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Salts of metals of constant valency as catalysts of radical-chain oxidation of hydrocarbons
0031--6458180/050162-04507.50[0
Petrol. Chem. U.S.R.IL Vol. 20, :No 3, pp. 162-165, 1980 Printed in Poland
© 1981 Pergamon Press :Ltd.
SALTS OF METALS OF CONSTANT VALENCY AS CATALYSTS OF RADICAL-CHAIN OXIDATION OF HYDROCARBONS* KH. E. KttARLAMPIDI, N. N. BATYRSttlN and V. G. Iva~lov S. M. Kirov Chemieo-tcchnelogieal Institut(~, Kazan (Received 25 June 1979)
THe: ability of salts of Mka3i and alkali-earth metals to eatalyse o x i d a t i o n ,,f hydroearb(ms was noted a long time ago however, catalysis b y metals of ,..natant v a l e n c y has only been examined (luring the past decade [1, 2]. la view of the faet t h a t metals of constant, v a l e n c y do not. have the ability" o undergo valence transformations, the mechanism of their i n t e r a c t i o n with. hydroperoxides, so far, remains difficult to explain. The most valid e x p e r i m e n t a l point of view and t h e r e f o r e the most aeeepi able one concerning the principle of action of metals of constant, v a l e n e y - ,:atalysts of o x i d a t i o n of h y d r o c a r b o n s - - i n our view is the fact t h a t t h e y ,,atalyse homolysis of hydroperoxides. The s t u d y proposed concerns h o m o l y t i e t r a n s f o r m a t i o n s of eumyl hy&roperoxide (CI-IP) b y the action of organic salts of alkali and alkali-earth metals°
Ccas~ J . 1o3, moleT.
f NaNd, Io~ mole/z. 14 8 i
I
Z
3
12
I
2.o
~, 18 -
b
J / _ : 1 '°
O.q
1
l 3
L
r_RoOHJ,10 z, ~oZe/Z.
I 5
2
14
g
EROON*10z, mole/L
Fro. 1. Dependence of the rate of initiation for cumene on the concentration of hydrogen peroxide, sodium napthenate (a) and calcium stearate (b) at 100°C: /--without catalyst; concentration l0 s, mole/].; a: 1--[NaNf]=]; 3-- [CHP]= 0.5; b: 2--[CaSta]=0.07; 3-[ C H P ] = 6. * Neftekhimiya 20. No. 5, 708-710, 1980. 162
Salts of metals of constant valency as catalysts
163
EXPERIMENTAL
A s the problem of purification of compounds used to remove traces o f metals of variable valency is important in studying catalysis b y metal compounds of constant valency, particular attention was given to this matter. Sodium naphthenate was obtained b y neutralization of !~aOH (analytically pure) using a naphthenic acid fraction of b.p. 160-170 ° purified b y distillation. Sodium stearate was obtained from alkali and stearic acid, calcium s t e a r a t e - - b y exchange reaction between calcium chloride and stearie acid. Hydroperoxide was purified b y distillation, chlorobenzene being the solvent and c u m e n e - - b y the sulphuric acid method. The rate of consumption of hydroperoxide was measured iodometrically. The rate of free radical formation W~ was measured b y the rate of radicalchain oxidation of cumene W in a reactor using a pressure gauge. The reactor was heated to the required temperature, including the device used for agitation, while the reagents were mixed and the initial rate of oxygen absorption measured. For the quantitative evaluation of the effect of salts of constant valency metals (Me ÷) on radical decomposition of CHP, we examined the type of chain rupture in the presence of C l I P and Me + and measured the value of k~[x/~ (ratio of rate constant of chain growth to the rate constant of rupture to the extent of ½ order of magnitude). Calculations concerning the experiment of oxidation of cumene with the simultaneous presence in the solution of two initiators--dicumyl peroxide ((DCP), k~ was calculated from formula [3] and found to be 2.76 × 10 -s sec -1, 100°)) and CI-IP~-Me showed that the presence of Me + has no effect on t h e ratio of k~/~/~ in experiments with variable concentrations of I)CP (0-~ 2.31 × × 10 -3 mole/1.). Concentrations (109, mole/1.) of C H P and metal s a l t s were constant: [ C H P ] : 0 - 3 2 ; [l~al~f]:l.0; C H P ~ 0 . 7 ; [CaSt,l:0.07. At 100 ° for l~aNf and CaSt2 it was found that (k2/~/~)× l0 s (1. mole.sec) was 1.17 and 1-29, respectively, which does not differ in practice from oxidation of pure eumene, for which the ratio of constants was 1.43. Consequently, an acceleration of oxidation in a solution containing hydroperoxide and a metal of constant valency is due to homolysis of hydroperoxide. Using the value of k~/~/~ derived from the formula W = k2/~/~[RH]" x / ~ rates of free radical formation W~ from C H P b y the action of salts of constant
valency metals in cumene (100 °) were calculated, having regard to the concentration of Me+ and C H P (Figs. 1 and 2). It follows from results of t h e Figures that b o t h the reaction of initiation and the reaction of gross-decomposition in chlorobenzene for sodium and calcium stearates and n a p h t h e n a t e s are of first order for reagent concentration
164
KH. E . K ~ M P I D I
e~ a/.
[W~-----k~[ROOH] [cat], W~-----k~[ROOH][eat]. Radical decomposition for salts represents a small part of gross decomposition. Thus, for [CaSts]=3×10 -3 mole/1, and [ C H P ] = 5 × 1 0 -s mole/l, the proportion of radical decomposition is 1-58% (100 W~/2W~o).
L/
/
2
1
#
IO
EGONf2] "IO~ rROOH],10 z rno/e/l. ]~'Ia. 2. Dependence of the rate constant of the gross deeoraposition of cumyl hydroperoxide in chlorobenezene at 100°Con the concentration ofcumyl hydroperoxide and calcium naphthenate: l~without eatalyst; 2--[CaNf~]=l × 10-~- mole/1.; 3--[CHP]=6× 10-~ mele/1. The catalytic effect of stearates varies in the order CaSt s > CdSt 2> BaSt 2> NaSt > MgSt 2 (numerical values are 16.5; 10; 7; I; 0.8, respectively. Wl,,s, is assumed to be one. For naphthenates CaNf > N a N f (12; 1, respectively), i.e. the ratio of effects of calcium attd sodium salts is about the same. The rate of initiation for calcium salts is independent of the type of acid residue; concentrations of CaSts and CaNfs (1 × 10 .3 mole/1.) and [CHP] being the same i.e. 7.6×10 -a mole/1, W~st=2.34×10 -7, W~N~ =2.58 × 10 -~ mole/1.-sec. The catalytic action of salts of metals of constant valency, as before [4], is explained by a reduction of the energy barrier of the reaction I ~ O O H - I - ~ O O H ~ 1~O' -t- 1~O'2+ [H~ONa +]
compared with the simple bimoleeular reaction of radical formation ROOH+ROOH -* RO'+RO',+H,O. I n fact, measurement of the activation energy of radical formation from C H P by the action of metals of constant valeucy under conditions described (10 s, mole/k); [Na~If]=l.0; [CHP]=0.32; [CaStd=0.07; [CHP]=0,7, gave a value of 83.7 and 79.5 kJ/mole, respectively for sodium naphthenate and calcium stoarate, which is noticeably lower t h a n the activation energy of simple bimoleeular decomposition of CHP E3=108.8 KJ/mole[5].
Salts of metals of constant valency as catalysts
165
• Results confirm the ability of salts of constant valency metals to catalyse oxidation of hydrocarbons with decomposition of hydroperoxide to free radicals; when hydroperoxide is absent from the system studied, oxidation does not take place. The type of catalytic homolysis of hydroperoxide by constant valency metals is, apparently, due to acidic (Lewis) properties [6]. SUMMARY
1. The rate of initiation and gross-decomposition of cumyl hydroperoxide in the presence of salts of metals of constant valency is of first order for the concentration of reagents W~=k~[CHP].[cat], Wp=kp[CHP] [cat]. The proportion of radical formation is 2~/o of the gross process of decomposition. 2. The catalytic effect of stearates intensifying gross-decomposition varies in the order CaSt2 ~ CdSt2~ B a S t 2 ~ NaSt 2~ l~aSt ~ M g S t 2. REFERENCES 1. V. K. PYSKOVSKII, S. S. BOTKINA, Ye. K. PROKOF'YEV and Yu. L: MOSKOVICH
Zh. pritdadnoi khlmii 45, 1299, 1972 2. L. V. PETROV, V. M. SOLYANIKOV and Z. Ya. PETROVA, I)okl. AN SSSR 280,
366, 1976 3. Ye. T. DENISOV, Rate Constants of Homolytic Liquid-phase Reactions, Nauka, Moscow, 1971 4. V. M. SOLYANIKOVand Ye. T. DENISOV, Dokl. AN SSSR 173, 1106, 1967 5. N. M. EMANUEL', Ye. T. DENISOV and Z. K. MAIZUS, Tsepnyye rcaktsii okilseniya uglevodorodov v zhidkoi faze {Chain Reactions of Liquid-phase Oxidation of Hydrocarbons), l~auka, Moscow, 1965 6. V. M. SOLYANIKO5, L. V. PETROV and Kh. E. KItARLAMPIDI, Dokl. ANt SSSR 223, 1412, 1975
Petrol. Chem. U.S.R.IL Vol. 20, :No 3, pp. 162-165, 1980 Printed in Poland
© 1981 Pergamon Press :Ltd.
SALTS OF METALS OF CONSTANT VALENCY AS CATALYSTS OF RADICAL-CHAIN OXIDATION OF HYDROCARBONS* KH. E. KttARLAMPIDI, N. N. BATYRSttlN and V. G. Iva~lov S. M. Kirov Chemieo-tcchnelogieal Institut(~, Kazan (Received 25 June 1979)
THe: ability of salts of Mka3i and alkali-earth metals to eatalyse o x i d a t i o n ,,f hydroearb(ms was noted a long time ago however, catalysis b y metals of ,..natant v a l e n c y has only been examined (luring the past decade [1, 2]. la view of the faet t h a t metals of constant, v a l e n c y do not. have the ability" o undergo valence transformations, the mechanism of their i n t e r a c t i o n with. hydroperoxides, so far, remains difficult to explain. The most valid e x p e r i m e n t a l point of view and t h e r e f o r e the most aeeepi able one concerning the principle of action of metals of constant, v a l e n e y - ,:atalysts of o x i d a t i o n of h y d r o c a r b o n s - - i n our view is the fact t h a t t h e y ,,atalyse homolysis of hydroperoxides. The s t u d y proposed concerns h o m o l y t i e t r a n s f o r m a t i o n s of eumyl hy&roperoxide (CI-IP) b y the action of organic salts of alkali and alkali-earth metals°
Ccas~ J . 1o3, moleT.
f NaNd, Io~ mole/z. 14 8 i
I
Z
3
12
I
2.o
~, 18 -
b
J / _ : 1 '°
O.q
1
l 3
L
r_RoOHJ,10 z, ~oZe/Z.
I 5
2
14
g
EROON*10z, mole/L
Fro. 1. Dependence of the rate of initiation for cumene on the concentration of hydrogen peroxide, sodium napthenate (a) and calcium stearate (b) at 100°C: /--without catalyst; concentration l0 s, mole/].; a: 1--[NaNf]=]; 3-- [CHP]= 0.5; b: 2--[CaSta]=0.07; 3-[ C H P ] = 6. * Neftekhimiya 20. No. 5, 708-710, 1980. 162
Salts of metals of constant valency as catalysts
163
EXPERIMENTAL
A s the problem of purification of compounds used to remove traces o f metals of variable valency is important in studying catalysis b y metal compounds of constant valency, particular attention was given to this matter. Sodium naphthenate was obtained b y neutralization of !~aOH (analytically pure) using a naphthenic acid fraction of b.p. 160-170 ° purified b y distillation. Sodium stearate was obtained from alkali and stearic acid, calcium s t e a r a t e - - b y exchange reaction between calcium chloride and stearie acid. Hydroperoxide was purified b y distillation, chlorobenzene being the solvent and c u m e n e - - b y the sulphuric acid method. The rate of consumption of hydroperoxide was measured iodometrically. The rate of free radical formation W~ was measured b y the rate of radicalchain oxidation of cumene W in a reactor using a pressure gauge. The reactor was heated to the required temperature, including the device used for agitation, while the reagents were mixed and the initial rate of oxygen absorption measured. For the quantitative evaluation of the effect of salts of constant valency metals (Me ÷) on radical decomposition of CHP, we examined the type of chain rupture in the presence of C l I P and Me + and measured the value of k~[x/~ (ratio of rate constant of chain growth to the rate constant of rupture to the extent of ½ order of magnitude). Calculations concerning the experiment of oxidation of cumene with the simultaneous presence in the solution of two initiators--dicumyl peroxide ((DCP), k~ was calculated from formula [3] and found to be 2.76 × 10 -s sec -1, 100°)) and CI-IP~-Me showed that the presence of Me + has no effect on t h e ratio of k~/~/~ in experiments with variable concentrations of I)CP (0-~ 2.31 × × 10 -3 mole/1.). Concentrations (109, mole/1.) of C H P and metal s a l t s were constant: [ C H P ] : 0 - 3 2 ; [l~al~f]:l.0; C H P ~ 0 . 7 ; [CaSt,l:0.07. At 100 ° for l~aNf and CaSt2 it was found that (k2/~/~)× l0 s (1. mole.sec) was 1.17 and 1-29, respectively, which does not differ in practice from oxidation of pure eumene, for which the ratio of constants was 1.43. Consequently, an acceleration of oxidation in a solution containing hydroperoxide and a metal of constant valency is due to homolysis of hydroperoxide. Using the value of k~/~/~ derived from the formula W = k2/~/~[RH]" x / ~ rates of free radical formation W~ from C H P b y the action of salts of constant
valency metals in cumene (100 °) were calculated, having regard to the concentration of Me+ and C H P (Figs. 1 and 2). It follows from results of t h e Figures that b o t h the reaction of initiation and the reaction of gross-decomposition in chlorobenzene for sodium and calcium stearates and n a p h t h e n a t e s are of first order for reagent concentration
164
KH. E . K ~ M P I D I
e~ a/.
[W~-----k~[ROOH] [cat], W~-----k~[ROOH][eat]. Radical decomposition for salts represents a small part of gross decomposition. Thus, for [CaSts]=3×10 -3 mole/1, and [ C H P ] = 5 × 1 0 -s mole/l, the proportion of radical decomposition is 1-58% (100 W~/2W~o).
L/
/
2
1
#
IO
EGONf2] "IO~ rROOH],10 z rno/e/l. ]~'Ia. 2. Dependence of the rate constant of the gross deeoraposition of cumyl hydroperoxide in chlorobenezene at 100°Con the concentration ofcumyl hydroperoxide and calcium naphthenate: l~without eatalyst; 2--[CaNf~]=l × 10-~- mole/1.; 3--[CHP]=6× 10-~ mele/1. The catalytic effect of stearates varies in the order CaSt s > CdSt 2> BaSt 2> NaSt > MgSt 2 (numerical values are 16.5; 10; 7; I; 0.8, respectively. Wl,,s, is assumed to be one. For naphthenates CaNf > N a N f (12; 1, respectively), i.e. the ratio of effects of calcium attd sodium salts is about the same. The rate of initiation for calcium salts is independent of the type of acid residue; concentrations of CaSts and CaNfs (1 × 10 .3 mole/1.) and [CHP] being the same i.e. 7.6×10 -a mole/1, W~st=2.34×10 -7, W~N~ =2.58 × 10 -~ mole/1.-sec. The catalytic action of salts of metals of constant valency, as before [4], is explained by a reduction of the energy barrier of the reaction I ~ O O H - I - ~ O O H ~ 1~O' -t- 1~O'2+ [H~ONa +]
compared with the simple bimoleeular reaction of radical formation ROOH+ROOH -* RO'+RO',+H,O. I n fact, measurement of the activation energy of radical formation from C H P by the action of metals of constant valeucy under conditions described (10 s, mole/k); [Na~If]=l.0; [CHP]=0.32; [CaStd=0.07; [CHP]=0,7, gave a value of 83.7 and 79.5 kJ/mole, respectively for sodium naphthenate and calcium stoarate, which is noticeably lower t h a n the activation energy of simple bimoleeular decomposition of CHP E3=108.8 KJ/mole[5].
Salts of metals of constant valency as catalysts
165
• Results confirm the ability of salts of constant valency metals to catalyse oxidation of hydrocarbons with decomposition of hydroperoxide to free radicals; when hydroperoxide is absent from the system studied, oxidation does not take place. The type of catalytic homolysis of hydroperoxide by constant valency metals is, apparently, due to acidic (Lewis) properties [6]. SUMMARY
1. The rate of initiation and gross-decomposition of cumyl hydroperoxide in the presence of salts of metals of constant valency is of first order for the concentration of reagents W~=k~[CHP].[cat], Wp=kp[CHP] [cat]. The proportion of radical formation is 2~/o of the gross process of decomposition. 2. The catalytic effect of stearates intensifying gross-decomposition varies in the order CaSt2 ~ CdSt2~ B a S t 2 ~ NaSt 2~ l~aSt ~ M g S t 2. REFERENCES 1. V. K. PYSKOVSKII, S. S. BOTKINA, Ye. K. PROKOF'YEV and Yu. L: MOSKOVICH
Zh. pritdadnoi khlmii 45, 1299, 1972 2. L. V. PETROV, V. M. SOLYANIKOV and Z. Ya. PETROVA, I)okl. AN SSSR 280,
366, 1976 3. Ye. T. DENISOV, Rate Constants of Homolytic Liquid-phase Reactions, Nauka, Moscow, 1971 4. V. M. SOLYANIKOVand Ye. T. DENISOV, Dokl. AN SSSR 173, 1106, 1967 5. N. M. EMANUEL', Ye. T. DENISOV and Z. K. MAIZUS, Tsepnyye rcaktsii okilseniya uglevodorodov v zhidkoi faze {Chain Reactions of Liquid-phase Oxidation of Hydrocarbons), l~auka, Moscow, 1965 6. V. M. SOLYANIKO5, L. V. PETROV and Kh. E. KItARLAMPIDI, Dokl. ANt SSSR 223, 1412, 1975