LACTIC ACID
Formula
C3H6O3 or CH3-CH(OH)-COOH
Preparation
Lactic acid can be prepared by brominating propionic acid and then hydrolyzing the product (2-bromopropionic acid) with dilute alkali. This converts it to sodium lactate, which finally gives lactic acid.
Tests for Purity
- Appearance: Clear, colourless, highly water-soluble liquid.
- Arsenic: Less than 1 ppm.
- Heavy metals: Less than 10 ppm.
- Citric, Oxalic & Phosphoric acid: When treated with calcium chloride, their insoluble salts would form turbidity. No turbidity should appear.
- No traces of ether-insoluble materials or volatile fatty acids.
- Methanol & Methyl ester: Less than 100 micrograms per 10 g.
- No reducing sugars (checked using Fehling’s reagent).
- Sulfated ash: Less than 0.1% w/w.
Assay
Method 1: Acid–base titration using NaOH.
1 ml of 0.1 M NaOH ≡ 0.09008 g of lactic acid.
Method 2:
A weighed amount is diluted with water, boiled with N/1 NaOH, and excess alkali is back-titrated with N/1 HCl using phenolphthalein. Boiling helps to break any condensed products.
Uses
- Widely used in dairy products.
- Helps in determining tidal volume in physiological studies.
- Ethyl and butyl lactates are used as plasticizers.
- Used as a food preservative, curing agent, and flavouring agent.
- Acts as a decontaminant in meat processing.
Detailed Notes:
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PATH: PHARMD/PHARMD NOTES/ PHARMD FIRST YEAR NOTES/ ORGANIC CHEMISTRY/ PHARMACEUTICAL ORGANIC CHEMISTRY/ LACTIC ACID.