JOURNAL OF CHEMICAL EDUCATION
THE FRIEDEL-CRAFTS REACTION IN ELEMENTARY ORGANIC LABORATORIES OSCAR L. WRIGHT,' DONALD FUHLHAGE, and EARL SHERIDAN College of Emporia, Emporia, Kansas
T w o verycommon reactions from the theoretical standpoint in the study of elementary organic chemistry are the Friedel-Crafts reaction and the Grignard reaction. In the study of synthetic preparations of alcbhols, ketones, and hydrocarbons, these organo-metallic reactions play a most important part. Yet very few nndergraduate college courses offer laboratory work utilizing these procedures. The fire hazard inherent in procedures involving the use of ether and carbon disulfide in the beginning laboratory is a well-known and highly respected factor. The Friedel-Crafts hydrocarbon synthesis using an alkyl halide and an aromatic compound with anhydrous aluminum chloride as a catalyst gives poor yields, for the most part, which are usually mixturesnot easily separated by means of simple techniques. Fractional distillation can be effected successfully only if the process is well handled in good equipment. 1 Present address: Central Research Laboratories, Continental Oil Co., Ponca City, Oklahoma.
The acylation procedures recorded in various laboratory manuals and other literature also call for apparatus and techniques not usually found in the beginning laboratory, since many procedures call for extended periods of reflux or reaction time. Not all courses include reduced pressure distillation techniques, either, and their use is essential to many preparations listed in the literature. Yields of aromatic ketones are recorded as between 80 and 90 per cent of the theoretical, depending upon the reaction conditions. Many deviations of procedures have been tried in order to improve yields; for purposes of investigation the yield of any product is an important consideration. The yield of product, to a large extent, depends upon the techniques and the ability of the chemist, however, and even though a great stress is placed upon the mastery of technique in the beginning laboratory, it is definitely a limiting factor. High percentage yields are not essential to good results in the achievement of the aims of student labora-
DECEMBER, 1952
tory work; nor is the handling of large amounts of various species. Budgets are csually the initial consideration in the selection of experiments to be done in all elementary laboratories, especially in small schools. It was with this thought in mind that we began to search the literature for experiments utilizing small, inexpensive equipment and semimicro techniques. Much can be said for the acquisition of fine techniques made possible by the efficient handling of small amounts of material. We have used many semimicro procedures in our laboratory experiments this year with a high degree of success. One of the procedures we used is a modification of the Perrier ketone synthesis, although it works just as well in the normal acylation reaction procedure. This reaction is run in an 8-inch test tube, without drying tubes, without condenser, without automatic stirring, and without gas trap. The reaction is run in 0.1-molar quantities (or smaller) and the time is reduced greatly. The use of small quantities diminishes the fire hazard. The washing of the product is as customary. The product is distilled in a small distilling flask a t atmospheric pressure, using a Bunsen flame as a source of heat. The product is collected in a weighed test tube. Yields of product in this reaction run as high as 85 per cent. Ammatie comvound Beneene Benzene Benzene Benzene Toluene Ethylbenzene Cumene Cumene Cumene sec-Butylbenzene sec-Butylhenzene see-Butylbenzene p-Cymene Brornobenzene o-Diehlorohenaene O-Bromotoluene Diphenyl ether Anisole Anethole Pyrrole
Aeylaling amnt
Yield,
a.
Aeetyl chloride 7.9 Propionyl chloride 8.3 Butyryl chloride 10.4 Benmyl chloride 7.8 Acetyl chloride 8.8 Acetyl chloride 9.0 Acetyl chloride 11.4 Propionyl chloride 12.7 Butyryl chloride 14.3 10.5 Acetyl chloride Propionyl chloride 12.0 Butyryl chloride 14.7 Acetyl chloride 9.0 Acetyl chloride 10.2 Acetyl chloride 9.6 Acetyl chloride 16.8 Acetyl chloride 6.6 Acetyl chloride 8.0 Acetyl chloride Polymerized Acetyl ohloride Polymerized
Yield,
% ..
66 43 66
72 75 72 40 50 51 84
The yields given in the table above were obtained by beginning students in the elementary organic course. They no doubt could be improved on by an experienced investigator, but they show the type of work which is possible by the student in an elementary course. This modification of the Friedel-Crafts acylation reaction reduces the time element, the cost (by using smaller quantities), the fire hazard, and eliminates the use of expensive equipment, thus making its use practical in the elementary course. Any or all of the aluminum chloride complexes may be isolated if' desired. All of the details of the reaction may be observed during the process. Where it is possible, reduced pressure techniques may be employed. The apparatus used in this laboratory for reduced pressure distillation can be made with but little glass-blowing technique (see the figure).
The experimental procedure is as follows: Weigh 16 g. (0.12 mol) of anhydrous aluminum chloride into a dry, 8-inch test tube. Add 15 ml. of carbon bisulfide and stir with a glass rod until the suspension is uniform. Cool the mixture in an ice-water bath, and add slowly 7.85 g. (0.1 mol) of acetyl chloride. Some effervesceuce of HCl may be noted here, and unless efficient coolmg is effected, some of the carbon bisulfide may boil out. After this mixture has been stirred and cooled thoroughly (5-10°C.) add slowly from a dropping funnel 10-15 ml. (excess) benzene. (Dry benzene will improve the yield but is not essential.) If no reaction is apparent a t this point the reaction mixture may be removed from the cooling bath and allowed to warm to room temperature; with some compounds it may be necessary to warm in a hot-water bath. It may be necessary to replace the test tube in the cooling bath if the reaction shows signs of boiling out of the tube. The reaction is usually complete in 10-15 minutes and is immediately poured into a mixture of HCl and crushed ice, separated, and the aqueous solution extracted twice with 10-ml. portions of ether. The oil and ether extracts are combined, washed once with water, once with 10 per cent sodium carbonate solution, and twice again with water. The ether extract is then dried with a few granules of calcium chloride and distilled. The fraction boiling from 180" to 210° is collected and, if purity is desired, redistilled. Derivatives may be prepared from the cut after one distillation. The 2,4dinitrophenylhydrazone is especially convenient in the case of acetophenone. The yield of acetophenone is 8-10 g.
