- Mechanistic Insights into the Aerobic Oxidation of Aldehydes: Evidence of Multiple Reaction Pathways during the Liquid Phase Oxidation of 2-Ethylhexanal
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The liquid-phase aldehyde oxidation by molecular oxygen (autoxidation) has been known for about 2 centuries and is a critical organic transformation in both industrial applications and academic research. However, the general reaction pathway proposed for the aerobic oxidation of aldehydes into the corresponding carboxylic acid exhibits some inconstancies, in particular, for β-substituted aliphatic aldehydes. Thus, the liquid-phase aerobic oxidation of 2-ethylhexanal was further studied in acetonitrile at 20 °C with O2 at atmospheric pressure. By precisely monitoring the primary intermediate (peracid), product (carboxylic acid), and byproducts as a function of time and catalysts used, we demonstrated the pivotal role of the acylperoxy radical. The direct formation of peracid and carboxylic acid from the latter was highlighted by analyzing the composition of the reaction mixture at low conversion. Peracid could be converted into carboxylic acid by metal catalysts or through reaction workup. Consequently, the commonly accepted pathway of aerobic oxidation of aldehyde via a Criegee intermediate can be overlooked under these conditions.
- Vanoye, Laurent,Favre-Réguillon, Alain
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p. 335 - 346
(2022/02/10)
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- A safe and efficient flow oxidation of aldehydes with O2
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A safe, straightforward, and atom economic approach for the oxidation of aliphatic aldehydes to the corresponding carboxylic acids within a continuous flow reactor is reported. Typically, the reaction is performed at room temperature using 5 bar of oxygen in PFA tubing and does require neither additional catalysts nor radical initiators except for those already contained in the starting materials. In some cases, a catalytic amount of a Mn(II) catalyst is added. Such a flow process may prove to be a valuable alternative to traditionally catalyzed aerobic processes.
- Vanoye, Laurent,Aloui, Asma,Pablos, Mertxe,Philippe, Regis,Percheron, Aurelien,Favre-Reguillon, Alain,De Bellefon, Claude
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supporting information
p. 5978 - 5981
(2014/01/06)
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- Oxidative degradation of fragrant aldehydes. Autoxidation by molecular oxygen
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The oxidative degradation of fragrant aldehydes by molecular oxygen has been investigated. The oxygen consumption was monitored and the bond dissociation energy (BDE) of the aldehyde C(O)-H bond were calculated by DFT method. The oxidation products were identified by GC/MS. The different pathways accounting for the oxidative degradation are discussed. The main product is the acid, beside the formate ester. Both oxidation products result from the Baeyer-Villiger reaction involving a peracid R(CO)OOH whereas minor products arise from the hydroperoxide ROOH intermediate derived either from the acyl peroxy radical, R(CO)OO or from the decarboxylation of the peracid RC(O)OOH.
- Marteau,Ruyffelaere,Aubry,Penverne,Favier,Nardello-Rataj
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p. 2268 - 2275
(2013/04/10)
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- Experimental and computational studies on solvent effects in reactions of peracid-aldehyde adducts
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Solvent effects on liquid phase oxidation of aldehydes by dioxygen and m-chloroperbenzoic acid were studied experimentally. The main products were the corresponding carboxylic acid and a formate ester formed by Baeyer-Villiger rearrangement. In alcohol solvents (particularly methanol) substantially higher acid to formate ratios were formed than in solvents not capable of forming hydrogen bonds. Formation of both main products can be rationalised via rearrangement reactions of two epimeric peracid-aldehyde adducts, of which the interactions with methanol were studied computationally employing DFT methods at the DNPP level with the Spartan program (v5.0). The calculations indicate that structures of the adducts rearranging to give two equivalents of acid resemble the transition state of the reaction more than structures of the epimeric adducts rearranging to the acid and formate ester in 1:1 ratio. Therefore, the enhanced favor of the formation of acid in the presence of methanol can be explained in the light of Hammond's postulate.
- Lehtinen, Christel,Nevalainen, Vesa,Brunow, G?sta
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p. 4741 - 4751
(2007/10/03)
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- Factors affecting the selectivity of air oxidation of 2-ethyhexanal, an α-branched aliphatic aldehyde
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Various solvents and metal catalysts were tested in air oxidation of 2-ethylhexanal to elucidate the effects of different variables on the reaction path of the substrate. The primary goal was to determine the optimal conditions for maximising the yield of carboxylic acid and minimising the formation of other products. Solvents and catalysts both had a significant impact on the product distribution. The best selectivity of 2-ethylhexanal to 2-ethylhexanoic acid, 84%, was obtained with octanoic acid as solvent and manganese(II) acetate as catalyst. Addition of an aromatic aldehyde, benzaldehyde, or p-methoxybenzaldehyde retarded the oxidation rate of both 2-ethylhexanal and aromatic aldehyde dramatically.
- Lehtinen, Christel,Brunow, Goesta
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p. 544 - 549
(2013/08/07)
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- Experimental and computational studies on substituent effects in reactions of peracid-aldehyde adducts
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Liquid phase oxidation of six branched and four linear aldehydes by dioxygen and m-chloroperbenzoic acid was studied experimentally. 2-Substituted (α-branched) aldehydes reacted to give formates (via Bayer-Villiger mechanism) whereas the related linear saturated aldehydes were converted to the corresponding carboxylic acids. Formation of both these products can be rationalized via rearrangement reactions of peracid-aldehyde adducts 1. Computational studies employing DFT methods at the DNPP level with the Spartan program (v5.0) were carried out in order to understand properties of those adducts. Conformational properties of the adducts 1 were found to shed light on the differences observed in the reactions of linear and branched adducts. (C) 2000 Elsevier Science Ltd.
- Lehtinen, Christel,Nevalainen, Vesa,Brunow, G?sta
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p. 9375 - 9382
(2007/10/03)
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- Epoxldation of terminal alkenes with oxygen and 2-ethyl hexanal, without added catalyst or solvent
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Two terminal alkenes, 1-decene and methyl 10-undecenoate, were epoxidized with oxygen using 2-ethyl hexanal as coreactant without any added solvent. Under optimal conditions, the yield of methyl 10, 11-epoxyundecanoate was 98.7%. 2-Ethyl hexanal was oxidized mainly to 2-ethyl hexanoic acid and also formed some byproducts. The tested metal complexes retarded the epoxidation reaction slightly and increased the amount of byproducts of 2-ethyl hexanal.
- Lehtinen, Christel,Brunow, C?sta
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p. 101 - 103
(2013/09/08)
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