Base catalyzed hydrolysis reaction

Aquatic HS inhibited the base-catalyzed hydrolysis of the n-octyl ester of 2,4-D (i.e., 2,4-DOE). The hydrolysis rate of 2,4-DOE at pH 9-10 decreased by a factor equal to the fraction of the ester associated with the DHS. These observations are consistent with an unreactive humic-bound 2,4-DOE in equilibrium with reactive aqueous-phase 2,4-DOE. Thus, association between Dha and 2,4-DOE inhibited the base-catalyzed hydrolysis reaction. 

Fig. 8.12. Activation of hemiester prodrugs of phenols by acid-catalyzed hydrolysis (Reaction a), base-catalyzed hydrolysis (Reaction b), and cyclization-elimination (Reaction c). Enzymatic hydrolysis not shown (adapted from [174]). 

Amides undergo an acid- or base-catalyzed hydrolysis reaction with water in the same way that esters do. Just as an ester yields a carboxylic acid and an alcohol, an amide yields a carboxylic acid and an amine (or ammonia). The net effect is a substitution of -N by -OH. This hydrolysis of amides is the key process that occurs in the stomach during digestion of proteins. 

CoDolvmer Characterization. The base-catalyzed hydrolysis reaction of polyacrylamide has been studied by several workers (27-29). Halverson, et al. (29) concluded from Interpretations of C NHR spectra that a well-spaced distribution of acrylate groups Is produced along the polymer chain. This hydrolysis procedure offered an opportunity to prepare nearly model copolymers free of chemical sequence heterogeneity. 

The Comparison of the Steps of Some Enz3rme-Catalyzed and Base-Catalyzed Hydrolysis Reactions... 

Scheme 6.4 Base-catalyzed hydrolysis reactions of an anhydride group in a copolymer of styrene and maleic anhydride, which renders the latter soluble in water.

In contrast, Perdue and Wolfe (1982) observed that DOM retarded the basic hydrolysis of the octyl ester of 2,4-D. They found that the base-catalyzed rate constant was reduced in proportion to the fraction of the hydrophobic ester that was associated with the DOM. Perdue (1983) has proposed a micelle-type model to rationalize these results and those presented for atrazine. Perdue compares the physical characteristics of DOM, which is negatively charged at environmental pHs, to those of anionic surfactants. Anionic surfactants have been demonstrated to increase hydrolysis rates for acid-catalyzed processes and decrease rates for base-catalyzed processes (Fendler and Fendler, 1975). Rate enhancements for acid-catalyzed hydrolysis reactions are attributed to stabilization of the positive charge that is developed in the transition state, whereas base-catalyzed hydrolysis reactions are impeded due to destabilization of the negatively charged transition state. Although this is an attractive model, it remains largely untested. 

Fig. 12 Schematic of base-catalyzed hydrolysis reaction in a SAMs of NHS-CIO and b ultrathin films of PNHSMA on oxidized silicon together with the definitions of surface and surface-near regions of the polymer film. The approximate depths in this tentative model were assigned based on the information depths of the techniques (CA 1 nm [148], IR the entire film, in other words 40 nm), the fact that only 25% of the NHS ester groups can be hydrolyzed, and that the reaction can be expected to start at the film-solution interface and to proceed homogeneously into the amorphous film. (Reprinted with permission from [128], copyright (2003), American Chemical Society)...

The filtration of toxic chemicals from contaminated air is of extreme importance in industrial enviromnents to provide the necessaiy personal protection for workers to operate safely. Ethylene oxide (EtO), classified as a toxic industrial chemical due to its high worldwide production and toxicity, is one chemical that poses a unique challenge in workplace enviromnents due to the inefficiency of removal by activated carbon, especially under conditions of high relative humidity (RH). EtO is known to undergo both acid and base catalyzed hydrolysis reactions 1,2). Although activated carbon impregnated with acidic or basic functional groups will facihtate hydrolysis reactions... 

Bases such as NaOH are less destructive to metals but attack living tissue quite readily. In this instance, the reaction is a base-catalyzed hydrolysis reaction hydrolysis—splitting apart a molecule using water). For example, a protein molecule with an amide bond can be split into a carboxylic acid and an amine by base-catalyzed hydrolysis ... 

Oppolzer s bornane-10,2-sultams have been used by Josien et al. [56] in the synthesis of a series of conformationally restrained arylalanines [for example, (28), Scheme 5.13] as binding probes for the tachykinin NK-1 receptor. Highly diastereoselective alkylation of the chiral glycinate equivalent (29) was followed by sequential acid- and base-catalyzed hydrolysis reaction to yield the unprotected a-amino acid (28). 

Hydrolyses of aminopyridopyrimidines to the corresponding pyridopyrimidones by means of acid, base, and nitrous acid have been reported. 4-Amino compounds are stable to nitrous acid, but are much more labile than the 2-amino derivatives toward acid- or base-catalyzed hydrolysis. The aminochloro-pyrido[2,3-d]pyrimidine (160) has been converted into the 2,4-dianilino analog (161) by reaction with aniline." ... 

Gold and Linder (17) studied the esterase catalyzed hydrolysis of A-(-)-acetoxymethyl-(l-phenylethyl)nitrosamine. They found that the stereochemistry of 1-phenylethanol produced in the reaction was the same as that observed in the base catalyzed hydrolysis of the nitrosamine and also of N-(l-phenylethyl)nitrosocarbamate. These results indicated that the same diazotate was produced in all three reactions. The fact that no irreversible inhibition of the enzymatic hydrolysis of the nitrosamine was observed, while extensive irreversible inhibition was obtained with the nitrosocarba-mate, led these workers to conclude that the a-hydroxynitro-samine produced by the hydrolysis had sufficient stability to diffuse away from the active site of the enzyme. 

Some elucidation of the mechanism of elastomer reinforcement is being obtained by precipitating chemically-generated fillers into network structures rather than blending badly agglomerated filler particles into elastomers prior to their cross-linking. This has been done for a variety of fillers, for example, silica by hydrolysis of organosilicates, titania from titanates, alumina from aluminates, etc. [85-87], A typical, and important, reaction is the acid- or base-catalyzed hydrolysis of tetraethylorthosilicate ... 

Hydrolysis of isofervenulins 268 with aqueous base occurred at the C2—N3 bond to give A -carboxy-TV-methylcarbamoyltriazines 301, which were transformed to 268 by acidification of the reaction mixture. On the other hand, base-catalyzed hydrolysis of 268 gave imidazo[4,5-< ][l,2,4]tri-azines 302 (87KGS1555). Hydrolysis of the pyrimidotriazine derivatives with alkali gave the triazines 303 and 304 (77JPR522 87JPR290). 

Unlike base-catalyzed hydrolysis, the acid-catalyzed hydrolysis is reversible. The reaction does not go to completion, thereby resulting in a lower percent yield. 

Bob s research interests and knowledge across chemistry were great. Throughout his career he retained an interest in biomimetic chemistry, specifically the study of metal ion-promoted reactions and reactions of molecules activated by metal ion coordination. His early interests in carbohydrate chemistry inspired him to study metal ion catalysis of both peptide formation and hydrolysis as well as studies in inorganic reaction mechanisms. He was particularly interested in the mechanisms of base-catalyzed hydrolysis within metal complexes and the development of the so-called dissociative conjugate-base (DCB) mechanism for base-catalyzed substitution reactions at inert d6 metal ions such as Co(III). 

It is possible to reverse the formation of an ester by a catalyzed hydrolysis reaction. In this reaction, the water reenters the molecule where it was removed. If an acid is the catalyst, the original acid and alcohol will reform. If a base is the catalyst, the alcohol will reform however, the acid will react further to produce its conjugate base. The base-catalyzed hydrolysis of an ester is saponification. 

Table III summarizes the parameters that affect Brrfnsted acid-catalyzed surface reactions. The range of reaction conditions investigated varies widely, from extreme dehydration at high temperatures in studies on the use of clay minerals as industrial catalysts, to fully saturated at ambient temperatures. Table IV lists reactions that have been shown or suggested to be promoted by Br nsted acidity of clay mineral surfaces along with representative examples. Studies have been concerned with the hydrolysis of organophosphate pesticides (70-72), triazines (73), or chemicals which specifically probe neutral, acid-, and base-catalyzed hydrolysis (74). Other reactions have been studied in the context of diagenesis or catagenesis of biological markers (22-24) or of chemical synthesis using clays as the catalysts (34, 36). Mechanistic interpretations of such reactions can be found in the comprehensive review by Solomon and Hawthorne (37).

Base-catalyzed hydrolysis is employed primarily for the liberation of carboxyl groups protected as esters. The reaction involves direct attack by the hydroxide anion... 

HS may alter the reactivities of bound substrates in a way similar to that of anionic surfactants (inhibiting base-catalyzed and accelerating acid-catalyzed reactions). These effects were attributed to electrostatic stabilization of the transition state for the acid catalysis in which the substrate becomes more positively charged, and to destabilization of the transition state for base-catalyzed hydrolysis in which the substrate becomes more negatively charged. 

In natural waters, the base-catalyzed hydrolysis rate of a weakly HS-as-sociated pollutant (e.g., Parathion) was not significantly affected by HS, while for more strongly associated pollutants (e.g., DDT) the effect of HS was clearly potentially significant in this reaction. 

In HO -catalyzed hydrolysis (specific base catalyzed hydrolysis), the tetrahedral intermediate is formed by the addition of a nucleophilic HO ion (Fig. 3.1, Pathway b). This reaction is irreversible for both esters and amides, since the carboxylate ion formed is deprotonated in basic solution and, hence, is not receptive to attack by the nucleophilic alcohol, phenol, or amine. The reactivity of the carboxylic acid derivative toward a particular nucleophile depends on a) the relative electron-donating or -withdrawing power of the substituents on the carbonyl group, and b) the relative ability of the -OR or -NR R" moiety to act as a leaving group. Thus, electronegative substituents accelerate hydrolysis, and esters are more readily hydrolyzed than amides. 

Lactams undergo both acid- and base-catalyzed hydrolysis [79]. The pH vs. log(rate constant) profiles of penicillins are V-shaped with rate constants at a minimum of ca. pH 7, whereas, for cephalosporins, these plots are U-shaped with minimum rate constants in the pH range of 3-7. The basis for this difference is that penicillins undergo no significant uncatalyzed (pH-independent) reaction, while, in contrast, for cephalosporins, a significant degree of spontaneous, pH-independent reaction between pH 3 and 7 is often observed [80],... 

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