Thermally enhanced hydrolysis

Thermally enhanced hydrolysis is generally the most cost-effective remediation method for halogenated alkanes, and many funaigants and pesticides. A listing of common compounds with their hydrolysis half-lives at 100 °C is shown in Table 24.4. In situ thermal methods have been successfully used to hydrolyze 1,1,1-trichloroethane (TCA), 1,1,2,2-tetrachloroethane (TeCA), dichloromethane (methylene chloride), and ethylene dibronaide to remediate groundwater. 

Oxime carbamates have high polarity and solubility in water and are relatively chemically and thermally unstable. They are relatively stable in weakly acidic to neutral media (pH 4-6) but unstable in strongly acidic and basic media. Rapid hydrolysis occurs in strongly basic aqueous solutions (pH > 9) to form the parent oxime/alcohol and methylamine, which is enhanced at elevated temperature. Additionally, oxime carbamates are, generally, stable in most organic solvents and readily soluble in acetone, methanol, acetonitrile, and ethyl acetate, with the exception of aliphatic hydrocarbons. Furthermore, most oxime carbamates contain an active -alkyl (methyl) moiety that can be easily oxidized to form the corresponding sulfoxide or sulfone metabolites. 

Dissolved iron(III) is (i) an intermediate of the oxidative hydrolysis of Fe(II), and (ii) results from the thermal non-reductive dissolution of iron(III)(hydr)oxides, a reaction that is catalyzed by iron(II) as discussed in Chapter 9. Hence, iron(II) formation in the photic zone may occur as an autocatalytic process (see Chapter 10.4). This is also true for the oxidation of iron(II). As has been discussed in Chapter 9.4, the oxidation of iron(II) by oxygen is greatly enhanced if the ferrous iron is adsorbed at a mineral (or biological) surface. Since mineral surfaces are formed via the oxidative hydrolysis of Fe(II), this reaction proceeds as an autocatalytic process (Sung and Morgan, 1980). Both the rate of photochemical iron(II) formation and the rate of oxidation of iron(II) are strongly pH-dependent the latter increases with... 

Pretreatments of the polymeric feedstocks to enhance the hydrolysis of the major components such as cellulose include size reduction, thermal-chemical treatments, and specific enzyme pretreatments (52,57). Although many of the pretreatment processes increase the rate and extent of potymer hydrolysis, the cost for treatment is prohibitive based upon the revenues generated for energy production alone in anaerobic digestion (32). 

The kinetics of aquation of a number of azidochromium(III) complexes have been investigated.303,655 Compared with other acidochromium(III) complexes, the chromium-azide bonds in these species seem remarkably stable to thermal substitution. Hence in the base hydrolysis of [CrN3(NH3)s]2+ a pathway involving initial loss of NH3 concurs with the usual base hydrolysis pathway involving loss of Nj. The aquation of azidochromium(III) complexes is H+-assisted with protonation of the azido ligand accounting for the enhanced reactivity. 

Supercritical water represents a potentially important component of sonochemistry, in addition to the free-radical reactions and thermal/pyrolytic effects. Because the reaction occurs at or close to the bubble/water interface, compounds more hydrophobic than p-NPA are expected to exhibit even higher hydrolysis rate enhancements. Finally, the existence of the supercritical phase in an ultrasonically irradiated solution suggests a modification of the conventional view of the reactive area at the cavitation site. This region is normally considered to consist of two discrete phases a high-temperature, low-density gas phase and a more condensed, lower temperature liquid shell. 

Other API amide hydrolysis examples include chloramphenicol (12), indomethacin under alkaline conditions (13), lidocaine (14), azintamide (15), terazosin (16), flutamide (17), oxazepam, and chlordiazepoxide (18). Lidocaine does not readily hydrolyze in aqueous solution under thermal or basic conditions (Fig. 7) (19). The enhanced stability is due to the steric hindrance of the two o-methyl groups. Hydrolysis does occur more readily in acidic conditions rather than basic conditions presumably because the rate-limiting step, protonation of the carbonyl, is not affected by the steric hindrance of the o-methyl. 

The role of water in governing the upper thermal limits for life also is based on covalent transformations in which water is a reactant. As emphasized earlier in this chapter, the removal of a molecule of water from reactants is common in diverse biosynthetic reactions, including the polymerization of amino acids into proteins and nucleotide triphosphates into nucleic acids. The breakdown of biomolecules often involves hydrolysis, and increased temperatures generally enhance these hydrolytic reactions. The thermal stabilities of many biomolecules, for instance, certain amino acids and ATP, become limiting at high temperatures. Calculations suggest that ATP hydrolysis becomes a critical limiting factor for life at temperatures between 110°C and 140°C (Leibrock et al., 1995 Jaenicke, 2000). Thus, at temperatures near 110°C, both the covalent and the noncovalent chemistries of water that are so critical for life are altered to the extent that life based on an abundance of liquid water ceases to be possible. 

Acetylated cottonseed protein demonstrated significantly higher water and oil holding capacities and improved foaming properties (38) compared to unmodified proteins (Table III). Thus, while acetylation does not significantly enhance functional properties of proteins, it improves thermal stability and since acetylated proteins are susceptible to enzyme hydrolysis in vivo it affords a useful reagent for protection of e-NH groups of lysine (11). 

Unlike the thermal and hydrothermal stabilities, the mechanical stability seems less dependent on the nature of mesoporous materials. All materials gradually collapse with the increase of pressure, accompanied with the decrease of surface area and pore volume. Recent studies show that cubic SBA-1 and MCM-48 are more mechanically stable than hexagonal mesoporous materials such as MCM-41 and SBA-15. Hydrolysis of Si-O-Si bonds by water adsorbed onto the silanol groups under compression was found as the main reason for mechanical instability. Organically functionahzed materials are more hydrophobic than unmodified counterparts, and thus show enhanced mechanical stability due to the water repelling ability. " ... 

---