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Hydrolysis is a bond-making, bond-breaking process in which a molecule, RX, reacts with water, forming a new R-O bond with the oxygen atom from the water and breaking the R-X bond in the substance’s molecule (March, 1977). One possible pathway is the direct displacement of X with OH.
R-X + H2O -> R-OH + HX
The most commonly used method to determine hydrolysis is to compare the target compound with an analogous compound or compounds containing similar functional groups and structure.
Pigment red 81:5 is composed mainly of organic functional groups that are generally resistant to hydrolysis. The only functional group present that is potentially susceptible to hydrolysis is the carboxylic ester.
Hydrolysis of carboxylic esters results in the formation of a carboxylic acid and an alcohol, both of which do not undergo further hydrolysis. The two most common mechanisms for hydrolysis are involving acyl-oxygen bond cleavage by acid catalysis (AAC2) and base mediation (BAC2). Hydrolysis via the AAC2 mechanism involves initial protonation of the carbonyl oxygen. Protonation polarises the carbonyl group, removing electron density from the carbon atom and making it more electrophilic and thus more susceptible to nucleophilic addition by water. The base-mediated mechanism (BAC2) proceeds via the direct nucleophilic addition of HO- to the carbonyl group. Base mediation occurs because the hydroxide ion is a stronger nucleophile than water. Although neutral hydrolysis of carboxylic acid esters does occur, the base-mediated reaction will be the dominant pathway in most natural waters. Generally, acid hydrolysis will dominate in acidic waters with pH values below 4.

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