1. The
ethyl oleate used by the submitters was prepared by esterification of
commercial U.S.P. grade oleic acid and fractionated through a Widmer column. The fraction boiling at
160–170°/1 mm.,
nD25 1.4482–1.4570, iodine value 83.6 (calculated 81.8), was used. The checkers distilled
ethyl oleate (technical, Eastman Kodak Company) and used the fraction boiling at
164–166°/1 mm.,
nD25 1.4522.
2. The purity of the absolute
ethanol is of prime importance.
Ethanol dried only by a lime process gives a low yield (
20–25%). The
ethanol used in this procedure was dried over lime and then over
aluminum tert-butoxide, after which it was distilled directly into the flask used for the reaction.
4. The temperature is controlled by selecting a liquid whose freezing point is approximately the temperature at which one wishes to carry out the crystallization, and crushed Dry Ice is added with stirring to keep just a slush. There must be an intimate mixture of solid and liquid at all times.
Carbon tetrachloride was used for temperatures of −20° to −25°.
5. The apparatus was as follows: A
50-ml. Pyrex sintered-glass funnel, with a sealed-on extension tube, was jacketed with an inverted
500-ml. wide-mouth bottle with the bottom cut off and the edges ground smooth. The jacketed funnel was then placed in a
250-ml. suction flask, the side arm of which was connected to a
three-way stopcock. One arm of the stopcock was connected to a
water aspirator; the other, to a large
test tube (1 1/8 in. by 8 in.) fitted with a
two-hole stopper. From the second hole in this stopper was led a tube extending to the bottom of a smaller test tube partly filled with
mercury. During crystallization, this large test tube was filled three-quarters full of Dry Ice, the
carbon dioxide gas evolved being allowed to bubble up through the bottom of the sintered-glass funnel. This prevents the solution from filtering through and also stirs the solution by the rise of small
carbon dioxide bubbles, and hence induces crystallization. The porosity of the sintered-glass funnel is a factor in the size and number of bubbles formed. The
mercury trap may be raised or lowered to adjust the pressure, and to act as a vent to prevent the accumulation of
carbon dioxide to give excessive pressures. After crystallization had taken place (about 1 hour) the stopcock was turned to the aspirator and the solution immediately filtered. With this apparatus, about 80 ml. of solution may be crystallized at a time, and no transferring from one container to another is necessary. The checkers found it more convenient to use a
500-ml. sintered-glass funnel along with a proportionally larger bottle, flask, etc. The
400 ml. of acetone solution was then poured into the funnel in 50-ml. portions with adequate cooling intervals.