Org. Synth. 1932, 12, 16
DOI: 10.15227/orgsyn.012.0016
DESOXYBENZOIN
Submitted by C. F. H. Allen and W. E. Barker.
Checked by C. S. Marvel and Tse-Tsing Chu.
1. Procedure
To 68 g. (0.5 mole) of phenylacetic acid (Note 1) in a 1-l. flask fitted with a reflux condenser and a system for absorbing hydrogen chloride, is added 35 g. (0.25 mole) of phosphorus trichloride. The mixture is heated on a steam bath for one hour. While the contents of the flask are still warm, 400 cc. of dry benzene is added. The benzene solution of phenylacetyl chloride is decanted from the residue of phosphorous acid onto 75 g. (0.56 mole) of anhydrous aluminum chloride in a dry, 1-l. flask which can be fitted to the same condenser. The reaction is vigorous at first and cooling is necessary. The mixture is refluxed for one hour on a steam bath, then cooled and poured into a mixture of 500 g. of cracked ice and 200 g. of concentrated hydrochloric acid. The benzene layer is separated, and the aqueous layer is extracted once with a mixture of 100 cc. of benzene and 100 cc. of ether (Note 2). The ether-benzene solution is washed once with 100 cc. of water (Note 3), and then dried over 40–50 g. of calcium chloride. The solution is filtered (Note 4) with suction into a 1-l. Claisen flask, and the solvent is removed by distillation under reduced pressure (Note 5); the residue consists of a brown oil which solidifies on cooling.
The crude material (91–92 g.) is purified by distillation under reduced pressure from a 250-cc. Claisen flask (Note 6). The product distils at 160°/5 mm. (172°/15 mm.; 200°/30 mm.) as a colorless oil which solidifies on cooling. The yield is 81–82 g. (82–83 per cent of the theoretical amount based on the phenylacetic acid used) of a product which melts at 53–54°. The product is recrystallized from methyl alcohol, using 4 cc. of solvent for each gram of product (Note 7); the yield is 55–56 g. of crystals melting at 55–56°. An additional 7 g. of crystals melting at 55–56° is obtained by cooling the filtrate in an ice-salt bath. On further cooling of the mother liquors, about 5 g. of crystals melting at 54–55° is obtained. The total yield of purified product is 67–70 g. (Note 8). Further recrystallization of the product from methyl alcohol does not raise the melting point above 55–56°.
2. Notes
1.
Directions for preparing
phenylacetic acid are given in
Org. Syn. Coll. Vol. I, 1941, 436. A very high grade of
phenylacetic acid can also be obtained from companies supplying essential oils and perfumers' supplies, and some of the acid from these commercial sources is superior to that prepared by the Organic Syntheses procedure. Since the quality of the
desoxybenzoin depends upon the quality of the
phenylacetic acid used, it is important to employ a superior grade of acid.
2.
A mixture of
benzene and
ether is used instead of
ether alone because a more efficient separation of the two layers is obtained.
3.
Washing with
sodium hydroxide at this point does not improve the quality of the product but does, as a result of the formation of emulsions, cause an 8–10 per cent loss in yield.
4.
It is better to remove the
calcium chloride by filtration than by decantation even though the solution looks clear. Small particles of
calcium chloride and
aluminum chloride not removed from the solution may cause bumping or even decomposition during the distillation.
5.
Removal of the solvent by distillation under reduced pressure on the steam bath makes fractionation unnecessary during distillation of the product.
6.
It is necessary to use a Claisen flask with a wide side-arm, since the
desoxybenzoin may solidify and clog the apparatus. The distillation under reduced pressure is quiet if directions are followed carefully.
7.
Methyl alcohol is the best solvent for purification.
Desoxybenzoin tends to separate from
ethyl alcohol as an oil.
8.
Desoxybenzoin is somewhat unstable to light and consequently must be stored in
dark bottles.
3. Discussion
Because of the availability of the starting materials, the most convenient methods of preparing
desoxybenzoin are the Friedel-Crafts reaction,
1 described above, and the reduction of
benzoin.
2 Desoxybenzoin can also be prepared, often with very good yields, by the treatment of
bromostilbene with water in a
sealed tube at 180–190°;
3 by the reduction of
benzil;
4 by the action of
zinc and
hydrochloric acid on
chlorobenzil;
5 from
benzene,
phenylacetic acid, and
phosphorus pentoxide;
6 from
benzoyl chloride and the
magnesium halide derivative of sodium phenylacetate;
7 from
benzylmagnesium chloride and
benzamide;
8 and by alkaline hydrolysis of
desylthioglycollic acid.
9This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Desoxybenzoin
ethyl alcohol (64-17-5)
calcium chloride (10043-52-4)
hydrogen chloride,
hydrochloric acid (7647-01-0)
Benzene (71-43-2)
methyl alcohol (67-56-1)
ether (60-29-7)
sodium hydroxide (1310-73-2)
benzoyl chloride (98-88-4)
benzamide (55-21-0)
aluminum chloride (3495-54-3)
Benzil (134-81-6)
Benzoin (119-53-9)
zinc (7440-66-6)
Phenylacetic acid (103-82-2)
phosphorus trichloride (7719-12-2)
benzylmagnesium chloride (6921-34-2)
phenylacetyl chloride (103-80-0)
bromostilbene
chlorobenzil
sodium phenylacetate (114-70-5)
desylthioglycollic acid
phosphorous acid (13598-36-2)
phosphorus pentoxide (1314-56-3)
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