Organic 2 Review Problem 51

Organic 2 Review Problem 51 - one or two extractions using...

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METHODS AND MANIPULATION 35 (A) (B) added and the mixture thoroughly \s shaken, the stopper at the top of fj the cylinder being occasionally ^x^~^\ opened to relieve any pressure of ether vapour caused by the heat of the hands. The mixture is allowed to settle until two well-defined layers have formed, and the lower aqueous layer is then run off and separated as completely as pos- sible. The remaining ethereal layer is run off, preferably by pouring it through the upper neck of the funnel, to avoid contamina- tion with any drops of aqueous solution still remaining in the stem of the funnel below the tap. The FIG. 16. aqueous solution is then returned to the funnel, and the extraction repeated, using fresh ether on each occasion, until it is judged that very little of the compound remains in the aqueous layer. It should be borne in mind, however, that if a given volume of ether is to be used for the complete extraction, a far more efficient result will be obtained by a number of consecutive extractions using only a small volume of ether for each extraction, than by
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Unformatted text preview: one or two extractions using a correspondingly greater volume of ether each time. The ethereal extracts are then united, dried with a suitable drying agent and filtered. The filtrate is then cautiously distilled, the ether being first distilled and finally the organic compound if volatile: if the compound is solid, the crude residue is puri-fied by recrystallisation. Very great care must be taken on all occasions when ether is distilled, because of the risk of fire or of an explosion: full experimental details for this operation are given, both on p. 80 (Preparation of Ether) and on p. 164 (Pre-paration of Aniline). Continuous ether extraction and continuous chloroform extraction. When a substance X is shaken up with ether and water it will distribute itself according to the relative solubilities in each solvent. ^, _ , . . rr - ^ Cone, in ether layer Thus K (partition coefficient) = ~-. vr Cone, in aqueous layer...
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