Thiocarbamate compounds

Thus the condensation of dichloroether or chloroacetone fails to give the parent compound, 2-hydroxythiazole (158a), Rj = R2 = R3 = H (221). However, 2-hydroxythiazole can be obtained in 12% yield from chloro-acetaldehyde (386). The condensation of ammonium thiocarbamate with cf-chloroketones gives the corresponding 2-hydroxy derivatives in 25 to 70% yields (76, 221, 304, 412) (Table 11-24). These compounds condensed with ClP(S)(OEt)2 give the corresponding 2-thiazolyl-thiophosphates (791). 

Hydroxythiazoles give 2-chIorothiazole derivatives almost quantitatively upon treatment with phosphorus oxychloride (221, 229, 428). This constitutes a convenient synthesis method for these compounds when the conversion of 2-aminothiazoles to 2-chlorothiazole derivatives fails. Esters of thiocarbamic acid or thiourethanes also react with a-halocarbonyl compounds to give the corresponding 2-alkoxythiazoles (50, 68, 209, 272). 

Human perception creates difficulty ia the characterization of flavor people often, if not always, perceive flavors differently due to both psychological and physiological factors. For example, certain aryl thiocarbamates, eg, phenylthiocarbamide, taste exceedingly bitter to some people and are almost tasteless to others (5). This difference is genetically determined, and the frequency of its occurrence differs from one population to another 40% of U.S. Caucasians are nontasters, whereas only 3% of the Korean population caimot perceive the strong bitter taste of the aryl thiocarbamates (6). Similar differences were found ia the sense of smell for compounds such as menthol, carvone, and ethyl butyrate (7). 

The growth inhibitory mechanism of the thiocarbamate herbicides, eg, EPTC, butylate, cycloate, diaHate, and triaHate, is not well defined. Cell elongation, rather than cell division, appears to be inhibited (183), although mitotic entry may be inhibited by diaHate (184). Thiocarbamates have a greater effect on shoot than toot tissue (163,184). The weU-documented inhibition of Hpid synthesis by thiocarbamates certainly contributes to the observed inhibitions of cell division and elongation. These compounds may also inhibit gibbereUic acid synthesis (185). 

The toxic nature of mercury and its compounds has caused concern over environmental pollution, and governmental agencies have imposed severe restrictions on release of mercury compounds to waterways and the air (see Mercury). Methods of precipitation and agglomeration of mercurial wastes from process water have been developed. These methods generally depend on the formation of relatively insoluble compounds such as mercury sulfides, oxides, and thiocarbamates. MetaUic mercury is invariably formed as a by-product. The use of coprecipitants, which adsorb mercury on their surfaces facihtating removal, is frequent. 

The encapsulation of herbicides has received much attention. Encapsulated alachlor is a high volume herbicide product generally sold as a Hquid formulation, although a dry granule version is also available. The capsules, produced by interfacial polymeri2ation (11), are reported to be spherical with a diameter of 2—15 p.m (75). Two thiocarbamate herbicides, EPTC and vemolate [1929-77-7], were encapsulated by interfacial polymeri2ation because they are volatile compounds. When appHed in unencapsulated form, they must be incorporated in the soil within two hours in order to provide effective weed control. When appHed as a microencapsulated formulation, the rate of volatili2ation is lower and soil incorporation can be delayed 24 hours (76). 

Accelerators are chemical compounds that iacrease the rate of cure and improve the physical properties of the compound. As a class, they are as important as the vulcanising agent itself. Without the accelerator, curing requires hours or even days to achieve acceptable levels. Aldehyde amines, thiocarbamates, thiuram sulfides, guanidines, and thiasoles are aU. classified as accelerators. By far, the most widely used are the thiasoles, represented by mercaptobensothiasole (MBT) and bensothiasyl disulfide (MBTS). 

Organosulfur Adsorbates on Metal and Semiconductor Surfaces. Sulfur compounds (qv) and selenium compounds (qv) have a strong affinity for transition metal surfaces (206—211). The number of reported surface-active organosulfur compounds that form monolayers on gold includes di- -alkyl sulfide (212,213), di- -alkyl disulfides (108), thiophenols (214,215), mercaptopyridines (216), mercaptoanilines (217), thiophenes (217), cysteines (218,219), xanthates (220), thiocarbaminates (220), thiocarbamates (221), thioureas (222), mercaptoimidazoles (223—225), and alkaneselenoles (226) (Fig. 11). However, the most studied, and probably most understood, SAM is that of alkanethiolates on Au(lll) surfaces. 

Other examples of nonionic compounds (Fig. 10, Table 3) are the phenyl-amide herbicides (e. g., Diphenamid, moderately water soluble and nonvolatile), thiocarbamate, and carbothioate herbicides (e. g., Thiobencarb, low water solubility, high vapor pressure, relative mobility in soil systems) and benzonitrile herbicides (e.g., Dichlobenil, low water solubility, low vapor pressure, relative immobility in most soils) [151]. 

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). 

The NMR chemical shifts for the carbamoyl sulfoxides (Table I) support their proposed structures. In examining the oxidation reactions, it is convenient to add MCPBA to a solution of the thiocarbamate in CDCI3 at -20°C and take frequent spectra during oxidation as the reaction mixture warms up to 40°C. Comparison of these spectra with that of the parent compound at -20 to 40°C allows recognition of short-lived intermediates and terminal products. With the parent thlocarbamates for compounds 5-2, the methyl group signals appear as one doublet at 40°C but two... 

Chloroallyl) thiocarbamate sulfoxides (. ., 5-2) un-.doubtedly rearrange in an analogous manner but in tbis case tbe sulfenate quickly undergoes an additional 1,2-elimination reaction (7 ). Tbe resulting products are tbe IJ, -dialkylcarbamoyl-sulfenyl chloride (M) and tbe carbonyl compound, aldehydes... 

Proherbicides. Thio- and dithiocarbamates probably require metabolic activation prior to exerting their herbicidal effects. Sulfoxide metabolites of the -alkyl thiocarbamates are generally more potent herbicides than the parent compounds ( -5). The herbicidal action of these sulfoxides probably results from their carbamylating action for thiols, although the specific target site or receptor is not defined (23, 24). It is conceivable that the -chloroallyl thiocarbamate herbicides may act in the same way, since their sulfoxides are also potent carbamylating agents... 

Figure 1. Oxidation and other reactions of dialiate and triallate indicating mutagenic activities of the products in the S. typhimurium TA 100 assay (revertants/ nanomole without activation/with activation / designates no data available). 2-Chloroacrolein is a dialiate metabolite in the mouse liver microsome-NADPH system. Dichloroallylsulfonic acid is a urinary metabolite of dialiate. The other compounds are potential metabolites of the respective thiocarbamates. The thio-carbamate sulfoxides are unstable at 25°C.

As in the case of propachlor mercapturic acid sulfoxide, the biological significance of xenobiotic mercapturic acids that contain oxidized sulfur is not known. Casida et al. (39) have reported that sulfoxidation of some thiocarbamate herbicides is a beneficial step in the detoxication process. However, cysteine conjugates can exhibit adverse biological activities. Smith (40) has reviewed work on the metabolism of the toxic principle in kale and has shown that C-S lyase action on S-methylcysteine sulfoxide produces the toxic principle. Virtanen ( ) has reviewed the processes in other plants that lead to the production of compounds with biological activity from -substituted cysteine sulfoxides. 

Oxidative desulfurization of the thiourea moiety is known to occur by an in vivo metabolism which forms the corresponding carbonyl compound, although there is no direct evidence for involvement of any activated oxygen species like superoxide, which is distributed widely in living cells. It was found that various thiocarbonyl derivatives such as thioureas, thioamides and thiocarbamates were readily desulfurized with 51 to the corresponding carbonyl compounds in almost quantitative yields at —35°C in CH3CN (equation 82). Desulfurization of thiourea with 02 was previously reported but the yields were comparatively low. ... 

The conversion of fatty acids into very long chain fatty acids is specifically inhibited by the thiocarbamate herbicides such as EPTC and triallate (Figure 2.19). These compounds are used pre-plant incorporated for the control of grass and some small seeded broad-leaved weeds in crops such as maize and small grain cereals. 

---