[CH:1]([C:4]1[CH:9]=[CH:8][C:7]([C:10](=[O:13])[CH2:11][CH3:12])=[CH:6][CH:5]=1)([CH3:3])[CH3:2].C(OCC)(OCC)[O:15][CH2:16][CH3:17].C(=O)(O)[O-].[CH2:28](O)[CH3:29]>C1(C)C=CC(S(O)(=O)=O)=CC=1.C(N(CC)CC)C>[CH2:28]([O:13][C:10]([O:15][CH2:16][CH3:17])([C:7]1[CH:8]=[CH:9][C:4]([CH:1]([CH3:3])[CH3:2])=[CH:5][CH:6]=1)[CH2:11][CH3:12])[CH3:29]
48 ml of absolute ethanol and 1 g of p-toluenesulphonic acid are placed in a round flask which is fitted with a stirrer, thermometer, condenser and dropping funnel. Now, there are added dropwise within 30 minutes while stirring 181.5 g of p-isopropyl-propiophenone and subsequently within 1 hour 152.5 g of triethyl orthoformate. The temperature is held at 30° C. by external cooling. The mixture is subsequently stirred for a further 22 hours at 20°-25° C. The mixture is then adjusted to pH 8 with 5 g of triethylamine and thereupon poured into 50 ml of 5% bicarbonate solution and 80 g of ice. The aqueous phase is separated and extracted with ether. The combined organic phases are washed with 5% bicarbonate solution and, after the addition of 0.3 g of sodium carbonate, the solvent is removed by evaporation under a vacuum and the residue is distilled over a 15 cm column. There are obtained 193.6 g of p-isopropyl-propiophenone diethyl ketal (yield: 75.1% of theory). B.p.=66° C./0.05 mmHg; nD20 =1,4778; d420 =0,9305.
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