Info

a Reproduced from D. W. Newton and R. B. Kluza, Drug Intell. Clin. Pharm., 12, 547 (1978).

b Value for normal soft, formed stools, hard stools tend to be more alkaline, whereas watery, unformed stools are acidic. c Studies conducted intracellularly in the rat.

acetylsalicylate ion acts as a base, because it accepts a proton to yield an acid. An acid and base represented by such an equilibrium is said to be a conjugate acid-base pair.

Scheme 3.1 is not a realistic expression, however, since protons are too reactive to exist independently and are rapidly taken up by the solvent. The proton-accepting entity, by the Lowry-Bronsted definition, is a base, and the product formed when the proton has been accepted by the solvent is an acid. Thus a second acid-base equilibrium occurs when the solvent accepts the proton, and this may be represented by

HbO+

The overall equation on summing these equations is shown in Scheme 3.2, or, in general,

By similar reasoning, the dissociation of benzocaine, a weak base, may be represented by the equilibrium a Reproduced from D. W. Newton and R. B. Kluza, Drug Intell. Clin. Pharm., 12, 547 (1978).

b Value for normal soft, formed stools, hard stools tend to be more alkaline, whereas watery, unformed stools are acidic. c Studies conducted intracellularly in the rat.

will donate a proton and a base is a substance which will accept a proton. Thus the dissociation of acetylsalicylic acid, a weak acid, could be represented as in Scheme 3.1. In this equilibrium, acetylsalicylic acid acts as an acid, because it donates a proton, and the

NH2C6H5COOC2H5 + H2O

base 1

or, in general,

acid 2

= NH+C6H5COOC2H5 + OH0

acid 1

base 2

Comparison of the two general equations shows that H2O can act as either an acid or a base. Such solvents are called amphiprotic solvents.

Scheme 3.1

0 0

Post a comment