Hydrolysis Reactions

Hydrolysis is the breaking of a bond by reaction with water. Halogenoalkanes are hydrolysed slowly by water to form an alcohol:R-X + H₂O → R-OH + H⁺ + X⁻For example, 1-iodopropane + water → propan-1-ol + H⁺ + I⁻. The water molecule acts as a nucleophile, and the halogen leaves as a halide ion. Hydrolysis is much faster with aqueous hydroxide ions, which is covered in later lessons.Detecting the halide ion: the hydrolysis is carried out with aqueous silver nitrate present. Halogenoalkanes do not dissolve in water, so ethanol is added as a solvent, so that the halogenoalkane and the aqueous solution mix. As halide ions are released, they react with silver ions to form a precipitate:Ag⁺(aq) + X⁻(aq) → AgX(s)The colour of the precipitate identifies the halogen:• AgCl: white
• AgBr: cream
• AgI: yellowThe colours can be hard to tell apart, so adding ammonia solution confirms the result: AgCl dissolves in dilute ammonia, AgBr dissolves only in concentrated ammonia, and AgI does not dissolve.So a halogenoalkane that gives a white precipitate, soluble in dilute ammonia, is a chloroalkane. The time taken for the precipitate to appear can be used to compare hydrolysis rates.