Hydrogenation of citral

Hydrogenation reactions, particularly for the manufacture of fine chemicals, prevail in the research of three-phase processes. Examples are hydrogenation of citral (selectivity > 80% [86-88]) and 2-butyne-l,4-diol (conversion > 80% and selectivity > 97% [89]). Eor Pt/ACE the yield to n-sorbitol in hydrogenation of D-glucose exceeded 99.5% [90]. Water denitrification via hydrogenation of nitrites and nitrates was extensively studied using fiber-based catalysts [91-95]. An attempt to use fiber-structured catalysts for wet air oxidation of organics (4-nitrophenol as a model compound) in water was successful. TOC removal up to 90% was achieved [96]. 

Selective hydrogenation of citral Rh/SiO, Geraniol, nerol Fragrances... 

Tuning Selectivity through the Support in the Hydrogenation of Citral over Copper Catalysts... 

Here we wish to report that the support acidity, investigated through IR spectroscopy of adsorbed CO, allows one to tune the selectivity towards different products in the hydrogenation of citral over Cu catalysts. 

Results obtained in the hydrogenation of citral by using Cu catalysts on these two supports are reported in Figure 9.3 and Figure 9.4. 

Determination of the acidic sites through IR spectroscopy of adsorbed CO is a valuable tool for the choice of the support when selective or multifunctional processes are to be set up. This technique allowed to identify a particular kind of silica as the support of choice for the selective hydrogenation of citral to citronellal and sepiolite as a Lewis acid support able to promote the one-step transformation of citral into menthol. 

The reactor system works nicely and two model systems were studied in detail catalytic hydrogenation of citral to citronellal and citronellol on Ni (application in perfumery industty) and ring opening of decalin on supported Ir and Pt catalysts (application in oil refining to get better diesel oil). Both systems represent very complex parallel-consecutive reaction schemes. Various temperatures, catalyst particle sizes and flow rates were thoroughly screened. 

To evaluate the performance of the reactor system, the catalytic hydrogenation of citral to citronellal and citronellol in ethanol was nsed as a sample reaction. The reaction scheme is displayed below. 

More recent advances in iridium-catalyzed aldehyde hydrogenation have been through the use of bidentate ligands [6]. In the hydrogenation of citral and cinnamaldehyde, replacing two triphenylphosphines in [IrH(CO)(PPh3)3] with bidentate phosphines BDNA, BDPX, BPPB, BISBI and PCP (Fig. 15.1) led to an increase in catalytic activity. 

Table 15.2 Bidentate ligands used for the hydrogenation of citral and cinnamaldehyde under 50 bar H2 at 100°C.

Table 15.4 Ru-BDNA-catalyzed hydrogenations of citral and cinnamaldehyde.

When the hydrogenation of citral is performed with supported nanoparticles of rhodium metal, for example Rh/Si02 under classical conditions [liquid phase, rhodium dispersion 80% (particles in the range of 1-2nm), citral/Rhs = 200, P(ti2) = 80bar, T = 340 K], the catalytic activity is very high but most of the above products are obtained and the reaction is totally non-selective, even if the major product was citronellal. 

Figure 3.33 Various pathways for the hydrogenation of citral application to the hydrogenation of citral with Rh covered with various amounts of naked tin or n-butyltin. For Sn/Rh = 0.3, only Sn adatoms are present for Sn/Rh = 0.8,...

Industrially relevant consecutive-competitive reaction schemes on metal catalysts were considered hydrogenation of citral, xylose and lactose. The first case study is relevant for perfumery industry, while the latter ones are used for the production of sweeteners. The catalysts deactivate during the process. The yields of the desired products are steered by mass transfer conditions and the concentration fronts move inside the particles due to catalyst deactivation. The reaction-deactivation-diffusion model was solved and the model was used to predict the behaviours of semi-batch reactors. Depending on the hydrogen concentration level on the catalyst surface, the product distribution can be steered towards isomerization or hydrogenation products. The tool developed in this work can be used for simulation and optimization of stirred tanks in laboratory and industrial scale. 

The model systems considered in the present work are hydrogenation of citral and xylose on nickel catalysts. The complete reaction schemes are displayed in Fig. 1. In an abbreviated form, the schemes can be presented as follows ... 

Figure 1. Reaction scheme for hydrogenation of citral, xylose and lactose.

Aumo, J., Oksanen, S., Mikkola, J. P., Salmi, T. and Murzin, D. Yu., Novel Woven Active Carbon Fiber Catalyst in the Hydrogenation of Citral, Cat Today 102-103 (2005), 128-132... 

Synthesis from Citral. Selective hydrogenation of citral to citronellal can be accomplished in the presence of a palladium catalyst in an alkaline alcoholic reaction medium [65]. 

HYDROGENATION OF CITRAL INTO GERANIOL AND NEROL ON TIN MODIFIED SILICA SUPPORTED RHODIUM. 

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