Benzoylprop-ethyl

The N-arylalanine ester herbicides such as benzoylprop-ethyl and flam-prop-methyl and difenzoquat (Figure 2.26) prevent cell elongation in certain grass weeds, allowing the crop to overtop them. The weeds are thus outcompeted and die. The exact mode of action is not certain but it is proposed that these compounds interfere with the site of action of the auxins. 

Propionic acid benalaxyl, benzoylprop-ethyl, clethodim, clodinafop, clomeprop, cloprop, 2 CPA dalapon, dichlorprop, diclofop, fenoprop, fenoxaprop, flamprop isopropyl, flamprop methyl, fluazifop, furalaxyl, haloxyfop, isoxapyrifop, mecoprop, metalaxyl, naproanilide, napropamide, prohexadione, propanil, pyroquilon, quizalofop ethyl, tralkoxydim Propoxy acetaldehyde pretilachlor n-Propylamine prochloraz, profluralin... 

Benzoylprop-ethyl (31) and flamprop-isopropyl (32), two anilide herbicides selective in cereals with specific efficiency for the control of wild oat Avena spp.), have been developed in the research latoratories of the Shell Research Ltd. 

Ethyl N-benzoyl-N-(3,4-dichlorophenyl)-DL-alaninate, its common name is benzoylprop-ethyl (WL 17731, 31). 

Treatment with benzoylprop-ethyl hinders the longitudinal growth of Avena sp. stunted plants develop which are unable to compete with the crop. 

Benzoylprop-ethyl itself is moderately phytotoxic. However, the absorbed compound hydrolyses in the plant the ester bond is ruptured and the acid formed ( benzoylprop ) is translocated in the phloem to the growing cells of the stem. During detoxication the acid is conjugated with the components of the plants, including sugars. Deesterification process most rapidly in oat and most slowly in... 

Benzoylprop-ethyl cannot be combined either with oil or with 2,4-D amine salt, because it antagonises both substances (Colbert and Appelby, 1972). For the same reason, benzoyl chloride does not accumulate in animal organisms (Crayford et al.. 

Benzoylprop-ethyl is a weakly toxic compound, its acute oral lDj for rats being 1555 mg/kg, for mice 716 mg/kg, and for poultry 1000 mg/kg. It is toxic to fish, the LC50 (lOO-hour exposure) for harlequins being 5 mg/1. 

Benzoylprop-ethyl is a postemergence wild oat herbicide selective in wheat, while the chemically closely related flamprop-isopropyl, isopropyl N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alaninate (WL 29762, 32) is a wild oat herbicide selective in barley. 

The herbicidal properties of flamprop-isopropyl were first described in 1974 (Mouillac et a .. 1974 Warley et al., 1974 Haddock et al.. 1974). The excellent wild oat killing properties of benzoylprop-ethyl could not be utilised in barley, because it occasionally causes considerable phytotoxic injuries, and hence a decrease in yield. Since the investigation of the mode of action and of the metabolism of benzoylprop-ethyl showed that the free acid is the carrier of the herbicidal action, it stood to reason that there might be a compound among those of closely related structure, which was selective also in other cereal species. 

Activity and selectivity of flamprop-isopropyl are similar to those of benzoylprop-ethyl. Flamprop-isopropyl too becomes active as the free acid ( flamprop ) after deesterification. The acid is rapidly translocated in the phloem to the growth sites of the plant cell. The rate of translocation is five times that for benzoylprop-ethyl. The growth of wild oat is stunted by the inhibition of cell elongation. 

The selectivity of flamprop depends on the rate of hydrolysis relative to the rate of subsequent detoxication. In the course of detoxication flamprop is metabolised to inactive conjugates in the plant. The activity of flamprop is about twice that of benzoylprop-ethyl (Jeflcoat and Harris, 1975). 

Haddock et al. (1974) described, along with flamprop-isopropyl, another compound, flamprop-methyl ester, code number WL 29761, which is selective in wheat (Mataven ). WL 29 761 gives a higher yield in wheat than benzoylprop-ethyl, and is also effective against Alopecuruspratensis (Chow, 1974 Gompf, 1974). Scott et al. (1976) reported on the preparation and biological activity of the levorotatory optical isomer of flamprop-isopropyl, known by its code number WL 43 425. 

Amides and anilides Benzoylprop-ethyl, difenamide, naptalam, pronamide, propanil... 

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