Benzyl alcohols selectivity

Many chromium oxidants suffer from problems of stability, light sensitivity or acidity, but tetrakis(py-ridine)silver dichromate is stable, nonphotosensitive, nonhygroscopic and a neutral oxidant It can be used to oxidize allylic and benzylic alcohols selectively in benzene. Unfortunately, it cannot be used in chlorinated solvents because it decomposes in these solvents. 

Figure 22.1. Toluene conversion and selectivity to partial oxidation products. Reaction conditions 160°C, 0.1 MPap02, 20 ml toluene, 0.8 g of catalyst (1 wt% AuPd/C prepared by sol-immobilisation with 1 1.85 Au/Pd ratio), toluene/metal molar ratio of 3,250 and reaction time 110 h. Key o conversion, selectivity to benzyl alcohol, selectivity to benzaldehyde, selectivity to benzoic acid, selectivity to benzyl benzoate.

Photolysis at 254 nm, CH3OH, CH2CI2, phenanthrene, 51-84% yield. These conditions are selective for ally lie and benzylic alcohols. In the absence of the phenanthrene, TBDMS ethers are also cleaved. ... 

Oxidizing toluene to benzaldehyde is a catalyzed reaction in which a selective catalyst limits further oxidation to benzoic acid. In the first step, benzyl alcohol is formed and then oxidized to benzaldehyde. Further oxidation produces benzoic acid ... 

The chemistry of indium metal is the subject of current investigation, especially since the reactions induced by it can be performed in aqueous solution.15 The selective reductions of ethyl 4-nitrobenzoate (entry 1), 2-nitrobenzyl alcohol (entry 2), l-bromo-4-nitrobenzene (entry 3), 4-nitrocinnamyl alcohol (entry 4), 4-nitrobenzonitrile (entry 5), 4-nitrobenzamide (entry 6), 4-nitroanisole (entry 7), and 2-nitrofluorenone (entry 8) with indium metal in the presence of ammonium chloride using aqueous ethanol were performed and the corresponding amines were produced in good yield. These results indicate a useful selectivity in the reduction procedure. For example, ester, nitrile, bromo, amide, benzylic ketone, benzylic alcohol, aromatic ether, and unsaturated bonds remained unaffected during this transformation. Many of the previous methods produce a mixture of compounds. Other metals like zinc, tin, and iron usually require acid-catalysts for the activation process, with resultant problems of waste disposal. 

Rapid loading of cross-linked PS Wang resin (4-(benzyloxy)benzyl alcohol PS) with a selection of /3-ketoesters was shown to reach completion within 1-10 min if microwave irradiation at 170 °C was employed. The conventional thermal method for acetoacetylation of hydroxymethyl-functionalized polystyrene resins takes several hours therefore, microwave heating allowed for... 

We have also found that BTMA Br3 can be used as a reagent for the oxidation of benzyl alcohols to benzoic acids. That is, the reaction of benzyl alcohols with 2-equiv. of BTMA Br3 in an aq. alkaline solution at room temperature or at 70°C afforded benzoic acids in good yields. Thus, we could selectively obtain the oxidation products, benzaldehydes and benzoic acids, from benzyl alcohols by using a stoichiometric amount of BTMA Br3 (Fig. 24) (ref. 32). 

Fig. 24. Selective oxidation of benzyl alcohols with BTMA Br3...

Similarly, Dakka and Sasson (ref. 26) showed that benzylic alcohols could be selectively oxidized to the corresponding aromatic aldehydes using HBr/H202 as the oxidant (Fig. 23). The reaction was not successful with electron-rich aromatics which underwent competing nuclear bromination. 

Under microwave irradiation and applying MCM-41-immobilized nano-iron oxide higher activity is observed [148]. In this case also, primary aliphatic alcohols could be oxidized. The TON for the selective oxidation of 1-octanol to 1-octanal reached to 46 with 99% selectivity. Hou and coworkers reported in 2006 an iron coordination polymer [Fe(fcz)2Cl2]-2CH30H with fez = l-(2,4-difluorophenyl)-l,l-bis[(l//-l,2,4-triazol-l-yl)methyl]ethanol which catalyzed the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as oxidant in 87% yield and up to 100% selectivity [149]. An alternative approach is based on the use of heteropoly acids, whereby the incorporation of vanadium and iron into a molybdo-phosphoric acid catalyst led to high yields for the oxidation of various alcohols (up to 94%) with molecular oxygen [150]. 

Seddon, K.R. Stark, A. (2002) Selective Catalytic Oxidation of Benzyl Alcohol and Alkylbenzenes in Ionic Liquids. Green Chemistry, 4(2), 119-123. 

In earlier work, Bhaumik and Kumar (1995) have reported that the use of two liquid phases in the oxidation of hydrophobic organic substances with aqueous H2O2 using titanium silicate as the catalyst not only enhances the rate of oxidation but also improves selectivity for species like toluene, anisole, and benzyl alcohol. For a single liquid phase acetonitrile was u.sed a solvent. The solid-liquid system gives high ortho selectivity. Thus, in the case of anisole the ratios of o to p for. solid-liquid and solid-liquid-liquid system were 2.22 1 and 0.35 1, respectively. 

Figure 4.29 An example of the use of ternary solvents to control mobile phase strength and selectivity in reversed-phase liquid chromatography. A, methanol-water (50 50) B, tetrahydrofuran-water (32 68) C, methanol-tetrahydrofuran-water (35 10 55). Peak identification 1 - benzyl alcohol 2 phenol 3 3-phenylpropanol 4 2,4-dimethylphenol 5 benzene and 6 -diethylphthalate. (Reproduced with permission from ref. 522. Copyright Elsevier Scientific Publishing Co.)...

Scheme 10.3 gives some examples of pinacol and related rearrangements. Entry 1 is a rearrangement done under strongly acidic conditions. The selectivity leading to ring expansion results from the preferential ionization of the diphenylcarbinol group. Entry 2, a preparation of 2-indanone, involves selective ionization at the benzylic alcohol, followed by a hydride shift. 

The preservatives I select for my formulations is much more limited than the ten listed in the above reference. The products which I develop for a company with natural ingredients image, restricted me to the para hydroxy benzoic acids, benzyl alcohol and phenoxyethanol. I have been allowed to use Myavert C during the last two years due to increase in customer complaints which was assumed to be due to the high levels of phenoxyethanol and benzyl alcohol used hence allergic reaction to the... 

Figure 8. The m/z 137 ion was selected from the source and colli-sionally decomposed (N ) to give the CAD spectra. The top spectrum is the fragment arising from the isolated xenognosin and the bottom two spectra arise from the isomeric benzyl alcohols ((3).

Devaky and Rajasree have reported the production of a polymer-bound ethylenediamine-borane reagent (63) (Fig. 41) for use as a reducing agent for the reduction of aldehydes.87 The polymeric reagent was derived from a Merrifield resin and a 1,6-hexanediol diacrylate-cross-linked polystyrene resin (HDODA-PS). The borane reagent was incorporated in the polymer support by complexation with sodium borohydride. When this reducing agent was used in the competitive reduction of a 1 1 molar mixture of benzaldehyde and acetophenone, benzaldehyde was found to be selectively reduced to benzyl alcohol. 

Ono and Kamimura have found a very simple method for the stereo-control of the Michael addition of thiols, selenols, or alcohols. The Michael addition of thiolate anions to nitroalkenes followed by protonation at -78 °C gives anti-(J-nitro sulfides (Eq. 4.8).11 This procedure can be extended to the preparation of a/jti-(3-nitro selenides (Eq. 4.9)12 and a/jti-(3-nitro ethers (Eq. 4.10).13 The addition products of benzyl alcohol are converted into P-amino alcohols with the retention of the configuration, which is a useful method for anri-P-amino alcohols. This is an alternative method of stereoselective nitro-aldol reactions (Section 3.3). The anti selectivity of these reactions is explained on the basis of stereoselective protonation to nitronate anion intermediates. The high stereoselectivity requires heteroatom substituents on the P-position of the nitro group. The computational calculation exhibits that the heteroatom covers one site of the plane of the nitronate anion.14... 

Generally, primary aliphatic alcohols are oxidized to their respective aldehydes, secondary aliphatic and aromatic alcohols to the corresponding ketones, and allyl and benzyl alcohols to their carboxylic acid or carboxylate ions. For instance, 2-propanol, acetaldehyde, and methyl-benzoate ions are oxidized quantitatively to acetone, acetate, and terephtalate ion respectively, while toluene is converted into benzoate ion with an 86% yield. Controlling the number of coulombs passed through the solution allows oxidation in good yield of benzyl alcohol to its aldehyde. For diols,502 some excellent selectivity has been reached by changing the experimental conditions such as pH, number of coulombs, and temperature. 

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