Herbicides, examples

Many formerly common herbicides now have been banned or restricted in their use, e.g., 2,4-D and 2,4,5-T. However, the number and diversity of herbicides far exceeds that of insecticides. There are both organic and inorganic herbicides. Examples of inorganic herbicides are CUSO4 and NaC104. 

The rationale of validation experiments with fatty matrices is the high amount of fat extracted with many organic solvents. If analytes are not fat soluble and extraction is performed with water or aqueous buffer solutions, the troublesome fat is not extracted together with the analyte. Such extractions are typical for, e.g., the class of sulfonylurea herbicides. Examples exist where in such cases the applicability of an analytical method to fatty matrices was accepted by the authority without particular validation. 

The insecticidal usefulness of the amines is hindered hy their tendency to severely injure plants (phytotoxie effects) to which they may be applied. Advanlagc of this property, however, is taken by using some amine compounds us herbicides. Examples include henefin. niirahn. and trifluralin,... 

Fig. 4.69. Reaction scheme for the formation of DNS derivatives of carbamate and urea herbicides (example, Linuron). 1 = Hydrolysis 2 dansylation of the aniline moiety.

A number of 2-trifluoromethylbezimidazole herbicides were developed in the 1960s, but they have since being replaced by newer, more effective herbicides. Examples of 2-trifluoromethylbezimidazole herbicides are chlorflurazole [63,64] and fluoromidine [65], The 2-trifluoromethylimidazopyridine heterocycle ring in fluoromidine is prepared from the reaction of trifluoroacetic acid and the corresponding 5-chloro-2,3-diaminopyridine (Fig. 17) [66], The mode of action of... 

Not all of the ACS program have been included in this book, which was edited by Jay J. Gan, Peter C. Zhu, Ann T. Lemley, and myself. Contributions from additional authors, who could not participate in the symposium but whose work contribute to an even more inclusive treatise, are included in this book. One particular contribution. Chapter 4 by Lawrence P. Wackett entitled Evolution of New Enz5nnes and Pathways Soil Microbes Adapt to 5-Triazine Herbicides is especially appropriate because it concerns our ability to respond to the environmental pollution problem. This chapter describes a Pseudomonas species as a model to understand how bacterial genes involved in the metabolism of anthropogenic chemicals may arise and spread in the environment. The author describes how the ability to metabolize Atrazine by a Pseudomonas species evolved by recruiting enzymes from the amido-hydrolase superfamily to form a metabolic pathway to efficiently metabolize 5-triazine herbicides. Examples of the bioremediation of Atrazine-contaminated soil are described by Edward Topp, et al. in Chapter 11. 

It has already been mentioned that the degradation of s-triazine herbicides such as atrazinc in soil can be described by two reaction types only, hydrolysis and reductive dealkylation (see Figure 10.3-8). Application oF these two reaction types to a specific s-triazinc compound such as atrazinc provides the reaction network shown in Figure 10,3-12. This can also be vcriFicd by running this example on h ttp //www2,chemie,uni-erlangen.de/semces/eros/,... 

Because of the special stabiHty of the hexafluoroarsenate ion, there are a number of appHcations of hexafluoroarsenates. For example, onium hexafluoroarsenates (33) have been described as photoinitiators in the hardening of epoxy resins (qv). Lithium hexafluoroarsenate [29935-35-1] has been used as an electrolyte in lithium batteries (qv). Hexafluoroarsenates, especially alkaH and alkaline-earth metal salts or substituted ammonium salts, have been reported (34) to be effective as herbicides (qv). Potassium hexafluoroarsenate [17029-22-0] has been reported (35) to be particularly effective against prickly pear. However, environmental and regulatory concerns have severely limited these appHcations. 

The inertness of chlorine in the meta position in Halex reactions is of commercial value. For example, 3,4-dichloronitroben2ene [99-54-7] forms 3-chloro-4-duoronitroben2ene [350-30-1/, which is then reduced to 3-chloro-4-duoroaniline [367-21-5] for incorporation in the herbicide damprop—isopropyl or the duoroquinolone antibacterials, nordoxacin and pedoxacin. 

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). 

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). 

Substances other than enzymes can be immobilized. Examples include the fixing of heparin on polytetrafluoroethylene with the aid of PEI (424), the controUed release of pesticides which are bound to PEI (425), and the inhibition of herbicide suspensions by addition of PEI (426). The uptake of anionic dyes by fabric or paper is improved if the paper is first catonized with PEI (427). In addition, PEI is able to absorb odorizing substances such as fatty acids and aldehydes. Because of its high molecular weight, PEI can be used in cosmetics and body care products, as weU as in industrial elimination of odors, such as the improvement of ambient air quaHty in sewage treatment plants (428). 

Phosphonic acid is an intermediate in the production of alkylphosphonates that are used as herbicides and as water treatment chemicals for sequestration, scale inhibition, deflocculation, and ion-control agents in oil weUs, cooling tower waters, and boiler feed waters. For example, aqueous phosphonic acid reacts with formaldehyde and ammonium chloride in the presence of hydrochloric acid to yield aminotri(methylenephosphonic acid) [6419-19-8]. 

The piedominant use of P-picoline (3) is as a starting material for agrochemicals and pharmaceuticals. For example, it is used to make insecticides such as chlorpyrifos (43), food additives such as niacin (27) and its amide (26), and herbicides such as fluazifop-butyl [69806-50-4] (63). 

The main by-products of this synthesis type are sulfides and the isomer resulting from the Markownikoff addition to the alkene. For example, in the synthesis of 1-butanethiol (eq. 4), 5-thianonane, C H SC H, and 2-butanethiol are produced as by-products. The 2-butanethiol has uses as a herbicide intermediate and a gas odorant blend component and is further processed. The 5-thianonane is incinerated or reprocessed for fuel value. Sulfides account for up to 10% of the thiols produced. Another 2—5% is the Markownikoff addition product. 

The commercial exploitation of our increased understanding of protein stmcture will not, of course, be restricted to the pharmaceutical industry. The industrial use of enzymes in the chemical industry, the development of new and more specific pesticides and herbicides, the modification of enzymes in order to change the composition of plant oils and plant carbohydrates are all examples of other commercial developments that depend, in part, on understanding the structure of particular proteins at high resolution. 

Contractors at Sites B, D, G, I, and J had incomplete sampling practices and as a result were not able to evaluate PPE levels based on monitoring data. Eor example, both contractors SSAHPs at Site I lacked provisions for monitoring site hazards such as metals, pesticides, herbicides, and semi-volatile organic compounds (SVOCs) that could not be evaluated with a PID. Since worker exposures to the range of hazards on site had not been characterized, PPE was not selected based on its performance relative to the nature and level of site hazards. 

Occupational and environmental exposure to chemicals can take place both indoors and outdoors. Occupational exposure is caused by the chemicals that are used and produced indoors in industrial plants, whereas nonoccupa-tional (and occupational nonindustrial) indoor exposure is mainly caused by products. Toluene in printing plants and styrene in the reinforced plastic industry are typical examples of the two types of industrial occupational exposures. Products containing styrene polymers may release the styrene monomer into indoor air in the nonindustrial environment for a long time. Formaldehyde is another typical indoor pollutant. The source of formaldehyde is the resins used in the production process. During accidents, occupational and environmental exposures may occur simultaneously. Years ago, dioxin was formed as a byproduct of production of phenoxy acid herbicides. An explosion in a factory in... 

The lens is an avascular transparent tissue surrounded by an elastic, collagenous capsule. Disturbances in the normal metabolism of the lens and rupture of the lens alter its optical characteristics, and may cause cataract, i.e., reduced transparency of the lens. For example exposure to a herbicide, 2,4-dichlorophenol, may cause cataract. 

Examples of modem fluonne-contaimng herbicides, insecticides, and fungicides are shown below Most of these compounds are prepared starting from fluonnated bulk chemicals, such as fluonnated carbocyclic and heterocychc compounds, benzotnfluonde, fluonnated acetic acid denvatives, and Freons Direct fluonnation is used only occasionally by producers of fme chemicals and wiU, at least in the near future, remain the domam of producers of bu Ik chemicals who have the necessary techmcal expertise Fungicides... 

---