EQUILIBRIUM I N T H E SYSTEMS ZINC CHLORIDE-PYRIDINE; AND CADMIUM CHLORIDE-PYRIDINE* BY RALPH B. MASON AND J. H. MATHEWS**
A compound of zinc chloride with pyridine has been described previously, viz., ZnC12.2C5H5Nby Langl and Monari2. Lachowicz8 described the compound ZnCl2.2C5H5N.2H20 and Lang the compound ZnC122(CSH5N.HC1). The compound ZnC12*2C6H5N has been used by Heap, Jones and Speakman4 in the preparation of pure pyridine. The compound is soluble in anhydrous alcohol and pyridine. I n some potential difference work (to be described in a separate paper) in anhydrous pyridine it was necessary to know the extent of the solubility of the ZnC12. With this end in view the equilibrium has been determined from oo to 105'C. Materials used. A sample of Baker's pure pyridine was dried for several weeks over fused potassium hydroxide and then distilled. After this treatment it was digested with potassium permanganate for ten to twelve hours, using a reflux condenser. It was then refluxed with barium dioxide and finally distilled with a fractionating column. The fraction used, boiled at 114.2-114.6' at 741 mm. Hg (corr.) Some pure zinc chloride was fused and then dissolved in anhydrous pyridine and the compound ZnC12.2CbHsN recrystallized three times from the anhydrous pyridine by heating and then cooling in a freezing mixture. The purified salt was kept in a desiccator. However the compound is not hygroscopic and a sample that has remained in the open air of the laboratory for over a year has as bright and shiny crystals as the day it was set out. Method. The solubility determinations were made with a modified Meyerhoff er-Saunders5 apparatus which was immersed in an electrically controlled hermostat. The mercury thermometer was graduated to 0 .'I and capable of being read to .oI'; it was compared with a thermometer standardized by the United States Bureau of Standards.
Analysis of Samples Determination of Zinc. Zinc was determined volumetrically by the ferrocyanide method. The pyridine interfered with the end-point and was therefore removed by boiling with sodium hydroxide before attempting the zinc determination. An analysis of the zinc chloride complex gave 2 2 . 2 8 percent zinc while the theoretical value is 2 2 . 2 0 percent. *A portion of a thesis submitted by Ralph B. Mason in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the University of Wisconsin. **Contributionfrom the Laboratory of Physical Chemistry of the University of Wisconsin. Ber. 21, 1578 (1888). Jahresber. 1884, 629. Monatsheft, 9, 516 (1888). J. Am. Chem. SOC.43, 1936 (1921). 5Waltonand Judd: J. Am. Chem. Soc. 33, 1039 (1911); Z. physik. Chem. 28,464 (1899)
ZINC AND CADMIUM CHLORIDES WITH PYRIDINE
1179
Determination of Chlorine. The chlorine was determined by Volhard's method. By analyzing a sample of zinc chloride with and without pyridine, it was found that the pyridine had no effect upon the chlorine determination. A one gram sample of zinc chloride complex was dissolved in dilute nitric acid and the chlorine determined in the usual manner. The value obtained for chlorine was 23.98 percent while the theoretical value is 24.08 percent. Since the chlorine determination was easier to carry out and more accurate, the solubility of zinc chloride a t different temperatures was calculated from the chlorine determinations. However zinc was determined in several samples as a check upon the chlorine determinations.
8
b
$95 T
S.85 $75
3
sG5 9.55 %
'
5 4 5 ? M f l * {
FIG.I
0
IO
20
30
do
50
60
T€MP€/?A TUR€S
70
80 90
FIG.2
Numerical Data The data obtained are given in Table I and shown graphically in Fig.
I.
Temperatures are plotted as abscissas and percentages of zinc chloride in the sample as ordinates. From the solubility determinations of ZnClz in pyridine from oo to I O j o it is evident that there is only one compound of ZnClz with pyridine, vie., ZnC1z.zC5HsN. There is a gradual increase in solubility with increase in temperature. Equilibrium i n the System: Cadmium Chloride-Pyridine. Only one compound of cadmium chloride with pyridine has been described previously, vie., CdCL.zC5HsN by Langl, who analysed the compound for cadmium, chlorine, and pyridine. Koenigs and Geigyzmention the fact that CdClz forms crystals from pyridine solutions. Lincoln3 says that CdClz is insoluble in pyridine or only very slightly soluble, forming a solution which is a very poor conductor Ber. 21, 1584 (1888). 17, 594 (1884). J. Phys. Chem. 3, 461 (1899).
* Ber.
I180
RALPH B. MASON AND J. H. MATHEWS
of the electric current. Naumannl reported CdClz as insoluble in pyridine. Kragen2 used pyridine for the quantitative precipitation of CdC12+2CsH5N. He stated that the CdCL.zCsH5N loses one molecule of pyridine at 115-120OC but no more, and weighed the cadmium as CdClz.C5HsN. He found that a t
TABLE I RTeight of Samples
Temperatures
4.220 3,990 5 4.073 IO 4.070 4.230 I5 3.531 20 3.646 24.12 3.628 3.945 3.643 3.492 35 2.921 2.950 45 2 .go8 2.529 55 3.613 3.272 65 3.627 75 2.621 85 2.098 95 2.146 105 2 .056 I cc. AgN03= ,00682 grams ZnClz. 0
CC.
Ag90,
9.93 9.33 I O . 76 12.22
12.46 11.79 13.67 14.87 16.40 14.92 18.72 15.82 20.16 19.86 21.58
31.08 35.20 48.20 42.68 41.84 51.09 48.87
Per cent ZnClz
1.60 1.59 I .80 2.04 2
.oo
2.28 2.55
2.79 2,81 2.79 3.65 3.69 4.66 4.65 5.82 5.89 7.33 9.06 11. I 1 13.60 16.24 16.26
b
2zoC, ninety nine percent pyridine (B. P. 114-116’C) dissolved 1.347 grams C ~ C ~ Z * ~ Cfor S each H ~ Nhundred grams of solution, a value which agrees with
the results of this research. Materials used. The pyridine was purified in the same manner as for the ZnClz. It boiled a t 114.2-114.4’ at 736 mm. Hg (corr). Cadmium chloride of “C. P.” grade was dissolved in water and precipitated as sulfide. The sulfide was dissolved in HC1 and the HzS removed by boiling. The chloride was then precipitated by HC1 gas. The calculated amount of NH4C1to form the double salt was added and the double salt recrystallized from water. The double salt was heated in a porcelain boat in a pyrex tube while a stream of HC1 gas was passing through the tube. After the Ber. 37, 46cg (1904). Monrttsheft, 37, 391 (1916).
ZINC AND CADMIUM CHLORIDES WITH PYRIDINE
I181
NH4C1had been sublimed away the tube was heated to redness and the CdC12 distilled. The beautiful white crystalline CdC12was preserved in a desiccator until used. Method. The solubility apparatus used was similar to that used for ZnClz, except that it was made entirely of pyrex with no rubber stopper. The stirrer was also made of pyrex and the apparatus was made air tight by a mercury seal. Some of the pure CdC12was fused in a small pyrex tube in an atmosphere of
Nz. After cooling it was added to the solubility apparatus and the pyridine distilled directly into the solubility chamber. The pipette was dried by passing hot dry air through it for half an hour. It was then allowed to come to the temperature of the bath before the sample was removed. Determination of Cadmium. Some pure CdCl2 was dissolved in absolute alcohol and the cadminum precipitated as CdClZ.zCsH5N. This compound was allowed to stand in excess anhydrous pyridine and then filtered and washed with pyridine. A sample of the CdCl2.zCsHsN was weighed and dissolved in hot water. Pyridine was liberated upon boiling. Excess pure potassium hydroxide was added and then COz passed until the cadmium was completely precipitated as CdC03. The CdCO, was washed upon a filter and dissolved in HC1. It was then evaporated on the water bath in a weighed poreclain crucible and changed to the sulfate by addition of cone. H2S04. After heating in an air bath until no more fumes of SO3 were given off, the crucible was weighed.
Chlorine Determination. The Volhard method was again used for the determination of chlorine. In the case of the CdClz the pyridine seemed to interfere with the end point. When the CdCl2.2CsH6Kis boiled with water for about ten minutes, the pyridine is given off and the determination can be carried out in the usual manner. Numerical Data The solubility of the CdC12 in pyridine at different temperatures was determined by analysing each sample for chlorine and then calculating the amount of CdClz present in each one hundred grams of solution. The data obtained are given in Table I1 and shown graphically in the accompanying curve. Temperatures are plotted as absicissa and percentages of cadmium chloride in the sample as ordinates. The solubility of CdClz in pyridine increases very rapidly from oo to go. From go to 100' there is a very gradual decrease in solubility. This abrupt change in solubility leads one to look for a transformation of one pyridinate into another with a smaller number of molecules of pyridination. Samples of the pyridinate stable at the room temperature were analysed for chlorine by the usual gravimetric method and showed 20.74% chlorine present, a value which agrees very closely with the theoretical value of 20.76% chlorine for the compound CdCl2.2CSH6N.
1182
RALPH B. MASON AND J. 11. MATI-IEWS
TABLE I1 Temperatures
Weight of Sample
0
CC.
3.616 5.157
I.79 2.62
25
5.113 4.987 4.71= 4.315 5.045 4.876 4.353 4.318 4.362 5.029
3.31 3.83
30
4.780
3.55
4.630
3.31 3.18 3.02 2.88
4 7.2
IO
15
40 50
4.30
4.803 4.553 4.905 4.709
Per cent CdClz
.46 .46 .77
4.71
.80 .92
4.28 5.18 4.87 3.78
.91 ,94 .92 .80
3.76
.79 .70 .70
4.33
2.90
.68 .66 .61
.61 '
54
.57 .54
60
4.648 4.628
2.72
80
4.446 4.616
2.35 2.46
.54 .49 .49
2.25
.51
2.66
'
2.71
4.082 4.899 cc: AgN03= .00921 grams CdC12.
IO0 I
.4gK03
50
CdC12.6CsHsN Some pure CdC12.2C6H5N(from alcohol) was added to an excess of pure anhydrous pyridine (B. P. 115.3' at 760 mm. Hg.) in a glass stoppered bottle. The bottle was placed in the ice box over night and the resulting crystals were dried between ice cold filter papers. The crystals were quickly transferred to weighing bottles, weighed and analysed for cadmium and chlorine. The average value obtained for cadmium was 16.76% and the average value for chlorine was 1 0 . 6 3 ~ ~The . compound CdC12.6C6HsNtheoretically contains 16.83% cadmium and 10.80% chlorine. Below 9' there is evidently a phase which corresponds to CdC12.6CsHsN. This compound has not been described previously in the literature. An analogous compound, CdBr%.6CsH&N, has been described by Varetl. The crystals of CdC12.6CsHbN are large, clear and transparent. Allowed to stand at room temperature they crumble away to a fine powder. The transition temperature is approximately go. Bull. (3) 5, 843 (1891).
ZINC AND CADMIUM CHLORIDES WITH PYRIDINE
1183
Summary I. The equilibrium in the system ZnClz-Pyridine has been determined from 0' to 105'. There is only one solid phase present, namely ZnC12.2C5HsN. The equilibrium in the system CdCL-Pyridine has been determined 2. from 0' to 100'. A new compound, CdC12.6C5H6N, has been identified. This compound is the stable solid phase below 9' while CdC12.zCsHsN is the stable phase above go. Madison, Wisconsin M a y 2986.
