2-Phenoxybenzaldehyde

The pyrethroid insecticides fenvalerate and cypermethrin are hydrolyzed under alkaline conditions at low substrate concentrations, but at higher concentrations the initially formed 3-phenoxybenzaldehyde reacts further with the substrate to form dimeric compounds (Figure 1.22) (Camilleri 1984). 

Fenvalerate is not significantly absorbed or translocated in plants. Cotton, apples, and lettuce treated with fenvalerate contained surface residues of parent fenvalerate 8 weeks after treatment (Reed 1981). In addition to the parent compound, which accounted for 80% of all residues, identified metabolites included 3-phenoxybenzaldehyde, 3-phenoxybenzyl methylbutyric acid, and conjugates of these compounds. Half-time persistence of fenvalerate on plant surfaces is between 2 and 4 weeks, and degradation is primarily a result of weathering (Reed 1981). 

Photolytic. Photolysis of permethrin in aqueous solutions containing various solvents (acetone, hexane, and methanol) under UV light (1 >290 nm) or on soil in natural sunlight initially resulted in the isomerization of the cyclopropane moiety and ester cleavage. Photolysis products identified were 3-phenoxybenzyldimethyl acrylate, 3-phenoxybenzaldehyde, 3-phenoxybenzoic acid, mono-chlorovinyl acids, cis- and fra/is-dichlorovinyl acids, benzoic acid, 3-hydroxybenzoic acid, 3-hydroxybenzyl alcohol, benzyl alcohol, benzaldehyde, 3-hydroxybenzaldehyde, and 3-hydroxybenzoic acid (Holmstead et ah, 1978). 

An impressive example of autoinduction (28) has been observed in the enantioselective hydrocyanation of 3-phenoxybenzaldehyde catalyzed by cyclo[( )-phenylalanyl-(ff)-hystidyl] (Scheme 8) (29). The ee... 

The situation is further complicated by chiral autoinduction, first reported by Danda et al. for the hydrocyanation of 3-phenoxybenzaldehyde [39]. It was found that the enantiomeric excess of the product increases with reaction time, and that addition of small amounts of optically pure cyanohydrin at the beginning of the reaction led to high ee of the bulk product, irrespective of catalyst ee. It was concluded that the active catalyst is not the diketopiperazine alone but a 1 1 aggregate with the product cyanohydrin of the opposite configuration (e.g. (R,R)-1 plus S-mandelonitrile) [39]. Lipton et al. later developed a mathematical model for this effect and exploited it to improve the enantioselectivity of the hydrocyanation of... 

The search for other amino acid-based catalysts for asymmetric hydrocyanation identified the imidazolidinedione (hydantoin) 3 [49] and the e-caprolactam 4 [21]. Ten different substituents on the imide nitrogen atom of 3 were examined in the preparation, from 3-phenoxybenzaldehyde, of (S)-2-hydroxy-2-(3-phenoxy-phenyl)acetonitrile, an important building block for optically active pyrethroid insecticides. The N-benzyl imide 3 finally proved best, affording the desired cyanohydrin almost quantitatively, albeit with only 37% enantiomeric excess [49]. Interestingly, the catalyst 3 is active only when dissolved homogeneously in the reaction medium (as opposed to the heterogeneous catalyst 1) [49]. With the lysine derivative 4 the cyanohydrin of cyclohexane carbaldehyde was obtained with an enantiomeric excess of 65% by use of acetone cyanohydrin as the cyanide source [21]. 

A large number of the most important modem insecticides are derived from cyanohydrins. Especially some esters formed from enantiopure cyanohydrins and chrysanthemum acid derivatives are known to be very potent [201]. Nowadays, the formation of 3-phenoxybenzaldehyde cyanohydrin is performed in a biocatalytic industrial process using Me HNL or 7/bHNL isolated from mbber trees (Hevea... 

The pH profile of the hydrolysis of the acetate of CPBA showed that the activity of the enzyme was not greatly influenced in the range of pH 4 to pH 7. An undesirable conversion from the liberated (S)-CPBA to 3-phenoxybenzaldehyde was sharply increased when the pH was higher than pH 5. The reaction was therefore carried out at pH 4 to pH 5 as shown in Table V. Other reaction behavior was similar to that for the HMPC ester. 

The reaction of 3-phenoxybenzaldehyde (351), sodium cyanide, and acyl halides 352 in the presence of DBU hydrochloride in aqueous heptane resulted in a-cyanoesters 353 in 99% yield (80MIP6222 81USP4254052 82USP4323685). 

Catalyst Conditions Benzaldehyde 2-CI-Benzaldehyde Phenylpropanal 3-Phenoxybenzaldehyde Acetophenone... 

Birds rapidly and efficiently metabolize fenvalerate by hydrolytic cleavage of the ester bond followed by extensive hydrox-ylation of the acid moiety at the carbon adjacent to the carboxyl group, the methyl group, or both. Major metabolites identified in liver preparations were 2-(4-chlorophenyl)-3-methylbut5Tic acid, 4-hydroxyfenvalerate, 3-phenoxybenzaldehyde, and 3-phenoxybenzoic acid. Liver microsomal drug-metabolizing enzymes usually play an important role in pesticide metabolism however, fenvalerate and other synthetic pyrethroids are very weak inducers of avian microsomal enzymes. Birds are more resistant to fenvalerate than are... 

The approved way of preparing the cyanohydrine 299 by the addition of prussic acid is no problem in the case of 3-phenoxybenzaldehyde 280, The use of acetone cyanhydrine as a source of prussic acid [629] seems to be advantageous. In order to circumvent the aldehyde 280, an alternative route from the trimethyl-3-phenoxy benzylammonium salt 296 and the corresponding 3-phenoxybenzyl nitrile 297 [630] was proposed, in which oxalic ester condensation and subsequent brominative degradation of this whole group was applied (Reaction scheme 211). This procedure supposedly yields a particularly pure a-bromobenzyl cyanide 298 [631]. 

The degradation pathways of cypermethrin, deltamethrin and fenpropathrin have been smdied. The fenpropathrin metabolism pathway of Achromobacter sp. (Fig. 3.21a) was proposed by Wang et al., it was suggested that fenpropathrin was hydrolyzed to 2,2,3,3-tetramethylcyclopropanecarboxylic add and 3-phenoxybenzaldehyde, which was later converted to 3-phenoxybenzoic acid. The phenoxybenzoic acid was transformed to 3-(4-hydroxyphenoxy)benzoic acid, which was oxidized to 3,4-dihydroxybenzoic acid (protocatechuate) and p-hydroquinone. The protocatechuate was further oxidized through an ortfe>-cleavage pathway, and p-hydroquinone was degraded via the metabolite benzene-1,2,4-triol (Wang etal. 2011). 

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