Dimethoate structure

A mixture of diethyl 2-bromo-l-phenylethenylphosphonite (30.3 g, 0.1 mol) and dimethyl maleate (14.4 g, 0.1 mol) was stirred for 4 h at room temperature under an argon atmosphere. At this time, hexane was added to the reaction mixture sufficient for complete precipitation, and the resultant crystals (unreacted dimethyl maleate) were removed by filtration. The oily residue was treated on a silica gel column (40/100 pm) using a pentane/acetone (8 2) mixture, allowing the elution and isolation after evaporation of pure l-ethoxy-2-phenyl-4,5-dimetho x yea rb o n y I - A2-X5-phospholene 1-oxide (8.9 g, 27%), which exhibited spectra and analytical data in accord with the proposed structure. 

Different OP compounds have structural similarities within classes. The phosphorus compounds have the characteristic phosphoryl bond, P=0. Most OP compounds have a phosphoryl bond or a thiophosphoryl bond (P=S). All OP compounds are esters of phosphorus with varying combinations of oxygen, carbon, sulfur, and nitrogen attached. These are classified as (1) phosphates (2) phos-phonates (3) phosphorothioates (4) phosphorodithioates (5) phosphorothiolates and (6) phosphoramidates. Further, the OP compounds are categorized as (1) aliphatic (2) phenyl and (3) heterocyclic derivatives. The aliphatic are carbon chainlike in structure. TEPP, which was used in agriculture for the first time in 1946, is a member of this group. Others include malathion, trichlorfon, monocrotophos, dimethoate, oxydemetonmethyl, dimethoate, dicrotophos, disulfoton, dichlorvos, mevinphos, methamidophos, and acephate. 

The chemistry of caracurine II and its dimetho derivative and of C-alkaloid D has been studied by Swiss (116) and English (113) groups of workers, with the final solution of the structures coming as the result of a joint effort (96). 

In the reverse mode, product ions can be used for structural elucidation work. In the case of etrimphos (Fig. 2), an unknown compound encountered in a pesticide residue sample, its identity could not have been inferred either by the El or Cl spectrum since both lacked fragment ions for structural detective work. However, the product ion spectrum derived from the protonated molecule yielded an indication that the compound could be a dimethoxyphosphorothionate or dithionate from the presence of the ion at m/z 125 (cf. dimethoate). The additional presence of ions at m/z 109 and 143 in conjunction with m/z 125 was strong evidence (Fig. 2) that the compound was a dimethoxyphosphorothionate. 

The toxic effects of some pesticide mixtures are additive, particularly when their toxic mechanisms are identical. The additive effects of the organophosphates chlorpyrifos and diazanon were demonstrated in one study. T Another study found the s-triazine herbicides atrazine and cyanazine to show additive toxic effects. Not all mixtures of similar pesticides produce additive effects, however. In one study, mixtures of five organophos-phate pesticides (chlorpyrifos, diazinon, dimethoate, acephate, and malathion) were shown to produce greater than additive effects when administered to laboratory animals. Another article discusses nonsimple additive effects of pyrethroid mixtures. Despite the similarities in their chemical structure, pyrethroids act on multiple sites, and mixtures of these produce different toxic effects. 10 ... 

The names of C-toxiferine (38), C-alkaloid H (49), and C-dihydrotoxiferine (46) have been assigned to the three distinct families of curare alkaloids, of which each of these is the major representative (see Chart). The individual diquaternary members of these families differ only in the oxidation level of the central dia-zacyclo-octane ring. Thus, various oxidation processes result in the conversion of C-toxiferine (38) to caracurine II dimetho-salt (50), C-alkaloid E (51), and C-alkaloid A (52). The partial structures of these alkaloids are given in Scheme 2. 

The Chart indicates those members of the three families which with respect to structure, chemical behaviour, u.v., i.r., and n.m.r. spectra, and colour reactions are extremely similar. The alkaloids thus depicted differ only in the oxidation states of C(18) and C(18 ) C-alkaloid A (52) possesses a hydroxy-group at each of these two centres, C-alkaloid F (57) at only one, and C-calebassine (55) at neither. The same relationship holds in the same order for C-alkaloid E (51), C-alkaloid G (56), and C-curarine (54). C-Alkaloid D (53) [no OH group at C(18) or C(18 )] has hydroxy-functions at C(17) and C(17 ). In caracurine II dimetho-salt (50) these are displaced by the C(18)- and C(18 )-hydroxy-groups, resulting in two seven-membered ether rings which are also present in caracurine V dimetho-salt... 

Acid-catalysed Isomerisations of Calabash-curare Alkaloids.— As has been described, C-toxiferine (38), C-dihydrotoxiferine (46), and C-alkaloid H (49), under the influence of aqueous acid, are readily cleaved via a retro-aldehyde-ammonia addition, into their two halves . This ready cleavage was a key reaction for the elucidation of the structures of these alkaloids. In contrast, the more highly oxidised forms [caracurine II dimetho-salt (50) and C-alkaloid D... 

Therefore, a silica-gel-based bonded phase was constructed. The new phase was constructed based on the dimetho)ypentylsilane-bonded poly-silicondioxide phase shown in Figure 3.13, and consisted of 991 atoms, 1051 bonds and 15 193 connectors, containing 171 silicons, 328 ojygens, 143 carbons and 349 hydrogens (Phase 4). Twenty dimetho ypentylsilanes and one trimethylsilane were bonded within an 900 area on the poly-silicondioxide phase. The trimethylsilane was considered an end-capped molecule. A pocket caused by a small molecule, trimethylsilane, was designed to follow the V-shape model of a porous silica gel. The optimized structure of a complex formed between this model phase and quinine is... 

Malathion is a widely used member of a class of pesticides known as organophospate derivatives. It is biodegradable and less toxic (LDg for female rats is 1000 mg/kg) than DDT. Several other organophosphorus compounds are modifications of this basic structure. They include dimethoate (LD = 387 mg/kg), chlorpyrifos (LD q = 95-270 mg/kg), and methyl parathion (LD o = 18 -50 mg/kg). These organophosphates often are used in the treatment of many pests that are found on vegetables, or, in the case of methyl parathion, on cotton plants. 

Omethoate and dimethoate are organophosphorus insecticides with similar chemical structures. Thus cross-sensitivity is possible. Allergic contact dermatitis caused from omethoate and dimethoate have been reported [72]. 

Scheme 1.1) 4d gives rise to caracurine II dimetho salt, C-alkaloid E, and C-alkaloid A, while 4f yields C-alkaloid D, curarine, and calebassine, as well as a number of further oxidation products of as yet unknown structure. 4e, the hybrid C-alkaloid H, forms C-alkaloids G and F. Although, as indicated above, the parent dimers can be cleaved with acid into the corresponding monomers, their more highly oxidized derivatives are found to undergo a series of isomerizations instead. 

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