Carbamates and dithiocarbamate

Carbamates and dithiocarbamates (carbofuran, carbaryl, ziram, and benthiocarb)... 

Substituted phenols Chlorophenoxy compounds Substituted acetic and propionic acids Amides and thioamides Substituted ureas Carbamates and dithiocarbamates Symmetrical triazines Benzoic acid derivatives Miscellaneous herbicides... 

The metal atoms in the resulting carbamates and dithiocarbamates are 8-coordinate, with two monodentate and three bidentate ligands. The C02 insertion is partially reversible so that the carbamates can exchange with labeled C02 ... 

Certain Cr° amides disproportionate upon heating and yield volatile Cr derivatives of the type [Cr(NR2)4] (R = Et, Pr). Their magnetic moments and electronic spectra are frilly consistent with tetrahedral structures. Reaction with tertiary alcohols yields the tetraalkoxides described above and insertions of CO2 or CS2 yield Cr ° carbamates and dithiocarbamates, respectively. 

No simple reactions between CO2 or CS2 and group IVB hydrides have been reported. On the other hand, a vast literature exists on insertion of CO2 and CS2 into N-H bonds. The reactions of NH3 with CO2 and CS2, to form ammonium carbamate and dithiocarbamate, respectively, are of commercial importance in the synthesis of urea, cyanates, and thiocyanates but are properly considered in the realm of organic chemistry. Secondary phosphines react with CS2 in the presence of a base ... 

Carbamates comprise the esters and the salts of carbamic acids. This is a systematic classification from chemical aspects. Microbicides of this class of substances widely differ in terms of both efficacy and mechanisms of activity. The carbamic and dithiocarbamic acids, the basis of the carbamates, lack chemical stability they occur only intermediarily and disintegrate instantly to form carbon dioxide (CO2), carbon disulphide (CS2) and amine (see Fig. 31). 

Some important exampies of dry film preservatives include benzimidazoles such as carbendazim, octylisothiazolinone, carbamates and dithiocarbamates such as thiram, zinc pyrithione and chlorotha-lonil. Representative exampies are shown in Figure 5.23. As with in-can preservatives, the optimum use ievels should be determined by experiments. 

It should be noted that tyrosinase can be inhibited by many different compounds such as carbamate and dithiocarbamate pesticides, diuron, atrazines, desisopropy-latrazine, chlorophenols, and thioureas. Based on this characteristic, tyrosinase has been used to develop enzymatic biosensors for the detection of many pesticides with a similar sensing mechanism with AChE and BChE (Fig. 11.4). Despite the... 

The salts of alkyl xanthates, A/,A/ -di-substituted dithio-carbamates and dialkyidithiophosphates [26] are effective peroxide decomposers. Since no active hydrogen is present in these compounds, an electron-transfer mechanism was suggested. The peroxide radical is capable of abstracting an electron from the electron-rich sulfur atom and is converted into a peroxy anion as illustrated below for zinc dialkyl dithiocarbamate [27] ... 

Zinc carbamate complexes are well known, and the structural types and stabilities can be compared with thiocarbamates and dithiocarbamates which are discussed in Sections 6.8.11.1.3 and 6.8.7.1.4482 Carbamates of zinc can be formed from the reaction of carbon dioxide with alkylzinc alkyl amides and further reaction with alkylzinc can give a distorted cubane structure.483 The tetrameric diethylcarbamate species initially formed can also be used to produce monomeric or dimeric carbamate structures in reaction with amines tetramethylethylenediamine forms a monomer [(Me2NCH2)2Zn(02CN(C2H5)2)2] with an octahedral zinc center and pyridine forms a dimer[CsH5NZn2Me(02CN(C2H5)2)3] with tetrahedral zinc centers.484... 

T. Noguer, B. Leca, G. Jeanty, and J.L. Marty, Biosensors based on enzyme inhibition detection of organophosphorus and carbamate insecticides and dithiocarbamate fungicides. Field Anal. Chem. Tech. 3, 171-178 (1999). 

Pseudo-allyl compounds are formed from reactions of [Re(CO)2(PPh3)2(OCHNC6H4-4-Me)] with excess of PhNCO or PhNCS. Whereas carbamate compounds are formed in the former case, a mixture of monothio- and dithiocarbamate compounds is obtained with the sulfur analogue. The formation of the latter complex proceeds via the intermediate formation of the first. The related compounds show similar structural features with distorted octahedral rhenium atoms and... 

Additional methods considered for 304(h) rule making and the parameters measured are the following (the numbers in parentheses indicate the number of compounds included in the method) 622, organophosphorus pesticides (19) 623, 4,4 -methylene bis(2-chloroaniline) 626, acrolein and acrylonitrile (2) 627, dinitroaniline pesticides (5) 628, carbofuran 629, cyanazine 630, dithiocarbamates (15) 631, carbendazim and benomyl 632, carbamate and urea pesticides (7) and 633, organonitrogen pesticides (7). Most of these are... 

Diones are normally synthesized from /3-hydroxy acids in two steps first, conversion into carbamates by reaction with sodium cyanate, and then cyclization with thionyl chloride (Scheme 103) (54JCS839). Alternative preparations utilize oxetanes, which may be combined either with isocyanates in the presence of boron trifluoride (68JAP6808278) or with S-alkylthioureas (Scheme 104) (69ZOR1844). In the last example the initial products are imines (224) which may readily be hydrolyzed to the required diones. Similar methods can be applied to the synthesis of tetrahydro-l,3-thiazine-2,4-diones, and, for instance, the 4-oxo-2-thioxo derivative (225) is obtained from /3-propiolactone and dithiocarbamic acid (Scheme 105) (48JA1001). 

Typical examples of this reaction involve the heterocumulenes C02, CS2, COS, RNCO, RNCS and other related molecules such as S02, S03, RC=N and RNC, and activated alkynes bearing strongly electron-withdrawing substituents such as C02Me. These reactions find utility in the syntheses of homoleptic carbamates (equation 77),223 monothiocarbamates and dithiocarbamates from homoleptic amides though redox reactions can occur in some instances (equations 78102 and 79224). 

Carbamates and ureas constitute important groups of pesticides that are used as herbicides (phenylureas, sulfonylureas, phenylcarbamates, and alkylthiocarbamates), insecticides (ben-zoylureas, methylcarbamates, and oximemethylcarbamates), or fungicides (dithiocarbamates, alkylenebisdithiocarbamates, and benzimidazolecarbamates) in different crops to control various weeds, pests, and diseases. 

Carbamates are substituted esters of carbamic acid (NH2COOH) with aliphatic or aromatic substituents on the oxygen and nitrogen atoms. Carbamate insecticides have an aryl or oxime N-methylcarbamate structure, and their mode of action is based on the inhibition of the enzyme acethylcholine esterase (1). However, this inhibition is reversible, and recovery from sublethal doses occurs rapidly. Some carbamate fungicides have a dithio, bisdithio, or benzimidazole carbamate basic structure, and dithiocarbamate fungicides inhibit the enzyme aldehyde deshydro-genase (2). The herbicides have an /V-alkylthiocarbamate or A-phenylcarbamate structure and interfere with photosynthetic activity or affect meristematic activity or lipid metabolism (3). Representative structures of carbamate pesticides are shown in Fig. 1. 

Selenium and tellurium dioxides react with alkali xanthates and dithiocarbamates to give xanthates and dithiocarbamates of selenium(IV) and tellurium(IV).1,2 Russell1 states that the product formed by sodium diethyldithio-carbamate and selenium dioxide sometimes appears as an equimolar mixture of selenium (II) dithiocarbamate and the corresponding bis(thiocarbamyl) disulfide, (R2NCS)2S2. The commercial selenium dithiocarbamates, prepared by the above-mentioned method, usually consist of such mixtures. The disulfide can, in most cases, be extracted from selenium (II) dithiocarbamate by means of cold benzene or chloroform. 

FIGURE 2. Correlation between dc—n = D1(A) and Xn according to reference 4 (by permission of the authors) A—anilines, B—naphthylamines, D—enamines, N—amidines, O or S—amides, carbamates, thioamides and dithiocarbamates... 

A variety of neutral complexes are formed with /3-diketonate, dithiocarbamate, carbamate, and related ligands. The Th(acac)4 is electrochemically reduced to [Thm(acac)4] which loses acac- to give Th(acac)3—one of the very few Thra complexes known.14... 

The chloro- and tetrahydroborato amide complexes (COT)U(NEt2)(THF)x(BH4), (COT)U(NEt2)(THF)x(X), which were readily formed upon addition of LiCl or KBH4, were stable in THF solution. They could, however, not be isolated in solid form and decomposed into U(COT)2 and other unidentified species by desolvation. Treatment of [U(COT)(NEt2)(THF)2][BPh4] with C02, CS2, or acetonitrile led to insertion of these small molecules into the U-N bond to form the carbamate or dithiocarbamate complex, respectively (Scheme 79).158... 

Hill and co-workers studied the thermal decomposition of a large number of metal complexes of various alkyl derivatives of xanthic and dithiocarbamic acids. The complexes were studied by using TG. DSC. and other TA techniques. Compounds investigated included Nil IB alkyl xanthates (79), Cu(II) dithiocarbamate complexes (80), dihalotin (IV) bisdiethyldithio-carbamates (81), bisldiethyldithiocarbamatoi diphenyl tin (IV) (82), tetrakis-(diethyldithiocarbamatoi tin(lV) (83, 84), and bisidieihyldithiocarbamato) tin(IV) (85). 

Maneb is a pesticide with fungicide properties and belongs to the carbamate (bfs-dithiocarbamate) group. Sensitization occurs mainly in farmers and agricultural workers. 

---