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Inhibiting action of dioxy benzene derivatives in liquid-phase oxidation of ethylbenzene
INHIBITING ACTION OF DIOXY BENZENE DERIVATIVES IN LIQUID-PHASE OXIDATION OF ETHYLBENZENE * 1~. V. KUCHER, A. I. PEICHEVA arid A. 1~. NIKOLAYEVSKII Donets State University (Received 28 December 197(~)
THE use of inhibitors is one of the most widespread and accurate methods of investigating the chemistry of hemolytic oxidation of organic materiMs. Various monographs [1, 2] contain considerable information concerning inhibited oxidation. The action of iahibitors is due to the chain mechanism of oxidation, therefore the problem arises concerning the reaction mechanism of inhibitors with peroxide radicals. Experimental information accumulated so far on inhibited oxidation [3-6] proves that two reaction mechanisms of inhibitors with peroxide radicals are possible: reactions (1) and (2) R O ' ~ I n l ~ ~ ROOI~-~In" RO'2~-IYIH ~ [I~,O'2...IIL~
(1) tb '
IRe', .... ~H]+RO'~ -* ROO~+RO~In~ 7
(2)
According to conditions of oxidation and the inhibitor used, both mechanisms or each mechanism separately m a y occur. Considerable information has now accumulated in connection with the study of the activity of inhibitors and their mechanism of action using rochebasic substituted phenols and naphthols. The activity and mechanism of action of dibasic unsubstituted phenols has been insufficiently studied. Information available [7-10] does not give us a fairly clear picture about the mechanism of reaction with peroxide radicals and enable us to conclusions about their reactivity. This paper seeks to examine the inhibiting action of bivalent tmsubstituted phenols (o-dioxybenzene, m-dioxybenzene and p-dioxybenzene) in liquidphase oxidation of ethylbenzene. EXPERIMENTAL
The chemically pure materials studied were purified by two-fold recrystallization from ethanol and distilled in vacuum. The "technical" a~oisobutyronitrile was purified as previously described [8]. * Neftekhimiya 12, No. 1, 53-58, 1972. 11
12
R.V.
KUCHER et a[.
Reactions of liquid-phase oxidation of ethylbenzene were examined gasometrically b y the rate of oxygen absorption and chemiluminescence. The possibility of using chemiluminescence to study the activity and mechanism of action of inhibitors in inhibited oxidation has been previously shown [11,
]3]. The selection of the material for oxidation is firstly governed by the fact that the rate constant of chain rupture in oxidation of ethylbenzene (ks) is known and secondly, that it is possible to compare some of the experimental data derived with literature data. Liquid-phase oxidation of ethylbenzene with atmospheric oxygen was carried out in the temperature range of 70 to 80 ° in the presence of dibasic phenols. These temperature conditions were selected to exclude oxidation of the inhibitors studied b y atmospheric oxygen and because in this temperature range the rate constant of initiation of azoisobutyronitrile is accurately known
[lS].
1.0
0.5
I
I
0.3
0.8
I
1.0 ~ - - , ~
0.0 [InH]aO,~o~/t.
"-~
0.3
L
0.8
i
O.S ~,H],~Of,,o/~/.
FIG. 1. Dependence of the luminescence intensity of oxidized ethylbenzene on the concentration of dioxybenzenes. Variation of the dependence of chemiluminescence intensity during oxidation of ethylbenzene on (InH). 2--m-Dioxybenzene; 3---o-dioxybenzene; 4--T-dioxybenzene; temperature 70°; W~~ 15 × 10-8 mole/see. The dependence of luminescence intensity of the ethylbenzene oxidized on the concentration of the inhibitor was studied b y a kinetic method. In this case a kinetic luminescence curve was plotted after each addition of the inhibitor. To characterize the efficiency of the inhibitors studied, kinetic parameter k~/k~ was determined by calculation using two independent methods. The first method involves measurement of the intensity of chemiluminescence for different inhibitor concentrations and plotting the relation in coordinates 1/lo-(InH ) and the transformation jlo/1-[InH] (Fig. la, b); the tangent t a n ~ of the gradient of the straight line is related to kT/k~ b y the expression kv tan ~ = ( 1 . 1 i 0 . 1 ) fl, where fl-~--keW,4 (3)
Inhibiting action of dioxy benzene derivatives
13
W i t h the second m e t h o d the angular coefficient o f t h e kinetic curve o f chemiluminescence [d (I/Io)/dt]max is m e a s u r e d k7 = ~ 4
tan q~[~]max
(4)
RESULTS AND DISCUSSION
T a b l e 1 shows kinetic p a r a m e t e r s derived from Fig. 1. F i g u r e 2 indicates kinetic chemiluminescence curves which t h e o r e t i c a l l y axe S-shaped. T h e value o f [d(I/I0) dt]~ax decreases slightly on increasing t h e initial c o n c e n t r a t i o n of imhibitors. To exclude t h e effect o f initial concent r a t i o n of the inhibitor on t h e value of [d(I/Io)dt]m~x, the d e p e n d e n c e o f m a x i m u m g r a d i e n t on initial c o n c e n t r a t i o n I n H was plotted; t h e value o f [d(I/lo)/dt]max was e x t r a p o l a t e d to [ I n H ] - ~ 0 a n d is shown in Table 1. F r o m the ratio k~/k~ values of k7 were d e t e r m i n e d f r o m the k6 value k n o w n for e t h y l b e n z e n e f r o m t h e literature, which is 1.9×107 1./mole.see [14]. D a t a in Table 1 indicate t h a t the value of k:/k~ depends slightly on the r a t e o f initiation and increases e v e n l y w i t h t e m p e r a t u r e . F r o m the d e p e n d e n c e o f k7 on t e m p e r a t u r e in Arrhenius coordinates the a c t i v a t i o n energies of t h e e l e m e n t a r y process R 0 ~ l n H were d e t e r m i n e d a n d expressions d e r i v e d for r a t e constants using the inhibitors e x a m i n e d (1./mole. "see) /Co'a~o~be,~ene=1"78 × 10~ exp (-- 4100/RT), kp~e~o~ --7"81 × 107 oxp (--6750/RT), k m - d t o x y b e n z e n e = 3"32 × l0 s exp (-- 7120/RT), k~-a~o,:e~en~ene=1"53 × l0 s exp (--3670/RT). T.a_BLE 1.
KIlhrETIC
PARAI~I~TERS
OF
IlqI~IBITED
OXIDATION
OF
ETHYLEBENZElqE
g ×~ d,.z
Inhibitor
CD I
X
× 60 70 75 70 75 80 70 75 80 70 75 80
Phenol m-Dioxybonzone
o-Dioxybenzone
p-Dioxybenzone
5 15.0 30.0 15.0 30.0 56.4 15.0 30.0 56.4 15.0 30.0 56.4
24"4q-4 60.5+10 94-2~10 18.4~-3 37-6~:5.3 58"3~-3-1
-0"35 0-28 t -0.221 0.66 --0"55 0.5 28.3 13.8 21-5 26.9 33.9 18'0 31.25 11.75 22-5 16-9 19.3 22-4
0.7 0.95:t:
0.10
1.09~:0.12 2.29~:0.21 2.75~:0.23 3-3=[=0.29 99.5_+15 108d:6 119:l:15 ll0:j:10 118i6 128~:5
0'3 0-408 0.47 0.98 1.18 1.42 42.00 46.4 51.6 47.5 51.5 55-9
14
R . V . KUeHE}~ et al.
Z/Zo J
://o
/¢ 5 [ '
23
l
x,y">~x~-5 "-i
o
0.5
'5
I
[
I
o
vo
80
[
0
I
I
40
80
t, see
f, sec
FIG. 2. Kinetic curves of the variation of chemiluminescence intensity in ethylbenzene at different initial concentrations of inhibitors, mole/1.: a---o-dioxybenzone: 1--0.116 x × 10-~; 2--0.26 x 10-5; 3--0.49 × 10-~; 4--0.55 × 10-5; 5--0"8 × 10-6; temperature 70°; W ( = 1 5 × 10 -s molo/1..sec; b~-dioxybenzene; 1--0-16× 10-~; 2--0.19X 10-s; 3 - 0.26×10-'; 4--0.42 ×10-5; temperature 70°; W ( = I 5 × 10 -8 mole/1..sec; 5--m-dioxybenzene 0.90 × 10 -5 mole/1. I f t h e a c t i v a t i o n e n e r g y of t h e r e a c t i o n of R O h - t - I n H is d e t e r m i n e d by t h e e n e r g y of r u p t u r e of t h e b o n d ( Q ) I n - , H , t h e r a t e c o n s t a n t k 7 should d e p e n d o n t h e u n s a t u r a t i o n of r a d i c a l I n ' . This c o r r e s p o n d s to t h e r e d o x p o t e n t i a l (Eo_r) of phenols, f r o m which a p h e n o x y l radical is formed. I n d e e d , as s h o w n b y Fig. 3, a linear r e l a t i o n s h i p was f o u n d b e t w e e n log k7 a n d
Eo_ r [12]. tosk~
5.0
l#o
0.5
1.0
Eo_~
FIG-, 3. Dependence of log k7 on the redox potential E o - r of dioxybe~zenes: /--phenol; 2--m-dioxybenzeno; 4--p-dioxybonzene. T h e c o m p o u n d s e x a m i n e d fall into t h e following order of inhibiting p r o p erties: m - < o - < p - d d o x y b e n z e n e . A t a t e m p e r a t u r e of 70 °, for e x a m p l e , t h e r a t e c o n s t a n t of t h e r e a c t i o n of p e r o x i d e radicals w i t h phenol is lower b y t w o
Inhibiting action of dioxy benzene derivatives
15
orders of magnitude t h a n the rate constant of the interaction of hydroquinone with the same peroxide radical. From a series of kinetic chemiluminescence curves for the dioxy compounds studied and from the dependence of the intensity of chemiluminescence on concentration not only the value of kT/k~, but also the rate of initiation W~, can be calculated. W, ~lo can therefore be compared with W~ ,i,~ which makes it possible to assess quantitatively the mechanism of action of inhibitors. The rate of initiation calculated from experimental data corresponds to the value only given for p-dioxybenzene, while for o-dioxybenzene W~ talC> > W~ gi,en" This fact suggests t h a t the inhibitor also acts in a way not specified by the system or t h a t each inhibitor molecule ruptures fewer chains, than is specified by systems (1) and (2); this is inconsistent with results of an earlier study [13]. I t was impossible to calculate the rate of initiation for m-dioxybenzene or for phenol because reaction products apparently inhibit oxidation and the intensity of luminescence does not increase to the initial value of I o without inhibitors (Fig. 2b, curve 5). TABT.E
2. R A T E CONSTANTS Or' Tm~ BEAeTION OF A P E R O X I D E ~ADIC.tL WITH AN INI~IB1TOI~ (k~) AND Ilq']tIBITION COEFFICYENTS (/)
Temperature 70°C, W~= 15 x 10-s mole/1..sec
Inhibitor
kJk,
kT, I f
1./mole. see
gasome~ry m-Dioxybonzene o-Dioxybenzeno p -Dioxybenzene
6000 0.54 x 10' 111,000 0.10× 106 285,500 0"257 X 10e
1./mole.see
f
chemiluminescence 0.5 2
2
0.98 × 10' 0.428 × 1 0 e 0.473 x 106
1.4-1.6
1.9-2.0
k~ values obtained by chemiluminescence agree qualitatively with k7 values determined fl'om the rate of oxygen absorption in a gasometric apparatus (Fig. 4, Table 2). The order of activity of dioxybenzenes is maintained in reactions with peroxide radicals. Figure 4a shows t h a t emergence from the induction period is more sudden for o- and p-dioxybenzenes and the rates of oxidation without inhibitor agree even after a complete reaction. This was not observed during oxidation of ethylbenzene in the presence of m-dioxybenzene and phenol. This is, apparently, due to the formation of products of radical conversion of dioxy-compolmds which inhibit oxidation. The coefficients of inhibition determined by two methods agree for pdioxybenzene, for o-dioxybenzene the values differ somewhat and do not agree within the range of experimental error. The addition to the phenol molecule of hydroxyl groups in the m-, o-
16
l:t. V. KUOHER et at.
and p- position therefore increases their reactivity in the reaction with R0~ radicals and makes them more effective inhibitors in liquid-phase oxidation of hydrocarbons.
Vo~lOrnl ,
b x
//
N ~ It
~ /5
// 12
20
N~5 28 [-,rnio
U
5
10 [inH]210-,3/./mole
FIG. 4. a - - K i n e t i c curves of oxygen absorption; b--dependence of the rate of oxygen absorption on [InI-I]-1, / - - p h e n o l , [InH]--0.3 × 103 mole/1.; 2--m-dioxybenzone, [In]=[]0.1 × 10 -a mole/1.; 3--o-dioxybenzene, [IaI-I] --0-108 × 10 -3 molo/l.; ~ - d i o x y b o n z o n o , [ I n H ] - - 0 . 0 7 0 6 × 10 -3 mole/1.; temperature 70°; W , = 1 5 X 10 -8 molo/1..soc; 5---ethylbenzene.
SUMMARY 1. A study was made of liquid-phase oxidation of ethylberszene initiated by azoisobutyronitrile in the presence of o-, m-, p-dioxybenzene using gasometric and chemiluminescence methods. Kinetic parameters, activation energies and pre-exponential factors were determined. 2. Dioxybenzenes occupy the following order in respect of inhibiting properties: m-dioxybenzene < o-dioxybenzene
Ir~hibibing action of dioxy bonzono derivatives 10. 11. 12. 13.
17
J. L. BOLLAND a n d P. TEN HAVE, Trans. F a r a d a y See. 43, 252, 1947 E. F. BRIN a n d O. N. KARPUKHIN, Izv. AN SSSR, Ser. khim., 468, 1969 L. F. FISER, J. Amer. Chem. Soc. 52, 5204, 1930 V. Ya. SI-LLYAPINTOKH, O. N. KARPUKHIN, L. N. POSTNIKOV, V. F. TSEPALOV, I. V. ZAKIIAROV and A. A. VICHUTINSKII, Khemilyuminostsentnye mctody issledovaniya medlennykh khimicheskikh protsessov (Chemiluminescent Methods of Investigating Slow Chemical Processes). Nauka, Moscow, 1966 14. V. F. TSEPALOV a n d V. Ira. SHLYAPINTOKH, Kine~ika i kataliz 3, 870, 1962 15. Z. K. KULITSKI, L. N. TERM.AN, V. F. TSEPALOV and V. Ya. SItLYAPINTOKH, Izv. A.N SSSR, Otd. khim. n., 253, 1962
THE use of inhibitors is one of the most widespread and accurate methods of investigating the chemistry of hemolytic oxidation of organic materiMs. Various monographs [1, 2] contain considerable information concerning inhibited oxidation. The action of iahibitors is due to the chain mechanism of oxidation, therefore the problem arises concerning the reaction mechanism of inhibitors with peroxide radicals. Experimental information accumulated so far on inhibited oxidation [3-6] proves that two reaction mechanisms of inhibitors with peroxide radicals are possible: reactions (1) and (2) R O ' ~ I n l ~ ~ ROOI~-~In" RO'2~-IYIH ~ [I~,O'2...IIL~
(1) tb '
IRe', .... ~H]+RO'~ -* ROO~+RO~In~ 7
(2)
According to conditions of oxidation and the inhibitor used, both mechanisms or each mechanism separately m a y occur. Considerable information has now accumulated in connection with the study of the activity of inhibitors and their mechanism of action using rochebasic substituted phenols and naphthols. The activity and mechanism of action of dibasic unsubstituted phenols has been insufficiently studied. Information available [7-10] does not give us a fairly clear picture about the mechanism of reaction with peroxide radicals and enable us to conclusions about their reactivity. This paper seeks to examine the inhibiting action of bivalent tmsubstituted phenols (o-dioxybenzene, m-dioxybenzene and p-dioxybenzene) in liquidphase oxidation of ethylbenzene. EXPERIMENTAL
The chemically pure materials studied were purified by two-fold recrystallization from ethanol and distilled in vacuum. The "technical" a~oisobutyronitrile was purified as previously described [8]. * Neftekhimiya 12, No. 1, 53-58, 1972. 11
12
R.V.
KUCHER et a[.
Reactions of liquid-phase oxidation of ethylbenzene were examined gasometrically b y the rate of oxygen absorption and chemiluminescence. The possibility of using chemiluminescence to study the activity and mechanism of action of inhibitors in inhibited oxidation has been previously shown [11,
]3]. The selection of the material for oxidation is firstly governed by the fact that the rate constant of chain rupture in oxidation of ethylbenzene (ks) is known and secondly, that it is possible to compare some of the experimental data derived with literature data. Liquid-phase oxidation of ethylbenzene with atmospheric oxygen was carried out in the temperature range of 70 to 80 ° in the presence of dibasic phenols. These temperature conditions were selected to exclude oxidation of the inhibitors studied b y atmospheric oxygen and because in this temperature range the rate constant of initiation of azoisobutyronitrile is accurately known
[lS].
1.0
0.5
I
I
0.3
0.8
I
1.0 ~ - - , ~
0.0 [InH]aO,~o~/t.
"-~
0.3
L
0.8
i
O.S ~,H],~Of,,o/~/.
FIG. 1. Dependence of the luminescence intensity of oxidized ethylbenzene on the concentration of dioxybenzenes. Variation of the dependence of chemiluminescence intensity during oxidation of ethylbenzene on (InH). 2--m-Dioxybenzene; 3---o-dioxybenzene; 4--T-dioxybenzene; temperature 70°; W~~ 15 × 10-8 mole/see. The dependence of luminescence intensity of the ethylbenzene oxidized on the concentration of the inhibitor was studied b y a kinetic method. In this case a kinetic luminescence curve was plotted after each addition of the inhibitor. To characterize the efficiency of the inhibitors studied, kinetic parameter k~/k~ was determined by calculation using two independent methods. The first method involves measurement of the intensity of chemiluminescence for different inhibitor concentrations and plotting the relation in coordinates 1/lo-(InH ) and the transformation jlo/1-[InH] (Fig. la, b); the tangent t a n ~ of the gradient of the straight line is related to kT/k~ b y the expression kv tan ~ = ( 1 . 1 i 0 . 1 ) fl, where fl-~--keW,4 (3)
Inhibiting action of dioxy benzene derivatives
13
W i t h the second m e t h o d the angular coefficient o f t h e kinetic curve o f chemiluminescence [d (I/Io)/dt]max is m e a s u r e d k7 = ~ 4
tan q~[~]max
(4)
RESULTS AND DISCUSSION
T a b l e 1 shows kinetic p a r a m e t e r s derived from Fig. 1. F i g u r e 2 indicates kinetic chemiluminescence curves which t h e o r e t i c a l l y axe S-shaped. T h e value o f [d(I/I0) dt]~ax decreases slightly on increasing t h e initial c o n c e n t r a t i o n of imhibitors. To exclude t h e effect o f initial concent r a t i o n of the inhibitor on t h e value of [d(I/Io)dt]m~x, the d e p e n d e n c e o f m a x i m u m g r a d i e n t on initial c o n c e n t r a t i o n I n H was plotted; t h e value o f [d(I/lo)/dt]max was e x t r a p o l a t e d to [ I n H ] - ~ 0 a n d is shown in Table 1. F r o m the ratio k~/k~ values of k7 were d e t e r m i n e d f r o m the k6 value k n o w n for e t h y l b e n z e n e f r o m t h e literature, which is 1.9×107 1./mole.see [14]. D a t a in Table 1 indicate t h a t the value of k:/k~ depends slightly on the r a t e o f initiation and increases e v e n l y w i t h t e m p e r a t u r e . F r o m the d e p e n d e n c e o f k7 on t e m p e r a t u r e in Arrhenius coordinates the a c t i v a t i o n energies of t h e e l e m e n t a r y process R 0 ~ l n H were d e t e r m i n e d a n d expressions d e r i v e d for r a t e constants using the inhibitors e x a m i n e d (1./mole. "see) /Co'a~o~be,~ene=1"78 × 10~ exp (-- 4100/RT), kp~e~o~ --7"81 × 107 oxp (--6750/RT), k m - d t o x y b e n z e n e = 3"32 × l0 s exp (-- 7120/RT), k~-a~o,:e~en~ene=1"53 × l0 s exp (--3670/RT). T.a_BLE 1.
KIlhrETIC
PARAI~I~TERS
OF
IlqI~IBITED
OXIDATION
OF
ETHYLEBENZElqE
g ×~ d,.z
Inhibitor
CD I
X
× 60 70 75 70 75 80 70 75 80 70 75 80
Phenol m-Dioxybonzone
o-Dioxybenzone
p-Dioxybenzone
5 15.0 30.0 15.0 30.0 56.4 15.0 30.0 56.4 15.0 30.0 56.4
24"4q-4 60.5+10 94-2~10 18.4~-3 37-6~:5.3 58"3~-3-1
-0"35 0-28 t -0.221 0.66 --0"55 0.5 28.3 13.8 21-5 26.9 33.9 18'0 31.25 11.75 22-5 16-9 19.3 22-4
0.7 0.95:t:
0.10
1.09~:0.12 2.29~:0.21 2.75~:0.23 3-3=[=0.29 99.5_+15 108d:6 119:l:15 ll0:j:10 118i6 128~:5
0'3 0-408 0.47 0.98 1.18 1.42 42.00 46.4 51.6 47.5 51.5 55-9
14
R . V . KUeHE}~ et al.
Z/Zo J
://o
/¢ 5 [ '
23
l
x,y">~x~-5 "-i
o
0.5
'5
I
[
I
o
vo
80
[
0
I
I
40
80
t, see
f, sec
FIG. 2. Kinetic curves of the variation of chemiluminescence intensity in ethylbenzene at different initial concentrations of inhibitors, mole/1.: a---o-dioxybenzone: 1--0.116 x × 10-~; 2--0.26 x 10-5; 3--0.49 × 10-~; 4--0.55 × 10-5; 5--0"8 × 10-6; temperature 70°; W ( = 1 5 × 10 -s molo/1..sec; b~-dioxybenzene; 1--0-16× 10-~; 2--0.19X 10-s; 3 - 0.26×10-'; 4--0.42 ×10-5; temperature 70°; W ( = I 5 × 10 -8 mole/1..sec; 5--m-dioxybenzene 0.90 × 10 -5 mole/1. I f t h e a c t i v a t i o n e n e r g y of t h e r e a c t i o n of R O h - t - I n H is d e t e r m i n e d by t h e e n e r g y of r u p t u r e of t h e b o n d ( Q ) I n - , H , t h e r a t e c o n s t a n t k 7 should d e p e n d o n t h e u n s a t u r a t i o n of r a d i c a l I n ' . This c o r r e s p o n d s to t h e r e d o x p o t e n t i a l (Eo_r) of phenols, f r o m which a p h e n o x y l radical is formed. I n d e e d , as s h o w n b y Fig. 3, a linear r e l a t i o n s h i p was f o u n d b e t w e e n log k7 a n d
Eo_ r [12]. tosk~
5.0
l#o
0.5
1.0
Eo_~
FIG-, 3. Dependence of log k7 on the redox potential E o - r of dioxybe~zenes: /--phenol; 2--m-dioxybenzeno; 4--p-dioxybonzene. T h e c o m p o u n d s e x a m i n e d fall into t h e following order of inhibiting p r o p erties: m - < o - < p - d d o x y b e n z e n e . A t a t e m p e r a t u r e of 70 °, for e x a m p l e , t h e r a t e c o n s t a n t of t h e r e a c t i o n of p e r o x i d e radicals w i t h phenol is lower b y t w o
Inhibiting action of dioxy benzene derivatives
15
orders of magnitude t h a n the rate constant of the interaction of hydroquinone with the same peroxide radical. From a series of kinetic chemiluminescence curves for the dioxy compounds studied and from the dependence of the intensity of chemiluminescence on concentration not only the value of kT/k~, but also the rate of initiation W~, can be calculated. W, ~lo can therefore be compared with W~ ,i,~ which makes it possible to assess quantitatively the mechanism of action of inhibitors. The rate of initiation calculated from experimental data corresponds to the value only given for p-dioxybenzene, while for o-dioxybenzene W~ talC> > W~ gi,en" This fact suggests t h a t the inhibitor also acts in a way not specified by the system or t h a t each inhibitor molecule ruptures fewer chains, than is specified by systems (1) and (2); this is inconsistent with results of an earlier study [13]. I t was impossible to calculate the rate of initiation for m-dioxybenzene or for phenol because reaction products apparently inhibit oxidation and the intensity of luminescence does not increase to the initial value of I o without inhibitors (Fig. 2b, curve 5). TABT.E
2. R A T E CONSTANTS Or' Tm~ BEAeTION OF A P E R O X I D E ~ADIC.tL WITH AN INI~IB1TOI~ (k~) AND Ilq']tIBITION COEFFICYENTS (/)
Temperature 70°C, W~= 15 x 10-s mole/1..sec
Inhibitor
kJk,
kT, I f
1./mole. see
gasome~ry m-Dioxybonzene o-Dioxybenzeno p -Dioxybenzene
6000 0.54 x 10' 111,000 0.10× 106 285,500 0"257 X 10e
1./mole.see
f
chemiluminescence 0.5 2
2
0.98 × 10' 0.428 × 1 0 e 0.473 x 106
1.4-1.6
1.9-2.0
k~ values obtained by chemiluminescence agree qualitatively with k7 values determined fl'om the rate of oxygen absorption in a gasometric apparatus (Fig. 4, Table 2). The order of activity of dioxybenzenes is maintained in reactions with peroxide radicals. Figure 4a shows t h a t emergence from the induction period is more sudden for o- and p-dioxybenzenes and the rates of oxidation without inhibitor agree even after a complete reaction. This was not observed during oxidation of ethylbenzene in the presence of m-dioxybenzene and phenol. This is, apparently, due to the formation of products of radical conversion of dioxy-compolmds which inhibit oxidation. The coefficients of inhibition determined by two methods agree for pdioxybenzene, for o-dioxybenzene the values differ somewhat and do not agree within the range of experimental error. The addition to the phenol molecule of hydroxyl groups in the m-, o-
16
l:t. V. KUOHER et at.
and p- position therefore increases their reactivity in the reaction with R0~ radicals and makes them more effective inhibitors in liquid-phase oxidation of hydrocarbons.
Vo~lOrnl ,
b x
//
N ~ It
~ /5
// 12
20
N~5 28 [-,rnio
U
5
10 [inH]210-,3/./mole
FIG. 4. a - - K i n e t i c curves of oxygen absorption; b--dependence of the rate of oxygen absorption on [InI-I]-1, / - - p h e n o l , [InH]--0.3 × 103 mole/1.; 2--m-dioxybenzone, [In]=[]0.1 × 10 -a mole/1.; 3--o-dioxybenzene, [IaI-I] --0-108 × 10 -3 molo/l.; ~ - d i o x y b o n z o n o , [ I n H ] - - 0 . 0 7 0 6 × 10 -3 mole/1.; temperature 70°; W , = 1 5 X 10 -8 molo/1..soc; 5---ethylbenzene.
SUMMARY 1. A study was made of liquid-phase oxidation of ethylberszene initiated by azoisobutyronitrile in the presence of o-, m-, p-dioxybenzene using gasometric and chemiluminescence methods. Kinetic parameters, activation energies and pre-exponential factors were determined. 2. Dioxybenzenes occupy the following order in respect of inhibiting properties: m-dioxybenzene < o-dioxybenzene
Ir~hibibing action of dioxy bonzono derivatives 10. 11. 12. 13.
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J. L. BOLLAND a n d P. TEN HAVE, Trans. F a r a d a y See. 43, 252, 1947 E. F. BRIN a n d O. N. KARPUKHIN, Izv. AN SSSR, Ser. khim., 468, 1969 L. F. FISER, J. Amer. Chem. Soc. 52, 5204, 1930 V. Ya. SI-LLYAPINTOKH, O. N. KARPUKHIN, L. N. POSTNIKOV, V. F. TSEPALOV, I. V. ZAKIIAROV and A. A. VICHUTINSKII, Khemilyuminostsentnye mctody issledovaniya medlennykh khimicheskikh protsessov (Chemiluminescent Methods of Investigating Slow Chemical Processes). Nauka, Moscow, 1966 14. V. F. TSEPALOV a n d V. Ira. SHLYAPINTOKH, Kine~ika i kataliz 3, 870, 1962 15. Z. K. KULITSKI, L. N. TERM.AN, V. F. TSEPALOV and V. Ya. SItLYAPINTOKH, Izv. A.N SSSR, Otd. khim. n., 253, 1962