sample tube 12 (2) or tube 13 (18-mm 0.d.) which contains a weighed fragile bulb of the sample 14 (3). Optimum sample weight is about 0.5 gram. Quantities greater than 1 gram become less manageable. The apparatus is then connected to a vacuum line via the inner standard taper joint 9 and pumped down to less than 10-5 Torr. The last traces of moisture are removed by flaming out, care being taken not to heat the sample. Access to the sample is gained by breaking fragile bulb 11 or 14 with the Teflon (DuPont) coated bar magnet 2 which is arrested in position by an externally taped magnet except when in use. If the solvent in 12 is to .be removed, it is distilled into the vacuum line where it is condensed in a trap by a cold bath. If solvent is to be added to the filtration apparatus, a known volume is distilled from the vacuum line to the tube 12 or bulb 16 where it is condensed by a cold bath. Stopcock 8 is then closed and the filtration apparatus is separated from the vacuum line. The nonvolatile solid and the solvent are agitated in tube 12 or 13 by manipulation of magnet 2. Filtration is then carried out by pouring the solution onto the filter 15. Gentle
cooling with an ice bath will hasten filtration if the solution is not too concentrated, in which case filter clogging might occur. The solute in the bulb 16 is visually examined by distilling away the solvent to a cold bath around tube 12. If the required effect has been accomplished, the solute is redissolved and poured into tube 18. The solvent is then gently condensed back on the raw mixture in tube 12 at a rate commensurate with the absence of bumping in tube 18. After repetition of the cycle to the extent necessary, the solvent is cooled and the constrictions 4 and 17 are sealed off. The filtrate in tube 18 and the insoluble components in 12 are then separately investigated by gaining access through the fragile bulbs 19 and 1, respectively. The procedure was developed for the preliminary study of the separation of the products from the reaction of FeC13 with CeHsMgBr under an atmosphere of HP (4). Subsequently, the apparatus was used to study the solubility of the hydride Mg4Br3.sClo.sFeH7 in volatile organic solvents.
(2) S. G. Gibbins, ANAL.CHEM., 43,621 (1971), (3) Zbid., p 295.
(4) S. G. Gibbins, 161st National Meeting, American Chemical Society, Los Angeles, Calif., March 1971.
Vapor Phase Extraction-A
RECEIVEDfor review January 21, 1971. Accepted April 20, 1971.
New Purification Method
Sydney G. Gibbins Department of Chemistry, University of Victoria, Victoria, B. C . , Canada
THE OBJECTIVE of this procedure is the purification of a compound which is the least soluble component of a mixture when dissolved in a solvent. The compound itself possesses appreciable solubility and cannot be freed of the contaminants by filtration and washing. The procedure is based on two principles: the solvent used to extract the more soluble components is saturated in these components; the driving force for the spontaneous addition of the solvent to the mixture depends on the difference in vapor pressure of the pure solvent and the solution formed. As the method employs organic solvents in an evacuated vessel for extended periods, the apparatus must be all glass and free of stopcocks and grease. While originally developed for the purification of the nonvolatile, air- and water- sensitive solid Mg4Br3, 5 Clo. 6FeHi(THF)8( I ) , the method is more generally applicable. So far as this author is aware, the principles and technique to be described have not been previously used. The observation leading to the development of the vapor phase extraction method occurred in the study of the reaction of an ethereal solution of ferric chloride with phenyl Grignard under a n atmosphere of hydrogen ( I ) . After liquid-liquid extraction with diethyl ether and filtration of the products, tetrahydrofuran was added to the black solid residue. The residue, appreciably “soluble,” produced an inky black “solution.” After part of the solution splashed on the upper walls of the evacuated container and the liquid drained away, a black solid deposit remained. Overnight, solvent vapor (1) S. G. Gibbins, Abstract Inorg. Chem. No. 155, 161st National
Meeting, American Chemical Society, Los Angeles, Calif., March 1971.
apparently condensed on the residue and washed away the black component and, as becomes obvious later, at least two white ones, An adherant yellow crystalline solid remained on the upper walls. As a result of this observation, the vapor phase extraction method was developed. Assuming that the effectiveness of extraction measured in terms of both rate and degree was dependent on an ample source of solvent vapor and the thin layer spreading of the impure solid, the following primary requirements of extractor design should be satisfied: there should be a large volume for solvent vapor along with a large surface for solid deposition; the liquid solvent should either be close to the solid or else a large orifice should connect the reservoir containing the solvent with that containing the solid to be extracted. The apparatus, Figure 1, is comprised of two 500-ml round bottom flasks whose necks are bent and sealed at 7. Length dimensions of tubing, 12 to 14 mm o.d., are a convenient minimum, Fragile bulb break seals are used rather than the hook type. Accidental breakage of the seals is avoided by sealing the tops closed when not in use (2). Although only two such seals are required, several additional ones are present for either additional extractions or unanticipated needs. All operations are carried out with the major plane of the extractor in the vertical orientation. This plane is determined by the centers of the two bulbs and tube 7. The extractor is rotated about a horizontal axis perpendicular to this plane. The addition to and the removal from the apparatus of materials is straight forward if they are not air- or water(2) S. G. Gibbins, ANAL.CHEM.,43, 621 (1971).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 10, AUGUST 1971
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1' I
Figure 1. Vapor phase extractor sensitive. If such sensitivity is a problem, special procedures utilizing the apparatus in Figure 2 are employed. The primary unit of Figure 2, designated as either the sample introduction vessel or the purified product receiver, is a 100- to 300-ml round bottom flask. When used as an introduction vessel, the introduction tube was sealed off at constriction 21 after the sensitive sample was initially transferred to bulb 26 by appropriate means. Transfer of the solution in bulb 26 to the vapor phase extractor is accomplished in the following manner. The extractor is clamped at 7 by a large type 3-finger clamp to a vertical '/*-inch support rod which is itself clamped to a permanent vertical lattice by means of two horizontal bars. The sample introduction vessel 26 is clamped at 25 in an inverted position to the support rod and the fragile bulb break seal 22 is sealed onto the extraction apparatus at 1 by the usual glass blowing techniques. The apparatus, connected to a high vacuum system by the inner standard taper joint 3, is pumped down to
