Alcohols benzylic, oxidation

C) Carboxylic adds For aryl-substituted alcohols, such as benzyl alcohol, oxidation readily gives the corresponding add (c/. p. 336). 

Scheme 4. Proposed triphasic benzyl alcohol oxidation mechanism on the lSrPyc catalyst with 30%...

Figure 9.(A) Reaction scheme for the selective benzyl alcohol oxidation without any over-oxidation to benzoic acid. (B) Plot of % of conversion over the reaction time for the benzyl alcohol oxidation reaction catalyzed by NPyc at various recyclic conditions with 30%H2O2. (C) The reaction step up picture.

Table 2. Benzyl alcohol oxidation reaction with different catalytic systems ...

Figure 11. Photographs of the filtered organic phase for the product of benzyl alcohol oxidation reaction catalyzed by (a) RuC13, (b) Ru02, (c) Pyc powders, and (d) NPyc membrane catalyst with 15 ml CH2C12 + 6ml NaOCl (4.1 mol)/pH 11 PBS.

Benzyl alcohol, oxidation, by ruthenium oxo complexes, 39 287-289 Benzylazide, NMR of, 4 263 Benzylidene diacetate, nitration of, 6 114 Berkelium... 

Caravati M, Grunwaldt J-D, Baiker A (2005) Benzyl alcohol oxidation in supercritical carbon dioxide spectroscopic insight into phase behaviour and reaction mechanism. Phys Chem Chem Phys 7(2) 278-285... 

Grunwaldt et al. (2003b) reported XAFS measurements recorded during palladium-catalyzed alcohol oxidation in supercritical CO2. A commercial shell-impregnated catalyst consisting of 0.5 wt% Pd on alumina was used for benzyl alcohol oxidation (to benzaldehyde) in supercritical CO2 with pure O2 as oxidant. The conditions were 353 K and 150 bar. The results are summarized in Table 8. The authors reported only Pd XANES data, not EXAFS data, and thus the analysis is limited to information about the average oxidation state of the palladium. 

This work was expanded in 2006, when the benzyl alcohol oxidation was conducted with cyclohexane as the solvent (Grunwaldt et al., 2006). The authors set out to address whether the active phase of the catalyst was oxidic or metallic palladium. The reaction conditions were as follows temperature 323 K reactant mixture, 200 p.1 of benzyl alcohol in 100 ml of cyclohexane saturated with 02. The catalytic activity was determined online by monitoring the intensity of the C=0 band in the benzaldehyde with IR spectroscopy. If the catalyst was not reduced in the XAFS reactor (by the H2-saturated cyclohexane), then no catalytic activity was measured, and the palladium remained oxidic. If the catalyst was prereduced, a highly active catalyst was obtained, and the XAFS data were found to be consistent with the presence of only metallic palladium. Thus, the conclusion was reached that palladium oxide exhibits hardly any activity at 323 K, whereas metallic palladium particles are much more active. 

Figure 3.36 Activation ofperacetic acid towards secondary and benzylic alcohol oxidation.

The values of kinetic and Freundlich parameters (k, Kp, and Ng), obtained from runs carried out with different amounts of catalyst, are reported in Figure 12 vs. the absorbed photon flow per unit mass of catalyst. These values show the same feature of Langmuir parameters obtained for benzyl alcohol oxidation, that is, they decrease by decreasing the photon flow absorbed by the unit mass of catalyst. As in the case of benzyl alcohol, the consideration that the photon flow absorbed by the unit mass of catalyst is the parameter mainly affecting the photoadsorption phenomenon is strengthened by the results reported in Figure 12. 

Benzyl alcohol oxidizes slowly in air to benzaldehyde and benzoic acid it does not react with water. Aqueous solutions may be sterilized by filtration or autoclaving some solutions may generate benzaldehyde during autoclaving. 

Most aliphatic alcohols react slowly if at all with 2,3-dichloro-5,6-dicyano-p-benzo-quinone (DDQ), allowing selective allylic or benzylic alcohol oxidation. 

The goal of maximum energy generation by oxidation of carbonaceous species often thwarted detailed examination of occasional selective oxidations, such as ethylene oxidation to acetaldehyde on Pd or Au (28, 29, 370) or to ethylene oxide on Ag (330) or methanol and benzyl alcohol oxidation to formates and benzaldehyde, respectively (6-32, 54, 250, 333). Product yields were usually determined at one potential only or even galvanostatically (330), and the combined effects of potential, catalyst, reactant concentration, and cell design or mixing on reaction selectivity are unknown at present. Thus, reaction mechanisms on selective electrocatalysis are not well understood with few exceptions. For instance, ethylene oxidation on solid pal-... 

Oxidation product analysis by GLC shows that the only dibenzyl ether oxidation product is benzaldehyde At the same time during the oxidation process small amounts of benzyl alcohol are detected in the reaction media Benzyl alcohol oxidation rate is five times higher than that for dibenzyl ether. The form of kinetic curves for benzyl alcohol oxidation is typical for intermediate products in consecutive processes. It must be emphasized that the benzyl alcohol formation is not a result of hydrolysis. Furthermore it was established that in early stages of oxidation both products benzaldehyde and dibenzyl ether are formed simultaneously. All these data obtained proved consecutive dibenzyl ether oxidation followed ... 

Kinetic investigations of dibenzyl ether oxidation shows that like benzyl alcohol oxidation, there are the same two areas of process parameters with different reaction kinetics area A with "low" acidity ([HC104]=5.0-5.8 M) and high oxygen partial pressure (( 0.5-1.0)x lO Pa), and area B with "high" acidities [HC104]= 5.8-6 6 M) and low oxygen pressures ((0.05-0.5)x 10 Pa). The main kinetic features of oxidation, that is rate dependence on concentrations and temperatures, both for dibenzyl ether and benzaldehyde are one and the same. The mechanism of dibenzyl ether oxidation appears as follows ... 

Also evident in the HMQC-TOCSY spectrum (Figure 5.12a), are (acetylated) ketones X6 (magenta contours). Products of benzylic alcohol oxidation are seen in various isolated lignins, notably from syringyl (3,5-dimethoxy-4-hydroxy-phenyl) units they may arise during lignin isolation (particularly in the ball-milling step). Ketones X6 provide additional conhrmatory evidence for the GPD structures X6 described above. 

Cha et al. provided the first experimental proof of hydrogen tunneling on an enzyme by reporting an elevated RS exponent for benzyl alcohol oxidation by yeast ADH (YADH) [10]. Isotope effects for benzyl alcohol oxidation were determined by the mixed-label tracer method, in which the primary and a-secondary positions of benzyl alcohol are either H or D, with stereochemically random, trace-level T incorporation. In this fashion, the observed ratios between the a-secondary (kH/feT)i H and (kD/feT)i°D KIEs are susceptible to both Swain-Schaad and RGM deviations and, thus, are sensitive probes for tuimeling (see Section 10.3.3.3). The observed a-secondary RS exponent, kn/feT = at 25 "C, greatly exceeded... 

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