[OH:1][C:2]1[CH:7]=[CH:6][C:5]([CH2:8][CH2:9][CH:10]=[O:11])=[CH:4][CH:3]=1.CC(C)=[O:14].OS(O)(=O)=O.O=[Cr](=O)=O>CC(C)=O>[OH:1][C:2]1[CH:3]=[CH:4][C:5]([CH2:8][CH2:9][C:10]([OH:14])=[O:11])=[CH:6][CH:7]=10.79 g (5.19 mmoles) of 3-(4-hydroxyphenyl)-1-propanal were dissolved in acetone (20 ml) and Jones reagent (chromic anhydride in sulphuric acid) (8 ml) was added to it drop by drop until the yellow-brown colour persisted. The solution was stirred for one hour at 0° C. The excess reagent was destroyed with methanol and the solution was filtered and evaporated at reduced pressure. The residue was extracted in ethyl acetate, dried over anhydrous sodium sulphate and concentrated, diving an impure residue (0.6470 g), which was chromatographed over silica gel, obtaining 0.545 g (63.1% yield) of 3-(4-hydroxyphenyl) propionic acid. Recrystallisation in methanol gave m.p.=121° C.
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