The Physical Properties of Lactic Acid and Derivatives

Abstract

Lactic acid is an important chemical, used in food-technology, medicine and cosmetics. It’s 2-hydroxypropionic acid. This paper deals with the physical properties of lactic acid and it’s derivatives. There’s not much known about the physical properties of pure lactic acid, because lactic acid appears mainly in the form of aqueous solutions. When physical properties of these solutions have been estimated one should consider that lactic acid in solution undergoes intermolecular esterification spontaneously, resulting after some time in an equilibrium solution containing, lactic acid, lactoyllactic acid, poly lactic acid and a very little dilactide. When it’s not mentioned whether intermolecular esters are present in lactic acid solutions, physical properties of these solutions are not that reliable. Also physical properties of lactic with other solvents than water are considered, like distribution coefficients, ternary phase diagrams and critical solution temperatures. The optical activity of lactic acid doesn’t have any influence on the physical properties, except the melting point. Racemic lactic acid has a lower melting point than optical active lactic acid, 25-27°C and 52.7-52.8°C respectively. Also the physical properties of the intermolecular esters and some derivatives are described. Not much is known about these esters. More is known about some common esters of lactic acid, like alkyl lactates. The physical properties of alkali and ammonium lactates, salts of lactic acid, are mentioned shortly. Some short articles deal with spectra of lactic acid. Here ultraviolet, infrared and microwave spectra are briefly discussed. Most of the data presented were published more than 40 years ago, one article was even published in 1894. Unfortunately there aren’t any recent articles about physical properties of lactic acid and derivatives.