Question

What happens when lactic acid is treated with ${\text{PC}}{{\text{l}}_{\text{5}}}$ ? Write the equation.

Answer 1

Hint: First we will draw the structure of lactic acid and see the reactivity of the attached groups in it. ${\text{PC}}{{\text{l}}_{\text{5}}}$ mainly releases the chloride ion as a nucleophile. This chloride nucleophile will attack the reactive site in the compound.

Complete step by step answer:
The formula of lactic acid is . It is a white crystalline solid and soluble in water. When in aqueous state it is a colorless solution. It is also called alpha-hydroxy acid because of the presence of the hydroxyl group in the adjacent carboxyl group. It is an ionizable molecule which dissociates in carboxylate ions and a proton. It is more acidic than acetic acid because of the intramolecular hydrogen bonding between hydroxyl group and carboxyl group. Lactic acid is a chiral molecule which has two enantiomers. D and L enantiomers are there and also can be present as racemic mixture.

  $\text{ Lactic acid

                                                                                                                                            Phosphorus pentachloride


Lactyl chloride.}$


From the substrate i.e. lactic acid we see that it has carbonyl carbon the nucleophile chloride will attack on the carbonyl carbon because it is electrophilic in nature. Due to the presence of electron withdrawing group carboxylic acid the hydroxyl group on the adjacent carbon also becomes acidic and becomes a good leaving group.


Note: Lactic acid can be fermented by the lactic acid bacteria. These bacteria can convert carbohydrates like glucose, sucrose into lactic acid. These bacteria are also present in the mouth and responsible for the tooth decay.

Lactic acid is made on a huge industrial scale with the help of bacterial fermentation of different types of carbohydrate. Most reliable and production method of the production of lactic acid is by the process of fermentation only.