen A. Gorman A NOTE ON REFERENCES Throughout this work, a reference system based on that introduced by A. R. - Katritzky and J. M. Lagowski in the monograph t'Chemistry of the Heterocyclic N±: - Oxides", Academic press, New York, 1971, will be employed. This system has been used for the highly acclaimed "Comprehensive Heterocyclic Chemistry" series, edited by A. R. Katritzky and C. W. Rees, Pergamon Press, 1984 and is currently used for the series "Advances in Heterocyclic Chemistry", edited by A. R. Katritzky, academic press, New York from volume 40, 1986, onwards. The references are designated by a number-letter coding of which the first two numbers denote the year of publication, the next one to six letters denote the journal, and the final numbers denote the page. A more detailed explanation may be found in the aforementioned publications. ABSTRACT The chemistry of some di- and tri-phenylmethane dyes. Stephen A. Gorman Two series of dyes have been prepared: a comprehensive series of novel, unsymmetrical Malachite Green type dyes containing different amino substituents in the 4-positions of the phenyl rings and a series of symmetrical Michier's Hydrol Blue type dyes. Both series of dyes have been synthesised from the relevant carbinols or hydrols. The amino substituents used were dimethylamino, diethylamino, pyrrolidino, piperidino, morpholino, thiomorpholino and N-methylpiperazino. The rates of ailcalirie hydrolysis of the dyes at various hydroxide ion concentrations and temperatures have been investigated with a view to elucidating the reaction mèchanism and the nature of substituent effects. The rate data obtained for each dye studied have been used to obtain thermodynamic activation parameters and to test the applicability of an isokinetic relationship in the dye systems. The various methods of computation and their results have been compared and discussed in relation to literature data for similar dyes. A stopped-flow technique was used for the kinetic investigation of the fast reactions associated with the unstable dyes studied. The analysis of kinetic data using single substituent parameter regression techniques has enabled substituent constants for piperidine, thiomorpholine and N-methylpiperazine to be interpolated. The steric and electronic effects of the terminal amino substituents on the visible absorption spectra of the dyes have been examined in solvents of varying acidity. The steric and electronic symmetry of the Malachite Green type dyes has been investigated and is discussed. The results from the spectral investigation and the kinetic study indicate that diphenylmethane dyes are considerably less stable than the corresponding triphenylmethane dyes and the reasons for this behaviour are discussed. In addition, piperidino, morpholino, thiomorpholino and N-methylpiperazino are less able to stabilise a dye by electron donation than dimethylamino, diethylamino and pyrrolidino and the reasons for this behaviour are also discussed. The 'H and 13C nmr spectra of the dyes and carbinols have been recorded. Certain chemical shifts have been used to determine the relative electron donor ability of the terminal amino groups. The results from the 'H and 13C nmr spectra are discussed in relation to the steric and electronic effects of the heterocycic moieties. CONTENTS Page 1. INTRODUCTION 1 ii Brief history of dyes 1 1.2 Hydrolysis of TPM/DPM dyes 6 1.3 Kinetics 7 1.3.1 The dependence of rate of reaction ontemperature 9 1.3.2 The dependence of rate of reaction on ionic strength 16 1.3.3 The influence of solvent 17 1.3.4 The influence of substituents in the benzene ring on the rate of reaction 18 1.4 Basic theory of colour 26 1.5 Electronic absorption spectroscopy 29 1.6 Colour and constitution 33 1.6.1 Early colour theories 33 1.6.2 Valence bond theory 34 1.6.3 Molecular orbital models 35 1.6.4 The Free-Electron Molecular Orbital method 41 1.6.5 The Huckel Molecular Orbital method 44 1.6.6 The Pariser-Parr-Pople Molecular Orbital method 46 1.6.7 Configuration Interaction 47 1.6.8 The Perturbational Molecular Orbital method 48 1.6.9 The Hammett equation 54 1.7 Electronic absorption spectra of TPM/DPM dyes 57 1.7.1 Introduction 57 1.7.2 The effect of terntal groups on the absorption spectra 59 of 1'PM/DPM dyes 1.7.3 The effect of substitution at the 2-position of the phenyl rings 64 on the absorption spectra of TPMIDPM dyes 1.7.4 The effect of substitution at the 3-position of the phenyl rings 68 on the absorption spectra of TPM!DPM dyes 1.7.5 TPMIDPM dyes with extended chromophoric systems 72 2. RESULTS AND DISCUSSION 86 2.1 Synthetic work 89 2.1.1 Preparation of leuco bases 90 2.1.2 Preparation of intermediates and precursors 93 2.1.3 Preparation of benzophenones 97 2.1.4 Preparation of diarylcarbinols / 101 2.1.5 Preparation oftriarylcarbinols I 104 2.1.6 Preparation of perchiorate salts - .121 2.2 Absorption spectra 132 2.2.1 The absorption spectra of the diphenylcarbinols 133 2.2.2 The absorption spectra of some unsymmetrical analogues of MG 137 2.2.2.1 The effects of increased acidity 155 2.2.2.2 Electronic and structural symmetry 165 2.3 Kinetic investigations 172 2.3.1 General 172 2.3.2 Unsymmetrical MGs . 178 2.3.3 Analogues of Michler's Hydrol Blue 227 3. EXPERIMENTAL 235 3.1 Organic synthesis 236 3.1.1 Preparation of disubstituted benzophenones 236 3.1.2 Preparation of monosubstituted benzophenones 237 3.1.3 Preparation of diarylhydrols 239 3.1.4 Preparation of intermediates 241 3.1.5 Preparation of aryllithium compounds 243 3.1.6 Preparation of the unsymmetrical derivatives of Malachite Green 244 3.1.7 Preparation of the perchlorate salts 251 3.2 Kinetic studies 260 3.2.1 Chemicals 260 3.2.2 Apparatus 260 3.2.3 Instrumentation 261 3.2.4 Experimental methods 263 4. CONCLUSIONS 266 5. REFERENCES 270 APPENDICES FIGURES Page 1A Conformational changes accompanying the hydrolysis of a TPM dye and the ionisation of its dye base 6 lB The proportion of molecules having energy in excess of E.. 10 1 C The concentrations of reactants (A), products (C) and intermediates (B) for a first order reaction as postulated in the Transition State Theory 12 1D A potential energy curve for a reaction 13 1E The proportionality of AG and AFT arising from the temperature invariance ofa 1 IF The nonLproportionality of AG and AH leading to a breakdown of the Hammett equation 24 1G The absorption spectra of the classes of cones 28 IH The wavelength and type of electromagnetic radiation 29 11 Apparatus used in the constant-flow technique 32 1J Apparatus used in the stopped-flow technique 32 1K Postulated resonance forms of MHB 34 1L Molecular and atomic orbitals 37 1M A Jablonski scheme 40 IN FEMO wave functions for a linear, conjugated molecule 43 10 m MOs for a linear, conjugated molecule in (a) the FEMO model and (b) the HMO model 45 1 P Some examples of alternant and non-alternant systems 49 1Q The effect on the energies of the orbitals and the first electronic transition by replacing a carbon atom of an odd-altemant with an atom of differing electronegativity 51 2A The relationship between a univalent cationic dye and its immediate precursors 89 2B A plot of 'H chemical shift for the proton adjacent to the amino-bearing carbon atom against & substituent constants 119 2C Enantiomers for the unsymmetrical MGs 120 2D Nitrogen-phenyl ring resonance interaction for N-phenylpyrrolidine 146 2E Nitrogen-phenyl ring resonance interaction for N-phenylpiperidine 146 2F Transition state formed during reaction of enamines with electrophile 150 2G The formation of protonated Pyrrolidine Green 159 211 Visible absorption spectrum of Pyrrolidine Green, PG, (A) and protonated Pyrrolidine Green, PGH2 , (B) 160 21 Two extreme resonance configurations for the structurally unsymmetrical dye Mo-Pi 166 2J A plot of s(x) against X,,(x) deviation for twelve unsymmetrical MGtype dyes 170 2K Plot of In absorbance against time for varying concentrations of EtDPM at 293.8K; (•) 4.67x104 , (U) 2.52x104 and(S) 1.12x104 moldni3 iø [OH-] = 0.5 mol dm 3 , I = 0.01 mol dm 3 175 21, Isokinetic relationship in the co-ordinates log k 2 versus log k293 with k2at 303 K(U),318K(•)and333K(S) 207 3A Schematic diagram of the Hi-Tech Scientific SFA-1 1 Rapid