Separation of Mixtures Encountered in'QualitativeOrganic Analysis: An Anomalous Case Aceordine t o the eeneral scheme1 for the seoaration of a mixture of water-insoluble comoounds. the mixture is mixed with ether nnznnv ins"olohle comoounds iresidie 1) are seoarated on a filter and washed wit'h ether.'The ether solution is The solution remaining after ether extraction is then treated further for additional separations depending on the number of components. This scheme in practice does not work satisfactorily for mixtures containing certain amines and carboxylic acids. Although individually these components are insoluble in water and are normally used to make up a water-insoluble mixture, they react to form an ammonium carhoxvlate salt (RqNHCR'CO?-) whichmav be water-soluble or -insoluble deoendine on the
of specific examples so that the limitations of the aminelacid combination may be better discerned in the future, The amine and earbaxylic acid components of the specific mixture under consideration were di-n-propylamine and henzoic acid. These react to form the salt di-n-propylammonium benzoate (n-Pr2NH2+PhC02-).Since this salt is insoluble in ether, these two components (as the salt) appear in the residue portion of the separation scheme. No procedure is given for seoaratine the residue if it should be a mixture (or as a salt as in the oresent case). Since the salt. di-n-oroovlammonium . .. hrnn;ore. 1s s l ~ ~ h tsduldr l, in water. the student might wi-h tu trrar ihc mixture ns n \voter-soluble m u n m depending on the c)ther ~ m n p m e n t s l .In ' ,uch an event, thc qalt would ctdl wind up os the r e i ~ d u efn.m the swam distillarim whk h is the fmr strp m the iepamion " f a water-bolublr mixture.' Procedure
for Separation of
Ammonium Carboxylate Salt Residue4
The fallowing procedure was found to be entirely satisfactory for separation of di-n-propylammonium benzoate into its components. In the case of other ammonium carboxylates where the amine or carboxylic a c ~ dcomponent is water soluble, the procedure would have t o be modified accordingly. The residue (ammonium salt) dissolved readily in 10%sodium hydroxide. Since sodium hydroxide is a stronger base than the amine, the latter is displaced from the salt to form free di-n-propylamine and sodium benzoate. This mixture was extracted several times with ether, combining the washings. The combined ether extracts were dried with anhydrous sodium sulfate and the ether removed, leaving di-n-propylamine as a liquid. The aqueous solution from the ether extraction was acidified with concentrated hydrochloric acid to farm a white precipitate of henzoic acid which was collected by filtration and washed on the filter in turn with small portions of ether and water. The author expresses appreciation t o Baylor University for a sabbatical leave during part of which this paper was written. 1 Shriner, R. L., Fuson, R. C., and Curtin, D. Y., "The Systematic Identification of Organic Compounds," 5th Ed., John Wiley & Sons, Inc., New Yark, 1964, pp. 101,102. 2 It is possible to have a mixture compmed of both water-soluble and water-insoluble compounds. In such a case, one would have to perform a preliminary separation into the two types of mixtures by adding water and then separating the two mixtures and then further separating the two mixtures according to the usual schemes. Fuson, Snyder, Curtin, reference in footnote 1,pp. 98-99. The author wishes to seknowledee the collaboration of Mr. Garv Berriesford in warkine out this seoaration scheme. Thiv ,chrnae works brtrer than the & n n t w one d attemptinc [
