Oxidation cinnamyl alcohol

C kinetic isotope effects (KIEs) of four cinnamyl alcohol oxidations have been determined by 13C NMR spectroscopy using competition reactions with reactants at natural 13C abundance. Primary 13C KIEs of the Pd(II)-catalysed oxidation and of the MnC>2 oxidation are similar ( 1.02) and indicate the C—H bond cleavages to be the irreversible and rate-limiting steps in the respective reactions. Low primary 13C KIEs in Swern and Dess-Martin oxidations, however, indicate that the initial C—H bond breakings and proton transfers are not the irreversible steps in these mechanisms, which control the rate.284... 

Good yields of ketones were obtained in the oxidation on Pt-Bi catalysts (Bi/ Pts = 0.5) of secondary alcohols insoluble in water under the same conditions as for cinnamyl alcohol oxidation (see Section 9.2.3.2). Table 2 shows that selectivity in excess of 95 % was obtained at 97-99% conversion [43]. 

Hydroxyapatite (CajQ(P04)g(0H)2) has also attracted considerable interest as a catalyst support. In these materials, wherein Ca sites are surrounded by P04 tetrahedra, the introduction of transition metal cations such as Pd into the apatite framework can generate stable monomeric phosphate complexes that are efficient for aerobic selox catalysis [99]. Carbon-derived supports have also been utihzed for this chemistry, and are particularly interesting because of the ease of precious metal recovery from spent catalysts simply by combustion of the support. Carbon nanotubes (CNTs) have received considerable attention in this latter regard because of their superior gas adsorption capacity. Palladium nanoparticles anchored on multiwalled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) show better selectivity and activity for aerobic selox of benzyl and cinnamyl alcohols [100, 101] compared to activated carbon. Interestingly, Pd supported on MWCNTs showed higher selectivity toward benzaldehyde, whereas activated carbon was found to be a better support in cinnamyl alcohol oxidation. Functionalized polyethylene glycol (PEG) has also been employed successfully as a water-soluble, low-cost, recoverable, non-toxic, and non-volatile support with which to anchor nanoparticulate Pd for selox catalysis of benzyl/cinnamyl alcohols and 2-octanol [102-104]. 

When heated in the presence of a carboxyHc acid, cinnamyl alcohol is converted to the corresponding ester. Oxidation to cinnamaldehyde is readily accompHshed under Oppenauer conditions with furfural as a hydrogen acceptor in the presence of aluminum isopropoxide (44). Cinnamic acid is produced directly with strong oxidants such as chromic acid and nickel peroxide. The use of t-butyl hydroperoxide with vanadium pentoxide catalysis offers a selective method for epoxidation of the olefinic double bond of cinnamyl alcohol (45). 

CHROMIUM TRIOXIDE-PYRIDINE COMPLEX, preparation in situ, 55, 84 Chrysene, 58,15, 16 fzans-Cinnamaldehyde, 57, 85 Cinnamaldehyde dimethylacetal, 57, 84 Cinnamyl alcohol, 56,105 58, 9 2-Cinnamylthio-2-thiazoline, 56, 82 Citric acid, 58,43 Citronellal, 58, 107, 112 Cleavage of methyl ethers with iodotri-methylsilane, 59, 35 Cobalt(II) acetylacetonate, 57, 13 Conjugate addition of aryl aldehydes, 59, 53 Copper (I) bromide, 58, 52, 54, 56 59,123 COPPER CATALYZED ARYLATION OF /3-DlCARBONYL COMPOUNDS, 58, 52 Copper (I) chloride, 57, 34 Copper (II) chloride, 56, 10 Copper(I) iodide, 55, 105, 123, 124 Copper(I) oxide, 59, 206 Copper(ll) oxide, 56, 10 Copper salts of carboxylic acids, 59, 127 Copper(l) thiophenoxide, 55, 123 59, 210 Copper(l) trifluoromethanesulfonate, 59, 202... 

Ros Barcelo, A. Pomar, F. Oxidation of cinnamyl alcohols and aldehydes by a basic peroxidase from lignifying Zinnia elegans hypocotyls. Phytochemistry 2001, 57, 1105-1113. 

Of particular interest are oxidations of unsaturated alcohols, for example, oxidation of cinnamyl alcohol to cinnamaldehyde,74,75 and special promoters have been added to increase selectivity (Fig. 6.13).75 Although the functions of these promoters are still not fully undestood, some authors attribute their increased selectivity to physical blocking of reaction sites. This blocking reduces the size of the active site ensemble and suppresses the tendency for alcohols to strongly adsorb and dissociate on Pt.75... 

The effect of a surfactant such as do-decylbenzene sulfonate (DBS) has been investigated and the DBS concentration slightly influences the current efficiency [213]. The oxidation of cinnamyl alcohol to cinnamaldehyde with a solid... 

Vinylogs of benzylic alcohols, e.g. cinnamyl alcohol, undergo easy saturation of the double bond by catalytic hydrogenation over platinum, rhodium-platinum and palladium oxides [39] or by reduction with lithium aluminum hydride [609]. In the presence of acids, catalytic hydrogenolysis of the allylic hydroxyl takes place, especially over platinum oxide in acetic acid and hydrochloric acid [39]. 

While most of the iminium salts studied are cyclic, several acyclic iminium salts have also been investigated. In 1997, Armstrong and coworkers reported the use of acyclic iminium salt 83 as chiral epoxidation promoter (Fig. 27) [156, 157]. 1-Phenylcyclohexene oxide could be obtained in 100% conversion and 22% ee with stoichiometric amounts of 83. In 2002 acyclic iminium salt 84, prepared from L-prolinol, was investigated by Komatsu and coworkers, and cinnamyl alcohol was epoxidized in 70% yield and 39% ee (Fig. 27) [158]. 

In plant cell walls, lignin monomers seem to be present in vivo in the form of cinnamyl alcohols. In vitro, their acid precursors can also be oxidized by peroxidases (3). In order to gain further insight into the possible... 

Two of the commonest models are benzyl and cinnamyl alcohols - the former because it is easily oxidised beyond benzaldehde to benzoic acid and the latter because its double bond is often attacked, so that oxidation to cinnamaldehyde would show that the oxidant is mild enough to avoid competing double-bond attack. Geraniol is also included as a model substrate as it is in the same category as cinnamyl alcohol. Since there are so many examples of smdies on their oxidations a limited selection only is given. 

In a separate experiment, groups of male CDl mice were given intraperitoneal injections of 0-200 mg/kg bw ciimamyl anthranilate daily for three days. At doses of 20 mg/kg bw and above, there were dose-dependent increases in relative liver weight, total cytochrome P450, and cyanide-insensitive palmitoyl-CoA oxidation. The hepatic effects of cinnamyl anthranilate are apparently due to the intact ester, since neither its expected metabolites alone nor an equimolar mixture of the hydrolysis products, cinnamyl alcohol and anthranilic acid, had a significant effect on the weight or marker enzyme content of mouse liver (Viswalingam Caldwell, 1997). 

Cinnamyl anthranilate is metabolized by hydrolysis to anthranilic acid and cinnamyl alcohol, which is oxidized to benzoic acid. In mice, but not in rats or humans, the hydrolysis is saturated at high doses, leading to excretion of unchanged cinnamyl anthranilate in the urine. 

Cinnamyl alcohols.1 These alcohols can be prepared by oxidation of 3-arylpropenes with selenium dioxide in dioxane. The yield compares favourably with that oblained by LiAlH4 reduction of esters of cinnamic acids. 

Potassium ferrate, K2Fe04, is isomorphous with chromates and readily oxidizes alcohols to carbonyl compounds in the presence of alkali.286,287 The purple color of ferrate ion fades with the progress of the reaction. Yields as high as 96% have been reported for the oxidation of cinnamyl alcohol to cinnamaldehyde (equation 111).287... 

Reaction of cinnamyl alcohol (36) catalyzed by Rh-BINAPHOS gives the product as lactol 37 (1 1 mixture of diastereomers at the anomeric carbon) with high enantioselectivity (88% ee) [94] (Scheme 7.7). The enantiopurity of lactol 37 is determined by oxidizing the lactol to the corresponding lactone 38. In the same manner, homoallyl alcohol (39) is converted to the corresponding a-methyl-y-butyrolactone (42) with 73% ee via lactol 40 [94] (Scheme 7.7). However, the regioselectivity of the reaction is not favorable to the formation of 40, forming achiral 6-lactol 41 as the major product. 

Interestingly, the simple p-quinone (84a) is also able to oxidize certain unsaturated alcohols under harsh conditions.98 Because of its lower oxidation potential, p-quinone only oxidizes unsaturated alcohols devoid of steric hindrance and able to generate very stabilized carbocations. Thus, it is able to react with primary cinnamyl alcohols but not with secondary cinnamyl alcohols, simple allylic alcohols and benzylic alcohols. 

Some commercial samples of precipitated manganese dioxide may be active enough for use directly in an oxidation process. To assess the activity of a sample of manganese dioxide, dissolve 0.25 g of pure cinnamyl alcohol in 50 ml of dry light petroleum (b.p. 40-60 °C) and shake the solution at room temperature for 2 hours with 2g of the sample of manganese dioxide (previously dried over phosphoric oxide). Filter, remove the solvent by evaporation and treat the residue with an excess of 2,4-dinitrophenylhydrazine sulphate in methanolt (Section 9.6.13, p. 1257). Collect the cinnamaldehyde 2,4-dinitrophenyl-hydrazone and crystallise it from ethyl acetate. An active dioxide should give a yield of the derivative, m.p. 255 °C (decomp.), in excess of 0.35 g (60%). 

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