COMMUNICATIONS TO THE EDITOR
4029
Table 11: Change in Molar Absorptivity with Temperature for the Fundamental OH Stretch of Phenol and Catechol in Carbon Tetrachloride Wavelength, m p
Phenol Catechol
@
Ae =
(e200
2777 2772 2808
- E ~ O ~ ) / ~ ~XO O100.
to 60" in all cases.
&%a
1l.Ob 11.3b 2.5b
The temperature range was 20
* Average of three samples.
solution does indeed exist. Evaporation of the solute in question may occur but not to such an extent to account for the observed change in the molar absorptivity provided small head spaces are used. We explain this temperature dependence in the manner of Finch and L i p p i n c ~ t t ;i.e., ~ the solute-free OH forms a weak hydrogen bond with the carbon tetrachloride. Some support for this can be derived from the work of Fumio and Katsuhiko, 9 who have isolated complexes of certain diols and carbon tetrachloride, and from Fletcher, lo who has presented evidence for the existence of a 1 : l complex between carbon tetrachloride and l-octanol.
Acknowledgment. The authors wish to acknowledge Lebanon Valley College for partial financial support for this research. (9) T.Fumio and A. Katauhiko, TetrahedronLett., 33,3695 (1968). (10) A. N.Fletcher, J . Phys. Chem., 73,2217 (1969). (11) To whom correspondence should be addressed.
DEPARTMENT OF CHEMISTRY LEBANON VALLEY COLLEGE ANNVILLE,PENNSYLVANIA 17003
G. P. HOOVER E. A. ROBINSON R. S. MCQUATE H. D. SCHREIBER J. N. SPENCER^^
RECEIVED AUGUST20, 1969
The Homoconjugation Constant of Picric Acid in Acetonitrile
Sir: I n a recent paper, D'Aprano and Fuossl reported that the homoconjugation constant, K'~pi,- = [HPi2-]/[HPi] [Pi-], of picric acid in acetonitrile (AN) is of the order 2 X lo2, a value some one hundred times greater than that reported previously by US.^ I n the where [SI denotes notation of FUOSS, = Kf~pi*-[S], the molarity of pure AN, i.e., 18.9 M . The method used by these authors is subject to unusually large errors. In brief, they added successive portions of solid picric acid to very dilute solutions of tetramethylammonium or tetrabutylammonium picrate. From the difference in electrical conductance of the mixtures after correction for basic impurities in the solvent and
x
that of the picrate solution without acid, they arrived at the large value of KfHpia- and the mobility of the HPi2ion ranging from 40 to 63 taking Xopi- = 77.a The correction to be applied for basic impurities was rather large as compared to the difference between the conductivity of the picrate solution with and without picric acid. From our work on the effect of picric acid on the solubility of potassium picrate in AN2 we arrived at the value of KfHpil- of the order of 2. Also, paH measurements in dilute mixtures of picric acid and tetrabutylammonium picrate indicated that KfHpig- must be very small. In order to substantiate our previous value we have measured the paH in mixtures of tetrabutylammonium picrate containing a large excess of picric acid. The equation used in the calculation of K f H p i n - from the experimental paH data had been derived previously.2 Also, we have estimated ioHPia by determining the effect of a large excess of picric acid on the conductance of dilute tetraethylammonium picrate solutions in AN. Acetonitrile was purified and dispensed as described previ~usly.~The water content as found from Karl Fischer titration was 1-2 X M . Picric acid2 and tetrabutylammonium picrate2 were products used previously. Tetraethylammonium picrate was prepared in this laboratory by H. Smagowski. Conductometric measurements and potentiometric paH techniques with the glass electrode have been described elsewhere. The following paH values were found in mixtures M in tetrabutylammonium picrate and 3.53 X 0.226, 0.439, and 0.835 M in picric acid: 8.92, 8.51, and 8.10, respectively, from which an average value of K f ~ p i a= - 2.4 f 0.5 was obtained. This value is in good agreement with that of 2.0 reported previously from solubility data of potassium picrate in presence of picric acid.2 Conductivity data of mixtures of picric acid and tetraethylammonium picrate are entered in Table I. Even after correction for viscosity, an appreciable decrease in conductivity was observed with increasing picric acid concentration a t a given salt concentration as observed by Fuoss.' The specific conductivity of 0.91 M picric acid alone was 1.5 X ohm-' cm-l, corresponding to C B H + = 1.1 X M . Since this value is less than 1% of the concentration of salt taken in the mixtures, C B H + can be neglected as compared to CEtrN t. Values of [Pis-], the subscript referring t o the simple ion in the solvent, and [HPiz-] in columns 5 and 6 in Table I were calculated using K f ~ p i e=- 2.0 and i4
(1) D. D'Aprano and R. M. Fuoss, J . Fhys. Chem., 73,223 (1969). (2) I. M.Kolthoff and M. K. Chantooni, Jr., J.Amer. Chem. Sac., 87, 4428 (1965). (3) J. F.Coetzee and C.P. Cunningham, ibid., 87,2529 (1965). (4) I. M. Kolthoff, S. Bruckenstein, and M. K. Chantooni, Jr., tbtd., 83,3927 (1961). Volume 73, Number 11 November 1969
COMMUNICATIONS TO THE EDITOR
4030 ~~
~~
~
Table I : Estimation of XoHPI1..from Conductivity of Picric Acid-Tetraethylammonium Picrate Solutions
CEtrNPi, CHPi, M
0.95 0 302 0.645 0.968 I
M
x IO'
Specific conduct.,a ohm-1 om-1
0 3.59 3.49 3.37
x
Viscosity,
104
0.015 4.93 4.64 4.42
CP
0.53 0.396 0.455 0,531
[HPiz-I?
[pi,-]? M x 108
M X 101
0.003 2.24 1.53 1.15
0.006 1.35 1.96 2.22
AH PI^-'
... Av
a Values corrected for viscosity; viscosity of solvent is 0.345 cP. atmosphere effects.
letting 5 = [HPiS-] and [Pis-] = [EtdN+] - 2. Since picric acid is in very large excess, its analytical and equilibrium concentrations are practically equal. In the calculation of XHPi2- from the specific conductance, L, of the picric acid-picrate mixtures the following relation was used in which the ionic mobilities a t infinite dilution of the tetraethylammonium and picrate ions were taken as 856 and 77,a respectively.
+
lo3 L = X E ~ ~ N + [ E ~ Nhpi,-[Pis-] +]
+ X~pi~-[HPiz-]
50 48.5 49 49
* Calculated using K f a p i p - = 2.0 (see text). ' Uncorrected for ion
approximately the same molecular size as the monoand dinitrophenols studied previously, the XoHA1values of which varied from 58 to 73,"the value of 57 for Xoapi,-seems reasonable.
Acknowledgment. This work has been supported by Air Force AFOSR Grant 1223-67. (6) D. S. Berns and R. M. Fuoss, J . Amer. Chem. Soo., 82, 6686 (1960). (6) I. M. Kolthoff, M. I(. Chantooni, Jr., and 8. Bhowmik, ibid., 88,6430 (1966).
From the data in Table I, an average value of XoEPiaequal to 57 was obtained. It is perhaps fortuitous SCHOOL OF CHEMISTRY I. M. KOLTHOFF that this value lies within the range reported by Fuoss.' M. K. CHANTOONI, JR. UNIVERSITY OF MINNESOTA Due to the instability of the HPi2- homoconjugate, MINNEAPOLIS, MINNESOTA 55455 large uncertainties are involved in the estimation of RECEIVED AUGUST25, 1969 XoaPia -. Nevertheless, considering that picric acid has
The Journal of Physical Chmiatry
