Feb., 1952
SOLUBnSrY 0F.CA AND S R
NITRATESI N
++
-
klNo),and, N H = (kkl klhC) NO k;CSo. This hCSo a t may be written in the form N H = kJVa a given concentration, and we further aarmmed that lea is fixed for all concentrations but that k3is not. The constants have been evaluated and a com-
ETHYLENE
GLYCOL DI'HERS
185
parison of calculated and experimental values for methyl ethyl ether and methanol has been made, Tables I-IV. The values of So were taken from water desorption isotherms, Fig. 8 , and the No values were taken from the dry approximate isotherms.
SOLUBILITIES OF CALCIUM AND STRONTIUM NITRATES I N MONOALKYL ETHERS OF ETHYLENE GLYCOL BY KENNETH A. KOBEAND WILLIAML. MCYTSCH~ Department o/ C h i s h y , University of Texas, Austin, Team Rscsiosd Noaeinbcr 20, 1860
The solubilities and phase relationships for calcium nitrate and strontium nitrate in methyl, ethyl and butyl Cellosolves have been determined. Butyl Cellosolve is the most selective of these solvents for the dissolution of calcium nitrate from mixtures containing strontium nitrate.
Strontium nitrate is used extensively in pyrotechnics. I n lower grade orea both strontium and calcium carbonates may be present, and it is necessary to remove the calcium nitrate from the strontium nitrate because the former is extremely hygroscopic and specifications require it to be absent. A fractional crystallization procedure has been outlined by Kobe and Stewarta who present the 25 and 60" isotherms for the aqueous ternary. Barber' has shown that the monobutyl ether of ethylene glycol will selectively dissolve calcium nitrate from anhydrous mixtures of strontium and calcium nitrates and has based a successful procedure in qualitative analysis on this fact. The authors have used this as a basis for a method of quantitative analysis of strontium and calciumJ4 similar to a method using acetone.5 Because of the quantitative separation possible, it was desired to h o w complete solubility and phase relationships, not only for the butyl ether but also the methyl and ethyl ethers which are also commercially available. Although the monoethyl ether of ethylene glycol is known as "CellosoIve," this word will be used here to designate a monoalkyl ether of ethylene glycol and the individual members will be designated by the name of the alkyl group, as methyl, ethyl or butyl.
Experimental Reagents.-The
calcium and strontium nitraterr were
analyt~calgrade reagents. The calcium nitrate tetrahy-
drate was dehydrated at 145" before use. The Cellosolves were technical grade supplied by the Carbide and Carbon Chemicals Division. Each was distilled under vacuum before use, using a Vigreux column and rejecting the iriitial 15% and !he 10%. All of the Cellosolvea form mnimum boiling point azeotro@ containing 7! to 78% water, so all traces of water should be removed m t h the initial 15% rejected. Procednre.-The warm nitrates from the drying oven were added to Pyrex test-tubes with restricted openings. (1) Ethyl Corporation. Baton Rouge, La. (a) K. A. Kobe .nd P. B. Btewart. J . Am. CAm. See., M, 1301 (1942). (3) E. E Barber. Id. B w . Chum.. A d . Ed., U,672 (1941). (4) K. A. Kobe and W. L. Motaeh, And. C h a . 98, 1498-9 (1961). (6) P. B. Stewart and E.A. Kobe, Id. Bng. C h . , A d . M., 14, 288 (1042). (6) Carbide and Cubon Chemic& Gorp.. "Csllosolva and Cubit01 801vont8," New York. N. Y .. 1947.
The tubes were then placed in the oven and held at 140" for 12 hours to remove any traces of moisture that may have been picked up. The tubes were removed from the oven, the desired amount of Celloso!ve added and the tube quickly sealed with a aa torch. If a sample was to be used at a temperature wiere solvated crystals were the stable form, the sample was dissolved completely by hesting to a higher temperature, around 100". and then cooling to form the solvated crystals. Often the ampoule had to be shaken vigorously to cause crystal formation. Calcium nitrate soluLions would reqdre several da s or not change at all to the stable form unless this i n i t d s t e p waa taken. Duplicate samples were rotated on a wheel submerged in the thermostat and one sample was allowed to rotate for a longer period of time. The agitation periods ranged from several s at 30" to about 6 hours at 120". Temperatures below and above 120" were not used because time to reach equilibrium was too great below 30° and above 120" the nitrate-Cellosolve solution dimlored after mveral hours. Thermosht temperatures were kept within 0.05" of the desired value. Sampling.-After equilibrium was attained, the sample was allowed to stand until the solution was clear. The top of the ampoule waa broken and the liquid sample was removed with a pipet. The pipet tip was covered with a piece of filter paper unless the solution was too viscou~,in which caae a pipet with an enlarged ti was used. In some cases heated pipete had to be used, gut when the system showed an inverted solubility curve a cooled pipet was used. Two samples of the solution were taken from each ampule and placed in weighing bottles. Various techniques were used to obtain samples of the solid phfu3es. For sam lea near room tem rature t.he excess h wd waa drawn o t a n d the solid quid$ transferred to a wei&ing bottle. The calcium nitrate disolvate of ethyl Cellosolve dried satisfactorily in a desiccator over'lmhydrous calcium sulfate. The disolvate of meth 1 Cellacl~lvehad to be placed on dried cotton to absorb t i e exem solvent. The deliquescence of the solvated crystals made it difficult to prepareathe crystals in pure form. Analysis.-Water was r e ~ t e d l yadded to the weiehed sample in an oven at 100" untd no Cellosolve odor rermuned when it reached dryness. U d y 5 or 6 evaporations were required. Direct evaporation of the Cellosolve invariably left carbonaceous matter. The sample was heally dried at 160" for 12 hours. The loss in weight represented the Cellosolve and the residue was the nitrate in the sample. Use of prepared a m lea showed this method was accurate to about one part in ! a. ' ' The observed crystal type wmpn aid in de solid hase. Calcium nitrate drsolvste of :?&=nr solve gas a cubic cryatsl whereat3 the monosolvste is hexagonal. Calcium nitrate disolvate of ethyl Celloeolve forms a needle-like crystal.
%'
Discussion The solubilities of calcium nitrate are given in Table I and those of strontium nitrate in Table 11.
186
KENNETH A. KOBEAND WILLIAML. MOTSCH
The phase relationships in the calcium nitrateCelIosolve system are shown in Figs. 1 , 2 and 3.
TABLEI SOLUBILITIES OF CALCIUM NITRATE IN CELLOSOLVES Solubility expressed a8 grams anhydrous calcium nitrate per 100 grams solvent; T = transition point of disolvate; M = congruent melting point of disolvate; m = metastable. t, * c .
TEMPERATURE, "C.
Fig. 1.-Calcium nitrate-methyl Cellosolve.
Vol. 56
30.0 45.0 60.0 75.0 82.5 87.2 87.5 88.8 89.2 90.0 91.1 91.2 93.8 95.0 96.5 105.0 120.0
Methyl g./100
e.
33.2 41.5 50.3 65.2 77.4 91.8
Cello- Ethyl Cello- Butyl solve p./lOO solve g./100 g. solvate g. solvate
2 2 2 2 2 2
5.9 12.7 22.3 40.1 54.9
2 2 2 2 2
64.0
2
114.2 2,l T 107.83 2 M 130.6 Om
Cellosolve solvate
58.4 52.5 46.9 41.5
0 0 0
35.4
0
31.1 27.2
0 0
0
80.1 2 81.2 2,O T
122.2
1
126.5 125.6 123.4
1 0 0
78.6
0
75.3 71.1
0 0
TABLEI1 SOLUBILITIES OF STRONTIUM NITRATE IN CELLOSOLVES Solubility expressed as grams anhydrous strontium nitrate per 100 grams solvent. All solid phases are unsolvated. oc. 30.0 60.0 90.0 120.0 t,
TEMPERATURE. "c.
Fig. 2.-Calcium nitrate-ethyl Cellosolve.
Methyl cellosolve,
&/loo $.
Ethyl cellosolve, g./100 g.
Butyl cellosolve, g./100 g.
1.66 0.663 .345 .187
0.048 .043 .027 .021
0.023 .021 .017 .015
% HzO in solvent
30.0
0.0 1.0 2.0 4.0 8.0
0.023 .048 .069 .195 1.21
In ethyl Cellosolve calcium nitrate forms only a disolvate which melts to form the anhydrous salt. No solvate is formed in butyl Cellosolve over the temperature range investigated. The unsolvated salt in all solvents shows a negative temperature coefficient of solubility, or an inverted solubility curve. The solubility of strontium nitrate is low in all TEMPERATWIE. 'C. solvents (Table 11) and only the unsolvated salt Fig. 3.--Calcium nitrate-butyl Cellosolve. exists. As with calcium nitrate, this form has an The system calcium nitrate-methyl Cellosolve is inverted solubility curve. A comparison of the unique in having a transition point of di- to mono- two salts shows that butyl Cellosolve is most selecsolvate a t 88.8", just below the congruent melting tive for the extraction of calcium nitrate from the point of dissolvate a t 89.2". The monosolvate mixed nitrates, and a quantitative method of analexist8 over a short range and the transition to the ysis is based on this.4 The effect of a small amount anhydrous salt would occur a t 97.2" and 127.4 g./ of water on the solubility of strontium nitrate in 100 g. Concentrated solutions, above about 100 butyl Cellosolve a t 30" is likewise shown in Table g./100 g., are extremely viscous and the rate of I1 where the solvent contains from 1.0 to 8.0% wasolution of the salt is low. It is easy to obtain solu- ter. The solubility is seen to increase rapidly, ao tions with metastable solid phases, and one such for quantitative separations the solvent must be point is indicated on the figure. anhydrous.
