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	All posts		Subject: Oxidation of mandelic acid to benzaldehyde etc.		Please login to post

		moo (Hive Bee) 09-18-03 07:55 No 459724				Oxidation of mandelic acid to benzaldehyde etc. (Rated as: excellent)
						Acta Chem. Scand. B38(4), 343-344 (1984) Oxidation of alpha-Hydroxy Carboxylic Acids with Sodium Hypochlorite General Procedure. A solution containing 10 mmol of the alpha-hydroxy carboxylic acid in 25 ml of diethyl ether was cooled in an ice-bath. Then 40 ml of a commercial bleach solution (containing 4.2% sodium hypochlorite and 0.5% sodium hydroxide), 22 mmol, was added over a 3 min period. The reaction mixture was then allowed to warm up to room temperature for 2-3 h. The organic layer was separated, washed with water, dried over anhydrous magnesium sulfate and the solvert evaporated. The crude product was purified by molecular distillation or recrystallization. Entry Substrate Reaction time, h Product Yield, % 1 PhCHOHCOOH 2 PhCHO 95 2 Ph2CHOHCOOH 1 (Ph)2CO 91 3 PhC(CH3)OHCOOH 1 PhCOCH3 93 4 C6H11CHOHCOOH 2 C6H11CHO 85 5 (CH3)2CHCHOHCOOH 2 (CH3)2CHCHO 47 6 PhCHOHCOONa 2 PhCHO 93 7 5-androsten-3beta,17alpha-diol-17-carboxylic acid 3 5-androsten-3beta-ol-17-one 85 A modification comes to mind. If the benzaldehyde to be prepared is a water-insoluble solid (such as piperonal), and the sodium salt of the corresponding mandelic acid is water-soluble enough, it might be possible to omit the organic phase from the reaction and filter the precipitated benzaldehyde from the reaction mass. The procedure posted could come in handy for those wishing to prepare benzaldehydes from mandelic acids, which can be prepared from the corresponding benzenes. The route is a close cousin of the chloral route. Related posts/threads: Post 226201 (Bwiti: "3,4-methylenedioxymandelic acid", Chemistry Discourse) Post 328397 (demorol: "Piperonal synthesis", Novel Discourse) Especially the following ref is a must-read for those interested in the preparation of piperonal from benzodioxole via 3,4-methylenedioxymandelic acid, or any other benzaldehyde. Org. Proc. Res. Dev. 4, 534-543 (2000) (https://www.rhodium.ws/pdf/md-mandelic2piperonal.pdf) It is a pity glyoxylic acid is a bitch to purify. fear fear hate hate

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Date: 11-27-24, Release: 1.6 (10-04-15), Links: static, unique