Paraquat herbicide

Quaternary Salts. Herbicides paraquat (20) and diquat (59) are the quaternary salts of 4,4 -bipyridine (19) and 2,2 -bipyridine with methyl chloride and 1,2-dibromoethane, respectively. Higher alkylpyridinium salts are used in the textile industry as dye ancillaries and spin bath additives. The higher alkylpyridinium salt, hexadecylpytidinium chloride [123-03-5] (67) (cetylpyridinium chloride) is a topical antiseptic. Amprolium (62), a quaternary salt of a-picohne (2), is a coccidiostat. Bisaryl salts of butylpyridinium bromide (or its lower 1-alkyl homologues) with aluminum chloride have been used as battery electrolytes (84), in aluminum electroplating baths (85), as Friedel-Crafts catalysts (86), and for the formylation of toluene by carbon monoxide (87) (see QuaternaryAA ONiUM compounds). 

Bipyridines. Siace the 1960s, the most important commercial agrochemical based on pyridine has been the herbicide paraquat (20) which is made from 4,4 -bipyridine (19). The isomeric herbicide diquat (59) is made by an analogous route, but utilising 2,2 -bipyridine [366-18-7] as a precursor. 

The photodegradation of the contact herbicide paraquat yielded many degradation products, but the major pathway produced l,2,3,4-tetrahydro-l-ketopyrido[l,2-fl]-5-pyrazinium that was further degraded to pyridine-2-carboxamide and pyridine-2-carboxylate (Figure 1.11) (Smith and Grove 1969). 

Salleh MA, JM Pemberton (1993) Cloning of a DNA region of a Pseudomonas plasmid that codes for detoxification of the herbicide paraquat. Curr Microbiol 27 63-67. 

Baldwin, R.C., Pasi, A., MacGregor, T.J. and Hine, C.H. (1975). The rates of radical formation fixjm the dipyridylium herbicides paraquat, diquat and morfemquat in homc nates of rat lung, kidney and liver an inhibitory effect of carbon monoxide. Tox. Appl. Pharmacol. 32, 298-304. 

Calderbank, A. 1975. Environmental effects of the herbicide, paraquat. Pages 136-139 in F. Coulston and F. 

Kimbrough, R.D. 1974. Toxic effects of the herbicide paraquat. Chest 65(4), April 1974 supplement 65S-67S. 

Holmstedt (1959) and Brown and Muir (1971) have reviewed perocular absorption of pesticides. More recently, Sinow and Wei (1973) have shown that the quartemary herbicide paraquat can be lethal to rabbits if applied directly to the surface of the eyes. Parathion, in particular, is exceedingly toxic when administered via the eye, a concern that must be kept in mind for the protection of pesticide applicators. 

This technique has been used to determine the following types of organic compounds in soil polychlorobiphenyls, chlorinated insecticides, triazine herbicides, paraquat and diquat. 

Electrophoretic and isotachoelectrophoretic techniques are gaining in popularity in soil analysis with applications to polyaromatic hydrocarbons, polychlorobiphenyls, tetrahydrothiophene and triazine herbicides, Paraquat and Diquat and growth regulators. Other lesser-used techniques include spectrophotometric methods (five determinants), spectrofluorimetric methods (two determinants), luminescence methods (one determinant), titration methods (one determinant), thin-layer chromatography (five applications), NHR spectroscopy (two applications) and enzymic immunoassays (one determinant). 

Isotachoelectrophoresis or capillary column isotachoelectrophoresis has been employed in a number of analyses (triazine, herbicides, paraquat, diquat, growth regulators, polyaromatic hydrocarbons, polychlorobiphenyls and tetrahydrothiophene). 

The herbicide paraquat is structurally similar to MPP". Paraquat is toxic since it can generate superoxide free... 

Paraquat (1,1 dimethyl, 4,4 bipyridyl) is a nonselective contact herbicide. It is used almost exclusively as a dichloride salt and usually is formulated to contain surfactants. Both its herbicidal and toxicological properties are dependent on the ability of the parent cation to undergo a single electron addition, to form a free radical that reacts with molecular oxygen to reform the cation and concomitantly produce a superoxide anion. This oxygen radical may directly or indirectly cause cell death. Diquat, l,T-ethylene-2,2 -dipyridylium, is a charged quaternary ammonium compound often found as the dibromide salt. The structure of diquat dibromide and that of the closely related herbicide paraquat can be seen in Fig. 4.5. 

Dalvie MA, White N, Raine R, et ah Long-term respiratory health effects of the herbicide, paraquat, among workers in the Western Cape. Occup Environ Med 56 391-396, 1999... 

Chlorophenoxy herbicides 2,4-D 2,4,5-T Bipyridyl herbicides Paraquat, diquat... 

The heterocyclic equivalent of the benzoin condensation offers a route to the important herbicide paraquat (Scheme 128) (73JOC3993) (see also Section 2.05.7). N- Alkylnicotinic acid and its derivatives readily undergo addition of cyanide and many other nucleophiles (see Section 2.05.4.8). In the example shown in Scheme 129, 1,2-addition is subject to kinetic, and 1,4-addition to thermodynamic, control. 

Bipyridyls are by-products in the Chichibabin reaction. The dimerization of methyl-pyridinium salts has been patented, as it provides a route to the important herbicide paraquat (69USP3478042). Pyridine may undergo reduction in the presence of other nftetals as mentioned in Sections 2.05.4.7.5 and 2.05.4.7.6. 

Bipyridyls A group of synthetic organic pesticides which includes the herbicide Paraquat. Blasting Agents Any material or mixture consisting of fuel and oxidizer intended for blasting, not otherwise defined as an explosive. 

The result of this is accumulation of phospholipids, or phospholipidosis, in the tissues where accumulation of the drug occurs. Active uptake of a toxic compound into the target tissue may also occur. For example, the herbicide paraquat is actively accumulated in the lung, reaches toxic concentrations in certain cells, and then tissue damage occurs (see chap. 7). 

As active transport uses a carrier system, it is normally specific for a particular substance or group of substances. Thus, the chemical structure of the compound and possibly even the spatial orientation are important. This type of transport is normally reserved for endogenous molecules such as amino acids, required nutrients, precursors, or analogues. For example, the anticancer drug 5-fluorouracil (Fig. 3.6), an analogue of uracil, is carried by the pyrimidine transport system. The toxic metal lead is actively absorbed from the gut via the calcium transport system. Active uptake of the toxic herbicide paraquat into the lung is a crucial part of its toxicity to that organ (see chap. 7). Polar and nonionized molecules as well as lipophilic molecules may be transported. As active transport may be saturated, it is a zero-order rate process in contrast to passive diffusion (Fig. 3.3). 

Specific uptake systems may account for selective localization in tissues, and this may be the explanation for toxic effects in those particular tissues. For example, the herbicide paraquat (Fig. 3.16) is taken up by the polyamine transport system into the lungs and thereby reaches a toxic concentration (see chap. 7 for a detailed description of this system). 

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