Process for preparing glycolic acid and its polymers

#This invention relates to a process for preparing glycolic acids. More particularly, it relates to a process for preparing glycolic acid and its polymers, starting from formaldehyde.

#Glycolic acid is an interesting intermediate for the synthesis of ethylene glycol. Furthermore, it is useful in the descaling and cleaning of metal surfaces owing to its complexing power with respect to the ions of many heavy metals. It is also employed in some formulations of synthetic detergents, as well as in the dyeing of wool and nylon.

#It is already known to obtain glycolic acid from formaldehyde by carbonylation in the presence of acid catalysts at high temperatures (200.degree. to 300.degree. C) and high CO pressures (about 700 atmospheres).

#111 ml of H.sub.2 SO.sub.4 (96% by weight) were introduced into a 500 cc flask made of Pyrex glass and equipped with thermometer, stirrer, burette for gas and feed tubes. The air was replaced by CO and the mass was thermoregulated at 30.degree. C. Subsequently, 2.86 g of Cu.sub.2 O (0.02 moles) were added.

#Under intense stirring, CO was gradually fed from the burette, at room pressure, as the absorption went on. 1070 Nml of CO were absorbed in 35 minutes. 40 ml of a formaldehyde aqueous solution at 38% (weight/vol.) were fed at a flow rate of 12ml/hr. At the conclusion of the formaldehyde feeding, CO absorption was allowed to continue; it stopped after about 13 hours (10,850 Nml were absorbed). The reaction mass was then poured into 500 cc of water and ice, and the insoluble part (consisting of polymers higher than glycolic acid) was filtered.

#After percipitation of sulphuric acid as the barium salt and removal of the cations present in the solution by percolation over Dowex 50W resin, glycolic acid was recovered along with its lowest polymers by evaporation of water.