Phenethyl alcohol, oxidation

Fig. 3 a Rate dependence of sec-phenethyl alcohol oxidation using various acetic acid concentrations. b Natural logarithm of sec-phenethyl alcohol concentrations versus time at various acetic acid concentrations. Reprinted with permission from Mueller JA, Goller CP, Sigman MS (2004) J Am Chem Soc 126 9724, Copyright 2004, American Chemical Society... 

The role(s) of acid in this system was further elucidated using mechanistic studies. " When the rate dependence of ec-phenethyl alcohol oxidation on AcOH concentration was determined, a rate increase at low concentrations of acid (up to 0.62 mol%) was observed followed by first-order inhibition at higher concentrations (up to 15mol%) (Figure 12.1a). 

Of all these, probably P-phenethyl alcohol (2) comes closest to the odor of fresh rose petals however, mixing all these components does not reproduce the total fine character of the natural oil. It has been determined that a number of trace constituents representing less than 1% of the volatiles are critical to the development of the complete rose fragrance (10). These include cis- and trans-i.ose oxide (1), nerol oxide (12), rose furan (13), /)i7n7-menth-l-en-9-al (14), P-ionone (15), P-damascone (16), and P-damascenone (3). 

Allylic and benzylic alcohols were oxidized to aldehydes or ketones with BnPhsPHSOs in refluxing CHsCN. The yield increased in the presence of bismuth chloride in a catalytic amount. Selective oxidation of various alcohols under solvent free conditions was also reported Interestingly, benzyl alcohols were oxidized selectively to benzaldehydes in very high yield (95-100%) when reacted with BnPhsPHSOs (1.2 eq.) and AICI3 (1 eq.) in the presence of an equimolar amount of 2-phenethyl alcohol, diphenyl carbinol or methyl phenyl sulfide (equation 72). 

Properties. Phenethyl alcohol is a colorless liquid with a mild rose odor. It can be dehydrogenated catalytically to phenylacetaldehyde and oxidized to phenylacetic acid (e.g., with chromic acid). Its lower molecular mass fatty acid esters as well as some alkyl ethers, are valuable fragrance and flavor substances. 

Friedel—Crafts Reaction of Benzene and Ethylene Oxide. In the presence of molar quantities of aluminum chloride, ethylene oxide reacts with benzene to give an addition product, which is hydrolyzed to phenethyl alcohol ... 

Hydrogenation of Styrene Oxide. Excellent yields of phenethyl alcohol are obtained when styrene oxide is hydrogenated at low temperature, using Raney nickel as a catalyst and a small amount of sodium hydroxide [140]. 

One research group has exploited the concept of polymer site-isolation in a multistep/one-chamber solution-phase synthesis in which all the reagents, catalysts, and downstream reactants required for a multistep synthesis were combined in one reaction chamber. For instance, a one-chamber/three-step synthesis of substituted acetophenones has been reported (Scheme 10).84 An a-phenethyl alcohol was introduced into a reaction chamber containing the polymer-supported reagents and reactants necessary to accomplish oxidation by polymer-supported pyridinium dichromate 60 bromination by the A-26 perbromide resin 61 and nucleophilic displacement by the A-26 phenoxide resin 62. Filtration afforded the... 

Iron-containing cytochrome P-450 constitutes the most famous example of a selective C-H bond oxidizer. Although the exact nature of the mechanism remains controversial, the reaction most likely proceeds through radical intermediates [2]. The hydroxylation of activated C-H bonds has also been carried out in the presence of synthetic porphyrin complexes. In these biomimetic processes, ruthenium plays a relatively minor role when compared with iron. Zhang et al. [50], however, recently reported the enantioselective hydroxylation of benzylic C-H bonds using ruthenium complexes supported by a D4-sym-metric porphyrin bearing a crafted chiral cavity. Thus, complex 23 reacts in a stoichiometric manner with ethylbenzene to give phenethyl alcohol with a... 

The tendency toward hydrogenolysis to give hydrocarbons is greatly reduced with phenylacetic esters where a homobenzyl-type alcohol is produced. If the hydrogenation was stopped before the absorption of hydrogen was complete, a 39.7% yield of 2-phenethyl alcohol was obtained over Cu-Ba-Cr oxide even at 250°C. The yield was further increased to 58.3% over Cu-Mg-Cr oxide (eq. 10.20), and the yields from the cyclohexyl ester was 58.7% over Cu-Ba-Cr oxide and 63.3% over Cu-Ca-Cr oxide. In contrast, over a catalyst containing no alkaline-earth metal oxide, the predominant product from the ethyl ester became ethylbenzene (88.7%), and 2-phenethyl alcohol was obtained in only 4.5% yield. 

The paper lists examples of further useful oxidation of ketals, diols, and ketols, as well as heteroaryl alcohols. It is not useful for phenethyl alcohols (39% yield of ketone). 

The effect of additives and of modified aluminum and borohydrides has been extensively examined in efforts to enhance reactivity and improve selectivity. The system of LAH and aluminum chloride was early applied to achieving opposite regioselectivity. For example, the reduction of styrene oxide with this system takes place at the benzylic position to give 3-phenethyl alcohol as the major product, and the same effect is observed with 1,4-dialkylcyclohexene oxide (equation 17). 4... 

Tetra-A-propylammonium perruthenate (TRAP) has been known as a homogenous and versatile reagent for the catalytic oxidation of alcohols. One of the problems in the use of TRAP is its removal from the reaction ntixture. Ley et al. disclosed a system that permits recycling and reuse of TRAP [39]. They used TRAP and alcohol in CH Cl in the presence of l-ethyl-3-methyl-lH-imidazolium hexafluorophosphate ([emim][PFg]) and Et NBr accompanied with A-methylmorpholine A-oxide (NMO) as cooxidant. They demonstrated that both Et NBr and [anim][PF ] may be used to enable the recovery and reuse of TRAP. Also, performing the reaction under moderate oxygen pressure (30-40 bar) in dichloromethane and Et NBr at room temperature resulted in rapid and clean oxidation of sec-phenethyl alcohol. 

Both Pt/C and Ru/C are effective for the oxidation of sec-phenethyl alcohol to acetophenone with yields > 85% in the 6 hour reaction time. 

Geraniol is converted into atmospheric pressure phenethyl alcohol gives phenylacetaldehyde cinnamaldehyde is obtained from cinnamyl alcohol in good yield by use of a silver catalyst at 200°/20 mm.429 Bremner et al.43° describe a laboratory method for oxidation of tetrahydrofurfuryl alcohol by air on silver wool. 

Strained cyclic ethers react with aromatic compounds with formation of hydroxyalkyl derivatives with ethylene oxide (oxirane) and aluminum chloride, benzene gives phenethyl alcohol in 70% yield,541 and with oxetane gives... 

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