It occurs in the juice of citrus fruits such as lemons, limes, galgals, and oranges. Lemon juice contains 7-10 percent of citric acid.
Citric Acid Preparation From Molasses. Molasses containing sucrose is diluted with water and subjected to fermentation with a microorganism Aspergillus niger.
The fermentation process is carried for 7 to 10 days at 26-28°C. The resulting solution of citric acid is neutralized with Ca(OH)2 to form insoluble calcium citrate. This is washed with water and decomposed with dilute sulphuric acid. The calcium sulfate is filtered off and the solution concentrated under vacuum to get crystals of citric acid.
Citric Acid Preparation From Lemon Juice. Small amounts of citric acid (less than 7%) are still made from citrus fruit wastes. The juice is extracted from them and boiled to coagulate proteins. The resulting clear solution is worked by the Ca(OH)2 –sulphuric acid scheme described above, to recover citric acid.
Citric Acid Preparation From Lemon Petroleum. Recently it has shown that certain strains of candida (a yeast) can produce citric acid from n-alkanes derived from petroleum. This method when developed will revolutionize the citric acid industry.
Citric Acid Uses.
- As acidulant in carbonated soft drinks, jams, jellies, candies, etc.
- As medicinal in the form of effervescent salts, magnesium citrate, a laxative.
- As mordant.
- As ferric ammonium citrate in the preparation of blueprint papers.
- As esters (e.g., tributyl citrate) that are good plasticizers for lacquers and varnishes.
Citric Acid Properties.
Physical Properties of Citric Acid. Citric acid forms large colorless crystals of monohydrate, citric acid H2O. The anhydrous acid melts at 152°C and has a strong acid taste. It is very soluble in water and alcohol but is sparingly so in ether. It is not optically active as it contains no asymmetric carbon atom. It is non-toxic.
Chemical Properties Of Citric Acid. The reaction of citric acid is those of a tricarboxylic acid tertiary alcohol.
(1) Acetylation. It reacts with acetyl chloride ( or acetic anhydride) to form monoacetylcitric acid.
(2) Reduction. When reduced with Hl, citric acid gives Tricarballylic acid.
(3) The action of Heat. When heated at 150°C. citric acid gives a molecule of water to form Aconitic acid.
(4) Reaction with fuming H2SO4. On heating with fuming sulphuric acid, it gives acetonecarboxylic acid.
Citric Acid Structure.
As determined by elemental analysis and molecular weight determination, the molecular formula of citric acid is C6H8O7. and molecular mass is 192.12 g/mol.
Citric Acid iupac name.
Citric acid IUPAC name is 2-Hydroxypropane-1,2,3-tricarboxylic acid.