Phenylacetaldehyde, formation

The biosynthesis of other volatile phenyl-propanoid-related compoimds such as phenyla-cetaldehyde and 2-phenylethanol, does not occur via trans-cinnamic acid and competes with PAL for Phe utilization [90, 96, 97]. Phenylacetaldehyde biosynthesis from Phe requires the removal of both the carboxyl and amino groups. A classical sequential two-step removal is believed to occur in tomato where Phe was shown to be first converted to phe-nylethylamine by aromatic amino acid decarboxylase (AADC) and further required the action of a hypothesized amine oxidase, dehydrogenase, or transaminase for phenylacetaldehyde formation [97]. On the other hand, in petunia, one bifunctional enzyme, phenylacetaldehyde synthase (PAAS) catalyzes the unprecedented efficient coupling of Phe decarboxylation to oxidation resulting in... 

Chromyl chloride oxidation of alkenes proceeds via the formation of adducts at a rate necessitating stopped-flow techniques. At 15 °C the formation of 1 1 adduct from styrene and oxidant in CCI4 solution is simple second-order with 2 = 37.0 l.mole .sec . Measurements with substituted styrenes yielded = — 1.99. E = 9.0 kcal.mole and = —23.8eu for styrene itself. Hydrolysis of the styrene adduct yields mostly phenylacetaldehyde (76.5 %)and benzaldehyde (21.1 %). Essentially similar results were obtained with a set of 15 alkenes and... 

No stereoselectivity was observed in the formation of a 1 1 diastereomeric mixture of 2-hydroxy-2-phenylethyl p-tolyl sulfoxide 145 from treatment of (R)-methyl p-tolyl sulfoxide 144 with lithium diethylamide . However, a considerable stereoselectivity was observed in the reaction of this carbanion with unsymmetrical, especially aromatic, ketones The carbanion derived from (R)-144 was found to add to N-benzylideneaniline stereoselectivity, affording only one diastereomer, i.e. (Rs,SJ-( + )-iV-phenyl-2-amino-2-phenyl p-tolyl sulfoxide, which upon treatment with Raney Ni afforded the corresponding optically pure amine . The reaction of the lithio-derivative of (-t-)-(S)-p-tolyl p-tolylthiomethyl sulfoxide 146 with benzaldehyde gave a mixture of 3 out of 4 possible isomers, i.e. (IS, 2S, 3R)-, (IS, 2R, 3R)- and (IS, 2S, 3S)-147 in a ratio of 55 30 15. Methylation of the diastereomeric mixture, reduction of the sulfinyl group and further hydrolysis gave (—)-(R)-2-methoxy-2-phenylacetaldehyde 148 in 70% e.e. This addition is considered to proceed through a six-membered cyclic transition state, formed by chelation with lithium, as shown below . ... 

The complex [Rh(COD)L L2]+, where L1 = PPh3 and L2 = pyridine, and a neutral benzoate complex, Rh(COD)(PPh3)(OCOPh), also effect highly selective hydrogenation of 1-alkynes to 1-alkenes as well as reduction of 1-alkenes and ketones to alcohols (139) the one equivalent of base required may be related to monohydride formation [Eq. (25)]. The bisphosphine complexes also catalyze reduction of styrene oxide to 2-phenylethanol and phenylacetaldehyde (140) ... 

Thermal decomposition of allylbenzene ozonide (58) at 37°C in the liquid phase gave toluene, bibenzyl, phenylacetaldehyde, formic acid, (benzyloxymethyl)formate, and benzyl formate as products. In chlorinated solvents, benzyl chloride is also formed and in the presence of a radical quench such as 1-butanethiol, the product distribution changes. Electron spin resonance (ESR) signals are observed in the presence of spin traps, adding to the evidence that suggests radicals are involved in the decomposition mechanism (Scheme 9) <89JA5839>. 

In some cases, oxidation of double bonds does not stop at the epoxide, but proceeds further to oxidative cleavage of the double bond. It was reported that the reaction of a-methyl styrene with H2O2 in the presence of TS-1 or TS-2 produces a-methyl styrene epoxide (15%), a-methyl styrene diol (10-40%) and acetophenone (40-60%) (Reddy, J. S. et al., 1992). However, results similar to those obtained with titanium silicates were obtained for many other catalysts, such as HZSM-5, H-mordenite, HY, A1203, HGa-silicalite-2, and fumed Si02. These materials have much different properties and differ significantly from titanium silicates thus, the results cast some doubt on the role of the catalyst in this reaction. Furthermore, the oxidation of styrene is reported to proceed with C=C cleavage and formation of benzaldehyde, in contrast to previous reports of the formation of phenylacetaldehyde with 85% selectivity (Neri et al., 1986). 

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... 

The production of hydrocarbons from aromatic alcohols is most readily explained by the hydrogenolysis of the alcohol, but an alternate possibility should be considered. The formation of an aldehyde and its subsequent decarbonylation under reaction conditions could lead to the hydrocarbon. Both toluene and 2-phenylethanol, the mixture of products secured from benzyl alcohol, may be regarded as derived from phenylacetaldehyde as an intermediate ... 

T he initiating effect of phenylacetaldehyde on the copolymerization of unsaturated polyesters with vinyl monomers has been described (9). The copolymerization proceeds at approximately the same rate as with the usual peroxide catalysts, but the reaction is much less exothermic hence, the effects of too rapid a polymerization such as fissures, bubble formation, and volume contraction do not occur. Investigation of a series of compounds of the benzene family showed that only enolizable phenyl-keto compounds were initiators (7). 

Extension of this reaction to phenylacetaldehyde leads to the unexpected formation of 3 in yields as high as 50% (equation I). Probable mechanisms for formation of 3 are discussed in the report. ... 

The biochemical oxidation of phenylacetaldehyde with cyclohexanone oxygenase produces phenylaeetic acid, in addition to smaller amounts of benzyl formate and benzyl alcohol (equation 351) [1034]. 

However, we have demonstrated the formation of a metallacycle [(dipy)(Cl)Rh-(0-CH2-CHPh) or (dipy)(Cl)Rh-(0-CHPh-CH2)] from styrene and dioxygen. These intermediates could give rise to both styrene oxide and the carbonate. The higher reaction rate when starting from styrene and dioxygen with respect to the epoxide can be, thus, justified. High temperature (> 353 K) often cause decomposition of the catalyst. Two mutually free cis positions are necessary for the formation of the metallacycle, that interacts with carbon dioxide and yields the carbonate so, in the presence of Rh(diphos)2Cl and Rh(dipy)2Cl, no conversion at all into the carbonate has been observed, either starting from styrene or from styrene oxide. In the latter case, only a minor isomerization into acetophenone and phenylacetaldehyde has been observed. 

Matsuda and Sugishita found that cyclooctatetraene monoepoxide (233 equation 99) gave only skeletally rearranged products, e.g. (234), when treated with Grignard reagents. In an effort to isolate the presumed intermediate cycloheptatrienecarbaldehyde, (233) was subjected to a catalytic amount of MgBra, but this resulted in the formation of phenylacetaldehyde. 

FIGURE 19.8 Free energy as a function of the reaction coordinate for the lowest activation energy path for epoxidation of styrene and formation of phenylacetaldehyde. 

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