4-Chloro-phenol acidity constant

The catalytic constants measured in 95% aqueous dioxan have been compared with piT-values in water. The twenty-four acids referred to in Table 3 are mainly carboxylic acids, but also include nitric acid, o-chloro-phenol and water. Two oximes show large positive deviations, and saccharin has considerably less catalytic activity than anticipated these substances have not been included in the correlation. A number of strong acids gave closely similar catalytic constants— HCl (3-05), HBr (2-30), CoHb.SOsH (2-30), MeSOsH (2-15), HCIO (1-25)—and the minor variations within this series are not in the expected order of acid strengths HCIO4 > HBr > HCl > ObHb. SO3H > MeSOsH. Presumably all these acids are converted in solution to the hydronium ion, the catalytic power of which is somewhat modified by ion-pairing with different anions in the solvent of low dielectric constant. The catalytic constants observed are consistent with the conventional value pJT = —1-74 for H36+. 

Halogenation of phenol also leads to phenol derivatives which are much more effective than the starting substance. At the same time, the dissociation constant increases with an increase in the number of halogen atoms, i.e. the acidic character of the phenol derivatives becomes more distinctive. The combination of alkylation and halogenation (the latter with preference in the p-position) has led to microbicides which have attained great practical significance as substances for the protection of materials and disinfection, e.g. p-chloro-o-benzyl phenol, p-chloro-m-cresol, p-chloro-/M-xylenol. 

---