Phenyl carbamates, alkaline

An application of Equation (13) is illustrated in Figure 6 for the alkaline hydrolysis of substituted phenyl carbamates. Here the points for resonating para substituents lie above the line. When a" is used for these points instead of g the data obey a linear equation and r - 1. 

Figure 6 Alkaline hydrolysis of substituted phenyl carbamates (p = 3.35, r = 0.785). para substituents uncorrected , meta substituents /5., para substituents...

Wolfe et al. (1978) have developed structure-activity relationships for the hydrolysis of a number of TV-substituted and TV,TV-disubstituted carbamates. An excellent correlation was found between the second-order alkaline hydrolysis rate constant (kb) for the carbamates and the pKa of the alcohol formed upon hydrolysis. The linear free energy relationships for the TV-phenyl and TV-methyl-TV-phenyl carbamates are illustrated in Figure 2.10. These data indicate that only the TV-phenyl carbamates will hydrolyze under environmental conditions. The half-life for the hydrolysis of these chemicals will be less than 6 months at pH 8 at 25°C. 

A solution of 3.1 g of (2-benzoyl-4-chlorophenyl-carbamoylmethyl)carbamic acid benzyl ester in 30 cc of 20% hydrobromic acid in glacial acetic acid was stirred for 45 minutes at room temperature. On addition of 175 cc of anhydrous ether, a gummy solid precipitated. After several minutes the ether solution was decanted. The resultant 5-chloro-2-gly-cylaminobenzophenone was not isolated, but about 155 cc of ether was added to the residue and after chilling in an ice bath, 10% sodium hydroxide was added until the mixture was alkaline. The ether layer was then separated, washed twice with water and dried over sodium sulfate. After filtration, the ether solution was concentrated to dryness in vacuo. The residue was crystallized from benzene to yield 7-chloro-5-phenyl-3H-1,4-benzodiazepin-2(1 H)-one. 

The condensation of an aldehyde, benzyl carbamate, and triphenyl phosphite, first described by Oleksyszyn et al., 25,26 affords a direct route to a-aminoalkylphosphonates 4 that are conveniently protected for subsequent reactions (Scheme 4). Since dealkylation of the quaternary phosphonium intermediate 3 is not possible in this case, formation of the pen-tavalent product 4 presumably involves activation of the solvent and formation of phenyl acetate. This method is useful for the synthesis of aliphatic and aromatic amino acid analogues. However, monomers with more elaborate side chains are often incompatible with the reaction conditions. The free amine can be liberated by treatment with HBr/AcOH or by hydrogenolysis after removal of the phenyl esters. The phosphonate moiety can be manipulated by ready exchange of the phenyl esters in alkaline MeOH and activation as described in Section 10.10.2.1.1. Related condensations with other trivalent phosphite derivatives have been reported. 27-30 ... 

Substituted Phenyl N-Methyl Carbamates Rate of alkaline hydrolysis in vitro (37)... 

Alkaline hydrolysis of ethiofencarb [(2-ethylthiomethyl)phenyl]-A-methyl carbamate (17), a carbamate insecticide, proceeds via an lcB mechanism (Scheme 6). ... 

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