Carbamates attributed

The carbamate and OP insecticides and the organophosphorous nerve gases soman, sarin, and tabun all act as anticholinesterases, and most of their toxicity is attributed to this property. The naturally occurring carbamate physostigmine, which has been used in medicine, is also an anticholinesterase. Some OP compounds can cause relatively long-lasting inhibition of the enzyme because of the phenomenon of... 

The chloride (60 1) and 2 volumes of water were mixed ready for subsequent addition of alkali to effect controlled hydrolysis. Before alkali was added, the internal temperature rose from 15 to 25° during 30 min, and then to 35°C in 5 min, when gas was suddenly evolved. This was attributed to the effect of liberated hydrochloric acid causing autocatalytic acceleration of the hydrolysis and then rapid release of carbon dioxide arising from decarboxylation of the carbamic acid. Hydrolysis by addition of the chloride to excess alkali would prevent the gas evolution. 

Carbamate esters of zinc, zineb, and ziram are carcinogenic and teratogenic in animals, but this is attributed to the action of the carbamate esters and not to zinc (Elinder 1986). Results of studies with small mammals showed zinc to be cocarcinogenic with 4-nitroquinoline-N-oxide on oral cancer, and with N-ethyl-N-nitrosourea on brain cancer (Leonard and Gerber 1989). 

This lowering of the selectivity may be attributed to competitive binding between the hydroxyl and amide groups to iridium [37]. In entries 6, 7 and 8, the directivity of the hydroxyl group at the bishomoallylic position effectively overrides the effect of the carbamate unit [38]. In the hydrogenation of methylenebi-... 

Pirkle and coworkers [59] compared retention and selectivity factors between HPLC and SFC using Poly Whelk-O chiral stationary phases and a-naphthyl-1-ethylamine carbamates. The results indicate that both retention and selectivity factors in SFC were higher than those in HPLC. This can be mainly attributed to the weaker solvating power of the carbon dioxide supercritical fluid as compared to a liquid such as methanol or hexane. 

An alternative method for cleaving carbamates is exhaustive reduction with LiAlFLt to yield methylamines (Entry 3, Table 3.22). Entry 9 in Table 3.22 is an example of the nucleophilic cleavage of a carbamate with sodium methoxide. The mild reaction conditions required in the case are attributable to the structure of the amine (a vinylogous amide) these conditions are unlikely to lead to the cleavage of simple A-alkyl- or A, A-dialkylcarbamates, although A-arylcarbamates are also susceptible to nucleophilic cleavage (Entry 6, Table 3.26). 

Table 6.4 shows first-order rate coefficients and tx/2 values for degradation of a number of pesticides in soils (Rao and Davidson, 1982). The k and t1/2 values calculated from field data are based on the disappearance of the parent compound (solvent extractable). Table 6.4 also includes k and t1/2 values calculated on mineralization (14C02 evolution) and parent-compound disappearance from laboratory studies. The t1/2 values were smaller for field than for laboratory studies. Rao and Davidson (1980) attribute this to the multitude of factors that can affect pesticide disappearance in the field while only one factor is studied in the laboratory. Rao and Davidson (1982) suggested that pesticides be classified into three groups based on values (Table 6.5) nonpersistent (t1/2 < 20 days), moderately persistent (20 < t1/2 < 100 days), and persistent (/1/2 > 100 days). Most chlorinated hydrocarbons are grouped as persistent, while carboxyl-kanoic acid herbicides are nonpersistent. The s-triazines, substituted ureas, and carbamate pesticides are moderately persistent. 

The action spectrum for DDT and its structural analogs is known to be quite broad and cannot be attributed to simple enzyme inhibition, as in the case of the carbamates or the organophosphates. The presence of chloroaryl moieties, as well as steric effects at receptor sites, both appear to be factors affecting insecticidal activity. In addition to DDT itself, its metabolites DDE and DDA and DDD have some activity. Efforts to overcome insect resistance and to produce more biodegradable analogs led to the introduction of substituents other than chlorine for... 

In contrast to the results presented above, silver-mediated silylene transfer to a, (3-unsaturated imines or imines with IV-carbamate groups did not produce silaaziridines (Scheme7.50).123 These substrates instead formed enamine 173oroxazoline 175. The authors attributed these products to a 67t-electrocyclization of ylide 172 and 174. 

Exposure of the (cycloalkenyl)methyl carbamates 304 to iodosylbenzene in the presence or absence of Rh2(OAc)4 gives the tricyclic aziridines 305 (Scheme 88) (02OL2137). Reactions of 305 with nucleophiles, facilitated with tosic acid or lithium perchlorate, proceed with cleavage of the C-N edge bond and afford the tf 7 z-spirooxazolidinones 306. Intramolecular aziridination of the indolyl carbamate 307 with DAIB, on the other hand, requires Rh(II)-catalysis and leads directly to the acetoxy-substituted YDi-spirooxazolidinone 308 (Scheme 88) (02OL2137). When iodosylbenzene is used instead of DAIB and alcohols are available in the reaction medium, alkoxy-substituted syn-spirooxazolidinones 309 are obtained. Whereas the conversion of 304 to 305 appears to proceed by direct cyclization of intermediate iminoiodanes, the production of 308 from 307 was attributed to the intervention of a rhodium nitrene, which collapses to 308 through zwitterionic intermediates (02OL2137). 

A considerable extension of the duration of activity together with a strongly reduced toxicity has been found (79) for a preparation with morphine-antagonistic activity [7 7 the place of its action being localized also in the central nervous system. Hie possibility of cleavage is in this case attributed to the activated ester, bound between the polymeric chain and the active substance. Besides the above-mentioned derivative of acrylic acid a derivative of vinyl carbamate has also been applied. 

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