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Often directions for the preparation of ketones by the Friedel-Crafts method from a hydrocarbon and an acid halide specify a reaction period of such length that hydrogen halide evolution ceases. These statements lead to ambiguous reaction conditions. A major difficulty is the problem of determining the point at which the hydrogen halide evolution stops. On the one hand, experience has shown that the reaction is seldom complete when there is no longer visible bubble formation a t room temperature. On the other hand, it is not possible to discern bubble formation during reflux especially if low-boiling solvents are weds2 Yet the ordinary test with ammonia shows some evolution of hydrogen halide as long as the reaction mixture is re$uxed.It has further been noted that prolonged reflux or extended reaction time actually decreases the yield of ketone beyond a certain period. This decrease in ketone is accompanied by an increase in the formation of high-boiling oxygen containing substances.In an effort to find, if possible, a method that would minimize the loss of ketone by reaction subsequent to formation, it was observed in the synthesis of acetophenone that the residues consisted primarily of dypnone which had resulted from the condensation of two molecules of acetophenone. CHI AlClS GHs-L -0 + CHs-C-GHs + CHa I II CsHs-hC-C-C a s I II H OCloser examination of this reaction revealed the fact that it is one that will take place to an extent approximating completeness only when the ketone is present in excess of molar quantities as compared with the aluminum chloride. Two moles of acetophenone per mole of aluminum chloride gave the highest yields (73%). Quan-(1) This work w8s initiated while one of us was a faculty member (2) Calloway, Chcm. Rev., 17, 327 (1935).at Tuskegn Institute. AND LOUIS D. GREENtities of aluminum chloride in excess of 1 mole per mole of acetophenone were essentially without effect in bringing about the reaction. Any excess of simple ketone beyond 2 moles tended to produce high molecular weight, viscous gums, and to reduce markedly the yield of dypnone. At low temperatures the condensation proceeds quite slowly and the formation of the gummy residues which are always present in small quantities when the reaction takes place a t room temperature is strongly inhibited. At 40-50' the time for the reaction is shortened and the residue is markedly increased. Stirring has little effect..Although hydrogen chloride is evolved continually during any period of heating of acetophenone and aluminum chloride, the simple explanation that the condensation is promoted by hydrogen halide is not tenable. This general type of condensation may be promoted by hydrogen halidesla it is true, but also by alkalie~,~ heat,& radiation, zinc alkyls17 organoaluminum halides,* acetic anhydride,Q sulfuric acid,g sodium pyrosulfate, lo sodamide, l1 and aluminum and alkyl halides. l2The fact that the three valences of aluminum in aluminum chloride are occupied by chlorine atoms seemed incidental to the process of condensation. ...

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