INDUSTRIAL A N D ENGINEERING CHEMISTRY
956
Vol. 16, No, 9
Purification of Methylethyl Ketone by Sodium Iodide' By H. L. Lochte UNIVERSITY 08
TEXAS, AUSTIN,TEXAS
T
ECHNICAL methylethyl ketone is one of the cheap organic chemicals, while the pure ketone is a comparatively expensive material. This fact is not surprising to persons who have tried to purify technical methylethyl ketone by the usual sodium bisulfite method. Shipsey and Werner2 describe a method of purifying acetone by dry distillation of its sodium iodide addition compound. This method has been employed frequently since and has proved satisfactory although the rather low temperature required for a good yield requires considerable time. It is now found that methylethyl ketone may be purified even more conveniently by the same method. The impure methylethyl ketone boiling between 70 O and 77" C . is placed in a round-bottom flask and connected to a reflux condenser. The flask is heated in a water bath and enough sodium iodide added to leave a small amount undissolved after refluxing for an hour. The saturated solution is rapidly filtered through a hot-water funnel. The addition compound crystallizes out on cooling the solution to room temperature. To improve the yield of crystals, the solution may be cooled by an ice bath but it is not necessary to cool with a freezing mixture as in the case of the corresponding acetone compound. The mass of white needles is then separated from the remaining liquid by filtering through a Buchner funnel without filter paper. The solid product is next placed in a round-bottom flask connected with a short fractionating column and a condenser. On heating in a water bath the crystals melt a t 73" to 74" C. and pure, moist ketone distils over. Toward the end of the distillation the boiling point gradually rises to about 77" C., but only a small amount distils over above 76" C. The ketone is dried in .the usual manner. The residual salt or aqueous solution of iodide may be used for subsequent runs after driving over some, but not all, of the water. I n a series of trial runs in which both the ketone and the sodium iodide had been carefully dried, no addition cpmpound crystallized out, even on cooling to -10" C. by means of a salt-ice freezing mixture. A small amount of moisture is sufficient to permit the isolation of a small yield of crystalline product, but moisture enough to form the dihydrate of sodium iodide seems to be required for a maximum yield. This phase of the problem, as well as the determination of the vapor pressure and other physical constants, is being taken up by members of the department of physical chemistry of this university. ANALYSIS OF ADDITION COMPOUND The analysis of the addition compound presents some difficulty, since the vapor pressure of ketone from the crystals is rather high and the substance is hygroscopic. The fact that no compound could be isolated in case carefully dried materials were employed made it difficult to obtain samples of compound not contaminated with dihydrate. A tentative formula for the compound was determined by means of a series of volatile matter determinations from a large number of different samples of material. The results show that, by varying conditions, mixtures may be obtained ranging in composition from pure sodium iodide dihydrate with 19.4 per cent volatile matter to practically pure NaI.CdHsO with 32.43 per cent. The latter may most easily be obtained by 1
2
Received June 25, 1924. J . Chem. Soc. ( L o n d o n ) , 103, 1255 (1898).
analyzing the first crystals obtained on cooling a mixture of iodide and ketone containing less than 5 per cent water. Three such samples gave 31.45,31.32, and 31.60 per cent volatile matter. Since no higher values were obtained, the tentative formula assigned seems justified, in spite of the fact that the corresponding acetone derivative has been assigned the formula NaI.3CaH60.2
EXPERIMENT WITH OTHERKETONES Diethyl ketone yields a small amount of crystalline product if treated with sodium iodide under the conditions previously outlined, but no crystalline compound could be obtained in experiments in which methylhexyl and methylnonyl ketones were employed instead of methylethyl ketone. Even in the case of diethyl ketone the small yield did not justify further study of the reaction. The only ketone that might be expected to interfere with the sodium iodide method of purification of methylethyl ketone is acetone. Experiments show that, if the mixture has been fractionated so that the boiling point lies within the limits indicated in this article, the common impurities encountered in the purification of methylethyl ketone do not interfere with this method. YIELD The yield of ketone that may be obtained under laboratory conditions varies between 10 and 20 per cent of original ketone per run. Since the iodide as well as the filtrate or uncombined ketone may be used over and over, the total yield may be raised to about 75 per cent of the original amount of ketone. It is usually more convenient to obtain the desired quantity of ketone by making a few runs on large batches and recovering the uncombined part as technical ketone rather than making a large number of runs on a small batch. The iodide may be used an indefinite number of times, depending on the purity of the crude ketone. DRYINGMETHYLETHYL KETONE The ketone obtained by this method is dried by the same methods as that obtained by the sodium bisulfite method. Although the use of calcium chloride is usually recommended as drying agent, experiments show that there is considerable loss due to the formation of an addition compound with the ketone. Probably because of mechanical interference by a layer of this compound, the product obtained from calcium chloride is usually not quite dry. Anhydrous copper sulfate was found to be best suited as a drying agent for small amounts of ketone. COMPARISON OF UNTREATED AND PURIFIED PRODUCTS Finally, the product obtained by the sodium iodide method was compared with the untreated ketone and with a sample of methylethyl ketone purified by means of the bisulfite method. The results in the table show that pure methylethyl ketone may be prepared cheaply and conveniently by dry distillation of its sodium iodide addition product. TABLE I SAMPLE Dried by Technical CuSOi CuSOd Purified by NaI Purified by bisulfite
..
n2:
1.3780 1 3775 1.3780
Density at 34'/4'C. 0.787 0.802 0.803
Boiling point
Pressure mm . 77 to 78 745 77 to 78.5 745 77 t o 7 Q . 5 745 'C.
