Hydrolytic activation energy

The hydrolytic depolymerisation of PETP in stirred potassium hydroxide solution was investigated. It was found that the depolymerisation reaction rate in a KOH solution was much more rapid than that in a neutral water solution. The correlation between the yield of product and the conversion of PETP showed that the main alkaline hydrolysis of PETP linkages was through a mechanism of chain-end scission. The result of kinetic analysis showed that the reaction rate was first order with respect to the concentration of KOH and to the concentration of PETP solids, respectively. This indicated that the ester linkages in PETP were hydrolysed sequentially. The activation energy for the depolymerisation of solid PETP in a KOH solution was 69 kJ/mol and the Arrhenius constant was 419 L/min/sq cm. 21 refs. 

Adachi and Mizushima [30] studied the deposition system DMTC + O2 + H2O in the 400-500 °C temperature range, hi the presence of water vapor, the deposition rate dependence on DMTC concentration increased from [DMTC] to [DMTC]° . They suggested that in the reaction of DMTC + O2, the rate-determining step is the oxidation of Sn-Cl bonds, while in the reaction of DMTC + O2 + H2O, the oxidation of Sn - CH3 bonds is rate determining. As will be seen below, this description of the chemistry is almost certainly incorrect (Sect. 5.2). They also reported an activation energy of 38 kcalmoC for the hydrolysis of DMTC (Fig. 7) and asserted that the hydrolytic decomposition of Sn - Cl bonds is much faster at these temperatures. 

Eichhom and his co-workers have thoroughly studied the kinetics of the formation and hydrolysis of polydentate Schiff bases in the presence of various cations (9, 10, 25). The reactions are complicated by a factor not found in the absence of metal ions, i.e, the formation of metal chelate complexes stabilizes the Schiff bases thermodynamically but this factor is determined by, and varies with, the central metal ion involved. In the case of bis(2-thiophenyl)-ethylenediamine, both copper (II) and nickel(II) catalyze the hydrolytic decomposition via complex formation. The nickel (I I) is the more effective catalyst from the viewpoint of the actual rate constants. However, it requires an activation energy cf 12.5 kcal., while the corresponding reaction in the copper(II) case requires only 11.3 kcal. The values for the entropies of activation were found to be —30.0 e.u. for the nickel(II) system and — 34.7 e.u. for the copper(II) system. Studies of the rate of formation of the Schiff bases and their metal complexes (25) showed that prior coordination of one of the reactants slowed down the rate of formation of the Schiff base when the other reactant was added. Although copper (more than nickel) favored the production of the Schiff bases from the viewpoint of the thermodynamics of the overall reaction, the formation reactions were slower with copper than with nickel. The rate of hydrolysis of Schiff bases with or/Zw-aminophenols is so fast that the corresponding metal complexes cannot be isolated from solutions containing water (4). 

Microwave heating has not evoked a great deal of attention in the area of starch modification. Effective starch modification is achieved when the microwave energy is coupled with hydrolytic activity originating from added mineral acid. The... 

The present study on Ti02 powder formation from Ti(0-iC3H7>4 in supercritical isopropanol has allowed the determination of reaction kinetic constants and activation energy in a temperature range from 531 to 568 K at 10 MPa. The proposed mechanism is based on a hydrolytic decomposition of the alkoxide initiated by water formed in alcohol dehydration catalysed by reactor walls. The derived reaction kinetic order is unity in accordance with experimental results. Such a mechanism also explains that special cares must be taken about the internal surface state of the reactor in order to obtain reproducible results. 

A simple concentration consideration alone is difficult to explain the above phenomenon. It is possible that the associated, liquid-like water can build a strong osmotic pressure at the interface that will stress the oxane bonds. The oxane bonds at the interface will be subjected to stress. When a tensile stress is applied to the bond, the mechanochemical effect lowers the apparent activation energy of the hydrolysis of the oxane bonds, making it easier to be hydrolytically cleaved. The aforementioned differences in the hydrothermal stability of various oxane bonds may become especially important under such circumstances, ily cleaved, non-siloxane bonds may become the source of water collection and exert pressure on the surrounding siloxane bonds, which will be cleaved easier than the siloxane bonds with pure silica surface. 

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