Hydrolysis temperature effects

Hydrolysis reactions involving tetrahedral intermediates are subject to steric and electronic effects. Electron-withdrawing substituents faciUtate, but electron-donating and bulky substituents retard basic hydrolysis. Steric effects in acid-cataly2ed hydrolysis are similar to those in base-cataly2ed hydrolysis, but electronic effects are much less important in acid-cataly2ed reactions. Higher temperatures also accelerate the reaction. 

Aminolysis of 0-aryloximes shows a third-order term for both pyrrolidine and piperidine bases temperature effects on different routes are reported and explained. Hydrolysis of a-hydroxy-a-phenylbenzeneacetic acid salicylidenehydrazide (33) in aqueous ethanol proceeds via fast protonation, followed by rate-determining attack of water the results are compared with several related molecules. 

Figure 13 Effect of pH and temperature on malathion degradation by hydrolysis (temperature in degrees C) degradation is faster at higher temperatures and pH values further away from 4.0 to 4.2 (from Ref. 11).

The acid catalyzed and ultrasound stimulated hydrolysis of solventless tetraethoxysi-lane-water mixtures was studied at 39°C as a function of HCl added to the mixtures (log(HCl) ranged from 0.8 to 2.0). The exothermal hydrolysis reaction causes an increasing temperature (A Tt) as a function of the reaction time, t. The isothermal hydrolysis rate constant, k, has been evaluated from the experimental (A TO versus t data, after corrections for the increasing temperature effects (Donatti and VoUet, 1996). 

Benzylideneamino)-phenols (49) can be oxidatively cyclized to form 2-phenyloxa-zols (50) (Eq. (13)) by direct anodic oxidation 2, by Pb(OAc)4AgjO " and nickel peroxide The oxidation of 49 proceeded disappointingly in t-butanoT. water at the nickel hydroxide electrode. 50 was isolated only in traces, benzaldehyde was the major product, which indicated that 49 hydrolysed under the reaction conditions. The hydrolysis could effectively be suppressed by electrolysis in an emulsion of water and cyclohexane, where the portion of water was kept low. The temperature was around 70 °C to secure a fast oxidation. With these reaction conditions good yields of 50 were obtained (Table 16). 

The investigations of the UV spectra, the rate constants of hydrolysis and additional investigations of deuterium isotope and temperature effects of TV-t-butylbenzaldoxime and 2-J-butyl-3-phenyloxaziridine57 suggest a mechanism which is shown in Scheme 3. If the protonated nitrone is the intermediate in both reactions, the formation from either nitrone or oxaziridine should have no effect on the subsequent behaviour under identical conditions. 

Hydrolysis temperature. The effect experienced particularly by polyester-based polyurethanes, where prolonged contact with water or water-based liquids causes breakdown and failure of the polyurethane. 

Washington J. W. (1995) Hydrolysis rates of dissolved volatile organic compounds principles, temperature effects, and literature review. Ground Water 33 3 ), 415 -424. 

Early work" established that Cu", Ni" and Co" promote the hydrolysis of glycinamide in the pH range 9.35 to 10.35 at temperatures of 6.5 to 75 °C. Bamann and his collaborators carried out an extensive series of studies on the metal ion-promoted hydrolysis of peptides and related compounds" and a review of this early work is available." Highly charged ions such as thorium(IV) were found to promote the hydrolysis of leucylglycylglycine at pH values as low as 5. The thorium(IV) species is very extensively hydrolyzed at this pH and the reaction is presumably heterogeneous. Gel hydrolysis is effective at relatively low temperatures (37 °C), whereas observable effects were only obtained with such ions as copper(II) at temperatures of ca. 70 °C. 

The procedure outlined above is fairly typical for a number of determinations of solubility products of metal selenites. Data from such investigations have been reevaluated by the review with the accepted protonation constants of the selenite ion, corrected for the hydrolysis of the metal ion when necessary, and the value of the solubility product extrapolated to standard state conditions. It has been observed that the initial and final pH values in cases are in conflict. This has been ignored and the calculations have been based solely on the data for the equilibrium solution. Complexation of the metal ion by the anions and temperature effects were neglected, which probably introduces a negligible error compared with other sources of error. Activity coefficients were calculated by the SIT expression with s = 0 kg-mol, which is a reasonable simplification due to the low ionic concentrations. The ionic strength was obtained by an iterative procedure from knowledge of the total metal concentration and the pH of the equilibrium solution. The results of the recalculations are entered in Chapter V. 

Methoxy- and 6-methoxypteridine behave similarly. Under more vigorous conditions of temperature and acidity, or basicity, the compounds decompose. Occasionally the use of acid hydrolysis is effective, for example, 2-methoxy-6,8-dimethylpteridin-7(8// )-one (5) is converted to 6,8-dimethylpteridine-2,7(1 //,8//)-dione (6) in reasonable yield by refluxing in 2.5 M hydrochloric acid for 1 h.183... 

A process for producing directly a low-moisture-content soap consists of subjecting the semidry ingredients to intensive smearing and shearing at low temperatures. Almost stoichiometric amounts of caustic are used, and complete hydrolysis is effected in a short time. ... 

FIGURE 19.8 Silica sohd microspheres TEOS hydrolysis process effect of temperature. 

Mechanism of Chlorination of ajS-Unsaturated Ketones in Methanol and in Trifluoroacetic Acid . Reactivity of Ethylenic Compounds. Bromination. XXXIII. Modification of Reaction Scheme in Trifluoroacetic Acid Solution [rate-determining step in CFj-COsH for bromination of RCHt CHtCHj is the disappearance (mechanism Ad%C, d) of a tight ion pair]. Solvent and Temperature Effects in the Neutral Hydrolysis of Methyl Trifluoroacetate and Chloromethyl Dichloroacetate in Dimethyl Sulphoxide-Water Mixtures . Electron Impact Studies. LiKXXVlII. Formation of an Adduct between the Trifluoroacetate Ion and Perfluoroacetic Anhydride by Ion Cyclotron Resonance . ... 

Temperature effects on rates of hydrolysis of sucrose in hydro-... 

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