2- Phenylacetaldehyde system

In the presence of the indane aldehyde, additional somewhat irreversible waves are seen at ( wO.l V), which probably refer to some Ru(III) intermediates (10) involved in the catalysis. In the corresponding phenylacetaldehyde system, additional waves are seen at about -0.08 and +0.08 V. On adding nBuoP to the indane aldehyde system, waves are seen at 0.30 V [RuIII(TPP)(nBu3P)2 + e RuII(TPP)(nBu3P)2]> and M).90 V [due to the couple shown... 

Phenylacetyl chloride and hydrocin-namoyl chloride are reduced at mercury to form both acyl radicals and acyl anions as intermediates [76]. From electrolyses of phenylacetyl chloride, the products include 1,4-diphenyl-2-butene-2,3-diol diphenylac-etate, phenylacetaldehyde, toluene, 1,3-diphenylacetone, and l,4-diphenyl-2,3-butanediol, and analogous species arise from the reduction of hydrocinnamoyl chloride. Reduction of phthaloyl dichloride is a more complicated system [77] the electrolysis products are phthalide, biph-thalyl, and 3-chlorophthalide, but the latter compound undergoes further reduction to give phthalide, biphthalyl, and dihydrobi-phthalide. 

Phenylacetaldehyde and its aldol condensation product with creatinine are very important intermediates in the formation of PhIP. The corresponding Schiff base could not be found in model systems or in fried meat.310... 

Gel emulsions were applied successfully for the first time in aldol additions of DHAP to phenylacetaldehyde and benzyloxyacetaldehyde as model aldehydes catalyzed by RAMA [24]. The first interesting observation was that the stability of RAMA in water-in-oil gel emulsions improved by 25-fold compared to that in dimethylformamide/water l/4v/v co-solvent mixture. The reported experimental data concluded that both the highest enzymatic activities and equilibrium yields were observed in water-in-oil gel emulsion systems with the lowest water-oil interfacial tension attained with the most hydrophobic oil component (i.e. tetradecane, hexadecane, and squalane). 

The post-modification with propylene oxide gives the best catalytic results, both with Sil-GP-tacn and MCM-GP-tacn. For the latter system, methanol seems a superior solvent in comparison with acetone and acetonitrile. The epoxide selectivity in reaction 7 is limited, but this is due to secondary reactions of initially formed epoxide to phenylacetaldehyde and the diol. When these secondary products are taken into account, the selectivity for the epoxide and its derived products increases to 76 %. 

The isomerization of styrene oxide to phenylacetaldehyde yields 100% using modified ZSM-5 zeolites, thereby the highest target achieved by catalysis has been fulfilled. A new process as well has been found for the heterogeneously-catalysed production of campholenic aldehyde from a-pinene oxide. By using low reaction temperatures of 0 °C and below in combination with HCl-treated H-US-Y zeolites, up to 85% yield is achieved. This process is competitive with the homogeneous ZnBr2 system. 

Water-in-oil (W/O) gel emulsions has been applied for the first time in a-chymotrypsin-catalyzed peptide synthesis (Clapds et al. 2001) and in aldolic condensation of DHAP with acceptor aldehydes such as phenylacetaldehyde and ben-zyloxyacetaldehyde, catalyzed by D-fructose-l,6-bisphosphate aldolase from rabbit muscle (RAMA). Gel emulsions of the ternary systems such as water/Ci4E4/oil, where C14E4 is a technical grade poly(oxyethylene) tetradecyl ether surfactant, with an average of four moles of ethylene oxide per surfactant molecule and oil can be... 

Fig. 6.5.9 Influence of the partition coefficient on the equilibrium product yield for the RAMA-catalyzed aldol addition of DHAP (30 mM) to phenylacetaldehyde (50 mM) in water/Ci4E4/oil 90/4/6 w/w gel emulsion systems at 25 °C...

Similar TS-1 films have been applied for phenol hydroxyl-ation reaction to dihydroxybenzenes (hydroquinone and catechol) [354] and catalytic oxidation of styrene to benzaldehyde and phenylacetaldehyde [355] with hydrogen peroxide as oxidant in batch-type membrane reactors. The dihydroxybenzenes and phenylacetaldehyde selectivity values increased with in-framework Ti content. In order to reduce the TS-1 membrane costs, Chen et al. [356] have successMly synthesized TS-1 on mullite tubes by replacing TPAOH with TPABr/EtjNH system (4% of the initial cost). The catalytic activity was tested in the probe reaction of isopropyl alcohol oxidation with hydrogen peroxide under pervaporation condition at 60°C. In general, future work on TS-1 film catalysts is required to improve mass transfer resistances and reaction conversion without compromising selectivity. 

A newer technology based on metal-peroxo chemistry, without most of the drawbacks just outlined, and usable in the above cases, employs the titanium silicalite (TS-1) heterogeneous catalyst. This works with aqueous hydrogen peroxide, with methanol as a co-solvent if required by the substrate, under relatively mild conditions. The epoxidation of a range of olefins has been demonstrated [72] some are oxidised to other products, such as styrene to phenylacetaldehyde. The system is powerful enough to oxidise terminal olefins and, e.g., allyl chloride. Its main limitation is upon the size of the substrate and products, which must pass down zeolite channels 5.5 A in diameter. 

Chan, F., G.A. Reineccins, Reaction kinetics for the formation of isovaleraldehyde, 2-acetyl-1-pyrroline, di(H)di(OH)-6-methylpyranone, phenylacetaldehyde, 5-methyl-2-phenyl-2-hexenal, and 2-acetylfuran in model systems, in Maillard Reactions in Chemistry, Food, and Health, T.P. Labuza, G.A. Reineccius, V. Monnier, J.O. O Brien, J.W. Baines, Eds., Royal Chem. Soc. London, London, 1994, p. 131. 

The oxidation of sulfamethoxazole by NH4VO3 in H2SO4 is first order in each reactant. Mechanisms have been proposed for the vanadium(V) oxidation of phenol and /3-naphthol in acidic media the reaction is first order in vanadium(V) in both systems and first order in substrate and acid in the case of the phenol system, but second order in substrate and independent of acid in the j8-naphthol system. In the vanadium(V) oxidation of phenyl styryl ketones (PSKs) under acidic conditions, benzoic acids and phenylacetaldehydes are produced via a proposed mechanism in which the carbonyl group is attacked by vanadium(V). The stoichiometry of the reaction is 2 1 [vanadium(V) PSK] and the rates are enhanced by electron-releasing substituents in both phenyl rings and retarded by electron-withdrawing substituents. The micellar-catalysed oxidation of glycine by vanadium(V) is first order in oxidant... 

Furthermore, the results revealed that, in addition to MBT level, 3-(methylthio)propanal and phenylacetaldehyde levels were significantly increased in the illuminated sample (Table 1). The formation of such Strecker aldehydes induced by light has also been observed earlier in model systems containing catechin, riboflavin, and the respective precursor amino acids [16] and has been reported for light-treated skim milk [17]. However, the mechanism of Strecker aldehyde formation induced by light is still unclear. 

Mutated Rhodococcus phenylacetaldehyde reductase (PAR) or Leifsonia alcohol dehydrogenase (LSADH) were applied to water-soluble ketone substrates. For example, 4-hydroxy-2-butanone was reduced to (S)/(R)-l,3-butanediol, with a high yield and stereoselectivity. Intact E coli cells overexpressing mutated PAR (Sar268) or LSADH were directly immobilized with polyethyleneimine or 1,6-hexanediamine and glutaraldehyde and evaluated in a batch reactor. This system produced (S)-l,3-butanediol (87% ee) with a space-time yield (STY) of 12.5 mg/h/mL catalyst or (R)-l,3-butanediol (99% ee.) with an STY of 60.3 mg/h/mL catalyst. The immobilized cells in a packed bed reactor continuously produced (R)-l,3-butanediol with a yield of 99% (about 49.5 g/L) from 5% (w/v) 4-hydroxy-2-butanoate over 500 h. The concentration of PEI used for immobilization influenced the operational stability of immobilized cells, and the cells treated with 3% PEI showed better stability than those treated with lower PEI concentrations The immobilized E. coli biocatalyst could be used more than 30 times (for about 500 h) with no decrease in conversion [54]. 

Chocolate represents a highly complex flavor system for which no single character impact has been identified. Vanillin and Furaneol contribute to the sweet, caramel background character of milk chocolate (57). 5-Methyl-2-phenyl-2-hexenal provides a deep bitter, cocoa note, and is the aldol reaction product from phenylacetaldehyde and 3-methylbutanal, two Strecker aldehydes formed in chocolate (58). 2-Methoxy-5-methylpyrazine and isoamyl phenylacetate have chocolate, cocoa, nutty and cocoa-like notes, respectively, and both are used in synthetic chocolate flavors (59). Systematic studies of key odorants in milk chocolate were performed using aroma extract dilution analysis however, character impact compounds unique to chocolate flavor were not reported (57,60). 

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