Carbonyl compounds alcohols oxidation

Aldehydes and ketones are usually prepared on insoluble supports by the acylation of arenes, C,H-acidic compounds, or organometallic reagents. Alcohols or other substrates can also be converted into carbonyl compounds by oxidation (Figure 12.1). Linkers that enable the generation of aldehydes and ketones upon cleavage from a support are considered in Section 3.14. 

NR = nonreactive toward hydrocarbons PO = oxidation of phosphines to phosphine oxides MF — peroxometallacyclic adduct formation with cyanoalkenes NSE — nonstereoselective epoxidation SE=stereoselective epoxidation AE = asymmetric epoxidation HA- hydroxylation of alkanes HB=hydroxylation of arenes OA = oxidation of alcohols to carbonyl compounds K = ketonization of Lermina 1 alkenes SO oxidation of S02 to coordinated S04 MO = metallaozonide formation with carbonyl compounds I = oxidation of isocyanides to isocyanates. 

Ozonolysis allows the cleavage of alkene double bonds by reaction with ozone. Depending on the work up, different products may be isolated reductive work-up gives either alcohols or carbonyl compounds, while oxidative work-up leads to carboxylic acids or ketones. 

Reduction of carbonyl compounds and oxidation of alcohols have always been key transformations of organic chemistry. In both cases, the use of stoichiometric toxic reagents is still widespread and new methods and catalysts offering greater activity, selectivity, and safeness are constantly being sought. 

Fig. 17.10. Mechanism of the Cr(VI) oxidation of alcohols to carbonyl compounds. The oxidation proceeds via the chromium(VI) acid ester A ("chromic acid ester") and yields chromium(IV) acid. The chromium(IV) acid may either disproportionate in an "inorganic" reaction or oxidize the alcohol to the hydroxy-substituted radical B. This radical is subsequently oxidized to the carbonyl compound by Cr(VI), which is reduced to Cr(V) acid in the process. This Cr(V) acid also is able to oxidize the alcohol to the carbonyl compound while it is undergoing reduction to a Cr(III) compound.

Unsaturated carbonyl compounds by oxidative fragmentation of y-tributylstannyl alcohols induced by IOB.BF3/ DCC [21]... 

NR s not reactive toward hydrocarbons S = stereoselective epoxidation E = epoxidation HA = hydroxylation of alkanes OA = oxidation of alcohols to carbonyl compounds PO oxidation of phosphines to phosphine oxides OC = oxidative cleavage of alkenes K= ketonization of alkenes DO = hydroxylation of alkenes to diols AO al1ylic oxidation of alkenes. 

Conjugate addition. Trialkylstannyllithium reagents prepared in ether solution undergo predominantly 1,2-addition to cyclohexenones, but solutions prepared in THF undergo conjugate addition to almost all enones, even hindered ones. The intermediate lithium enolates can be alkylated with reactive alkyl halides. These reactions are useful because secondary alkylstannanes are converted into the corresponding carbonyl compound by oxidation with Cr03-2Py. Tertiary alkylstannanes are also oxidized by CrOa-lPy, but mixtures of alcohols and products of dehydration are formed. 

Additional examples of synthetic application of periodic acid as an oxidant include the oxidative iodination of aromatic compounds [1336-1341], iodohydrin formation by treatment of alkenes with periodic acid and sodium bisulfate [1342], oxidative cleavage of protecting groups (e.g., cyclic acetals, oxathioacetals and dithioacetals) [1315, 1343], conversion of ketone and aldehyde oximes into the corresponding carbonyl compounds [1344], oxidative cleavage of tetrahydrofuran-substituted alcohols to -y-lactones in the presence of catalytic PCC [1345] and direct synthesis of nitriles from alcohols or aldehydes using HsIOe/KI in aqueous ammonia [1346],... 

A major difference between alcohols and thiols concerns their oxidation. We have seen earlier in this chapter that oxidation of alcohols produces carbonyl compounds. Analogous oxidation of thiols to compounds with C=S functions does not occur. Only sulfur is oxidized, not carbon, and compounds containing sulfur in various oxidation states are possible. These include a series of acids classified as sulfenic, sulfinic, and sulfonic according to the number of oxygens attached to sulfur. 

Another related set of reactions are reactions in which alcohols and carbonyl compounds are oxidized and reduced (Sections 12.2—12.4). For example, primary alcohols can be oxidized to aldehydes, and aldehydes can be reduced to alcohols ... 

Flavor deterioration of food lipids is caused mainly by the presence of volatile lipid oxidation products that have an impact on flavor at extremely low concentrations, often at the parts per billion (ppb) levels. An understanding of the sources of volatile oxidation products provides the basis for improved methods to control and evaluate flavor deterioration. The decomposition of lipid hydroperoxides produces carbonyl compounds, alcohols and hydrocarbons under various conditions of elevated temperatures and in the presence of metal catalysts. 

The position of these substances in the chromatogram is determined by the polarity of the parent compound. Menthofuran migrates just behind guaiazulene [182 a, 247]. The terpene and sesquiterpene epoxides follow, lying in the upper part of the ester zone on silica gel G layers (Table 23) (cf. also [155]). in agreement with El-Deeb [55]. The carbonyl and alcohol oxides follow with lower hRf-values. This sequence holds even at — 9° C using Freon (Frigen 21) as solvent [255]. 

Lipid autoxidation is generally believed to involve a free- radical chain mechanism (1) initiation steps that lead to free radicals (R ), (2) propagation of the free radicals (R -I-O2 —> ROO, ROO -1-RH — ROOH-I-R ), and (3) termination steps R -H R R—R, R- ROO- ROOR, ROO ROO O 2 ROOR (or alcohol and carbonyl compound). The oxidation of lipids results in peroxides as primary oxidation products, which in turn degrade further to secondary oxidation products, including aldehydes, ketones, epoxides, hydroxy compounds, carboxylic acids, oligomers, and polymers. 

Carbonyl Compounds by Oxidation of Alcohols and Aldehydes. Salts of palladium, in particular PdCl2 in the presence of a base, catalyze the CCI4 oxidation of alcohols to aldehydes and ketones. Allylic alcohols carrying a terminal double bond are transformed to 4,4,4-trichloro ketones at 110 °C, but yield halo-hydrins at 40 °C. These can be transformed to the corresponding trichloro ketones under catalysis of palladium acetate (eq 56). The latter transformation could be useful for the formation of ketones from internal alkenes provided the halohydrin formation is regioselective. 

Carbonyl Compounds by Oxidation of Alcohols and Aldehydes. A critical assessment of the use of palladium catalysts in the aerobic oxidation of alcohols has concluded that Pd(OAc)2-Et3N is the most versatile and convenient catalyst system and that this often functions under especially mild conditions.There have been many other recent advances in this field and such that there is now a wealth of methods available for effecting the palladium-catalyzed oxidation of alcohols. A procedure using pyridine under an oxygen atmosphere has been shown to convert benzylic and aliphatic alcohols into the corresponding aldehydes or ketones. The yields of product are frequently over 90%. Replacing pyridine with (—)-sparteine in such processes allows for the oxidative kinetic resolution of chiral secondary alcohols. 

An example of a flow chemistry process is the Oppenauer oxidation of secondary benzylic alcohols using partially hydrated zirconia and various carbonyl compounds as oxidants (Scheme 53). The authors applied this procedure to electron-rich and electron-deficient substrates, with improvement in temperature (as low as 40 °C) and an easy reaction workup. The reuse of the catalyst was performed several times, without loss in catalytic efficiency. 

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