NOTES
438
.-$
14,0001
e
O
1 Ca- Bentonite
12,000.
: 10,0001
t? I+
0 20 40 60 80 100 120 Mg. HaO adsorbed/g. bentonite. Fig. 4.-Isosterio heats of adsorption of water vapor by sodium and calcium bentonites.
Ordinarily, isosteric heats are calculated from a pair of reversible isotherms at two temperatures. In this instance, however, there was hysteresis in the adsorption-desorption process, particularly with the monoionic clays, and the isosteric heats obtained in this manner may not be strictly valid. I n spite of this, isosteric heats of adsorption, cslculated from data collected a t 14.0 and 27.0" for the adsorption process, not only agree well with the heats of adsorption derived from heat of immersion studies,* but they further agree with the proposal that there is a discontinuity in the adsorption process. Figure 4 summarizes the isosteric heats for sodium and calcium bentonite, with points A and B corresponding t o the discontinuities A and B in Figs. 1 and 2 for sodium and calcium bentsonitelrespectively. Table I lists the isosteric heats a t the two V , values obtained from BET plots. These conclusions are further substantiated by the fact that similar calculations on the desorption isotherms give almost the same results. TABLE I ISOSTERIC HEATSOF ADSORPTION CORRESPONDING TO THE Two VALUESOF Vm DERIVEDFROM BET PLOTS, IN KCAL. PER MOLE OF ADSORBED WATER,AND BET AREASWITH ARGON Cation type clay
Li Na (oven-dried) Na (freeze-dried)
K H Mg Ca Ba
Sn Zn Cd Cn Fe
Ni
AX1
14.0 12.5 11.4 11.1 12.9 15.6 14.6 14.9 13.8 15.1 13.0 16.4 12.8 9.8
AH8
.. 10.0 10.6 10.0 11.3 12.5 11.0 12.6 12.4 11.6 11.9 13.5
.. ..
Area, m.l/g.
22.4 10.3 13.9 29.6
Vol. 63
ported that the chromic acid oxidation of isopropyl alcohol is slightly but significantly catalyzed by pyridine. The reaction was carried out in aqueous solution at 25" with a pyridine-pyridinium ion buffer and about 0.005 M (H+). Recently2RoEek and KrupiEka have repeated this work and find that the catalysis by pyridine is less than that previously' reported, and in fact is too small to be of importance. When we use the exact experimental conditions described by the respective authors, we can (at least approximately) repeat both sets of data. However, a reconsideration of these experimental conditions shows that, in conformity with RoEek and KrupiEka's claim, the catalysis by pyridine is very small. Roc'ek and KrupiEka added crystalline pyridinium perchlorate to their solution of alcohol, perchloric acid and chromic acid. We have confirmed that their procedure is satisfactory. I n the earlier experiments, * however, the acidities of the solutions containing sodium perchlorate on the one hand and pyridinium perchlorate on the other were matched by adjusting the solutions until a spectrophotometric determination of indicator color was the same for the two solutions. This method involved the assumption that, a t constant ionic strength, the effects of the two salts (sodium and pyridinium perchlorates) on the activity coefficients of the dye were the same. Reinvestigation has shown that this assumption is not correct. Experimental
Materials.-Thymolsulfonphthalein (Eastman Kodak) of m.p. 212-214' (with dec.) showed only a single spot in
paper chromatography.3
4-Chloro-2,6-dinitrophenol4 was
TABLE I SALTEFFECT O N THYMOLSULFONPHTHALEIN molar, T = 25". Indicator, 3.45 x HC104, M
pH0.b
ds~rnp'
Indicator alone 0 00473 2.36 0.227 NaClO4, 0.195 M ,00473 2.35 .224 PyHC104, 0.195 M .00473 2.33 .192 PgHClO4, 0.195M .00608 2.22 .223 N-MePyC104, 0.195M .00473 2.35 .186 N-MePyC104, 0.195 M .00629 2.24 ,224 Measured with a, a Average of three measurements. glass electrode and a Beckman model G pH meter.
TABLE I1 EFFECT ON 4CHLORO-2,6-DINITROPHENOL molar, T = 25' Indicator, 5.22 X
SALT
HClO4, M
21.0 33.6 26.4 35.0
PYRIDINE CATALYSIS OF THE OXIDATION OF ISOPROPYL ALCOHOL BY CHROMIC ACID BY F. H. WESTHEIMERA N D Y.W. CHANG Contribution from the Mallinckrodt Labo~atoriesof Halvard Universe'tu Cambridge, Maes. Received September 0, 1068
In 1951, Holloway, Cohen and Westheimer' re-
pH'*b
drrarnr"
0,00473 2.36 0.081 .00473 2.36 .086 .00473 2.35 .lo4 .00625 2.19 .086 N-MePyC104, 0.195 M ,00473 2.37 .I08 ,00702 2.18 .087 Measured with a Average of three measurements. glass electrode and a Beckman model G pH meter. Indicator alone NaC104, 0.195 M PyHC104, 0.195 M
purified by recrystallization of the potassium salt, and then Merck reagent grade perof the phenol; m.p. 81-82'. ( 1 ) F. Holloway, M. Cohen and F. H. Westheimer, J. Am. Chrm. Soe., 78, 65 (1951). (2) J. R o h k and J. Krupifka, Coll. Czech. Chem. Communicaliona,
in press: J. Rofek, private oommunioation. (3) G. T. Franglen, Nature, 176, 144 (1955). (4) M. Dubois, 2. Chem., 10, 206 (1867).
?
e
March, 1959
TABLE I11 RATESOF CHROMIC ACIDOXIDATION OF HClOi (mole/l.)
439
NOTES
NaClOr (mole/l.)
PyHC104 (mole/l.)
ISOPROPYL
N-MePyC104 (mole/l.)
0.0053 0.195 .0055 .195 .0053 0. 195d .0055 .195e .0055 0.195 ,0046 ,195 .0046 .190d ,0046 .16 .0046 .1@ a Measured with a glass electrode and a Beckman model G pH meter. urements. By matching. a Crystalline pyridinium perchlorate.
ALCQHOL AT 25'
pH0
dsrsb
2.34 2.34 2.22 2.33 2.35
0.233 .235 .239 .197 .190
k , l./mole min. - 1 x 104
0.83 0 . 91' 1.54' 1.04' 0. 9oc 0.591' 1.221 0. 722
0.872 b
Thymolsulfonphthalein.
Average of two meas-
chloric acid was standardized and used without further arose from the method of measuring acidity. The purification; Mallinckrodt analytical reagent chromic acid was twice recrystallized from water. Merck reagent implication of these facts for the mechanism of the grade pyridine was dried over BaO, distilled from KMn04 oxidation of isopropyl alcohol will be considered in and fractionated; the fraction boiling at 115-116' was used. later publications. Pyridinium perchlorate, recrystallized from water and Acknowledgment.-The authors wish t o thank dried under high vacuum a t room temperature, melted a t 284-286'. Anal. Calcd. for C5He04NCl: C, 33.43; the U. S. Rubber Company for a grant in support H , 3.37; C1, 19.73. Found: C, 33.42; H, 3.47; C1, 19.69. of this work. N-Methylpyridinium perchlorate was pre ared from the calculated amounts of silver perchlorate an$N-methylpyriINTERACTION OF IMIDAZOLE dinium iodide.6 The salt, recrystallized from aqueous methanol, melted a t 135-136". Anal. Calcd. for CEHSO~NCI: WITH COBALT(I1) C,37.21; H,4.16. Found: C, 37.60; H,4.21. Indicator Characteristics.-Thymolsulfonphthdein (3.45 BY R, MATHURAND HIRAL A L ~ X 10-5 M ) gave an optical density of 1.305 at, 545 mp in 12.N hydrochlorjc acid, 1.338 in 6 N acid and 1.329 in 2 N Physical Chemistry Division, National Chemical Laboratory, Poona 8 , India acid, a t 25". Since these values are closely the same, the Received August 88, 196'8 value of 1.33 was chosen. The optical density of the indicator solution a t pH 4 or 6.85 was 0.051. A series of Studies on the interaction of imidazole with measurements with 0.002 to 0.05 M hydrochloric acid established the indicator constant (extrapolated to infinite Cu,II Zn,II CdII and N i I I have been made by earlier dilution) as 0.025. The full color of 4-chloro-2,6-dinitroworker^.^-^ The present note describes the interphenol (5.22 X M , a t 25') is obtained in 0.02 N alkali action of imidazole with Co.11 a t 446 mN; the optical density is 0.384. I n 0.5 N HCI the Experimental optical density is zero. pH Measurements were made with R Beckman model G pH meter. Potentiometric measurements were made with a Beckman Salt Effects.-The salt effects upon the indicators are general purpose glass electrode in conjunction with a preshown in Tables I and 11. cision potentiometer and an electrometer null-detector inRates of Oxidation.-The rates of oxidation of isopropyl corporating an Osram electrometer tube ET1. A Beckman alcohol in the resence of erchloric acid and sodium per- saturated calomel half-cell was used a6 reference electrode. chlorate, pyrdnium perc&orate or N-methylpyridinium The over-all accuracy of measurements was expected to be perchlorate are shown in Table 111. The rates are com- within =!=0.01pH unit. pared under conditions where the acidities of the three Measurements on freshly prepared mixtures of imidazole systems are the same as measured by glass electrode, and nitiate, NaOH and cobaltous nitrate were made in an airalso under conditions where the colors of the indicator conditioned room maintained at 25.0 & 0.5". An ice(thymolsulfonphthalein) have been matched. water bath was used for measurements at 2.0 i 0.5'.& In general, the experimental procedure described by Edsall Discussion and co-workers2 was followed. Both pyridinium perchlorate and N-methylpyriAnalytical grade reagents were used throughout. A dinium perchlorate lower the activity of the acid stock solution of cobalt nitrate was standardized gravimetrically as cobaltinitroso-6-naphthol.6 Imidazole was an form of thymolsulfonphthalein and of dinitrophenol Eastman Co. product used after prolonged drying more than sodium perchlorate does, so that the as- over P& Kodak All measurements were made in a nitrate mesumption (implicit in the work of Holloway, Cohen dium of 0.15 ionic strength. The procedure for the evaluation of successive formation and Westheimer) that there is no specific salt efconstants was as described by Li and co-workers for the fect, was in error. NiII-imidazole.4 The Scatchard functliqn $?( - u / Under the experimental conditions shown in Ta- system: ( N - i ) ( I m ) , where 5 is the average number of imdarole ble 111, and using the technique of matching indi- molecules bound per metal ion, (Im)the equilibrium con-
cator colors to control acidity, the rates are not far from those reported earlier. However when the acidity is controlled by glass electrode measurements, the rate of chromic acid oxidation is only about 15% faster, in the presence of pyridinium perchlorate, than in the presence of N-methylpyridinium perchlorate or sodium perchlorate. These findings are in agreement with those of RoEek and KrupiEka. Most of the error (and perhaps all of it)
(6) E. D. Bergmann, F. E. Crane, Jr., and R. M. Fuoss, J . A m . ohem. Soc., 74, 5979 (1952).
(1) Indian Institute of Technology, Worli, Bombay 18. (2) J. T. Edsall, G. Felsenfeld, D. 8. Goodman and F. R. N. Gurd, J . A m . Chem. Soo., 7 6 , 3054 (1954). (3) C. Tanford and M. L. Wagner, ibid., 71, 434 (1953). (4) N.C.Li, T.L. Chu, C. T. Fujii and J. M. White, ibid., 71, 859 (1955). ( 5 ) The glass electrode was first introduced into the solution. After the temperature had become reasonably constant, the tip of the calomel electrode waa then introduced into the aolution and the reading taken after ten minutes. No significant error waa introduced even when readings were taken after longer periods. (6)F. J. Welcher, "Organic Analytical Reagents," Vol. 111, D. Van Nostrand Co., Inc., New York, N. Y., 1949, p. 303.
