Oxidation of primary alcohols to aldehydes

Catalytic dehydrogenations of primary alcohols are achieved by passing vapors of the alcohols at 275-350 °C over a catalyst, usually supported on asbestos, silica gel, pumice, etc. Ethyl alcohol is converted into acetaldehyde in 88% yield at 93% conversion by passing it at 275 °C over a mixture of oxides of copper, cobalt, and chromium on asbestos [1135]. 

Over copper chromite on Celite (diatomaceous earth) at 300-350 °C, aliphatic alcohols with three to eight carbons are converted into aldehydes in 53-67% yields [354. Catalytic dehydrogenations over copper, silver, or both [7, 345] are carried out in a current of an insufficient amount of air or oxygen at 300-380 °C and give aldehydes in yields ranging from 70 to 100%. An example of an industrial dehydrogenation is the conversion of methallyl alcohol into methacrolein [4] (equation 204). 

Vapor-phase dehydrogenation of primary alcohols to aldehydes takes 

The vapor-phase dehydrogenations just mentioned are applicable only to the preparation of aldehydes that tolerate such high temperatures. A catalytic oxidation of alcohols carried out by passing a current of air or oxygen through solutions of alcohols in solvents such as heptane [56] or ethyl acetate [55] in the presence of platinum [55, 56], or, better still, platinum dioxide [56], or active cobalt oxide [1136 is applicable even to alcohols that cannot be vaporized and that contain double bonds (equation 205) [56]. 

Both aliphatic and aromatic alcohols, as well a s unsaturated alcohols, are oxidized in the liquid phase with argentic oxide in nitric or acetic acid at temperatures from -10 through 60 °C [5S6]. 

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To the synthetic chemist the most important of the reactions m Table 17 1 are the last two the oxidation of primary alcohols to aldehydes and secondary alcohols to ketones Indeed when combined with reactions that yield alcohols the oxidation methods are so versatile that it will not be necessary to introduce any new methods for preparing aide hydes and ketones in this chapter A few examples will illustrate this point... 

Oxidation of primary alcohols to aldehydes (Section 15.10) Pyridinium dichromate (PDC) or pyridinium chloro-chromate (PCC) in anhydrous media such as dichloromethane oxidizes primary alcohols to aldehydes while avoiding overoxidation to carboxylic acids. 

Dipyridiue-chromium(VI) oxide2 was introduced as an oxidant for the conversion of acid-sensitive alcohols to carbonyl compounds by Poos, Arth, Beyler, and Sarett.3 The complex, dispersed in pyridine, smoothly converts secondary alcohols to ketones, but oxidations of primary alcohols to aldehydes are capricious.4 In 1968, Collins, Hess, and Frank found that anhydrous dipyridine-chromium(VI) oxide is moderately soluble in chlorinated hydrocarbons and chose dichloro-methane as the solvent.5 By this modification, primary and secondary alcohols were oxidized to aldehydes and ketones in yields of 87-98%. Subsequently Dauben, Lorber, and Fullerton showed that dichloro-methane solutions of the complex are also useful for accomplishing allylic oxidations.6... 

Compared with ketoreductases, the synthetic application of alcohol oxidases has been less explored. However, selective oxidation of primary alcohols to aldehydes is superior to the chemical methods in terms of conversion yields, selectivity, and environmental friendliness of reaction conditions. In addition, coupling of alcohol oxidase with other enzymes provides a tremendous opportunity to develop multi-enzyme processes for the production of complex molecules. Therefore, a growing impact of alcohol oxidases on synthetic organic chemistry is expected in the coming years. 

Oxidation of ascorbate (reduction of 02 to H20) Oxidation of primary alcohols to aldehydes in sugars (reduction of 02 to 11202) Removal of amines and diamines Electron-transfer... 

Oxidation, of primary alcohols to aldehydes, 52, 5 of terminal olefins with chromyl chloride, 51, 6 of 2,4,4-trimethyl-1-pentene with chromyl chloride, 51, 4 with chromium trioxide-pyridine complex, 52, 5... 

TEMPO 2,2,6,6-Tetramethylpiperidinyl-1-oxy (20 TEMPO) works as a mediator for the oxidation of primary alcohols to aldehydes. The oxidation of secondary alcohols is much slower than that of primary alcohols as exemplified by the oxidation of (19) to (21) (Scheme 7) [48]. Active species is the oxo-ammonium generated from TEMPO. 

Scheme 35 Oxidation of primary alcohols to aldehydes with nickel(lll) as mediator.

A better reagent for oxidation of primary alcohols to aldehydes in good yield is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl. 

M. Hasan, M. Musawir, P. N. Davey, I. V. Kozhevnikov Oxidation Of Primary alcohols to aldehydes with Oxygen Catalyzed by Tetra-n-propyl ammonium perruthenate,, J. Mol. Catal. A Chem. 180 (2002) 77-84. 

R A General Synthetic Method for the Oxidation of Primary Alcohols to Aldehydes S(+)-2-Methylbutanal... 

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]. 

Aerobic oxidation of primary alcohols to aldehydes and secondary alcohols to ketones was accomplished in ionic liquids (bmim, l-butyl-3-methyl-imidazolium cation) as RuCl2(PPh3)j/(bmim)V80°C RuClj or [RuCl Cp-cymene)] were also used... 

Abstract This is one of the most important classes of oxidation effected by Ru complexes, particnlarly by RnO, [RuO ] , [RnO ] and RuCljCPPhj), though in fact most Ru oxidants effect these transformations. The chapter covers oxidation of primary alcohols to aldehydes (section 2.1), and to carboxylic acids (2.2), and of secondary alcohols to ketones (2.3). Oxidation of primary and secondary alcohol functionalities in carbohydrates (sugars) is dealt with in section 2.4, then oxidation of diols and polyols to lactones and acids (2.5). Finally there is a short section on miscellaneous alcohol oxidations in section 2.6. 

Typical examples are listed in Table 2.1. A few oxidations are effected by RuO but in general it is too powerful an oxidant for this purpose. The system RuCyaq. NaCl-CCy Pt anode oxidised benzyl alcohol to benzaldehyde and benzoic acid and p-anisaldehyde to p-anisic acid [24], and a wide range of primary alcohols and aldehydes were converted to carboxylic acids, secondary alcohols to ketones, l, -diols to lactones and keto acids from RuOj/aq. NaCl pH 4/Na(H3PO )/Pt electrodes (Tables 2.1-2.4). The system [RuO ] "/aq. K3(S303)/Adogen /CH3Cl3 oxidised benzyhc alcohols to aldehydes [30]. The oxidation catalyst TPAP (( Pr N)[RuO ]) (cf. 1.3.4) is extremely useful as an oxidant of primary alcohols to aldehydes and secondary alcohols to ketones without... 

For a synthesis of the anti-cancer drug taxol TPAP/NMO was used in three steps, two for oxidation of primary alcohols to aldehydes (by TPAP/NMO/PMS/ CHjClj) and one for a secondary alcohol to ketone (by TPAP/NMO/PMS/CHjClj-CHjCN) [66], cf. also [111] and for the SERCA inhibitor thapsigargin (two primary alcohol and one secondary alcohol oxidation steps) [112], This system was also used during synthesis of the cholesterol biosynthesis inhibitor 1233A [52], the antibiotic and anti-parasitic ionophore tetronasin [113, 114] and for the cytotoxic sponge alkaloids motopuramines A and B [115]. 

COPPER(II) CATALYZED OXIDATION OF PRIMARY ALCOHOLS TO ALDEHYDES WITH ATMOSPHERIC OXYGEN... 

Copper(II) complex 1 selectively catalyzes the oxidation of primary alcohols to aldehydes in high yields by atmospheric oxygen in the presence of 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO).This procedure does not require an... 

In conclusion, a novel procedure has been described for the oxidation of primary alcohols to aldehydes.This method can be used for the selective oxidation of... 

Material 3 has been found to serve as a highly effective and clean catalyst for the oxidation of primary alcohols to aldehydes with a superior performance over that of the previously reported polymer based system (PSP). The oxidations, using our previously published protocol, produced the corresponding aldehydes in less than three hours using a 10 wt% of solid catalyst,22 significantly, the aldehydes were free of contaminants. 

Uhromic acid, in a variety of acidic media, has been used extensively for the oxidation of primary alcohols to aldehydes Itul. rarely has provided aldehydes in greater than 50% yield.5 Uhromium trioxide in pyridine was introduced as a unique, hniiacidic reagent for alcohol oxidations and has been used extensively to prepare ketones, but has been applied with only limited success to the preparation of aldehydes. While o-metlmxybenzaldehyde was obtained in 89% yield, 4-nitro-beir/.uldehyde and n-heptanal were obtained in 28% and 10% yields, respectively.7... 

The most widely used chromium(VI)-oxo reagents for synthetic use in organic chemistry are the Collins reagent, Cr03(py)2,273 and the Corey reagent, Cr03CrpyH+,297 with the latter being superior for the oxidation of primary alcohols to aldehydes.275... 

A GENERAL SYNTHETIC NETHOD FOR THE OXIDATION OF PRIMARY ALCOHOLS TO ALDEHYDES (S)-(+)-2-METHYLBUTANAL (Butanal, 2-methyl-, (S)-)... 

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