422
DON.\LD
R.IT Af.\RTIK .1ND \VILLI.\M
BRUCE HICKS
employing acid molalities ranging from 0.05 to 8.0. Ethanol percentages ranged from 10 to 80 per cent. 2. From the electromotive-force values ohtained, the activity coefficientb of the acids have been calculated. REFERENCES (1) HARNEU, H. b'., A N D HABIER, bv. J.: J. . h i . Cheln. h.67, . 27 (1035). (2) HARNED, H. S., A N D OWEN,B. €3.: Physical C h o t t i s t r ! / .-J Electrolytic S o t i d i o m , 1). 438. Ileinhold Publishirig Corporation, New York (1943). (3) PRZHEBOROVhKIi, Y A . s., ~ C O R D I E V S K I I , lr. G . , .\XI> F I I J P F O Vs. A ,13.: %. \)hJ7Sik. Cheiii. 146, 276 (1929).
C O ~ R D I N A T I O XCOMPOUNDS OF BORON TRICHLORIDE.
111'
SYSTEMS WITH METHYLCHLORIDE AND ETHYL CHLORIDE DONA4LDRAY JIAILTIN ASLIWILLIAICI BRUCE HICIiS S o y s Chcinicnl Laboratory, Universaty of Illinoia, Urbana, Illinois Received April 2 , 1946
It has been demonstrated previously that the boron atom of boron trichloride acts as an acceptor atom in the formation of coordination compounds (8, 9). There are only a few compounds of chlorine which coordinate with boron trichloride. It has been shown that neither chlorine (5, 10) itself nor hydrogen chloride (6) does so. It was decided, therefore, to ascertain the behavior of two other compounds of chlorine,-namely, methyl chloride and ethyl chloride, -toward boron trichloride by making thermal analyses of the liquid systems methyl chloride-boron trichloride and ethyl chloride-boron trichloride. The apparatus and procedure for such a study have been described previously (1, 2, 4, 9), except that with these systems the pressures in the calibrated and ice-cooled storage flasks for the boron trichloride and the ethyl chloride, whose vapor pressures are 477.0 (10) and 454.5 (7) mm. a t O'C., were never greater than 450 and 400 mm., respectively. Check analyses, indicated by the solid circles in figures 1 and 2, were made with samples of the components which had been fractionally distilled under different pressures than the components used for the first analyses. THE SYSTEM METHYL CHLORIDE-BORON
TRICHLORIDE
The boron trichloride used in this thermal analysis was prepared by the reaction of boron trifluoride with aluminum chloride (3). It was purified by fractional distillation. The methyl chloride was obtained from the Ansul Chemical Company and was also purified by fractional distillation. 1
For the second gaper in this series, see reference 9.
COORDINATION COMPOUNDS O F BORON TRICHLORIDE.
I11
423
The freezing point of the purified boron trichloride was found to be - 107.G"C. of the purified methyl chloride -97.1'C. f 0.4". The data in table 1, dcpictcd in the phase-rule diagram in figure 1, indicate that methyl chloride and boron trichloride do not form a compound. A eutectic point was found a t 51.8 A 0.2 mole per cent boron trichloride and -125.1'C. f 0.4". It is of interest to note that Wiberg and Heubaum have reported that a yellow solid, \\.hose conipositioli according to the analysis corresponds to the =t0.4', and that
TABLE 1 Data $or the systenb mclh2/1 chloride-boron trichloride MOLE FRACTION OF
BClr
FREEZING POINT
____
-"C.
-"C.
f0.4 97. I 97.0 101.8 102.2 108.3 109.0 112.5 114.2 117.3 ll0.S 11s.4 121.4 120.4 121.9, 118.5 117.1 315.0 113.0 111.7 110.3 107.6 107.5
f0.002 0.000
O.0OOk 0.100 0.112* 0.196 0.252* 0.298 0.348' 0.372 0.418 0.422* 0.503 0.550' 0 . GOO 0. G49* 0.703 0.755' 0.s02 0.856* 0.904 I .OOO' 1.000 .
* Check
-
EUTECTIC TEXPERATURE
f0.4
125.2
124.!) 125.4 125.0
125.1
-___I
analysis.
compound (CsHb)3CCl:UC13, results i v h i triphenylchloromethane and boron trichloride arc allon.etl to react at room temperature (12). T H E SYSTEM ETHYL CHLORIDE-BORON
TRICIILORIDE
The boron trichloride used for this study \vas prcpared in the same manner as described above in the study \\.it11 methyl chloride. Tlic et,hj,l cliloiide \\.as obtained from the Frnnco American Chemical Works and \vas purified by fractional distillsL' t'1011. The freezing point of the separately generated and purified boron trichloride was found to be -107.2'C. & 0.4' and that of' the purified ethyl chloride -138.2OC. =t 0.4". The dsta in table 2, depicted in the phasc-rule diagram in
-OC. 96
I
I
I
101
IO8
I II
I16
I21
I26 20
CHSCI
40
68
FIG.1. Boron trichloride-inethyl chloride system: 0, first
B CI,
80
:ltidysis: 0 , second analysis
TABLE 2 Data Jor [he siistem olhiil chloride-boron trichloridc MOLE FRACTION OF
BC13
FREEZING POINT
__
1
MOLE FRACTION OF
0.000 0 . 000* 0.099 0.145* 0.200 0.256* 0.301 0.358* 0.400 0.449*
* Check
I
FREEZING POINT ~~
-"C.
f O .002
RCl8
~
-0C.
k0.4 138.4 138.0 142.3 143. 6 139.2 134.5 127.4 125.5 121.2 119.5
0.499
0.550* 0.613 0.651" 0.701 0. i 4 9 * 0.800 0.851" 0.904 1.000" 1.000
analysis. 424
116.0 116.G 116.3 115.8 116.1 115.8 113.9 112.0 ll0.G 106.8 107.5
COORDINATION COMPOUNDS O F BORON TRICHLORIDE.
425
111
figure 2, indicate a maximum at approximately 66.7 mole per cent boron trichloride, corresponding to a compound containing ethyl chloride and boron trichloride in a molar ratio of 1:2, the freezing point of which is -115.8'C. =t 0.4". Eutectic points mere found on each side of this maximum. One was
-0C. IO5
I13
I21
129
I37
I45 C2HSCI
20
40
60
80
B Clg
FIG.2. Boron trichloride-ethyl cliloride system: 0 , first analysis; 0 , second analysis
+
fouiid a t 14.3 i 0.2 mole per cent boron trichloride and -143.9"C. 0.4', while the other was at)72.8 =t 0.2 mole per cent boyon trichloride and -116.3"C. =t 0.4". Molecular weights and the types of bonding forces at play in molecules are not, established by this type of research. However, in vien- of the fact that boron trichloride forms many coordination compounds, it is proper to postulate the possible arrangements of the molecules in the compound, most simply w i t ten as C2H5C1:2BC13.
426
DONALD RAY MARTIN AND WILLI.4M BRUCE HICKS
It is interesting that one molecule of ethyl chloride should coordinate with two molecules of boron trichloride, instead of just one molecule of ethyl chloride coordinating with one molecule of boron trichloride. From the flatness of the maximum it is evident that the compound CzH5C1: 2BC13 is somewhat dissociated above its melting point, indicating that the chlorine in ethyl chloride does not have much tendency to donate a pair of electrons t o the boron atom of boron trichloride. This dissociation may be due to the fact that the chlorine might be sharing two pairs of electrons with two boron atoms, thus: BC13 7 CzHsC1 Another possible explanation of the structure of this compound is that the boron trichloride forms a dimer which then coordinates with the ethyl chloride, thus : H H c1 c1
I
H-C-C
I
-CI+$-Cl+$--C1
There is no evidence in the literature for the association of two molecules of boron trichloride to form a dimer. No coordination compound containing 1 mole of the donor to 2 moles of boron trichloride has been identified and only one such compound has been postulated. Tarible (11) in 1901 reported the formation of a double chloride when PzT4:2BBr3was allowed to react with chlorine. If total displacement of the halogen atoms is assumed, the compound P2C14: 2 K 1 3 would result. However, PzC14 is difficult to prepare and therefore this assumption is questionable. It does not seem likely that the compound CzHsC1:2RC13 contains boron trichloride as a dimer. SUMMARY
1. The thermal analysis of the system methyl chloride-boron trichloride revealed only a eutectic point a t 51.8 f 0.2 mole per cent boron trichloride and -125.1"C. & 0.4". 2. The thermal analysis of the system ethyl chloride-boron trichloride revealed eutectic points a t 14.3 & 0.2 mole per cent boron trichloride and -143.9"C. =t0.4" and a t 72.8 =k 0.2 mole per cent boron trichloride and -116.3"C. f 0.4", with an intervening maximum at approximately 66.7 mole per cent boron trichloride and -115.8"C. f 0.4", corresponding to a compound which is most simply expressed as CzHSC1: 2BC13. REFERENCES (1) BOOTH, H. S. A N D RIARTIN,I). It.: Chem. Rev. 33, 57-85 (1943). (2) BOOTH, H. S., A N D MARTIN,D. R.: J. Am. Chem. SOC.64, 2198-2205 (1942).
ABSOLUTE DECOMPOSITION VELOCITY O F VAPORS
427
(3) GAMBLE, E. L., GILJIONT,P., A N D STIFF, J. F.: J. Am. Chem. SOC. 62, 1257-S (1940). (4) GERMANS,A. F. O., A N D BOOTH,H . S.: J. Phys. Chem. 30, 369-77 (1926). (5) GRAPF,W.: Compt. rend. 196, 1390-2 (1933). (6) GRAFF,W.: Compt. rend. 197. 754-5 (1033). (7) International Critical Tablcs, 1st edition, Vol. 111, pp. 215, 217. McGraw-Hill Book Company, Inc., Xew Yorlc (192s). (8) MARTIN,D. R.: Chem. Rev. 34, 461-73 (1941). (9) MARTIN,D. R.: J. Am. Chem. SOC.67, 108s-91 (1915). (10) STOCK, A . , A N D PREISS,0.: Ber. 47, 3109-13 (1914). (11) TARIBLE, J.: Compt. rend. 132, 204-7 (1901). (12) WIBERG,E., A N D HEUBAUM, U.:Z. anorg. allgem. Chem. 222, 9s-1OG (1935).
T H E ABSOLUTE DECOR4POSITION VELOCITY OF V24PORS GEORC-MBRIA SCHWAB
AND
NICOLAOS THEOPHILIDES
Department of Inorganic, Physical, and Catalytic Chemistry, Institute of Chemistru and Agriculture Nicolaos Canellopoulos, Piraeus, Greece Received October 17, 1046 INTRODUCTION
It is known that the application of the equation of Arrhenius
or log L = B - q/4.571T
(2)
t o heterogeneous catalysis provides the basic contributions to the quantitative understanding of this topic. This is mainly true for the activation energy p; the frequency term B has been less fully considered. At any rate, calculations of this number, based on statistical mechanics or gas kinetics, have shown good agreement with experiment.’ Still it seems desirable to espand and to specify more precisely the experimental material of this kind and thus to arrive a t a firmer knowledge of catalysis, especially with respect to the “active centers.” From this point of view n e have investigated a number of reactions in an zipparatus of a new type and have evaluated the constants quantitatively. APPARATUS
An apparatus suitable for the rapid measurement of the temperature coefficient of heterogeneous catalysis and thus of the activation energy and frcquency factor has been developed in our laboratory during the last few years (8, 9, 10). Its principle is to distil the reactant over the catalyst, to condense 1 A review of the recent work of Topley, Tenikin, Eyring, and others may be found in the Handbook of Cafalysis, 1701. V, which is now in course of preparation.
