Anhydride, hydrolytic reactivity

The previous discussion can be used to interpret the hydrolytic behavior of a series of compounds that possess the same acyl group but varied leaving groups. For example, the order of hydrolytic reactivity for an amide, an ester, an anhydride, and an acid chloride is ... 

By virtue of their fused /3-lactam-thiazolidine ring structure, the penicillins behave as acylating agents of a reactivity comparable to carboxylic acid anhydrides (see Section 5.11.2.1). This reactivity is responsible for many of the properties of the penicillins, e.g. difficult isolation due to hydrolytic instability (B-49MI51102), antibacterial activity due to irreversible transpeptidase inhibition (Section 5.11.5.1), and antigen formation via reaction with protein molecules. 

The above types of catalysis function by stabilizing the transition state of the reaction without changing the mechanism. Catalysts may also involve a different reaction, pathway. A typical example is nucleophilic catalysis in an acyl transfer or hydrolytic reaction. The hydrolysis of acetic anhydride is greatly enhanced by pyridine because of the rapid formation of the highly reactive acetylpyridinium ion (equation 2.12). For nucleophilic catalysis to be efficient, the nucleophile... 

This method is mainly restricted to the synthesis of amino acids with aromatic side-chains since the required unsaturated azlactones [e.g. (30)] are most readily prepared using aromatic aldehydes. Typically, benzaldehyde condenses under the influence of base with the reactive methylene group in the azlactone (29) which is formed by the dehydration of benzoylglycine (28) when the latter is heated with acetic anhydride in the presence of sodium acetate (cf. Expt 8.21). The azlactone ring is readily cleaved hydrolytically and compounds of the type (30) yield substituted acylaminoacrylic acids [e.g. (31)] on boiling with water. Reduction and further hydrolysis yields the amino acid [e.g. phenylalanine,... 

The desire to find a heterocyclic inhibitor that balanced hydrolytic stability, enzyme reactivity, and acyl-enzyme stability better than the above lactones and coumarins resulted in explorations of a variety of other oxycarbonyl-containing heterocycles including derivatives of isatoic anhydride [190], 6-chloropyrone [191], quinazoline [192], anthranilate [192], isobenzofure-none [193], and benzoxazinone. 

Poly(N-vinylpyrrolidone), P(NVP), is a nonionic, water-soluble polymer with high thermal and hydrolytic stability (7-9). Copolymers of N-vinylpyr-rolidone (NVP) with various carboxylate and carboxylate-precursor monomers (e.g., acrylic acid, sodium acrylate, crotonic acid, itaconic acid, and maleic anhydride) are also well-known (10). In addition, the homo- and copolymerization kinetics of these monomers are well-established. On the other hand, reports of copolymerizations of NVP with sulfonate monomers are sparse 11, 12). This chapter describes the synthesis, kinetics, and reactivity ratios for the copolymerization of NVP and some of the newer sulfonate monomers. A comparison of some of the solution properties for such copolymers is also included. 

As mentioned previously, the anhydride moieties in P(NB/MA) are remarkably hydrolytically stable and do not appreciably facilitate resin dissolution in aqueous TMAH (0.262 N TMAH). Poly(noibomene-alt-maleic anhydride-co-acrylic add) P(NB/MA/AA) dissolution in aqueous base is similarly not dependent on anhydride hydrolysis rather, it varies as a function of acrylic add content. These findings suggest that the anhydrides remain predominantly latent non-hydrolyzed) during the development under the conditions employed, or conversely, that the developer, while basic enough to solubilize acidic fiinctionalities such as caiboxylic acids, lacks the reactivity to effidently promote anhydride hydrolysis in the hydrophobic and sterically congested polymer. We have explored three approaches towards modifying the dissolution behavior of P(NB/( ) polymer matrices ... 

The S5mthetic approach of in situ activation of carboxylic acids is based on the preliminary reaction of the carboxylic acid with a specific reagent to give an intermediate reactive daivative which can be prepared prior to the reaction with cellulose or converted directly in a one-pot process. This approach opens the way to a broad variety of new esters, because for numwous acids, for example unsaturated or hydrolytically unstable ones, reactive derivatives such as anhydrides or chlorides simply cannot he synthesized. The mild reaction conditions apphed for the in situ activation prevent common side reactions hke pericychc reactions, hydrolysis, and oxidation. Moreover, due to their hydrophobic charactCT, numa-ous anhydrides are not soluble in organic media used for cellulose modification, resulting in unsatisfactory yields and insoluble products. In addition, the conversion of an anhydride is combined with the loss of half of the acid during the reaction. Consequently, in situ activation is much more efficient. 

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