Hydrolysis aspirin

Aspirin hydrolysis CTABr and cetylpyridinium chloride + NaOH or buffer. Enhancement at high and inhibition at low pH Broxton, 1982... 

The solution to this problem is to compare the rate constant for the intramolecular reaction with that for the corresponding intermolecular process. In the case of aspirin hydrolysis [3] this would be general base catalysis of the hydrolysis [5] of aspirin by an external carboxylate group, RCOO-, of the same basicity as the carboxylate group of aspirin. The necessary data are... 

Hussain, A. Yamasaki, M. Truelove, J. Kinetics of hydrolysis of acylals of aspirin hydrolysis of (I -ethoxy) ethyl 2-acetoxybenzoate. J. Pharm. Sci. 1974, 63, 627-628. Hussain, A. Truelove, J. Kostenbauder, H.B. Effect of hydroxyl group substituents of pyran ring on hydrolysis rate of benzoates 2-tetrahydropyranyl benzoate. J. Pharm. Sci. 1979, 68, 235-236. 

C. W. Spancake, A. K. Mitra, andD. O. Kildsig, Kinetics of aspirin hydrolysis in aqueous solutions and gels of poloxamines (Tetronic 1508)—Influence of microenvironment, Int. J. Pharm. 75, 231-239(1991). 

S. Choudhury and A. K. Mitra, Kinetics of aspirin hydrolysis and stabilization in the presence of 2-hy-droxypropyl-P-cyclodextrin, Pharm. Res. 10, 156-159(1993). 

The kinetics of aspirin hydrolysis were studied in CPG mixtures containing 5% aspirin. The pore diameters of CPG varied from 75 to 3000 A. Plots of the first-order rate constants at 50A° under the two different relative humidities versus the pore diameter of CPG are shown in Fig. 9 [20]. In the CPG mixtures where the pore diameter was less than 300 A, the rate constants of aspirin decomposition were independent of CPG pore diameters in the cases of both 0% RH and 79% RH. However, the rate constant in the mixtures with CPG of large pore size decreased with increasing CPG pore diameter. The pore diameter profiles of the rate constant indicate that the stability of aspirin was closely related to changes in the crystal-... 

Matsumoto et al. [24] investigated to the stability of aspirin in mixtures of aspirin and PCC at various temperatures and humidities. They calculated the intrinsic rate constants of aspirin hydrolysis from the relationship between the apparent first-order hydrolysis rate constant and the amount of water adsorbed at each temperature. The apparent first-order rate constant of aspirin and the amount of adsorbed water in the heated mixture of PCC and aspirin at different temperatures are listed in Table 1. It was suggested that the apparent first-order decomposition rate constants of aspirin in the heated mixtures were closely related to the amount of adsorbed water. 

Edwards [25] investigated the hydrolysis of aspirin in aqueous solution at 17A° and demonstrated that the aspirin is hydrolyzed by general acid-base catalysis and water molecules for ionic and nonionic aspirin, comprising six simultaneous reactions involving H O, O H, and H2O for ionic and nonionic aspirin. The intrinsic hydrolysis rate constant in the heated mixture was comparable with the hydrolysis rate constants of the two-element reactions of nonionic aspirin and H2O or ionic aspirin and H2O in aqueous solution. As aspirin molecules would be adsorbed onto the pore surface of PCC in the molecular state, as a possible mechanism of aspirin hydrolysis in the mixture with PCC it was suggested that the aspirin is dispersed monomolecularly in the heated mixture and reacts with water molecules rather than by acid-base catalysis. 

This effect has been demonstrated for the surface chemistry of aspirin. Hydrolysis is a well-known degradation chemical reaction occurring for aspirin (Fig. 6.16). 

Acetyl transfer between aspirin and sulfadiazine is a bimolecular reaction in which the translational diffusion of reactant molecules becomes rate determining when molecular mobility is limited in the solid state [33]. Therefore, it can offer a useful reaction model for understanding the ways in which chemical degradation rates in lyophilized formulations are affected by molecular mobility. Figure 17A shows the temperature dependence of the rate constant of acetyl transfer in lyophilized formulations containing dextran. Figure 17B shows the pseudo rate constant of aspirin hydrolysis that occurs in parallel with acetyl transfer in the presence of water. The rate constant of acetyl transfer ( t) and the pseudo rate constant of hydrolysis ( H> pseudo) are described by following equations ... 

Figure 17 Temperature dependence of acetyl transfer between aspirin and sulfadiazine (A) and aspirin hydrolysis (B) in lyophilized formulations containing dextran at 12%RH (A) and 60%RH ( ).

Aspirin, hydrolysis of salicylic acid determined in the presence of aspirin at any pH by measuring absorbance at isos-bestic point at 298.5 m/i... 

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