Herbicides nitrofen

A foreign compound, which may act in this way is the herbicide nitrofen (2,4-dichloro-4 -nitro diphenyl ether), which causes a variety of malformations lethal to the neonate. There is no growth retardation or embryolethality at doses, which are teratogenic, however (Fig. 6.27), and therefore this exhibits the first type of dose-response relationship (see above). The... 

FIGURE 6.18 The dose-response patterns for teratogenicity caused by the herbicide nitrofen (2,4-dichloro-4 -nitro diphenyl ether). Pregnant rats were treated on day 11 with nitrofen. Data from Manson, J.M., Teratogens, in Casarett and Doull s Toxicology, edited by C.D.Klaassen, M.O.Amdur andJ. Doull (New York Macmillan), 3rd Edition, 1986. 

In Japan, bifenox is the only registered diphenyl ether herbicide. The tolerance and/or maximum residue limits (MRLs) are established at 0.1 mg kg for cereals such as rice grain, barley and wheat, and 0.05mgkg for potatoes (Ministry of Health, Labour and Welfare, Japan). Ibe California Department of Food and Agriculture (CDFA) established the minimum detectable quantity of diphenyl ether herbicides at 0.1 mgkg for bifenox, nitrofen and oxyfluorfen. ... 

Okumura et al reported State regulatory programs for pesticide residues in food crops analyzed by the CDFA. In the multiresidue analysis of several organochlorine pesticides including diphenyl ether herbicides, bifenox, nitrofen and oxyfluorfen, HPLC has also been used. 

Diphenyl ether herbicides. The diphenyl ether class of herbicides belongs to a broader area of herbicides known as protoporphyrinogen oxidase (Protox) herbicides [20,21], Diphenyl ether herbicides were initially introduced over four decades ago in the 1960s with the discovery of nitrofen by Rohm and Haas (now Dow AgroSciences) [22] and bifenox by Mobil [23], These early diphenyl ether herbicides did not attain a significant role in the control of weeds in commercial crops until the 1970s, with the introduction of the trifluoromethyl compounds oxyfluorfen [24] and acifluorfen-sodium [25], Replacement of the chlorine with a trifluoromethyl group resulted in a dramatic increase in the herbicidal properties of these compounds, in terms of both potency and the spectrum of weeds controlled. 

PCDEs are used as intermediates in chemical syntheses, e.g. production of herbicides chloroxuron, 2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen) and binofex [300]. Because PCDEs have physico-chemical properties like PCBs, they are or were used also as heat exchangers. One product is Dowtherm A, a PCDE - PCB mixture, with heat transfer applications. However, in general their use pattern is unknown [301]. Beside the use as heat-exchange fluids, the lower chlorinated PCDEs have been used as flame retardants. It must be also stated that the PCDEs were never directly produced in large quantities. Nevertheless, these aromatic chlorinated compounds have been identified as widespread environmental contaminants. The widespread appearance of PCDEs in the aquatic and terrestrial environment could be most likely due to their presence as... 

Many herbicides are nitro-PCDEs such as nitrofen and DNP [28,29]. Different diphenyl ether herbicides are presented in Table 3. The use of nitrofen, 2,4-di-chloro-4 -nitro-diphenyl ether, was restricted to crops without detectable residues at harvest in the 1980s, since it has caused neonatal deaths in rats [30]. A aminoderivative of PCDEs, Aminofen, is an intermediate in the chemical industry and has been used in the manufacture of herbicides Illoxan and Diclofop-methyl [4]. Amino-PCDEs are also impurities of Eulan WA New that contains... 

The development of this selective herbicide group begun in the 1960s in the United States. Nitrofen (1) was the first member of this group, introduced by Rohm and Haas (Wilson and McRae, (1960). 

The action of the tested herbicides was classified as follows (a) growth inhibition in the light without rapid phytotoxicity (metribuzin), (b) bleaching of the cells without rapid phytotoxicity (fluridone), (c) rapid phytotoxicity in the light (nitrofen, paraquat), (d) rapid phytotoxicity in the dark (PCP), (e) direct and rapid inhibition of cell division but not of cell growth (amiprophos -methyl, chlorpropham, trifluralin) and (f) indirect (delayed) inhibition of cell division and growth (alachlor). 

PCP, Herbicide no. 1, nitrofen, 2,4-D, dalapon, pro-panil, NAA, 920 (gibberellins), MCPA, Ethephon... 

The diphenyl ether nitrofen (1) [24], introduced in 1963 by Rohm and Haas, now Dow AgroSciences the oxadiazolinone oxadiazon (2) [25, 26] (Explorer , Herbstar , Romax , Ronstar ), introduced in 1968 by Rhone-Poulenc and the tetrahydrophthalimide chlorophthalim 3 [27], introduced in 1972 by Mitsubishi, represent the earliest examples of Protox herbicides (Fig. 3.2). Though all three classes are chemically quite different, they share a common mode of action, inhibition of the protoporphyrinogen oxidase enzyme, though this was not known until the late 1980s. 

Following the discovery of the herbicidal activity of nitrofen (1) in 1963, intense research by several agrochemical companies resulted in a vast number of highly active and diverse chemistries [28, 29]. As mentioned earlier, the diphenyl ether chemistry represents the first class of Protox herbicides. Replacement of the aromatic 4-chloro group with a trifluoromethyl, as is the case with oxyfluorfen (5) (Goal ) [30], resulted in a significant improvement in biological activity, and 2-... 

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