Alkyl methylphosphine

These results encouraged us to design and prepare monosalts of alkylphosphinate to compare the herbicidal activity and enzymatic-selectivity between alkyl-phospinate and their phosphonate counterparts. Therefore, a novel series of sodium [1-(substituted phenoxyacetoxy)alkyl]methylphosphinates IIIH was further designed through replacing the MeO group in IIIA-IIIG by NaO (Scheme 1.30). 

One methoxyl group of 0,0-dimethyl moiety in alkylphosphonates 1C was replaced by methyl group to produce 0-methyl [1-(substituted phenoxyacetoxy) alkyl]methylphosphinates lllA-lllG which hydrolyzed to give sodium [l-(substi-tuted phenoxyacetoxy)alkyl]methylphosphinates lllH (Scheme 4.1). Indeed, the preliminary bioassay results showed that most of the alkylphosphinates IIIC-IUH exhibited different herbicidal activity from their corresponding alkylphosphonates. 

First, three series of phosphinates including O-methyl [l-(2-nitrophenoxyacetoxy) alkyl]methylphosphinates niA, O-methyl [l-(2-chloro-4-nitrophenoxyacetoxy)... 

Scheme 4.3 Design of [l-(substituted phenoxyacetoxy)alkyl]methylphosphinates IIIA-IIIC...

O-methyl [1-(substituted phenoxyacetoxy)alkyl]methylphosphinates IIIA-IIIG were easily synthesized by the reaction of O-methyl (l-hydroxyalkyl)meth-ylphosphinates with substituted phenoxyacetyl chlorides. The synthetic route of IIIA-IIIG is shown in Scheme 4.6. O-Methyl methylphosphinate Mil was prepared in a two-step sequence starting from phosphorus trichloride, methyl iodide, and aluminium trichloride. O-Methyl (l-hydroxyalkyl)methylphosphinates M12 were prepared by the addition of Mil and several kinds of aldehydes using tri-ethylamine as the catalyst. Substituted phenoxyacetic acids M4 and substituted phenoxyacetyl chlorides MS were prepared using the method which has been introduced in Chap. 2. IIIA-IIIG were obtained by the condensation of M12 with different substituted phenoxyacetyl chlorides MS. 

Table 4.4 Structure of O-methyl [l-(2,4-dichlorophenoxyacetoxy)alkyl]methylphosphinates...

Table 4.5 Structure of 0-methyl [l-(3-trifluoromethylphenoxyacetoxy)alkyl]methylphosphinates o...

Herbicidal Activity of O-Methyl [l-(Substituted Phenoxyacetoxy) Alkyl]Methylphosphinates IIIA and IIIB... 

As shown in Table 4.10, most of O-methyl [l-(2-nitrophenoxyacetoxy)aIkyl] methylphosphinates IIIA and O-methyl [l-(2-chloro -nitrophenoxyacetoxy)alkyl] methylphosphinates IIIB were almost inactive in pre-emergence application at 2.25 kg ai/ha except that IIIA-8 (R =2-ClPh) and IIIB-1 (R =Me) showed >90 % inhibitory activity against lettuce or crab grass, respectively. 

Table 4.10 Structure and pre-emergence herbicidal activity of <3-methyl [1-(substituted phenoxyacetoxy)alkyl]methylphosphinates...

Table 4.12 Stmcture and pre-emergence heibicidal activity of 0-methyl [l-(2,4-dichlorophen-oxyacetoxy)alkyl]methylphosphinates niC ...

The results in Tables 4.12 and 4.13 showed that most of [l-(2,4-dichlorophen-oxyacetoxy)alkyl]methylphosphinates IIIC displayed significant inhibitory activity against tested species except wheat in pre-emergence and post-emergence appU-cations at 2.25 kg ai/ha. Compared with phosphinates IIIA (Y =2-N02) and IIIB (Yn=2-Cl,4-N02), the herbicidal activity of phosphinates IIIC was greatly... 

Table 4.13 Stracture and post-emergence herbicidal activity oxyacetoxy)alkyl]methylphosphinates IIIC ...

Herbicidal Activity of 0-Methyl [l-(3-Trifluoromethyl phenoxyacetoxy)Alkyl]Methylphosphinates HID... 

Therefore, sodium [1-(substituted phenoxyacetoxy)alkyl]methylphosphinates IIIH might have more powerful inhibition and herbicidal activity than the corresponding 1-aIkylphosphinate. IIIH were designed through the replacement of the MeO group that attached to phosphorus by NaO in alkylphosphinates niA-IHG (Scheme 4.11). 

Sodium [1-(substituted phenoxyacetoxy)alkyl]methylphosphinates lllH could be easily prepared from the corresponding 0-methyl [1-(substituted phenoxyacetoxy) alkyl]methylphosphinates which were prepared by the condensation of substituted phenoxyacetyl chlorides M5 and 0-methyl (l-hydroxyalkyl)methylphosphinates M12. The synthetic route is shown in Scheme 4.12. A detailed synthetic procedme for IIIH is introduced in the Sect. 9.1.18. The structures of HIH-l-IIIH-lO are listed in Table 4.21. 

In this section, we describe the synthesis and herbicidal activity of 0-methyl [1-(5-methylisoxazol-3-yloxyacetoxy)alkyl]methylphosphinates IIIJ. 

Table 4.26 Structure and post-emergence heibicidal activity of O-methyl [l-(5-methylisoxazol-3-yloxyacetoxy)alkyl]methylphosphinates 111.1 ...

Methyl [l-(5-Methylisoxazol-3-yloxyacetoxy)Alkyl] Methylphosphinates IIIJ... 

General procedure To a stirred solution of appropriate (9-methyl (1-hydroxy-alkyl)methylphosphinates M12 (0.005 mol) and triethylamine (0.0072 mol) in 5 mL of trichloromethane, (5-methyl-isoxazol-3-yl)oxyacetyl chloride M16 (0.006 mol) in 5 mL of trichloromethane was added dropwise below 0 °C. The mixture was stirred at room temperature for 4—6 h. Normal workup and purification by column chromatography on silica gel and elution with petroleum ether/acetone (5/1, v/v) gave the corresponding pure tide compound. IIIJ-l-IIIJ-8 could be obtained by this procedure in 23-55 % yields [32]. 

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