Aldehydes green oxidation

Chromic acid test. Aldehydes are oxidized to carboxylic acids by chromic acid ketones are not oxidized. A positive test results in the formation of a blue-green solution from the brown-red color of chromic acid. 

Yamaguchi K, Kobayashi H, Wang Y, Oishi T, Ogasawara Y, Mizuno N (2013) Green oxidative synthesis of primary amides from primary alcohols or aldehydes eatalyzed by a... 

Zhang Y, Zhao G, Zhang Y, Huang X. Highly efficient visible-hght-driven photoelectro-catalytic selective aerobic oxidation of biomass alcohols to aldehydes. Green Chem. 2014 16 3860-3869. 

The central carbon atom is derived from an aromatic aldehyde or a substance capable of generating an aldehyde during the course of the condensation. Malachite green is prepared by heating benzaldehyde under reflux with a slight excess of dimethyl aniline in aqueous acid (Fig. 2). The reaction mass is made alkaline and the excess dimethylaniline is removed by steam distillation. The resulting leuco base is oxidized with freshly prepared lead dioxide to the carbinol base, and the lead is removed by precipitation as the sulfate. Subsequent treatment of the carbinol base with acid produces the dye, which can be isolated as the chloride, the oxalate [2437-29-8] or the zinc chloride double salt [79118-82-4]. 

Ten Brink et al. (2000) have shown how biphasic systems, sometimes with the sparingly soluble alcohols as one phase and an aqueous phase as the other phase, benefit from the strategy for air oxidation to aldehydes/ketones by using water soluble Pd complex of bathophenanthroline disulphonate. This is a nice example of green technology. 

Vitamin Ai (retinol) is derived in mammals by oxidative metabolism of plant-derived dietary carotenoids in the liver, especially -carotene. Green vegetables and rich plant sources such as carrots help to provide us with adequate levels. Oxidative cleavage of the central double bond of -carotene provides two molecules of the aldehyde retinal, which is subsequently reduced to the alcohol retinol. Vitamin Ai is also found in a number of foodstuffs of animal origin, especially eggs and dairy products. Some structurally related compounds, including retinal, are also included in the A group of vitamins. 

The system (4- Bu-pyH)3[Ru(0)3Cl ]/NM0/PMS/CH2Cl3 catalysed the oxidation of primary alcohols to aldehydes and of secondary alcohols to ketones like TRAP (Tables 2.1 and 2.2), such oxidations did not attack double bonds. As stoich. trans-(PPh )2[Ru(0)2Cl ] -/CH3CN it is a two electron oxidant for alcohols [561]. For tran -[Ru(0)2Cy - in solution the effective oxidant or oxidant precursor is [Ru(0)2Cl3]", and this species is coordinatively unsaturated. That this is the case is suggested by the observation that addition of extra Cl" (as (PPh )Cl) to the green [Ru(0)2Cl3]" in solution (Eq. 1.4) generating the red franx-[Ru(0)3Cl ] ", a markedly less effective catalytic oxidant for alcohols than [Ru(0) Cl ]" [561]. 

In continuous processing, the aldehyde product is removed from the reaction before any over-oxidation can occur, offering significant Green Chemistry advantages. This is shown diagramahcally in Scheme 11.6. 

Oxidation-Reduction in Blood Analysis Demonstrating the Reaction in a Breathalyzer," J. Chem. Educ., Vol. 67,1990, 263. The oxidation of a primary alcohol by the orange dichromate ion is shown to first form an aldehyde, then a carboxylic acid, and green chromium(III) ion. The use of this reaction, principles of spectrometry, and gas laws in a commercial device for measuring blood-alcohol content are discussed. 

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