PCT No. PCT/EP97/05186 Sec. 371 Date Apr. 1, 1999 Sec. 102(e) Date Apr. 1, 1999 PCT Filed Sep. 22, 1997 PCT Pub. No. WO98/14441 PCT Pub. Date Apr. 9, 1998A process for preparing phthalides of the general formula I, where R1, R2, R3 and R4 are independently hydrogen, C1-C4-alkyl or C1-C4-alkoxy, by hydrogenating phthalic anhydrides of the general formula II, where R1, R2, R3 and R4 are each as defined above, with hydrogen in the presence of suspended catalysts of the Raney type in a hydrogenation apparatus by using a mixing apparatus to mix a liquid phase, which includes the catalyst and the phthalic anhydride used and resulting phthalide, and a gas phase, which includes the hydrogenating hydrogen, comprises using the mixing apparatus to introduce a mixing intensity of at least 50 W/l into the liquid phase.