4345
QUANTUM YIELDOF PHOTONITROSATION OF CYCLOHEXANE
Quantum Yield of Photonitrosation of Cyclohexane in Homogeneous System
by Hajime Miyama, Kuya Fukuzawa, Noriho Harumiya, Basic Research Laboratory, Toyo Rayon Go., Ltd., Tebiro, Kamakura, J a p a n
Yoshikazu Ito, and Shigeru Wakamatsu Nagoya Laboratory, Toyo Rayon Go., Ltd., Minato-ku, Nagoya, J a p a n
(Receiued J u n e 80, 1069)
Quantum yield of photonitrosation of cyclohexane was measured in a homogeneous system, where the oxime hydrochloride formed was dissolved by adding chloroform to the reaction mixture. Obtained values were 0.80 f 0 . 0 6 at 365 mp, 0.79 =$ 0 . 0 6 at 436 mp, and 0.97 f 0.13 at 578 mp. These results were discussed from the mechanistic viewpoint.
In a previous; study, we have measured the quantum yield of photonitrosation of cyclohexane by using an integrating sphere to remove the effect of light scattering by the precipitated oxime hydrochloride and obtained a value of 0.72 independent of wavelengths. However, an estimated experimental error was as high as f 20%. In order to obtain the more accurate value, chloroform which is inert to nitrosyl chloride and dissolves the oxime hydrochloride was added to the reaction mixture and the measurement was performed at 365, 436, and 578 mp, in a homogeneous system by using conventional techniques.
Experimental Section A conventional optical system for measuring quantum yield was used and its schematic diagram is shown in Figure 1. The reaction vessel was a quartz cylinder (5 cm in diameter and 5 cm long) with flat quartz surfaces a t both ends and kept a t a constant temperature in an air bath. As the light source, a highpressure mercury lamp of 2 KW was used in combination with various Toshiba glass filters and an aqueous solution of copper sulfate to obtain monochromatic light. That is, UV-DIC was used to obtain the light of 365 mp, a combination of V-V 40, V-Y 42, and a 1% aqueous solution of copper sulfate for 436 mp, and a combination of V-0158 and a 1% aqueous solution of copper sulfate for 578 mp. The absorption characteristics of the glass-filters are shown in Figure 2. Absolute light intensities at 365 and 436 mp, were measured by using a potassium ferrioxalate actinometerlZand that at 578 mp, by a Reinecke's salt actinometer. Since the latter actinometer was considered less reliable tha,n the former one, a Kip & Zonen thermopile CA1 calibrated by the potassium ferrioxalate actinometer was used also a t 578 mp, giving the same results as those obtained with the chemical actinometer. Light absorption by the reaction system during the reaction was followed by means of the thermopile equipped with a recorder. Commercial cyclohexane was washed with concen-
trated sulfuric acid, water, sodium hydroxide and water dried over calcium chloride, refluxed over metallic sodium, and distilled in an argon atmosphere. Chloroform of the first grade was washed with water, dried with calcium chloride, and distilled. Hydrogen chloride in cylinder was used after being dried by passage through a calcium chloride tube. The quantitative analysis of the product of the photonitrosation was carried out by converting cyclohexanone oxime formed into chloronitrosocylohexane (CNC) by treatment with chlorine, and measuring the absorption of CNC spectrophotometrically. Since CNC was invariably present to some extent in the original product, the same analysis without the chlorine treatment was carried out as a control. The experimental procedure was as follows. An equal volume mixture of cyclohexane and chloroform was saturated with hydrogen chloride, and a definite quantity of nitrosyl chloride was bubbled into the mixture. This solution was then introduced into the reaction vessel. All of these operations were carried out in an argon atomsphere. The photoreaction was carried out at 24" for a given time, and the products were analyzed as described above. Since the dark reaction observed in the previous study' did not occur because of the high purity of the reactants used in the present system, no correction for the dark reaction was made.
'
Results and Discussion Results obtained at 365 mp, 436 mp, and 578 mp are shown in Tables I, 11,and 111, respectively. Here, the quantum yield was calculated by dividing the sum of the quantities of the oxime and CNC by the light quantity absorbed during the reaction. The reason for adopting the sum of the oxime and CNC is that the CNC present in the reaction mixture is derived from the oxime ac(1) H.Miyama, N. Harumiya, Y . Ito, and S. Wakamatsu, J. Phys. Chem., 72,4700 (1968). (2) C.A. Parker, Proc. Roy. Soc., A220, 104 (1963). (3) E.E.Wegner and A. W. Adamson, J. Amer. Chem. SOC.,88, 394 (1966).
Volume 78, Number 12 December 1069
H. MIYAMA, K. FUKUZAWA, N. HARUMIYA, Y . ITO,AND S. WAKAMATSU
4346
Table I : Results a t 365 mp
/I: 5
Figure 1. Schematic diagram of experimental apparatus L, light source, MI and M,, mask; Q1 and Q2, quartz condenser lense, F1, glass filter; F,, copper sulfate filter; Qa, quartz collimating lense; R, reaction vessel; A, air bath; T,thermopile. 100
-g
80
2 60
8
40
F
20 0200
Reaotion time, min
NOC1, weight%
CNC,a
120 240 240 121 100 181 242 242 120 240 362 120 121 100
0.76 0.62 0.54 0.68 0.71 0.30 0.25 0.35 0.35 0.35 0.35 0.35 0.35 0.38
100 100 76.4
%
50 50 10.7 5.9 2.9 24.0 >
Quantum yield
0.78 0.67 0.77' 0.88 0.86 0.74 0.77.A~0.81 f 0.06 0.80 0.88
Molar per cent expressed by [CNC]/( [oxime]
+ [CNC]) X
100(%). 300
500
400
600
700
800
Wave length I m p )
Figure 2. Absorption characteristics of glass filters.
-
cording to the following reaction. C~HI&=NOH
+ 2NOC1 r
Table I1 : Results at 436 r n M
In fact, this reaction
--f
y
c1H1o-C
c1 /
\
+ 2 N 0 + HC1
(I)
NO
was observed in our preliminary experiments and also reported by other researcher^.^ These tables show that the higher the concentration of nitrosyl chloride the larger the amount of CNC produced in the mixture. In the previous study1, this reaction was hardly observed because the oxime hydrochloride had precipitated and the concentration of nitrosyl chloride was low. Table I shows that no significant difference in quantum yield is present between the cases of high and low concentrations of nitrosyl chloride at 365 mp and that an average quantum yield is 0.80 f 0.06. Table I1 shows a similar tendency and an average quantum yield a t 436 mp is 0.79 f 0.06. On the contrary, Table I11 shows that the quantum yield a t 578 mp is 0.77 f 0.07 when the nitrosyl chloride concentration is high and 0.97 f 0.13 when it is low. From these results, the following main features are obtained; (1) the quantum yield does not exceed unity, (2) the higher the concentration of nitrosyl chloride, the larger the amount of CNC produced during the reaction, and (3) the quantum yields at 365 mp and 436 mp are about 0.8 independent of the nitrosyl chloride concentration, while that at 578 mp is close to unity for the low concentration and equal to 0.77 for the high concentration. The Journal of Physical Chemistry
Reaotion time, min
NOCl, weight%
CNC,
120 120 100 100 60 121 183 240 121 180 180 120 120 120 120 120 101 100 302
0.76 0.81 0.80 0.71 0.27 0.27 0.27 0.27 0.31 0.30 0.38 0.37 0.37 0.37 0.35 0.35 0.38 0.38 0.38
100 87.0
%
10.8 10.9 9.7 20.7 84.7 65 28.8
0.80'Av 0.78 f 0.06 0.75 0.78' 0.81 0.84 0.84
0.88 0.67.A~0.80 f 0.07 0.75 0.68 0.81 0.82 0.81 0.85 0.74,
The first feature suggests that a chain mechanism is not adequate as discussed in the previous reports. 1 ~ 6 The second is to be expected on the consideration of the reaction I. The third is very interesting and will be discussed below from the mechanistic viewpoint. Since the absorption of CNC begins at about 530 mp and has a maximum at 650 mp, CWC does not decompose a t shorter wavelengths. However, at longer wavelengths, CNC (4) E. Mtiller, H. G. Padeken, M. Salarnon, and G. Fiedler, Chem. Ber., 98, 1893 (1965). (6) K.F u k u z a w a and H. M i y a m a , J. Phys. Chem., 72,371 (1968).
4347
QUANTUM YIELDOF PHOTONITROSATION OF CYCLOHEXANE decomposes photochemically.6 Therefore, when the nitrosyl chloride concentration is high a t a longer wavelength, CNC derived from the oxime via reaction I Table I11 : Results at 578 rnp Reaction time, min
40 35 37.5 21 42 64 90 120 40 40 60 61 30 62 91 122 94 61 63 30 46 60 73 61 61 120 180 240 300 124 180 243 185 241 30 45 60 75 91 241 105 63 90 120 30 46 60 30 45 60 93 91 95 93 90 90 94 91
NOCl n
NOIC1, weight%
0.132 0.82 0.82 0.61 0.61 0.61 0.61 0.61
0.71 0.71 0.65 0.65 0.56 0.56 0.56 0.56 0.78 0.93 0.81 0.72 0.:72 0.:72 0.62 0.76 0.78
CNC, %
97.6 95.6 92.5 100 98.0 100 96.2 100 100
2.5
0.22 0.22 0.22
3.9 21.7 14.9 13.5 27.9 26.6 24.0 96.8
0.20 0.31
0.31 0.20 0.20
0.20 0.20 0.20
0.22 0.33 0.25 0.25 0.25 0.30 0.30 0.30 0.32 0.32 0.32 0.37 0.37 0.37 0.37 0.39 0.39 0.39 0.39
0.73' 0.72 0.79 0.77 0.83 0.68 0.70 0.72 0.69 0.68 0.77 0.80 0.92,Av0.77 It 0.07 0.76 0.83 0.73 0.80 0.76 0.82 0.76 0.78 0.82
0.22
0.20 0.20
Quantum yield
77.4 78.2 90.0 76.1 13.3 29.5
0.75 0.63 0.89 1.02( 1.09 1.23 1.22 0.88 0.87 0.88 1.06
0.85 0.83 1.10 l.lObAv 0.97It 0.13 1.05 1.05 0.81 0.96 0.95 0.72' 0.85 1.07 0.86 0.81
1.04 0.98 0.95 0.97 0.96 0.97,
CbHio-CH2
+ hv +NO + C1.
n + C1. +CjHio-CH + HCl
r i CaHlo-CH2
+ [NOCl]*
--+
0 H c - N.. n/
C5Hio-C
(A)
m
n
H
/ +CbH10-C +HC1 \
H ----, C1
r
i
NO
*
(B)
