Phenoxypropanoic acid

Chlorinated phenoxypropanoic acid herbicides have been very widely used following the introduction of products such as Dalapon in the 1950s. More recently Mecoprop and... 

The tetrahydro derivative shown in Scheme 233 affords the linear chromanone (63AJC690). A further extension of this route leads to the formation of 3-substituted chromanones (73BCJ1839). However, difficulties in the synthesis of the appropriate phenoxypropanoic acid limit its value. 

Conversion of the phenoxypropanoic acid into the acid chloride enhances the ease of cyclization and the use of phosphorus pentachloride and aluminum chloride provides an example of this technique (51JA4205). The formation of 3-aminochroman-4-one has been achieved in this way starting from 2-amino-3-phenoxypropanoic acid (76TL271). Cyclization of the phenoxyethanoic acid shown in Scheme 234 occurs on reaction with sodium methoxide to give the chroman-3-one (63JCS5322). 

Gaffney [89] reported the reverse order of elution of 2-phenoxypropanoic acid on Chiralcel OB CSP when different alcohols were used. In 2001 Aboul-Enein and Ali [63] observed the reverse order of elution of nebivolol enantiomers on a Chiralpak AD chiral stationary phase when ethanol and 2-propanol were used separately as the mobile phases. However, the best resolution was obtained when ethanol served as the mobile phase. The inversion of the elution may be due to the different conformation of the polysaccharide CSPs [63]. The pattern of conversion of order of elution using different ratios of ethanol and 2-propanol is shown in Figure 15. 

Phenoxypropanoic acid, 3-(phenylthio)propanoic acid, 4-phenylbutanoic acid and the corresponding ethyl and methyl esters have been pyrolysed between 520 and 682 K.10 Analysis of the pyrolysates showed the elimination products to be acrylic acid and the corresponding arene. The thermal gas-phase elimination kinetics and product analysis have been found compatible with a thermal retro-Michael reaction pathway involving a four-membered cyclic transition state. 

C9H10O3 3-phenoxypropanoic acid 7170-38-9 32.41 1.1490 2 16890 C9H11N 2,3-dihydro-1 H-inden-5-amine 24425-40-9 20.64 1.0208 2... 

Only the D-isomer of these compounds shows strong herbicidal activity, while the L-isomer is inactive, and any additional substituents on the benzene ring significantly decrease the activity (6). Thus we speculated that the phenoxypropanoic acid part of the structure is the essential moiety, which interacts with a receptor in plant tissues. And if this is so, the pyridinyloxy moiety may serve to optimize the hydrophobicity of the whole molecule for maximum herbicidal activity, enhancing the translocation of the molecule through the plant. 

Liq. phenol shaken with 0.5 mole anhydrous KF, then heated 5 min. at 130 with 2-chloropropanoic acid 2-phenoxypropanoic acid. Y 95%. F. e. s. J.H. Clark and J. M. Miller, Chem. Commun. 1976, 229. 

Esterification of racemic 2-phenoxypropanoic acids with arylalkanols can be doubly enantioselective for both compounds with Candida cylindracea lipase (CCL) in hexane [82]. The enantiomeric ratio E of acids and alcohols depend on the relative structures and, for instance, as shown in Scheme 10, a maximum value E = 108) is reached for the p-chlorophenoxy acid when the alcohol counterpart is 1-phenyl-1-ethanol E = 5.2). 

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