Studies on the Kinetics of Addition Reactions of Carbon Monoxide with Organic Compounds in Hydroiodic Acid Under High Pressure (Part 1)*

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Studies on the Kinetics of Addition Reactions of Carbon Monoxide with Organic Compounds in Hydroiodic Acid under High Pressure (Part 1)*

-The Addition Reaction of Carbon Monoxide with Ethyl lodide-

by Hiroshi Teranishi**, Kumao Hamanoue**, Yoshiaki Manki** and Toshiharu Takagi**

Summary: The addition reaction of carbon monoxidewith ethyl iodide in aqueoushydroiodic acid was investigatedunder high pressure in the range of 30 to 90kg/cm2. The yield of propionic acid was fairly high and the rate offormation was thefirst order reactionwith respectto carbon monoxideand ethyl iodide. The overall activation energy has beenfound to be 13.0kcal/mole, which containsthe molar enthalpychange of equilibrium reaction(2), i. e., the heat of dissociation of C2H5I and the activation energyof reaction (3), i.e., the reactionbetween the ethyl cation and carbon monoxide.

hydrogen iodide as a catalyst which is expected 1 Introduction to be the strongest acid medium and investigated Addition reactions of carbon monoxide with kinetically the addition reaction of carbon mono- olefins in various acid media, such as concentrated xide with ethyl iodide. sulfuric acid1)～6), phosphoric acid7), anhydrous 2 Experimental hydrogen fluoride3),6), monohydroxyfluorboric acid Ethyl iodide (E. P. grade), hydroiodic acid and its mixture with phosphoric or sulfuric acid8) and aqueous boron trifluoride9)～10)have been well (G. R. grade, 57wt% aqueous solution of HI), silver carbonate (C. P. grade) and sodium hydro- known, and those olefins higher than C4 react xide (E. P. grade) were all purchased from Nakarai quite readily with carbon monoxide11)～13). On the other hand, those olefins lower than C3 react Chemicals, Ltd., and were used without further with carbon monoxide under more severe con- purification. Carbon monoxide was kindly supplied by the ditions14).Recently, Kanbara et al. obtained pro- Institute for Chemical Research, Kyoto Univer- pionic acid in good yields through the reaction of sity, which was prepared from formic acid and ethyl fluoride in aqueous hydrogen fluoride15) hot concentrated sulfuric acid having a purity of In these reactions, it is expected that the more than 97% by a gas chromatography. activity of acidic catalysts might have a linear The reaction was carried out in a glass vessel relationship with the acid strength. Usually, the inserted into a stainless steel autoclave (capacity: acidity function (Ho) is used as a measure of acid 100ml) equipped with a magnetic stirrer. Weigh- strengths. When Ho has a large negative value, ed amounts of hydroiodic acid and ethyl iodide its acid strength is large. The approximate were charged into the autoclave. After the pKa values of HF, HCl, HBr and HI are 3, -7, temperature of the autoclave had become constant -9 and -10 , respectively16). Therefore, HI has at the desired level, carbon monoxide was intro- the largest negative Ho value, which means HI duced and the stirring started. Carbon monoxide is the strongest acid among them. was supplied continuously to maintain the total Considering the relationship between the acidity function and acid concentration, it may be pressure of the autoclave constant during the reaction. At the end of reaction time the auto- concluded that even a strong acid, such as conc. clave was quickly cooled with ice water. The HCl or HBr, is insufficient to act as a catalyst aqueous solution was neutralized with Ag2CO3 under atmospheric pressure. Thus, we have used to remove the hydrogen iodide and filtered, then * Received July 11, 1975. ** Department of Chemistry . Kyoto Institute of Te- the filtrate which contained the Ag-salt of organic chnology (Matsugasaki, Sakyo-ku, Kyoto 606) acid was converted into free acid by passing it

Bulletin of The Japan Petroleum Institute Studies on the Kinetics of Addition Reactions of Carbon Monoxide with Organic Compounds in Hydroiodic Acid 63 through a column of exchange resin (Amberlite tions given in the figure suggesting that stirring 120B) and titrated with aqueous 0.1 N-NaOH. speed of 1,000rpm was sufficient to make the Prior to quantitative analysis, some mixtures of liquid phase reaction the rate-determining under propionic acid and hydroiodic acid were prepared. the conditions used. These mixtures were analysed by the same Figure 2 shows the relationship between the mole procedure as mentioned above to obtain the ratio of HI to C2H5I and the yield of acid. From factor of propionic acid yield. this result, one can see that the yield of propionic 3 Results acid increases with mole ratio and it becomes constant above the mole ratio 40. The broken 3.1 Preliminary Experiments line in Fig. 2 gives the results obtained by the Before the study of kinetic treatment, prelimi- reaction in which carbon monoxide was charged nary experiments were carried out. The aqueous first and then the temperature was raised. The solution, after passing through the column of results thus obtained are higher than those exchange resin, was analysed with a gas chro- obtained by usual methods. This means that the matography (Hitachi K53) equipped with a flame reaction occurs during the period of rising tem- ionization detector. A column (2m×3mm) with perature. 20% polyethylene glycol or SE-30 on 60/80 mesh Figure 3 shows the effects of temperature on Chromosorb W-NAW was used. And nitrogen the reaction. The maximum yield was obtained was used as the carrier gas. Propionic acid was at near 180℃. Above 180℃, the reaction the only acid produced. The yield of propionic involved some side reactions such as polymeriza- acid was determined by NaOH titration. tion. And after the run, some dark brown oily Figure 1 shows the relationship between the material was obtained. stirring speed and the rate of propionic acid From the results described above, the following formation. Above 1,000rpm the stirring speed conditions were adopted for the kinetic measure- did not affect the reaction rate under the condi- ments: reaction temperature lower than 180℃, HI/C2H5I mole ratio 45, stirring speed 1,000rpm. 3.2 Kinetic Measurements Effects of temperature on the yield examined at 100, 120 and 140℃ are shown in Fig. 4. From the results one can see that the yield of propionic acid increased with increasing temperature. In the Figure, the ordinate is given by the apparent yield of propionic acid which includes the additional yield resulting from the reaction during the cooling period. Namely, the apparent yield at zero time in the Figure must be attributed to the

Fig. 1 Effect of Stirring Speed on Yield of Propionic Acid

Fig. 2 Effect of Mole Ratio of HI to C2H5I on Yield Fig. 3 Effect of Temperature on Yield of Propionic of Propionic Acid Acid at Reaction Time of 60 and 120min

Volume 18, No. 1, May 1976 64 Teranishi, Hamanoue, Manki and Takagi: Studies on the Kinetics of Addition Reactions of

Fig. 4 Effect of Temperature on Apparent Yield of Propionic Acid Fig. 6 Effect of Pressure on Corrected Yield of Propionic Acid

4 Discussion

According to the reaction mechanism proposed by Kanbara et al.15), the following modified reaction scheme is assumed:

C2H5I+HI(aq.)→←C2H5+I-H3O+I- (2)

C2H5+I-H3O+I+CO

→C2H5COI+HI(aq.) (3)

C2H5COI+H2O→C2H5COOH+HI (4)

Namely, ethyl iodide in aqueous HI dissociates Fig. 5 Effect of Temperature on Corrected Yield of partly to produce an ionic intermediate cation Propionic Acid (may be a carbonium cation), and an equilibrium reaction exists. The ionic intermediate formed reaction taking place during the cooling period. will combine with the dissolved carbon monoxide In order to get the real yield, the following to produce propionyl iodide, followed by the correction was made: As a first approximation, fast hydrolyzation reaction to form propionic the yield of propionic acid obtained during the acid. period of cooling was assumed to be proportional Taking into account that HI is pressent in to the amount of reactant which remained un- large excess over C2H5I, reaction (2) is assumed reacted, giving a proportionality constant equal to be a pseudo first order reaction; reaction (4) to Y0/(1-Y0) at zero time. is very fast and the rate of formation of propionic Therefore the following correction equation was acid is equal to that of propionyl iodide. used in each run. Assuming the rate determining process to be Eq. (3) and a steady state condition for the intermediate cation, the following rate equation is derived: where Yc is the corrected mole fraction of propionic acid, Ya the apparent mole fraction and Yo the d[C2H5COOH] d[C2H5COI] dt dt mole fraction at zero time. =k2HcoPco[C2H5+I-H3O+I-] In Fig. 5 we show the results thus corrected. k1k2HcoPco Hereafter, we shall use these corrected results. ([C2H5I]0-[C2H5COOH]) k-1+k2HcoPco Figure 6 shows the effects of pressure on the (5) yield of acid at 180℃. Obviously the yield was increased with increasing pressure. Integrating this equation:

Bulletin of The Japan Petroleum Institute Carbon Monoxide with Organic Compounds in Hydroiodic Acid under High Pressure (Part 1) 65

Fig. 9 Plot of koverall VS. Pco

Fig. 7 Plot of ln{[C2H5I]0/([C2H5I]0- [C2H5COOH])} vs. Reaction Time

Fig. 10 Arrhenius Plot of Overall Rate Constant

Fig. 8 Plot of 10/ln{[C2H5I]0/([C2H5I]0- Pco/(k-1+k2HcoPco) being still a function of [C2H5COOH])} vs. 1/Pco carbon monoxide pressure. An alternative expression of Eq. (6) is given [C2H5I]0 k1k2HcoPco by Eq. (7): In t [C2H5I]0-[C2H5COOH] k-1+k2HcoPco t (6) In{[C2H5I]0/([C2H5I]0-[C2H5COOH])} k-1 1 where Hco is Henry's constant for CO in the (7) solution and Pco the pressure of CO over the k1k2HcoPco k1 reaction medium. giving a linear relationship between the term on In the derivation of the above equation, it is the right-hand side and 1/Pco at constant time. assumed that CO is present in large excess over In Fig. 8 we show the result of the plot of the C2H5I and its concentration is constant during term on the right-hand side of Eq. (7) against the reaction. I/Pco at the reaction time of ten minutes. The Figure 7 shows the plot of In{[C2H5I]0/ result is a good straight line whose slope and ([C2H5I]0-[C2H5COOH])} against reaction time intercept give the value of 500 for k-1/k2Hco・ in good linear relationship consistent with Eq. (6). This means that k2Hco is negligibly small com- Thus the slope of this straight line gives the pared with k-1. apparent rate constant, namely koverall=k1k2Hco・ Figure 9 shows the relation between koverall„

Volume 18, No. 1, May 1976 66 Studies on the Kinetics of Addition Reactions of Carbon Monoxide with Organic Compounds in Hydroiodic Acid

and Pco, and a good linear straight line is also and carbon monoxide to form propionyl iodide.

obtained, where Pco results from the difference Acknowledgement between the vapor pressure of aqueous solution and the total pressure. Thus one can conclude The authors wish to express their sincere thanks to Prof. Yoshimasa Takezaki of Institute for that koverall is equal to k1k2/k-1. Chemical Research, Kyoto University for his Figure 10 is an Arrhenius plot of the overall kind supply of carbon monoxide. Thanks are rate constant resulting in a straight line. The also due to The Asahi Foundation for the Con- slope gives the overall activation energy of 13.0 tribution to Industrial Technology for financial kcal/mol, which contains the molar enthalpy support. change of reaction(2) and the activation energy of reaction (3). References From the above discussions one can conclude 1) Koch, H., Brennstoff-Chem., 36, 321 (1955). as follows: 2) Koch, H., Rev. dei Combustibili, 10, 77 (1956). 3) Koch, H., Belg. 518, 682 (1955); Brit. 743, 597 Propionic acid can be produced in good yields (1957); U. S. 2,831,877 (1958). in the HI catalyzed carbonylation reaction when 4) Koch, H., Haaf, W., Angew. Chem., 70, 311 (1958). ethyl iodide is used as the raw material. 5) Koch, H., Haaf, W., Ann. der Chem., 618, 251 (1958). 6) Koch, H., Ger. 972, 315 (1961). The rate equation derived from the proposed 7) Koch, H., U. S. 3,061,621 (1963). mechanism involving the liquid phase reaction of 8) Koch, H., Huisken, W., U. S. 2,876,241 (1959). 9) Koch, H., Haaf, W., Ann. der Chem., 638, 111 (1960). dissolved carbon monoxide with ethyl cation as 10) Koch, H., Ger. 1,095,802 (1962). the rate determining, which is the first order 11) Friedman, B. S., Cotton, S. M., U. S. 2,975,199 reaction with respect to CO pressure and C2H5I, (1961). 12) Friedman, B. S., Cotton, S. M. J. Org. Chem., 26 has been shown to elucidate the observed facts 3751 (1961). satisfactorily. 13) Friedman, B. S., Cotton, S. M., ibid., 27, 481 (1962). The overall activation energy was found to be 14) Takezaki, Y., Fuchigami, Y., Teranishi, H., Sugita, N., Kudo, K., Bull. Japan Petrol. Inst., 8, 31 (1966). 13.0kcal/mol, which contains the molar enthalpy 15) Kanbara, M., Sugita, N., Kudo, K., Teranishi, change of reaction(2), i. e., the heat of dissociation H., Takezaki, Y., ibid., 11, 48 (1969). 16) Day, M. C. Jr., Selbin, J., "Theoretical Inorganic of C2H5I and the activation energy of reaction Chemistry", 254 (1966) Reinhold Publishing Co., (3), namely, the reaction between ethyl cation New York.

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