2714
NOTES
third phase formed below this temperature was approximately constant. Cyclohexane-Nitrobenzene Mixtures. The inadequacy of any explanation of tliird-phase formation based on the bulk dielectric constant of the organic phase was demonstrated by experiments with solutions of MDOA in cyclohexane-nitrobenzene mixtures, since the addition of nitrobenzene to a three-phase system, followed by re-equilibration, was found to cause an increase in the volume of the middle phase. Table IV shows the results of quantitative experiments with 5 ml. of aqueous nitric acid, 5 ml. of 0.11, 0.22, and 0.44 M MDOA in cyclohexane, and 1 ml. of nitrobenzene.
Table IV : Third-Phase Formation with Solutions of MDOA i n Cyclohexane-Nitrobenzene
Initial
“Os concn., aq. phase,
iM
6.78 6.78 6.78 8.97 8.97 8.97
Total amount of
MODA, rnrnoles
0.55 1 10 2.20
0.55 1.10 2.20
Vol. of equil. aq. phase, rnl.
Vol. of
equil. concn., middle equil. aq. phase, phase, .W rnl. HNOa
5.0 4.9 4.85 5.0 4.9 4.85
6.49 6.38 6.05 8.62 8.42 8.07
1.0 1.5 2.4 0.8 1.5 2.4
Amount of HNOa in equil. middle phase, mrnoles
1.11 2.16 2.40 1.12 2.67 3.17
Amount of HNOa in equil. upper phase, mrnoles
0.103
0.067 0.046 0.116 0.078 0.066
Compared with the results in Table 111, the most pronounced changes are (a) a considerable increase in the amount of acid in the upper organic phase, and (b) an increase in the volume of the middle phase. The nitrobenzene must be distributed between the two organic phases, which probably accounts for the increased acidity of the upper phase. In general then, third-phase formation in the nitric acid-ILIDOA-cyclohexane system is not a siniple function of solubility or dielectric constant. The third phase contains the quaternary ammonium nitrate plus solvent, and the high viscosity niay be due to aggregates of salt solvent water. Froni a practical point of view, this effect can be avoided by using polar diluents. Finally, we collect our qualitative observations on a number of mineral acid-M3OA-diluent systems. With cyclohexane as diluent, third-phase formation occurs with 2 M hydrobromic, hydrochloric, nitric, perchloric, and sulfuric acids; with chloroform and the same strength acids, no third phase occurs (although sulfuric acid forms three phases at higher acid concentra-
+
T h e J o u m a l of Physical Chemistry
+
tions’). Carbon tetrachloride gives two phases with hydrobromic, hydrochloric, and nitric acids, but three phases with perchloric acid.
Experimental Materials. Methyldioctylamine and aqueous acids were as in previous work.’ Cyclohexane (May and Baker laboratory grade) was used as received; all other solvents were analytical or laboratory grade. The experimental procedure was as before. Volume Measurements. The appropriate solutions were shaken manually in calibrated stoppered measuring cylinders for 30 min. and then allowed to separate on standing for several hours. The middle phase separated slowly, due to its apparently high viscosity; droplets adhering to the cylinder walls were removed by further gentle agitation. The total final volume was always equal to the separate initial volumes of the solutions within experimental error. The total weight of the middle phase was obtained from the volume and the density measured with a weight pipet. Acknowledgment. We wish to thank the University of Yottingham for the award of a postgraduate studentship to s. s. C.
The Action of Ionizing Radiations on Aqueous Oxygenated Solutions of Acetaldehyde’ by J. T. Allan Radiation Research Laboratories, Mellon Institute, Pittsburgh, Pennsylvania (Receioed April 30,1064)
I n previous radiation-chemical studies of dilute aqueous systems containing oxygen and an organic the conibined yields of the reducing and oxidizing radicals, “HJ1and OH, formed in the decomposition of mater molecules have been detcrniined on the basis of the observed peroxide yields, since each organic peroxy radical intermediate produced after initial reaction of an OH radical with the organic solute normally yields HOz by uniniolecular decomposition or hydrogen peroxide, or a stable hydroperoxide, by reaction with another peroxy radical and “H” radicals yield hydrogen peroxide via the intermediate formation of HOz radicals. The radical yields have thus been obtained from the relationship (1) This work was supported, in p a r t , by the Atomic Energy Commission.
(2) G . Scholes and J. J. Weiss, Radiation Res. Suppl., 1 , 177 (1969)
NOTES
G("H")
27115
+ (;(OH)
=
2{G(peroxide) - G"(H20s)
}
The results presented here for the 02-acetaldehyde system indicate, however, that processes such as
RO2
+ RO, --+ 2R' + HZ02 +
ROz
+ HOz
0 2
(1)
0 2
(2)
and +R'
+ HzOz +
occur to only a minor extent which suggests that thle above relationship is a n unreliable guide to the estimation of G("H") and G(OH) in oxygenated solutions.
peroxide yields determined by the two experimental techniques mere identical and equal to the initial H202 yield, indicating that all the hydroperoxide decayed and that decomposition of the hydroperoxides did not lead to additional hydrogen peroxide. The decomposition of the hydroperoxides in aqueous acetaldehyde solutions is attributed to the reactions CH3CO01H
Results and 1)iscussion The initial products detected in irradiated aqueous 02-CH3CH0 solutions were acetic acid, formaldehyde, hydrogen peroxide, and two hydroperoxides. One of the hydroperoxides was subsequently identified as peracetic acid, CH&OOZH; the second is assumed to be peroxyacetaldehyde, OHCCHs02H. Ethanedial' and dialkyl peroxides were tested for and found to bte absent. Quantitative estimations of HCHO, H202, and R02H yields were carried out. G values were obtained from yield-dose dependencies, using doses of up to 2 X 10'8e.v. g.-'. Identi$cation of the Hydroperozides. The hydroperoxides were produced in solutions a t p H >4 and decayed at a rate which was independent of the initial p H in the range pH 4-9 and dependent upon the acetaldehyde concentration. Twenty hours after irradiation the
2CH3COOH ( 3 )
and CHzOzH I
Experimental Irradiations were carried out with 6oCo y-rays or with 2.5-Mev. electrons from a Van de Graaff accelerator. The dose rate of the cobalt-GO source (3.80 X 1 0 I 6 e.v. g.-I min.-I) was determined by the Fricke dosimeter taking G(FelI1) = 15.5. Doses employed in the electron irradiations were determined absolutely by the charge input method (dose rate -2 X l O I 9 e.v. g.-I rnin.-'). Techniques employed in the preparation of the oxygenated aqueous solutions have been described previously. Fornialdehyde was quantitatively determined in the presence of acetaldehyde by a modification of the chroinotropic acid technique. Yields were identical in solutions tested immediately after and 20 hr. after irradiation. Hydrogen peroxide was determined using the titanium sulfate method.5 Color formation was suppressed to some extent by acetaldehyde when present in concentrations greater than -2 x M . Corrections were applied to account for this effect. Hydroperoxide yields were obtained using the iodide6 and titanium sulfate methods in conjunction.
+ CH3CH0
+ CH3CHO + ka
CHO CHZOH
1
+ CH3COOH
(4)
CHO The pseudo-first-order rate constants were found to be k3 = 0.83 + 0.1 1. mole-' niin.-' and ka = 0.45 h 0.1 1. mole-l min.-1, respectively. Using commercially produced peracetic acid, reaction 3 was found to have a rate constant of k = 0.73 ==I 0.1 1. mole-' niin.-'. Peracetic acid accounted for approxiinately 37% of the hydroperoxide yield. The values quoted for G(R02H) in Tables I and I1 were obtained by extrapolating the plots of the hydroperoxide yields measured as a fund ion of time to zero time after completion of the irradiation. The data presented in Table I for 6oCoy-rays indicate that the peroxide yields mere largely determined by radiation-induced chain processes involving acetaddehyde. Similar results mere obtained with 2-propanol-02 solutions in which the radiation-induced chain reactions produced effects which were more pronounced in the presence of acid and resulted in higher yields of the organic products relative to h,ydrogen peroxide.8 I n solutions irradiated with the higher dose-rate electron radiations, the radical-solute reactions responsible for chain initiation are effectively eliminated. Thus in Jf acetaldehyde solutions a reaction such as (G), together with the molecular yield of hydrogen peroxide, would account for a major portion [G(K2O2) 1.01 of the H202 yields shown in Table 11.
-
(3) J. T. Allan, J . P h y s . Chem., 6 8 , 2697 (1964). (4) W. -M. G r a n t , I n d . Eng. Chem., Anal. Ed., 20, 267 (1948). ( 5 ) G. XI. Eisenberg, ibid., 15, 327 (1943). (6) A. 0. Allen, C. J. Hochanadel, J. A. Ghorrnley, and T. W. Davies, J . P h y s . Chem., 56, 575 (1952).
(7) J. M. Dechary, E. Kun, and H. C. Pitot, Anal. Chem., 26, 449 (1954). ( 8 ) J. T. Allsn and C. Scholes, to be published.
Volume 68, rVurnber 9
September, 1.964
NOTES
2716
Table I : Hydrogen Peroxide and Hydroperoxide Yields as a Function of Radiation Dose Rate and Acetaldehyde Concentration in Oxygen-Saturated Solutions Irradiated at p H 1.20 and a t pH -7 Acetaldehyde
,---------doc0
concn.,
PH
M
1.20
-7
2
x
7
x
2 5 7
x x x
y-ray8
G(Hz0z)
10-3 10-2 10-9 10-1
1.60 f 0 . 2 2.30 4.50
10-3 10-3 10-2 10-2 10-1
1.90 zt 0 . 2 2.15 2.53 3.40
G(R0zH)
...
1.50 2.15 i 0 . 4 4.50 6.50 ...
, . .
, . .
Table 11: pH Dependence of the Peroxide and Formaldehyde Yields in Oxygen-Saturated M Acetaldehyde Solutions Irradiated with 2.5-Mev. Electrons G(R0zH)
G(Ha0z)
1.20 2.80 4.50 5.80 6.40 7.00 8.80 9.80 10.20
1.40rtO.l 1.45 1.40 1.28 1.25 1.24 1.25 1.07
0 0 0 0 0 0 0
0 . '39
1 12
CHsCHO OzCHzCH(0H)z
U(HCH0)
f 0 2
10 60 65 86 85
2HCHO
0 0 0 0
80
. . ,
1.50
...
0.86 f 0 . 2 ... 1.30
The hydrogen peroxide yields shown in Table I1 are too sniall t o be accounted for on the basis of reactions such as (1) and (2). It is apparent, therefore, that reactions can occur between the various peroxy radicals which do not yield Hz02. These mechanisiiis have not been elucidated.
Kinetics of Ion Exchange in a Chelating Resin
80 82
+ HZOz +
0 2
School of Chemistry, Rzitgers, T h e State University, S e w Brzinswick, ,\'eu Jersey (Received March 5 , 1964)
(5) (6)
(7)
0 2
+ 0%
1 . 2 4 i0 . 1
, . .
by Albert Varon and William Rieman, I11
+ eaq- +CHBCHO-
CH3CHO-
, . .
73
Acetaldehyde (CH3CHO) will coinpete with H 3 0+ and/or O2 for the radiation-produced electrons in this system The fact that the H 2 0 zyields obtained for 2.5Mev. electron irradiations vary only slightly with increase in acetaldehyde concentration indicates that the peroxy radicals resulting from CHsCHO
, . .
O75fOI
+ HZO 1-CH,CH(OH)2
+ HOz +
2.5-hlev. electrons G(Hz0z) G(R0zH)
1.44 f 0 . 1 1.40
, . .
PH
-
CH3CHOH
(8)
In a previous report' from this laboratory, it was concluded that the actual chemical reaction was the rate-controlling step iii ion-exchange processes involving a chelating resin (Dowex A-1) and any cation capable of forming a chelate with the iniinodiacetate groups of the resin. On the other hand, it was recently reported2 that diffusion within the resin is the slow step in the exchange of calcium, strontium, and magnesium with the hydrogen form of the same resin. The conclusion of Turse and Riemanl had been drawn from a study of the kinetics of exchange reactions by the limited-bath method, in which supposedly equivalent amounts of the resin and exchanging solution had been taken. However, recent work in this laboratory3 revealed an error
react in a niannner stoichiometrically equivalent to 0 2
The Journal of Physical Chemistry
(1) R. Turse and W.Rieman, J . P h y s . Chem., 6 5 , 1821 (1961). (2) C. Heitner-Wirguin and G. Markovits, ibid., 67, 2263 (1963). (3) A. Varon, Thesis, Rutgers, T h e State University, New Brunswick, N.J., 1963.
