SEPTEMBER, 1948
481
PREPARATION
OF ACYL CHLORIDES WITH
CHLORIDE
THIONYL
SAVERIO ZUFFANTI Northeastern University, Boston, Massachusetts
J. Chem. Educ. 1948.25:481. Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 09/17/18. For personal use only.
A
of organic chemistry laboratory manuals and widely shows that thionyl chloride, a common used reagent, is not even mentioned as a halogenating agent in most of them. One manual (4) discusses the purification of thionyl chloride and its use in preparing benzoyl chloride from benzoic acid. A second book (6) merely states “In recent years thionyl chloride has also been brought into use...; it has the advantage that its decomposition products are gaseous and hence do not interfere with the working up of the reaction mixture.” Most of the other manuals make no mention whatsoever of thionyl chloride. Numerous laboratory experiments involving the use of phosphorus halides can be found in the literature, but only two papers (1> 7) were found which deal with the use of thionyl chloride. A comparison of the following equations, however, points out the advantage of thionyl chloride as a halogenation agent. R—COOH + PC15 R—COC1 + HC1 (g) 4- POCl3 R—COOH + SOCl2 R—COC1 4- HC1 (g) 4- SOa (g) survey
A simple, efficient, and successful experiment using thionyl chloride has resulted from one of our research projects (6) carried out a few years ago. Our need for some o-toluyl chloride led us to prepare it from 0toluic acid and thionyl chloride.
^yCH> + ^XJOOH
heated on a water bath which is kept at 60-65°, a 20ml. (32.75 grams, 0.275 mole) portion of freshly distilled thionyl chloride is gradually added from the separatory funnel. The temperature of the water bath is maintained at 60 to 65° for 2 to 3 hours until the vigorous evolution of gas has nearly ceased. As soon as the reaction has been completed, the separatory funnel is replaced by a thermometer and the excess thionyl chloride is carefully recovered by distillation. The acyl chloride is next distilled over at 208-209° and collected, rejecting the first few drops. About 2 ml. of a dark brown liquid remains in the flask. A yield of 20.7 grams (91 per cent of the theoretical quantity) of clear, water-white, o-toluyl chloride boiling at 212° (cor.) is obtained. Discussion. The excess thionyl chloride which is reclaimed upon distillation may be used again in subsequent preparations. Because of the great difference between the boiling points of thionyl chloride and 0toluyl chloride a complete separation is possible. However, to insure the purity of the product it is advisable to discard the first few drops which distill -
over.
For the more advanced students the preparation of o-toluic acid from o-toluidine supplies additional laboratory experience in organic synthesis. CH,
/\/CHa
(3)
4- S02 4- HC1
SOCln
^^COCl
The following directions for this experiment have been very carefully checked and with a reasonable amount of care the students will find them highly satisfactory. Experimental. In a 250-ml. distilling flask fitted with a separatory funnel is placed 20 grams (0.147 mole) of o-toluic acid. The side-arm of this flask is attached to a long downward condenser, which in turn is connected by means of an adapter to a 500-ml. filter flask. A calcium chloride drying tube is joined by a short piece of rubber tubing to the tubulature of the filter flask. While the flask containing the acid is
CHn
CN LITERATURE
V\
COOH
CITED
(1) CarrIs, P., and D. Libermann, Compt. rend., 199, 1422 (1934). (2) Clarke, H. T., and R. R. Read, “Organic Syntheses,” Coll. Vol. I, John Wiley & Sons, Inc,, New York, 1932, p. 500. (3) Clarke, H. T., and E. R. Taylor, ibid., Vol. XI, 1931, p. 96. (4) Fieser, L. F., “Experiments in Organic Chemistry,” D. C.
Heath & Company, New York, 1935. (5) Gattermann, L,, and H. Wieland, “Laboratory Methods of Organic Chemistry,” The Macmillan Company, New York, 1941. (6) Geyer, B. P., and Saverio Zuffanti, J. Am. Chem. Soc., 57, 1787 (1935).
(7)
McMaster, L.,
and
F. F. Ahmann, ibid., 50, 145 (1928).
