Nucleophilic acyl substitution defined

A characteristic reaction of carboxylic acid derivatives is nucleophilic acyl substitution. In this reaction a negative or neutral nucleophile replaces a leaving group to form a substitution product. The leaving groups and nucleophiles are the groups that define the various acid derivatives as a result, the reaction usually involves the conversion of one acid derivative into another. The order of reactivity of acid derivatives is acid chloride > anhydride > acid or ester > amide. In general, reaction of any of these derivatives with water produces acids with alcohols, esters result and with amines, amides are formed. 

The reaction of nucleophiles with various heterocumulenes, such as isothiocyanates or acyl isothiocyanates, has been widely studied, and the scope and limitation of these reactions have been defined (5). The utility of heterocumulenes as building blocks to a variety of A/ 5-heterocycles prompted us to investigate the behavior of acyl isothiocyanates toward A -substituted anilines (d). 

As already mentioned, although the use of commercially available phosphines as acylation nucleophiles is well documented, their potential for organocatalyzed polymerizations has been certainly underexploited so far. There is only one report in 2002, by Myers et al. where phosphines, such as PBus, PPhMe2, PPh2Me, and PPhs, were employed as trae catalysts for the ROP of LA in the presence of an alcohol initiator. The catalytic efficacy was found to depend on the substitution pattern of the phosphine for instance, trialkylphosphines proved more active (being more basic and more nucleophilic) than the triaryl phosphines. Polymerizations could be carried in bulk at 135 °C, yielding well-defined PLAs with a TOF of 0.01 s (Table 4, entry 1). 

Structural alerts or chemical motifs known to be associated with toxicity through either the parent compound or reactive metabolites have also been used to predict potential toxicity from chemical structures. These expert algorithms appear in commercial software programs and in onhne open access sites. For instance, there are seven chemical domains that are used to define and predict the covalent interaction between a chemical and a macromolecule (biological target) that leads to an initiating event at the beginning of an AOP [34]. These include Michael addition, acylation, Schiff base formation, aromatic nucleophilic substitution, unimolecular... 

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