O.[Na+].[OH:3][C:4]1[CH:14]=[CH:13][C:7]([CH:8]([OH:12])[C:9]([O-:11])=[O:10])=[CH:6][CH:5]=1.[OH-].[K+].[I-].[Na+].[CH2:19](Br)[CH:20]=[CH2:21].[CH2:23](Cl)[C:24](=[CH2:26])[CH3:25]>CO>[CH2:21]([O:3][C:4]1[CH:14]=[CH:13][C:7]([CH:8]([OH:12])[C:9]([OH:11])=[O:10])=[CH:6][CH:5]=1)[CH:20]=[CH2:19].[CH2:25]([O:3][C:4]1[CH:14]=[CH:13][C:7]([CH:8]([OH:12])[C:9]([OH:11])=[O:10])=[CH:6][CH:5]=1)[C:24](=[CH2:23])[CH3:26]
20.8 g (0.10 mol) of 4-hydroxymandelic acid sodium salt monohydrate and 6.6 g (0.10 mol) of potassium hydroxide are dissolved with 1.0 g (6.7 mmol) of sodium iodide in 75 ml of methanol. Then 0.12 mol of allyl bromide (methallyl chloride in the case of methallyl) is added and the reaction mixture is refluxed for 16 hours under nitrogen. The reaction mixture is concentrated on a vacuum rotary evaporator and the residue is acidified with concentrated hydrochloric acid. The product is extracted 3 times with butyl acetate. The organic phases are washed with water, combined, dried over sodium sulfate and concentrated on a vacuum rotary evaporator. Crystallisation of the residue from toluene/petroleum ether give 4-allyloxymandelic acids such as 4-allyloxymandelic acid as an amorphous powder (70%) and 4-methallyloxymandelic acid, m.p. 121°-126° (65%).
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