JANUARY, 1955
0
PREPARATION OF ANHYDROUS PYRIDINE HYDROCHLORIDE MODDlE D. TAYLOR and LOUIS R. GRANT Howard University, Washington, D. C.
RECENTLY the use of pure anhydrous pyridine hydrochloride was required in this laboratory. The usual procedure for preparing such com]comds, i. e., neutralizing an aqueous solution of pyridine with hydrochloric arid and evaporating the ~vater,is time-consuming and fails to yield an anhydrous product. Pyridine hydrochloride is very hygroscopic. The procedure described below is much more convenient and gives a high yield of essentially pure material. It should prove suitable as an exercise in inorganic preparations for advanced students. A 2040 per cent solution of pure pyridine in anhydrous ether is treated with gaseous hydrogen chloride until precipitation is complete.
which was inserted the stem of a 100-ml. droppingfunnel, a piece of glass tubing bent in a right angle t o serve as a delivery tube, and a straight piece of glass tubing. Twenty-four ml. of concentrated sulfuric was poured into the dropping funnel, which was closed by a one-hole rubber stopper carrying a glass tube. Rubber tubing connected the top of the dropping funnel and the top of the Erlenmeyer flask and served as a pressure equalizer. The outlet tube from the Erlenmeyer flask was connected with rubber tubing to a four-inch funnel which dipped into the ether solution of pyridine. The sulfuric acid was run slowly into the hydrochloric acid solution so that the HC1 would not be generated faster than it could be absorbed. The CsHsN + HC1- CsHsN.HCI ether solution of pyridine was coded to prevent the Pyridine hydrochloride is quantitatively insoluble large heat of reaction from boiling the mixture. There in ether. The excess ether is distilled away on a steam resulted 98.5 g. of 99.8 per cent pure (m.p. = 143.4) bath and finally quantitatively removed by pumping pyridine hydrocholoride, which amounted to a 98.5 the salt in uacw in a vacuum desiccator. The crystals, per cent yield. Heilbronl lists the melting points as when first prepared, have the appearance of pure dry 82°C. The material was anzlyzed for chloride by sodium chloride. They absorb moisture readily and precipitating silver chloride and for pyridiie by the become sticky, however, if not rigorously protected technique suggested in Chemical Abstra~ts.~ Pyridine hydrochloride is soluble in pyridine and from the atmosphere. In a typical preparation 69.0 g. of anhydrous pyr- its solubility increases rapidly with temperature. A idine nras dissolved in 200 ml. of anhydrous ether in saturated solution conteins 0.113 g./ml. at 30' and a t 50°C. an 800-ml. beaker. Seventv-five ml. of concentrated 0.1758 -e./ml. , hydrochloric acid and 50 g. of NaCl were placed in a , HEILBRON, I. M., of Organic Compounds,,, dry 500-ml. wide-mouth Erlenmeyer flask. The Eden- Oxford University Press, New York, 1938, VOI. III. meyer flask was clased with a mbber stopper through Chem. Abd~aels,19,2181 (1924).
