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Suggestion on a new alternative mechanism of the sulfuric acid catalyzed isioparaffin-olefin alkylation
Studies in Surface Science and Catalysis 130 A. Corma, F.V. Melo, S.Mendioroz and J.L.G. Fierro (Editors) 9 2000 Elsevier Science B.V. All fights reserved.
251
Suggestion on a New Alternative Mechanism of the Sulfuric Acid Catalyzed Isioparaffin-Olefin Alkylation. V.B.Kazansky, T.V.Vasina N.D. Zelinsky Institute of Organic Chemistry of Russian Academy of Sciences, Leninsky prospect 47, Moscow B-334, Russia.
ABSTRACT 13C NMR study of the two-step isoparaffin-olefin alkylation indicated that alkyl carbenium ions are formed instead of protonation of olefins by protonation of alkylsulfates. In the case of sulfuric acid catalyzed alkylation of isoparaffins with propylene the low yield of propane indicates only a minor role in alkylation of a hydride transfer. Both those findings are in contradiction with the classical mechanism by Schmerling. Therefore, a new alternative mechanism of the two-step isoparaffinolefin alkylation is proposed. It involves a direct alkylation of isoparaffins by alkylsulfates.
1. INTRODUCTION The sulfuric acid catalyzed isoparaffin-olefin alkylation is traditionally considered as a classical carbenium ion reaction [1]. The mechanism of alkylation has been originally proposed by Schmerling almost fifty years ago [2]. Since that time it remained unchanged. For the isobutane-butene alkylation the most important reaction steps are the following: 1) C4H8 +
H + ---* C4H9+
2) C4H9+ +
(1)
C4H8 ---* t-C8H17+
3) t-C8H17+ +
i-C4Hlo
4) t-C4H9+ +
C4H8 - 4
--~
i-C8H18
+
t-C4H9 +
t-C8H17+ etc.
The main features of this chain mechanism is formation of alkyl carbenium ions by protonation of olefin and a subsequent cationic oligomerization via interaction of these species with the next olefin molecule. To explain the high selectivity in formation of C8 paraffins, it is also postulated that reaction of hydride transfer from
252 isoparaffin to alkyl carbenium ion (3) is very fast. In addition, the hydride transfer also explains propagation of the reaction chains. One of the most important recent achievements in understanding of a more realistic mechanism of alkylation is a discovery by Albright et. al. that isoparaffinolefin alkylation can be carried out in two separate steps via intermediate formation of alkylsulfates [3-5]. Indeed, it is well known from the general organic chemistry that interaction of olefins with 95 % sulfuric acid results in formation of esters instead of alkyl carbenium ions [6]. The alkylsulfates with primary and secondary alkyl fragments are relatively stable compounds. They also don't react with isoparaffin unless the sulfuric acid is in excess. On the other hand, in the presence of excess of 95 % sulfuric acid the esters readily react with isoparaffins yielding products of alkylation. Their composition mainly corresponds to recombination of two alkyl fragments: that one resulting from the olefin with another one resulting from isoparaffin: RSO4H +
i-RiH
~
R-RI
+
H2SO4
(2)
Thus, the two step alkylation is rather a reaction of isoparaffin with the ester than with olefin. We explained the role of excess of 95% acid in Refs. [7-8]. It was suggested that similar to self-protonation of sulfuric acid the protonation of the ester with sulfuric acid results in formation of alkyl carbenium ions weakly solvated with the acid: RSO4H + H2SO4 ~
R+H2SO4 + HSO4-
(3)
Such possibility was confirmed by the 13C NMR study of mixtures of penthyl sulfates with excess of 95 % sulfuric acid and by the ab initio quantum chemical calculations [8]. Moreover, we estimated the concentration of the resulting alkyl carbenium ions from the experimentally observed ~3C chemical shifts with account of the rapid proton exchange between the protonated and non-protonated species. The obtained results indicated that amount of alkyl carbenium ions does not exceed only few percents of the total concentration of the esters. The present paper is a continuation of those works. It is devoted to the study of the two step alkylation of 3-methyl pentane and 2-methyl butane with propylene. The choice of these reagents allowed a better understanding of the role in alkylation of hydride transfer from isoparaffins to carbenium ions. Indeed, for propyl carbenium ions, the hydride transfer should result in formation of propane. The latter by-product of alkylation could be easily discriminated from other hydrocarbons. Therefore, we used the yield of propane as a measure of the rate of hydride transfer. 2. E X P E R I M E N T A L Di-isopropylsulfate or mixtures of di- and mono-isopropylsulfates were prepared at 0 C by interaction of propylene with 95% sulfuric acid. This reaction was either carried out at the pressure of 1-2 atm in a glass autoclave with a constant stirring of solution or by passing of a propylene flow through the 95% acid. The amount of sulfuric acid was equal to 5-6 g. The reaction was finished in approximately 30 min. In the static experiments this was indicated by stoichiometry of propylene absorption by the acid at the end of reaction or by a strong decrease of the reaction rate.
253 Aikylation of 3-methyl pentane and 2-methyl butane with isopropyl esters of sulfuric acid was carried out in a closed glass system at 0 C with a constant stirring of the reaction mixtures. The 4-5 fold molar excesses of isoparaffins and of the 95% acid relative to the esters were used. The resulting gaseous hydrocarbons were collected in a gas burette and analyzed with a capillary gas chromatograph at the end of the reaction. The chemical analysis of the final products of alkylation was also carried out with the same gas chromatograph. The 13C NMR spectra of mono- and dipropylsulfates were measured with a Varian "Gemini 300" NMR spectrometer operating at the frequency of 300 Ml-lz fbr protons. 3. RESULTS AND DISCUSSION Practically quantitative formation of di-isopropylsulfate was proven by the proton decoupled high-resolution 13C NMR spectrum depicted in Fig. 1. The lines at 79.5 and 77.3 ppm correspond to the carbon atoms in the CH-O-SO4 fragments of the di- and monoester, respectively. This assignment was based on the nondecoupled J3C NMR spectrum of diester and on the NMR spectra of the reaction mixtures with a lower amount of absorbed propylene, when the yield of the monoester was considerably higher. The weakest line at 70.8 ppm most likely belongs to isopropyl oxonium ions.
80
70
60
50
40
30
20 ppm
Fig. 1. The proton decoupled ~3C NMR spectrum of di-isopropylsulfate. In the case of the lower amount of propene absorbed by the acid the reaction products represent a mixture of monoesters and diesters while amount of the former predominates. The composition of the liquid products of alkylation of 2-methyl pentane with diisopropylsulfate is shown in Table 1. The conversion of di-isopropylsulfate as estimated from these data was about 50%. Only a very little amount of propane was formed at the end of the reaction. As one can see from Table l, the yield of nonane isomers is close to 70 %. About 10 % of" lower C7 - Cs paraffins are formed in parallel, while the heavier paraffins are
254 mainly represented by Ci0 and Cli isomers (about 15 %). The most surprising result was a practical absence of propane formation. This obviously indicates only a minor role in alkylation of hydride transfer, since otherwise the reaction of isopropyl carbenium ions with isohexane would result in formation of propane: i-C3H7+ +
i-C6Hl4 ~
C3H8 +
t-C6Hi
(4)
This is in an obvious contradiction with the above-mentioned classical mechanism of isoparaffin-olefin alkylation by Schmerling, where a fast hydride transfer explains both the propagation of the reaction chains and a high selectivity in formation of C9 isoparaffins. TABLE 1
Composition of alkylate resulting from reaction of 4.2 g of di-isopropylsulfate with 11 g of 3-methyl pentane at 0 C in presence of 10.5 g of 95% sulfuric acid. Fraction
C7
C8
C9
Clo+
Hydrocarbons 2,4-dimethylpentane 2-methylhexane 2,3-dimethylpentane 3-methylhexane 2-methylheptane 2,4-dimethylhexane 2,2,5-trimethylhexane 2,4-dimethylheptane 2,6-dimethylheptane 2,5-dimethylheptane 2,3-dimethylheptane 3,4-dimethylheptane Mainly Clo and Cil
Yield in weight % 2.2 5 1.5 1.2 Z=9.9% 5 1.6 Z= 6.6 % 2.5 9.9 9.3 32.2 12.4 1.2 Z= 67.5 % 16.5 % Total:
100.5 %
The results obtained for alkylation with isopropylsulfates of 2-methylbutane were quite similar. The yield of propane was also practically negligible while the main product of alkylation was the mixture of C8 isoparaffins (Table 2). This also confirms only a minor importance of hydride transfer. Another contradiction with the classical mechanism of alkylation consists in the absence in the reaction mixture of propylene. The latter was neither detected in our experiments by ~3C NMR at the beginning, nor at the end of the reaction. This is, however, quite natural since a concentrated sulfuric acid has been for a long time used
255 in gaseous analysis for absorption of olefins. Therefore, in the presence of an excess of 95% acid the concentration of propylene in the reaction mixture certainly is very low. Thus, the two step reaction definitely represents a direct alkylation of isoparaffin with alkyl sulfate instead of its alkylation with olefin as it was postulated by the classical mechanism by Schmerling. This conclusion is also in line with our previous finding that alkyl carbenium ions are formed by protonation of alkyl sulfates by excess of the 95% acid instead of a direct protonation of olefins. TABLE 2
Composition of liquid alkylate resulting from reaction of 3 g of isopropylsulfate with 7 g of 2-methyl butane at 0 C in presence of 7.05 g of 95% sulfuric acid. Fraction C3
Hydrocarbons
Yield in weight %
C4
propane isobutane
C6
2-methylpentane 3-methylpentane
C7
2-methylhexane
C8
C9
Cio
2,5-dimethylhexane + 2,4-dimethylhexane 2,3,4-trymethylpentane 3,4-dimethylhexane 2,5-dimethylheptane 2,3-dimethylheptane isoparaffins
2.5 5.4 2=7.9 3 2.6 2=5.6% 1 27.3 46.5 1.4 Z = 75.2% 5.1 2.7 Z =7.8% 2.6 Total: 100.1%
To explain the above-presented experimental results, and th contradictions with the classical mechanism of alkylation, we propose the following alternative new mechanism of a direct alkylation of isoparaffins with protonated esters. It includes two new reactions. First of them is formation of the nonclassical carbonium ion from isoparaffin and the protonated ester: i-RiH + R+H2SO4 ~
[R! H R] + H2SO4
(5)
This is an analog of the well-known reaction of carbenium ions with isoparaffins in the gas phase [9,10]. Normally this results in a hydride transfer upon dissociation of the nonclassical carbonium ion:
256 R! + + HR
~
[RI
H R] + ~
RIH
+
R+
(6)
In the case of carbonium ions solvated with sulfuric acid the reaction of hydride transfer is slow. This indicates a relatively high stability of the nonclassical carbonium ions. Therefore, they are involved in the second reaction of recombination with HSO4anions. This results in a direct alkylation of isoparaffin with alkylsulfate: [Rl H R] § H2SO4
+
HSO4 ~
RIR
+ 2 H2SO4
(7)
Reaction (7) is a reverse of the well-known protolytic cracking of paraffins that has been well proven both for liquid superacids and for zeolites [11- 12]. Thus, the central point of a new alternative mechanism of the two step isoparaffinolefin alkylation is a suggestion that this reaction involves a direct alkylation of isoparaffins by protonated esters via intermediate formation of nonclassical carbonium ions. This explains the composition of reaction products of alkylation without assumption on a predominant role of the reaction of carbenium ions with olefin and on the fast hydride transfer. It is also most likely that the similar alternative mechanism could better explain the conventional isoparaffin-olefin alkylation as proceeding via following sequence of elementary steps: olefin--, the mixture of alkyl sulfates-.~ the protonated esters ---* nonclassical carbonium ions ---~- alkylate.
Acknowledgements: The authors express their best thanks to Prof. Avelino Corma for the interest to the present work and a fruitful discussion of the obtained results. REFERECES 1. A.Corma, A.Martinez, Cat. Rev. Sci. Eng. 35(1993)483. 2. L.Schmerling, Ind. Eng. Chem.45(1953)1447. 3. L.F.Albright, M.A.Spalding, J.S.Nowinsky, R.M.Ybarra and .E.Eckert, Ind. Eng. Chem.Res. 27(1988)381. 4. L.F.Albright, M.A.Spalding, C.G.Kopser, R.E.Eckert, Ind. Eng. Chem. Res. 27(1988)391. 5. L.F.Albright, M.A.Spalding, J.Faunce, R.E.Eckert, Ind. Eng. Chem.Res. 27(1988)381. 6. V.N.Ipatiev, r162 Reactions at High Temperatures and Pressures~, Academy of Sci. USSR Pub., Moscow-Leningrade 1936. 7. V.B.Kazansky, R.A.van Santen, Catal. Lett., 38(1996) 115. 8. D.A.Zhurko, M.V.Frash,V.B.Kazansky, Catal.Lett.55(1998)7. 9. T.F.Magnera, P.Kebarle, in ~donic Processes in the Gas Phase~, ed. by M.A.Almoster-Ferreira, Reidel, Dortrecht, 1984, p,135. 10. M.V.Frash, V.N.Solkan, V.B.Kazansky, J. Chem. Soc. Far. Trans. 93(1977)515. 11. M.Brower, H. Hogeveen, Prog. Phys. Org. Chem., 9(1972)179. 12. Haag, R.M.Dessau in Proceedings of 8th International Congress on Catalysis, Dechema, Frankfurt-on-Main, 1984, Vol. 2, p.305.
251
Suggestion on a New Alternative Mechanism of the Sulfuric Acid Catalyzed Isioparaffin-Olefin Alkylation. V.B.Kazansky, T.V.Vasina N.D. Zelinsky Institute of Organic Chemistry of Russian Academy of Sciences, Leninsky prospect 47, Moscow B-334, Russia.
ABSTRACT 13C NMR study of the two-step isoparaffin-olefin alkylation indicated that alkyl carbenium ions are formed instead of protonation of olefins by protonation of alkylsulfates. In the case of sulfuric acid catalyzed alkylation of isoparaffins with propylene the low yield of propane indicates only a minor role in alkylation of a hydride transfer. Both those findings are in contradiction with the classical mechanism by Schmerling. Therefore, a new alternative mechanism of the two-step isoparaffinolefin alkylation is proposed. It involves a direct alkylation of isoparaffins by alkylsulfates.
1. INTRODUCTION The sulfuric acid catalyzed isoparaffin-olefin alkylation is traditionally considered as a classical carbenium ion reaction [1]. The mechanism of alkylation has been originally proposed by Schmerling almost fifty years ago [2]. Since that time it remained unchanged. For the isobutane-butene alkylation the most important reaction steps are the following: 1) C4H8 +
H + ---* C4H9+
2) C4H9+ +
(1)
C4H8 ---* t-C8H17+
3) t-C8H17+ +
i-C4Hlo
4) t-C4H9+ +
C4H8 - 4
--~
i-C8H18
+
t-C4H9 +
t-C8H17+ etc.
The main features of this chain mechanism is formation of alkyl carbenium ions by protonation of olefin and a subsequent cationic oligomerization via interaction of these species with the next olefin molecule. To explain the high selectivity in formation of C8 paraffins, it is also postulated that reaction of hydride transfer from
252 isoparaffin to alkyl carbenium ion (3) is very fast. In addition, the hydride transfer also explains propagation of the reaction chains. One of the most important recent achievements in understanding of a more realistic mechanism of alkylation is a discovery by Albright et. al. that isoparaffinolefin alkylation can be carried out in two separate steps via intermediate formation of alkylsulfates [3-5]. Indeed, it is well known from the general organic chemistry that interaction of olefins with 95 % sulfuric acid results in formation of esters instead of alkyl carbenium ions [6]. The alkylsulfates with primary and secondary alkyl fragments are relatively stable compounds. They also don't react with isoparaffin unless the sulfuric acid is in excess. On the other hand, in the presence of excess of 95 % sulfuric acid the esters readily react with isoparaffins yielding products of alkylation. Their composition mainly corresponds to recombination of two alkyl fragments: that one resulting from the olefin with another one resulting from isoparaffin: RSO4H +
i-RiH
~
R-RI
+
H2SO4
(2)
Thus, the two step alkylation is rather a reaction of isoparaffin with the ester than with olefin. We explained the role of excess of 95% acid in Refs. [7-8]. It was suggested that similar to self-protonation of sulfuric acid the protonation of the ester with sulfuric acid results in formation of alkyl carbenium ions weakly solvated with the acid: RSO4H + H2SO4 ~
R+H2SO4 + HSO4-
(3)
Such possibility was confirmed by the 13C NMR study of mixtures of penthyl sulfates with excess of 95 % sulfuric acid and by the ab initio quantum chemical calculations [8]. Moreover, we estimated the concentration of the resulting alkyl carbenium ions from the experimentally observed ~3C chemical shifts with account of the rapid proton exchange between the protonated and non-protonated species. The obtained results indicated that amount of alkyl carbenium ions does not exceed only few percents of the total concentration of the esters. The present paper is a continuation of those works. It is devoted to the study of the two step alkylation of 3-methyl pentane and 2-methyl butane with propylene. The choice of these reagents allowed a better understanding of the role in alkylation of hydride transfer from isoparaffins to carbenium ions. Indeed, for propyl carbenium ions, the hydride transfer should result in formation of propane. The latter by-product of alkylation could be easily discriminated from other hydrocarbons. Therefore, we used the yield of propane as a measure of the rate of hydride transfer. 2. E X P E R I M E N T A L Di-isopropylsulfate or mixtures of di- and mono-isopropylsulfates were prepared at 0 C by interaction of propylene with 95% sulfuric acid. This reaction was either carried out at the pressure of 1-2 atm in a glass autoclave with a constant stirring of solution or by passing of a propylene flow through the 95% acid. The amount of sulfuric acid was equal to 5-6 g. The reaction was finished in approximately 30 min. In the static experiments this was indicated by stoichiometry of propylene absorption by the acid at the end of reaction or by a strong decrease of the reaction rate.
253 Aikylation of 3-methyl pentane and 2-methyl butane with isopropyl esters of sulfuric acid was carried out in a closed glass system at 0 C with a constant stirring of the reaction mixtures. The 4-5 fold molar excesses of isoparaffins and of the 95% acid relative to the esters were used. The resulting gaseous hydrocarbons were collected in a gas burette and analyzed with a capillary gas chromatograph at the end of the reaction. The chemical analysis of the final products of alkylation was also carried out with the same gas chromatograph. The 13C NMR spectra of mono- and dipropylsulfates were measured with a Varian "Gemini 300" NMR spectrometer operating at the frequency of 300 Ml-lz fbr protons. 3. RESULTS AND DISCUSSION Practically quantitative formation of di-isopropylsulfate was proven by the proton decoupled high-resolution 13C NMR spectrum depicted in Fig. 1. The lines at 79.5 and 77.3 ppm correspond to the carbon atoms in the CH-O-SO4 fragments of the di- and monoester, respectively. This assignment was based on the nondecoupled J3C NMR spectrum of diester and on the NMR spectra of the reaction mixtures with a lower amount of absorbed propylene, when the yield of the monoester was considerably higher. The weakest line at 70.8 ppm most likely belongs to isopropyl oxonium ions.
80
70
60
50
40
30
20 ppm
Fig. 1. The proton decoupled ~3C NMR spectrum of di-isopropylsulfate. In the case of the lower amount of propene absorbed by the acid the reaction products represent a mixture of monoesters and diesters while amount of the former predominates. The composition of the liquid products of alkylation of 2-methyl pentane with diisopropylsulfate is shown in Table 1. The conversion of di-isopropylsulfate as estimated from these data was about 50%. Only a very little amount of propane was formed at the end of the reaction. As one can see from Table l, the yield of nonane isomers is close to 70 %. About 10 % of" lower C7 - Cs paraffins are formed in parallel, while the heavier paraffins are
254 mainly represented by Ci0 and Cli isomers (about 15 %). The most surprising result was a practical absence of propane formation. This obviously indicates only a minor role in alkylation of hydride transfer, since otherwise the reaction of isopropyl carbenium ions with isohexane would result in formation of propane: i-C3H7+ +
i-C6Hl4 ~
C3H8 +
t-C6Hi
(4)
This is in an obvious contradiction with the above-mentioned classical mechanism of isoparaffin-olefin alkylation by Schmerling, where a fast hydride transfer explains both the propagation of the reaction chains and a high selectivity in formation of C9 isoparaffins. TABLE 1
Composition of alkylate resulting from reaction of 4.2 g of di-isopropylsulfate with 11 g of 3-methyl pentane at 0 C in presence of 10.5 g of 95% sulfuric acid. Fraction
C7
C8
C9
Clo+
Hydrocarbons 2,4-dimethylpentane 2-methylhexane 2,3-dimethylpentane 3-methylhexane 2-methylheptane 2,4-dimethylhexane 2,2,5-trimethylhexane 2,4-dimethylheptane 2,6-dimethylheptane 2,5-dimethylheptane 2,3-dimethylheptane 3,4-dimethylheptane Mainly Clo and Cil
Yield in weight % 2.2 5 1.5 1.2 Z=9.9% 5 1.6 Z= 6.6 % 2.5 9.9 9.3 32.2 12.4 1.2 Z= 67.5 % 16.5 % Total:
100.5 %
The results obtained for alkylation with isopropylsulfates of 2-methylbutane were quite similar. The yield of propane was also practically negligible while the main product of alkylation was the mixture of C8 isoparaffins (Table 2). This also confirms only a minor importance of hydride transfer. Another contradiction with the classical mechanism of alkylation consists in the absence in the reaction mixture of propylene. The latter was neither detected in our experiments by ~3C NMR at the beginning, nor at the end of the reaction. This is, however, quite natural since a concentrated sulfuric acid has been for a long time used
255 in gaseous analysis for absorption of olefins. Therefore, in the presence of an excess of 95% acid the concentration of propylene in the reaction mixture certainly is very low. Thus, the two step reaction definitely represents a direct alkylation of isoparaffin with alkyl sulfate instead of its alkylation with olefin as it was postulated by the classical mechanism by Schmerling. This conclusion is also in line with our previous finding that alkyl carbenium ions are formed by protonation of alkyl sulfates by excess of the 95% acid instead of a direct protonation of olefins. TABLE 2
Composition of liquid alkylate resulting from reaction of 3 g of isopropylsulfate with 7 g of 2-methyl butane at 0 C in presence of 7.05 g of 95% sulfuric acid. Fraction C3
Hydrocarbons
Yield in weight %
C4
propane isobutane
C6
2-methylpentane 3-methylpentane
C7
2-methylhexane
C8
C9
Cio
2,5-dimethylhexane + 2,4-dimethylhexane 2,3,4-trymethylpentane 3,4-dimethylhexane 2,5-dimethylheptane 2,3-dimethylheptane isoparaffins
2.5 5.4 2=7.9 3 2.6 2=5.6% 1 27.3 46.5 1.4 Z = 75.2% 5.1 2.7 Z =7.8% 2.6 Total: 100.1%
To explain the above-presented experimental results, and th contradictions with the classical mechanism of alkylation, we propose the following alternative new mechanism of a direct alkylation of isoparaffins with protonated esters. It includes two new reactions. First of them is formation of the nonclassical carbonium ion from isoparaffin and the protonated ester: i-RiH + R+H2SO4 ~
[R! H R] + H2SO4
(5)
This is an analog of the well-known reaction of carbenium ions with isoparaffins in the gas phase [9,10]. Normally this results in a hydride transfer upon dissociation of the nonclassical carbonium ion:
256 R! + + HR
~
[RI
H R] + ~
RIH
+
R+
(6)
In the case of carbonium ions solvated with sulfuric acid the reaction of hydride transfer is slow. This indicates a relatively high stability of the nonclassical carbonium ions. Therefore, they are involved in the second reaction of recombination with HSO4anions. This results in a direct alkylation of isoparaffin with alkylsulfate: [Rl H R] § H2SO4
+
HSO4 ~
RIR
+ 2 H2SO4
(7)
Reaction (7) is a reverse of the well-known protolytic cracking of paraffins that has been well proven both for liquid superacids and for zeolites [11- 12]. Thus, the central point of a new alternative mechanism of the two step isoparaffinolefin alkylation is a suggestion that this reaction involves a direct alkylation of isoparaffins by protonated esters via intermediate formation of nonclassical carbonium ions. This explains the composition of reaction products of alkylation without assumption on a predominant role of the reaction of carbenium ions with olefin and on the fast hydride transfer. It is also most likely that the similar alternative mechanism could better explain the conventional isoparaffin-olefin alkylation as proceeding via following sequence of elementary steps: olefin--, the mixture of alkyl sulfates-.~ the protonated esters ---* nonclassical carbonium ions ---~- alkylate.
Acknowledgements: The authors express their best thanks to Prof. Avelino Corma for the interest to the present work and a fruitful discussion of the obtained results. REFERECES 1. A.Corma, A.Martinez, Cat. Rev. Sci. Eng. 35(1993)483. 2. L.Schmerling, Ind. Eng. Chem.45(1953)1447. 3. L.F.Albright, M.A.Spalding, J.S.Nowinsky, R.M.Ybarra and .E.Eckert, Ind. Eng. Chem.Res. 27(1988)381. 4. L.F.Albright, M.A.Spalding, C.G.Kopser, R.E.Eckert, Ind. Eng. Chem. Res. 27(1988)391. 5. L.F.Albright, M.A.Spalding, J.Faunce, R.E.Eckert, Ind. Eng. Chem.Res. 27(1988)381. 6. V.N.Ipatiev, r162 Reactions at High Temperatures and Pressures~, Academy of Sci. USSR Pub., Moscow-Leningrade 1936. 7. V.B.Kazansky, R.A.van Santen, Catal. Lett., 38(1996) 115. 8. D.A.Zhurko, M.V.Frash,V.B.Kazansky, Catal.Lett.55(1998)7. 9. T.F.Magnera, P.Kebarle, in ~donic Processes in the Gas Phase~, ed. by M.A.Almoster-Ferreira, Reidel, Dortrecht, 1984, p,135. 10. M.V.Frash, V.N.Solkan, V.B.Kazansky, J. Chem. Soc. Far. Trans. 93(1977)515. 11. M.Brower, H. Hogeveen, Prog. Phys. Org. Chem., 9(1972)179. 12. Haag, R.M.Dessau in Proceedings of 8th International Congress on Catalysis, Dechema, Frankfurt-on-Main, 1984, Vol. 2, p.305.