. 1124
J. R. LACHER, A. KIANPOUR AND J. D. PARK
T701. 61
REACTION HEATS OF ORGANIC HALOGEN COMPOUNDS. x. VAPOR PHASE HEATS OF HYDROBROMINATION OF CYCLOPROPANE AND PROPYLENE1 BY J. R. LACHER, A. KIANPOUR AND J. D. PARK Department of Chemistry, University of Colorado, Boulder, Colorado Received May 3,1067
The vapor phase heats of hydrobromination of propylene and cyclopropane have been redetermined. For propylene a value of -20,430 cal./mole agrees well with that of -20,140 previously reported. For cyclopropane the value of -25,590 cal./ mole is 3100 cal. more exothermic than that previously reported.
I n a previous paper2 we reported on the vapor phase heats of hydrobromination of cyclopropane and propylene. The data were used, together with a calculated value for the heat of isomerization of normal to isopropyl bromide, to calculate the heat of formation of cyclopropane. The value of 9,392 cal./mole deviated considerably from that of 12,740 cal./mole. given Knowlton and Rossini. Recently L. Bjellerup4has measured the heats of combustion of 1-bromopropane, 2-bromopropane and 2-bromobutane. His data yield values for the heat of formation of 2-bromopropane and 2-bromobutane which are consistent with our hydrobromination data.6 The heat of formation of 1-bromopropane obtained from our hydrobromination of cyclopropane is not consistent with the combustion data. Accordingly we have restudied the heats of hydrobromination of propylene and cyclopropane. Experimental Details.-The modifications made in the calorimeter since the early hydrobromination data have been described previously .e The temperature difference between calorimeter and the surrounding condensing vapor bath was measured with a 25 junction copper-constantan thermocouple. Instead of connecting the thermocouple to a high sensitive galvanometer, the output was sent to a d.c. breaker amplifier.' The amplifier was connected to an Esterline-Angus recorder. The latter instrument was adjusted so that the pen drew a line down the center of the chart when both junctions of the thermocouple were at the same temperature. It would move to one side of the other when the calorimeter temperature was too high or low. The new system is much more convenient to operate (because of the variable gain) and is also more sensitive. Hydrogen bromide, propylene and cyclopropane were purchased from the Matheson Company and were used without further purification.
Experimental Results and Discussion.-The calorimeter was checked to see if it was operating properly by measuring the knowns heat of formation of gaseous HC1. The results are given in Table I. I n these runs hydrogen was used in excess and it reacted quantitatively with the chlorine. The rate of formation was determined in two ways. The first consisted in sending the exit gases to an absorption tower for a definite period of time and (1) This research is being supported by United States Air Force Research and Development Command: Contract Number AF 18(600)1151. (2) J. R. Lacher. J . D. Park, el al., J . Am. Chem. Soc., 73,331 (1950). (3) John W. Knowlton and F. D. Roasini, J . Research Natl. Bur. Standards, 43, 113 (1949) (4) L. Bjellerup, Trans. Faraday Soc., 63,1153 (1956). (5) J. R. Lacher, J. D. Park, et al., J . Am. Chem. Soc.. 74, 5291 (1952). ( 6 ) J. R. Laoher, L. Casali and J. D. Park, TRIEJOURNAL, 60, 608(1966). (7) Liston-Becker Model 14. ( 8 ) F. D. Rossini, J , Research Natl. Bur. Standards, 9, 679 (1932).
titrating the acid obtained with a standard base. I n the second method, the chlorine was directed to a tower and absorbed in potassium iodide solution. The liberated iodine was titrated with sodium thiosulfate. Both methods gave results which were in agreement with Rossini's interpolated value7 of -22,146 cal./mole at this temperature. TABLE I HEATOF FORMATION OF HYDROGEN CHLORIDE AT 128" HCI c1
Run 1 2 3 4
5
proconducsump-A HIOIOK. tion tion Energy cal./mole mo!e;1/ eqiijv./ input, min. min. ca!./ Based on X 104 x 104 mm. HC1 C1z 22,749 22,435 13.695 6.020 6.014 22,176 21,870 17.109 7.823 7.715 22,310 22,002 17.902 8,136 8.024 22,324 22,016 17.497 7.837 7.947 22,639 22,060 17.699 7.912 8,023 Heat of formation of HCl Based on HC1 analysis -22,294 =t168 aal./mole Based on Ch analysis -21,987 =!c 208 cal./mole
The procedure used in studying the hydrobromination of propylene and cyclopropane was essentially the same as that previously used.2 The reactants were sent to the calorimeter at a faster rate; even so, it took 12 t o 14 hours to obtain a steady state when cyclopropane was used. Propylene gave steady state conditions in 10 to 12 hours. VAPOR Run
PAARE
TABLE I1 HEATSO F HYDROBROMINATION AT 128"
Olefin flow, moles/min.
x
104
HBr flow, moles/min. X 104
Energy input. cal./min.
-A H ~ o u . ,
cal./mole
Cyclopropane 1
5.2 3,389 8.610 25,400 5.2 3.654 9.451 25,870 5.2 3.508 0.021 25 ,720 5.2 3.191 8.279 25,950 5.2 3.362 8 .i s 3 26,040 5.2 3.305 8.519 25,780 AH,, = -25,790 f 320 cal./mole; 2 X standard deviation f 0.72% product: 99.7% n-propyl bromide; 0.3% iso2 3 4 5 6
propyl bromide 1
4.3 2.712 5.488 20,240 2 4.3 2.647 5.437 20,540 3 5.4 3.421 6.988 20,430 7.104 20,520 4 5.4 3.462 Ha,= -20,430 f 150 cal./mole; 2 X standard deviation 0.65% product: 98.5% isopropyl bromide; 1.5% n-
*
propyl bromide
August, 1957
NOTES
The results are summarized in Table 11. The present value of -20,430 for the heat of hydrobromination of propylene agrees well with the value of -20,140 previously reported.z The value of -225,790 crtl./mole for the heat of hydrobromi-
nation of cyclopropane is 3100 cal. more exothermic than the value previously obtained. We believe that the earlier experiments were in error due possibly to not achieving complete equilibrium on the catalyst.
1125
NOTES REACTION HEATS O F ORGANIC HALOGEN COMPOUNDS. IX. THE CATALYTIC HYDROGENATION OF VINYL AND PERFLUOROVINYL BROMIDE1 BY J. R. LACHER.A. KIANPOUR P. MONTGOMERY, H. KNEDLER AND J. D. PARK Department of Chemistrg. University of Colorado, Boulder, Colorado Received April 6 , 1067
The present paper of this seriesZdeals with the catalytic hydrogenation of vinyl bromide and perfluorovinyl bromide. In the case of vinyl bromide, the reaction was quantitative, and calorimetric measurements could be carried out. In the case of the perfluoro compound, the activity of the catalyst varied. Initially the catalyst was sufficiently active to replace the bromine and saturate the double bond. With increasing use, it would continue to replace the bromine, but it would become less effective in saturating the double bond. Accurate calorimetric data could not be obtained. Experimental Details.-Vinyl bromide was purchased from the Matheson Company, and perfluorovinyl bromide was prepared according to the method described by Hasaeldine.s The compounds were purified in a high temperature Podbielniak distillation column. Since it was necessary for them to be completely free of air, the distillation was carried out in an atmosphere of nitrogen, which was removed by the following procedure. (The cylinder containing the compound was cooled to -78' in a Dry Iceisopropyl alcohol bath, evacuated for 15 minutes, and then allowed to warm up to room temperature. It was placed on a shaker for 15 minutes, then cooled down to -78" again.) This procedure was repeated until a purity of >99% was obtained. Purity was determined by means of a double beam infrared spectrometer with sodium chloride prism and by chromatographic gas phase analysis. The catalyst used consisted of 2.5% by weight of palladium-on-carbon. The carbon was sized to pass a 6- and be retained on a 14-mesh screen. In order to remove sulfur from the carbon, it was first washed with 10% hydrochloric acid and then heated in a stream of hydrogen at 400' for five days. The purified carbon was cooled to room temperature and poured directly into a dilute palladium chloride solution. Reduction took place immediately, and the metal produced a silvery coating on the carbon. The catalyst was dried in vacuo; when drying was complete, the vacuum was broken with hydrogen, which was passed over the catalyst for 24 hours at 250'. I n making a run, vinyl bromide and hydrogen in excess were sent to the catalyst chamber at a constant rate. An examination of the product gases by infrared and vapor phase chromatographic equipment showed that the following reaction was taking place quantitatively. (1) This research is being supported by United States Air Force Research and Development Command, Contract Number AF 18(600)1151. (2) For the previous paper Bee J. R. Lacher, A. Kianpour and J. Park. THISJOURNAL, 60, 1454 (1956). (3) R. N. Haszeldine, J . Chem. Soo., 4259 (1952).
D.
+
+
CHz=CHBr 2Hz +CHgCHa HBr I n order to determine the amount of reaction which took place in a given time, the product gases were sent to an absorption tower. The hydrobromic acid formed was titrated with 0.05 N potassium hydroxide. The experimental data obtained are given in Table I.
TABLE I HEATOF HYDROGENATION OF VINYLBROMIDE, 128" HBr flow, moles/min.
Energy rate, cal./min.
2.115 1.628 1.950 1.475 1.635 1.6125 1.598
10.344 7.823 0.638 7.158 7.812 7.790 7.631
x
104
- AH, kcal./mole
48.86 48.02 49.43 48.53 47.78 48.31 47.70 - - . A H av. = 48.38 Twice the stand. dev. from the mean &0.94% When perfluorovinyl bromide was used, the reaction appeared to give CFZH-CFHZ quantitatively, and the heat liberated was about 56,000 cal. per mole. On succeeding runs, the heat liberated per mole fell off, and an examination of the product gases showed the presence of a considerable amount of CFI-CFH. I n one of the latter experiments, this olefin was produced in 95% yield, and the heat liberated was 26,000 cal./mole. The catalyst activity was not reproducible; thus, reliable thermochemical measurements could not be made. I n the reaction between hydrogen and vinyl bromide, sufficient heat capacity data are available to permit a calculation of the temperature variation of A H . The heat capacities for HI, CIHB and HBr have been tabulated by the Bureau of Standards.' R. E. Richards5 has calculated the heat capacity of C H F C B r H . With this information, the reaction a t 25' was calculated to be less exothermic by 772 cal. The correct A H is entered in Table 11. The heats of formation of gaseous HBr and CzHs are given as -8,660 and -20,266 cal. per mole, respectively.4 Using this information, we calculated the heat of formation of vinyl bromide. The result is included as the second entry in Table 11. We have found no literature value for the heat of formation of vinyl bromide.
TABLE I1 HEATSOF REACTION AT 25"
+ +
Reaction
+
CzHsBr 2Hz + CzHs HBr 2C(gr) 3/2Hs 1/2Brz(l) + CzHaBr CH2=CHBr Hz -c CHFCH~ HBr
+
+
+
- AH, cal./mole 47,610
- 18,680
14,880
However, if we asmme that the heat of addition of hydrogen to vinyl bromide is the same as it is to vinyl chloride: (4) "Selected Values of Properties of Hydrooarbons," A.P.I. Research Project 44, National Bureau of Standards. (5) R. E. Richards, J . Chem. SOC.,1931 (1948). (6) J. R. Lacher, A. Kianpour, F. Oetting and J. D. Park, Trans. Faraday Soc., 52 (1956).
