Ethyl benzoate hydrogenation

Ethyl benzoate hydrogen chloride as a catalyst). Pass dry hydrogen chloride (Section 11,48,1) into a 600 ml. round-bottomed flask containing 116 g. (145 ml.) of absolute ethyl alcohol, cooled in an ice bath, until the increase in weight is 6 g. Add 30 g. of benzoic acid and reflux the mixture for 4 hours. Isolate the pure ester, b.p. 212-214°, as described for Methyl Benzoate. The yield is 32 g. 

Uses of hydrogen chloride—Hydrogen chloride is sometimes used in the preparation of an ester, for example ethyl benzoate, where it acts as both an acid catalyst and a dehydrating agent. Hydrochloric acid is used primarily to produce chlorides, for example ammonium chloride. It is extensively used in the manufacture of anilme dyes, and for cleaning iron before galvanising and tin-plating. 

Cinnamic acid can be readily esterified by the Fischer-Speier method without any risk of the addition of hydrogen chloride at the double bond. Proceed precisely as for the preparation of ethyl benzoate (p. 104), using 20 g. of cinnamic acid and 20 ml. of rectified spirit. When the crude product is poured into water, a sharp separation of the ester is not readily obtained, and hence the addition of about 10 ml. of carbon tetrachloride is particularly desirable. Finally distil off the carbon... 

The catalyst is inactive for the hydrogenation of the (isolated) benzene nucleus and so may bo used for the hydrogenation of aromatic compounds containing aldehyde, keto, carbalkoxy or amide groups to the corresponding alcohols, amines, etc., e.g., ethyl benzoate to benzyl alcohol methyl p-toluate to p-methylbenzyl alcohol ethyl cinnamate to 3 phenyl 1-propanol. 

The mixed Claisen condensation of two different esters is similar to the mixed aldol condensation of two different aldehydes or ketones (Section 23.5). Mixed Claisen reactions are successful only when one of the two ester components has no a hydrogens and thus can t form an enolate ion. For example, ethyl benzoate and ethyl formate can t form enolate ions and thus can t serve as donors. They can, however, act as the electrophilic acceptor components in reactions with other ester anions to give mixed /3-keto ester products. 

Hydrogenation over nickel catalyst at high temperatures and pressures affects aromatic rings. Over Urushibara nickel at 106-150° and 54atm, ethyl benzoate gave ethyl hexahydrobenzoate in 82% yield [48]. 

Conversion data listed in Table 2 indicate that in the hydrogenation of 4-amino-ethyl benzoate using cyclohexane as a solvent the AI2O3 supported Ru and Rh catalysts are more active than the carbon supported ones. In addition, the conversion of aromatic ester is smaller on Pd/C catalyst than on the carbon supported Ru and Rh. In ethyl acetate the hydrogenation proceeded slower than in cyclohexane, and Rh being more active than Ru. The trans/cis isomer ratio estimated from TLC results varied between 1/3 and 1/1. The UV active by-products were formed in coupling reactions. 

Table 2 Hydrogenation of 4-amino-ethyl benzoate on alumina and carbon supported Ru, Rh and catalysts. Effect of catalyst, solvent and temperature...

Methyl />-acetylbenzoate has been prepared by the esterification of -acetylbenzoic acid with methanol in the presence of hydrogen chloride,6 by the hydrogenation of methyl -trichloro-acetylbenzoate in the presence of a palladium on calcium carbonate catalyst,6 and by the air oxidation of methyl / -ethyl-benzoate.4... 

A crossed Claisen condensation is carried out by first adding the ester without a hydrogens to a solution of the alkoxide base. The ester with a hydrogens is slowly added to this solution, where it forms an enolate and condenses. The condensation of ethyl acetate with ethyl benzoate is an example of a crossed Claisen condensation. 

Aromatic esters are hydrogenated without solvent or in alcohol. Ethyl benzoate (eq. 11.49),11 ethyl phenyl acetate,183 methyl salicylate (eq. 11,50),86a and diethyl phthalate (eq. 11.51)183 were hydrogenated almost quantitatively to the corresponding cyclohexane derivatives over Ni-kieselguhr at 150-200°C. The hydrogenation of the ethyl... 

When one ester has no a hydrogens, a crossed Claisen reaction often leads to one product. Common esters with no a H atoms include ethyl formate (HC02Et) and ethyl benzoate (CjH5C02Et). For example, the reaction of ethyl benzoate (as the electrophile) with ethyl acetate (which forms the enolate) in the presence of base forms predominately one p-keto ester. 

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