Alcohols, secondary, oxidation with silver oxide

Silver is well known in its abihty to oxidize alcohols, with tertiary and secondary alcohols being oxidized into ketones or tetrahydrofuran derivatives, respectively. 

Oxides of copper and silver are used to oxidize secondary alcohols in the vapor phase at 250-300 °C [349] or in the liquid phase at room temperature [380], respectively. A similar effect is achieved with lead tetraacetate in pyridine at room temperature. Benzhydrol is thus converted into benzophenone in 80% yield [442], The oxidation of codeine with silver carbonate requires 1 h of refluxing in benzene to give a 75% yield of codeinone [376],... 

That the dimethyl-D-araboascorbic acid (LXXXHI) still contains two hydroxyl groups, one a primary alcoholic and the other a secondary alcoholic grouping, is shown by the observation that it affords a 6-trityl derivative XCII from which by methylation with silver oxide and methyl iodide there is formed 6-trityl-2,3,5-trimethyl-D-araboascorbic acid (XCIII). Removal of the trityl group with hydrogen chloride yields... 

The same allylic alcohols (142) undergo regiospecific oxidative cleavage with pyridinium chloro-chromate at the ethylenic bond to give, after saponification, a-hydroxyacids (145). Extension of this reaction to a -unsaturated ketones (146), obtained by oxidation of secondary alcohols with silver carbonate on celite, affords a-ketoacids (147) <88TL626l>. 

It is possible to run a controlled over-oxidation reaction with silver carbonate. Fetizon discovered that 1,3-and 1,4-diols are smoothly oxidized to butyrolactone and valerolactone derivatives in good yield. Oxidation of a diol can be accomplished in the presence of a variety of functional groups, even another alcohol. A primary alcohol, for example, will be oxidized faster than a secondary alcohol, as illustrated by the conversion of 113 to 114.173... 

Simple reactions on the substituents can also be performed without destroying the complexes. Thus the aldehyde (CII R=CHO) undergoes borohydride reduction to the alcohol (CII R=CH20H), silver oxide oxidation to the acid (CII R=COOH), and adds methyl magnesium bromide to give the secondary alcohol (CII R=CHOHMe) after hydrolysis. The NMR spectra are consistent with their formulation as (CII) (see Section V, D). The complex (XVIII) thus behaves analogously to ferrocene and cyclopentadienylmanganese tricarbonyl. 

Dichromate oxidation of secondary alcohols produces ketones in good yield, with little additional oxidation. For example, CH,CH2CH(OH)CH3 can be oxidized to CH CH2COCH3. The difference between the ease of oxidation of aldehydes and that of ketones is used to distinguish them. Aldehydes can reduce silver ions to form a silver mirror—a coating of silver on test-tube walls—with Tollens reagent, a solution of Ag1" ions in aqueous ammonia (Fig. 19.3) ... 

The oxidative effects of silver(II) complexes of pyridine carboxylates have been studied for a variety of substrates. With ar-amino acids, a rapid reaction occurred at 70 °C in aqueous solution with bis(pyridyl-2-carboxylato)silver(II). 4 The product was the next lower homologous aldehyde and yields were generally greater than 80%. Other substrates included primary and secondary amines, alcohols, monosaccharide derivatives, alkenes, arylalkanes and arylalkanols.90 Only minor differences were detected in efficiencies when 2-, 3- or 4-mono-, or 2,3-di-carboxylates were used as the oxidant. 

Sulfonic esters are most frequently prepared by treatment of the corresponding sulfonyl halides with alcohols in the presence of a base. This procedure is the most common method for the conversion of alcohols to tosylates, brosylates, and similar sulfonic esters. Both R and R may be alkyl or aryl. The base is often pyridine, which functions as a nucleophilic catalyst, as in the similar alcoholysis of carboxylic acyl halides (16-61). Propylenediamines have also been used to facilitate tosylation of an alcohol. Silver oxide has been used, in conjunction with KI. Primary alcohols react the most rapidly, and it is often possible to sulfonate selectively a primary OH group in a molecule that also contains secondary or tertiary OH groups. The reaction with sulfonamides has been much less frequently used and is limited to A,A-disubstituted sulfonamides that is, R— may not be hydrogen. However, within these limits it is a useful reaction. The nucleophile in this case is actually RO . However, R may be hydrogen (as well as alkyl) if the nucleophile is a phenol, so that the product is RS020Ar. Acidic catalysts are used in this case. Sulfonic acids have been converted directly to sulfonates by treatment with triethyl or trimethyl orthoformate, HC(OR)3, without catalyst or solvent and with a trialkyl phosphite, P(OR)3. ... 

Oxidation of the primary alcoholic group to a carboxyl group in diols with primary and secondary hydroxyls is accomplished by silver carbonate [377]. Unfortunately, an extremely large excess of the reagent is needed. Similar results are obtained with a rather exotic oxidant, 4-methoxy-2,2,6,6-tetramethyl-l-oxopiperidinium chloride, which is prepared by treatment with chlorine of a stable radical, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl. The compound oxidizes 1,4-butanediol to y-butyrolactone in 100% yield (isolated yield 81%) and 1,5-pentanediol to 8-valerolactone in 61% yield (isolated yield 40%) [995] (equation 292). 

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