Benzyl alcohol, carbonylation

Hydrogenation of the carbonyl group yields benzyl alcohol. 

Hydrogenolysis of aliphatic carbonyls usually does not occur readily unless certain types of structures prevail (78), but hydrogenolysis of an aromatic carbonyl will occur easily, mostly via an intermediate benzyl alcohol. 

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. 

In 1983, Nozaki, Takai, Hiyama, and their coworkers disclosed that vinyl and aryl iodides or bromides are reduced with chromium(n) chloride, and that the resulting organochromium(in) species react smoothly with a host of aldehydes to give allylic or benzylic alcohols in excellent yields.6 As shown in Scheme 1, the chromium(n) chloride-mediated carbonyl addition can be conducted efficiently at... 

Manganese dioxide (Mn02) supported on silica provides an expeditious and high-yield route to carbonyl compounds. Benzyl alcohols are selectively oxidized to carbonyl compounds by use of 35 % Mn02 doped silica under MW irradiation conditions (Scheme 6.28) [96]. 

Table 4 The effects of a-carbonyl and a-thiocarbonyl substituents on the relative stabilities of a-methyl benzyl alcohols R-[16]-OH and the corresponding styrenes R-[17] (Scheme 13)"...

Lin and Yamamoto described a Pd-catalyzed carbonylation of benzyl alcohols [131]. Thus, under the agency of palladium catalysis and promotion by HI, 3-thiophenemethanol was carbonylated to give 3-thiopheneacetic acid as a major product along with methylthiophene as a minor one. 

The three-component synthesis of benzo and naphthofuran-2(3H)-ones from the corresponding aromatic alcohol (phenols or naphthols) with aldehydes and CO (5 bar) can be performed under palladium catalysis (Scheme 16) [59,60]. The mechanism involves consecutive Friedel-Crafts-type aromatic alkylation and carbonylation of an intermediate benzylpalla-dium species. The presence of acidic cocatalysts such as TFA and electron-donating substituents in ortho-position (no reaction with benzyl alcohol ) proved beneficial for both reaction steps. 

Adogen has been shown to be an excellent phase-transfer catalyst for the per-carbonate oxidation of alcohols to the corresponding carbonyl compounds [1]. Generally, unsaturated alcohols are oxidized more readily than the saturated alcohols. The reaction is more effective when a catalytic amount of potassium dichromate is also added to the reaction mixture [ 1 ] comparable results have been obtained by the addition of catalytic amounts of pyridinium dichromate [2], The course of the corresponding oxidation of a-substituted benzylic alcohols is controlled by the nature of the a-substituent and the organic solvent. In addition to the expected ketones, cleavage of the a-substituent can occur with the formation of benzaldehyde, benzoic acid and benzoate esters. The cleavage products predominate when acetonitrile is used as the solvent [3]. 

Spindler and Frechet used 3,5-bis((benzoxy-carbonyl)imino)benzyl alcohol which decomposed thermally in THF solution containing DBTDL as a catalyst [97]. The resulting polymer was found to be insoluble unless an end-capping alcohol was added from the beginning. The end-capping groups determined the properties of the polymers such as glass transition temperature, thermal stability, and solubility. 

Carbonyl, stretching frequency, 30 191 Carbonylation, 28 80, 31 39-46 ethanol, 31 45-46 ethylene, 31 46 higher alcohols, 31 45-46 methanol, 31 39-45 of primary linear alcohols, 34 90-94 activation parameters for, 34 91 benzyl alcohol, 34 90 ethanol, 34 90 1-propanol, 34 90 mechanism for, 34 93 variation of products with pressure, 34 92... 

Antimony(III) trichloride can be used as a catalytic mediator in the electroreduction of carbonyl compounds. The advantage of the procedure is illustrated by the selective reduction of acetophenones (497), leading to the corresponding benzylic alcohols (498) (Scheme 173) [575]. The electroreduction is performed in an EtOH/BuOH(l/1.5)-aq.HCl-(Pt/Pb) system in the presence... 

The Boots Hoechst Celanese (BHC) ibuprofen process involves palladium-catalyzed carbonylation of a benzylic alcohol (IBPE). More recently, we performed this reaction in an aqueous biphasic system using Pd/tppts as the catalyst (Figure 9.6 tppts = triphenylphosphinetrisulfonate). This process has the advantage of easy removal of the catalyst, resulting in less contamination of the product. 

Figure 9.7 Carbonylation of benzyl alcohol-catalyzed by tppts/Pd.

In the same way, the biphasic carbonylation of benzyl alcohol (Figure 9.7) was achieved.Phenylacetic acid was obtained in 11% yield, 100% selectivity, and 100% atom utilization. 

As, for the most part, the corresponding ester derivatives are a more important synthetic target, recent literature has demonstrated methods to prepare the esters directly. Examples include the use of nickel carbonyl in a methanol/dimethylformamide solvent system(37) the direct conversion of benzyl alcohol to methylphenyl-acetate using cobalt carbonyl(38) and a reaction system which utilizes an ammonium salt bound to an organic polymer(39). 

The reaction conditions were mild (room temperature, 1 atm CO) and a two-fold excess of base was used along with a catalytic amount of cobalt carbonyl. The product distribution was quantified by VPC. The mixtures contained starting material, ester product, and various amounts of methyl benzyl ether. No detectable amounts of benzyl alcohol, ketones, or hydrocarbons were seen. Potassium methoxide alone afforded mostly the ether. A mixture of potassium methoxide and alumina gave a slight improvement in ester yield but the predominant product was again the ether. In contrast, when potassium methoxide on alumina was used, the carboxyalkylated product, methyl phenylacetate, was prepared in 70 yield with little ether detected. Benzyl chloride reacted in a similar fashion under these mild reaction conditions. Other alkoxide and carbonate bases could be used as... 

Since lignin is not a uniform entity, chemical criteria for its characterization have centred around analytical detenninations of its functional groups, e.g. total hydroxyl content, phenolic hydroxyls (56), methoxyl and other ether groups, benzyl alcohol groups (7a), carbonyl groups (6), etc., and estimations of its content of special structural features, e.g. phenylcoumaran units (5), biphenylyl linkages (123), etc. 

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