Hydrogenation of benzaldehyde

Benzyl alcohol, [100-51 -6] C H CH20H (bp, 205.4°C at 101.3 kPa), produced by the hydrogenation of benzaldehyde is used in color photography as a parenteral solution preservative as a general solvent and as an intermediate in the manufacture of various benzoate esters for the soap, perfume, and flavor industries (see Benzyl alcohol and P-phenethyl alcohol). 

In the catalytic hydrogenation of benzaldehyde to benzyl alcohol, it is very important to prevent the hydrogenolysis of the product. Nickel60-63 and copper... 

Equation 11.43 Transfer hydrogenation of benzaldehyde with ruthenium catalysis. 

If some metal hydride species catalyzes the hydrogenation of benzaldehyde ... 

Kinetic and mechanistic studies by Casey et al. provided further insight into the mechanistic details of the hydrogenation of ketones and aldehydes, using a more soluble analogue of Shvd s catalyst (with p-tolyl groups instead of two of the Ph groups) [72]. The kinetics of hydrogenation of benzaldehyde by the Ru complex shown in Eq. (43) were first order in aldehyde and first order in the Ru complex the... 

This catalytic system was further studied by Strohmeier and Steigerwald, who performed reactions at 10 bar without solvent to achieve hydrogenation of a series of aldehydes (Table 15.1) [2]. Turnover numbers (TON) of up to 8000 were achieved in the case of the hydrogenation of benzaldehyde. The chemoselectivity of this catalyst towards carbonyl hydrogenation over alkene hydrogenation was... 

For example, hydrogenation of benzaldehyde with 1 mol of ammonia gave 89.4% of primary and 7.1% of secondary amine while the reaction with 0.5 mol of ammonia afforded 11.8% of the primary and 80.8% of the secondary amine [956]. 

Electrocatalytic hydrogenation is also achieved by reaction of carbonyl compounds with aluminium and nickel(ll) chloride in tetrahydrofuran. Nickel(li) is reduced to finely divided nickel(o) which is deposited on the aluminium.This se-tsup corrosion cells where aluminium dissolves, liberating electrons which are transferred to the nickel. Protons are then reduced to hydrogen at the nickel surface. Hydrogenation of benzaldehydes to the alcohol has been effected under these conditions [206]. 

Hydrogenation of benzaldehyde yields benzyl alcohol, condensation with aliphatic aldehydes leads to additional fragrance substances or their unsaturated intermediates. Unsaturated araliphatic acids are obtained through the Perkin reaction, for example, the reaction with acetic anhydride to give cinnamic acid. 

HYDROGENATION OF BENZALDEHYDE TO BENZYL ALCOHOL IN A SLURRY AND FIXED-BED REACTOR... 

The catalytic hydrogenation of benzaldehyde is a model reaction of hydrogenations of aromatic aldehydes. The principal reaction is ... 

The kinetic model developed in this study can be used to design and analyze various chemical reactors for the hydrogenation of benzaldehyde. Although it is based on a Langmuir-Hinshelwood mechanism, it does not prove that this is the correct mechanism. 

Carbonyl)chlorohydridotris(triphenylphosphine)ruthenium(II) was used as a catalyst in the transfer hydrogenation of benzaldehyde with formic acid as a hydrogen source. Under these conditions, the reduction ofbenzaldehyde to benzyl alcohol is accompanied by esterification of the alcohol with the excess of formic acid to provide benzyl formate (Scheme 4.16). In this microwave-assisted reaction, the catalyst displayed improved turnover rates compared to the thermal reaction (280 vs. 6700 turnovers/h), thus leading to shorter reaction times36. 

Asymmetric transfer hydrogenation of benzaldehyde-l-d with (R,R)-28 and (CH3)3COK in 2-propanol gave (R)-benzyl-l-d alcohol quantitatively in 98% ee (Scheme 41) [114], Introduction of electron-donating and electron-accepting groups at the 4 position had little effect on the enantioselectivity. Catalytic deuteration of benzaldehydes was achieved by use of the same complex (R,R)-28 and a 1 1 mixture of formic acid-2-d and triethylamine to give the S deuter-io alcohols in up to 99% ee (Scheme 42) [114], The dt content in the product alcohol was >99%. Only a stoichiometric amount of deuterium source is required to complete the reaction. 

Another polymer-mediated synthesis used a lyotropic liquid-crystal (LLC) template to obtain 4- to 7-nm crystalhtes of Pd (Ding and Gin, 2000). In this study, Pd2+ was ion exchanged into the channels of a cross-linked LLC and reduced with H2. The resultant catalysts were found to be active for efficient hydrogenation of benzaldehyde. 

Copper-chromium oxide catalyst is effective for the hydrogenation of aldehydes at a temperature of 125-150°C.1 The hydrogenation of benzaldehyde over copper-chromium gives a high yield of benzyl alcohol even at 180°C without hydrogenolysis to give toluene (eq. 5.5).7... 

Figure 6 Hydrogenation of benzaldehyde over Ni-monoliihic catalyst 420 K, 16 bar, 1250 RPM. benzaldehyde, + benzyl alcohol, toluene. (From Ref. 28.)...

E. Otten, Hydrogenation of Benzaldehyde over Monolithic Catalysts, Masters thesis. Delft University of Technology, Delft, The Netherlands, 1994. 

We have prepared the supported Rh(DiPFc) on alumina using PTA as the anchoring agent and have used this catalyst for the hydrogenation of benzaldehyde and several substituted benzaldehydes. Table 2 lists the rate data for the benzaldehyde hydrogenations run in both ethanol and i-propanol. While... 

Table 2 Reaction data for the hydrogenation of benzaldehyde over Rh(DiPFc)/PTA/A1203 run at room ten5)erature and 50 psig in different solvents.

Reduction of carbonyl groups. Aldehydes and ketones are subjected to enantioselective reduction. Hydrogenation of benzaldehyde-a-d, a-alkoxyketones " or )3-ketoesters can be accomplished using either the Ru dihalide complexes or some modified forms. a-Ketoesters are also similarly reduced. 

Supported Pd/C catalysts, Raney nickel, and nickel boride are good catalysts for the hydrogenation of benzaldehyde. By measuring the take up of hydrogen in a batch reactor, it was found that the reaction is zero order in the reactants benzaldehyde and hydrogen at pressures above 3 bar and aldehyde concentrations in excess of 1 mol/L. With the catalyst 3 % Pd/C a reaction rate of 1.6 x 10 molg min was measured at 22 °C and was independent of the solvent [2]. 

Fig. 13-15 Kinetic study ofthe hydrogenation of benzaldehyde in a stirred autoclave operating in suspension mode [15] (with permission of Elsevier, Amsterdam)...

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