Well-Known Insecticides

At an early date it was noticed that di-isopropyl phosphorofluoridate (DFP) (Section 12.13) and other nerve gas compounds were very effective against flies and other pests. Pioneering work in this field carried out in Germany by Schrader over 60 years ago led to his proposing the general insecticide formula (12.95a), where R = alkyl, alkoxy, amino, X=0 or S, and acyl = any acid anion such as F, CN, SH and so on. 

Most organophosphorus insecticides are based on a single P atom, which is linked directly to some combination of O, S, C or N atoms. These inclnde phosphate esters, phosphonates, amides and their thioated analogues. Comparatively few commercial insecticide molecules contain more than one P atom and these are usually pyrophosphate esters or their derivatives. Common types of insecticide inclnde those in Table 12.31. 

Thioated derivatives are generally less polar, hydrolytically more stable, and less toxic to animal species. In the case of enantiomers, one is usually more active thau the other, but conunercial products are usually racemates. 

The first organophosphorus compounds used as insecticides were very toxic to humans and they inclnded TFPP (12.96a), HFTP (mainly TFPP), parathion (12.96b) and paraoxon (12.96c). 

These compounds, while effective against a wide range of pests, could easily be absorbed through the skin and were very dangerous to use. Several fatalities occurred when they were first employed on crops. Like most nerve gases, however, the toxicity of organophosphorus insecticides is usually ranoved on hydrolysis. In fact the removal of insecticide residuals by rainwater is often relied upon before crop harvesting. 

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Pesticides. Dichlorodiphenyl trichloroethane (DDT) is one of the most well-known insecticides. During World War II it saved thousands of Allied... 

A report published thirty years ago (Ref. 164) outlined the potential insecticidal activity of 2,2-dichlorovinyl carbamates and carbonates. However, progress in this area has been stifled because 2,2-dihalovinyl chloroformates were unknown. For the preparation of the phosphonato ester (A) assumed to exhibit interesting insecticidal properties as compared to the well known insecticide Dichlorvos, we needed the heretofore unknown 2,2-dichlorovinyl chloroformate [see scheme 113]. 

Compounds that have common names are listed under their common as well as their chemical names, but the reference entries may be made under either. For example, styphnic acid has the chemical name 2,4, 6-trinitroresorcinol, but the index entries are under styphnic acid with a cross reference to Resorcinol, 2,4,6-trinitro-, see Styphnic acid. On the other hand, the well-known insecticide DDT is listed with a "see reference to its chemical name and the reference entries are under the latter, "Ethane, l,l,l-trichloro-2,2-bis (p-chlorophenyl). In general, it may be said to be the exception, not the rule, for the common name of a compound not to be listed. All names, common and chemical, are listed alphabetically. 

Photochlorination of aromatic compounds, for example, can lead efficiently to fully chlorinated products. Benzene is converted to 1,2,3,4,5,6-hexachlorocyclohexane with 0 = 2500 (Scheme 6.225).1308 One of the stereoisomers, lindane, is a well-known insecticide (banned today), which was produced and used globally in agriculture in annual amounts of 106 tonnes.1309... 

Malathion, the well-known insecticide, and the much more toxic isomalathion, (83) have one and two chiral centres, respectively. Chiral forms of the former have been prepared from the appropriate diethyl malate by sequential reaction with trifluoromethanesulphonic anhydride and sodium 0,0-dimethyl phosphorodithioate thus, for example, (-)-malic acid yields (/f )-malathion (84). Monodemethylation of the malathion enantiomers with strychnine, and methylation (dimethyl sulphate) of the... 

The well-known insecticidal benzoyl phenyl ureas (BPUs), exemplified by diflubenzuron, are chitin biosynthesis disrupters, but at an uncharacterized site distinct from chitin synthase (2), Figure 1. The related bridge-cyclized oxazoline chemistries from DuPont and Yashima, represented by etoxazole, are also commercial or near-conunercial insecticides with the same mechanism of action (5), Figure 1. 

Dichlorovinyl chloroformate (for a preparation, see Section 4.2.1 Chloro-formylation ), the key intermediate for the preparation of the phosphonato ester 294, which is assumed to exhibit interesting insecticidal properties by analogy with the well-known insecticide Dichlorvos, was synthesized from chloral and phosgene in the presence of reusable naked chloride ions and subsequent dechlorination with Zn [215]. 

It would seem obvious that efforts should be concentrated on following up the many leading observations which have been reported and determining the structure of the substances already isolated. However, re-examination of the biology and chemistry of species which have yielded insecticidal compounds in the past certainly should not be overlooked. Dr. Beckman will show that careful investigation of such a well-known commercial preparation as pyre-thrum extract can reveal the presence of unsuspected and active new constituents Dr. Moore will indicate how some such observations may be turned to profit through synthesis of simple analogs. 

The biochemistry or mode of action of pyrethrum is not as well known as its chemistry. There are several theories of the toxic action of pyrethrum. Lauger et al. (26) consider that a highly effective contact insecticide must possess a toxic component (toxaphore) and must have groups attached which absolutely insure pronounced lipid solubility. They consider in the case of pyrethrins that in the cyclopro-... 

Ryanodine is a neutral plant alkaloid from Ryania speciosa and was used as an insecticide. It also has been well known by the characteristic action on mammalian skeletal muscle of slowly developing, and intensive and irreversible contracture. Ryanodine binds specifically to the open RyR channel at the stoichiometry of 1 mol/mol homotetramer with a high affinity (ATD nM) and leads the channel to ryanodine modified state characteristic of long-lasting subconductance ( 50% of normal) opening. At higher concentration, it blocks the channel. 

Marine Worms. (Platyhelminthes, Rynchocoela, Annelida, Sipunaelida.) A variety of species from worm phylla have been found to contain toxins. There are approximately 56,000 species of worms (14,000 annelids, 25,000 platyhelminthes, 15,000 nematodes, and 800 nemertines), and of these, most of the toxic species are found in the nemertines. The most well-known toxin is nereisotoxin which has been modified to form a very useful insecticide. 

The main purpose of this work is development of small-scale and mobile dsMmposition system of these chemicals. A number of studies on decomposition of organophosphorus insecticides have been conducted [1-3]. It is well known that or nophosphorus insecticides are decomposed by hydrolysis under alkaline condition, and its meciianisms have been studied [4], Even so, relatively few papers have address the devdopment of kinetic equations for reactor desipi. In this study, we aim to get kinetic equaticms for their decomposition under alkaline condition. As organophosphtous, we used parathion, fenitrothion, diazinon, malathion and phenthoate. 

The control of insects is no easy or simple task. Even for those species that are well known and for which control measures are fairly standardized, many things have to be considered. In cases where the suitable insecticide is known, there is need for accuracy in using the correct concentration and rate of application. That is usually the simplest part of the operation. Timing the application may mean the difference between success and... 

All these facts and many more are well known to any commercial man in the insecticide or fungicide industry today. When agricultural scientists and advisers talk with growers, they frequently overlook many of these factors. On the other hand, the men of industry frequently forget some of the complex problems associated with the widespread use of potent chemicals. 

Organophosphate Ester Hydraulic Fluids. A number of studies have been conducted on organophosphate ester hydraulic fluids because of the well known neurotoxic effects caused by organophosphorus insecticides, organophosphorus nerve gases, and tri-ort/w-cresyl phosphate (TOCP). The following manifestations of acute exposure to organophosphorus compounds have been described ... 

Trigard 75 WP is a new insecticide with a unique mode of action and a unique triazine structure. It is a solid formulated as a wettable powder and is packaged in water-soluble bags. The active ingredient in Trigard has the common name cyromazine. Cyromazine is a triazine, but, unlike the well-known triazine herbicides, this compound has insecticidal properties and no herbicidal activity. Cyromazine has low mammalian toxicity and low vapor pressure. It is hydrophilic, so dermal penetration is expected to be... 

A few illustrative examples of important agrochemicals and pharmaceuticals that contain a CF3 group are given in Fig. 5.1. They include the insecticide triflumuron (5-1), the neuroleptic fluphenazene (5-2), which is used in the treatment of schizophrenia, and the well-known antidepressant drug, PROZAC (5-3). 

Phenothiazines are well-known as intermediates for pharmaceuticals, and are also active as insecticides and antioxidants. These compounds are usually prepared by the thiation of diphenylamines with elemental sulfur. In this context, the group of Toma has elaborated a synthesis of 3-phthalimidophenothiazine, as shown in Scheme 6.265 [455]. Using a variety of high-boiling solvents under conventional thermal reflux conditions, low isolated yields of the desired product were obtained. The highest conversion and isolated product yield (55%) was achieved by microwave irradiation of a mixture of the starting N-(4-phenylaminophenyl)phthalimide with... 

Compound (V) is used as an insecticide and is marketed as a 50 per cent solution under the name of hanane, which also contains 5 per cent of O.M.P.A. Hanane properly placed at the roots of cocoa trees kills mealy-bugs in the crown of the tree without harming beneficial insects such as ants which effect pollination. Five hundred trees infested with mealy-bugs were treated 2 10 per cent of the trees, chosen at random, were cut down before treatment and after treatment, and the number of mealy-bugs counted under a binocular microscope. After 6 weeks only thirty-five mealy-bugs were present on the treated trees as opposed to 42,971 counted before treatment in the untreated portion, a reduction of 99-9 per cent. It is well known that several species of mealy-bug, especially Pseudococcus ujalensis, transmit strains of swollen shoot virus, which kill the cocoa tree in 2-4 years. Thus the spread of the disease can be effectively controlled by this systemic insecticide (see also p. 171). 

Most of the well-known chlorinated hydrocarbon insecticides will kill horseflies and the percentages required are small. But none of them will protect livestock adequately from horseflies, as the bites are made and the damage done before these relatively slow acting materials take effect. Probably most horseflies attacking an animal sprayed with DDT, lindane, chlordan, or toxaphene (chlorinated camphene) would eventually die, but the fly reduction thereby made in an area would be insignificant unless all hosts both wild and domestic were treated frequently. 

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 members of the plant family Piperaceae are well known in traditional pharmacology in Asia and Africa as medicines and insecticides. Piper nigrum L. (Piperaceae, black pepper) has traditionally been used as a... 

It Is well known that phosphorothlonate insecticides such as parathlon (, 0-diethyl p-nitrophenyl phosphorothloate) and malathion [0, -dimethyl -(l,2 -dlcarbethoxy)ethyl phosphoro-dithioate] are Intrinsically poor inhibitors of acetylcholinesterase and in vivo activation to the respective anticholinesterases paraoxon and malaoxon is required before animals exposed to the phosphorothionates are intoxicated. Since metabolic activation is essential to the biological activity of these thiono sulfur-containing organophosphorus insecticides, compounds of this type may be considered as propesticides or, more specifically, prolnsectlcldes. 

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