Alcohols large-scale oxidations

Secondary alcohols are oxidized easily and in high yield to give ketones. For large-scale oxidations, an inexpensive reagent such as Na2Cr207 aqueous acetic acid might be used. For a more sensitive or costly alcohol, however, pyridinium chlorochromate is often used because the reaction is milder and occurs at lower temperatures. 

For large-scale oxidations of secondary alcohols and of carbohydrates by RuO cf 2.3.7. 

For natural product syntheses involving alcohols to acids cf. 2.1.3 below for large-scale oxidations cf. 2.3.7. For other examples of primary alcohol to aldehyde oxidations cited in Ch. 1 cf. 2.3.6. 

Large-Scale Oxidations of Alcohols, Carbohydrates and Diols... 

Primary and secondary alcohols are easily oxidized by a variety of reagents, including chromium oxides, permanganate, nitric acid, and even household bleach (NaOCl, sodium Oxidation hypochlorite). The choice of reagent depends on the amount and value of the alcohol. We of AI CO h OIS use cheap oxidants for large-scale oxidations of simple, inexpensive alcohols. We use the most effective and selective reagents, regardless of cost, for delicate and valuable alcohols. 

If a secondary alcohol is not easily oxidized by other methods the ruthenium(Vin) oxide catalyzed procedure is often recommended. As mentioned previously, this is a strong oxidation method which is not compatible with a number of functional groups. Sodium periodate usually serves as the stoichiometric oxidant, but sodium hypochlorite has also been used in the oxidation of secondary alcohols [94]. Because of the cheap oxidants and a straightforward work-up this reaction is well suited for large-scale oxidations [95]. The TEMPO procedure also employs a cheap stoichiometric oxidant and has been applied in the oxidation of 23 on a kilogram scale [87]. The TPAP-catalyzed method is a milder procedure and many functional groups are stable to these conditions. However, secondary alcohols are still oxidized to ketones in high yield with NMO as the co-oxidant [24]. 

On the large scale, oxidation (dehydrogenation) of secondary alcohols to ketones is usually achieved using air and a catalyst - copper oxide is an established one. Aldehydes are often prepared by hydroformylation of olefins rather than from the corresponding alcohol. However, on the smaller scale, a large and diverse number of carbonyl compounds are... 

Di-t-butyl chromate and its pyridine adduct are suitable for large-scale oxidations of alcohols to ketones, thus cyclododecanol was converted into cyclododecanone (97 Alcohols are easily separated from non-hydroxylic compounds via their calcium chloride complexes. This method was used to separate cyclododecanone and cyclododecanol and is suitable for the separation of large quantities of material." All-cis-cyclododecane-l,5,9-triol was converted into the all-cis-tri-amine by tosylation, azide substitution, and reduction, and the amine acylated with 2,3-dimethoxybenzoyl chloride to give the tri-amide, an analogue of enterochelin. ... 

Dehydrogenation. Before the large-scale availabiUty of acetone as a co-product of phenol (qv) in some processes, dehydrogenation of isopropyl alcohol to acetone (qv) was the most widely practiced production method. A wide variety of catalysts can be used in this endothermic (66.5 kj/mol (15.9 kcal/mol) at 327°C), vapor-phase process to achieve high (75—95 mol %) conversions. Operation at 300—500°C and moderate pressures (207 kPa (2.04 atm)) provides acetone in yields up to 90 mol %. The most useful catalysts contain Cu, Cr, Zn, and Ni, either alone, as oxides, or in combinations on inert supports (see Catalysts, supported) (13-16). 

Other Processes. Isopropyl alcohol can be prepared by the Hquid-phase oxidation of propane (118). It is produced iacidentaHy by the reductive condensation of acetone, and is pardy recovered from fermentation (119). Large-scale commercial biological production of isopropyl alcohol from carbohydrate raw materials has also been studied (120—123). 

One feature of this oxidation system is that it can selectively oxidize primary alcohols in preference to secondary alcohols, as illustrated by Entry 2 in Scheme 12.5. The reagent can also be used to oxidize primary alcohols to carboxylic acids by a subsequent oxidation with sodium chlorite.34 Entry 3 shows the selective oxidation of a primary alcohol in a carbohydrate to a carboxylic acid without affecting the secondary alcohol group. Entry 5 is a large-scale preparation that uses NaC102 in conjunction with bleach as the stoichiometric oxidant. 

Autoxidation may in some cases be of preparative use thus reference has already been made to the large-scale production of phenol+ acetone by the acid-catalysed rearrangement of the hydroperoxide from 2-phenylpropane (cumene, p. 128). Another example involves the hydroperoxide (94) obtained by the air oxidation at 70° of tetrahydro-naphthalene (tetralin) the action of base then yields the ketone (a-tetralone, 95), and reductive fission of the 0—0 linkage the alcohol (a-tetralol, 96) ... 

On a large scale ethylene chlorhydrin is prepared by the addition of hypochlorous acid to ethylene, by passing C02 and ethylene simultaneously into a solution of bleaching powder. Concentrated potassium hydroxide solution converts chloroethyl alcohol into ethylene oxide, by removal of HC1 ... 

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