Richard F. Smith and Alvin c. Bates State University College Geneseo, N e w York 14454
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Preparation 01 p - h h i t r i l e A n organic chemistry experiment
Nitrile syntheses that have been adapted for the elementary organic laboratory include the dehydration of amides (1) and aldoximes ($9,nucleophilic substitutions by cyanide ion (S), and the cyanohydrin reaction (4). In the present experiment, p-anisaldehyde is converted to p-anisonitrile by a modification of the threestep aldehyde-nitrile synthesis of Smith and Walker (5). p-Anisaldehyde is converted to its N,N-dimethylhydrazone (I)by a simplification of the reported procedure that circumvents the use of a Dean-Stark water separator. The I\'$-dimethylhydrazone is then converted, without isolation, to the crystalline quaternary hydrazone (11) by reaction with methyl p-toluenesulfonate. Finally, the quaternary hydrazone is converted to p-anisonitrile by a rapid elimination reaction conducted in methanolic potassium hydroxide.
The yield of the crystalline nitrile is good and the synthesis can be completed in a single laboratory period. The sequence of reactions employed in this experiment also provides examples of three classes of reactions (nucleophilic addition, nucleophilic substitution, and base-catalyzed elimination) which are given intensive treatment in mechanistically oriented organic courses. The instructor may wish to have the student devise a method of identification of the trimethylamine liberated in the last step. Further extensions might also include determination and analysis of the infrared spectrum of the product and hydrolysis of the nitrile to p-anisic acid. 1 All organic chemicals required for this experiment may be purchased from Distillation Products Industries. Use of this large flask prevents foaming in the condenser during the distillation.
174 1 Journal o f Chemical Education
The Experiment' N,N-dimethylhydrazine is reported to be a skin irritant and should be handled carefully.
Mix 6.8 g (6.1 ml, 0.05 mole) of p-anisaldehyde and 3.8 ml (0.05 mole) of 1,l-dimethylhydrazine in a 125-ml erlenmeyer flask. Stopper the flask loosely and swirl occasionally while the exothermic reaction proceeds. During this reaction period a solution of 2.8 g (0.05 mole) of potassium hydroxide in 30 ml of solvent methanol is prepared in a 125-ml erlenmeyer flask and set aside for use in the elimination reaction. After approximately 20 min the condensation reaction is complete and the reaction temperature (50 "C maximum) begins to fall. Solvent benzene (50 ml) is added to the flask and the benzene solution is decanted from the water layer into a 250-m12round bottom flask. Further quantities of water are removed by rapid azeotroping during distillation of half of the benzene. To the distillation residue is added 9.3 g (0.05 mole) of methyl p-toluenesulfonate and the resulting solution is heated under reflux on the steam bath for 20 min. Separation of the crystalline quaternary hydrazone is frequently observed during the reflux period. The reaction mixture is cooled and the product filtered by suction and washed with two 25-ml portions of solvent ether. The crude quaternary hydrazone is added (hood!) in one portion to the alcoholic potassium hydroxide solution previously prepared. The reaction flask is vigorously swirled. The exothermic elimination reaction is complete within 10 min. The reaction mixture is poured into 200 ml of water and the crystalline product isolated by suction filtration. Student yield of air dried product is 3.5-5.0 g, mp 53-55'C. The product may be recrystallized from ethanol-water to give 1.73.6 g of white needles, mp 57-5VC. Literature Cited (1)
(2) (3)
(4)
(5)
JOHNSON, F. R., AND WILCOX,C. F., "Lahoratory Experiments in Organic Chemistry," (5th Ed.), The Mscmillan Co., Inc., New York, 1963, p. 252. H., "Laboratory Text in (b) C a s o ~ ,J., A N D RAPAPORT, Organic Chemistry," (2nd Ed.), Prentice-Hall, Inc., Englewood Cliffs, N. J., 1962, p. 104. MARMOR, S., "Laboratory Guide for Organic Chemistry," D. C. Heath and Co., Boston, 1964, p. 276. (a) Ref. (lb) p. 380. (b) ROBERTSON, G. R., AND JACOB+ T. L., "Laboratory Praclice of Organic Chemistry,'' (4th Ed.), The Macmillan Co., Inc., New York, 1962, D. 271. F&R, L. F., "Organic Experiments," D. C. Heath and Co., Boston, 1964, p. 109. SMITH,R. F., AND WALKER,L. E., J. 01g. Chem., 27, 4372 (1962). ( 8 )ADAMS, R.,
