Fluorenol, oxidation

Oxidation of diphenylmethane in basic solutions involves a process where rate is limited by and equal to the rate of ionization of diphenylmethane. The diphenylmethide ion is trapped by oxygen more readily than it is protonated in dimethyl sulfoxide-text-butyl alcohol (4 to 1) solutions. Fluorene oxidizes by a process involving rapid and reversible ionization in text-butyl alcohol solutions. However, in the presence of m-trifluoromethylnitrobenzene, which readily accepts one electron from the carbanion, the rate of oxygen absorption can approach the rate of ionization. 9-Fluorenol oxidizes in basic solution by a process that appears to involve dianion or carbanion formation. Benzhydrol under similar conditions oxidizes to benzophenone by a process not involving carbanion or dianion formation. 

Some lactol-to-lactone oxidations were effected by TPAP/NMO/PMS/CH Clj [498, 499], or TPAP/NMO/PMS/CH3CN [159]. The system RUCI3 or RuO / Na(Br03)/aq. M Na3(C03) generates [RuO ]" in aqueous solution and oxidised secondary alcohols to ketones in high yield (Table 2.2) [213]. Kinetics of the oxidation of benzhydrol and 9-fluorenol by TPAP/NMO/CH3CN/30°C were measured. 

The present work demonstrates that the oxidation of diphenylmeth-ane in basic solution follows a pattern similar to triphenylmethane and not to fluorene. At high concentrations of good electron acceptors it is possible to realize a situation wherein the rate of oxidation of fluorene is limited by and equal to the rate of ionization. The oxidations of benzhydrol and 9-fluorenol in basic solution are considered the difference in acidity of the methine hydrogens has a pronounced effect on the course of these oxidations. 

Table III summarizes some information on the initial rates of oxidation of fluorene in several solvents. In the alcohol-containing solvents the stoichiometry was nearly one molecule of oxygen per mole of fluorene, an observation that excludes 9-fluorenol as an intermediate. In all solvents, including HMPA, interrupted oxidations yielded only fluorenone (or the DMSO-fluorenone adduct) and fluorene. Apparently Reaction 6 or 7 occurs readily in the presence of hydroxylic solvents. In HMPA the high...

Oxidation of 9-Fluorenol and 9-Xanthenol in Basic Solution. Fluor-enol and xanthenol react with base and oxygen to give high yields of the ketones, or in the case of fluorenol in DMSO solution, the DMSO-fluore-none adduct. The stoichiometry of the oxidation (Table XI) varies with... 

The oxidations involving lithium ferf-butoxide reach completion (3 minutes for fluorenol, 12 minutes for xanthenol) much sooner than the corresponding reactions utilizing potassium terf-butoxide as base (35 minutes for fluorenol, 27 minutes for xanthenol). This behavior obviously involves Reaction 20 since the initial rates of oxidation were all approximately the same for the lithium- and potassium ferf-butoxide-catalyzed reactions. 

Figure 5. Oxidation of 0.15M 9-fluorenol in tert-butyl alcohol containing 0.4M potassium tert-butoxide...

The oxidation of xanthenol and fluorenol showed a number of differences from the oxidation of benzhydrol. No induction period was observed (Figure 5). The rate was enhanced by ferric ion, and the stoichiometry was altered to 0.5 mole of oxygen per mole of fluorenol (Figure 5), apparently because of Reaction 25. 

No deuterium isotope effect was observed in the oxidations of 9-deuterio-9-fluorenol. The rates of oxidation varied considerably with solvent... 

Table XII. Initial Rates of Oxidation of Fluorenol and Xanthenola...

Oxidation of xanthenol or fluorenol with deficient quantities of oxygen in tert-butyl alcohol produced large quantities of the ketyl, as did reaction of equal molar amounts of the ketone and alcohol in basic solution. In fact, the reaction of the pinacol of fluorenone with excess base in tert-butyl alcohol produced an essentially quantitative yield of the ketyl (19). 

The oxidation of benzhydrol and 9-fluorenol in basic solution again shows a difference in regard to mechanism that can be primarily attributed to a difference in acidity as carbon acids. In tert-butyl alcohol benzhydrol enters into an oxidation scheme as the mono (oxy) anion. The data strongly suggest a free radical chain. Under these conditions the more acidic fluorenol or xanthenol oxidizes via carbanions or dianions. These oxidations can be catalyzed to occur via a free radical chain process by one-electron acceptors, such as nitrobenzene, and a free radical chain process may well be involved in the absence of the catalyst. 

Cpe oxidation of other alcohols (fluorenol and 2-naphthalenemethanol) were not successful due to severe filming at the electrode. 

Hypochlorites are very good oxidizers of alcohols and are frequently selective enough to oxidize secondary alcohols in preference to primary alcohols see equations 288-291). Solutions of sodium hypochlorite in acetic acid react exothermically with secondary alcohols within minutes [693]. Calcium hypochlorite in the presence of an ion exchanger (IRA 900) oxidizes secondary alcohols at room temperature in yields of 60-98% [76 5]. Tetrabutylammonium hypochlorite, prepared in situ from 10% aqueous sodium hypochlorite and a 5% dichloromethane solution of tetrabutylammonium bisulfate, oxidizes 9-fluorenol to fluorenone in 92% yield and benzhydrol to benzophenone in 82% yield at room temperature in 35 and 150 min, respectively [692]. Cyclohexanol is oxidized to cyclohexanone by teit-butyl hypochlorite in carbon tetrachloride in the presence of pyridine. The exothermic reaction must be carried out with due precautions [709]. 

The kinetics of oxidation of fluorenol to fluorenone with CBT in aqueous acetic acid was studied [82IJC(B)1095] (Scheme 87). 

Reflecting the typical reactivity of a ketyl species, hydrolysis of 2a gives the corresponding pinacol-coupling product 4, while air oxidation of 2a yields flu-orenone almost quantitatively (Scheme 3). Reaction of 2a with one equivalent of la produced a THF-insoluble purple precipitate which upon hydrolysis afforded fluorenol quantitatively, suggesting that a fluorenone dianion intermediate was formed [7,9]. 

Oxidation of fluorenol and xanthenol alcoholates in f-butanol and mixtures with pyridine and dimethylsulfoxide is accelerated by nitrobenzene [113]. The mechanism suggested is... 

Quinine, as a jS-amino-alcohol, cannot be satisfactorily oxidized under standard Oppenauer conditions however, it can be oxidized completely at room temperature to quinidinone in dry, deoxygenated DMF, by fluorenone and sodium hydride.It is of interest that little fluorenol is obtained as a result of the hydride transfer, and virtually none (only 1%) is obtained if the oxidation is conducted at -50 C instead the major reduction product is the pinacol derived from fluorenone. This presumably arises by condensation of the carbanion, derived from fluorenol in the presence of strong base, with unchanged fluorenone. 

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