Claisen's Flask and Its Evolution

The present emphasis on semimicro (0.1-5.0 g) preparation and handling of chemical compounds in the laboratory evidences the shortcomings of the semimicro Claisen distillator, the only apparatus available to carry out reduced pressure distillations at this scale.The main advantage of the macro Claisen device is the strong reduction of the effects of "bumping", the semi-explosive vaporization which generally would project part of the liquid distilland into the distillate, contaminating the latter with unwanted components.This advantage can disappear in semimicro scale Claisen distillators. A very good remedy has consisted in allowing a strong centrifugal field induced by a suitable shape of the distilling flask to carry out a density separation of splashes and droplets produced by bumping and entrained by the high speed vapors intrinsic of low pressure distillation. Such an expedient gives distillates of superior purity, and completely avoids the necessity of repeating the distillation, avoiding the consequent loss of time and products.The current note presents two types of semimicro distilling flask, plus a vapor condenser, all exploiting a centrifugal field, (together with an order-of-magnitude calculation of the field's strength).