Acetic Anhydride → (2E)-3-(3,4-Dimethylphenyl)prop-2-enoic acid

Reaction equation

[CH3:1][C:2]1[CH:3]=[C:4]([CH:7]=[CH:8][C:9]=1[CH3:10])[CH:5]=O.[C:11]([O-:14])(=[O:13])[CH3:12].[Na+].C(OC(=O)C)(=O)C>>[CH3:1][C:2]1[CH:3]=[C:4]([CH:7]=[CH:8][C:9]=1[CH3:10])/[CH:5]=[CH:12]/[C:11]([OH:14])=[O:13]

Participants

Reactant 3

HCID 7918Acetic Anhydride

HCID 222783,4-Dimethylbenzaldehyde

HCID 517045Sodium Acetate

Product 1

HCID 13548376(2E)-3-(3,4-Dimethylphenyl)prop-2-enoic acidYield 97%

Procedure

A 1 L single-neck round bottom flask equipped with a condenser, magnetic stir bar, and a nitrogen inlet was charged with 3,4-dimethylbenzaldehyde (Lancaster 97%, 70.0 g, 0.52 mol), sodium acetate (anhydrous, 47.1 g, 0.57 mol), and acetic anhydride (300 mL, 3.2 mol). The mixture was stirred and heated to reflux. After 48 hours heating was discontinued and the reaction mixture was quenched, while still hot, by the cautious addition of water (300 mL). Ice-water was added to double the volume and the mixture was extracted with diethyl ether (700 mL); the organic phase was separated, washed with water (4×1 L), dried over anhydrous magnesium sulfate, and evaporated to dryness. Recrystallization of the crude product from methanol gave trans-3,4-dimethylcinnamic acid (64.0 g, 97% purity by GC) as yellow crystals. 1HNMR (CD2Cl2, 500 MHz) δ7.74 (d, JAB=16 Hz, 1H); 7.36 (br s, 1H); 7.32 (d, JAB=8 Hz, 1H); 7.18 (d, JAB=8 Hz, 1H); 6.41 (d, JAB=16 Hz, 1H); 2.29 (s, 6H).