1 Introduction ................................................. l
1.1 Why are non-aqueous solvents important? ................. 3
1.1.1 Range of accessible pH-values .................... 3
1.1.2 Reactivity of acids and bases .................... 5
1.1.3 Ionizable compounds and high-performance
liquid chromatography (HPLC) ..................... 5
1.2 Classification of solvents and their properties ......... 5
1.2.1 Electron donor-acceptor properties of solvents ... 6
References ................................................... 9
2 Acid-Base Equilibria: Quantitative Treatment ................ 10
2.1 Definitions ............................................ 10
2.2 pH and acid-base ratios ................................ 11
2.3 pH-dependence of species distribution .................. 12
2.4 Acid strengths and molecular structure: dissociation
constants in water ..................................... 15
2.4.1 The strength of the X-H bond .................... 15
2.4.2 Charge dispersion on anions, A-, or cations,
BH+ ............................................. 16
2.4.3 The nature of X in R-X-H ........................ 17
2.5 Carbon acids ........................................... 17
2.6 Acid-base equilibria ................................... 19
Appendix 2.1 Species distribution in acid-base systems ...... 19
References .................................................. 20
3 Solvation and Acid-Base Strength ............................ 21
3.1 Solvation and acid dissociation constants: free
energies of transfer ................................... 21
3.1.1 Solvent-transfer activity coefficients .......... 23
3.2 Determination of free energies of transfer ............. 23
3.2.1 Non-electrolytes ................................ 23
3.2.2 Electrolytes .................................... 25
3.3 Free energies of ion solvation ......................... 27
3.3.1 Hydration of ions ............................... 27
3.3.2 Solvation in pure solvents ...................... 28
3.3.3 Solvation in mixed solvents ..................... 31
3.4 Solvation of non-electrolytes .......................... 32
3.5 Solvation energies and solvent properties .............. 33
3.6 Solvation and acid strength ............................ 34
3.7 Summary ................................................ 35
Appendix 3.1 Composition of mixed solvents .................. 36
References .................................................. 38
4 Determination of Dissociation Constants ..................... 39
4.1 pH-scales .............................................. 39
4.1.1 pH in aqueous media ............................. 39
4.1.2 pH in non-aqueous media ......................... 41
4.2 Influence of solution concentration: activity
coefficients ........................................... 41
4.3 Ion association ........................................ 43
4.4 Homohydrogen-bond formation ............................ 44
4.5 Experimental methods for the determination of
dissociation constants ................................. 46
4.5.1 Potentiometrie titration using a glass
electrode ....................................... 47
4.5.2 Acid-base indicators ............................ 50
4.6 Autoionization constants of solvents ................... 53
Appendix 4.1 Dissociation of acetic acid in the presence
of sodium chloride ..................................... 54
Appendix 4.2 Ion-pair formation and pKa-determination ....... 54
Appendix 4.3 Determination of homohydrogen-bond
association constants, Kaha ............................ 55
References .................................................. 57
5 Protic Solvents ............................................. 59
5.1 Autoionization constants ............................... 59
5.2 Methanol ............................................... 60
5.2.1 Neutral acids: carboxylic acids, phenols ........ 61
5.2.2 Cationic acids: protonated anilines, amines,
N-heterocycles .................................. 64
5.2.3 Summary ......................................... 66
5.3 Higher alcohols ........................................ 66
5.4 Alcohol-water mixtures ................................. 68
5.5 Salt formation in alcohols and aqueous-alcohol
mixtures ............................................... 70
5.6 Formamide, acetamide, N-methylpropionamide ............. 72
5.7 Formic acid ............................................ 74
References .................................................. 75
6 High-Basicity Polar Aprotic Solvents ........................ 76
6.1 Dimethylsulphoxide .................................... 77
6.1.1 Neutral acids: carboxylic acids, phenols and
thiophenols, water and methanol, anilines and
amides, carbon acids ............................ 78
6.1.2 Cationic acids (neutral bases) .................. 86
6.1.3 Amino acids ..................................... 87
6.2 JV-methylpyrrolidin-2-one, N, N-dimethylformamide,
N, N-dimethylacetamide ................................. 89
6.2.1 Neutral acids ................................... 89
6.2.2 Cationic acids (neutral bases) .................. 92
6.3 Liquid ammonia ......................................... 93
6.4 Summary ................................................ 95
6.5 Estimation of dissociation constants in basic aprotic
solvents ............................................... 96
References .................................................. 97
7 Low-Basicity and Low-Polarity Aprotic Solvents .............. 99
7.1 Acetonitrile .......................................... 100
7.1.1 Neutral acids: carboxylic acids and phenols,
carbon acids ................................... 100
7.1.2 Cationic acids (neutral bases) ................. 105
7.2 Propylene carbonate, sulpholane, acetone, methyl
wo-butyl ketone, nitrobenzene ......................... 108
7.3 Tetrahydrofuran ....................................... 111
References ................................................. 115
8 Acid-Base Equilibria and Salt Formation .................... 111
8.1 Charge-neutral equilibria ............................. 118
8.2 Charge-forming equilibria ............................. 120
8.2.1 Alcohols and mixed-aqueous solvents ............ 120
8.2.2 Polar aprotic solvents ......................... 124
8.2.3 Non-polar aprotic solvents ..................... 127
References ................................................. 128
9 Appendices: Dissociation Constants in
Methanol and Aprotic Solvents .............................. 130
9.1 Methanol .............................................. 130
9.1.1 Carboxylic acids and phenols ................... 130
9.1.2 Protonated nitrogen bases ...................... 131
9.2 Dimethylsulphoxide .................................... 132
9.2.1 Carboxylic acids, alcohols, phenols ............ 132
9.2.2 Inorganic acids and miscellaneous .............. 133
9.2.3 Anilines, anilides, amides (N-H-ionization) .... 133
9.2.4 Carbon acids: ketones, esters, nitroalkanes .... 133
9.2.5 Carbon acids: nitriles, sulphones .............. 134
9.2.6 Carbon acids: fluorenes ........................ 134
9.2.7 Cationic acids: anilinium, ammonium,
pyridinium ions ................................ 135
9.3 N, N Dimethylformamide ................................ 135
9.3.1 Neutral acids .................................. 135
9.3.2 Cationic acids ................................. 136
9.4 Acetonitrile .......................................... 136
9.4.1 Neutral acids .................................. 136
9.4.2 Inorganic acids and miscellaneous .............. 137
9.4.3 Cationic acids: ammonium, anilinium,
pyridinium ions ................................ 138
9.4.4 Phosphazene bases .............................. 138
9.5 Tetrahydrofuran ....................................... 140
9.5.1 Neutral acids .................................. 140
9.5.2 Cationic acids ................................. 140
Index ......................................................... 141
|
