NOTES
3498
four independent subsets with ncrjof 1,1,1,2. Thus the probability of column 3 is 100(2!1!1!1!/5!) or 1.791,. For benzene-carbon tetrachloride there are three independent subsets among the five points as 1,1,3,yielding 5%. For the anthracene-iodine system, however, effective evaluation of the data’s significance is difficultO5 There the subsets (two) overlap in their range of abscissas, and the probability of column 3 cannot be assigned as it was for the carbon tetrachloride systems. (The subsets in each of these systems have been assigned on the basis of the data uncertainty reported in the work.) It is apparent, however, that for the system the average ordinate of the subset with smaller abscissa is less than that of the subset with the larger abscissa, and that the data represents a trend is shown by the nonzero slope noted previously. Perhaps some limit may be established by considering the probability of the smaller average ordinate and the smaller average abscissa coinciding. This is 5091,. The probabilities of column 4 that the data in the systems represent members of a single population are, by the above considerations: mesitylene-carbon tetrachloride, 0.05% ; benzene-carbon tetrachloride, 0.15%; and anthracene-iodine, 0.8%. Person concluded with the 99% criterion that for the two systems containing carbon tetrachloride, the reported K values are not significantly different from zero, and for the third system K different from zero is just barely proved. Results by the present approach are in variance with this, however. It appears that the third system is the most doubtful of the three, although in all of them the probability of a single population is less than 1%. Clearly a systematic trend in behavior established with a sufficient number of data points can hardly be disregarded in establishing the statistical validity of the results. This is so, even though the uncertainty in slope and intercept may be relatively large because of a sizable uncertainty in the experimental determination of A . It is, of course, true that the statistical significance of the data does not in itself establish that the sole effect is complexation to the exclusion of solvation factors.
Reactions of Acetyl a n d Methyl Radicals with Nitric Oxide by H. E. Avery, D. M. Hayes, and L. Phillips’ Exploaines Research and Development Eatablishment, Ministry of Technology, W a l t h a m Abbey, Essex, U.K., and Department of Chemistry, Liverpool Regional College of Technology, Liverpool, U.K. (Received February 86,1969)
Disproportionation of nitric oxide by multiple addition to alkyl2and acetyl radicals3is now well established. T h e Journal of Physical Chemistry
Re RNO
+ NO-RNO
+ 2N0
(1)
RN(NO)O.NO
RN(iSO)O.NO A Re
+ N2 + *NO3
+ NO 2N02 R * + NO2 RNO2 R * + NOzRO. + NO RO. + NORON0 RO. + NO2 RON02 *NO3
(2) (3)
(4)
A
(5) (6)
-
(7) (8)
Although nitroalkanes, nitrites, nitrates, and nitrogen have been detected as products, attention has been directed mainly to the rates of nitrogen dioxide formation. Allen and Bagleyy4in studies on the photolysis of acetone at 3130 A in the presence of 5-100 Torr of nitric oxide a t 25”, have reported methyl acetate, formamide, nitromethane, and nitrogen dioxide as major products; methyl nitrate, but not nitrite, was a minor product. Results with biacetyl were said to be similar. The formation of methyl acetate by combination of methoxyl and acetyl radicals was thought unlikely, because it was not suppressed by nitric oxide pressures of 50 Torr, while that of acetone, from methyl and acetyl radicals, was. A reaction between nitrosomethane and nitrosoacetyl was proposed as 0 CHaNO
II + CHaC*NO
CH3COOCH3
+ Nz0
(9)
We have studied the reactions of acetyl and methyl radicals with nitric oxide,ousing the photolysis of 20 Torr of biacetyl at >2900 A as radical source, in a 60-ml silica reactor a t 25”, using a Hanovia S 500 mediumpressure lamp. Irradiation times of 3 hr were necessary because the quantum yield in biacetyl photolysis is very small.5 Table I presents our results. Organic products were estimated by gas-liquid chromatography and confirmed by mass spectrometry; nitrogen and carbon monoxide were separated by fractionation at -210’ and estimated mass spectrometrically. Nitromethane, nitrogen dioxide, and C02 were also formed as major products but were not estimated ; nitromethane yields can be estimated since6 k5/ks 0.5. The conversion of biacetyl, based N
(1) To whom correspondence should be addressed a t ERDE. (2) J. F. Brown, J . A m e r . Chem. Soc., 79,2480 (1957); M.I. Christie, C. Gilbert, and M. A. Voisey, J . Chem. SOC.,3147 (1964); M. I. Christie, J. 5. Frost, and M.A. Voisey, Trans. Faraday Soc., 61,674 (1965). (3) M. I. Christie, J. M. Collins, and M. A. Voisey, ibid., 61, 462 (1965);M.I. Christie and M. A. Voisey, ibid., 63,2459 (1967). (4) E.R. Allen and K. W. Bagley, Ber. Bunsenges. Phys. Chem., 72, 227 (1968). (5) J. G. Calvert and J. N. Pitts. “Photochemistrv,” John WiIey & Sons, Inc., New York, N. Y.,1967,p 421. (6) L. Phillips and R,Shaw, Tenth Symposium (International) on Combustion, Cambridge, U. K. 1965,p 453.
NOTES
3499
Table I: Products of Reaction of Acetyl and Methyl Radicals with KO Initial N O pressure, Torr
---___-
r
10.7
2.5 2.4 6.7 6.3 8.7 7.3
10.7 31.0 31.0 75.0 77.0
~ 0 . 4 -0.4 NO.1 NO.1 Nil Nil
on total acetyl radicals, is about 1.5%; this is a minimum figure since some photolysis of methyl nitrite and nitrate occurs. Methyl acetate is a major product and is only suppressed at nitric oxide pressures in excess of 31 Torr, in general agreement with Allen and Bagley. However, we find methyl nitrite but not formamide, as a major product; the absence of nitrite in Allen and Bagley’s work is difficult to understand since nitrate was found, and for methoxy radicalsj7k,/ks = 1.6. Reaction 9, proposed by Allen and Bagley, to explain the formation and persistence of methyl acetate at nitric oxide pressures of up to 50 Torr, seems unlikely. Of the two possible radical routes to methyl acetate
+ NO2 +CH3C02. + NO CH3COz + CH3 +CH3COzCH3 CH3CO + C H 3 0 . +CH3C02CH3
CH30
*
*
(15) (10)
(11)
reaction 10 seems improbable since Rembaum and Sawarcs found no methyl acetate in the gas-phase pyrolysis of diacetyl peroxide. At 10.7 Torr of nitric oxide, acetone is clearly formed by combination of methyl and acetyl radicals CH3
+ CH&O +CH3COCHs
2CH3C0
-
CHa
- + CHaGO
CzHG
(CH3C0)2
A
CHsCOCH3
0.18 0.18
0.69 0.53 0.71
0.21
0.22 0.05 0.05
CHsCOCHs
CHaONOz
0.25 0.20 0.02 0.02 0.02
Trace Trace 0.12 0.18 0.18 0.15
0.02
bination of methoxyl radicals12 (1012.2mol-’ cm3 sec-’) gives kll = mol-’ cm3 sec-’. On this basis the ratio of the rates of formation of acetone and methyl acetate and its variation with nitric oxide pressure are determined by [CHs.]/ [C?&O-]. Since kl < 1Ol1 mol-’ cm3 sec-’, allowing for falloff on the basis of Christie’s result^,'^ and12 k7 = 109.6mol-’ cm3 sec-’, [CH,.] will decrease more rapidly than [CH30 ] with increasing nitric oxide pressure. Acetone formation is therefore more easily suppressed than is methyl acetate; it is not necessary to invoke a nonradical mechanism for formation of the latter. 0
(7) G. Baker and R. Shaw, J . Chem. SOC.,6965 (1965). (6) A. Rembaum and M. Szwarc, J . Amer. Chem. Soc., 76, 1965 (1954). (9) A. Shepp, J . Chem. Phys., 24, 939 (1956). (10) S. W. Benson, “Thermochemical Kinetics,” John Wiley & Sons, Inc., New York, N. Y., 1968, pp 200,204. (11) A. F. Trotman-Dickenson, “Gas Kinetics,” Butterworth and Co. Ltd., London, 1955, p 111. (12) P. Gray, R. Shaw, and J. C. J. T h y m e , Progr. Reaction Kinetics, 4 , 83 (1967). (13) M,I. Christie, Proc. Roy. Soc., A249, 246 (1958).
(12)
since the results at higher nitric oxide pressures show that only a small fraction of the acetone comes from direct photolysis of biacetyl. There would therefore appear to be no compelling reason to exclude reaction 11 as the source of methyl acetate, unless kll is considerably less than k12. Application of the geometric mean rule to the systems A
0.02 0.02 0.88
-
----
Products, pmo-l CHsONO CHsCOzCHs
co
N 2
Production and Reactivity of Carbon-11 in Solid Compounds’
by Hans J. Ache and Alfred P. Wolf Chemistry Departments, Virginia Polytechnic Institute, Blacksburg, Virginia i.4061, and Brookhaven National Laboratorv, Upton, New York 11973 (Received April 16,1969)
(13) (14) (12)
takinge k13 = 1013.3and JCl4 = 1012.9mol-’ cm2 sec-1 (the latter is estimated taking So = 91.6 and 63.5 e.u., respectively, for biacetyP and acety1,’O and’’ L14= 1015e7sec-l) gives klz = 1013.2mol-’ cm3 sec-’. A similar treatment for the combination of methoxyl and acetyl radicals, using the estimated value for the recom-
The reactions of energetic carbon atoms produced by nuclear reactions have been studied in numerous organic systems. Results and postulated mechanisms are the subject of various review^.^-^ Only a few studies (1) Research performed under the auspices of the U. S. Atomic Energy Commission. (2) A. P. Wolf, Advan, Phys. Org.Chem., 2, 202 (1964). (3) C. MacKay and R. Wolfgang, Science, 148, 899 (1965). Volume 78, Number 10 October 1989
