JOURNAL OF CHEMICAL EDUCATION
A NEW FRIEDELCRAFTS SYNTHESIS FOR THE BEGINNING STUDENT W O L DW
T
Michigan State College, East Lansing, Michigan
IN
SPITE of the tremendous use of anhydrous aluminum chloride in organic chemistry,' the well-known laboratory manuals for an elementary course ofler a mthrr small number of alternative illustrntions of the Frirclel-Cmfts synthesis. Thus, one is largely limited to diphenylmethnnc, ethylbenzene, cymcnr, cumene, and the butyl benzenes as exnmples of hydrocarbon synthrws or acetophenone, benzophenone, or orthohrnzoylbenzoic acid as examples of ketone syntheses, or triphenylmethyl chloride.' The.se preparations usually involve more thnn one lahorntory period, and a few involve vacuum or fractional distillation. In connection with the teaching of a course in elementary organic chemistry designed primarily for home eronomics and agriculture studrnts, it wns desirnhle to devise a simple example of the important 1:riedrlCrafts reaction which might be cnrried out by a lxtginning student in one two-hour laborntory period. The alkylation of phenol with tertiary butyl chloride has txcn found to satisfy all of the desired requirements. T h r rrnction may be cnmrd out in an ICrlenmeyer flnsk, is complete in twenty to thirty minutes a t m m tempemture, and gives visual evidence of completion. The product is resdily purified by recrystallization to yirld a benutifully crystallinr, relatively nonhygroscopic mntrrinl in nearly quantitative yirlds.
A neneml discussion of the salient mints connected T n o u q C. A., "Anhydmua Aluminum Chloride in Organic Chemistry," Reinhold Publishing Corporation, New York, 1941. 'This is the total fare glcnned from thirteen well-known Inhomtory mnnuals.
with this experiment is pertinent before giving the experimental procedure in detail. The starting materials are readily arnilable and inexpensive, the tertiary butyl chloridr frequently having txcn prepared by the students themwlves, earlier in the term. The use of t h r product ns nn nntioxidant and its manufncture on a commercial scale mny Iw pointed out to the practically mindrd fitudent. T h r materials are mixed (using a slight exeens of the tcrtinry hutyl chloride, assome of this volatile s u h n c e is lost with the evolved hydrogen chloride) and treated wit11 a catalytic quantity of anhydrous aluminum chloride. The flnsk mny simply he placed in an efficient hood to remove the hyclrogcn chloride fumes, or a g~ trnp of thc inverted funnrl type mny he used. Whereas the product melts a t 99-100°C. and the starting materials are a liquid and n low-melting solid, and since no solvent is uscd, the reartion mixture solidifies upon completion of the reartion. The need for careful weighing of the quantities of starting materials i~ thrreforr evident, although it should 1% pointed out that only fire failures to solidify were oh.served in a n o u p of 135 students, each prrforming the experiment for the first timr. T h r solid cnkr of product is hroken up with a spatula under water, filtered, pressed dry, and recrystallized from pet,roleum ether using n steam hnth. Sincr no flnmes are nrceasnry during the experiment, there is little fire hnznrd during the rccrystallizati~m. The yirld, even for the beginning student, is Irequrntly over 90 per cent and in the hands of n graduate ntudcnt this procedure consistently gave BT+JR per cent yields. The author hclicvcs that the lnck of "good" reactions which give high yields is sometimes owremphasized in thc labomtory c l a w s in organic chemistry. There are many organic reactions which are nenrly quantitative and this experiment calls attention to this fact.' 'The reaction under dimusion, for example. has been shown ta be quantitative at 4O'C. even in the absence of aluminum chloride; nee i l ~ r t r ,If., AND J. 11. Sruo~a,J . A m . Chrm. Soc..
71.345110441.
JULY. 1950
It should be noted, incidentally, that the procedure described below gives considerably better yields of para-tertiary-butyl phenol in a shorter time than the methods described in the literature.' It has been of considerable use, therefore, in preparing para-tertiarybutyl phenol for research purposes, using the identical procedure described below, but with 5-10 times the quantities.
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0.5 g. of anhydrous aluminum chloride, a few granules a t a time. Hydrogen chloride gas evolution should start immediately. Add the aluminum chloride a t such a rate as to maintain evolution of hydrogen chloride without appreciable rise in temperature of the reaction mixture. (Should the reaction mixture become warm, cool the flask momentarily in a beaker of cold water.) Stir or shake the flask occasionally for a period of 20 to 30 minutes in order to expose new surfaces of the catalyst. At the end of this time, if the amounts EXPERIMENTAL of the reagents were carefully determined, the contents To 6.5 ml. (5.5 g.) of tertiary butyl chloride contained of the flask should solidify, in a small, dry Erlenmeyer flask add 4.7 g. of phenol When the of the flask have solidified, add and stir until the phenol is all or nearly all dissolved. 25 ml. of water and break up the lumps with spatula, (Caution: Avoid any contact of phenol with the skin. The water should be acidic (litmus); if it is not, add In Of a wash with Or ml. of concentrated hydrochloric acid. When all of dilute bromine water followed by an excess of water. the lumps have been up into a finely divided Treat the burn with a Ointment') The powder, filter the water from the solid, using a Biichner reaction flask is then placed in the hood. (Since the funnel, Press the solid as dry as possible and allow quantities used are small, an efficient hood will easily air to he drawn through it on the funnel for several keep hydrogen chloride fumes from the laboratory. minutes. However, a gas trap of the usual inverted funnel type Transfer the to a 400-ml, beaker and add may be used, if thought desirable.) Add about 0.3- sufficient ether or ligroin (150-200 ml,) From pl-butylbenEene sulfonio acid, see FIESEE, L, F,, to just dissolve the solid when the solvent is boiling on a "Experiments in Organic Chemistry," 2nd ed., D. C. ~ ~ and ~ steam t hbath. Filter the hot solution rapidly through a Company, New York, 1941, p. 182. From phenol, isobutyl Buchner funnel and cool the filtrate in an ice bath. slcohol, and zinc chloride, see Lucns, H. J., AND D. PRESSW, White crystals of para-tertiary-butyl phenol should "Principles and Practice in Organic Chemistry," John Wiley appeal. Filter, dry, and weigh. The usual yield is and Sons, New York, 1949, p. 398. 6.9 to 7.3 g., m. P. 99'. Unlike phenol, the product From isobutyl- or t-butyl-phenyl ether, see S ~ T E R. , A,, J . Am. Chern. Soe., 55,3718 (1933). is not highly hygroscopic in air.
