Chemical Degradation Hydrolysis

Endosulfan undergoes hydrolysis to endosulfan diol in surface water and groundwater. The rate of hydrolysis is influenced by pH. Half-life values reported in the literature vary somewhat. The chemical degradation of a- and P-endosulfan was studied under both anaerobic and aerobic environments. Under aerobic conditions, both hydrolysis and oxidation of endosulfan can occur, while under anaerobic conditions, only hydrolysis can occur. The hydrolytic half-lives for a- and P-endosulfan under anaerobic conditions at pH 7 were 35 and 37 days, respectively (Greve and Wit 1971). At pH 5.5 the half-lives were 151 and 187 days, respectively. Under aerobic conditions, the half-lives decreased. At pH 7, the half-lives of the chemical degradation (hydrolysis and oxidation) of both a- and P-endosulfan were 23 and 25 days, respectively, while at pH 5, the half-lives were 54 and 51 days, respectively. At T=20 and pHs of 5.5 and 8.0, the half-lives of a-endosulfan in distilled water were 11.3 and 5.3 days. 

Oxime carbamates are generally stable in aqueous solutions at pH 4-6. Their chemical degradation (hydrolysis) in water depends strongly on pH. Strongly basic conditions... 

Chemical degradation (141), whether thermally or photo-iaduced, primarily results from depolymerization, oxidations, and hydrolysis. These reactions are especially harmful ia objects made from materials that coataia ceUulose, such as wood, cottoa, and paper. The chemistry of these degradation processes is quite complex, and an important role can be played by the reaction products, such as the acidic oxidation products which can catalyze hydrolysis. 

Tolypomycins. The addition of small amounts of iron salts to the fermentation medium increases the production of tolypomycin Y (48) (7,203,204), the stmcture of which was arrived at by chemical degradation (205,206) and confirmed by x-ray crystallographic analysis (207) (Fig. 5). Mild acid hydrolysis of tolypomycin Y yields tolypomycinone [22356-23-6] (49, R = H), C27H42NO23, and tolyposamine [34174-76-0] C23H23NO2, (50). Further hydrolysis of tolypomycinone using acid yields tolyponone [24317-12-2] (51), which is also formed upon mild acid hydrolysis of rifamycia S. 

Many tracer chemicals are inherently unstable even as the unlabeled forms. Susceptibility of a chemical to hydrolysis, oxidation, photolysis, and microbiological degradation needs to be evaluated when designing suitable storage conditions for the labeled compound. Eactors that reduce radiolytic degradation, such as dispersal in solution, are apt to increase chemical degradation or instability. 

Nail sickness Nail sickness is chemical decay associated with corroded metals in marine situations. Chemical degradation of wood by the products of metal corrosion is brought about by bad workmanship or maintenance, or unsuitable (permeable) timber species, all of which permit electrolyte and oxygen access which promotes corrosion. Chemical decay of wood by alkali occurs in cathodic areas (metal exposed oxygen present). Softening and embrittlement of wood occurs in anodic areas (metal embedded oxygen absent) caused by mineral acid from hydrolysis of soluble iron corrosion products. 

The following physico-chemical properties of the analyte(s) are important in method development considerations vapor pressure, ultraviolet (UV) absorption spectrum, solubility in water and in solvents, dissociation constant(s), n-octanol/water partition coefficient, stability vs hydrolysis and possible thermal, photo- or chemical degradation. These valuable data enable the analytical chemist to develop the most promising analytical approach, drawing from the literature and from his or her experience with related analytical problems, as exemplified below. Gas chromatography (GC) methods, for example, require a measurable vapor pressure and a certain thermal stability as the analytes move as vaporized molecules within the mobile phase. On the other hand, compounds that have a high vapor pressure will require careful extract concentration by evaporation of volatile solvents. 

The pollutant or solute cycle — that may encompass the processes of advection, diffusion, volatilization, adsorption and desorption, chemical degradation or decay, hydrolysis, photolysis, oxidation, cation or anion exchange, complexation, chemical equilibria, nutrient cycles, and others (see section 3.0). 

First order rate constants are assumed for all degradative processes soil and water microbial degradation, hydrolysis, oxidation, photodegradation in air and water and any other mechanisms of transformation that may apply. The rate at which the chemical degrades will then be equal to the summation of the rate constants acting on the amount of chemical in each compartment summed over all compartments. 

Skipper HD, Gilmour CM, Furtick WR (1967) Microbial versus chemical degradation of atrazine in soils. Soil Sci Soc Am Proc 31 653-656 Sliwinski MK, Goodman RM (2004) Comparison of cienarchaeal consortia inhabiting the rhizosphere of diverse terrestrial plants with those in bulk soil in native environments. Appl Environ Microbiol 70 1821-1826 Stumm W, Morgan JJ (1996). Aquatic chemistry - chemical equlibrium and rates in Natural Waters (3rd edn). Wiley, New York Vega D, Bastide J (2003) Dimethylphthalate hydrolysis by specific microbial esterase. Chemosphere 51 663-668... 

Meier, E.R, M.C. Warner, W.H. Dennis, W.F. Randall, and T.A. Miller. 1976. Chemical Degradation of Military Standard Formulations of Organophosphate and Carbamate Pesticides. I. Chemical Hydrolysis of Diazinon. U.S. Army Med. Bioengin. Res. Dev. Lab., Fort Detrick, Frederick, MD. Tech. Rep. 7611. 32 pp. 

Humidity Chemical degradation, swelling, diffusion, additive extraction, cracking, hydrolysis... 

Even when hydrolysis and epimerization can be avoided during sample preparation and handling, it is not possible to conclude definitively whether the compounds found in plasma and urine are true metabolites or simply degradation products. Indeed, chemical degradation can also occur within the body since urine and plasma contain a wide variety of potential catalysts, including metal ions, phosphate ions, proteins, and sugars (see Sect. 5.2.6). Whereas the existence of mammalian enzymes that act on penicillins and cephalosporins is considered possible [155], no such mammalian enzyme appears to have been identified to date. 

Chemical degradation has been investigated by Shlh and Dal Porto Q) and by Lande ( ) under EPA auspices as an alternative approach (to landfill disposal) for the removal of pesticide residues. Among candidate reactions for the safe detoxification of pesticides, only alkaline hydrolysis was recommended. Several organophosphates and carbamates were identified as amenable to a degradation procedure using strong base/aqueous alcohol. The... 

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