Cinnamyl alcohol from cinnamaldehyde

The selectivities in forming cinnamyl alcohol from cinnamaldehyde using these catalysts were poor, and generally resulted in the formation of the saturated aldehyde. This could be overcome by the use of a large excess of phosphine, though at the expense of yield. The same group have demonstrated that ruthenium analogues of the BDNA complex are more active and selective [7]. 

Fig. 15.15 Cinnamyl alcohol selectivity as a function of conversion in the selective hydrogenation of cinnamaldehyde over differently supported Ru catalysts. Reactions conditions as listed in Tab. 15.4. Data compiled from literature [120,122,123,126], HSAG high-surface area graphite AC activated carbon.

Many more examples exist for reduction of the carhonyl only. Over an osmium catalyst [763] or platinum catalyst activated by zinc acetate and ferrous chloride [782] cinnamaldehyde was hydrogenated to cinnamyl alcohol. The same product was obtained by gentle reduction with lithium aluminum hydride at —10° using the inverse technique [609], by reduction with alane (prepared in situ from lithium aluminum hydride and aluminum chloride)... 

Thioacidolysis allows the distinction between products derived from lignin and products derived from />coumaric and ferulic acids, and the distinction between products derived from cinnamaldehydes and cinnamyl alcohols. Recent improvements have made it possible to estimate the fraction of free phenolic groups in uncondensed lignin (see Section 1.3.1), and to depolymerize the dimers, so that they can be included in the analysis of the lignin composition. 

Some commercial samples of precipitated manganese dioxide may be active enough for use directly in an oxidation process. To assess the activity of a sample of manganese dioxide, dissolve 0.25 g of pure cinnamyl alcohol in 50 ml of dry light petroleum (b.p. 40-60 °C) and shake the solution at room temperature for 2 hours with 2g of the sample of manganese dioxide (previously dried over phosphoric oxide). Filter, remove the solvent by evaporation and treat the residue with an excess of 2,4-dinitrophenylhydrazine sulphate in methanolt (Section 9.6.13, p. 1257). Collect the cinnamaldehyde 2,4-dinitrophenyl-hydrazone and crystallise it from ethyl acetate. An active dioxide should give a yield of the derivative, m.p. 255 °C (decomp.), in excess of 0.35 g (60%). 

The reductive sequence from an appropriate cinnamic acid to the corresponding cinnamyl alcohol is not restricted to lignin and lignan biosynthesis, and is utilized for the production of various phenylpropene derivatives. Thus cinnamaldehyde (Figure 4.23) is the principal component in the... 

The relatively inexpensive and safe sodium borohydride (NaBH4) has been extensively used as a reducing agent because of its compatibility with protic solvents. Varma and coworkers reported a method for the expeditious reduction of aldehydes and ketones that used alumina-supported NaBH4 and proceeded in the solid state accelerated by microwave irradiation (Scheme 7) [50]. The chemoselectivity was apparent from the reduction of frarcs-cinnamaldehyde to afford cinnamyl alcohol. 

The lithium aluminium hydride reductions often proceed at room temperature or below and are usually rapid and free from side reactions. The compound to be reduced is added slowly to an excess of the reagent suspended or dissolved in ether (normal addition). Selective reduction of polar groups in the presence of other reducible functions can frequently be achieved by an inverse addition method the reagent is added slowly to the substance to be reduced, so that the reagent is never present in excess. Thus, by inverse addition cinnamaldehyde (6.44) is reduced to cinnamyl alcohol (6.3). Normal addition gives dihydrocinnamyl alcohol (6.4). 

The activity of cinnamyl alcohol dehydrogenase (CAD EC 1.1.1.195) was already described in the 1970s and was mainly investigated with respect to lignin biosynthesis (see Petersen et al, 1999, for further information). It catalyses the reduction of cinnamaldehydes to cinnamyl alcohols with the help of NADPH the reaction is readily reversible (Fig. 4.7). From a functional point of view, CAD activity is involved in developmental lignification and in the formation of defence compounds. Several reviews have treated the involvement of this enzyme in lignin monomer formation (Boudet et al, 1998,... 

Different types of end-groups are shown in Figure 7.7. End-groups of the cinnamyl alcohol (47) and cinnamaldehyde (48) types have been detected in both isolated lignins and lignins in wood. Quantitative analysis of MWL from spruce wood by H NMR spectroscopy suggests the presence of about 1% units of type 47 [40] and... 

Geraniol is converted into atmospheric pressure phenethyl alcohol gives phenylacetaldehyde cinnamaldehyde is obtained from cinnamyl alcohol in good yield by use of a silver catalyst at 200°/20 mm.429 Bremner et al.43° describe a laboratory method for oxidation of tetrahydrofurfuryl alcohol by air on silver wool. 

Jones reagent (1, 142-143). Primary allylic or benzyUc alcohols are oxidized in high yield with chromic acid in acetone. Thus cinnamyl alcohol is oxidized to cinnamaldehyde in 84% yield, and benzaldehyde is obtained from benzyl alcohol in 76% yield. Manganese dioxide has usually been used in such oxidations. 

In the hydrogenation of cinnamaldehyde over the same Ru/C catalysts, selectivity to cinnamyl alcohol changed with Ru content. The influence of Ru loading on the selectivity to cinnamyl alcohol is reported in Fig. 1. The highest selectivity to cinnamyl alcohol was observed on the 10 wt.% Ru sample. On the Ru/C samples an increase of the Ru loading results in the formation of larger Ru metal particles. This is supported by the chemisorption data, which show a decrease of the CO/Ru ratio (table 1), and by a TEM analysis [2] which has shown that the average Ru particle size increases from 3 nm on the 0.5 wt.%... 

The rearrangement of (a-hydroxyalkyl)phosphonate into phosphate ester is not universal (l-hydroxy-2-nitroalkyl)phosphonic esters do not rearrange under the influence of heat whether aided, or not, by added base and the reaction between (Me0)2P(0)H and MeCOCH=CHPh at 130-160 °C yields the 1,2-adduct (105 R = Me) which is stable to base (MeO or EtjN). On the other hand, 105 (R = H) partially decomposes in the presence of MeO and the products include the phosphate 106 together with methyl cinnamate and cinnamyl alcohol, as might be expected from the action of base on cinnamaldehyde Other compounds which undergo base-catalysed rearrangements include 107, the indanones 108 (R = H or the hydroxy phosphinic esters 109 (X = O or S, R =... 

Cinnamyl alcohol refluxed with dibenzo[a,j]xanthylium diloride in anhydrous benzene until the red color has disappeared cinnamaldehyde. Y 97%. F. e., also from ketones, s. G. Casnati, G. P. Gardini, and G. Palla, G. 105, 447 (1975). 

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