Aerobic Oxidation of Benzylic Halides to Carbonyl Compounds with Molecular Oxygen Catalyzed by TEMPO/KNO₂ in Aqueous Media

Abstract

Benzylic halides were successfully oxidized to the corresponding aldehydes and ketones in good to excellent yields in aqueous media with molecular oxygen as oxidant in the presence of catalytic amounts of TEMPO (2,2,6,6-tetramethylpiperidyl-1-oxy) and potassium nitrite (KNO₂).

Keywords:

• Benzylic halide
• oxidation
• potassium nitrite
• TEMPO

Notes

^a Reaction conditions: 4-isopropylbenzyl bromide (0.5 mol), reflux, under O₂ atmosphere.

^b Conversions are based on the GC with area normalization.

^c Isolated yields.

^d 30 g cumenic acid was obtained from the distillated residue.

^e The main product (76%) was 4-isopropylbenzyl alcohol.

^a Reaction conditions: halide (0.5 mol), KNO₂ (25 mmol), TEMPO (15 mmol), H₂O (30 mol), reflux, under O₂ atmosphere. In the case of chloride, 10 mol% KBr (50 mmol) was added.

^b Isolated yield.

^c Partial polymerization occurred with vacuum distillation.

^d 1-(Dimethoxymethyl)4-methoxybenzene (23%) and 4,4-oxy-bis-(methylene)diphenol (28%) were formed as two by-products.

^e 45% of starting material was recovered.

^f 5-Bromo-thiophene-2-aldehyde was formed as major by-product in 4.5%.

^g An intractable mixture.

^h No oxidation reaction was observed.