The molecular formula of lactic acid is C3H6O3 and the structure formula CH3.CH(OH).COOH. It is found in two forms –
d-lactic acid: – It is obtained from the extract of meat. Its specific rotation is +2.24°. It is dextrorotatory substance. It is also called d-lactic acid or (+)-lactic acid, this D-(+) lactic acid.
l-lactic acid: – It is obtained from sucrose by fermentation method. It has a specific rotation –2.24°. It is a laevorotatory substance. It is also called l-lactic acid, (-)-lactic acid or L-(-)-lactic acid.
The d and l letter and (+) and (-) sign in the above names represent the direction of optical activity. D and L demonstrate the feature of letter configuration.