P-nitrophenyl diphenyl phosphate

Fig. 1 Micellar effects upon reaction of p-nitrophenyl diphenyl phosphate with benzimidazolide ion (solid points) open points are for reaction in the absence of benzimidazole , 10 4 M benzimidazole, pH 10.7 , 1.2 x 10-4 M benzimidazole, pH 11 O, pH 10.7, and 11 respectively. The solid lines are theoretical. (Reprinted by permission of the American Chemical Society)...

Reactions of hydrophilic anions in microemulsions can be treated in terms of the ion-exchange formalism. The extent of ion binding to microemulsion droplets has been estimated conductimetrically, and the rates of reactions of OH- and F with p-nitrophenyl diphenyl phosphate are consistent with the extent of ion binding and competition between reactive and inert anions. Alternatively the data could be accommodated to variations in the estimated surface potential of the droplet (Mackay and Hermansky, 1981 Mackay, 1982). 

Dephosphorylation of p-nitrophenyl diphenyl phosphate by arenimidazo-lide ions is very strongly accelerated by the tri-n-octylethylammonium bromide or mesylate (TEABr or TEAMs respectively) (Scheme 9). The... 

Fig. 6 Reaction of p-nitrophenyl diphenyl phosphate in non-micellar aggregates of tri-n-octyl ethylammonium mesylate (TEAMs) at pH 10.7 , 10 4M naphth-2,3-imidazole and O, 10-4 and 2 x KT4 M benzimidazole, respectively. (Reprinted with permission of the American Chemical Society)...

Rate constants of bimolecular, micelle-assisted, reactions typically go through maxima with increasing concentration of inert surfactant (Section 3). But a second rate maximum is observed in very dilute cationic surfactant for aromatic nucleophilic substitution on hydrophobic substrates. This maximum seems to be related to interactions between planar aromatic molecules and monomeric surfactant or submicellar aggregates. These second maxima are not observed with nonplanar substrates, even such hydrophobic compounds as p-nitrophenyl diphenyl phosphate (Bacaloglu, R. 1986, unpublished results). 

One of the earliest reports on the use of dendrimers in catalysis is the unimolecu-lar decarboxylation of 6-nitro-benzisoxazole-3-carboxylate in the presence of a dendrimer comprising ether dendrons which are functionalized at their periphery with tetra-alkylammonium cations (e.g. 20, Scheme 21) [30]. In aqueous media, the quaternary ammonium groupings promote the reactivity of organic anions which presumably bind in high concentration to the polycationic periphery of the dendrimer. The latter species enhances the rate of the bimolecular hydrolysis of p-nitrophenyl diphenyl phosphate catalyzed by o-iodosobenzoate ion. 

Two types of amphiphilic quaternary 3-pyridinium ketoximes (253a, b) with different positioning of the hydrophobic alkyl chain have been synthesized and tested as hydrolytic micellar catalysts. A considerable positive deviation from the expected first-order curve was observed in the absorbance vs time plot when p-nitrophenyl diphenyl phosphate (252 R = Ph) and p-nitrophenyl diethyl phosphate... 

The reactions of a phosphate triester, p-nitrophenyl diphenyl phosphate with hydroxide and fluoride ions has been demonstrated to be catalyzed strongly by cationic surfactants and inhibited by NaLS and a non-ionic surfactant (Bunton and Robinson, 1969a Bunton et al., 1969, 1970). Hexadecyltrimethylammonium bromide (CTAB) increased the second-order rate constant for the reaction ofp-nitrophenyl diphenyl phosphate with hydroxide ion by a maximum factor of approximately 11 and that with fluoride ion by a maximum factor of approximately 33 at CTAB concentrations of 3 x 10 m and 2 x 10 m respectively. At higher detergent concentrations the catalysis became progressively less pronounced (Fig. 11). This behavior does not fit equation (10) (Bunton and Robinson, 1969a). However, a number of other micelle-catalyzed reactions between anions and neutral molecules have been found to... 

Fig. 11. Catalysis of the reaction of p-nitrophenyl diphenyl phosphate with 0 01 m sodium hydroxide by CTAB , at 25-0 , at 15-4 , at 5-0° Bunton and Robinson, 1969a).

Robinson, 1969a). It is probable that the hydrophobic nature of the phenyl groups of p-nitrophenyl diphenyl phosphate results in deep penetration of the neutral ester in the Stern layer, thus shielding the phosphoryl group from nucleophilic attack. Unlike other reactions between nucleophiles and neutral substrates catalyzed by cationic micelles (Bunton and Robinson, 1968, 1969a) and the hydrolysis of dinitrophenyl phosphate dianions in the presence of cationic micelles (Bunton et al., 1968), the catalysis of the hydrolysis of -nitrophenyl diphenyl phosphate by CTAB arises from an increase in the activation entropy rather than from a decrease in the enthalpy of activation. The Arrhenius parameters for the micelle-catalyzed and inhibited reactions are most probably manifestations of the extensive solubilization of this substrate. However, these parameters can be composites of those for the micellar and non-micellar reactions and the eifects of temperature on the micelles themselves are not known. Interpretation of the factors which affect these parameters must therefore be carried out with caution. In addition, the inhibition of the micelle-catalyzed reactions by added electrolytes has been observed (Bunton and Robinson, 1969a Bunton et al., 1969, 1970) and, as in the cases of other anion-molecule reactions and the heterolysis of dinitrophenyl phosphate dianions, can be reasonably attributed to the exclusion of the nucleophile by the anion of the added salt. 

The CTAB-catalyzed reaction between p-nitrophenyl diphenyl phosphate and hydroxide or fluoride ion is also inhibited by phenyl, diphenyl, and p-t-butylphenyl phosphates (Bunton et al., 1969). The inhibition by these bulky anions decreases, however, with decreasing pH, and at lower pH values, where the hydroxide ion reaction becomes negligible, the reaction of p-nitrophenyl diphenyl phosphate with p-t-butylphenyl, phenyl, and inorganic phosphate ions is enhanced significantly by CTAB (Fig. 12 and Table 8). The order of the micellar rate enhancement for these nucleophilic reactions (p-t-BuC6H40P03 >C6H60P0 > HOPOf ). The cationic micellar catalysis is thus not dependent on the nucleophilicity of the anions but is explicable in terms of hydrophobic interactions between the nucleophiles and the micelle (Bunton et al., 1969). 

The effectiveness of three isomers, 2-, 3- and 4-hydroxyiminomethyl-l-pyridinium iodide (61) as agents to catalyse the hydrolysis in cationic micellar media of p-nitrophenyl acetate (PNPA) and p-nitrophenyl diphenyl phosphate (PNPDPP) were studied at pH 8. The 2-isomer was found to be the most effective for the hydrolysis of the carboxylic ester PNPA, but the 4-isomer for the hydrolysis of the triphosphate ester PNPDPP. ... 

VassUev K, Ford WT (1999) Poly(propylene imine) dendrimer complexes of Cu(II), Zn(II), and Co(III) as catalysts of hydrolysis of p-nitrophenyl diphenyl phosphate. J Polym Sci A Polym Chem 37 2727... 

Bunton CA, Robinson LB. Micellar effects upon the reaction of P-nitrophenyl diphenyl phosphate with hydroxide and fluoride ions. J Org Chem. 1969 34 773-780. 

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