COORDIXATIO~~COMPOUSDS WITH BOROX TRICHLORIDE.
IV
125
freezing. The tendency to flocculate was increased, also, by extending the time the systems were held in the frozen state. 6. The age of the stock solution was found to have an effect on the sols prepared from it when the pH values of the latter mere just outside the pH range of no flocculation. Flocculation passed through a minimum with increase in age of the stock solution a t pH values corresponding to transitions between maximum and minimum flocculation. The author wishes to acknowledge the assistance given him in this work by The Philadelphia Quartz Company. REFEREKCES (1) (2) (3) (4) (5) (6)
BOBERTAG, FEIST,IND FISCHER: Ber. 41, 3675 (1908). BRLXI:Ber. 42, 563 (1909). DJATSCHKOWSKY: Kolloid-Z. 54,278 (1931). HAZEL:J. Phys. Chem. 42, 409 (1938). LOTTERYOSER: Ber. 41, 3976 (1908). LOTTERMOSER . ~ X DLASGESSCHEIDT: Iiolloid-%.68, 336 (1933).
C O ~ R D I K A T I O NCOMPOUKDS OF BOROX TRICHLORIDE. IV
SYSTEMSWITH
THE
DOSBLD RAT MARTIS
PROPYL CHLORIDES
AXD
ALBERT S. HUMPHREY
.VoUes Chemical Laboratory, Uniuerszty of Illinois, Urbana, Illznois
Receiced September 3, 1946
A survey of the literature reveals that few chlorine-containing compounds form coordination compounds with boron trichloride (4). In the previous paper of this series (6) it was observed that methyl chloride does not form a coordination compound with boron trichloride, whereas ethyl chloride does. It was proposed to study the behavior of the next higher members of the alkyl chloride series with respect to the donor properties of the chlorine atom. The purpose of this paper was to conduct this study by means of thermal analyses of the systems propyl chloride-boron trichloride and isopropyl chloride-boron trichloride. The apparatus and procedure employed in this study have been described previously (1, 2, 5, 6), with the exception of the technic used for the establishment of the mole fractions. Inasmuch as all three components are liquids at the temperature of melting ice, the calibrated flasks 1% ere ala ays filled with gas to a pressure a t least 15 mm. below the vapor pressure of the gas a t 0°C. Two thermal analyses were made of each system, using components which were purified by fractional distillation under different pressures. The check
42G
DONALD R . i T Y.\IiTIS AXD ALBERT 5. HUSfPHREY
analyscs arc indicated by asterislcs in the data listed in tables 1 and 2 and I)y solid circles in the phase-rule diagrams depicted in figures 1 and 2. The boron trichloride used in these studies v a s prepared by allou.ing boron trifluoride to react with sublimed aluminum chloride (3) and was purified by fractional distillation. The propyl chlorides were obtained from the Eastman Kodalc Company and were purified similarly by fractional distillation. TABLE 1 Data for the systein n-propyl chloride-boron trichloride YOLE PMCTION O F
BCli
*0.010
PPEEZINO POINT
f0.4 -T.
*
O.W* 0.062' 0.100 0.145 0.149' 0.202 0.251* 0.302 0.351 0.372 0.400 0.450' 0.495: 0.525 0.550' 0.600 0.649* 0.701 0.702 0.751* 0.m 0.851* 0.900 0.951* l.OoO*
139.2 137.3 132.2 129.3 127.5 123.6 120.5 116.8 118.2 115.6 113.0 111.7 108.6 108.0 107.2
1.000
106.7
122.3 123.7 126.0 127.3 129.1 130.5 131.9 134.0 135.9
EUTECTIC IEXPEPATUPE
*0.4 -"C.
142.0
142.0 141.7 141.8 141.9 141.8 141.8
= check analyses. THE SYSTEM PROPYL CHLORIDE-BORON
TRICHLORIDE
There is no evidence for the formation of a compound between propyl chloride and boron trichloride a t low temperatures. The thermal analyses data shown in table 1 and depicted in figure 1 indicate that no maximum exists but only a eutectic point which lies at 42.4 f 1.0 mole per cent boron trichloride and a t -141.8"C. f 0.4".
COORDINATIOS COMPOUBDS WITH BOROK TRICHLORIDE.
IV
427
The freezing points of the purified samples of boron trichloride were observed - 106.7"C. and - 107.2"C. 0.4'. The freezing point of the purified propyl chloride \vas found to be - 122.3"C. =!z 0.4". Considerable difficulty was experienced in the determination of this freezing point, owing to the tendency of the propyl chloride to form a glass. The value obtained is 0.5OC. higher than the accepted value of Timmermans (7) of - 122.8OC. -*c
as
.
I28
I36
I44
I n-C3H,Cl
I
I
I
1
20
40
60
60
BCIJ
FIQ:1
Some trouble was encountered in the determination of the freezing points of the mixtures having a composition of less than 50 mole per cent boron trichloride, owing to severe supercooling coupled with a tendency towards glass formation. This difficulty w&s particularly acute between 15 and 35 mole per cent boron trichloride. THE SYSTEM ISOPROPYL CHLORIDE-BORON
TRICHLORIDE
The freezing points of the purified samples of boron trichloride used for this system were found to be -107.0'C. and -107.3OC. f 0.4'. The samples of purified isopropyl chloride were observed to have freezing points of -117.5"C. and -117.8OC.
428
DONALD RAY MARTIN AND ALBERT S. HUMPHREY
The data recorded in table 2 and delineated in figure 2 indicate a maximum at 25.0 mole per cent boron trichloride, corresponding to the compound most simply expressed as (i-CaH&1)3:BC13. The freezing point of the compound is -105.0"C. f 0.4".
TABLE 2 Data f o r the system isopropyl chloride-boron trichloride YOLF. FRACTION OF
BClr
10.009
FREEZING P O l N I
10.4 -0C.
0.000
O.ooO* 0.047 0.098*
0.104 0.149 0.197* 0.235* 0.242* 0.294 0.297* 0.346 0.397* 0.445 0.496* 0.546 0.596* 0.633 0.664 0.690 0.725* 0.750* 0.777 0.825* 0.861* 0.899 0.929 0.950* 0.980" 1.OOO 1.ooO
*
117.5 117.8 118.3 113.3 113.8 111.2 107.3 105.3 105.0 105.4 105.9 106.0 106.8 107.7 109.0 110.6 111.9 112.7 113.8 114.8 114.7
f0.4
-'C.
118.3 118.7
114.8
114.G
113.1 112.8 110.6 109.4 108.0 107.8 106.9
107.0 107.3
= check analyses.
Minima exist on each side of the maximum, occurring a t 6.4 f. 0.9 mole per cent boron trichloride and -118.5"C. f 0.4" and a t 70.7 3~ 0.9 mole per cent boron trichloride and -114.7%. f 0.4". Consideration of the maxima in the systems involving ethyl chloride (6) and
COORDINATION COMPOUNDS W I T H BORON TRICHLORIDE
429
isopropyl chloride with boron trichloride, with respect to their flatness and the temperature a t which they exist, indicates that the isopropyl chloride-boron trichloride compound is more stable than the ethyl chloride-boron trichloride compound. It is well known that isopropyl compounds are more reactive than the corresponding n-propyl derivatives. I t is not surprising therefore that the chlorine atom of isopropyl chloride coordinates with the boron atom of boron trichloride, although the chlorine atom in n-propyl chloride does not. -'C. I02
I07
112
117
I22 I-C3H,CI
I
I
I
I
20
40
60
80
BClg
FIG.2
However, it is surprising that a compound having 3 moles of isopropyl chloride to 1 mole of boron trichloride should exist, rather than the simplest possibility of a 1:l molecular ratio. This becomes more apparent when consideration is given to the bonding forces at play in the compound. One molecule of isopropyl chloride undoubtedly coordinates through its chlorine atom to the boron atom of boron trichloride. The two additional molecules of isopropyl chloride can be accounted for only by hydrogen bonding. This hydrogen bonding might take place between the hydrogen atom on the secondary carbon atom of isopropyl
430
DONALD RAY MARTIN AND ALBERT 5. HUMPHREY
chloride and the chlorine atom of another isopropyl chloride giving rise to a trimer, thus: CH3 CH3 C1 CH3 H-c-ci-I -H-C-Ci---H-~-Ci-ts-c~ I II
II
II
1
CHI C1 CHI CH3 An objection to this proposed structure is that there is no experimental evidence to indicate that isopropyl chloride is associated in the liquid state a t low temperatures. Another possible structure to account for this compound involves the ttssumption that the hydrogen bonding takes place between the hydrogen atoms on the secondary carbon atoms of the isopropyl chloride molecules and the chlorine atoms of the boron trichloride molecule, thus : CH3 c1 CHI
I
ci--c--H-
I
CHn
--ci-B-ci-I
r c1 I
- -H-&-ci
I
CH8
CH3-C-CHn
I
H Inasmuch as the chlorine atoms around the boron atom are at the corners of a tetrahedron in coordination compounds of boron trichloride, it is difficult to understand why three molecules of isopropyl chloride would not attach themselves to the three chlorine atoms of the boron trichloride by hydrogen bonds instead of only to two. SCMJIARY
1. The thermal analysis of the system propyl chloride-boron trichloride disclosed only a eutectic point a t 42.4 Z!Z 1.0 mole per cent boron trichloride and a t -141.8'C. f 0.4'. 2. The freezing point of propyl chloride was found to be -1223°C. i 0.1", a value which is higher than the accepted value in the literature. 3. The thermal analysis of the system isopropyl chloride-boron trichloride revealed a maximum a t 25.0 =k 0.9 mole per cent boron trichloride and a t -105.0°C. f 0.4",corresponding to the compound most simply expressed as (CC3H7C1)3:BC&. Minima exist on each side of the maximum, one at 6.4 f 0.9 mole per cent boron trichloride and - 118.5"C. f0.4" and the other at 70.7 f 0.9 mole per cent boron trichloride and - 114.7OC. f 0.4'. (1) (2) (3) (4) (5) (6) (7)
REFERENCES BOOTH,H. S., A N D MARTIN, D. R . : J . Am. Chem. SOC.64,2198-2205 (1942). BOOTH,H . S . , AND MARTIN,D. R . : Chem. Rev. 8s,57-88 (1943). GAMBLE, E . L . , GILMONT, P., AND STIFF,J. F.: J. Am. Chem. SOC.62, 1257-5 (1940). MARTIN,D. R.: Chem. Rev. 34, 461-73 (1944). MARTIN,D. R . : J . Am. Chem. SOC. 67, 1088-91 (1945). MARTIN,D. R . , AND HICKS,W. B.: J. Phys. Chem. 60,422-7 (1946). TIMYERMANFJ, J . : Bull. SOC. chim. Belg. 27, 3 3 4 4 3 (1913).
