Here´s an article about a quite "non-traditional"
FC reaction I came across a while ago. I can see no reason why it shouldn´t work on substituted benzenes and Al/Hg shouldn´t be a problem for the MD bridge. What do you think?
The Use of Amalgamated Aluminum as a Catalyst in the Friedel and Crafts Reaction
It has been shown by the writer(1) that a series of alkylbenzenes could be prepared via Friedel and Crafts procedure using amalgamated aluminum catalyst. Isolated examples of the use of amalgamated aluminum or aluminum have been reported but no systematic investigation under carefully controlled conditions in which the structure and yields of products were carefully established has been carried out.(2) The identity and yields of principal products obtained were carefully established and by using this catalyst in the alkylation type reaction it was shown that the alkylbenzenes could be prepared in general with less rearrangement, formation of tars, disproportionation and dimerization than by the use of aluminum chloride in the usual Friedel and Crafts alkylation reaction.
The following series of alkylbenzenes and also s-butyl-a-naphthalene were prepared in good yields : ethylbenzene, isopropylbenzene, s-butylbenzene, t-butylbenzene, and s-butyl-a-naphthalene.
Synthesis of Alkylbenzenes
Six hundred cc. of thiophene free-benzene was placed in a liter round-bottom flask and 100 cc. distilled off to thoroughly dry the benzene and the flask. One hundred cc.of the dry benzene was mixed with 1 mole of the alkyl chloride and set aside in a stoppered bottle until ready for use. The liter flask was fitted with a 250-cc. graduated dropping funnel and a reflux condenser with a hydrogen chloride absorption device(3) connected to the lop of the condenser through a calcium chloride tube. The activated aluminum catalyst(4) was added to the benzene in the reaction flask, the dropping funnel and condenser placed in position and the chloride-benzene mixture poured into the dropping funnel. A calcium chloride tube was inserted in the top of the funnel and about 25 cc. of the chloride solution allowed to run into the flask a t room temperature. The reaction ordinarily began immediately. After the evolution of hydrogen chloride began to subside, the addtion of the chloride solution was continued at the rate of 1cc. per min. This maintained a fairly vigorous evolution of gas. About four hours were required for the addition after which the reaction mixture was allowed to stand overnight. If any moisture was present a flocculent precipitate of aluminum hydroxide formed and heating was necessary to start the reaction. After the completion of the reaction the solution was a reddish brown color and a small brown oily layer about the thickness of the catalyst was present in the bottom of the flask. After the decomposition with dilute hydrochloric acid approximately one-half of the unreacted aluminum catalyst was present. After standing overnight, the reaction was heated to gentle refluxing for five to ten minutes, cooled and washed with a 5% solution of hydrochloric acid and with water twice. The benzene layer was separated and dried over calcium chloride for distillation.
Separation and purification of the alkylbenzenes was accomplished by means of fractional distillation using a highly efficient column 60 X 1 cm. inside dimensions. The column(5) was packed with glass helices, and fitted with a partial take off type distillation head. A column6 with a similar packed section 41 X 1 cm. has been found by Fenske to have an efficiency of 11-12 plates. The inner tube containing the packings was surrounded by an electric heater which was in turn enclosedin a Pyrex vacuum jacket. Solid p-acetamino derivatives of some of the alkylbenzenes were prepared according to the procedure of Ipatieff and Schmerling.(6)
In conclusion, amalgamated aluminum has been shown to have certain decided advantages over aluminum chloride in alkylation reactions of aromatic hydrocarbons. (a) Higher yields of the desired product are obtained in most cases than those cited in literature using aluminum chloride(7). (b) The reaction proceeds smoothly with the formation of smaller amounts of rearranged products and tars(
. (c) The use of this catalyst affords certain manipulative advantages. 1. Temperature remains fairly constant during the entire reaction and the use of the catalyst simplifies experimental procedures. 2. Reaction may be allowed to proceed overnight without observation.
(1) Research work completed under the supervision of Dr. W, T.
Miller, Cornell University, in partial fulfillment of the requirements
for the degree of Master of Science (Thesis, 1939).
(2) Boeseken and Bastet, Rec. trav. chim., 32, 184 (1914); von Korczynski, Ber., 35, 868 (1902); Radziewanowski, ibid., 28, 1135(1895).
(3) H. Gilman, “Organic Syntheses,” Vol. 14, p. 2.
(4) The amalgamated aluminum catalyst was prepared by Washing 2 g. of granulated Aluminum metal (30 mesh) with dilute sodium hydroxide and water, then treating with 10 cc. of a 5% solution of mercuric chloride in a test-tube for two to three minutes. Small globules of mercury were visible on the surface of the aluminum after this treatment. The supernatant liquid was poured off and the catalyst washed with water, two 5-m. portions of ethyl alcohol, and several portions of dry benzene. Alternately, the benzene could be distilled from the catalyst to ensure absolutely anhydrous conditions. To activate this amalgam 3 cc. of an equal volume of the alkyl chloride to be used in the preparation was added to the amalgam in a test-tube, warmed if necessary to start the reaction and allowed to react until the gas evolution slowed down, then added quickly to the reaction flask. The activated catalyst must be used immediately.
(5) Fenske, Ind. Eng. Chem., 26, 1213 (1934).
(6) Ipatieff and Schmerling, J . Chem. Soc., 59, 1056 (1937).
(7) Schreiner, J . prakt. Chem., 81, 558 (1910); Bert, Ber., 36,
3086 (1903); Radziewanowski, ibid., 28, 1137 (1895); 33, 439 (1900),
Boedtker, Bull. Soc. Chim., 45, 647 (1929); 25, 844 (1901); 31, 966
(1904); Chem. Zentr., VIII, 12, 1112 (1904).
(
Calloway, Chem. Rev., 17, 327 (1935); Read, THIS JOURNAL,
49, 3153 (1927); 48, 1606 (1926); Wagner, Ber., 11, 1251 (1878).
