Brian G. Cox
- Published in print:
- 2013
- Published Online:
- May 2013
- ISBN:
- 9780199670512
- eISBN:
- 9780199670512
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199670512.003.0001
- Subject:
- Physics, Condensed Matter Physics / Materials
Non-aqueous solvents typically lack water’s ability to solvate effectively both anions and cations, and consequently have acidity scales that differ considerably from those in water. These ...
More
Non-aqueous solvents typically lack water’s ability to solvate effectively both anions and cations, and consequently have acidity scales that differ considerably from those in water. These differences often lead to profound changes in the available range and reactivity of acids and particularly bases, which has important consequences in synthetic and analytical chemistry and in the formation and isolation of salts. Properties of solvents are reviewed. The presence (protic solvents) of absence (aprotic solvents) of acidic protons capable of hydrogen-bond donation is a key distinguishing feature of solvents. Important also is the ability to stabilize charged species through donation or acceptance of electron pairs, as represented by parameters such as solvent Donor Numbers, Acceptor Numbers, and hydrogen-bond basicity. The dielectric constant is strongly influential in determining the extent of ion-association, which is a dominant factor in acid–base equilibria in low-dielectric media.Less
Non-aqueous solvents typically lack water’s ability to solvate effectively both anions and cations, and consequently have acidity scales that differ considerably from those in water. These differences often lead to profound changes in the available range and reactivity of acids and particularly bases, which has important consequences in synthetic and analytical chemistry and in the formation and isolation of salts. Properties of solvents are reviewed. The presence (protic solvents) of absence (aprotic solvents) of acidic protons capable of hydrogen-bond donation is a key distinguishing feature of solvents. Important also is the ability to stabilize charged species through donation or acceptance of electron pairs, as represented by parameters such as solvent Donor Numbers, Acceptor Numbers, and hydrogen-bond basicity. The dielectric constant is strongly influential in determining the extent of ion-association, which is a dominant factor in acid–base equilibria in low-dielectric media.
Brian G. Cox
- Published in print:
- 2013
- Published Online:
- May 2013
- ISBN:
- 9780199670512
- eISBN:
- 9780199670512
- Item type:
- book
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199670512.001.0001
- Subject:
- Physics, Condensed Matter Physics / Materials
Acids and bases are ubiquitous in chemistry. Our understanding of them, however, is dominated by their behaviour in water. Transfer to non-aqueous solvents leads to profound changes in acid-base ...
More
Acids and bases are ubiquitous in chemistry. Our understanding of them, however, is dominated by their behaviour in water. Transfer to non-aqueous solvents leads to profound changes in acid-base strengths and to the rates and equilibria of many processes: for example, synthetic reactions involving acids, bases, and nucleophiles; isolation of pharmaceutical actives through salt formation; formation of zwitter-ions in amino acids; and chromatographic separation of substrates. This book seeks to enhance our understanding of acids and bases by reviewing and analysing their behaviour in non-aqueous solvents. The behaviour is related where possible to that in water, but correlations and contrasts between solvents are also presented. Fundamental background material is provided in the initial chapters: quantitative aspects of acid–base equilibria, including definitions and relationships between solution pH and species distribution; the influence of molecular structure on acid strengths; and acidity in aqueous solution. Solvent properties are reviewed, along with the magnitude of the interaction energies of solvent molecules with (especially) ions; the ability of solvents to participate in hydrogen bonding and to accept or donate electron pairs is seen to be crucial. Experimental methods for determining dissociation constants are described in detail. In the remaining chapters, dissociation constants of a wide range of acids in three distinct classes of solvent are discussed: protic solvents, such as alcohols, which are strong hydrogen-bond donors; basic, polar aprotic solvents, such as dimethylformamide; and low-basicity and low-polarity solvents, such as acetonitrile and tetrahydrofuran. Dissociation constants of individual acids vary over more than twenty orders of magnitude among the solvents, and there is a strong differentiation between the response of neutral and charged acids to solvent change. Ion-pairing and hydrogen-bonding equilibria, such as between phenol and phenoxide ions, play an increasingly important role as the solvent polarity decreases, and their influence on acid–base equilibria and salt formation is described.Less
Acids and bases are ubiquitous in chemistry. Our understanding of them, however, is dominated by their behaviour in water. Transfer to non-aqueous solvents leads to profound changes in acid-base strengths and to the rates and equilibria of many processes: for example, synthetic reactions involving acids, bases, and nucleophiles; isolation of pharmaceutical actives through salt formation; formation of zwitter-ions in amino acids; and chromatographic separation of substrates. This book seeks to enhance our understanding of acids and bases by reviewing and analysing their behaviour in non-aqueous solvents. The behaviour is related where possible to that in water, but correlations and contrasts between solvents are also presented. Fundamental background material is provided in the initial chapters: quantitative aspects of acid–base equilibria, including definitions and relationships between solution pH and species distribution; the influence of molecular structure on acid strengths; and acidity in aqueous solution. Solvent properties are reviewed, along with the magnitude of the interaction energies of solvent molecules with (especially) ions; the ability of solvents to participate in hydrogen bonding and to accept or donate electron pairs is seen to be crucial. Experimental methods for determining dissociation constants are described in detail. In the remaining chapters, dissociation constants of a wide range of acids in three distinct classes of solvent are discussed: protic solvents, such as alcohols, which are strong hydrogen-bond donors; basic, polar aprotic solvents, such as dimethylformamide; and low-basicity and low-polarity solvents, such as acetonitrile and tetrahydrofuran. Dissociation constants of individual acids vary over more than twenty orders of magnitude among the solvents, and there is a strong differentiation between the response of neutral and charged acids to solvent change. Ion-pairing and hydrogen-bonding equilibria, such as between phenol and phenoxide ions, play an increasingly important role as the solvent polarity decreases, and their influence on acid–base equilibria and salt formation is described.
