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Synthesis of isoprene from propylene—I. Analysis of alkylaluminiums in the dimerization of propylene
SYNTHESIS OF ISOPRENE FROM PROPYLENE--I. ANALYSIS OF A L K Y L A L U M I N I U M S IN T H E D I M E R I Z A T I O N
OF PROPYLENE* V. SH. I~EL'DBLUM, G. P . KOMISSAROVA, L . D . MYASNIKOVA,
S. I. KRYUKOV and M. I. FARBEROV Scientific Research Institute of Monomers for Synthetic Rubber, Yaroslav Technological Institute (Received 9 June 1962)
IN 1952, Ziegler [1, 2] published papers on the polymerization and, in particular, the dimerization of olefins in the presence of triethylaluminium and other alkylaluminiums. In the case of propylene, this reaction led to the formation of 2-methylpent-l-ene. The latter [3, 4] in the presence of acid catalysts readily isomerizes into 2-methylpent-2-ene, which is already being used for the synthesis of valuable products [5]. The most promising use of 2-methylpent-2-ene is its selective pyrolysis to isoprene and methane [7, 11]. In view of this, the dimerization of propylene by Ziegler's method is the first stage of the synthesis of isoprene from propylene. The aim of the present work was to study some questions connected with methods of analysis of the activity and composition of alkylaluminiums--the catalysts for the dimerization of propylene.
Method of performing the dimerization The reaction was carried out in a stainless steel rocking autoclave with a capacity of 950 ml. The autoclave was fitted with a jacket for an electric heater, a thermocouple pocket, a pressure gauge, and a syphon head for charging and discharging liquid products. The propylene fraction used for the experiments had, according to the results of chromatographic analysis, the following composition ( % by weight): propylene--81.6; propane-- 12.0; ethane-Fethylene-- 1.7; isobutane--0.9; nb u t a n e - 0.3; butylene -- 2.1; divinyl -- 0.7. The catalyst used was technical tri-isobutylaluminium in the form of a concentrated solution in n-heptane. This solution was diluted before use with 2-methylpent-l-ene to give a concentration of the catalyst of ~ 3 0 % by weight. * Neftekhimiya 3, No. 1, 13-19, 1963.
2
V. SH. FEL'DBLUMet ¢~.
The autoclave was charged with 100 ml of catalyst solution and 200 g of liquid propylene fraction, after which it was heated to 250 °. The original pressure of 110-125 arm fell after two hours to 50-70 arm. After cooling, the contents of the autoclave were discharged and were distilled in a laboratory column of medium efficiency. First the dissolved gases (propane, propylene) were eliminated, and then a small amount of light fraction (amylenes, 4methylpent-2-ene) passed over and, finally, 2-methylpent-l-ene. The yield of the latter was 60-70%, calculated on the propylene charged, a n d 80-90% calculated on that which had reacted. The still residue consisted of the catalyst - - t h e alkylaluminium--and higher hydrocarbons forming by-products of the dimerization. This residue was re-used as catalyst for t h e succeeding experiment, the yield of dimer calculated on the initial propylene in the second experiment being, as a rule, 1 0 - 1 5 ~ higher t h a n in the first. When the still residue was re-used successively without the addition of fresh catalyst, the yield of propylene direCT gradually fell, the fall becoming particularly appreciable after the catalyst had been used five times.
Analysis of the initial tri-isobutylaluminium The analysis consisted in determining the total aluminium content and the content of "active" aluminium in the compounds RaA1, where R represents a hydrocarbon radical. The ratio of active aluminium to that o f total aluminium, expressed in %, is defined as the "activity" of the catalyst. The total aluminium content in the initial catalyst was determined by the method of reference [12]. Several methods were used to determine the contents of active aluminium in order to compare the results. As can be seen from Table 1, the indicator method of Razuvayev and Grayevskii [13] and the ammonia method of Ziegler [15] give similar figures, while the oxidationreduction method of Tepenitsyna and Farberov [14] gives a lower figure. TABLE1. RESULTS OF THEANALYSISOF TECHNICALTRI-ISOBUTYLALUMINIUM BYVARIOUSMETHODS (Total aluminium content-- 0"086 g/ml) hod determined
Indicator [13]
Oxidationreduction [14]
Ammonia [153
Gasometric
With dimethylamine *
Content of active alumin-[ ium, g/ml ] 0.062-~ 0"001 0"041± 0"0005 0"063-4- 0"001 0"087i 0"003 0"075q- 0"001 Activity of [ the catalyst, ] % by weight ] 73"0 49-0 74"0 N 100 80"0 * Total aluminium content 0"094 g/ml
Synthesis of isop~n¢ from propylene--I A gasometric method based on measuring the amount of gas liberated on decomposing a weighed sample of the catalyst with water gives a content of active aluminium close to the total content, which agrees with an extremely low content of alkoxides of the type RsAIOR. This leads to the thought that all the methods mentioned except the last apparently give low results. Chromatographic analysis of the gas obtained on decomposing tri-isobutylaluminium with water gives the following composition ( ~ by weight): isobutane-- 95.8; n-butane-- 2-6; isobutylene-- 0.9; propane-- 0.4; propylene 0.3; hydrogen--traces. From this it may be concluded that the anomalous decomposition of an alkylaluminium reported by Bonitz [17] was inconsiderable in our case. The method of Razuvayev and Grayevskii, which is characterized by simplicity and rapidity of performance, possesses certain disadvantages in the determination of the colour change of the indicator during titration. In this respect, the ammonia method [15], based on the interaction of the alkylaluminium with ammonia by the equation RsAI+ NHs-=RsA1NHs+ RH is satisfactory. The sample to be analyzed is treated with a current of ammonia to saturation, the ammonia which has not reacted is eliminated, and then t--e amine R2A1NH2 is decomposed with alcohol and the ammonia is absorbed in acid, the excess of which is back-titrated. A disadvantage of Ziegler's ammonia method is the length of time for the analysis. In the present paper, we propose a simple method based on the use of di- or trimethylamine instead of ammonia. It is known [16] that the lower alkylaluminiums form complexes with secondary and tertiary amines which are quite stable at room temperature. The boiling point of dimethylamine or trimethylamine is sufficiently high to permit the amount of amine used in the analysis to be weighed out, and, at the same time, sufficiently low for the amine which has not reacted with the sample for analysis to be readily removed. This fact permits the time of analysis to be reduced to a fraction of that necessary for Ziegler's method. Dimethylamine or trimethylamine was obtained by the action of alkali on the corresponding hydrochloride and was dried with granulated caustic potash and distilled over sodium. The amines were stored in glass tubes from which small amounts were distilled over into the apparatus for analysis. The glass apparatus for analysis is illustrated in Fig. 1. It consists of two bulbs (1 and 4) connected by the ground joint 6. With the aid of the device described below, 0-1-0-5cm s of the tri-isobutylaluminiuIn solution to be analysed was introduced into bulb 4 through joint 6 under a current of nitrogen (side-arm with cock 5). About 1 cm s of liquid amine was condensed (ice) through side=arm with cock 2 into bulb 1, after which ground joint 6 was
V . SH. FEL'DBLUMet al.
closed, a bubbler dipping into a flask containing 20-30 ml of 0.5 N HCI solution was connected to side-arm 5, and cock 5 was opened. Cock 3 was carefully opened and the amine was transferred into bulb d, where it immediately reacted with the sample, the excess of amine being absorbed by the acid. 3 6
~
5
FIG. 1. Apparatus for the determination of the active alumim'um with dimethylamine:/--bulb for the weighed amount of amine; 2, 3, 5--cocks; 4--bulb for the weighed tri-isobutylaluminium sample; 6--ground joint.
Then a gentle current of nitrogen was passed through side-arm 2 for l5 rain to eliminate the unchanged amine dissolved in the sample being analysed and, finally, the excess of acid was back-titrated with 0.5 N alkali solution in the presence of methyl orange. The content of active aluminium in the sample (g) was calculated from the formula X - -
g × 27 M -
-
(vi--vz) × 0.5 × 27 1000
where g and M are the weight and molecular weight of the amine, respectively; vI is the volume of 0.5 N HC1 taken for the analysis; and v~ is the volume of 0.5 N alkali consumed in the titration. Figure 2 illustrates the simple device which we constructed for introducing the samples to be analysed, measured by weight or by volume, into the apparatus without contact with the air. Cylinder 1 containing the catalyst solution to be analysed in an atmosphere of nitrogen, bears in a ground joint the sleeve 2 in which, in its turn, a pipette 3 with a 3-way cock 4 moves freely. The pipette is connected with the sleeve by a piece of soft rubber tubing. The side-arms of the sleeve and cock are also connected by tubing of suitable length (not shown in the Figure). By pressing this tubing with the hand the
Synthesis of isoprene from propylene--I liquid is forced by nitrogen pressure (through the side:arm of the cylinder) into the pipette. The tubing is released and the required volume of liquid is enclosed in the pipette by turning the cock. The current of nitrogen is transferred to the upper arm of the cock and the pipette is raised into the upper position, after which it is removed from the cylinder together with the sleeve (Fig. 2, B).
4
32
A
3
B
FIG. 2. Device for taking small volumes and weights of liquids in a current of inert gas (A--in assembled form; B--pipette with sample of liquid): /--cylinder with ground joint and side-arm; 2--sleeve with ground joint and side-arm; 3--pipette; 4--3-way cock. A current of nitrogen passes over the end of the pipette, protecting it from contact with the air. The sleeve with the pipette is fixed into the neck of the bulb 4 of the analytical apparatus (Fig. 1) and the sample is run out. The weight of the sample is determined from the difference in the weights of cylinder 1, closed with a ground stopper, before and after the sample is taken. This device can also be used to determine the density of liquids which ignite on contact with air.
Analysis of the al]cylaluminlums after dimerization The results of some experiments in autoclaves o n t h e dimerization of propylene are given in Table 2. In view of the statements which have been made [18] on the possibility of the intensive decomposition of alkylalumininms a t temperatures above 200 °, w e d e t e r m i n e d the t o t a l content of alumininm in the catalyst when it was used repeatedly (experiments 1-5, Table 2). As the
V. Sti. FEL'DBLUMet al. analyses show, the a m o u n t of aluminium charged originally is maintained, which indicates the absence at the reaction temperature of the thermal decomposition of the catalyst to metallic aluminium. Attempts to use, for the determination of the active aluminium after reaction, the same methods as for the initial tri-isobutylaluminium did not give satisfactory results. Titration of the organic bases in a non-aqueous medium by Razuvayev and Grayevskii's method was impossible because of the decolorization of the indicator. The presence in the catalyst after dimerization of compounds intensively decolorizing a permanganate solution made the oxidation-reduction method unusable. The results of a determination of active aluminium by Ziegler's method are given in Table 2 (experiments 6, 7). The low values obtained for the activity TABLE 2. EXPERIMENTS ON THE DIMERIZATIOlg OF PROPYLENE IN AI~"AUTOCLAVE
(Charge of propylene -- 160 g; charge of tri-isobutylaluminium--30 g; temperature -- 250°; reaction time-- 2 hr)
Tri-isobutylaluminium catalyst
1.
2. 3. 4.
5. 6o
7. 8. 9. 10.
Fresh ("activity" 68%) Still residue from experiment 1 Still residue from experiment 2 Still residue from experiment 3 Still residue from experiment 4 Fresh ("activity"76.0~o'~ Fresh ("activity" 70%) After being used once After being used twice
73"0
56"5
6"58
98"0
82"1
3"96
82.0
104"4
3"45 •
73"0
128"5
3"05
50"0 97"0 82"0 75"0 80.0 82"0
146"1 59"2 64.2 65"0 110"0 121"2
2'74 6"73 5"53 5"83
m
37"4 41"5 1100 97O 8OO
after a single use of the catalyst are clearly not in agreement with the fact t h a t when it is used repeatedly the yield of product does not fall. Analogous results are obtained by the use of the ammonia method.
Synthesis of isoprene from pr0pylene--I
7
The gasometric method, which is also unsuitable for determ~nlng the activity of the catalyst under these conditions, permits data to be obtained on the change in the alkyl composition of the catalyst during its use. The results of a gasometric analysis of the catalyst after it had been used once, twice, and three times for dimerization (Table 2, experiments 8-10) show a rapid replacement of about half the isobutyl groups of the initial catalyst by heavy alkyl groups. (When the initial catalyst was decomposed with water, about 2500 ml of gas were liberated per 1 g of aluminium). When the cat~]yst is used repeatedly, the amount of gases liberated by decomposition with water slowly decreases. This may be due both to a continuation of the replacement of the remaining light alkyl residues and also to their oxidation into the corresponding alkoxides on contact with air. Chromatographic analysis of the gas after decomposition with water of the once-used catalyst shows that about 50% of the isobuty| groups which have not been replaced by higher alkyl groups are replaced by propyl groups. (Molar ratios of isobutane and propane in the gas are approximately equal). If a once-used catalyst, a comparison of the weight of which with the initial catalyst indicates a considerable content of higher by-products, is heated to 240-250 °, only a small amount of light fraction boiling up to 100° (mainly n-heptane) dlstils from it. Decomposition of this catalyst with acidified water leads to the formation, in addition to gas, of a mixture of hydrocarbons with a wide boiling range (from 100 to 200 °) which is difficult to separate. Free higher oleflns (trimers and tetramers of propylene) distil off from the catalyst only after it has been used two or three times. Consequently, the first portions of the higher hydrocarbons formed in the reaction either remain attached to the aluminium or replace part of the lower alkyl groups, after which the accumulation of free higher olefins commences. It is also worthy of attention that no considerable amount of 2-methylpentane could be isolated from the products of decomposition with water. Consequently, the number of isohexyl groups in the catalyst after dimerization is extremely low, which contradicts certain statements in the literature [19]. The capability of higher olefins (by-products) for taking part in an exchange reaction with tri-isobutylaluminium was confirmed by supplementary experiments. On heating a mixture of one mole of tri-isobutylaluminium and a stoichiometric excess of these hydrocarbons to 110 ° in a flask with a reflux condenser, about 1 mole of isobutylene was liberated in 2 hr. Further replacement took place extremely slowly. The product of this reaction is also a catalyst for the dimerization of propylene. It is interesting that pure tri-isobutylaluminium on heating to 110 ° liberates practically no isobutylene. This shows that the replacement of the isobutyl group by a higher alkyl group, at least up to 110°, is a bimoleeular reaction AI(C~Hg)s+C,Hs, ---~AI(C4Hg)sC,HI,+1+C4Hs,
8
V. SH. FEL'DBLUMet al.
and not a sequence of two reactions [20]: AI(C,Hp)8 ~ A1H(C4H0)~+C,Hs, A1H(C4Hp)2+C,i'is, --* AI(C4I'I-I9)2C,i'iz, + z. F r o m what has been said above, it is clear t h a t a catalyst used repeatedly for the dimerization of propylene consists of a complex mixture of alkylaluminiums the molecules of which contain light alkyl residues (propyl and isobutyl) and a t least one heavy group (Cp-Cz~). I n conclusion, the authors express their thanks to A. G. P a n k o v and M. F. K n y a z e v a for carrySng out the chromatographic analyses of the propylene and the gases resulting from the decomposition of the catalyst. SUMMARY 1. A comparative evaluation o f the results obtained by the most widely used methods of analysis of alkylaluminiums in the dimerization of propylene has been carried out. 2. Supplementing the existing methods, a simple method of determining the activity of the initial dimerization c a t a l y s t based on its reaction with dimethylamine or trimethylamine has been proposed. 3. The compos!tion of alkylaluminiums repeatedly used as catalysts for t h e dimerization of propylene has been investigated. Tranelat~ by B. J. HAZZARD REFERENCES 1. K. ZIEGLER, Angew. Chemie 64, 323, 1952 2. K. ZlEGLER, Brennst, Chemie 33, 193, 1952 3. M. I. FARBEROV, S. I. KRYUKOV, G. D. MANTYUKOV and B. F. USTAVSHCHIKOV, U.S.S.R. Authors' Certificate No. 143,393, 1960 4. S. I. KRYUKOV and M. L FARBEROV, Zh. prikl, khim. 35, 2319, 1962 5. G. D. MANTYUKOV, M. I. FARBEROV and S. I. KRYUKOV, Uch. zap. Yaroslavsk. tekh. inst. 6, 31, 1961 6. A. G. OBLAD and E. GORIN, U.S. Fat. 2,430,137, 4.11.1947 7. L N. NAZAROV, Ye. I. KT.ABUNOVSKII and N. A. KRAVCHENKO, Izv. Akad. Nauk SSSR, otd. khim. nauk 1960, 73 8. V. J. ANHORN, G. S. SCHAFFEL, K. J. FRENCH and BROWN, Chem. Engng. Progr. 57, 43, 196i 9. I. Ya. TYURYAYEV and S. V. KOLYADYUK, Neftekhimiya 2, No. 2, 170, 1962 10. Brit. Pat. 840,028, 6.07.1960 11. Brit. Pat. 841,351, 13.07.1960 12. S. I. KRYUKOV, A. M. KUT'IN, G. S. LEVSKAYA, Ye. P. TEPENITSYNA, Z. F. USTAVSHCHIKOVA and M. I. FARBEROV, Izv. vuzov. Khim. i khim. tekh. No. 1, 86, 1958 13. C. A. RAZUVAYEV and A. I. GRAYEVSKII, ])old. Akad. Nauk SSSR 128, No. 2, 309, 1959
Synthesis of isoprene from propylene--II
9
14. Ye. P. TEPENITSYNA, M. I. FARBEROV, A. M. KUT'IN and G. S. LEVSKAYA, Vysokomolek. soyed. 1, 1148, 1959 15. K. ZIEGLER and H. GELT.EI~T, Liebigs Ann. 629, 20, 1960 16. M. DAVIDSON and H. BROWN, J. Amer. Chem. Soc. 64, 316, 1942 17. E. BONITZ, Chem. Ber. 88, 742, 1955 18. K. ZIEGLER, K. NAGEL and W. PFOHL, Liebigs Ann. 629, 210, 1960 19. Brit. Pat. 831,249, 23.03.1960 20. K. ZOSEL, Brennst. Chemie, 41, 321, 1960
OF PROPYLENE* V. SH. I~EL'DBLUM, G. P . KOMISSAROVA, L . D . MYASNIKOVA,
S. I. KRYUKOV and M. I. FARBEROV Scientific Research Institute of Monomers for Synthetic Rubber, Yaroslav Technological Institute (Received 9 June 1962)
IN 1952, Ziegler [1, 2] published papers on the polymerization and, in particular, the dimerization of olefins in the presence of triethylaluminium and other alkylaluminiums. In the case of propylene, this reaction led to the formation of 2-methylpent-l-ene. The latter [3, 4] in the presence of acid catalysts readily isomerizes into 2-methylpent-2-ene, which is already being used for the synthesis of valuable products [5]. The most promising use of 2-methylpent-2-ene is its selective pyrolysis to isoprene and methane [7, 11]. In view of this, the dimerization of propylene by Ziegler's method is the first stage of the synthesis of isoprene from propylene. The aim of the present work was to study some questions connected with methods of analysis of the activity and composition of alkylaluminiums--the catalysts for the dimerization of propylene.
Method of performing the dimerization The reaction was carried out in a stainless steel rocking autoclave with a capacity of 950 ml. The autoclave was fitted with a jacket for an electric heater, a thermocouple pocket, a pressure gauge, and a syphon head for charging and discharging liquid products. The propylene fraction used for the experiments had, according to the results of chromatographic analysis, the following composition ( % by weight): propylene--81.6; propane-- 12.0; ethane-Fethylene-- 1.7; isobutane--0.9; nb u t a n e - 0.3; butylene -- 2.1; divinyl -- 0.7. The catalyst used was technical tri-isobutylaluminium in the form of a concentrated solution in n-heptane. This solution was diluted before use with 2-methylpent-l-ene to give a concentration of the catalyst of ~ 3 0 % by weight. * Neftekhimiya 3, No. 1, 13-19, 1963.
2
V. SH. FEL'DBLUMet ¢~.
The autoclave was charged with 100 ml of catalyst solution and 200 g of liquid propylene fraction, after which it was heated to 250 °. The original pressure of 110-125 arm fell after two hours to 50-70 arm. After cooling, the contents of the autoclave were discharged and were distilled in a laboratory column of medium efficiency. First the dissolved gases (propane, propylene) were eliminated, and then a small amount of light fraction (amylenes, 4methylpent-2-ene) passed over and, finally, 2-methylpent-l-ene. The yield of the latter was 60-70%, calculated on the propylene charged, a n d 80-90% calculated on that which had reacted. The still residue consisted of the catalyst - - t h e alkylaluminium--and higher hydrocarbons forming by-products of the dimerization. This residue was re-used as catalyst for t h e succeeding experiment, the yield of dimer calculated on the initial propylene in the second experiment being, as a rule, 1 0 - 1 5 ~ higher t h a n in the first. When the still residue was re-used successively without the addition of fresh catalyst, the yield of propylene direCT gradually fell, the fall becoming particularly appreciable after the catalyst had been used five times.
Analysis of the initial tri-isobutylaluminium The analysis consisted in determining the total aluminium content and the content of "active" aluminium in the compounds RaA1, where R represents a hydrocarbon radical. The ratio of active aluminium to that o f total aluminium, expressed in %, is defined as the "activity" of the catalyst. The total aluminium content in the initial catalyst was determined by the method of reference [12]. Several methods were used to determine the contents of active aluminium in order to compare the results. As can be seen from Table 1, the indicator method of Razuvayev and Grayevskii [13] and the ammonia method of Ziegler [15] give similar figures, while the oxidationreduction method of Tepenitsyna and Farberov [14] gives a lower figure. TABLE1. RESULTS OF THEANALYSISOF TECHNICALTRI-ISOBUTYLALUMINIUM BYVARIOUSMETHODS (Total aluminium content-- 0"086 g/ml) hod determined
Indicator [13]
Oxidationreduction [14]
Ammonia [153
Gasometric
With dimethylamine *
Content of active alumin-[ ium, g/ml ] 0.062-~ 0"001 0"041± 0"0005 0"063-4- 0"001 0"087i 0"003 0"075q- 0"001 Activity of [ the catalyst, ] % by weight ] 73"0 49-0 74"0 N 100 80"0 * Total aluminium content 0"094 g/ml
Synthesis of isop~n¢ from propylene--I A gasometric method based on measuring the amount of gas liberated on decomposing a weighed sample of the catalyst with water gives a content of active aluminium close to the total content, which agrees with an extremely low content of alkoxides of the type RsAIOR. This leads to the thought that all the methods mentioned except the last apparently give low results. Chromatographic analysis of the gas obtained on decomposing tri-isobutylaluminium with water gives the following composition ( ~ by weight): isobutane-- 95.8; n-butane-- 2-6; isobutylene-- 0.9; propane-- 0.4; propylene 0.3; hydrogen--traces. From this it may be concluded that the anomalous decomposition of an alkylaluminium reported by Bonitz [17] was inconsiderable in our case. The method of Razuvayev and Grayevskii, which is characterized by simplicity and rapidity of performance, possesses certain disadvantages in the determination of the colour change of the indicator during titration. In this respect, the ammonia method [15], based on the interaction of the alkylaluminium with ammonia by the equation RsAI+ NHs-=RsA1NHs+ RH is satisfactory. The sample to be analyzed is treated with a current of ammonia to saturation, the ammonia which has not reacted is eliminated, and then t--e amine R2A1NH2 is decomposed with alcohol and the ammonia is absorbed in acid, the excess of which is back-titrated. A disadvantage of Ziegler's ammonia method is the length of time for the analysis. In the present paper, we propose a simple method based on the use of di- or trimethylamine instead of ammonia. It is known [16] that the lower alkylaluminiums form complexes with secondary and tertiary amines which are quite stable at room temperature. The boiling point of dimethylamine or trimethylamine is sufficiently high to permit the amount of amine used in the analysis to be weighed out, and, at the same time, sufficiently low for the amine which has not reacted with the sample for analysis to be readily removed. This fact permits the time of analysis to be reduced to a fraction of that necessary for Ziegler's method. Dimethylamine or trimethylamine was obtained by the action of alkali on the corresponding hydrochloride and was dried with granulated caustic potash and distilled over sodium. The amines were stored in glass tubes from which small amounts were distilled over into the apparatus for analysis. The glass apparatus for analysis is illustrated in Fig. 1. It consists of two bulbs (1 and 4) connected by the ground joint 6. With the aid of the device described below, 0-1-0-5cm s of the tri-isobutylaluminiuIn solution to be analysed was introduced into bulb 4 through joint 6 under a current of nitrogen (side-arm with cock 5). About 1 cm s of liquid amine was condensed (ice) through side=arm with cock 2 into bulb 1, after which ground joint 6 was
V . SH. FEL'DBLUMet al.
closed, a bubbler dipping into a flask containing 20-30 ml of 0.5 N HCI solution was connected to side-arm 5, and cock 5 was opened. Cock 3 was carefully opened and the amine was transferred into bulb d, where it immediately reacted with the sample, the excess of amine being absorbed by the acid. 3 6
~
5
FIG. 1. Apparatus for the determination of the active alumim'um with dimethylamine:/--bulb for the weighed amount of amine; 2, 3, 5--cocks; 4--bulb for the weighed tri-isobutylaluminium sample; 6--ground joint.
Then a gentle current of nitrogen was passed through side-arm 2 for l5 rain to eliminate the unchanged amine dissolved in the sample being analysed and, finally, the excess of acid was back-titrated with 0.5 N alkali solution in the presence of methyl orange. The content of active aluminium in the sample (g) was calculated from the formula X - -
g × 27 M -
-
(vi--vz) × 0.5 × 27 1000
where g and M are the weight and molecular weight of the amine, respectively; vI is the volume of 0.5 N HC1 taken for the analysis; and v~ is the volume of 0.5 N alkali consumed in the titration. Figure 2 illustrates the simple device which we constructed for introducing the samples to be analysed, measured by weight or by volume, into the apparatus without contact with the air. Cylinder 1 containing the catalyst solution to be analysed in an atmosphere of nitrogen, bears in a ground joint the sleeve 2 in which, in its turn, a pipette 3 with a 3-way cock 4 moves freely. The pipette is connected with the sleeve by a piece of soft rubber tubing. The side-arms of the sleeve and cock are also connected by tubing of suitable length (not shown in the Figure). By pressing this tubing with the hand the
Synthesis of isoprene from propylene--I liquid is forced by nitrogen pressure (through the side:arm of the cylinder) into the pipette. The tubing is released and the required volume of liquid is enclosed in the pipette by turning the cock. The current of nitrogen is transferred to the upper arm of the cock and the pipette is raised into the upper position, after which it is removed from the cylinder together with the sleeve (Fig. 2, B).
4
32
A
3
B
FIG. 2. Device for taking small volumes and weights of liquids in a current of inert gas (A--in assembled form; B--pipette with sample of liquid): /--cylinder with ground joint and side-arm; 2--sleeve with ground joint and side-arm; 3--pipette; 4--3-way cock. A current of nitrogen passes over the end of the pipette, protecting it from contact with the air. The sleeve with the pipette is fixed into the neck of the bulb 4 of the analytical apparatus (Fig. 1) and the sample is run out. The weight of the sample is determined from the difference in the weights of cylinder 1, closed with a ground stopper, before and after the sample is taken. This device can also be used to determine the density of liquids which ignite on contact with air.
Analysis of the al]cylaluminlums after dimerization The results of some experiments in autoclaves o n t h e dimerization of propylene are given in Table 2. In view of the statements which have been made [18] on the possibility of the intensive decomposition of alkylalumininms a t temperatures above 200 °, w e d e t e r m i n e d the t o t a l content of alumininm in the catalyst when it was used repeatedly (experiments 1-5, Table 2). As the
V. Sti. FEL'DBLUMet al. analyses show, the a m o u n t of aluminium charged originally is maintained, which indicates the absence at the reaction temperature of the thermal decomposition of the catalyst to metallic aluminium. Attempts to use, for the determination of the active aluminium after reaction, the same methods as for the initial tri-isobutylaluminium did not give satisfactory results. Titration of the organic bases in a non-aqueous medium by Razuvayev and Grayevskii's method was impossible because of the decolorization of the indicator. The presence in the catalyst after dimerization of compounds intensively decolorizing a permanganate solution made the oxidation-reduction method unusable. The results of a determination of active aluminium by Ziegler's method are given in Table 2 (experiments 6, 7). The low values obtained for the activity TABLE 2. EXPERIMENTS ON THE DIMERIZATIOlg OF PROPYLENE IN AI~"AUTOCLAVE
(Charge of propylene -- 160 g; charge of tri-isobutylaluminium--30 g; temperature -- 250°; reaction time-- 2 hr)
Tri-isobutylaluminium catalyst
1.
2. 3. 4.
5. 6o
7. 8. 9. 10.
Fresh ("activity" 68%) Still residue from experiment 1 Still residue from experiment 2 Still residue from experiment 3 Still residue from experiment 4 Fresh ("activity"76.0~o'~ Fresh ("activity" 70%) After being used once After being used twice
73"0
56"5
6"58
98"0
82"1
3"96
82.0
104"4
3"45 •
73"0
128"5
3"05
50"0 97"0 82"0 75"0 80.0 82"0
146"1 59"2 64.2 65"0 110"0 121"2
2'74 6"73 5"53 5"83
m
37"4 41"5 1100 97O 8OO
after a single use of the catalyst are clearly not in agreement with the fact t h a t when it is used repeatedly the yield of product does not fall. Analogous results are obtained by the use of the ammonia method.
Synthesis of isoprene from pr0pylene--I
7
The gasometric method, which is also unsuitable for determ~nlng the activity of the catalyst under these conditions, permits data to be obtained on the change in the alkyl composition of the catalyst during its use. The results of a gasometric analysis of the catalyst after it had been used once, twice, and three times for dimerization (Table 2, experiments 8-10) show a rapid replacement of about half the isobutyl groups of the initial catalyst by heavy alkyl groups. (When the initial catalyst was decomposed with water, about 2500 ml of gas were liberated per 1 g of aluminium). When the cat~]yst is used repeatedly, the amount of gases liberated by decomposition with water slowly decreases. This may be due both to a continuation of the replacement of the remaining light alkyl residues and also to their oxidation into the corresponding alkoxides on contact with air. Chromatographic analysis of the gas after decomposition with water of the once-used catalyst shows that about 50% of the isobuty| groups which have not been replaced by higher alkyl groups are replaced by propyl groups. (Molar ratios of isobutane and propane in the gas are approximately equal). If a once-used catalyst, a comparison of the weight of which with the initial catalyst indicates a considerable content of higher by-products, is heated to 240-250 °, only a small amount of light fraction boiling up to 100° (mainly n-heptane) dlstils from it. Decomposition of this catalyst with acidified water leads to the formation, in addition to gas, of a mixture of hydrocarbons with a wide boiling range (from 100 to 200 °) which is difficult to separate. Free higher oleflns (trimers and tetramers of propylene) distil off from the catalyst only after it has been used two or three times. Consequently, the first portions of the higher hydrocarbons formed in the reaction either remain attached to the aluminium or replace part of the lower alkyl groups, after which the accumulation of free higher olefins commences. It is also worthy of attention that no considerable amount of 2-methylpentane could be isolated from the products of decomposition with water. Consequently, the number of isohexyl groups in the catalyst after dimerization is extremely low, which contradicts certain statements in the literature [19]. The capability of higher olefins (by-products) for taking part in an exchange reaction with tri-isobutylaluminium was confirmed by supplementary experiments. On heating a mixture of one mole of tri-isobutylaluminium and a stoichiometric excess of these hydrocarbons to 110 ° in a flask with a reflux condenser, about 1 mole of isobutylene was liberated in 2 hr. Further replacement took place extremely slowly. The product of this reaction is also a catalyst for the dimerization of propylene. It is interesting that pure tri-isobutylaluminium on heating to 110 ° liberates practically no isobutylene. This shows that the replacement of the isobutyl group by a higher alkyl group, at least up to 110°, is a bimoleeular reaction AI(C~Hg)s+C,Hs, ---~AI(C4Hg)sC,HI,+1+C4Hs,
8
V. SH. FEL'DBLUMet al.
and not a sequence of two reactions [20]: AI(C,Hp)8 ~ A1H(C4H0)~+C,Hs, A1H(C4Hp)2+C,i'is, --* AI(C4I'I-I9)2C,i'iz, + z. F r o m what has been said above, it is clear t h a t a catalyst used repeatedly for the dimerization of propylene consists of a complex mixture of alkylaluminiums the molecules of which contain light alkyl residues (propyl and isobutyl) and a t least one heavy group (Cp-Cz~). I n conclusion, the authors express their thanks to A. G. P a n k o v and M. F. K n y a z e v a for carrySng out the chromatographic analyses of the propylene and the gases resulting from the decomposition of the catalyst. SUMMARY 1. A comparative evaluation o f the results obtained by the most widely used methods of analysis of alkylaluminiums in the dimerization of propylene has been carried out. 2. Supplementing the existing methods, a simple method of determining the activity of the initial dimerization c a t a l y s t based on its reaction with dimethylamine or trimethylamine has been proposed. 3. The compos!tion of alkylaluminiums repeatedly used as catalysts for t h e dimerization of propylene has been investigated. Tranelat~ by B. J. HAZZARD REFERENCES 1. K. ZIEGLER, Angew. Chemie 64, 323, 1952 2. K. ZlEGLER, Brennst, Chemie 33, 193, 1952 3. M. I. FARBEROV, S. I. KRYUKOV, G. D. MANTYUKOV and B. F. USTAVSHCHIKOV, U.S.S.R. Authors' Certificate No. 143,393, 1960 4. S. I. KRYUKOV and M. L FARBEROV, Zh. prikl, khim. 35, 2319, 1962 5. G. D. MANTYUKOV, M. I. FARBEROV and S. I. KRYUKOV, Uch. zap. Yaroslavsk. tekh. inst. 6, 31, 1961 6. A. G. OBLAD and E. GORIN, U.S. Fat. 2,430,137, 4.11.1947 7. L N. NAZAROV, Ye. I. KT.ABUNOVSKII and N. A. KRAVCHENKO, Izv. Akad. Nauk SSSR, otd. khim. nauk 1960, 73 8. V. J. ANHORN, G. S. SCHAFFEL, K. J. FRENCH and BROWN, Chem. Engng. Progr. 57, 43, 196i 9. I. Ya. TYURYAYEV and S. V. KOLYADYUK, Neftekhimiya 2, No. 2, 170, 1962 10. Brit. Pat. 840,028, 6.07.1960 11. Brit. Pat. 841,351, 13.07.1960 12. S. I. KRYUKOV, A. M. KUT'IN, G. S. LEVSKAYA, Ye. P. TEPENITSYNA, Z. F. USTAVSHCHIKOVA and M. I. FARBEROV, Izv. vuzov. Khim. i khim. tekh. No. 1, 86, 1958 13. C. A. RAZUVAYEV and A. I. GRAYEVSKII, ])old. Akad. Nauk SSSR 128, No. 2, 309, 1959
Synthesis of isoprene from propylene--II
9
14. Ye. P. TEPENITSYNA, M. I. FARBEROV, A. M. KUT'IN and G. S. LEVSKAYA, Vysokomolek. soyed. 1, 1148, 1959 15. K. ZIEGLER and H. GELT.EI~T, Liebigs Ann. 629, 20, 1960 16. M. DAVIDSON and H. BROWN, J. Amer. Chem. Soc. 64, 316, 1942 17. E. BONITZ, Chem. Ber. 88, 742, 1955 18. K. ZIEGLER, K. NAGEL and W. PFOHL, Liebigs Ann. 629, 210, 1960 19. Brit. Pat. 831,249, 23.03.1960 20. K. ZOSEL, Brennst. Chemie, 41, 321, 1960