Gibson, Emma K. (2007) Amine hydrochloride salts : a problem in polyurethane synthesis. PhD thesis . http://theses.gla.ac.uk/3070/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] Amine hydrochloride salts: a problem in polyurethane synthesis Emma K Gibson For the degree of Doctor of Philosophy Department of Chemistry UNIVERSITY of GLASGOW July 2007 -_ ... , , '~-(..1.. ~\ .:- ,? J.! •• , f;' .' I ! , , . 2 Declaration The work contained in this thesis, submitted for the degree of Doctor of Philosophy is my own original work, except where due reference is made to other authors and has not been previously submitted for a degree at this or any other university. Emma K Gibson © Emma K Gibson 2007 ,. 3 Abstract A major problem encountered during the industrial s}1lthesis of isocyanates, is the loss of amine starting material through reaction with the hydrogen chloride (HCI) by-product. HCI is formed by the phosgenation of polymeric amines and also by the subsequent decomposition of the carbamyl chloride, Equation (I). HCI readily reacts with the polymeric amine to form an unwanted and highly insoluble amine hydrochloride salt. R-NH2 + COCI 2 ~ R-NHCOCI + HCI R-NHCOCI R-NCO + HCI c .. (1) R-NH + HCI 2 Methylene dianiline (MDA) and 4-benzylaniline (4-BA) were used as models for the industrial amine starting material with their hydrochloride counterparts methylene dianiline dihydrochloride (MDA.2HCI) and 4-benzylaniline hydrochloride (4-BA.HCI) as models for the industrial waste material. To understand the forces controlling the structure and stability of these solid amine hydrochloride salts the solid state structures of MDA, MDA.2HC1, methylene dianiline monohydrochloride (MDA.HCI), 4-BA and 4-BA.HCI were investigated using single crystal X-ray diffraction which led to the determination of their lattice energies. The XRD studies were also used as a basis for Density Functional Theory (DFT) calculations, which were validated against Inelastic Neutron Scattering (INS) spectra. These calculations facilitated the assignment of the vibrational modes in FTIR spectra. The information obtained from the solid state structures, combined with an investigation of the solution phase behaviour of 4-BA.HCI(s)' resulted in the determination of a kinetic model for the recovery of amine starting material. The solution phase was investigated using quantitative IH NMR spectroscopy, for which a pre-saturation pulse programme had been developed. The proposed reaction scheme describes the conditions under which the dissociation of 4-BA.HCl(s) can occur. Reaction in a closed system shows no amine production while reaction in an open system permits, within solubility limits, the complete consumption of solid waste to produce free amine. From these two extremes the conversion of waste hydrochloride salt in the industrial reactor can be rationalised. 4 Acknowledgements I would like to thank everyone who has contributed to this project and whose help and support has been very much appreciated. • A special thanks to my supervisors Prof John Winfield and Dr. David Lennon who have been a constant source of guidance and encouragement. Thank you also for your patience and sound advice over the past four years. • Huntsman Polyurethanes and my supervisors Dr Rob Carr and Dr Archie Eaglesham. Your informative and friendly discussions made our many project meetings a pleasure. Thanks also for a new found love of Belgian beer. • The crystallography studies were a great experience thanks to the immense knowledge and patience of Dr Ken Muir. • Dr Stewart Parker at the Rutherford Appleton Laboratory for the INS, calculations and understanding ofthe vibrational spectra. • Dr David Rycroft and Jim Gall for all their help with the NMR and especially Dr David Adam for his help with the pulse program. • Prof A Gavezzotti for the calculations of the lattice energies. • Dr Alice Miller for being cajoled into doing maths over your Christmas holidays. • Ally, lain, Neil and June for the great times I've had in the lab, cheers. And a big thanks to my mates for all the advice, singing lessons and unwavering belief that one day I'll learn some grammar. • Finally, but most importantly, a huge thanks to Mum and Doreen. Your infinite common sense and great humour usually keeps me sane. And I promise to get a proper job some day. 5 Contents 1 Introduction .................................................................................................. 15 1.1 A problem encountered in isocyanate synthesis .......................................... 15 1.2 Project aims and achievements ................................................................... 16 1.3 Polyurethanes .............................................................................................. 16 1.4 Industrial isocyanate synthesis ..................................................................... 17 1.5 Polyurethane market and history of manufacture ............... ~ ......................... 19 1.6 Amine hydrochlorides ................................................................................... 21 1.7 Background theory ....................................................................................... 22 - 1.7.1 Equlhbna ........................................................................................................... 22 1. 7 "2 De f I"n l" t"I on 0 f reac t"I on envl.r onmen t ..................................................................... 23 1.7.3 Definition of acids and bases ............................................................................ 23 1.7.4 Gas dissolution - ideal and non-ideal solutions ................................................. 26 1.7.5 Solvents ............................................................................................................ 27 1.7.6 Lattice energies ................................................................................................. 29 1.7.7 Description of traditional methods for calculating lattice energies ...................... 30 1. 8 Analytical techniques ......... 32 II ••• II •••• II •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1.8.1 Fourier Transform Infrared Spectroscopy (FTIR) ............................................... 33 1.8.2 X-ray diffraction (XRD) ...................................................................................... 34 1.8.3 Density Functional Theory (DFT) ...................................................................... 38 1.8.4 Inelastic Neutron Scattering, INS, spectroscopy ................................................ 39 1.8.5 Thermal analysis ............................................................................................... 41 1.8.6 Solution phase 1H NMR spectroscopy ............................................................... 43 1.9 Kinetics ......................................................................................................... 46 1.9.1 Types of reaction ............................................................................................... 46 1. 10 Statistical analysis ........................................................................................ 51 2 Exper"lmental .................................................................. ............................... 53 2 .1 Chlorobenzene .. ........................................................... ..... ........................... 53 2 .2 Hydrogen chlor'lde (Hel) .. ............................................ .. ............................... 55 2.2.1 Preparation of anhydrous HCI ........................................................................... 55 2.2.2 HCI dissolution in chlorobenzene using the vacuum line ................................... 56 2.2.3 Flow HCI apparatus ........................................................................................... 57 2.3 Synthesis of amine hydrochloride salts ........................................................ 58 2.3.1 Direct reaction between HCI(Q) and solid amine ................................................. 59 2.3.2 Liquid phase ...................................................................................................... 59 2.3.3 Direct gas - solid vs. solution phase reaction: MDA.2HCI ................................. 60 2.3.4 Direct gas-solid vs. solution phase: 4-BAHCI ................................................... 60 2.3.5 Development of method to make monohydrochloride (MDAHCI) ...................... 61 2.4 Analytical techniques used ........................................................................... 63 6 2.4.1 FTIR spectroscopy ............................................................................................ 63 2.4.2 Single crystal x-ray diffraction (XRD) ................................................................. 64 2.4.3 Lattice energies ................................................................................................. 66 2.4.4 Inelastic Neutron Scattering (INS) spectroscopy ............................................... 66 2.4.5 DFT ................................................................................................................... 67 2.4.6 Thermal Gravimetric Analysis (TGA) ................................................................. 67 2.4.7 Proton nuclear magnetic resonance spectroscopy (1H NMR) ............................ 69 2.5 The behaviour of 4-BAHCI in chlorobenzene .............................................. 85 2.5.1 Solubility determinations ................................................................................... 86 2.5.2 Dissociation experiments on 4-BA.HCI(s) ........................................................... 86 2.5.3 Filtered solutions ............................................................................................... 88 2.5.4 Dissociation of MDA,2HCI experiment at reflux ................................................. 88 2.5.5 Dissociation of 4-BA.HCI(solv) kinetic experiments .............................................. 89 3 Dissolution of HClln chlorobenzene, characterisation and thermal stability of amine hydrochloride salts. ....................................................... 94 3.1 Distillation of monochlorobenzene (chlorobenzene) ..................................... 94 3.1.1 Addition of water to MBC ................................................................................... 95 3.1.2 FTIR spectroscopy of chlorobenzene ................................................................ 97 3.2 Dissolution of Hel in chlorobenzene ............................................................. 97 3.2.1 Gas phase FTIR ................................................................................................ 98 3.2.2 Dissolution of HCI - using the vacuum line ....................................................... 99 3.2.3 Dissolution of HCI - bubbling through chlorobenzene ....................................... 99 3.2.4 Dissolution curve ............................................................................................. 101 3.2.5 Proposed HCI - chlorobenzene interaction ..................................................... 102 3.2.6 1H NMR of HCI in chlorobenzene .................................................................... 104 3.3 Characterisation of amines and amine hydrochloride salts ........................ 105 3.3.1 Melting points and Differential Scanning Calorimetry (DSC) of amines and amine hydrochloride salts ........................................................................................................ 106 3.3.2 FTIR spectroscopy as a simple diagnostic tooL ............................................... 108 3.3.3 Thermal Gravimetric Analysis (TGA) ............................................................... 110 3.3.4 1H NMR of amine hydrochlorides in DMSO and methanol ............................... 120 3.3.5 Ageing of samples ........................................................................................... 127 3.3.6 Dissolution of amines and amine hydrochlorides in chlorobenzene ................. 129 3.3.7 MDA.2HCI reflux experiment ........................................................................... 137 3.4 Summary .................................................................................................... 138 3.4.1 Water in chlorobenzene .................................................................................. 138 3.4.2 HCI in chlorobenzene ...................................................................................... 138 3.4.3 Amines and amine hydrochlorides .................................................................. 139 4 Crystal Structures and Lattice Energies .................................................. 141 4.1 Crystallography .......................................................................................... 141 7 4.1.1 4-Benzylaniline (4-BA) .................................................................................... 144 4.1.2 MOA ................................................................................................................ 145 4.1.3 4-BA.HCI ......................................................................................................... 149 4.1.4 MDA.2HCI ....................................................................................................... 152 12 4.1.5 The basic hydrochloride [MDAH2 +.2Cr.2MDA.H20 ........................................ 155 4.1.6 Other structural features .................................................................................. 163 4.1.7 Correlation of crystallographic studies with solubility ....................................... 166 4.2 Lattice energies .......................................................................................... 168 4.2.1 Amines: 4-BA and MDA .................................................................................. 168 4.2.2 Hydrochloride salts: 4-BA.HCI and MDA.2HCI ................................................ 171 4.2.3 Estimate of [MDAH212+.2Cr.2MDA.H20 lattice energy ...................................... 172 4.2.4 Summary of lattice energies ............................................................................ 173 5 Vibrational Spectroscopy .......................................................................... 175 5.1 Inelastic neutron scattering spectroscopy (INS) and Density functional theory calculations (OFT) ...................................................................................... 175 5.1.1 4-BA and 4-BA.HCI ......................................................................................... 176 5.1.2 MDA and MDA.2HCI ....................................................................................... 177 5.1.3 [MDAH2]2+.2Cr.2MDA.H20 ............................................................................. 179 5.1.4 Summary of INS spectra ................................................................................. 180 5.2 FTIR ........................................................................................................... 181 5.2.1 4-BA and 4-BA.HCI ......................................................................................... 181 5.2.2 MDA and MDA.2HCI ....................................................................................... 187 5.2.3 Methylene dianilinie monohydrochloride (MDA.HCI) ........................................ 191 5.2.4 Summary of FTIR spectra ............................................................................... 195 6 Investigations and development of the kinetic model of the dissolution and dissociation of 4-BA.HClln chlorobenzene ...................................... 197 6.1 Investigations of the dissociation of 4-BA.HCI(s) ......................................... 197 6.1.1 Dissociation of 4-BA.HCI(s) .............................................................................. 198 6.1.2 Solution reaction; 4-BA.HCI(sOlv) ~ 4-AB(solv) .................................................... 204 6.1.3 Review of investigations of the dissociation of 4-BA.HCI(s) .............................. 206 6.2 Reaction scheme ........................................................................................ 207 6.2.1 Experiments under closed conditions .............................................................. 209 6.2.2 Open experiments ........................................................................................... 215 6.3 Development of a kinetic model ................................................................. 219 6.3.1 Justification of first stage: oth order .................................................................. 220 st 6.3.2 Justification of second stage: 1 order ............................................................ 221 6.3.3 Derivation of the rate equations for a Oth, 1s t order consecutive process .......... 222 st 6.3.4 Modelling the data to a Oth, 1 order consecutive process ............................... 226 6.4 Summary .................................................................................................... 233 7 Conclusions ................................................................................................ 235 8 7.1 Reaction model .......................................................................................... 236 7.1.1 The closed system .......................................................................................... 236 7.1.2 The open system ............................................................................................. 237 7.2 Consequences of this work .................................................. ,. .................... 239 8 References .................................................................................................. 240 9 List of Figures Figure 1 Glossary of chemical formulae of amines and amine hydrochlorides encountered in this project. ..... 17 Figure 2 Synthesis of methylene diphenyl diisocyanate (MDI) from benzene .......•.................•...•.........•..•....... 18 Figure 3 Plot of pressure v.s. mole fraction of a solute obeying Henry's Law .....••.•...•.•••..•..•..••.....•..••.......•..... 27 Figure 4 Enthalpy of solution (faHsol). Showing the balance between the enthalpy of solvation (faHsolY) and the lattice energy (-U) .•..•...•......•......••......•.............•.........••......•......••..•...••.•.............................••..••.........................3 0 Figure 5 Internal reflection element of an ATR probe •..••.••..••......••..•.•.•..•.....•.•..•..•...•....••......•..•..•..•............••. 34 Figure 6 Overview of X-ray diffraction experiment. ..•.••..••..•..••..••.•••.•••.•..•....•..••.•••....••..•......•..•..•..••.••.....••...... 35 Figure 7 Bragg diffraction by a 3-dimensional crystal structure ..•..••..•....•••..••.••...•..•..•...•.••..••.•...•.....•..•.......... 35 Figure 8 Tosca spectrometer ...........................................................................................................................4 0 Figure 9 Mass loss of Mg(OH}2 observed during temperature ramp from 333 -1233 K. •.............................. .42 Figure 10 Example of a Differential Scanning Calorimetry trace .....•...............................................................4 3 Figure 11 Effect of a 90 pulse .......................................................................................................................4 4 0 Figure 12 Reaction profile for a 1S I order consecutive process ...........•••..••..•••••.....•.....••..••....••....•.....•..•......... .49 Figure 13 Reaction profile for a 1S f then oth order consecutive process ..•..•.••••••.•..•.....••.••.....•.••..••.•.....•.•......•. 50 Figure 14 Vacuum line ...•••..•..••...••..•.....•...•.•..••....••..•••..•.•.••..•••.••.•.•••..••...•......•...•..•......•........••.....•........••....•... 53 Figure 15 Apparatus used to prepare anhydrous HCL.. ••.•....••••••••.••••.•••.••...•.•••..•..•......•.•.•.....••.••.••..•.....•........ 55 Figure 16 Apparatus for transfer of HCI-chlorobenzene solution to the liquid phase FTIR cell. ..•.•••.•..•..•..•.••.. 57 Figure 17 Apparatus used to flow anhydrous HCI(g) through solutions .••.••••••.•••.•••..••..••.•••......•.••.••.•...•.••....••.• 58 Figure 18 Apparatus for preparation of a stoichiometric amount of HCI(O) .•••......•.......•••.••••.•...•..•.•..••..•..•..•.••.. 62 Figure 19 Experimental set up for vapour-diffusion crystallisation procedure ........•.....•..•.•...•.••........••............. 64 Figure 20 'H NMR spectrum of MDA.2HCI in DMSO ............................•..•..................••..................................7 0 Figure 21 Deuterated solvent NMR capillary tube ..•.••...•..•••..•........•....•.....•.•..•.••.•.•.••••......•..••.••..••......•..••.••...• 71 Figure 22 ' H NMR spectrum of 4-BA in chlorobenzene ...•••..•••....•....•...•.•••••........•••.••••••.••............••......••...••.... 71 Figure 23 Assignment of protons In the 'H NMR spectra of 4-BA as used in Table 10 ................................... 73 Figure 24 Plot of the integrals of the CH2 and NH2 signals of 4-benzylaniline (4-BA) as a function of concentration of 4-BA in chlorobenzene ...........................................................................................................7 4 Figure 25 Full width at half maxima (FWHM) of the 'H NMR signals of the NH2 and CH2 of 4-BA and the water of chlorobenzene, as a function of concentration of solutions of 4-BA in chlorobenzene ................................. 75 Figure 26 'H NMR spectrum of 0.1 mmoIL·' 4-BA solution, over 8000 scans ..............•.........•......••.......•......••. 76 Figure 27 'H NMR spectrum of chlorobenzene ....•••......•....•..••....•..•...•.••..•.....••.....••...•.•....•..•.••...•...•....•.••..••... 77 Figure 28 Ic1 pnf2 pulse sequence ••.••••.•••..•••...•••...•••.....•••..••..•••.•••......•.....•..••..•..••.•...•..••..••.•.•.•...•••.....••......•.. 78 Figure 29 Comparison of a 'H NMR spectrum of a solution of 4-BA in chlorobenzene (3 mmol L·') (a) without and (b) with the pre-saturation pulse sequence .•••..........•...•..........•....•.•...•......•......•................•...•.••....•..•......••. 81 Figure 30 Calibration curve of the integrals of the CH2 'H NMR signals of solutions 4-BA in chlorobenzene. 82 Figure 31 The full width at half maxima of the CH2 'H NMR signal of solutions of 4-BA in chlorobenzene as a function of concentration .••••••...••........•.••...•...•••.......................•.....................•.........•..•......•.......••.........•............8 3 Figure 32 'H NMR spectra of solutions of 4 -BA in chlorobenzene using the presaturation pulse program .•.• 84 Figure 33 'H NMR spectra of two solutions of 4-BA in chlorobenzene (a) 0.05 mmol L·' and (b) 0.01 mmol L·' • ••..••.•••...••....••....••...•••••...•...•...•..................••..••.....•......••.•...•......••...•......••.••..•...•.•........•...•.......•..•....•...•........•.•.• 84 Rgure 34 Apparatus for the experiments on the dissociation of 4-BA.HCI(s) in chlorobenzene ............•.•....•... 87 Figure 35 Apparatus built at Glasgow used for the kinetic experiments .•...•...•.••...•.....•...•..••..••........•...•.•.•..••.. 90 Figure 36 Radley's carousel 6 reaction station ................................................................................................9 1 Figure 37 'H NMR spectra of distilled and Sigma-Aldrich anhydrous chlorobenzene ...................................... 95 Figure 38 'H NMR spectra of (a) distilled chlorobenzene, (b) addition of 0.19 mol L·' (c) addition of a further 0.36 mol L·' of water to distilled chlorobenzene •.•••.••...••.••••.••...••.••••.••••••.....••.............••..•....•..•••••...••..•••••.•••...•• 96 Figure 39 FTIR spectrum of distilled and non distilled chlorobenzene .••.....•.•..••.••...•...•..••...•....•••.••.•••.••..•...•..•• 97 Figure 40 Gas phase FTIR spectrum of HCI.. ..................................................................................................9 9