[OH-].[K+].O.[CH3:4][C:5]1[CH:6]=[C:7]([CH:10]=[CH:11][CH:12]=1)[CH:8]=O.[CH:13](=[O:16])[CH2:14][CH3:15]>C(O)CO>[CH3:15]/[C:14](=[CH:8]\[C:7]1[CH:10]=[CH:11][CH:12]=[C:5]([CH3:4])[CH:6]=1)/[CH:13]=[O:16]A solution of potassium hydroxide (24 g, 0.36 mol, 0.6 eq, with a purity of 85%) in ethylene glycol (120 g) and water (12 g) was charged into a 500 mL three-necked round-bottom flask equipped with a reflux condenser and a mechanical stirrer. 3-methyl benzaldehyde (70 g, 0.59 mol) was added dropwise. The stirred reaction mixture was heated at 38-42° C. and propionaldehyde (41 g, 0.71 mol, 1.2 eq) was dosed in over 3.25 h. After a further hour at 40° C., the reaction mixture was cooled to ambient temperature and the two layers separated. The organic layer thus obtained was washed with water (2×100 mL), dried over magnesium sulphate and concentrated. The resulting crude product was distilled via a Vigreux column (1.0 mBar, 87-92° C.), to give (2E)-2-methyl-3-(3-methylphenyl)acrylaldehyde (65.9 g, gc purity>95%; yield 70%).
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