Cyclohexanol oxidation rate

The alcohol 3) , 28-diacetoxy-6 -hydroxy-18i -12-oleanene was oxidised in an aqueous acetic acid medium Deuteration at the six position had no effect on the rate in solvents of high (> 80 %) acetic acid content, but the isotope effect reached 2 in 60 % acetic acid. Increasing the acetic acid content of the medium produced a much larger effect on the oxidation rate of cyclohexanol than of the polycyclic alcohol. 

Typical non-enolising aldehydes are formaldehyde and benzaldehyde, which are oxidised by Co(III) Ce(IV) perchlorate and sulphate , and Mn(III) . The main kinetic features and the primary kinetic isotope effects are the same as for the analogous cyclohexanol oxidations (section 4.3.5) and it is highly probable that the same general mechanism operates. kif olko20 for Co(III) oxidation of formaldehyde is 1.81 (ref. 141), a value in agreement with the observed acid-retardation, i.e. not in accordance with abstraction of a hydroxylic hydrogen atom from H2C(OH)2-The V(V) perchlorate oxidations of formaldehyde and chloral hydrate display an unusual rate expression, viz. 

Most of the work reported with these complexes has been concerned with kinetic measurements and suggestions of possible mechanisms. The [Ru(HjO)(EDTA)] / aq. HjOj/ascorbate/dioxane system was used for the oxidation of cyclohexanol to cw-l,3-cyclohexanediol and regarded as a model for peroxidase systems kinetic data and rate laws were derived [773], Kinetic data were recorded for the following systems [Ru(Hj0)(EDTA)]702/aq. ascorbate/dioxane/30°C (an analogue of the Udenfriend system cyclohexanol oxidation) [731] [Ru(H20)(EDTA)]70j/water (alkanes and epoxidation of cyclic alkenes - [Ru (0)(EDTA)] may be involved) [774] [Ru(HjO)(EDTA)]702/water-dioxane (epoxidation of styrenes - a metallo-oxetane intermediate was postulated) [775] [Ru(HjO)(EDTA)]7aq. H O /dioxane (ascorbic acid to dehydroascorbic acid and of cyclohexanol to cyclohexanone)... 

The inhibiting effect of NaHC03 on chain oxidation was established by studying the effect of ions on the oxidation of cyclohexanol. The latter was oxidized at 75°C. with AIBN as initiator (R = 6.9 X 107 mole liter"1 sec."1). To dissolve NaHC03, 9% of water was added to cyclohexanol. The rate of oxidation was measured volumetrically. 

Figure 5. Dependence of rate of cyclohexanol oxidation with AIBN on concentration of HCOs ...

In a study by Corma and coworkers, the rate of epoxidation of 1-hexene on Ti,Al-P matched, for a homogeneous series of solvents, the trend of adsorption. However, it was twice as fast in acetonitrile than in methanol, in contrast to partition coefficients which are ordered in the reverse direction [77, 167]. The relationship for cyclohexanol oxidation was more complex, the rate increasing with the polarity of aprotic solvents and decreasing with polarity increase in protic ones [77]. 

Inhibition of initiated cyclohexanol oxidation by Br" is peculiar. It starts a certain time after the addition of Br" and the rate of the inhibited oxidation does not depend on the Br" concentration. Cyclohexanone has no effect. Obviously, the inhibiting action is not due to Br" ions but to bromine oxides and bromoxygen acids. 

Polmer-snpported IBX Reagents. Two different phenoxide linked polymer-based IBX reagents have been developed. The silica supported reagent (Poly-IBX) is used in THE The oxidation rate increases relative to DMSO as solvent. The primary alcohol in the cyclohexanol may be oxidized preferentially, and thus avoid formation of the cyclohexanone expected from the secondary alcohol (eq 8). This selectively is retained even with a threefold... 

For the pyridine-free systems, the best efficiency (15%) was obtained in acetone but the principal product was cyclohexanol. For the GoChAgg system, Geletii et al described good results obtained in acetonitrile/pyridine 2 1, but assured that pyridine was essential and must be present in the system. On the other hand, in a very recent publication Barton etal reported that pyridine can be completely replaced by ferf-butanol with only a small reduction of the total hydrocarbon activation and a slightly reduced onerol ratio. However, the initial oxidation rate was pH dependent and buffering of the system was necessary. 

A few results have been reported on the oxidation of cyclohexanol by acidic permanganate In the absence of added fluoride ions the reaction is first-order in both alcohol and oxidant , the apparent first-order rate coefficient (for excess alcohol) at 25 °C following an acidity dependence k = 3.5-1-16.0 [H30 ]sec fcg/A , depends on acidity (3.2 in dilute acid, 2.4 in 1 M acid) and D2o/ H20 is f-74. Addition of fluoride permitted observation of the reaction for longer periods (before precipitation) and under these conditions methanol is attacked at about the same rates as di-isopropyl ether, although dioxan is oxidised over twenty times more slowly. The lack of specificity and the isotope effect indicates that a hydride-ion abstraction mechanism operates under these conditions. (The reactivity of di-isopropyl ether towards two-equivalent oxidants is illustrated by its reaction with Hg(II).) Similar results were obtained with buffered permanganate. 

A brief study of the oxidations of cyclohexanol and cyclohexanol-l-t/ by Tl(III) indicated the rate expression to be ... 

Two studies have been performed by Littler on the oxidation of cyclohexanol by Hg(II), the second leading to more detailed and reliable data. The reaction is first-order in both oxidant and substrate but the rate is independent of acidity. E is 24.8 kcal.mole AS is 1 eu, Ath/Acd is 3.0 and ko ol HzO 1-30-At 50 °C di-isopropyl ether is attacked at about one-half the rate of isopropanol, which implies that hydride ion abstraction is occurring in both cases. This is supported in the case of cyclohexanol by the isotope effects. 

This type of fission has been observed in a detailed examination of the oxidation of tertiary alcohols by Co(ril). The kinetics are similar to those reported for cyclohexanol vide supra) although the rate is about 40 times less. The possibility of alkoxyl radical formation seems attractive, for Co(III) is known to oxidise... 

The first term is analogous to the rate expression for the Mn(II[) oxidation of cyclohexanol vide supra) and displays a primary isotope effect of similar magnitude (2.2 at 50 °C). The second term shows an isotope effect of 4.3 for replacement of HCO2H by DCO2H. The oxidations of malonic acid and Hg(l) ° involve [Mn(III)] /[Mn(ll)] terms and these are readily explained by the equilibrium... 

This reaction was proposed in 1960 for compounds with a weak C—H bond [33] and was experimentally proved in the reactions of oxidation of cyclohexanol and tetralin [34,35], The rate of this reaction was found to obey the following equation ... 

Let us compare the ratio of radicals in oxidized 2-propanol and cyclohexanol at different temperatures when oxidation occurs with long chains and chain initiation and termination do not influence the stationary state concentration of radicals. The values of the rate constants of the reactions of peroxyl radicals (kp) with alcohol and decomposition of the alkylhydroxy-peroxyl radical (k ) are taken from Table 7.4 and Table 7.5. 

In the absence of an initiator, alcohols are oxidized with self-acceleration [7-9]. As in the oxidation of hydrocarbons, the increase in the reaction rate is due to the formation of peroxides initiating the chains. The kinetics of radical formation from peroxides was studied for the oxidation of isopropyl alcohol [58] and cyclohexanol [59,60]. 

Ketones play an important role in the decomposition of peroxides to form radicals in alcohols undergoing oxidation. The formed hydroxyhydroperoxide decomposes to form radicals more rapidly than hydrogen peroxide. With an increase in the ketone concentration, there is an increase in the proportion of peroxide in the form of hydroxyhydroperoxide, with the corresponding increase in the rate of formation of radicals. This was proved by the acceptor radical method in the cyclohexanol-cyclohexanone-hydrogen peroxide system [59], The equilibrium constant was found to be K — 0.10 L mol 1 (373 K), 0.11 L mol 1 (383 K), and 0.12 L mol 1 (393 K). The rate constant of free radical generation results in the formation of cyclohexylhydroxy hydroperoxide decomposition and was found to be ki = 2.2 x 104 exp(—67.8/7 7) s 1 [59]. 

Oxalic acid does not form intramolecular hydrogen bonds. The decarboxylation of oxalic acid occurs by the direct reaction of the peroxyl radical with the carboxylic group. The rate constants of the peroxyl radicals of the oxidized cyclohexanol in co-oxidation with oxalic acid was found to be pi2 = 7.4 x 107exp(—60.2/RT) L mol-1 s-1 in cyclohexanol at 348-368 K [106],... 

The presence of ascorbic acid as a co-substrate enhanced the rate of the Ru(EDTA)-catalyzed autoxidation in the order cyclohexane < cyclohexanol < cyclohexene (148). The reactions were always first-order in [H2A]. It was concluded that these reactions occur via a Ru(EDTA)(H2A)(S)(02) adduct, in which ascorbic acid promotes the cleavage of the 02 unit and, as a consequence, O-transfer to the substrate. While the model seems to be consistent with the experimental observations, it leaves open some very intriguing questions. According to earlier results from the same laboratory (24,25), the Ru(EDTA) catalyzed autoxidation of ascorbic acid occurs at a comparable or even a faster rate than the reactions listed in Table III. It follows, that the interference from this side reaction should not be neglected in the detailed kinetic model, in particular because ascorbic acid may be completely consumed before the oxidation of the other substrate takes place. 

K[Ru(0)(PDTA)].3Hj0 and Ru(0)(HEDTA) (PDTA=(propylenediaminetetra-acetate) -) are made by oxidation of K[Ru "Cl(PDTA.H)] or K[Ru" Cl(EDTA.H)] with PhIO electronic and ESR spectra were recorded. Rates and activation energies for epoxidation by stoich. Ru(0)(PDTA)] or Ru(0)(HEDTA)/water-dioxane of cyclo-alkanes were measured, as were those for oxidation of cyclohexane to cyclohexanol and cyclohexanone [632],... 

In any case, the initial reagents must be oxidized in the presence of the reaction products, and it is always best if the concentration of products can be increased because it corresponds to a better conversion rate per run—e.g., cyclohexane oxidation must be done in the presence of cyclohexanol and cyclohexanone—and recent advances have increased the amount of conversion per run from 8 to 15% without any loss of selectivity. 

H202 decomposes to free radicals in 2-propanol by the action of H+. Free radicals are also produced by the reaction between tert-BuOOH and Br in 1-propanol. The HCOf ions inhibit the oxidation of cyclohexanol initiated by AIBN, destroying many oxyperoxide radicals—i.e., HCOf is a negative catalyst. Appropriate reaction schemes and rate equations are proposed. 

Pentanol reacts much faster than 3-pentanol. The ratio of reactivities calculated from data at 50% H202 conversion is 12 1. Because in term of diffusion rates and chemical behavior these two alcohols are similar to each other, the results are explained by restricted transition-state selectivity, a steric influence of the catalyst pores. Cyclohexanol is oxidized at a very low rate, and this is best... 

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