Hydrolysis Constants of n-Aliphatic Amine Salts W. H. SLABAUGH Department o f Chemistry, Oregon State College, Corvallis, O r e .
VERNON E. CATES Department o f Chemistry, Kansas State College, Manhattan, Kan.
The hydrolysis constants of n-priniary amines in approximately 22% ethyl alcohol solutions were determined from potentiometric titration data. The p& values determined by extrapolation to zero ionic strength were in good agreement with published values of pKh in water solutions determined by conductance and e.m.f. methods.
I
N AX’ ordinary titration of an amine solution a i t h a strong acid, using a glass electrode p H meter, it was noted that the data obtained at the end point provided a very simple method of calculating the hydrolysis constant of the ainine ion. In view of the agreement of this method with more rigorous and conventional methods, it was considered of interest t o apply this titration method to a group of amines in order to assess its value. An excellent summary of references and data is made by Hoerr and coworkers ( 4 ) who used the conductance ratio method and by Hall and Sprinkle ( 2 ) who measured electromotive force values of cells without liquid junctions. Both groups of workers overcame the problem of solubility of the higher amines in water by making measurements on alcohol solutions of various concentrations and subsequently extrapolating the results to zero alcohol concentration. These v,-orkers have shown that the change in conductance and electromotive force, both attributed to the ionization of the systems involved, is relatively small in dilute alcohol solutions. Consequently, the present study was based on amine solutions R hich contained approximately 22Y0 ethyl alcohol at the end point of the titration. In titrating a weak base with a strong acid, a salt is formed which undergoes partial hydrolysis according to the equation
B+
+ H20 % BOH + H +
According to typical derivations ( 3 ) of the hydrolysis constant pI
