Hydrolysis temperature dependence

Wang, T., and D. W. Margerum, Kinetics of Reversible Chlorine Hydrolysis Temperature Dependence and General Acid/Base-Assisted Mechanisms, Inorg. Chem., 33, 1050-1055 (1994). 

Wang T. X. and Margemm D. W. (1994) Kinetics of reversible chlorine hydrolysis temperature dependence and general-acid/base-assisted mechanisms. Inorg. Chem. 33, 1050-1055. 

The hydrolysis of urea is strongly temperature-dependent, with the rate being negligible at room temperature. The rate of hydrolysis, and thus the rate of precipitate formation, can be controlled by adjusting the solution s temperature. Precipitates of BaCr04, for example, have been produced in this manner. 

Chemical Properties. The hydrolysis of PET is acid- or base-catalyzed and is highly temperature dependent and relatively rapid at polymer melt temperatures. Treatment for several weeks in 70°C water results in no significant fiber strength loss. However, at 100°C, approximately 20% of the PET tenacity is lost in one week and about 60% is lost in three weeks (47). In general, the hydrolysis and chemical resistance of copolyester materials is less than that for PET and depends on both the type and amount of comonomer. 

Commercial condensed phosphoric acids are mixtures of linear polyphosphoric acids made by the thermal process either direcdy or as a by-product of heat recovery. Wet-process acid may also be concentrated to - 70% P2O5 by evaporation. Liaear phosphoric acids are strongly hygroscopic and undergo viscosity changes and hydrolysis to less complex forms when exposed to moist air. Upon dissolution ia excess water, hydrolytic degradation to phosphoric acid occurs the hydrolysis rate is highly temperature-dependent. At 25°C, the half-life for the formation of phosphoric acid from the condensed forms is several days, whereas at 100°C the half-life is a matter of minutes. 

Hydrolysis of TEOS in various solvents is such that for a particular system increases directiy with the concentration of H" or H O" in acidic media and with the concentration of OH in basic media. The dominant factor in controlling the hydrolysis rate is pH (21). However, the nature of the acid plays an important role, so that a small addition of HCl induces a 1500-fold increase in whereas acetic acid has Httie effect. Hydrolysis is also temperature-dependent. The reaction rate increases 10-fold when the temperature is varied from 20 to 45°C. Nmr experiments show that varies in different solvents as foUows acetonitrile > methanol > dimethylformamide > dioxane > formamide, where the k in acetonitrile is about 20 times larger than the k in formamide. The nature of the alkoxy groups on the siHcon atom also influences the rate constant. The longer and the bulkier the alkoxide group, the lower the (3). 

CDU in pure form is a white powder. It is made slowly available to the soil solution by nature of its limited solubihty in water. Once in the soil solution, nitrogen from CDU is made available to the plant through a combination of hydrolysis and microbial decomposition. As with any CRE which is dependent on microbial action, the mineralization of CDU is temperature dependent. Product particle size has a significant effect on CDU nitrogen release rate. Smaller particles mineralize more rapidly because of the larger surface contact with the soil solution and the microbial environment. The rate of nitrogen release is also affected by pH because CDU degrades more rapidly in acidic soils. 

The next stage is neutralization of the alkenesulfonic acids with NaOH yielding water-soluble sodium alkenesulfonates, and hydrolysis of the sultones leading to sodium 3-hydroxyalkanesulfonates and sodium 4-hydroxyalkanesulfon-ates. The proportion of the latter two compounds in the mixture will depend on the conditions employed in the aging step. A hydrolysis temperature of 150-160°C and a hydrolysis time of 40-45 min ensures virtually complete hydrolysis of sultones 1,3-sultones will be present in ppb quantities and 1,4-sultones in ppm quantities. 

Arrhenius proposed his equation in 1889 on empirical grounds, justifying it with the hydrolysis of sucrose to fructose and glucose. Note that the temperature dependence is in the exponential term and that the preexponential factor is a constant. Reaction rate theories (see Chapter 3) show that the Arrhenius equation is to a very good approximation correct however, the assumption of a prefactor that does not depend on temperature cannot strictly be maintained as transition state theory shows that it may be proportional to 7. Nevertheless, this dependence is usually much weaker than the exponential term and is therefore often neglected. 

Anandamide is inactivated in two steps, first by transport inside the cell and subsequently by intracellular enzymatic hydrolysis. The transport of anandamide inside the cell is a carrier-mediated activity, having been shown to be a saturable, time- and temperature-dependent process that involves some protein with high affinity and specificity for anandamide (Beltramo, 1997). This transport process, unlike that of classical neurotransmitters, is Na+-independent and driven only by the concentration gradient of anandamide (Piomelli, 1998). Although the anandamide transporter protein has not been cloned yet, its well characterized activity is known to be inhibited by specific transporter inhibitors. Reuptake of 2-AG is probably mediated by the same facilitating mechanism (Di Marzo, 1999a,b Piomelli, 1999). 

A more recent, extended study of purine synthesis via polymerisation of ammonium cyanide, described at the beginning of this section, showed that the yield of adenine from the non-hydrolyzed solution was only slightly temperature dependent. Shorter hydrolysis times for the insoluble polymerisation products led to higher adenine yields. When the solution is hydrolyzed at pH 8, the adenine yield is comparable to the value of 0.1% found for acidic hydrolysis (a model for the primeval ocean ). Increasing the hydrolysis time has no effect on the adenine yield because of its greater stability at pH 8. Hydrolysis of the black NH4CN polymer under acidic or neutral conditions results in an adenine yield of about 0.05% (Borquez et al., 2005). 

Amino-2-deoxy aldoses. The behaviour of O-unprotected sugars is exemplified in D-gluco series after basic hydrolysis of the starting 2-benzamidoglycoside followed by buffering the medium with carbon dioxide and treatment with thiophosgene, an intermediate isothiocyanate was obtained.320 However, NMR revealed a temperature-dependent equilibrium of this isothiocyanate with a trans-fused OZT (Scheme 5). 

The presence of cross-linked phosphates may be recognized by their ready hydrolysis, which leads to a rapid drop in the viscosity of the solution and a parallel decrease in its pH. Aqueous solutions of all cross-linked phosphates are hydrolyzed after twenty hours. In contrast to the hydrolysis of normal P—O—P bonds in meta- and polyphosphates, that of the cross-linking sites is practically independent of concentration, pH, ionic strength and the nature and concentration of added salts. It does, however, follow a first-order law, as for normal P—O—P bonds, and is strongly temperature dependent. Activation energies of 18.9 and 15.4 kcal/mole have been... 

As indicated in Table 13.7,1,2-dibromoethane (BrCH2-CH2Br) and 1,1,1-trichloro-ethane (CH3-CC13) are examples in which both hydrolysis and elimination are important. If in such cases the reactions occur by SN2 and E2 mechanisms, respectively, the ratio of the hydrolysis versus elimination products should vary with varying pH and temperature, since the two competing reactions likely exhibit different pH and temperature dependencies. On the other hand, if the reaction mechanisms were more SN1- and El-like, a much less pronounced effect of temperature or pH on product formation would be expected, since the rate-determining step in aqueous solution may be considered to be identical for both reactions ... 

The rate of hydrolysis is dependent on the mineral, lactose, and galactose concentrations, as well as on the temperature and pH. Many kinetic studies are available on lactose hydrolysis systems and enzymes (MacBean 1979). Inhibition of hydrolysis can be caused by galactose or sodium and calcium ions, so demineralization is often necessary. 

The persistence of the triazine herbicides in surface and groundwater and in soil is dependent to some extent on their susceptibility to chemical hydrolysis. The environmental stability of the triazine herbicides to hydrolysis is dependent upon environmental parameters such as temperature, pH of the water or soil solution, and the presence of dissolved constituents that may catalyze hydrolysis. 

The formation of the amide is pH and temperature dependent. Solutions of cimetidine in hydrochloric acid at pH v5.4 showed no decomposition at 50° over a period of thirty days. Hydrolysis to the guanylurea (B) occurred when the compound was heated at 45° for 36 hours with an excess of IN hydrochloric acid at pH <1. The guanidine was formed by heating cimetidine for two hours at 100°C with concentrated hydrochloric acid. 

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