Xiaosong Tan

Synthesis and Herbicidal Activity of 2-(Substituted phenoxyacetoxy)alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one

A series of 2-(substituted phenoxyacetoxy)alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-ones IIa-s were designed and synthesized on the basis of the previous work for the modification of alkylphosphonates I, and their structures were confirmed by (1)H NMR, (31)P NMR, (13)C NMR, IR, MS, and elemental analysis. Their herbicidal activities against seven species of weeds were evaluated in a greenhouse. A part of the title compounds such as IIa-g, IIk, IIo, and IIr exhibited significant postemergence herbicidal activity against Abutilon theophrasti, Brassica juncea, Amaranthus retroflexus, and Eclipta prostrate at a dosage of 150 g ai/ha. Structure-activity relationship analyses indicated that the introduction of a phosphorus-containing heterocyclic ring had a favorable effect on herbicidal activity, and their herbicidal activity could be further increased by a reasonable combination of X, Y, and R in parent structure II. It could be found that the title compounds IIa 2-[(2,4-dichlorophenoxy)acetoxy](methyl)methyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one and IIr 2-[(4-chloro-2-methyl-phenoxy)acetoxy](methyl)methyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one possess high activity and a broad spectrum against all of the test broadleaf weeds with 70-100% inhibition effect at a dosage of 75 g ai/ha, and the title compounds IIa and IIr are safe for corn and wheat at a dosage of 150 g ai/ha. Furthermore, the title compound IIa possesses low rat toxicity. These results suggest that the title compounds IIa and IIr could be potential and selective postemergence herbicides for further development.

A Well-Defined Cyclotriphosphazene-Based Epoxy Monomer and Its Application as A Novel Epoxy Resin: Synthesis, Curing Behaviors, and Flame Retardancy

Abstract A novel cyclotriphosphazene-based epoxy monomer, hexa-[4-(glycidyloxycarbonyl) phenoxy]cyclotriphosphazene (HGCP), was synthesized via a four-step synthetic route, and fully characterized by 1H, 13C, and 31P NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis. Thermosetting systems based on HGCP with three curing agents, for example, 4,4′-diaminodiphenylsulfone (DDS), 4,4′-diaminodiphenylmethane (DDM), and dicyandiamide (DICY), were used for making a comparison of their thermal curing behaviors. The curing behaviors were measured by differential scanning calorimetry. Moreover, flame retardancy of HGCP thermosetting systems was estimated by Limiting Oxygen Index (LOI) and Vertical Burning Test (UL-94). The resulting HGCP thermosetting systems exhibited better flame retardancy than the common epoxy resins diglycidyl ether of bisphenol A (DGEBA) and the regular brominated bisphenol A epoxy resin (TBBA) cured by DDS, respectively. When HGCP was cured by DDS, its thermosetting system gave the most char residues, met the UL-94 V-0 classification, and had a limiting oxygen index value greater than 35. GRAPHICAL ABSTRACT

Synthesis and herbicidal activities of 2-methylpropan-2-aminium O -methyl 1-(substituted phenoxyacetoxy)alkylphosphonates

A series of 2-methylpropan-2-aminium O-methyl 1-(substituted phenoxyacetoxy)alkylphosphonates (5a-5o) was selectively synthesized by reacting the corresponding O,O-dimethyl 1-(substituted phenoxyacetoxy)-alkylphosphonates with an excess of 2-methylpropan-2-amine. The results of preliminary bioassays show that the title compounds exhibit moderate to good herbicidal activities against Brassica napus and Echinochloa crusgalli. Furthermore, compounds 5a-5j, which show much higher activities than compounds 5k-5o, were selected to further evaluate their post-emergence herbicidal activity at a dosage of 150 g/ha(1 ha=10000 m2). Especially, 2-methylpropan-2-aminium O-methyl 1-[2-(4-chloro-2-methylphenoxy)acetoxy]butylphosphonate(5h) shows 100% inhibitory effect on the growth of Brassica juncea and Amaranthus retroflexus, which is comparable with the commercial herbicide 2,4-dichlorophenoxy acetic acid(2,4-D).

The Synthesis and Biological Activities of N-(3-pyridylmethyl) N ′-(trans-2-thio-4-substitutedphenyl- 5,5-dimethyl-1,3,2-dioxaphosphinane-2-yl)thioureas

A series of novel title compounds were synthesized by the addition reaction of trans 2-isothiocyano-4-substitutedphenyl-5, 5-dimethyl-1,3,2-dioxaphosphinane 2-sulfide to 3-aminomethylpyridine or 2-chloro-5-amino methylpyridine. Their structures were confirmed by 1H NMR, 31P NMR, IR, MS, and elemental analyses. Results of preliminary bioassay showed that all new compounds possess good fungicidal activity and insecticidal activity to some extent.

Synthesis and Herbicidal Activities of 2-Methylpropan-2-Aminium Methyl 1-(Substituted Phenoxyacetoxy) Alkylphosphonates

Abstract A series of 2-methylpropan-2-aminium methyl 1-(substituted phenoxyacetoxy) alkylphosphonates were selectively synthesized by reacting the corresponding dimethyl 1-(substitutedphenoxyacetoxy)alkylphosphonates with an excess of 2-methylpropan-2-amine. All the title compounds were identified by IR, 1H NMR, and 31P NMR, some of them were further analyzed by 19F NMR and 13C NMR. Their herbicidal activity was investigated and the results showed that most of the demethylated aminium salts exhibited notable herbicidal activities against Brassica napus L. and Echinochloa crusgalli. Supplementary materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional text, figures and tables. GRAPHICAL ABSTRACT

Evaluation and Application of Clacyfos and HWS

The R&D progresses of two alkylphosphonates, namely clacyfos and HWS, are introduced in this chapter. Clacyfos (HW02), had received a temporary registration in ICAMA (Institute for the Control of Agrochemical s Ministry of Agriculture) in 2007 in China. HWS was considered as a candidate herbicide. Both compounds were confirmed to be effective plant PDHc inhibitors, and as herbicide candidate were evaluated by a number of fields’ trials in different regions in China. The toxicology, eco-toxicity, residues, environmental fate and their properties as herbicide are also introduced.

Cyclic Phosphonates and Caged Bicyclic Phosphates

Several different types of cyclic phosphonates IVA-IVF and caged bicyclic phosphates IVG-IVH were further designed and synthesized. On the basis of systematic bioassay, several cyclic phosphonates were found to be effective against broadleaves by post-emergence application at 18.5~75 g ai/ha in the greenhouse.

Optically Active Alkylphosphonates

Numerous studies demonstrated that the biological activities of chiral phosphonates depend largely on their absolute configuration. Several kinds of optically active 1-(substituted phenoxyacetoxy)alkylphosphonates were prepared and their herbicide activities were evaluated. The asymmetric synthesis, enantiomeric selectivity in herbicidal activity, and acute aquatic toxicity are introduced.

Salts of Alkylphosphonates

Based on the bioisosterism, the salts of 1-(substituted phenoxyacetoxy) alkylphosphonic acid were speculated to have more powerful inhibitory effect against plant PDHc E1 and better herbicidal activity than the corresponding alkylphosphonates. Nine series of novel alkali metal salts of O-alkyl 1-(substituted phenoxyacetoxy)alkylphosphonates IIA-IIJ were first designed and synthesized as potential plant PDHc E1 inhibitors.

Biochemical Mechanism of Alkylphosphonates

Alkylphosphonates Io were expected to be effective plant PDHc E1 inhibitors because they were obtained by the chemical modification of sodium O-methyl acetylphosphonate as a hit compound, which is a potent plant PDHc E1 inhibitor. Therefore, it is interesting to examine inhibitory activity against plant PDHc E1. The biochemical mechanism was explored through the method of theoretical calculations and biochemical experiments. Several representative alkylphosphonates Io were found to be powerful inhibitors against plant PDHc, but show no significant inhibition against PDHc E1 from pig heart. The degree of herbicidal activity of these compounds positively correlated with their enzyme inhibition.