SOLUTIONS IN DIFLUOROPHOSPHORIC ACID ' -by William Reed A THESIS SUBMITTED IN PARTIAL FULFILMENT OF -THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Chemistry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January 196S 0 William Reed 1968 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his represen• tatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver 8, Canada Date February 27, 1968 (ii) ABSTRACT - The physical and inorganic chemistry of solutions in difluorophosphoric acid, HPO^Fg, has been studied, as part of a general study of solutions in non-aqueous protonic solvents. Difluorophosphoric acid is a colourless, associated liquid which might be expected to have solvent properties similar to those of other protonic systems such as H^O, I-^SO^ and HSO^F. However, electrical conductivity studies of solutions of various electrolytes and nuclear magnetic resonance studies of solutions of alkali metal difluorophosphates indicate that the acid is a poor solvent for electrolytes and that ion-pairing is probably extensive. Acid-base behaviour in HPO2F2 has been extensively in• vestigated. Compounds which behave as bases in this system in• clude metal difluorophosphates, chlorides, nitrates and carbonates, organic amines, and some organic nitro-compounds and carboxylic acids. Inorganic molecules such as F^SO^, HSO^F and SbF^ behave as acids. Reaction between an acid and a base in HPO2F2 commonly result in the formation of an insoluble salt. The reaction between KPO2F2 and SbF^, for example, has been used to prepare the new compound KSbF^P02F2« To further investigate the factors affecting acid strengths, cryoscopic and electrical conductivity studies of various inorganic oxy-acids were carried out in nitrobenzene, as solvent. The acids H^SO^, HSO3F and HPO2F2 appeared'to be vir• tual non-electrolytes in nitrobenzene, vrith ^SO^ apparently exhibiting some polymerization. (iii) TABLE OF CONTENTS • PAGE CHAPTER I General Introduction ' 1 1.1 Properties of difluorophosphoric acid 1 1.2 Acid-base behaviour in protonic solvents 4 1.3 Outline of present work 6 CHAPTER II Solutions of Metal Difluorophosphates 8 2.1 Introduction 8 2.2 Experimental 8 A) Preparation and purification of materials 8 i difluorophosphoric acid ii metal difluorophosphates B) Electrical conductivity 10. C) Nuclear magnetic resonance 17 D) Viscosity 18 E) Density 19 2.3 Results and discussion 19 A) Electrical conductivity 19 B) Nuclear magnetic resonance 30 C) Density 41 D) Viscosity 1+6 CHAPTER III Miscellaneous Bases 48 - A) Organic solutes 48 3.1 Introduction 48 3.2 Experimental 48 A) Electrical conductivity 48 B) Preparation and purification of materials 48 3.3 Results and discussion 49 (iv) • . PAGE B) Inorganic solutes . 53 3.4 Introduction 53 3.5 Experimental 54 3-6 Results and discussion " 54 CHAPTER IV Acids and Acid-Base Reactions 62 4.1 Introduction 62 4.2 Experimental 63 A) Preparation and purification of materials 63 B) Electrical conductivity 64 C) Nuclear magnetic resonance 65 4.3 Protonic acids: results and discussion 65 4.4 SbF^ solutions: results and discussion 72 4.5 Studies on KSbF5P02F2 95 CHAPTER V Nitrobenzene. Solutions 102 5.1 Introduction 102 5.2 Experimental 103 A) Cryoscopy 103 B) Electrical conductivity 108 C) Preparation of materials 109 5.3 Results and discussion 109 A) Fluorosulphuric acid solutions 110 B) Sulphuric acid solutions 117 C) Pifluorophosphoric acid solutions 121 5.4 Conclusion 121 CHAPTER VI Summary and Suggestions for Further Work 123 6.1 -Summary 123 6.2 Suggestions for further work 125 BIBLIOGRAPHY .127 (v) LIST OF TABLES . • TABLE PAGE 1. Physical Properties of Difluorophosphoric Acid t 2 2. Specific Conductivities of the Alkali and Some Alkaline 20 Earth Metal Difluorophosphates at 25° 3. Equivalent Conductivities of Some Difluorophosphates at 25° . 23 4. Specific Conductivities of Some Potassium Salts in Various Solvents 26 1 19 1 5. H, F and ^ P Chemical Shifts for Solutions of MP0„F9 in HP02F2 32 6. Densities and Viscosities of Some Solutes in HP02F2 at 25° 42 7. Specific Conductivities of Some Organic Bases in KPOoFo at 25° . 50 • #. Specific Conductivities of Various Electrolytes in HPO F at 25° 55 2 2 9. Specific Conductivities of Some Acids in HP02F2 at 25° 66 10. 19F.and 31p Ch emical Shifts and Coupling Constants for Some Complex Antimony-Fluorine Species 82 11. Infrared Spectra .of Various Inorganic Fluorine Compounds 96 12. Infrared Snectrum of Gaseous Products from the Decomposition of KSbF5P02F2 100 13. Cryoscopic Measurements in Nitrobenzene 111 14. Specific Conductivities of Some Electrolytes in Nitrobenzene at 25° 114 15. Equivalent Conductivities of Some Electrolytes in Nitrobenzene at 25° 119 (vi) LIST OF FIGURES FIGURE PAGE 1. Difluorophosphoric Acid Distillation Apparatus 9 2. Electrical Conductivity Cell - 11 3. Injector, used for Solute Additions to the Conductivity . Cell ' 13 4. Microburette, used for Solute Additions to the Conductivity Cell 16 5. Specific Conductivities of Some Difluorophosphates at 25° 21 6. Equivalent Conductivities of Some Dif luorophosphates at 25° plotted against the Square Root of the Ionic Strength 25 7. N.M.R. Chemical Shifts for MP02F2 in HP02F2 34 19 8. F N.M.R. Chemical Shifts for MPOgFg in HP02F2 35 31 9. P N.M.R. Chemical Shifts for MP02F2 in HP02F2 36 10. Densities of Some Metal Difluorophosphates in HPO^Fo 44 at 25° 11. Specific Conductivities o-f Some Organic Bases in HP09F9 at 25° 51 12. Specific Conductivities, of Various Electrolytes in HP02F2 at 25° 56 13- Specific Conductivities of Various Potassium Salts in HP02F2 at 25° 59 14. Specific Conductivities of Some Acids in HP02F2 at 25° 08 15. Acid-Base Titrations in HP02F2 at 25° 70 16. - Acid-Base Titrations for SbF against KPO F in HPO F at 25° 5 . 1 Z 1 75 19 17. F N.M.R. Spectrum of a 3.63 molal SbF£./HP0oFo Solution 5 at 30° ^ d. 7g 19 18. F N.M.R. Spectrum of a 3.63 molal 3bF_/HP0oF Solution at -65° 5 2 2 79 19. 19F N.M.R. Spectrum of a 7.0 molal SbF /HPO F Solution at 30° 5 2 2 80 (vii) FIGURE . PAGE 20. 1^F N.M.R. Spectra of the P-F Region for a 2.31 molal SbF5/HP02F2 Solution at 30° and -70° 84 21. 19F N.M.R. Spectrum in the Sb-F Region for a 2.31 molal ' SbF5/HP02F2 Solution at -70 (peak M) 85 22a) X9F N.M.R. Spectra in the Sb-F Region for a 2.31 molal • SbF5/HP02F2 Solution at -70° (peaks K, L and P) 86 22b) ^F.N.M.R. Spectrum in the Sb-F Region for a 2.31 molal SbF5/HP02F2 Solution at -70° (peaks N & 0) 87 23. X9F High-Resolution N.M.R. Spectrum of the P-F Region for a 2.31 molal SbF5/HP02F2 Solution at 30° 92 24. 51P N.M.R. Soectrum of a 2.62 molal•SbFr/HPO-F- Solution at 30° ? 93 25. Details of the31 P N.M.R. Spectrum of a 2.62 molal SbF./ 5 HP02F2 Solution at 30° 94 26. Vacuum Line used for the Decomposition of KSbF^P02F2 98 27. Cryostat, used for Nitrobenzene Solutions 104 28. Depression of Freezing Point (AT) for Various Solutes in Nitrobenzene 112' 29. Specific Conductivities of Some Solutes in.Nitrobenzene at 25 116 30. Equivalent Conductivities of Some Electrolytes in Nitrobenzene at 25° 118 (viii) ACKNOWLEDGMENTS The author wishes to express gratitude to Dr. R. C. Thompson who first suggested the problem, and under whose guidance the work was done. Thanks are due to Mr. S. Rak who constructed the glass apparatus, to Mr. R. Burton who operated the H.A..100 n.m.r. spectrometer, to Mr. R. Wolfe who assisted with the operation of the platinum resistance thermometer and finally to Mr. L. Neering for many helpful suggestions. The generous gift of difluorophosphoric acid by the Czark-Mahoning Chemical Company is also gratefully acknowledged. CHAPTER I '• ..' -General Introduction At the turn of the century solution chemistry was largely, concerned with reactions carried out in aqueous media. During the past five decades, however, studies on a variety of non• aqueous solvents have resulted in the development of many new solvent systems. The experience so obtained has greatly broad• ened the scope of synthetic chemistry and has considerably in• creased the understanding of the physical and chemical properties of solutions. Although the number of solvents which have been investigated is very large, extensive and systematic studies on the physical properties of solutions have been limited to rather few solvents, notably HF, H^SO^ and NH^ and to a smaller extent -HSO^F, S02 and HC1. The purpose of the work described in this thesis was to study the properties of solutions in anhydrous difluorophosphoric acid and to investigate the possibility of HP02F2 as a prepara• tive medium. At present, the range of suitable and readily available fluorinated solvents of use for the preparation of fluorides is limited essentially to hydrogen fluoride, fluoro• sulphuric acid and bromine trifluoride and it is hoped that HP02F2 will extend this range. 1.1 Properties of difluorophosphoric acid The literature regarding difluorophosphoric acid has been 2 reviewed recently >3,4 and as little fresh information has ap• peared since these reviews were written, the usual historical 2 review of the solvent will be dispensed with.