Hydrolysis of carbonates

Commercial-scale processes have been developed for the production of hydrogen sulfide from heavy fuel oils and sulfur as well as from methane, water vapor, and sulfur. The latter process can be carried out in two steps reaction of methane with sulfur to form carbon disulfide and hydrogen sulfide followed by hydrolysis of carbon disulfide (116). 

Bicarbonate alkalinity The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are produced, and the solution is alkaline. 

The hydrolysis of carbon-nitrogen double bonds involves initial addition of water and elimination of a nitrogen moiety ... 

The reaction of cycloheptaamylose with diaryl carbonates and with diaryl methylphosphonates provides a system in which a carboxylic acid derivative can be directly compared with a structurally analogous organo-phosphorus compound (Brass and Bender, 1972). The alkaline hydrolysis of these materials proceeds in twro steps, each of which is associated with the appearance of one mole of phenol (Scheme Y). The relative rates of the two steps, however, are reversed. Whereas the alkaline hydrolysis of carbonate diesters proceeds with the release of two moles of phenol in a first-order process (kh > fca), the hydrolysis of methylphosphonate diesters proceeds with the release of only one mole of phenol to produce a relatively stable aryl methylphosphonate intermediate (fca > kb), In contrast, kinetically identical pathways are observed for the reaction of cycloheptaamylose with these different substrates—in both cases, two moles of phenol are released in a first-order process.3 Maximal catalytic rate constants for the appearance of phenol are presented in Table XI. Unlike the reaction of cycloheptaamylose with m- and with p-nitrophenyl methylphosphonate discussed earlier, the reaction of cycloheptaamylose with diaryl methylphosphonates... 

T. L. Huang, A. Szekacs, T. Uematsu, E. Kuwano, A. Parkinson, B. D. Hammock, Hydrolysis of Carbonates, Thiocarbonates, Carbamates, and Carboxylic Esters of a-Naph-thol, /LNaphthol, and p-Nitrophenol by Human, Rat, and Mouse Liver Carboxylesterases , Pharm. Res. 1993, 10, 639 - 648. 

Fig. 8.7. a) Mechanism of the HCT-catalyzed, (and presumably also of the enzyme-catalyzed) hydrolysis of carbonic acid esters, b) Alternative mechanisms of the HO -catalyzed hydrolysis ofN-carbamates. Reaction b is restricted to monosubstituted carbamates, whereas Reaction a is also possible for A.iV-disubstituted carbamates. 

Carbonic acid esters (alkoxycarbonyl derivatives) are diesters of general formula R-O-CO-O-R. A single mechanism operates in the HO -catalyzed (and presumably also in the enzyme-catalyzed) hydrolysis of carbonic acid esters, namely a rate-determining addition of the base to the carbonyl C-atom to form an intermediate whose breakdown yields the drug (ROH), C02, and an alcohol (R OH) (Fig. 8.7,a) [153],... 

In order to generate antibodies which catalyse the hydrolysis of carbonates (6, 10), carboxylic esters (9) and amides with a certain degree of specificity, the phosphates (7a. lOai and phosphonates 9a were used as haptens that mimic the tetrahedral negatively charged transition state of the spontaneous hydrolysis reaction (see Scheme 11.3) [27] [29]. 

Chemical/Physical. Under laboratory conditions, carbon tetrachloride partially hydrolyzed in aqueous solutions forming chloroform and carbon dioxide (Smith and Dragun, 1984). Complete hydrolysis yields carbon dioxide and HCl (Ellington et al., 1993 Kollig, 1993). The estimated hydrolysis half-life in water at 25 °C and pH 7 is 7,000 yr (Mabey and Mill, 1978) and 40.5 yr (Jeffers et al., 1989 Ellington et al, 1993). The estimated hydrolysis half-life reported by Mabey and Mill (1978) was based on second-order neutral kinetics. Jeffers et al. (1996) reported that hydrolysis of carbon tetrachloride is first-order, contrary to findings of Mabey and Mill (1978). Jeffers et al. (1996) report that the extrapolated environmental half-life at 25 °C is 40 years. 

Elliott, S. Effect of hydrogen peroxide on the alkaline hydrolysis of carbon disnlfide. Environ. Scl. Technol, 24(2) 264-267, 1990. 

Levich V.G. (1962) Physicochemical Hydrodynamics. Englewood Gliff, NJ Prentice-Hall. Lewis M. and Glaser R. (2003) Synergism of catalysis and reaction center rehybridization a novel mode of catalysis in the hydrolysis of carbon dioxide. /. Phys. Chem. A 107, 6814-1818. 

Let us now look at some examples to illustrate what we have discussed so far to get a feeling of how structural moieties influence the mechanisms, and to see some rates of nucleophilic substitution reactions of halogenated hydrocarbons in the environment. Table 13.6 summarizes the (neutral) hydrolysis half-lives of various mono-halogenated compounds at 25°C. We can see that, as anticipated, for a given type of compound, the carbon-bromine and carbon-iodine bonds hydrolyze fastest, about 1-2 orders of magnitude faster than the carbon-chlorine bond. Furthermore, we note that for the compounds of interest to us, SN1 or SN2 hydrolysis of carbon-fluorine bonds is likely to be too slow to be of great environmental significance. 

Jeffers, P. M., C. Brenner, and N. L. Wolfe, Hydrolysis of carbon tetrachloride , Environ. Toxicol. Chem., 15, 1064-1065... 

Scheme 6 System used by Wulff to catalyse the hydrolysis of carbonate (32) imprinting the cavities with the TSA phosphonate (31)...

Wulff and collaborators, for instance, reported the preparation of TSA imprinted beads for the hydrolysis of carbonate and carbamate [61, 62], exploiting the amidine (33) functional monomer previously developed by the same group and successfully applied to the bulk format [63]. The polymers were prepared using a suspension polymerisation that produced beads with sizes in the range 8-375 pm, depending on the polymerisation conditions. The pseudo-first order reaction rate of the imprinted beads (Tyrrp/ soin) was enhanced by a factor of 293 for the carbonate hydrolysis and 160 for the carbamate, when compared with the background. 

As the first test reaction, the hydrolysis of carbonates and esters was selected according to the above criteria (Figure 18.2). Corresponding antibodies were indeed found. Typically, such antibodies catalyze reactions by a factor of 103-104 over back-... 

Figure 18.2 Hydrolysis of carbonates and esters by catalytic antibodies (Lerner, 1991).

Metal ions are vital to the function of many enzymes that catalyze hydrolytic reactions. Coordination of a water molecule to a metal ion alters its acid-base properties, usually making it easier to deprotonate, which can offer a ready means for catalyzing a hydrolytic reaction. Also, the placement of a metal center in the active site of a hydrolytic enzyme could permit efficient delivery of a catalytic water molecule to the hydrolyzable substrate. In fact, the first enzyme discovered, carbonic an-hydrase, is a metalloenzyme that requires a Zn2+ center for its catalytic activity (32). The function of carbonic anhydrase is to catalyze the hydrolysis of carbon dioxide to bicarbonate ... 

Perfluorocarbons are essentially inert to hydrolysis unless heated to very high temperatures, although it has been calculated that the free energy of hydrolysis of carbon tetrafluoride is exothermic by 304kJmoP [12], and the inertness therefore stems from a high activation barrier. The carbon backbone in a perfluorocarbon is shielded towards attack by nucleophiles by the non-bonding electron pairs associated with the many adjacent fluorine atoms, and this is undoubtedly a major factor contributing to the relative inertness of fluorocarbons. 

Similar to catalytic antibodies, we observed some product inhibition. In the case mentioned, the reaction rate was calculated from the amount of released acid. If the calculation is based on phenol release, the rate enhancement turned out to be nearly doubled. Hydrolysis of carbonates should avoid this difficulty. Therefore, diphenyl phosphate was used as template, and the hydrolysis of diphenyl carbonate was then investigated [13]. Compared to solution an enhancement of 982-fold was obtained and typical Michaelis-Menten kinetics were observed (K ,ax = 0.023 mM/min, = 5.01 mM, = 0.0115/min, kaalK = 2.30/min/M). 

Catalytic activity of rare earth elements (i.e., lanthanides, symbol Ln) in homogeneous catalysis was mentioned as early as 1922 when CeCls was tested as a true catalyst for the preparation of diethylacetal from ethanol and acetaldehyde [1]. Solutions of inorganic Ln salts were subsequently reported to catalyze the hydrolysis of carbon and phosphorous acid esters [2], the decarboxylation of acids [3], and the formation of 4-substituted 2,6-dimethylpyrimidines from acetonitrile and secondary amines [4]. In the meantime, the efficiency of rare earth metals in heterogeneous catalysis, e. g., as promoters in lanthanide (element mixtures)-... 

Enzymatic cleavage PPL was found to cleave carbonates bearing an unsaturated substituent. This also results in the resolution of the diol and the remaining carbonate, since only one enantiomer is hydrolyzed preferentially. The yields and enantiomeric excesses depend on the level of conversion. This method may be useful for the hydrolysis of carbonates that cannot be treated with base. ... 

Microbial degradation of large amounts of carbon disulfide in soil would not be expected to be significant since this compound is a soil disinfectant and toxic to bacteria. Hydrolysis of carbon disulfide on wet soil surfaces is also unlikely (EPA 1986b). Oxidation of carbon disulfide by a Thiobacillus species isolated from soil has been observed (Plas et al. 1993). 

During the combustion of the hydrogen sulfide some of the sulfur reacts with hydrocarbons normally present to form carbon disulfide and methyl mercaptan. Carbonyl sulfide is also formed either by the partial hydrolysis of carbon disulfide and/or by the reaction of carbon dioxide and hydrogen sulfide. Some hydrogen and carbon monoxide are also formed in the Claus combustion step. 

PROBABLE FATE photolysis direct photochemical degradation in the atmosphere or in the upper layers of surface waters should not be an important fate process half-life for the atmospheric reaction with photochemically produced hydroxyl radicals 10 hrs oxidation could occur, but too slow to be important hydrolysis gradual hydrolysis of carbon-chlorine bond is a probable principle fate mechanism, can be expected in comparison to other chlorine containing compounds, half-life for this pH independent process 0.5-2 yrs volatilization not important, volatilization from water should be a slow process half-life from a model pond 1 lyrs, volatilization from the soil to the atmosphere might occur, but will be a slow process, volatilization from moist soil should not be an important fate process sorption possible importance as catalyst for hydrolysis biological processes biodegradation not expected to be an important fate process, but there is not enough data to draw a conclusion... 

PROBABLE FATE photolysis-, aqueous photolysis is not expected to be important, reaction with photochemically produced hydroxyl radicals has a half-life of 13.44 hr, direct photolysis is not expected to be important since it should not adsorb wavelengths >290 nm oxidation photooxidation is not expected to be important, photooxidation only in atmosphere, photooxidation half-life in air 9.65 hrs-4.02 days hydrolysis very slow, maybe significant, hydrolysis of carbon-chloride bonds, release to water results in hydrolysis with a half-life of 40 days when released to soil, it may hydrolyze hydrolyzed slowly in aqueous dimethylformamide at pH 7, first-order hydrolytic half-life 22yrs volatilization expected to volatilize if released to water, volatilization half-lives from lakes, rivers, and streams 3.5, 4.4, and 180.5 days respectively sorption not an important process biological processes biodegrades in water after several weeks of acclimation, biodegradation not important under natural conditions, no bioaccumulation noted... 

PROBABLE FATE photolysis-, direct photolysis is probably not important, if released to atmosphere, will degrade by reaction with photochemically produced hydroxyl radicals (estimated half-life 1.15 days) oxidation photooxidation in atmosphere can occur, photooxidation half-life in air 4.61-46.1 hrs hydrolysis slow hydrolysis of carbon-chlorine bond, may be important fate mechanism volatilization if released to water, volatilization is expected to be the principle removal process, but may be slow, volatilization half-lives for a model river (1 m deep) and a model environmental pond 13.9 hr, and 6.6 days respectively sorption adsorption on organic matter is possible biological processes no data on bioaccumulation or biodegradation... 

In practice, a degree of substitution of 0.5-0.6 xanthate groups per glucose unit is sufficient to yield a soluble xanthate. Hydrolysis of carbon disulfide by alkali is an unavoidable side reaction which consumes 20-30 per cent of the carbon disulfide charged. 

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