Hydrolysis of Acid Chloride | Acyl Chloride | Mechanism

Hydrolysis of Acid Chloride | Acyl Chloride Hydrolysis | Mechanism

Acid chloride compounds (acyl chloride) such as ethanoyl chloride, benzoyl chloride hydrolysis easily in the water and give carboxylic acid and HCl as the products. We know carboxylic acid is a weak acid and HCl is a strong acid in the water.

Note that, acid chlorides are also named as acyl chlorides or carboxylic acid chlorides.

Acid chloride aqueous solution | Reaction of acid chloride and water

Aqueous acid chloride is a very acidic solution due to formation of a mixture of strong acid and a weak acid. This hydrolysis reaction is a elimination reaction and water is participated as a reagent. This reaction completely converts acid chloride to a carboxylic acid and HCl (Hydrochloric acid). Carboxylic acids are weak acids while HCl is a strong acid.

Calculate pH of strong acid and weak acid solution

Several examples of hydrolysis of acyl chloride compounds are explained below.

Ethanoyl chloride and water reaction

Ethanoyl chloride is an acid chloride compound with two carbon atoms. Ethanoic acid and HCl are given as products by the hydrolysis of ethanoyl chloride. Ethanoyl chloride is soluble in water and form a strong acidic solution due to formation of HCl acid. HCl is one of the strongest acid. pH value of the solution will be lower than seven and that pH value may depend mainly on the formed HCl concentration.

carboxylic acid chloride and water reaction

Benzoyl chloride hydrolysis

Hydrolysis of Benzoyl chloride gives benzoic acid and HCl as products. Benzoic acid is a white precipitate which is not a soluble organic compound in water. Benzoic acid is the weak acid.

Mechanism of hydrolysis

  • We know, carbonyl carbon is positively charged due to the oxygen atoms which has sp2 hybridization. Also H2O is a good nucleophile which loves attack positvely charged parts.
  • Water molecule attacks the carbonyl carbon. Now, it's going to form a new C-O bond. With that step, two electrons of one bond of existed C=O bond is gone to the oxygen atom as a lone pair. See the mechanism figure.
  • Next, C-Cl bond is broken and Cl- ion is given. With that, existed C=O bond forms once again.
  • Now oxygen atom has a positive +1 charge. Oxygen does not like to hold positive charge due to oxygen's high electronegativity. So one O-H bond is broken and hydrogen atom is eliminated as H+.
  • Cl- combines with H+ to form HCl.
carboxylic acid chloride hydrolysis mechanism

Aqueous carboxylic acid chloride show following reactions also


What is the pH value after after hydrolysis of acyl chloride

In this lesson, you learned that acyl chloride will give a strong acid and a weak acid as products. Then, aqueous solution is definitely an acidic solution and should show low pH values (below than 7). If 0.1 mol of acyl chloride hydrolysis in 1 dm3 of water, that solution should have a pH value below than 1 theoretically.

hydrolysis of acetyl chloride

Acetyl chloride is another name used for ethanoyl chloride. So hydrolysis reaction is same as ethanoyl chloride. Acetyl chloride is an acyl chloride with two carbon atoms. It will hydrolysis in the water and give HCl acid and acetic acid (ethanoic acid) as products. Acetic acid is a carbonic compound while HCl is an inorganic acid.

acyl chloride + water

Acyl chloride + water reaction will form an electrolyte solution due to formation of HCl acid. HCl acid dissociates completely in the water and give H+ ions and Cl- ions to the water.

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