Crop protection chemicals

The packaging of liquid insecticides and herbicides in specially treated metal containers is problematic owing to corrosion and other problems. The natural choice would be HDPE, but many formulations contain solvents such as xylene and other hydrocarbons that permeate through HDPE, leading to product loss11 and, in many cases, to severe paneling of the container.12,12 1 

A generally accepted method for studying solvent permeation involves high-temperature exposure of the contained fluid over a set time period to determine the amount of fluid loss from permeation through the container walls. 

To determine the suitability of fluorinated HDPE containers as packaging material for the solvent-based formulations, the containers were placed in well-ventilated ovens at 50°C for 28 days. During this period the mass loss of the contents was monitored. To date more than 130 liquid crop protection chemical formulations have been evaluated at the AEC by this method with at least 91 of them having serious permeation problems through the untreated HDPE containers. In only two cases fluorinated containers did not have acceptable barrier properties. 

The performance of a number of representative formulations in fluorinated and untreated natural HDPE containers is summarized in Table 16.1. It must be kept in mind that owing to the larger ratio of volume to exposed surface area, the mass loss for larger containers would be significantly lower, as indicated by the results in brackets in the table. 

Product Mass loss (%) Improvement Container appearance  

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DIFLUOROBENZENES Interest in the commercialization of difluoroaromatics in crop protection chemicals and dmgs (Table 5) continues to be strong. Numerous liquid crystals containing the 1,2-difluorobenzene moiety have been synthesized. Table 6 lists physical properties of commercially significant intermediates such as o-, m-, and -difluorobenzene, 2,4-difluoroaniline and 2,6-difluorobenzonitrile. The LD q values for the three isomeric difluorobenzenes are identical 55 g/m for 2 h (inhalation, mouse) (127). 

Trifluoromethyl aromatics are used widely ia the production of dmgs, crop-protection chemicals, germicides, dyes, etc. 

Applications. Table 12 Hsts crop-protection chemicals and pharmaceuticals containing the aryl fluoroaLkyl ether group. 

Ring- or side-chain fluoriaated nitrogen heterocycHcs have been iacorporated iato crop-protection chemicals, dmgs, and reactive dyestuffs. Key iatermediates iaclude fluoriaated pyridines, quiaolines, pyrimidines, and tria2iaes. Physical properties of some fluoriaated nitrogen heterocycHcs are Hsted ia Table 13. 

Applications. Until recently, haloxydine, a herbicide, was one of the few early examples of crop-protection chemicals containing riag-fluofinated pyridines. Fluroxypyr-(l-methylheptyl) and pyroxofop are new herbicides that are being commercialized (Table 14). 

PERFLUOROALKYLPYRIDINES New developments ia trifiuoromethylpyridine technology are associated with the commercialization of numerous crop-protection chemicals as herbicides, fungicides, and iasecticides (Table 15). Physical properties for representative trifiuoromethylpyridines are fisted ia Table 13. 

Table 15. Trifluoromethylpyridine-Based Crop-Protection Chemicals ...

A significant development ia trifluoromethylpyridine synthesis strategy is the use of fluoriaated aUphatic feedstocks for the ring-constmction sequence. Examples iaclude the manufacture of the herbicide dithiopyr, utilising ethyl 4,4,4-trifluoroacetoacetate [372-31-6] CF2COCH2COOC2H (436,437). 2,3-Dichloro-5-trifluoromethylpyridine [69045-84-7], a precursor to several crop-protection chemicals (see Table 15), can be prepared by conversion of l,l,l-trichloro-2,2,2-trifluoroethane [354-58-5], CF CCl, to 2,2-dichloro-3,3,3-trifluoropropionaldehyde [82107-24-2], CF2CCI2CHO, followed by cycUzation with acrylonitrile [107-13-1] (415). 

Crop Protection Chemicals Reference (CPCR), 6th ed.. Chemical and Pharmaceutical Press, John Wiley Sons, Inc., New York, 1990. Includes brand names and product labels. 

Sustainable Agriculture. The third factor that will influence the future of pesticide sales is the emphasis on sustainable agriculture systems that rely on more natural pest control methods and reduced pesticide usage. These are integrated systems that requke nutrients and crop protection chemicals from on-farm natural sources and cultural methods. Many current sustainable farms are site-specific systems that may depend on the soils in a... 

Ring-fluonnated aromatics have found wide applications in pharmaceuticals, crop protection chemicals, polymer intermediates, liquid crystals, etc [10] Routes based on aromatic amines represent one of the major synthetic approaches to these compounds The scope and the techniques have been sufficiently described in reviews [//, I2 and monographs [13, 14, fi] Therefore, only reactions and techniques published after 1971 are discussed... 

Downing et al. (1997) have reported a number of examples, including isomerization of 2,3-dimethyl-2,3-epoxide to methyl-rer/-butyl ketone, which is required for the production of photographic and crop-protection chemicals. 

Crop protection chemicals undergoing field testing to determine dissipation, wildlife exposure and toxicological effects will have undergone extensive laboratory tests to... 

Although the results presented only reflect agricultural practices of a single year, findings confirm that herbicides are the most widely used type of pesticide, as weeds are the major constraint that limit yield in many crops in conventional crop cultivation systems. According to CropLife (2004), herbicides represent around 50% of all crop protection chemicals used throughout the world, compared with insecticides and fungicides that each account for around 17%. 

Commercially the most exploited uses of surface fluorination are fluorinated HDPE fuel tanks for automotive vehicles and to a lesser extent fluorinated HDPE containers for the packaging of solvent-based crop protection chemicals. These products can be fluorinated using either in-line or postfluorination processes.10... 

Table 16.1. Performance of Crop Protection Chemicals in Natural 100ml HDPE Fluorinated and Unfluorinated Containers at 50°C after 28 Days...

The total world consumption of surfactants as agricultural adjuvants was estimated to be 60,000 t in 1993 [10], and this figure is expected to continue to increase as more concerted efforts are made to reduce the amounts of crop protection chemicals used. Indeed, whilst figures in 1995 showed the worldwide adjuvant market valued at only 3% that of the corresponding agrochemicals, the increase in use per annum was 5% as compared with 1.5% per annum for the agrochemicals [9]. 

CPCR. 1992. Crop protection chemicals reference. Di-Syston. 8th ed. New York, NY Chemical and Pharmaceutical Press, 1160-1171. 

Formation of bonnd residnes is related mainly to the fate of crop protection chemicals and other toxic waste organics in the biologically active soil snrface, dnring and after chemical redistribntion in the snbsnrface over long periods of time. 

Crop protection chemicals are an important group of contaminants that exhibit biologically mediated transformation in aerobic or anaerobic subsurface environments. We consider two well-known contaminants the insecticide parathion, which is an organophosphate compound, and the herbicide atrazine, from the triazine group. 

The persistence (half-life) of atrazine in the subsurface is governed by chemically and biologically mediated transformations. Because the solubility of atrazine is relatively high ( 30mg/L) compared to its toxicity level in water (5 Lig/L), atrazine has become a hazard to groundwater quality. Atrazine has been detected in groundwater more than any other crop protection chemical two examples of atrazine persistence-transformation in aquifer environments are discussed next. 

Lastly, always follow the label. Any material sold as a crop protection chemical in the United States must be registered with the Environment Protection Agency (EPA) and labeled. The label must be followed. Failure to do so is illegal and can be dangerous. Labels list time and rate of application and the vegetables and pests on which the product can be used. They also contain other information, such as safety precautions. Always read the label and use the chemical only where and how it is permitted. It is possible to cause severe environmental or bodily injury if agricrrltural chemicals are misused. In no case does the Agricultirral Extension Service recommend the use of any plant protection substance in a marmer inconsistent with its label. 

To protect people and the environment, crop protection chemicals must be used safely. This is everyone s responsibility, especially the user. Read and follow label directions, carefully before you buy, mix, apply, store or dispose of these chemicals. According to laws regulating them, they must be used only as directed by the label. 

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