Organic Syntheses, Coll. Vol. 1, p.523 (1941); Vol. 4, p.77 (1925).
In a 3-l. flask
, fitted with a stirrer
and a fractionating column
for downward distillation, are placed 912 g. (815 cc., 2.75 moles) of ethyl propane-1,1,2,3-tetracarboxylate (p. 272)
and 950 cc. of a solution of equal volumes of pure concentrated hydrochloric acid
and distilled water. A receiver with a side tube
is attached to the condenser; this side tube leads to a water trap
. The mixture is boiled, with continual stirring, at such a rate that the alcohol is removed as fast as it is formed, but without undue removal of water from the flask (Note 1)
. The progress of the reaction can be followed by noting the rate at which carbon dioxide
passes through the trap. When the temperature at the head of the column approaches 100°, the flame is turned down so that very little liquid distils over. Heating is continued until evolution of carbon dioxide
ceases (Note 2)
The flask is now disconnected from the stirrer and column, and the contents distilled off as completely as possible on the steam bath
under reduced pressure. The remaining solid is freed from residual moisture and hydrochloric acid
by allowing a slow current of dry air to pass over it, while still heating on the steam bath and maintaining a partial vacuum (Note 3)
. It is then redissolved in distilled water; the solution is filtered with the use of decolorizing carbon
, and again evaporated under reduced pressure.
The residue, when completely dry, is ground up, mixed to a paste with dry ether
, filtered by suction, washed with dry ether
, and dried. The product so obtained (Note 4)
is practically pure and melts at 160–161°
. The yield is 474–479 g.
per cent of the theoretical amount).
The temperature at the head of the column will give some idea of the relative amount of water passing over with the alcohol
, but allowance must be made for the lowering of the distilling temperature by the carbon dioxide
Twelve hours' heating is necessary to complete the reaction.
The dry air is best introduced through a tube leading to the bottom of the flask; it is well not to disconnect the condenser, but to note the point at which no more drops condense. The current of dry air should be quite slow—not more than two bubbles per second in the sulfuric acid wash bottle
is readily soluble in water (requiring about twice its weight at room temperature), but may, if desired, be recrystallized from it. Dry ether
may also be employed, about 50 parts by weight being necessary.
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