780
The Journal of Physical Chemistry, Vol. 83, No. 7, 7979
TABLE 11: Analytical I R Frequencies and Cross Sections l O I 9 cross section/cm2 substance freq, em-' molecule-' (base e ) HONO, NO? H2 0 NO
1325 1629 3855 1875
12.4,' 25.1,b 17.3a3 1.08" 1.06b
Spectrometer resolution 2 cm-l. Pressure l o 5 Pa. Resolution 0.2 cm-I. Pressure l o 5 Pa. Prior value Prior value 1 3 x 9.3 x at 2 cmML (ref 9). a t 4 cm-' (ref 10). a
of the flow patterns when they were used to mix nitrogen dioxide with nitrogen. Capillary flowmeters with a pressure transducer (National Semiconductor Type LX16QlD) as measuring element were calibrated by volumetric measurement of gas flow. Spectrophotometric measurements were made on a Perkin-Elmer Model 180 spectrometer operated a t 2-cm-l resolution in the linear absorbance mode. At the frequencies used, careful Calibration established linear dependence of absorbance on mole fraction of the substance measured. The frequencies and approximate cross sections are given in Table 11. They are in approximate agreement with other available values. Data Treatment. The experiments were simulated using the values of k z / k 3 ,k3, and k 4 / k 5indicated earlier. It was
M. N. Schuchmann and C. von Sonntag
assumed that the gases entered the reactor with a uniform composition and maintained uniform composition over the cross section of the reactor. The value of k z was varied until the computed composition of nitrogen dioxide at the position of measurement equaled that obtained experimentally.
Acknowledgment. We gratefully acknowledge financial support of this work by the Australian Research Grants Commission. M. J. McEwen and L. G. Phillips, University of Canterbury, N.Z., gave us the principle of the mixers and sliding seal in the reactors. H. S. Johnston (University of California, Berkeley) gave hospitable comment. References and Notes Smith, J. H. J . Am. Chem. SOC.1947, 69, 1741. Godfrey, T. S.;Hughes, E. D.;Ingold, C. K. J. Chem. SOC.1965,
1063. Johnston, H. S.;Foering, L.; White, J. R. J. Am. Chem. Soc., 1955, 77, 4208. Johnston, H. S.;Foering, L.; Thompson, R. J. J. fhys. Chem., 1953, 57, 390. Kaiser, E. W.; Wu, C. H. J . fhys. Chem. 1977, 87,187. JANAF Thermochemical Tables; Dow Chemical Company: Midland, Mich. Jones, L. H.;Badger, R. M.; Moore, G. E. J . Chem. fhys. 1951, 79,
1599. Weast, R. C., Ed. "Handbook of Chemistry and Physics", 57th ed.; CRC Press: Cleveland, Ohio, 1976; p D215. Graham, R. A. Thesis, University of California, Berkeley, 1975. Harker, A. B. Thesis, University of California, Berkeley, 1972.
Hydroxyl Radical-Induced Oxidation of 2-Methyl-2-propanol in Oxygenated Aqueous Solution. A Product and Pulse Radiolysis Studyt Man Nien Schuchmann and Clemens von Sonntag" Institut fur Strahlenchemie im Max-flanck-lnstitut fur Kohlenforschung, 0-4330 Mulheim a.d. Ruhr, West Germany (Received October 6, 1978) Publication costs assisted by the Institut fur Strahlenchemie im Max-flanck-lnstitut fur Kohlenforschung
The reactions of the 2-methyl-2-hydroxypropylperoxylradical were investigated by y and pulse radiolysis of aqueous oxygenated solutions of 2-methyl-2-propanol. The products and their G values [in brackets] on y radiolysis of a NzO/02 (80/20 v/v) saturated solution at 20 "C are formaldehyde (I [1.3]),acetone (I1 [1.6]), 2-methyl-2-hydroxypropionaldehyde(I11 [2.0]),2-methyl-2,3-propanediol (IV [0.5]),an organic peroxide, very likely di(2-methyl-2-hydroxypropyl)peroxide (V [0.7]),and hydrogen peroxide (VI [2.0]). Two major decay processes for the 2-methyl-2-hydroxypropylperoxylradical are proposed: (i) formation of O2 and two 2methyl-2-hydroxypropyloxyl radicals which either combine (product V), disproportionate (products I11 and IV), or fragment (products I and 2-hydroxypropyl-(2) radicals), and (ii) formation of VI and 111. The 2hydroxypropyl-(2) radicals add oxygen to give the corresponding peroxyl radicals which rapidly eliminate HOz. (product 11). The HOz-radicals largely disproportionate (products VI and 02),At pH 9.4 the rate of the formation of 02-.(pK,(HO,.) = 4.75) is determined by the bimolecular decay of the primary peroxyl radicals. The rate constant of the latter reaction was obtained pulse conductometricallyas 2k = (8 f 2 ) X 10' M-' s-'. Competition among the different modes of reaction is evident from the effect of deuterium substitution and temperature on the distribution of products yields.
Introduction The radiolysis of dilute aqueous 2-methyl-2-propanol solutions in the presence of oxygen provides a unique and
'Radiation Chemistry of Alcohols XXII. For part XXI see R. Ford, H.-P. Schuchmann, and C. v. Sonntag, J . Chem. Soc., Perkin Trans. 2, 1338 (1975). 0022-365417912063-0780$01.0010
convenient way to study the behavior of P-hydroxyalkylperoxyl radicals. Here the radiation energy is absorbed by the solvent water. The primary reactive species are OH radicals, solvated electrons, and H atoms. OH radicals attack 2-methyl-2-propanol by preferentially abstracting carbon-bound hydrogen atoms,' generating the 2-hydroxy-2-methylpropyl radical (reaction 1). The latter
0 1979 American Chemical Society
The Journal of Physical Chemistry, Vol. 83, No.
Radical Induced Oxidation of 2-Methyl-2-propanol
7, 1979 781
TABLE I: Products and Their G Values in y Irradiated 2-Methyl-2-propanol Solutions (0.01 M ) Saturated with N,O/O, Effect of Temperature and Deuterium Substitution
( 8 0 / 2 0 v/v) or Oxygen.a
l___l_-
G value 2-Me-2-PrOH 0 2
a
Droduct
0 "C
20 " C
70 " C
N,O/O, 20 " C
formaldehyde, I acetone, I1 2-hydroxy-2-methylpropionaldehyde, I11 2-methyl-2,3-propanediol, IV di( 2-hydroxy-2-methylpropyl) peroxide, V hydrogen peroxide, VI 2-hydroxy-2-methylpropylhydroperoxide, VI1 hydrogen, VI11
0.6 0.6 1.0
0.7 1.0 0.9 0.3 0.4 2.2 absent 0.4
1.7 2.2 0.8 0.2 0.8 2.0 absent nd
1.3 1.6 2.0 0.5 0.7 2.0 absent nd
0.3 0.1 2.4 nd nd
2-Me2-Pr OH-d N,O/O, 20 " C 2.0 2.4 1.1 0.6 0.7 1.6 nd nd
Dose rate 0.48 W kg-'. nd, not determined.
adds olxygen a t a nearly diffusion-controlled rate2 (reaction 2) to form the corresponding peroxyl radical. CH,
+ 'OH
CH,-C-CH, I
9 5% ---+
CH3 I
+ H,O
CH,-C-CH; I
A (1)
OH
OH
CH3 I
CH,-C-CH; I
CH,
+
0, -+ CH,-C-CH,O,. I
(2)
OH
OH
The H atoms and solvated electrons are scavenged by oxygein (reaction 3 and 4). Alternatively, the solvated
H.+ O2 eaq-
-+ H02. eaq- O2
+ NzO
+
(pK, = 4.75)3 02-.
*OH + OH-
+ N2
(3)
R-'
t
B
(4) (5)
electrons can be converted by N 2 0to OH radicals (reaction 5) using a gas mixture of N 2 0 and O2 (4:l v/v). The /3-hydroxyalkylperoxy1 radical derived from 2methyl-2-propanol, unlike the a-hydroxyalkylperoxyl radicals derived from primary and secondary alcohol^,^-^ cannot undergo an HOz. elimination reaction through intramolecular 1,4 H transfer.618 Bimolecular reactions between two peroxyl radicals (CH3)2C(OH)CI-120z-, possibly through the formation of a tetroxide as an intermediate: are therefore the expected mode of reaction.
Results y Radiolysis. The y radiolysis of 2-methyl-2-propanol was studied with N20/02 (80/20 v/v) or 02-saturated 0.01 M aqueous 2-methyl-2-propanol solutions irradiated at 0.48 W kg-' to conversions
