Bacteriological, physiological, etc

1917 The Analyst  
It is shown that lactic acid may be estimated as guanidine lactate, identified by its melting-point, 160" C., alfter separation by esterification from citric and tartaric acids and by fractional distillation from formic and acetic acids. Lactic acid may be separated from mixtures containing formic, acetic, propionic, butyric, and citric acids, and accurately estimated by weighing as quinine lactate, which is identified by its melting-point, 165" to 166.5" C. (racemic). The separation from
more » ... paration from citric acid and other acids whose ethyl esters have high boiling-points is effected by esterification with the vapour of alcohol containing dry hydrogen chloride in solution passed through the mixture suspended in vaseline a t 100" to 110" C., using zinc chloride as a second catalyser ; the ethyl lactate passes quantitatively into the distillate, while the ethyl citrate remains in the flask. By fractional distillation of the distillate through a Hempel fractionating column filled with glass beads the ethyl formate and acetate, together with a large part of the propionate and butyrate, are removed. The residue in the flask containing the ethyl lactate is hydrolysed and converted into quinine salts, and the quinine lactate separated from the propionate and butyrate by the solubility of the la,tter in carbon tetrachloride. Esterification of mixtures containing lactic acid is efEected in a distillation flask of 75 C.C. capacity, with sideneck connected with a condenser. This is charged with the lactic acid mixture, 1 grm. of zinc chloride, 25 C.C. of vaseline, and 10 C.C. of absolute alcohol containing in solution 2.5 grms. of hydrogen chloride per litre. It is kept at 100" to 110" C. by a glycerol bath, and 190 O.C. of similar acid and alcohol are distilled through the mixture from another flas:k, connected with the esterification flask, during a period of one and a half hours. The distillate of esters is fractionated through a 15 cm. Hempel column until the volume of residue is 20 c.c.; 100 C.C. of alcohol are added and distillation continued this is again repeated. The beads in the column are washed with dcohol, and the distillation residue treated with excess of silver
doi:10.1039/an9174200087 fatcat:wfwqr3dw6vav7ja7uchkcecw3i