A Molecular Sieve Reflux Extractor for Dehydration of Volatile Solvents and Solutions Paul Arthur, W. M. Haynes,l and L. p. Varga, Department of Chemistry, Oklahoma State University, Stillwater, Okla.
N THE DIRECT analysis of paints, 'petroleum, and petroleum products for heavy metals and in the polarographic determination of organic s u b s t a n c e s e.g., acid halides (1)-which react with water, we have found that extremely small amounts of water in reagents or in organic diluents often strongly affect the analytical results. Thus when amines were employed with heavy metals, either as reagents for the determination of these metals or as bases to provide a suitable environment for the determination of the metals with chelating agents, water interfered. The interference apparently was of two types; water provided competition for coordination sites on the metal ions, and the resulting hydrated cations reacted with the amines to form basic salt precipitates. These behaviors are especially important when low concentrations of metals are present; for in such cases, surprisingly low concentrations of water become significant. Thus the water concentration in 2propanol containing only 0.1% water is about 9 times the concentration of the C u t 2 in a solution 0.005M with the latter. Common methods for drying alcohols (3, 5) generally have yielded products containing no better than 0.1% water as tested by Karl Fischer titration (I). Furthermore, these methods normally are concerned with pure solvents and not with solutions containing solutes to be dehydrated-particularly not with solutes which are difficult to dehydrate without decomposition. The procedure described here is capable of rapidly producing ultra-dry solutions in systems initially at equilibrium with respect to water content. It has also proved effective in systems in which water is a product of reaction and in which, therefore, dehydration can be used to drive the reaction to completion-e.g., dehydration of dissolved salts, the esterification of nonvolatile acids in preparation for their determination by gas-liquid partition chromatography, etc. Initial attempts to dry solutions of dissolved salts by simply passing the solution through a bed of Molecular Sieve 4.4 (Linde Co., Division of Union Carbide Corp.) (4) were successful, but resulted in loss of metal ions to the bed. The principle employed in the a p paratus finally developed is similar to that of a Soxhlet extractor. Here,
however, the unwanted water which has some vapor pressure over the solution is swept along with the rising solvent vapor and, as the condensed phase passes down through a bed of Molecular Sieve in its return to the vaporization flask, the water is removed. Even firmly hydrated ions lose their water in this process, and the competition of solvent molecules for coordination sites on the ions undoubtedly aids the dehydration process, while the sweeping of water from the solution by the boiling process prevents establishment of a steady state condition. Consequently, either solvents alone or solutions of salts become progressively drier, and in a surprisingly short time can be made extremely dry, though any nonvolatile solutes in such solutions never come into contact with the Molecular Sieve bed.
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1.
PART A
Present address, South East Missouri State College, Cape Girardeau, Mo. 1630
ANALYTICAL CHEMISTRY
EXPERIMENTAL
Apparatus. Figure 1 shows the apparatus employed. The space above the coarse frit in Part A is filled with Molecular Sieve 4A in I/le-inch pellet form, about 2 pounds being required. For best results, the Molecular Sieve should be dried before use and between uses by heating to about 290' C. for 2 hours while purging with a dry gas such as nitrogen. The upper part of A is a reflux condenser. Part B is a moisture trap filled with Molecular Sieve 4A which is fitted to the top of the reflux condenser. As further protection against moisture, a large container of indicating-type silica gel is attached with rubber tubing to the outlet tube of Part B, and when the dehydration is to be performed under vacuum, this is followed by a suitable trap connected to the source of vacuum. The vacuum line requires an
Figure 1.
PART C Molecular sieve reflux extractor
air bleeder to control the vacuum and, hence, the evaporation rate. Part C is a %liter flask fitted with a sampling tube equipped with a 2mm. stopcock having a plug of Teflon. All ground glass joints were greased with a silicone stopcock grease, especially when vacuum was applied. Operation. The method of operating this apparatus depends upon the nature of the liquid to be dehydrated. For solvents or solutions which distill readily without decomposition, a voltage-controlled electric heating mantle is recommended as a heat source. For others, a temperature-controlled bath is required. The flask C is filled two-thirds to three-fourths full with the liquid to he dehydrated. A rubber septum inserted in the outer end of the sampling tube was found convenient for the removal, by means of a hypodermic needle, of samples for analysis and for use. The heating mantle around C is adjusted so that steady evaporation, condensation, and siphoning take place without flooding. A shorter return flow tube from the Molecular Sieve compartment can be used to reduce hold-up somewhat, although the tube should be high enough to serve as a vapor trap. Results and Warning. I n testing this apparatus with 0.1M nickel per-
chlorate in 1-butanol, i t was observed that when the dehydration had proceeded for about 4 hours, spurts of flame occurred and black products formed on the hot glass above the liquid in flask C. Apparently the higher water content present earlier had been sufficient to quench the oxidieing action of the perchlorate since in many earlier experiments such reaction had never been observed. When the dehydration was performed a t reduced pressure with a water hath a t 45O C. replacing the heating mantle, no difficulty was encountered with either nickel perchlorate or copper(I1) perchlorate. The efficiencyof drying was measured by titrations with Karl Fischer reagent, the procedure employed estimated as being able to determine as little as 0.0005% water. Results were as follows. A 0.1M 1-butanol solution of nickel perchlorate containing originally 0.81370 water by weight was found, after six hours‘ treatment employing the vacuum technique, to contain so little water that all that could be said with certainty was that it was between aero and 0.000570. With %propanol containing 0.28% water and no salt, 4 hours treatment reduced the water to 0.0014%; 6 hours dropped it to less
than 0.001%, and 10 hours dropped it t o between 0.000570 and zero. It would he expected that the dehydration should he more rapid with liquids of higher hailing point. This undoubtedly partly explains why 2 propanol required a longer time than did 1-butanol. (A reviewer of this paper has pointed out that the formation of a butanol-water azeotrope containing 42.5% of water and a %propanol-water azeotrope containing less than one third as much water probably contributes even more to the greater ease of dehydration of 1-butanol solutions compared to %propanol solutions.) LITERATURE CITED
(1) Arthur, P., Lyons, H., ANAL.CHEM. 24. 1422 (1952). (2) Carley, D. A,, M.S. Thesis, Oklahoms. State University, May 1964. (3) Hatch, L. F., “Isopropyl Alcohol,” pp. 11-12, McGrm-Hill, New Yark, 1961. (4) Hemh, C. K., “Molecular Sieves,” pp. 73-9, Reinhold, New York, 1961. (5) Jolly, W;, L., “Synthetic Inorganic Chemistry, pp. 121-3 and cited references, Prentice-Hall, Englewood Cliffs, N. J., 1960. A s s n u c ~ ~ in o part fmm the Ph.D. thesis of W. M. Heynes, Oklahoma State University, May 1966.
Recording Photometer for Monitoring Ultraviolet Absorbing Effluent from Chromatographic Columns Joseph F. Vincent, The Woman’s College of Georgia, Milledgeville, Ga.
H E l S b T R U I l t N T clrLrribed hrrr Was Tsperifirally drsignivl to monitor r~ir protein etTiuvnt from a chroniatogrn1ihic rolumn in nrdrr t u rerover sprritic frartions, hur ir might bi, uird IO moniror any ultrariolrt absorbinc: rffluent from a rhromarograpliir rolunin or ion exrhange rolunin. l’h Iihotmnrirr is a dotilh-hram type which minimizes flurtuations
