Cyclohexanols oxidation

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. 

Another situation is observed when salts or transition metal complexes are added to an alcohol (primary or secondary) or alkylamine subjected to oxidation in this case, a prolonged retardation of the initiated oxidation occurs, owing to repeated chain termination. This was discovered for the first time in the study of cyclohexanol oxidation in the presence of copper salt [49]. Copper and manganese ions also exert an inhibiting effect on the initiated oxidation of 1,2-cyclohexadiene [12], aliphatic amines [19], and 1,2-disubstituted ethenes [13]. This is accounted for, first, by the dual redox nature of the peroxyl radicals H02, >C(0H)02 and >C(NHR)02 , and, second, for the ability of ions and complexes of transition metals to accept and release an electron when they are in an higher- and lower-valence state. 

Cyclohexanol oxidation, 41 299-300 reactions over reduced nickel oxide catalyst, 35 355-357 Cyclohexanone... 

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)... 

Figure 4. Kinetic curves of oxygen consumption in cyclohexanol oxidation at 75°C. with 0.01M AIBN Ri = 6.9 X 10 7 mole/liter/second...

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

First the amino group was converted to a hydroxy group via a diazonium ion (Section 17.10). The benzene ring was reduced with hydrogen and a catalyst to produce cyclohexanol. Oxidation with potassium dichromate (Section 10.14) gave cyclohexanone. The bonds between the carbonyl carbon and both a-carbons were then cleaved by a series of reactions not covered in this book. The carbon of the carbonyl group was converted to carbon dioxide in this process. One-half of the original radioactivity was found in the carbon dioxide, and the other one-half was found in the other product, 1,5-pentanediamine. Additional experiments showed that the 14C in the diamine product was located at C-l or C-5. 

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]. 

Nitrosation may potentially also occur on cyclohexanol in fact, cyclohexanol can be oxidized at much lower temperatures than cyclohexanone. The active reactant is H NO2 therefore, in this case, the first product of cyclohexanol oxidation is cyclohexyl nitrite. The latter is then rearranged into 2-nitrosocyclohexanone, which is also the key intermediate in the main reaction pathway involving cyclohexanone. 

In the direct oxidation of cyclohexanol a significantly higher conversion is obtained with HPTP / Fe complexes, contrasting with that of monouclear iron complexes [12] or the blanc reaction. Thus cyclohexanone is not only formed through CHHP decomposition, but also by direct cyclohexanol oxidation (table 6). 

Table 6. Cyclohexanol oxidation in absence and presence of catalyst for 2 - 24 h at 293K.

The catalytic activity of the samples prepared were analyzed for cyclohexanol oxidation and cyclohexane oxidation reactions using 30 wt.% H2O2. Table 2 gives the TON for cyclohexanol oxidation for various catalysts. 

The activity of the catalysts for cyclohexane oxidation are shown in Table 3. Similar trends analogous to cyclohexanol oxidation is observed in this case also. It can be observed that the conversion for cyclohexane oxidation of Mo-MCM-41 is higher than that reported for TS-1 [16]. This is apparently because of the larger pore size of Mo-MCM-41 permitting a bulky molecule like cyclohexane into the pores in comparison to TS-1. Ulf Schuchardt et al. [16] have reported that the turn over numbers are in the range of 1-100 for cyclohexane oxidation on TS-1 under comparable experimental conditions. The selectivity ratio of cyclohexanol to cyclohexanone is around 1 for TS-1 [14] whereas it is of the order of 0.15 for Mo-MCM-41 and is of the order of 0.40 for the impregnated samples. It is seen that Mo-MCM-41 is more selective to the production of cyclohexanone. 

The mechanism of cyclohexanol oxidation has been studied in detail and is rather complex [23,26,32,48—50,57,58]. Various reactions involving H202 decomposition and cyclohexanone oxidation play the main part in the later stages of the process. 

Hydrogen peroxide decay in cyclohexanol oxidation occurs by several routes, (a) By reaction with hydroxycyclohexyl radicals [57]... 

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. 

Cheng Q, Thomas SM, Kostichka K, Valentine JR, Nagarajan V. (2000). Genetic analysis of a gene cluster for cyclohexanol oxidation in Acinetobacter sp. Strain SE19 by in vitro transposition. J Bacterial, 182, 4744—4751. 

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