Lactic Acid : Preparation, Properties, Reaction As Well As Uses

Lactic Acid.

Lactic acid is the top dog component subdivision of milk that has gone sour in addition to thence its advert (L. Lactis=milk).

Preparation. (1) By the hydrolysis of acetaldehyde cyanohydrin.

From Molasses. (2) Lactic acid is manufactured past times fermentation of molasses (or milk whey containing lactose) past times the microorganism Bacillus acidi lactiti (BAL).

A dilute solution of molasses (or whey) is treated alongside BAL (sour milk). The fermentation is carried at 35-40°C inwards the presence of CaCO₃, As the lactic acid is produced, it reacts alongside CaCO₃, to cast calcium lactate. The calcium lactate is filtered off in addition to decomposed alongside calculated quantity of dilute H₂SO₄. The insoluble Calcium sulphate is removed in addition to the lactic acid gear upwards gratis inwards the solution is recovered past times distillation inwards vacuo. The production is D-lactic acid.

Physical Properties.

Lactic acid is a colourless, crystalline solid, mp 53°C, in addition to has a sour taste. The acid obtained from molasses is D-isomer. The synthetic production is racemic lactic acid, mp 18°C, specific rotation [α] = +3.82, Lactic acid is soluble inwards water, alcohol, in addition to ether.

Chemical Properties.

Lactic acid molecule contains a secondary alcohol grouping (>CHOH) in addition to a carboxyl grouping (COOH), in addition to gives reactions of both.

Reaction Involving COOH Group.

(1) Formtion of salt. It reacts alongside alkalis to cast salts.

Reaction Involving OH Group.

(2) Reaction alongside CH₃COCl. The alcoholic OH grouping is acetylated on reaction alongside acetyl chloride inwards the presence of a base of operations (pyridine).

(3) Reduction. When heated alongside Hl, it is reduced to propionic acid.

(4) Oxidation. On oxidation alongside Fenton's reagent (H₂O₂/Fe³⁺) it is converted to pyruvic acid. With KMnO₄ it yields acetic acid.

Reaction Involving Both OH And COOH.

(5) Reaction alongside PCl5. Both the OH in addition to COOH groups are attacked past times phosphorus pentachloride to cast lactyl chloride.

(6). Action of Heat. When heated alone, it forms an intermolecular cyclic diester called a Lactide.

(7) Reaction With H₂SO4. When heated alongside dilute sulphuric acid at 130°C, lactic acid is decomposed to yield acetaldehyde in addition to formic acid.

With concentrated H₂SO₄, formic acid is farther decomposed to CO in addition to H₂O. (test)

Uses.

Lactic acid is used.

1. in dairy products.
2. as acidulant inwards beverages in addition to candies.
3. for deliming of hides.
4. as a mordant.
5. Ethyl in addition to butyl lactates are used every bit plasticisers.
6. Calcium in addition to Fe lactates are used inwards medicine.