587
DISSOCIATION CONSTANTS OF GLYCOLIC ACID IN SALT SOLUTIONS
Feb. 5, 1953
for the chlorides of potassium, sodium and lithium. The logarithm of the ratio of the dissociation constants a t infinite dilution from conductance data is 1.441. The agreement between the observed Values of log KA,B~ and those calculated by equation 4 is poorer for the points below 0.5 M . Table I1 gives the dissociation constant of acetic acid in methyl and ethyl alcohol and ethy1:ne glycol. The Kc/Ka ratios are in accord with the results for benzoic acid in the same solvents.
[CONTRIBUTION FROM
THE
TABLE I1 T~~ D~~~~~~~~~~~ coNsTANT OF A~~~~~ T,25'; solvent salt, LiCl
2liter 2, o 0.05 .10
CHaOH
CzHaOH
IN
A~~~~~~~ (CHz0H)z
10" Kel 10'0 10'0 Kc/ KA,B~ Kc Ka KA,B, K C K a KA,B, Kc 0.576 2.42 1.00 0.680 0.592 ... .573 13.2 5.46 ,680 9.40 15.9 0.447 101 .580 21.9 9.05 . . . ...
CHICAGO, ILLINOIS
DEPARTMENT OF CHEMISTRY OF
THE UNIVERSITY OF PENNSYLVANIA AND THE CHEMISTRY O F ILLINOIS INSTITUTE OF TECHNOLOGY ]
DEPARTMENT OF
The Dissociation Constants of Acids in Salt Solutions. III. Glycolic Acid BY MARTINKILPATRICK AND R. DEANEANES RECEIVED AUGUST22, 1952 The dissociation constant of glycolic acid has been determined in salt solutions using acetic, benzoic and the solvated proton as reference acids.
The equilibrium constants for the reaction HG
+ Bo ----t Ao + G-
(1)
where HG represents glycolic acid and A0 represents the reference acid, have been determined by the experimental method given in papers I' and 112 of this series. The results are summarized in Table I for the reference acids, benzoic, acetic and the solvated proton. The agreement between the experimental results is satisfactory. Extrapolation of the values for the equilibrium constant of equation (1) to iniinite dilution yields 1.51 and 1.45 X for the dissociation constant of glycolic acid on the for benzoic acid and 1.745 X basis of 6.32 X 10-5 for acetic acid. The values in the literature TABLE I
-
R d e n c e K A , B ~ K O X 10: add Benzoic
0.05 .10 .20 .30 .40 .50
.60 .70 .80 .90 1.00 1.50 2.00 2.50 3.00
2.47 2.39 2.64 2.50 2.60 2.56 2.54 2.51
.. .. 2.53 2.54
KA,B,
Kc X Acetic
x 104 10' Hydrochloric
Lithium chloride 2.26" 8.40 2.21b 2.65 8.47 2.68 3.03 8.52 2.79 2.97 8.57 2.91 3.36 8.59 3.15 3.32 8.63 3.13 3.30 8.64 3.12 3.25 8.66 3.11 8 . 6 1 3.08 8.77 3.18 3.26 8.83 3.20 3.20 9.05 3.21 9.60 3.05 10.51 2.83 10.75 2.77
2.34 2.62 2.77 2.99 3.03 3.05 3.12 3.13 3.19 3.25 3.21 3.13 3.06 2.99 2.85
(1) M. Kilpatrick, THIS JOURNAL, 75, 584 (1953). (2) M . Kilpatrick and R . D. Eanes, ibid., 76, 5W1 (1953).
2.04 2.26 2.58 2.70 2.71 2.86 2.94 2.82 2.84 2.86 2.82 2.58 2.33 1.98 1.80
1.44 1.58 1.70 1.81 1.87 1.92 1.87 1.90 1.86 1.83 1.82 1.74 1.54 1.27 1.10
Potassium chloride 1.46 2.20 8.29 2.15 .n 2.38 1.55 8.07 2.28 IU .20 8.39 2.43 2.55 1 . 6 5 8 . 4 8 2.54 2.64 1.72 .30 .40 8.53 2.60 2.68 1.76 .50 8.70 2.65 2.72 1.80 .60 8.75 2.66 2.72 1.80 2.70 1.73 .70 8.69 2.55 2.68 1.72 .80 8.79 2.54 2.53 1.70 .90 8 . 7 9 2.51 1.00 8.82 2.43 2.51 1.65 1.50 2.20 1.51 9.12 2.23 2.00 1.86 1 . 3 1 9.20 1.93 2.50 1.53 1 . 0 8 9.30 1.60 3.00 1.21 0.92 9.45 1.35 Based on K Ovalues from paper 1.' Based on K Ovalues from paper 1 1 . 2 e K OFrom column 5; K. = 1.475 X lo-'.
.
KC
moles/liter
.
Sodium chloride 2.43 2.22 8.36 2.12 2.43 2.44 8.35 2.33 2.52 2.42 8.42 2.51 8 . 5 3 2.67 2.48 2.82 8 . 5 1 2.76 2.52 . 2 . 9 7 8.65 2.83 2.53 3.01 8.52 2.76 2.52 2.99 2.50 2.95 8 . 7 5 2.80 8.82 2.74 2.53 2.97 2.52 2.91 8 . 8 3 2.70 8.97 2.68 2.54 2.89 2.53 2.65 9.38 2.56 9.82 2.27 2.60 2.39 10.1 1.88 2.63 1.99 1.63 2.68 1.74 10.4
0.05
DISSOCIATION CONSTANTS OF GLYCOLIC ACID AT 25' Electrolyte
0.05 .IO .20 .30 .40 .50 .60 .70 .80 90 1.00 1.50 2.00 2.50 3.00
Ke/ Ks
1.5OC 1.82 1.89 1.97 2.14 2.12 2.12 2.11 2.09 2.16 2.17 2.18 2.07 1.92 1.88
for the dissociation constant of glycolic acid are 1.475aand 1.54 X CHICAGO,ILL. (3) L.F. Nims, ibid., UI, 887 (1936). (4) J. BBcscken and H. Kalsbowen, R c c . fraa. chim., 87, 130 (1918).
