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Interaction of carbonyl triplets with α-phenylethyl hydroperoxide in CCl4
Journal of Luminescence 42 (1988) 103—107 North-Holland, Amsterdam
103
INTERACI1ON OF CARBONYL TRIPLETS WITH a-PHENYLETHYL
HYDROPEROXIDE IN CC!4 L.I. MAZALECKAJA
“,
G. MOGER and D. GAL
International Laboratory, Central Research Institute for Chemistry of the Hungarian Academy of Sciences, H-1525 Budapest, P0 Box 1 7~Hungary Received 24 November 1987 Revised 10 March 1988 Accepted 31 March 1988
Photochemical reactions of the triplets of benzophenone, 9,10-anthraquinone, anthrone, 1,4-naphthoquinone 1,2-benzanthracene with a-phenylethyl hydroperoxide in Cd4 at 303 K have been investigated. Benzene was used as spin trap for OH radicals, producing phenol. The quantum yields (~)of the formation of products have been measured. By exciting the carbonyl compounds (but not 1,2-benzanthracene) to their first triplet states at 366 nm in both the presence and the absence of C6H6 only methyiphenyl carbinol (HROH) and acetophenone (RO) were formed as products with ~HRoH/~Ro= 0.95 ±0.05at [HROOH]0 = 0.01—0.1 M. With excited 1,2-benzanthracene ~HROH/cZ~ROH was 1.32 ±0.08in Cd4 and ca. 2.9 in C6H6. No phenol was detected in CCI4. It can be assumed that the decomposition proceeds via sensitized 0—0 cleavage in the presence of 1,2-benzanthracene and via hydrogen abstraction in the presence of the other sensitizers. For systems in which hydrogen abstraction prevails, the ratios of the rate constants of physical quenching by HROOH to the rate constants of chemical reactions vary between 0.3 and 2.4 depending on the structure of the carbonyl compound.
1. Introduction Several quantitative data can be found in the literature on the reactivity of carbonyl triplets toward hydrocarbons, alcohols and phenols [1,2]. However, similar data on hydroperoxide molecules are very scarce [3,4]. Recently we have shown [5] that the decomposition of a-phenylethyl hydroperoxide (HROOH) in chlorobenzene at temperatures T ~ 363 K in the presence of tnplet anthraqumone (TQ) proceeds both via the rupture of the 0—0 bond and the abstraction of hydrogen from the parent molecule, HROO-H. This type of interaction is of principal interest because according to Scaiano and Wagner [3,6,7] highly reactive triplet
*
Present address: Institute of Chemical Physics, Moscow, USSR.
carbonyl compounds react similarly to alkoxyl radicals. In the present paper the interaction of the n-it triplets of various quinones, like anthraquinone, 9,10-dihydro-9-oxo-anthracene (anthrone), 1,4naphthoquinone and benzophenone, with HROOH is discussed.
2. Experimental Expenments were carned out in a Pyrex vessel, irradiated with a high-pressure mercury lamp “VEB NARVA HB200” at 304 K and A = 366 nm. CC!4 was used as solvent [8,9] and HROOH was synthesized as described earlier [10]. Light intensity was monitored by ferric oxalate [11,12]. Analyses were performed by both gas chromatography (XE-60 supported on Gaschrome Q) and high-pressure liquid chromatography.
0022-2313/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)~
104
L.1. Mazaleckaja et al.
/ Interaction of carbonyl triplets
3. Results
Table I of Values
It is we!! known [5,13] that the thermal decomposition of HROOH yields methyl phenyl carbinol (HROH) and acetophenone products. The same products are formed (RO) in theasphotochemical decomposition (see fig. 1), and the quantum yield of their formation is time independent at low conversions. The quantum yields of the formation of the products, can be expressed as: ~,
=
w/(I~ — I)
where w is the rate of the formation of the given product, and I~and I are the incident and transmitted light intensities, respectively. The quantum yields of HROH in the presence of various sensitizers, except 1,2-benzanthracene, and at various incident light intensities at the initial concentration [HROOH] 0 = 0.1 M are given in table 1. It can be seen from table 1 that X~ does not depend on (I~ I), while it increases with increasing concentration of HROOH (see fig. 2). The ratios of the quantum yields of HROH and RO are close to unity as shown in table 2. According to the data of table 2, the ratio ~HRoH/~Ro = 1, indicating, as will be shown, that under our conditions the triplet sensitizer
1~HR0H ~
concentrations of
at various incident light intensities and
Q
in air-saturated Cd
4, T= 304 K, 0.1 M, X = 366 nm _________________________________________ 4 I~x iO~ (Io — I) W X 10 ~HROH TQ C x i0 (M) x106 (M ~_1) (mol photon I ~1) [HROOH]0
=
Benzophenone
33 1.3
7.0 3.3 16.3
3.05 1.4 2.9
11.6 5.6 10.0
0.38 0.40 0.34
Anthraquinone
2 2 0.8
7.0 3.3
16.3
4.0 1.75 4.1
15.6 7.6 18.2
0.39 0.43 0.44
Anthrone
5 5 2
7.0 3.3 16.3
3.2 1.4 2.9
12.8 6.3 12.0
0.40 0.45 0.41
1,4-Naph-
1 1 0.4
6.8 3.3 16.3
3.0 1.5 3.0
10.8 6.0 7.8
0.36 0.40 0.26
thoqui-
none
—
1
ci
2
ci
8
04
08
0.2
abstracts hydrogen from HROOH yielding peroxy radicals, HRO [5]. In the photochemical decomposition of HROOH at A> 300 nm in the presence of 1,2(TQ)
0
005
01
0
-
005
(HROOH]0M
01 IHROOHIOM
3
4.
ci
0.4
ci 04
-
02
-
5.0
02
‘I —
0 0.0
20
T, mm
Fig. 1. Concentration of HROH (x) and RU (s) vs time in the photochemical decomposition of HROOH in the presence6of molphotonl1 1,4-naphthoquinone s1, in(HROOH] air-saturated CC14. 10—I=3x10 0=0.005 M, T=304 K, [Q]0 = io~ M, A = 366 nm.
I
I
005
0.1
I —
[HROOHI0M
0
005
0.1 EHR00H~0M
Fig. 2 Quantum yield of the formation of HROH (0) and RU (•) in the photochemical decomposition of HROOH in the (2x104 presence of M), (1) benzophenone (3) anthrone (3(5X104 x i0~ M),M), (2) anthraquinone (4) 1,4-naph4 M) in air-saturated Cd thoquinone (1x10 4, T=304 K, I~=1.63 x i0~ mol photon/s. A = 366 nm.
L. I. Mazaleckaja et aL
/
Table 2 ~HRoH/’I’Ro
values in reaction of TQ with HROOH in
air-saturated CCI4, 304 K, [HROOH] 0.01—0.1 M _______________________________________ =
TQ
~HRoH/~’RO
Benzo-
Anthra-
phenone
quinone
Anthrone 1,4-naphthoquinone
0.96 ±0.04 0.96 ±0.04 0.93 ±0.05 0.93 ±0.05
benzanthracene (1 x 10 ~ M) the ratios of the quantum yields of formation of products differ from unity: ~HROH
~RO
=1
.32 ±0.08,
supporting that the homolysis of HROOH is the prevailing pathway of the decomposition. The ratio increases up to about 2.9 with increasing amounts of benzene added to the system, in agreement with earlier results of Scaiano [3]. Since benzene is a good scavenger for OH radicals [14,15], phenol (PhOH) is expected to form in the system if the decomposition proceeds via the rupture on the 0—0 bond, Actually, with 1,2-benzanthracene sensitizer irradiated at A = 366 nm we were able to detect phenol, and found that in pure benzene
Interaction of carbonyl triplets
105
neat Cd4, supporting our assumption according to which the main route of the process is the rupture of the 0—H bond, with the exception of 1,2-benzanthracene as sensitizer where the rupture of the 0—0 bond occurs. In the presence of anthraquinone, anthrone, naphthoquinone and benzophenone, QH radicals formed in the TQ~induceddecomposition react with oxygen and yield H0 [16]. It has been shown [5] that at the HROOH concentrations applied in the experiments, H0 radicals are consumed mainly in their interaction with HROOH, and therefore their self-combination as well as process HO; + HRO can be neglected.
4. Discussion We have shown earlier that the hydrogen abstraction by H0 and HRO radicals from the a-position of HROOH can be neglected under the given conditions. This is the reaction i-io; (HR0;) + HROOH H202(HROOH)
+
ROOH -*
~HROH/~PhOH
=
1.5 ±0.1.
If, under some conditions, the decomposition is realized via hydrogen abstraction yielding HRO, ben.zene added to the system would not affect the formation rates of the products significantly. Table 3 shows the results obtained with sensitizers, except 1,2-benzanthracene, and in the presence of added benzene (1.32 M) at A = 366 nm. Phenol was not detected (table 3). According to table 3 the ratios of the quantum yields are practically identical to those obtained in
RO
+
OH
yielding RO molecules. Consequently, the following elementary processes can be assumed [16—19] to describe the overall reaction of the carbonyl triplet sensitized HROOH decomposition:
Q TQ
TQ TQ
+ +
+ 02
HROOH HROOH
T ....~
Q Q + 02
(0) (1)
—*
Q
(2) (3)
_,
+
QH
HROOH HR0~
+
~H+02-,Q+H0
(4)
Table 3 Ratios of the quantum yields of HROH and RO in the decomposition of HROOH by TQ in the presence of [C6H6] 2 M; = A=366 1.32 M. tim; Solvent: [0 CC14 3T=304 M K, [HROOH]=5x10 2]=1.8x10 Q Benzo- Anthra- Anthrone 1,4-Naphthophenone quinone quinone
According to processes (0) to (6), HROH and RO are formed exclusively in process (6) and taking into account the earlier data of Russell [20]
0.99 0.95 0.96 0.92 0.19 0.32 0.28 0.20 _________________________________________
and Howard et al. [13] the ratio of their concentration should be unity as was observed.
~HROH/~RO ~‘~HROH
HO; + HROOH HRO + HRO
_~
—s
HRO + H202 HROH + RO + 02
(5) (6)
106
LI. Mazaleckaja et aL
/ Interaction of carbonyl triplets
2 1,
10
/
raquinone, in case of anthrone benzophenone and naphthoquinone, rate coefficient whereas of thethephysical quenching by the oxygen exceeds the
-
. 5 “S
0
I
I
25
50
___________________
0
100
[HRO0H)~M~1
200 (HR00H]~M-1
4 8~
10
____________________
I
0
100
___________________
I
200 [HROOH]~M~1
0
100
I
200 R0~h0~M1
formation HROH and ROof(I~) against yields [HROOH]1 Fig. 3. Theofreciprocal values the quantum of the (based on data represented by fig. 2). [021 = 1.8 X i03 M.
Based on this mechanism we obtain =
~a +
1 ab 2 [HROOH]’
where di~is the total quantum yield + ~~Ro) and a
(i =
(~
yields is ~max = (2~~)~/2 = 0.77. This latter value is very close to the maximum quantum yield observed by Scaiano et al. [3] for the interaction of benzophenone and tert.-butyl hydroperoxide (0.65 in C6H6). A somewhat lower value (0.27) was obtained with cumyl hydroperoxide in C6H6 [4]. According to the literature data [17,18] the value of k1 does practically not vary in different solvents. Therefore, we used 5 s5 for anthraquinone k = 2 x iO~M and anthrone, 3 x iO~M1 s~1for benzophenone and 4
(7)
—
former value of (k2 + k3) by a factor of three. At the same time the interaction of benzophenone with HROOH leads preferably to a chemical transformation and the maximum of the quantum
~HROH
X
iO~M
s~ for naphthoquinone.
Consequently, (k 1 S1 for benzophenone,2 +1.3 s~ for k3)X=108 0.4 xM1 108 M anthraquinone, 1.2 x 108 M1 s~ for anthrone and 4 x 10~M~ s5 for naphthoquinone.
k
+
i—), 2\
b= k2+k3 k1[02]
References
Plotting the experimental data according to eq. (7) we have calculated the kinetic parameters given in fig. 3 and table 4. Table 4 shows that the values of k1/k3 and (k2 + k3)/k1 are nearly identical for anth-
Table 4 Calculated values of ~ k2/k3 and (k2 + k3)/k1 [02] =1.8x io~ M _______________________________________________ TQ (1/~)~ (k1[02]) (k2 + k3) k2/k3 /2k3
/k1
(M) Benzophenone 0.65 0.09 0.013 0.3 Anthraquinone 1.01 0.028 0.065 1.02 Anthrone 1.16 0.034 0.061 1.32 1,4-naphthoquinone 1.69 0.033 0.092 2.38 _____________________________________________________
[1] H. R.D. Small and J.C. Scaiano, J. Am. Chem. Soc. 100 Paul, (1978) 4520. [2] S.J. Formosinho, J. Chem. Soc. Faraday Trans. II 72 (1976) 1313. [3] L.C. Stewart, D.J. Carlsson, D.M. Wiles and J.C. Scaiano, J. Am. Chem. Soc. 105 (1983) 3605. [4] G. Geuskens and Q. Lu-Vinh, Eur. Polym. J. 18 (1982) 307. [5] L.A. Tavadyan, A.B. Nalbandyan, T. Vidôczy and D. Gal, Oxid. Commun. 4(1983)189;
G. MOger, A. Rockenbauer and P. Simon, Radiochem. Radioanal. Lett. 42 (1980) 407.
[6] P.J.
Wagner, Topics in Current Chemistry, Vol. 66, Triplet States (Springer, Berlin, Heidelberg, New York, 1976) p.
1. [7] J.C. Scaiano, J. Photochem. 2 (1973/74) 81. [8] J. Chateaneuf, J. Lusztyk and KU. Ingold, J. Am. Chem. Soc. 109 (1987) 897. [9] P.J. Wagner, R.J. Truman and J.C. Scaiano, J. Am. Chem. Soc. 107 (1985) 7093.
LI. Mazaleckaja et al.
E.
/ Interaction of carbonyl triplets
Danbczy, S. Holly, G. Jalsovszky and D. Gal, J. Phys. Chem. 88 (1984) 1190. [11] C.A. Parker, Proc. Roy. Soc. A220 (1953) 104. [12] J.N. Demas, W.D. Bowman, E.F. Zalewski and R.A. Velapoldi, J. Phys. Chem. 85 (1981) 2766. [13] J.A. Howard, Adv. Free Radicals Chem., Vol. 4, ed. C.H. Williams (Logos Press, London, 1972) p. 49. [14] 5. Gordon, K.H. Schmidt and E.J. Hart, J. Phys. Chem. 81 (1977) 104. [15] L.M. Dorfman, J.A. Taub and RE. BUhier, J. Chem. Phys. 36 (1962) 3051. [10]
107
[16] H. Inque, K. Ikeda, H. Mihara, M. Hida, N. Nakashima and K. Yoshihara, Chem. Phys. Lett. 95 (1983) 60. [17] A. Gamer and F. Wilkinson, Chem. Phys. Lett. 45 (1977) 432; J. Chem. Soc. Faraday Trans. II 72 (1972) 1010. [18] 5K. Chattopadhyay, G.V. Kumar and P.K. Pas, J. Photochem. 30 (1985) 81. [19] A.P. Darmanyan, Chem. Phys. Lett. 96 (1983) 383. [20] G.A. Russell, J. Am. Chem. Soc. 79 (1957) 3871.
103
INTERACI1ON OF CARBONYL TRIPLETS WITH a-PHENYLETHYL
HYDROPEROXIDE IN CC!4 L.I. MAZALECKAJA
“,
G. MOGER and D. GAL
International Laboratory, Central Research Institute for Chemistry of the Hungarian Academy of Sciences, H-1525 Budapest, P0 Box 1 7~Hungary Received 24 November 1987 Revised 10 March 1988 Accepted 31 March 1988
Photochemical reactions of the triplets of benzophenone, 9,10-anthraquinone, anthrone, 1,4-naphthoquinone 1,2-benzanthracene with a-phenylethyl hydroperoxide in Cd4 at 303 K have been investigated. Benzene was used as spin trap for OH radicals, producing phenol. The quantum yields (~)of the formation of products have been measured. By exciting the carbonyl compounds (but not 1,2-benzanthracene) to their first triplet states at 366 nm in both the presence and the absence of C6H6 only methyiphenyl carbinol (HROH) and acetophenone (RO) were formed as products with ~HRoH/~Ro= 0.95 ±0.05at [HROOH]0 = 0.01—0.1 M. With excited 1,2-benzanthracene ~HROH/cZ~ROH was 1.32 ±0.08in Cd4 and ca. 2.9 in C6H6. No phenol was detected in CCI4. It can be assumed that the decomposition proceeds via sensitized 0—0 cleavage in the presence of 1,2-benzanthracene and via hydrogen abstraction in the presence of the other sensitizers. For systems in which hydrogen abstraction prevails, the ratios of the rate constants of physical quenching by HROOH to the rate constants of chemical reactions vary between 0.3 and 2.4 depending on the structure of the carbonyl compound.
1. Introduction Several quantitative data can be found in the literature on the reactivity of carbonyl triplets toward hydrocarbons, alcohols and phenols [1,2]. However, similar data on hydroperoxide molecules are very scarce [3,4]. Recently we have shown [5] that the decomposition of a-phenylethyl hydroperoxide (HROOH) in chlorobenzene at temperatures T ~ 363 K in the presence of tnplet anthraqumone (TQ) proceeds both via the rupture of the 0—0 bond and the abstraction of hydrogen from the parent molecule, HROO-H. This type of interaction is of principal interest because according to Scaiano and Wagner [3,6,7] highly reactive triplet
*
Present address: Institute of Chemical Physics, Moscow, USSR.
carbonyl compounds react similarly to alkoxyl radicals. In the present paper the interaction of the n-it triplets of various quinones, like anthraquinone, 9,10-dihydro-9-oxo-anthracene (anthrone), 1,4naphthoquinone and benzophenone, with HROOH is discussed.
2. Experimental Expenments were carned out in a Pyrex vessel, irradiated with a high-pressure mercury lamp “VEB NARVA HB200” at 304 K and A = 366 nm. CC!4 was used as solvent [8,9] and HROOH was synthesized as described earlier [10]. Light intensity was monitored by ferric oxalate [11,12]. Analyses were performed by both gas chromatography (XE-60 supported on Gaschrome Q) and high-pressure liquid chromatography.
0022-2313/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)~
104
L.1. Mazaleckaja et al.
/ Interaction of carbonyl triplets
3. Results
Table I of Values
It is we!! known [5,13] that the thermal decomposition of HROOH yields methyl phenyl carbinol (HROH) and acetophenone products. The same products are formed (RO) in theasphotochemical decomposition (see fig. 1), and the quantum yield of their formation is time independent at low conversions. The quantum yields of the formation of the products, can be expressed as: ~,
=
w/(I~ — I)
where w is the rate of the formation of the given product, and I~and I are the incident and transmitted light intensities, respectively. The quantum yields of HROH in the presence of various sensitizers, except 1,2-benzanthracene, and at various incident light intensities at the initial concentration [HROOH] 0 = 0.1 M are given in table 1. It can be seen from table 1 that X~ does not depend on (I~ I), while it increases with increasing concentration of HROOH (see fig. 2). The ratios of the quantum yields of HROH and RO are close to unity as shown in table 2. According to the data of table 2, the ratio ~HRoH/~Ro = 1, indicating, as will be shown, that under our conditions the triplet sensitizer
1~HR0H ~
concentrations of
at various incident light intensities and
Q
in air-saturated Cd
4, T= 304 K, 0.1 M, X = 366 nm _________________________________________ 4 I~x iO~ (Io — I) W X 10 ~HROH TQ C x i0 (M) x106 (M ~_1) (mol photon I ~1) [HROOH]0
=
Benzophenone
33 1.3
7.0 3.3 16.3
3.05 1.4 2.9
11.6 5.6 10.0
0.38 0.40 0.34
Anthraquinone
2 2 0.8
7.0 3.3
16.3
4.0 1.75 4.1
15.6 7.6 18.2
0.39 0.43 0.44
Anthrone
5 5 2
7.0 3.3 16.3
3.2 1.4 2.9
12.8 6.3 12.0
0.40 0.45 0.41
1,4-Naph-
1 1 0.4
6.8 3.3 16.3
3.0 1.5 3.0
10.8 6.0 7.8
0.36 0.40 0.26
thoqui-
none
—
1
ci
2
ci
8
04
08
0.2
abstracts hydrogen from HROOH yielding peroxy radicals, HRO [5]. In the photochemical decomposition of HROOH at A> 300 nm in the presence of 1,2(TQ)
0
005
01
0
-
005
(HROOH]0M
01 IHROOHIOM
3
4.
ci
0.4
ci 04
-
02
-
5.0
02
‘I —
0 0.0
20
T, mm
Fig. 1. Concentration of HROH (x) and RU (s) vs time in the photochemical decomposition of HROOH in the presence6of molphotonl1 1,4-naphthoquinone s1, in(HROOH] air-saturated CC14. 10—I=3x10 0=0.005 M, T=304 K, [Q]0 = io~ M, A = 366 nm.
I
I
005
0.1
I —
[HROOHI0M
0
005
0.1 EHR00H~0M
Fig. 2 Quantum yield of the formation of HROH (0) and RU (•) in the photochemical decomposition of HROOH in the (2x104 presence of M), (1) benzophenone (3) anthrone (3(5X104 x i0~ M),M), (2) anthraquinone (4) 1,4-naph4 M) in air-saturated Cd thoquinone (1x10 4, T=304 K, I~=1.63 x i0~ mol photon/s. A = 366 nm.
L. I. Mazaleckaja et aL
/
Table 2 ~HRoH/’I’Ro
values in reaction of TQ with HROOH in
air-saturated CCI4, 304 K, [HROOH] 0.01—0.1 M _______________________________________ =
TQ
~HRoH/~’RO
Benzo-
Anthra-
phenone
quinone
Anthrone 1,4-naphthoquinone
0.96 ±0.04 0.96 ±0.04 0.93 ±0.05 0.93 ±0.05
benzanthracene (1 x 10 ~ M) the ratios of the quantum yields of formation of products differ from unity: ~HROH
~RO
=1
.32 ±0.08,
supporting that the homolysis of HROOH is the prevailing pathway of the decomposition. The ratio increases up to about 2.9 with increasing amounts of benzene added to the system, in agreement with earlier results of Scaiano [3]. Since benzene is a good scavenger for OH radicals [14,15], phenol (PhOH) is expected to form in the system if the decomposition proceeds via the rupture on the 0—0 bond, Actually, with 1,2-benzanthracene sensitizer irradiated at A = 366 nm we were able to detect phenol, and found that in pure benzene
Interaction of carbonyl triplets
105
neat Cd4, supporting our assumption according to which the main route of the process is the rupture of the 0—H bond, with the exception of 1,2-benzanthracene as sensitizer where the rupture of the 0—0 bond occurs. In the presence of anthraquinone, anthrone, naphthoquinone and benzophenone, QH radicals formed in the TQ~induceddecomposition react with oxygen and yield H0 [16]. It has been shown [5] that at the HROOH concentrations applied in the experiments, H0 radicals are consumed mainly in their interaction with HROOH, and therefore their self-combination as well as process HO; + HRO can be neglected.
4. Discussion We have shown earlier that the hydrogen abstraction by H0 and HRO radicals from the a-position of HROOH can be neglected under the given conditions. This is the reaction i-io; (HR0;) + HROOH H202(HROOH)
+
ROOH -*
~HROH/~PhOH
=
1.5 ±0.1.
If, under some conditions, the decomposition is realized via hydrogen abstraction yielding HRO, ben.zene added to the system would not affect the formation rates of the products significantly. Table 3 shows the results obtained with sensitizers, except 1,2-benzanthracene, and in the presence of added benzene (1.32 M) at A = 366 nm. Phenol was not detected (table 3). According to table 3 the ratios of the quantum yields are practically identical to those obtained in
RO
+
OH
yielding RO molecules. Consequently, the following elementary processes can be assumed [16—19] to describe the overall reaction of the carbonyl triplet sensitized HROOH decomposition:
Q TQ
TQ TQ
+ +
+ 02
HROOH HROOH
T ....~
Q Q + 02
(0) (1)
—*
Q
(2) (3)
_,
+
QH
HROOH HR0~
+
~H+02-,Q+H0
(4)
Table 3 Ratios of the quantum yields of HROH and RO in the decomposition of HROOH by TQ in the presence of [C6H6] 2 M; = A=366 1.32 M. tim; Solvent: [0 CC14 3T=304 M K, [HROOH]=5x10 2]=1.8x10 Q Benzo- Anthra- Anthrone 1,4-Naphthophenone quinone quinone
According to processes (0) to (6), HROH and RO are formed exclusively in process (6) and taking into account the earlier data of Russell [20]
0.99 0.95 0.96 0.92 0.19 0.32 0.28 0.20 _________________________________________
and Howard et al. [13] the ratio of their concentration should be unity as was observed.
~HROH/~RO ~‘~HROH
HO; + HROOH HRO + HRO
_~
—s
HRO + H202 HROH + RO + 02
(5) (6)
106
LI. Mazaleckaja et aL
/ Interaction of carbonyl triplets
2 1,
10
/
raquinone, in case of anthrone benzophenone and naphthoquinone, rate coefficient whereas of thethephysical quenching by the oxygen exceeds the
-
. 5 “S
0
I
I
25
50
___________________
0
100
[HRO0H)~M~1
200 (HR00H]~M-1
4 8~
10
____________________
I
0
100
___________________
I
200 [HROOH]~M~1
0
100
I
200 R0~h0~M1
formation HROH and ROof(I~) against yields [HROOH]1 Fig. 3. Theofreciprocal values the quantum of the (based on data represented by fig. 2). [021 = 1.8 X i03 M.
Based on this mechanism we obtain =
~a +
1 ab 2 [HROOH]’
where di~is the total quantum yield + ~~Ro) and a
(i =
(~
yields is ~max = (2~~)~/2 = 0.77. This latter value is very close to the maximum quantum yield observed by Scaiano et al. [3] for the interaction of benzophenone and tert.-butyl hydroperoxide (0.65 in C6H6). A somewhat lower value (0.27) was obtained with cumyl hydroperoxide in C6H6 [4]. According to the literature data [17,18] the value of k1 does practically not vary in different solvents. Therefore, we used 5 s5 for anthraquinone k = 2 x iO~M and anthrone, 3 x iO~M1 s~1for benzophenone and 4
(7)
—
former value of (k2 + k3) by a factor of three. At the same time the interaction of benzophenone with HROOH leads preferably to a chemical transformation and the maximum of the quantum
~HROH
X
iO~M
s~ for naphthoquinone.
Consequently, (k 1 S1 for benzophenone,2 +1.3 s~ for k3)X=108 0.4 xM1 108 M anthraquinone, 1.2 x 108 M1 s~ for anthrone and 4 x 10~M~ s5 for naphthoquinone.
k
+
i—), 2\
b= k2+k3 k1[02]
References
Plotting the experimental data according to eq. (7) we have calculated the kinetic parameters given in fig. 3 and table 4. Table 4 shows that the values of k1/k3 and (k2 + k3)/k1 are nearly identical for anth-
Table 4 Calculated values of ~ k2/k3 and (k2 + k3)/k1 [02] =1.8x io~ M _______________________________________________ TQ (1/~)~ (k1[02]) (k2 + k3) k2/k3 /2k3
/k1
(M) Benzophenone 0.65 0.09 0.013 0.3 Anthraquinone 1.01 0.028 0.065 1.02 Anthrone 1.16 0.034 0.061 1.32 1,4-naphthoquinone 1.69 0.033 0.092 2.38 _____________________________________________________
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