1. The use of this column prevents loss of
acetic anhydride during the heating process and permits volatile products formed during the reaction to be removed by distillation. The checkers used a 1 by 12 in. column packed with 6 by 6 mm. glass rings.
6. Since
ethyl diethoxymethylmalonate is difficult to separate from
ethyl ethoxymethylenemalonate by distillation, it is necessary to follow the course of the distillation by observation of the change in refractive index instead of the change in boiling point. After a low-boiling fraction is collected, there is obtained an intermediate fraction (
nD20 1.4142–1.4580), the size of which depends upon the amount of
ethyl diethoxymethylmalonate present. Under the best of conditions it amounts to
15 g. In each of three runs, the checkers obtained about
300–400 g. of material having a refractive index in this range.
The
ethyl ethoxymethylenemalonate was collected at
nD20 1.4580–1.4623. The checkers used a
5-in. Vigreux column and observed that at the low pressures the boiling point of the distillate in several runs was about 10° lower than that reported by the submitters. For example, in one run at 0.25 mm. (gauge pressure) the boiling point of the distillate never rose above 97.2°; however, the refractive indices of twelve 50-ml. fractions taken in the course of this distillation were all in the proper range,
nD20 1.4612–1.4623.
Interruption of the heating during the reaction period should be avoided. In an experiment in which the heating was discontinued after about 8 hours and resumed the next day the yield was about
50%.