Preparation and Rearrangement of 2,3-Diphenyl-2,3-butanediol The formation of pinacols and their aeid-catalyzed rearrangements to ketones are topics covered in most organic chemistry texts, many laboratory manuals, and on several occasions this Journal (1-3). We have found that the title reactions constitute an interesting experiment and a convenient system for demonstrating migratory aptitudes. The photochemical reductive dimerimtion of acetophenone (I) affords a mixture of dl and meso diols (41,which is used directly in the next step. Other methods for the preparation of I1 are known ( 5 , 6 ) ,and the diastereomers have been separated and characterized (6.7). Rearrangement of I1 yields only I11 (8);none of the isomer IVis observed. An attractive feature of the present system is the variety of direct methods for distinguishing between I11 and IV. Experimental To a 50-ml Erlenmeyer flask are added I (2.0 g), glacial acetic acid ( 1 drop), and 2-propanol (volume t o fill flask). The flask is capped with a rubber serumstopper (wired), leaving the smallest possible air bubble. The solution is irradiated one week: similar results were obtained with either a oair of 275-Watt sunlamos or a Ravonet RMR-400 reactor. The oroeress
be recyrstaliized from ethanol-water. 3.3-Diphenyl-2-butonone(III):mp 4041°C, bp 13Z°C (1mm); ir (CC14) 1709 em-' (9); nmr (DCCld 6 1.84 s (3H), 2.05 s (3H), 7.23 m (10H); iodoform test, positive; oxime, mp 149-151°C; 2,4-DNP, mp 132'C. 2-Methyl-1,2-diphenyl-1-propanone(IV): mp 45-4fiPC, hp 126-130°C (1mm);ir (CCII) 1686 cm-' (9); nmr (DCC13) d 1.58 s (6H), 7.37 m (10H); iodoform test, negative; oxime, mp 192-193'C; 2,4-DNP, mp 154%. We thank Professor L. Giral (Montpellier) far an authentic sample of IV ( 9 ) . Llterature Cited
(9) Crm.G..and Gird. L..Rull.Soc. Chim. Franei., 1115 (19701.
Williams College Williamstown, Massachusetts 01267
344 1 Journal of Chemical Education
J. Hodge Markgraf Thomas A. Newton
