Consider the reaction given below, which is very important in the pharmaceutical industry. Which one of the following compounds (I-IV) is a possible structure for product A?

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The question presents a reaction between a salicylic acid derivative (an ortho-hydroxy benzoic acid) and a diester acylating agent, asking which of the structures I–IV could be the product A. The key considerations are which functional group participates in the acylation under typical conditions and how the regiochemistry would be reflected in the product.

Option I: The depicted product shows acetylation or ester formation at the carboxylic acid moiety appended in a way that suggests the carboxyl group has been converted into an ester linkage while the phenolic OH remains unmodified or is differently substituted. In standard acylation reactions with acid derivatives, the carboxyl group is less reactive toward forming esters under mild conditions when an activated ester or anhydride is used to selectively acetylate the more nucleophilic phenolic OH. Therefore, this structure is unlikely to be the major product because it implies selective modification at the carboxyl group rather than the phenolic OH.

Option II: This structure displays esterification occurring at the phenolic OH while the carboxyl group remains in place (i.e., the phenolic oxygen is acylated with an acetyl-type group, producing a phenolic acetate, with the carboxylic acid intact). The phenolic oxygen is more nucleophilic than the carboxyl oxygen in this context, and acylating agents of appropriate reactivity often give selective acetylation at the phenolic OH. Hence this arrangement aligns well with a selective O-acylation of the phenol while preserving the carboxylic acid functionality.

Option III: The drawing for III appears to swap substituents such that the acetyl group ends up attached to the carboxyl-derived moiety or in a position that would alter the acid functionality or create an unintended intramolecular or mixed anhydride arrangement. Such regiochemistry would be unusual under standard conditions aimed at phenolic acetylation and is chemically less favorable given the relative reactivities of phenolic OH versus carboxyl OH toward acylation under typical conditions.

Option IV: This structure presents the acetyl (or ester) group directly on the carboxyl-derived portion in a manner that again suggests alteration of the carboxyl functionality or formation of a different ester linkage than a simple phenolic acetate. It diverges from the expected selectivity pattern for acetylation of the phenolic OH and could imply loss or modification of the carboxyl group pattern that would not correspond to the most straightforward product A under standard acetylation conditions.

In summary, comparing the four options against plausible regiochemical outcomes, Option II best matches selective O-acylation at the phenolic hydroxyl while leaving the carboxyl group intact, which is a common and reasonable outcome for this type of reaction. The other options require less favorable regiochemical changes (modification of the carboxyl group or incorrect placement of the acetyl group) that are not consistent with the likely reaction pathway given the reactants and typical acylating conditions.

CHM1052 - MUM S2 2025 CHM1052 2022 practice exam 1

Consider the reaction given below, which is very important in the pharmaceutical industry. Which one of the following compounds (I-IV) is a possible structure for product A?

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