Water, ethyl alcohol and carbon tetrachloride form a ternary
mixture boiling at about 61'0. This vapor mixture, on condensation,
separates into two phases; the heavier liquid consists of carbon
tetrachloride and alcohol with only small amounts of water;
the lighter liquid consists of approximately 65 per cent alcohol,
25 per cent water and 10 per cent carbon tetrachloride.
By taking advantage of this fact, it is possible to conduct
the esterification at a temperature so low that the ethyl hydrogen
oxalate first formed does not decompose into ethyl formate
and other products, as is the case when the customary methods
of esterification are employed.
The reaction may be carried out somewhat more expeditiously
if the oxalic acid be dehydrated independently before it is mixed
with the alcohol; indeed, it is also possible to remove the bulk
of the water from the alcohol itself by a similar method, before mixing
it with the oxalic acid. However, since water is formed during
the esterification, little is gained by this procedure.
It is not absolutely necessary to remove the last traces of water from
the alcohol-carbon tetrachloride layer by means of potassium carbonate
before returning it to the reaction mixture; this process is, however,
so simple and requires so little attention that there is no doubt
that it is of material aid in cutting down the time of operation.
The advantages of using crystallized oxalic acid and commercial 95
per cent alcohol, instead of the anhydrous reagents, are obvious.
When technical oxalic acid is used, the yields are usually smaller
by 5 to 10 per cent.
The apparatus shown in Fig. 1 may be somewhat more simply constructed
by using rubber connections in several places, thus eliminating a certain
amount of glass blowing, and making a more flexible piece of apparatus.
The side-arm of the separator may be made with two rubber connections,--
one above and one below the tube leading to the potassium carbonate tube.
The long return tube to the flask may be constructed with a rubber
joint very near the carbonate tube and one near the flask.