GB620320A - Manufacture and use of dehydrated lactic acid - Google Patents

Abstract

A solution of anhydro-condensation products of lactic acid free from sugars, gums and inorganic salts is obtained from commercial aqueous lactic acid by removing water from it until the dehydrated acid is soluble in an aromatic, hydroaromatic or paraffin hydrocarbon solvent, dissolving it in the solvent as it is formed or after its formation, and separating the resulting solution from insoluble material. Benzene, toluene, xylene, cyclohexane, white spirit, or petroleum ether may be used as solvent. The water may be removed by distillation under reduced pressure, or in the presence of an entrainer. In the latter case the hydrocarbon solvent may be used as entrainer. In an example, "fermentation" aqueous lactic acid containing 7.7 parts by weight of C3H6O3 was boiled with excess xylene in a vessel fitted with a condenser and separator from which the xylene layer was returned to the vessel. Boiling was continued until the xylene contained in solution 7.42 parts of dehydrated lactic acid (calculated as C3H6O3). The solution was decanted from insoluble matter, and the xylene removed by evaporation. In another example, 75 per cent lactic acid was concentrated by evaporation under reduced pressure until it contained 106.2 per cent C3H6O3. The solution was then boiled under reflux for 30 minutes with about 4 parts of xylene. The solution was decanted off and the residue refluxed with a further quantity of xylene. The extraction was repeated 4 more times. In a further example, the aqueous lactic acid was boiled with benzene in a vessel fitted with a condenser and separator. The supernatent benzene solution in the vessel was continuously withdrawn and transferred to a second vessel from which the benzene was removed by distillation and returned to the first vessel. After several hours nearly all the original lactic acid was in the second vessel in the dehydrated state, while the insoluble impurities remained in the first vessel.ALSO:A solution of anhydro-condensation products of lactic acid free from sugars, gums and inorganic salts is obtained from commercial aqueous lactic acid by removing water from it until the dehydrated acid is soluble in an aromatic, hydroaromatic or paraffin hydrocarbon solvent, dissolving it in the solvent as it is formed or after its formation, and separating the resulting solution p from insoluble material. Benzene, toluene, xylene, cyclohexane, white spirit, or petroleum ether may be used as solvent. The water may be removed by distillation under reduced pressure, or in the presence of an entrainer. In the latter case the hydrocarbon solvent may be used as entrainer. Examples are given (see Group III). The purified dehydrated lactic acid may be used for various purposes, either in solution or after being freed from the solvent. Thus it may be used for the preparation of lactic acid esters, or for producing purified lactic acid by hydrolysis. The dehydrated lactic acid may be reacted with formaldehyde, lactose, furfuraldehyde, or monohydric or polyhydric alcohols, to produce resinous products.