PEROXYSALTS OF THE ALKALI METALS AND RELATED SPECIES. A Thesis Submitted for the Degree of DOCTOR OF PHILOSOPHY of the University of London BY DAVID PHILIP JONES, B.SC., A,R,C.S, Department of Chemistry, Imperial College of Science and Technology, London, SW7 2AY August, 1979. 2 ABSTRACT Peroxysalts of the Alkali Metals and Related Species. David Philip Jones The work described in this thesis is concerned mainly with the preparation, characterisation and physicochemical properties of a series of different inorganic peroxysalts, in particular the alkali metal percarbonates. Extensive use has been made of vibrational spectroscopy as a tool for obtaining structural information, with both 2H and 13C isotopic substitutions helping in the assignments of vibrational modes. All of the peroxysalts studied fall into either of two categories. The first are perhydrates, which contain hydrogen peroxide of crystallisation, such as sodium oxalate monoperhydrate, Na2C204.H202 and " sodium percarbonate", Na2CO3.11H2O2. The second group contain peroxo moieties bound to atoms other than hydrogen, e.g., boron in " sodium perborate" , Na2B2(02)2(OH)4.6H20 or carbon in potassium peroxydicarbonate, K2C206, these types of compounds being referred to as " true" peroxysalts. The structures of both of the commonly used bleaching agents " sodium percarbonate" and " sodium perborate" are described, full X-ray structural determinations having been carried out in the Chemical Crystallography Laboratories during the course of this work. 3 Due to particular interest in percarbonates, one of the very few known transition metal peroxycarbonato complexes, bistriphenyl- phosphine peroxycarbonato platinum(II) has been prepared and its structure also determined by X-ray crystallography. Towards the latter part of this work, the potential use of the " true" percarbonates of the alkali metals and " sodium perborate" as oxidising agents has been studied as they resemble the relatively hazardous organic peroxides, ROOR, hydroperoxides, ROOH, and peracids RC(0)00H in their structures and thus would be expected to possess similar oxidising properties. 4 C0NTENTS PAGE: Abstract 2 Contents 4 List of Tables and Figures 6 Acknowledgements 10 Nomenclature, Abbreviations and Symbols 11 CHAPTER ONE : Alkali Metal and Ammonium Salt Perhydrates 14 Abstract 14 Section 1-A Summary of the Chemistry of Perhydrates 14 Section 1-B The Alkali Metal and Ammonium Oxalate 16 Perhydrates, MZC204.nH2O2 Section 1-C The Alkali Metal and Ammonium Carbonate 33 Perhydrates, M2CO3.nH2O2 Section 1-D Other Perhydrates 42 Section 1-E Experimental 53 CHAPTER TWO : The " True" Alkali Metal Percarbonates and 69 " Sodium Perborate" Abstract 69 Introduction 69 Section 2-A The Alkali Metal Peroxydicarbonates, M2C206 70 Section 2-B The Alkali Metal Peroxybicarbonates, MIHCO4 89 Section 2-C Lithium Peroxycarbonate Monohydrate, Li2C04.H2O 100 Section 2-D Percarbonate Species in Solution 106 Section 2-E BleachingAction of the Percarbonates K2C206j 112 KHCO4 and Li2C04.H20 S PAGE: Section 2-F " Sodium Perborate", Na 2B2(02 ) 2(OH)4.6H20 114 Section 2-G Experimental 118 CHAPTER THREE : The Oxidising Properties of Percarbonates, 123 Percarbonato Complexes and Perborates Abstract 123 Section 3-A Some Observations on the Oxidising Properties of 123 The Alkali Metal Percarbonates and " Sodium Perborate" Section 3-B The X-Ray Crystal Structure and Oxidising 134 Properties of Bistriphenylphosphine Peroxy- Carbonato Platinum(II) Section 3-C Experimental 141 Physical Measurements 146 References 147 6 LIST OF TABLES AND FIGURES PAGE: Table 1-1 List of Perhydrates that have been 17 Structurally Characterised by Single Crystal X-Ray Methods. Table 1-2 Elemental Analyses for the Alkali 54 Metal and Ammonium Oxalate Perhydrates. Table 1-3 Vibrational Spectra of Lithium and 19 Sodium Oxalate Monoperhydrates. Table 1-4 Vibrational Spectra of Potassium, Rubidium 20 and Caesium Oxalate Monoperhydrates. Table 1-5 Raman Spectra of Higher Oxalate Perhydrates. 21 Figure 1-1 Normal Modes of Vibrational Motion for the 23 Hydrogen Peroxide Molecule. Figure 1-2 Normal Modes of Vibrational Motion for the 24 Oxalate Ion with D2h Symmetry. Figure 1-3 Infrared Spectrum of K2C204.H202 . 26 Figure 1-4 Raman Spectrum of K2C204.H202. 27 Figure 1-5 Raman Spectrum of K2C204.H202, 800-900 cm-1. 28 Figure 1-6 Infrared Spectrum of K2C204.2H202. 29 Table 1-6 Vibrational Spectra of Normal and 13C-Enriched 32 Oxalate Ion. Table 1-7 Elemental Analyses for the Alkali Metal and 57 Ammonium Carbonate Perhydrates. 7 PG: Table 1-8 Vibrational Spectra of the Alkali Metal 35 and Aiiunonium Carbonate Perhydrates. Figure 1-7 A [0011 Projection of the Structure of " Sodium 37 Percarbonate", Na2CO3.l H202. Figure 1-8 Disorder of the Hydrogen Peroxide Molecules in 38 Na 2CO3.12H202 . Figure 1-9 T.G.A. Trace for Na2CO3.11H202. 43 Figure 1-10 D.S.C. Trace for Na2CO3.1zH 202• 44 Table 1-9 Vibrational Spectra of Sulphate Perhydrates. 46 Table 1-10 Vibrational Spectra of Acetate and Formate 51 Perhydrates. Table 1-11 XRD Data for Na 2CO3.1'zH202. 59 Table 1-12 XRD Data for Na 2SO4.2H202•H20. 59 Table 1-13 XRD Data for 4Na2SO4.NaCt.2H202. 62 Table 1-14 XRD Data for KHSO4 .3 H202. 62 Table 1-15 Indication of Stability of Perhydrates. 68 Table 2-1 Elemental Analyses for the Alkali Metal 119 Peroxydicarbonates, M2C206 . Table 2-2 XRD Data for K2C206 (Form " A") . 72 Table 2-3 XRD Data for K2C206 (Form " B") . 73 Table 2-4 XRD Data for K2C206 (Form " C") . 74 Table 2-5 Vibrational Spectra of the Alkali Metal 76 Peroxydicarbonates, M2C206. Figures 2-1 Normal Modes of Vibrational Motion for the 78 and 2-2 C206 Anion with C21 Symmetry. 79 8 PACE: Figure 2-3 Infrared Spectrum of K2C206 (Form " A") . 80 Figure 2-4 Raman Spectrum of K2C206 (Form " A" ) . 81 Figure 2-5 E.s.r..Spectrum of K2C206 (Form " A"). 85 Figure 2-6 E.s.r. Spectra of K2C206 (Form " B") . 87 and 2-7 88 Table 2-6 Elemental Analyses for the Alkali Metal 121 Peroxybicarbonates, MIHC04. Table 2-7 XRD Data for KHC04. 90 Table 2-8 Vibrational Spectra of the Alkali Metal 92 Peroxybicarbonates, MIHC04 . Figure 2-8 Raman Spectrum of KHC04. 94 Figures 2-9 Normal Modes of Vibrational Motion for 95 and 2-10 the HC04 Anion with Cs Symmetry. 96 Table 2-9 Vibrational Spectra of Li2C04.H20. 101 Figure 2-11 Raman Spectrum of Li2C04.H20. 103 Figure 2-12 Normal Modes of Vibrational Motion for the 104 C0Z Anion with C Symmetry. s Table 2-10 XRD Data for Li2C04.H20. 105 Figure 2-13 13C n.m.r. Spectrum of a Hydrogen Peroxide 108 Solution of HCO3 Anion. Figures 2-14 Curves Obtained for Plots of S vs. pH for 109 and 2-15 HCO3/H2O2 Solutions. 110 Table 2-11 Raman Spectra of Hydrogen Peroxide Solutions 112 of HCO3 and H13CO3 Anions. Figure 2-16 Structure of the Cyclic [B2(02)2(OH)4 12 116 Anion. 9 PAGE: Table 2-12 Vibrational Spectra of Na2B2(02 ) 2(OH)4.6H20. 117 Figure 3-1 Potential-pH Diagram for H202-Water Solutions 127 at 1 mole/litre H202 Concentration, Figure 3-2 X-Ray Molecular Structure of Bistriphenyl- 136 phosphine Peroxycarbonato Platinum(II), (PPh3 ) 2Pt0CO3 . Table 3-1 Vibrational Frequencies of the Pt0CO3 Group 138 in (PPh3 ) 2Pt0CO3. 10 ACKNOWLFDGEI' E TTS I would like to thank my Academic Supervisor, Dr. W.P. Griffith for his enthusiastic help, advice and encouragement during the period of this research work and also for the beer that he has bought me. Thanks are also due to Interox Chemicals Ltd., for generous financial aid and hospitality and in particular to Dr. A. Smith, my Industrial Supervisor for useful comments and for results obtained at the Laporte Research Laboratories, Widnes and Solvay et Cie of Brussels. I would also like to thank Drs. D.F. Evans, J.F. Gibson and L. Pratt and Mr. P. Beardwood for their time spent in constructive discussions over parts of this work and Mr. B.P. O'Hare for his invaluable aid in the recording of Raman spectra. Special thanks to Miss Moira Shanahan for her typing of this Thesis. Finally, my thanks to the Science Research Council for a maintenance grant (C.A.S.E. Award with Interox Chemicals Ltd.). 11 NOMENCLATURE, ABBREVIATIONS AND SYMBOLS. Nomenclature. The nomenclature of various peroxysalts is still not definitive in the literature. In the case of inorganic percarbonates,four different types have been reported and each is often referred to as simply the metal percarbonate.' For convenience to the reader, rather than using the rather long-winded nomenclature based on IUPAC recommendations, the following names have been used through- out this thesis:- (a) Compounds containing hydrogen peroxide of crystallisation are referred to as " perhydrates" with compounds containing both hydrogen peroxide and water of crystallisation being termed " perhydrate hydrates", e.g., Na2C204.H202, sodium oxalate monoperhydrate [IUPAC, sodium oxalate - hydrogen peroxide (1/1)]; Na2SO4.1H2O2.H2O, sodium sulphate hemiperhydrate monohydrate [IUPAC, sodium sulphate - hydrogen peroxide - water (2/1/2)]. (b) Compounds containing the anion C206 are termed " peroxydi- carbonates", e.g., K2C206, potassium peroxydicarbonate [IUPAC, dipotassium peroxodicarbonate]. (c) Compounds containing the anion HC04 are termed " peroxy- bicarbonates", e.g., KHC04, potassium peroxybicarbonate [IUPAC, potassium hydrogenperoxomonocarbonate]. (d) Compounds containing the anion CO4 are termed simply " peroxycarbonates", e.g., Li2C04.H20, lithium peroxycarbonate mono- hydrate [IUPAC, dilithium peroxomonocarbonate - water (1/1)]. 12 Vibrational Spectra. Frequencies for infrared and Raman spectra are quoted in wave- -1 numbers, cm . Bands obtained are described as s, strong ; m, medium ; w, weak ; b, broad or sh, shoulder and v, very. Raman bands are also described as p, polarised or dp, depolarised for solution spectra.