This paper is a report of the potentiometric determination of the relative acid strengths of the substituted benzoic acids in the solvents ethylene glycol and «-butyl alcohol. The paper also includes a discussion of the results presented for the solvents methyl alcohol (10) and ethyl alcohol (11), together with the results available for aqueous solution (5).
experimental partThe experimental method has already been described (10) and the only difference noted in the application of the method was that longer times were necessary for the establishment of electrode equilibrium in «-butyl alcohol. In addition, an electrode would occasionally become poisoned and have to be replaced. The poisoning of an electrode showed itself by an appreciable potential difference between two electrodes in the same solution, the e.m.f. usually changing with time. It was found that gold-on-glass electrodes prepared by the method of Newberry (23) gave more reproducible results in «-butyl alcohol, since these electrodes could be cleaned by heating to redness in the flame of an alcohol lamp. All measurements were carried out at 25°C.Ethylene glycol was purified by the method of Akerlof (1). The glycol was allowed to stand over powdered, freshly calcined calcium oxide for several days. The calcium oxide was removed by filtration and the ethylene glycol distilled through a Widmer column. The boiling point for each distillation was very constant. The distillation temperature was 90.0°C. at 6 mm. of mercury and 95.5°C. at 11 mm.The index of refraction was nl°= 1.4321. The purity, calculated from a density determination on the assumption that the only impurity was water (20), was 99.93 per cent.«-Butyl alcohol was purified by the method of Mason and Kilpatrick 1 This paper was abstracted from the dissertation presented by John Habersham Elliott to the Faculty of the Graduate School of the University of Pennsylvania in partial fulfilment of the requirements for the degree of Doctor of Philosophy, April, 1940. It was read at the Ninety-ninth Meeting of the American Chemical Society, which was held in Cincinnati, Ohio, April, 1940.
The purpose of this work is to investigate, by an experimentally consistent method, the effect of substituents on acid strength. The acids chosen for study were the monosubstituted benzoic acids. These acids have the advantages that much theoretical work has been done on the subject of benzene derivatives, and that the geometrical relationships between the groups in the benzoic acids are relatively simple. Ideally, a thorough investigation of relative acid strengths and the effect of substituents on acid strengths would involve the determination of the thermodynamic quantities free energy, entropy, and heat of reaction in a number of solvents. In aqueous solution and in dioxane-water and water-methyl alcohol mixtures, a part of this task has been completed by Harned and his coworkers (18) for the aliphatic-carboxylic acids by measurement of 1 This paper was abstracted from the dissertation presented by John Habersham Elliott to the Faculty of the Graduate School of the University of Pennsylvania in partial fulfilment of the requirements for the degree of Doctor of Philosophy, April, 1940. It was read at the Ninety-ninth Meeting of the American Chemical Society, which was held in Cincinnati, Ohio, April, 1940.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.