Benzyl alcohols conversion

Figure 8.2 Benzyl alcohol conversion as function of the rate of H202 addition in the presence of silica-entrapped TPAP. (Reproduced from ref. 2, with permission.)...

Benzyl alcohol conversion to benzaldehyde is generally accepted to follow a dehydrogenation mechanism via two elementary steps as shown in the following ... 

A pillar structure of small rectangular posts was incorporated near the outlet of the reaction channel to retain the catalyst. The reaction was studied in the temperature range of 80-120 °C and at inlet pressures up to 5 bar. Benzyl alcohol conversion and benzaldehyde selectivity at 80 and 120 °C were very close to those from conventional glass stirred reactors. The best conversion of benzyl alcohol of 95.5% with selectivity to benzaldehyde of 78% was obtained for a micropacked bed reactors with catalyst sizes of 53-63 pm and a catalyst bed length of 48 mm at 120 °C and 5 bar. The effect of catalyst particle size on the reaction was examined with two ranges of particle size 53-63 pm and 90-125 pm. Lower conversion was obtained with particle sizes of 90-125 pm, indicating the presence of internal mass transfer resistances. In situ Raman measurements were performed and could be used to obtain the benzaldehyde concentration profile along the catalyst bed. 

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

Nearly all of the benzyl chloride [100-44-7], henzal chloride [98-87-3], and hen zotrichl oride /P< -(97-i manufactured is converted to other chemical intermediates or products by reactions involving the chlorine substituents of the side chain. Each of the compounds has a single primary use that consumes a large portion of the compound produced. Benzyl chloride is utilized in the manufacture of benzyl butyl phthalate, a vinyl resin plasticizer benzal chloride is hydrolyzed to benzaldehyde hen zotrichl oride is converted to benzoyl chloride. Benzyl chloride is also hydrolyzed to benzyl alcohol, which is used in the photographic industry, in perfumes (as esters), and in peptide synthesis by conversion to benzyl chloroformate [501-53-1] (see Benzyl ALCOHOL AND p-PHENETHYL ALCOHOL CARBONIC AND CARBONOCm ORIDIC ESTERS). 

Certain functional groups may be protected from reduction by conversion to anions that resist reduction. Such anions include the alkoxides of allylic and benzylic alcohols, phenoxide ions, mercaptide ions, acetylide ions, ketone carbanions, and carboxylate ions. Except for the carboxylate, phenoxide, and mercaptide ions, these anions are sufficiently basic to be proton-ated by an alcohol, so they are useful for protective purposes only in the... 

A one-pot conversion of benzyl alcohols to benzyl fluorides by treatment of the alcohols with a combination of methanesulfonyl fluoride, cesium fluoride and 18-crown 6 ether in tetrahydrofuran has been repotted The reaction involves mesylation of the alcohols followed by cleavage of the resultant mesyl esters with a fluoride ion The reaction has been extended also to certain heterocycles bearing the N hydroxymethyl group [43] (equation 31)... 

Hydrogenolysis of aromatic carbonyls occurs mainly by conversion to the benzyl alcohol and its subsequent loss. If hydrogenolysis is desired, the usual catalyst is palladium 38). Hydrogenolysis is facilitated by polar solvent and by acid (55). For instance, hydrogenation of 3,3-dicarbethoxy-5,8-dimethoxy-l-tetralone (5) over 5% Pd-on-C gave 6 quantitatively 54) when hydrogen absorption ceased spontaneously. 

It is important to note that the one-step conversion of 27 to 28 (Scheme 4) not only facilitates purification, but also allows differentiation of the two carbonyl groups. After hydrogenolysis of the iV-benzyl group (see 28—>29), solvolysis of the -lactone-ring in 29 with benzyl alcohol and a catalytic amount of acetic acid at 70 °C provides a 3 1 equilibrium mixture of acyclic ester 30 and starting lactone 29. Compound 30 can be obtained in pure form simply by washing the solid mixture with isopropanol the material in the filtrate can be resubjected to the solvolysis reaction. 

Acid chloride 5 is readily available from the known benzylic alcohol 6,4e but intermediate 4 is still rather complex. It was recognized that compound 4 could conceivably be formed in one step from 2-methoxyfuran (9)10 and iodotriflate 10. The latter compound was designed with the expectation that it could be converted to benzyne 8," a highly reactive species that could be intercepted in an intermolecular Diels-Alder reaction with 2-methoxyfuran (9) to give 7. The intermediacy of 7 is expected to be brief, for it should undergo facile conversion to the aromatized isomer 4 either in situ or during workup. 

Diphenylphosphoryl azide also gives good conversion of primary alkyl and secondary benzylic alcohols to azides in the presence of the strong organic base diazabicyc-loundecane (DBU). These reactions proceed by O-phosphorylation followed by Sw2 displacement.78... 

The presence of water is essential for the success of these reductions. In anhydrous THF, for example, treatment of iV-benzoylimidazole with NaBH4 leads to benzyl benzoate as the main product (73%), along with 19% benzyl alcohol.[33] Other reports, however, describe the conversion of carboxylic acid imidazolides to the corresponding alcohols by complex hydrides in organic solvents. Further alcohols have been synthesized via imidazolides ... 

Improved control was observed, however, upon addition of benzyl alcohol to the dinuclear complexes.887 X-ray crystallography revealed that whereas (296) simply binds the alcohol, (297) reacts to form a trinuclear species bearing four terminal alkoxides. The resultant cluster, (298), polymerizes rac-LA in a relatively controlled manner (Mw/Mn=1.15) up to 70% conversion thereafter GPC traces become bimodal as transesterification becomes increasingly prevalent. NMR spectroscopy demonstrates that the PLA bears BnO end-groups and the number of active sites was determined to be 2.5 0.2. When CL is initiated by (298) only 1.5 alkoxides are active and kinetic analysis suggests that the propagation mechanisms for the two monomers are different, the rate law being first order in LA, but zero order in CL. 

Unsymmetrical ethers may be produced from the acid-promoted reactions of aldehydes and organosilicon hydrides when alcohols are introduced into the reaction medium (Eq. 173).327,328 An orthoester can be used in place of the alcohol in this transformation.327 335 A cyclic version of this conversion is reported.336 Treatment of a mixture of benzaldehyde and a 10 mol% excess of triethylsilane with methanol and sulfuric, trifluoroacetic, or trichloroacetic acid produces benzyl methyl ether in 85-87% yields.328 Changing the alcohol to ethanol, 1-propanol, 2-propanol, or 1-heptanol gives the corresponding unsymmetrical benzyl alkyl ethers in 45-87% yield with little or no side products.328 A notable exception is the tertiary alcohol 2-methyl-2-propanol, which requires 24 hours.328 1-Heptanal gives an 87% yield of //-lie ply I methyl ether with added methanol and a 49% yield of benzyl n-heptyl ether with added benzyl alcohol under similar conditions.328... 

Benzophenone, conversion to ethyl /S-hydroxy-0,0-diphenylpro-pionate, 44, 57 Benzophenone oxime, 44, 52 Benzopyrazole, 42, 69 3-Benzoylpropionic add, condensation with benzaldehyde to give a-benzylidene-y-phenyl-A y -bu-tenolide, 43, 3 N-Benzylacetamide, 42,18 n-Benzyiacrylamide, 42,16 Benzyl alcohol, reaction with acrylonitrile, 42,16... 

For example, whereas the solid oxidation catalyst MCM-41-entrapped perruthenate can be used for the conversion of benzyl alcohols only, a similarly perruthenated-doped amorphous ORMOSIL is equally well suited for a variety of different alcohol substrates.35 On the other hand, a uniform pore structure ensures access to the active centres, while in an amorphous material made of non-regular porosity hindered or even blocked sites can well exist (Figure 1.16), rendering the choice of the polycondensation conditions of paramount importance. 

---