Thiocarbamate insecticides

An example of the profound effect which change in physical property may have on the toxicological properties of a methylcarbamate insecticide is made apparent from toxicological data for a series of thiocarbamate derivatives of carbofuran (Table 1) (12). 

Many organosulfur compounds undergo biological oxidation at the sulfur atom to yield products which have pronounced physiological activity or serve as intermediates in generating bioactive compounds. Three examples are the lachrymating agent in onions ( ) (1), the oxo intermediate ( ) in metabolic desulfuration of phosphorothionate insecticides to form potent cholinesterase inhibitors (2), and the sulfoxides QJ produced on metabolism of thiocarbamate herbicides (3). 

Carbamate pesticides are used as (1) insecticides, (2) fungicides and (3) herbicides. Insecticides are generally derived from carbamic acid fungicides, from thiocarbamic acid. The herbicide carbamates are a more complex class of compounds. Tables 21 and 22 list some commercial carbamate pesticides in approximate order of decreasing toxicity. It should be noted that the relative classification of highly and moderately toxic is no measure of the relative carcino-, muta- or teratogenicities of these carbamates, since it is based solely on acute LD q data (Morgan, ref. 20). 

Carbamates and thiocarbamates are an important family of pesticides, finding applications both as insecticides and herbicides. 

Carbamate compounds are usually subdivided into at least three main groups with respect to their structure and general use (see Figure 1) insecticides, herbicides, and thio- or dithiocarbamates. A variety of R groups may be substituted in the molecule producing, as is the case for insecticides, a variety of alkyl or aryl esters of carbamic acid. Although technically characterized as carbamate pesticides, thio- and di-thiocarbamate fungicides are not included in this... 

Many fungicides and insecticides also contain one or more sulfur atoms. This is certainly true of dithiocarbamates, reduced to form thiocarbamic acids due to the oxidation-reduction balance. These compounds are reputedly as unstable as their oxygenated counterparts. Thiocarbamic acids are precursors of isothiocyauates, which constitute the active ingredients in fungicides (Figure 8.22). 

Carbamates are nonpersistent pesticides that exhibit low toxicity for warm-blooded animals and human beings. Depending on the structure (see Fig. 3), quite different pesticidal activity is obtained. V-methyl- (IX) and V,A-dimethyl-carbamates (X) possess insecticidal activity, while V-aryl-carba-mates (XI) show herbicidal activity (66). Introducing a sulfur atom or atoms into the carbamate molecule instead of oxygen atom(s) yields thiocarbamate (XII) herbicides and dithiocarbamate (XIII)... 

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