Dinitroanilines, selective

Uses A trilluoromethyl dinitroaniline selective preemeigence herbicide for control of aimual grasses and some broad-leaved weeds in vegetables and turf. 

Formation of diamines from dinitro compounds, which are unable to interact intramolecularly, presents no problem. Very large volumes of diaminotoluene, a precursor to toluene diisocyanate, are produced by hydrogenation of dinitrotoluene over either nickel or palladium-on-carbon. Selective hydrogenation of one or the other of two nitro groups is much more of a challenge, but a number of outstanding successes have been recorded. A case in point is the hydrogenation of 2,4-dinitroaniline (11) to 4-nitro-l,2-benzenediamine (12) (2) or to 2-nitro-l,4-benzenediamine (10). 

To determine the residue levels of dinitroaniline herbicides, GC/NPD or GC/ECD is used in general. An aliquot of GC-ready sample solution is injected into the gas chromatograph under the conditions outlined below. Further confirmatory analysis is carried out using gas chromatography/mass spectrometry (GC/MS) in the selected-ion monitoring (SIM) mode. 

Dinitroaniline herbicides are generally stable in soil. Residue methods were developed for both the parent molecule and selective soil degradates. 

Substituted dinitroanilines (Fig. 10, Table 3) are an important series of selective herbicides commercially introduced in agriculture in the 1960s. Trifluralin is the most prominent member of this series. Nitralin and Benfluralin have also received widespread usage, while Profluralin is a relatively recent herbicide of this class. Dinitro anilines show very low water solubilities. Nitralin and Benfluralin have low vapor pressures and are nonvolatile, while Trifluralin is relatively volatile. All these compounds have been shown to be relatively immobile in soil systems. 

Studies were initiated at Iowa State University in 1977 to determine if pesticides would be contained and degraded when deposited in water/soil systems. Although the addition of known amounts of the selected pesticides was controlled, the physical environment was not temperature, humidity, wind speed, etc. were normal for the climate of Central Iowa. Four herbicides and two insecticides were chosen on the basis of three factors. Firstly, they represented six different families of pesticides. The four herbicides, alachlor, atrazine, trifluralin, and 2,4-D ester, represent the acetanilides, triazines, dinitroanilines, and phenoxy acid herbicides, respectively. The two insecticides, carbaryl and para-thion, represent the carbamate and organophosphorus insecticides, respectively. Secondly, the pesticides were chosen on the basis of current and projected use in Iowa Q) and the Midwest. Thirdly, the chosen pesticides were ones for which analytical methodology was available. 

The synthesis of TATB (14) from the reaction of 2,3,4,5,6-pentanitroaniline (31) with ammonia has been reported. " In one route, 2,3,4,5,6-pentanitroaniline (31) is synthesized from the nitration of 3,5-dinitroaniline (30) " the latter is obtained from the selective reduction of TNB ° or via a Schmidt reaction with 3,5-dinitrobenzoic acid. Another route to 2,3,4,5,6-pentanitroaniline (31) involves the selective reduction of TNT (1) with hydrogen sulfide in ammonia followed by nitration of the resulting 4-amino-2,6-dinitrotoluene (46), during which the methyl group is lost by oxidation-decarboxylation. 

P7 Over the past decade, electron monochromator-mass spectrometry (EM-MS) has been shown to be a selective and sensitive technique for the analysis of a wide variety of electrophilic compounds in complex matrixes. Here, for the hrst time, three different dinitroaniline pesticides, flumetralin, pendimethalin, and trifluralin, have been shown to be present in both mainstream and sidestream tobacco smoke using an EM-MS system. (From Dane et ah, 2006)... 

Selective herbicides are relatively recent developments in the 5000-year history of sugarcane production. After 1945, when phenoxy herbicides were first sold, one person using 2,4-D in a backpack sprayer could accomplish the work of 15 others using hoes and with far more lasting results than simply severing weeds with a steel tool at the soil surface. While three herbicide families (triazines, phenoxys, and dinitroanilines) are of major importance in sugarcane production, the triazines, atrazine and ametryn clearly predominate. 

More than 130 different organic chemicals are currently employed as herbicides in the U.S. All of the main families of organic compounds are represented aromatic, aliphatic, and heterocyclic. Herbicidal activity is found in a variety of classes of compounds haloaliphatic, phenoxy, and benzoic acids carbamates dinitroanilines acetanilides amino triazines quaternary pyridinium salts uracils and ureas. A few selected key examples are reviewed below. 

Lyle and LaMattina selectively hydrogenated 4-substituted 2,6-dinitroanilines to the corresponding nitrophenylenediamines over 10% Pd-C in 1,2-dimethoxyethane-chloroform as solvent (eq. 9.56).135 With use of ethanol instead of 1,2-di-methoxyethane, 4-trifluoromethyl-2,6-dinitroaniline was completely hydrogenated to give the corresponding triaminobenzene. 

Aromatic dinitro compounds may be selectively reduced by hydrazine in the presence of transition metal catalysts.136 Pitre and Lorenzotti obtained 3-amino-5-nitrobenzoic acid in 82% yield by treating 3,5-dinitrobenzoic acid with Raney Ni and an appropriate amount (3.6 equiv) of hydrazine in water (eq. 9.57).137 Similarly, 2,4-dinitrophe-nol and 2,4-dinitroaniline were reduced to 2-amino-4-nitrophenol and 2-amino-4-nitroaniline, respectively, with 10% Pd-C and hydrazine in ethanol solution. 

Pd-C in both ethanol and DMF, little, if any, selectivity was obtained product ratios were 50 50 in ethanol and 60 40 in DMF. Palladium black in ethanol, which afforded 4-amino-5-nitroveratrole in 70-75% yield from 4,5-dinitroveratrole, provided no selectivity with 2,4-dinitroaniline, as well as with o- and m-dinitrobenzenes both nitro groups were hydrogenated.140 Reduction by sodium borohydride and Pd-C in methanol also does not appear to be selective, as 1,2,4-triaminobenzene is formed.141 It is of interest that over Pt-C in acidic alcohol 2,4-dinitroaniline is selectively hydrogenated at the 4-nitro group to give 4-amino-2-nitroaniline in 70% yield.142... 

The dinitroanilines are some of the most widely used herbicides. They am used almost exclusively as soil-incorporated, preemergent, selective herbicides. Uptake occurs from the soil via germinating seeds or the roots. 

Before Radosevich and De Villiers found in 1975 that isolated chloroplasts of resistant common groundsel were insensitive to atrazine and simazine (2), it had been erroneously assumed that all living plants would die if the herbicides could reach their target site intact. We now know that mechanisms of selectivity in crops can be due to differences in metabolism rates, uptake, translocation, site of action or avoidance mechanisms. However, the mechanisms of herbicide resistance that have evolved in weeds are usually different from the mechanisms of herbicide selectivity in most crops. This is certainly true with the most prevalent and thoroughly studied cases of herbicide resistance, including the triazines, dinitroanilines, and AHAS inhibitors. 

The dinitroaniline herbicides, trifluralin and pendimethalin, have been utilized in greater than 80% of the cotton acreage in the Southern United States because of their very effective weed control in this crop (1). Many of these fields are essentially in cotton monoculture and hence the continued use of these herbicides has constantly selected out those weeds most tolerant of these herbicides. Under such a selection pressure, the appearance of weed biotypes resistant to dinitroaniline herbicides is expected (2). The first report of a resistant biotype did not appear until 1984, Mudge si gl. (3) described the occurrence of dinitroaniline-resistance in Eleusine indica in counties in South Carolina where cotton is extensively cultivated. Since that initial report, dinitroaniline-resistant Eleusine has been detected throughout the midsouth (H. LeBaron, personal communication). 

So far, the resistant biotypes obtained from other areas have all been of the highly-resistant (R) rather than I type (unpublished). Although all of the biotypes arose under the same situations (cotton monoculture and dinitroaniline herbicide as a pre-plant herbicide treatment) only the populations from two counties in South Carolina apparently have this lower level of resistance. As our case scenarios on other occurrences of dinitroaniline resistance increase, we may be able to relate this to certain sets of unique environmental conditions that may have allowed selection of one type of resistance phenotype over another. 

Selective hydrogenation of one or two nitro groups in an aromatic dinitro compound is the basis for the synthesis of otherwise unattainable molecules. Carefully chosen catalysts, under totally different reaction conditions, have been met with success. Partial reduction of 2,6-dinitroanilines to nitrophenylenediamines occurs in 60-90% yield over 10% palladium-on-carbon at RT [equation (a)], although most heterogeneous catalysts do not afford such selectivity. 

Butralin is a preplanting selective herbicide to be incorporated into the soil. At a rate of 1-3 kg active ingredient/ha it is selective in cotton, soybean and vegetables. Unlike the other dinitroanilines, it also has a growth-modifying action and is used for the control of tobacco sucker. 

The herbicidal properties of profluralin (CGA 10 832,14) were first described by Taylor (1973). It is a selective, preplanting incorporated soil herbicide, applied at a rate of 0.75-1.5 kg active ingredient/ha. At this rate its action lasts for one year, and it is used mainly for the control of annual grass weeds and several broad-leaved weeds. It is well tolerated by cotton, sunflower and peanut. In soybean profluralin is, besides chlomidin, the dinitroaniline herbicide that can be most safely used in overdose amounts (Harvey, 1973), and it is very effective against Setaria faberi. It can also be used selectively in several vegetables. 

In the soil and in plants its behaviour is similar to that of the other dinitroaniline herbicides. It affects both photosynthesis and respiration in sensitive plants. The degree of its selectivity is related to the lipid content of the plants and their seeds. Profluralin is degraded in tolerant plants to polar metabolites. In the soil it is degraded mainly by the microbial route. At the recommended rates its half-life is 80-120 days, depending on the type of soil. 

---