Organic 2 Review Problem 257

Organic 2 Review Problem 257 - should be available. Now...

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PREPARATIONS 241 for the later distillation use the adaptor and receiver (Fig. 23(A) and (B), p. 45) in place of G in Fig. 67(6).) Place 20 g. of dry powdered benzoic acid in C, add 15 ml. (25 g., i.e., a 30% excess) of thionyl chloride and some frag- ments of porcelain, and then clamp the apparatus on a boiling water-bath as shown so that no liquid can collect in the side-arm of C. Heat for one hour (with occasional gentle shaking), by which time the evolution of gas will be complete. Cool the flask C, detach the condenser and fit it to the side- arm for distillation, using a 360° thermo- meter for the neck of C. To the lower end of the condenser fit a small conical flask G (Fig. 67(6)) by a cork carrying also a cal- cium chloride tube. In place of the con- ical flask G, a small Buchner flask may be used with the calcium chloride tube fitted to the side-arm, but in either case a dupli- cate flask for the second fractio n
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Unformatted text preview: should be available. Now distil the contents of C by heating carefully over a gauze. A small initial fraction of unchanged thionyl chloride boiling at 78-80 comes over, and the temperature then rises rapidly to 194. Directly this happens, stop the distillation, allow the condenser to drain thoroughly, and then replace G by the duplicate receiver. Run the water out of the condenser so that it acts as an air-condenser, and then continue the distillation. Collect the benzoyl chloride as the fraction boiling at 194-198. Yield, 19 g. In the distilling-flask remains a very small high-boiling fraction of benzoic anhydride (b.p. 366), formed by the dehydrating action of the thionyl chloride on the benzoic acid : 2C 6 H 5 COOH + SOCl 2 = (C 6 H 5 CO) 2 O -f SO 2-f 2HCl. Benzoyl chloride is a colourless highly refractive liquid, having (B) FIG. 67....
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