Org. Synth. 1925, 5, 55
[Orthoformic acid, triethyl ester]
Submitted by W. E. Kaufmann and E. E. Dreger.
Checked by F. C. Whitmore and H. F. Herzog.
In a 5-l. round-bottomed flask, fitted with an 80-cm. reflux condenser, are placed 3 l. of absolute alcohol (Note 1) and 490 g. (327 cc., 4.1 moles) of chloroform (Note 2). The flask is arranged for outside cooling by running water. To the solution, 207 g. (9 atoms) of clean sodium cut into pieces which will conveniently drop through the condenser is added during the course of about two hours. In order to add the sodium at this rate, the flask must be cooled during the addition. When the sodium has entirely reacted and the mixture has been cooled to room temperature, the sodium chloride which has separated is removed by suction filtration with the use of thoroughly dry apparatus (Note 3). The salt is washed on the filter with 200 cc. of absolute alcohol, and the washings are allowed to run into the main filtrate.
The solution is placed in a 3-l. flask fitted with an 80-cm. fractionating column (Note 4), and the excess chloroform and most of the alcohol are distilled off on a steam or water bath. The distillate is caught in a 2-l. suction flask protected from moisture by a drying tube. This distillation requires five or six hours. A mixture of chloroform and alcohol, weighing about 2000 g., is recovered and saved for the next run (Note 3). The liquid remaining in the flask is decanted from the small amount of salt which has separated, into a Claisen flask with a 30-cm. fractionating column (Note 5). The mixture is distilled at atmospheric pressure. The fraction boiling below 85° is mainly alcohol and is discarded. An intermediate fraction of about 100 g., boiling at 85–140°, contains about one-fourth of the total yield. This may be fractionated but is best added to a subsequent run. The orthoformic ester is collected at 140–146° and weighs 120–140 g. (27–31 per cent of the theoretical amount). There is practically no higher-boiling material. Another distillation gives almost all the material boiling over a 2° range.
After the first run, 400 g. of chloroform and enough absolute alcohol (800–1000 cc.) are added to the recovered chloroform-alcohol mixture to give a total volume of 3 l. The sodium is then added as before. After the excess of chloroform and alcohol has been distilled through the fractionating column, the intermediate fraction from the previous run is added before fractionating. The yield from such a run is about 200 g. (45 per cent of the theoretical amount) (Note 6) and (Note 7).
.—Good absolute alcohol
is essential. The use of alcohol of about 98 per cent
gives only about two-thirds the yields obtained with absolute alcohol
. Alcohol dried over lime usually runs about 98.5–99.5 per cent. A good method of obtaining a higher grade of absolute alcohol
is to treat this alcohol with a little sodium
. When the sodium
has dissolved, the alcohol is distilled from a steam bath. Under these conditions, any trace of water that may be present on account of the equilibrium
remains in the concentrated solution of sodium ethoxide
and sodium hydroxide
. See, also, p. 249
and, Note 1, on p. 251
must be used to keep the solution from being alkaline at the end of the reaction.
If care is taken to prevent moisture from getting into the recovered alcohol-chloroform
mixture, this mixture may be used repeatedly. After it has been used four or five times, the yield begins to fall.
The long fractionating column
used by Clarke and Rahrs1
is satisfactory. If such a column is not available, an 80-cm. reflux condenser without any water in it, may be used, connecting it at the top by means of a wide, bent glass tube to a condenser set downward for distillation.
A satisfactory type of flask for the distillation is that illustrated on p. 130
The present method is better than that which uses dry ether
as a solvent.
Yields equally good as those mentioned in the above procedure are obtained by first preparing a sodium ethoxide
solution, taking the quantities given above and adding this to an alcohol-chloroform
solution. One decided disadvantage in this alternative procedure is that, unless a great deal more alcohol is employed, the sodium ethoxide
solution tends to become semi-solid and cannot be
introduced easily into the chloroform-alcohol
solution. If one attempts to use recovered alcohol, containing chloroform
, the sodium chloride
which separates as soon as sodium
is added increases the tendency to become semi-solid.
The reaction is carried out best without stirring, thus allowing the sodium to float on top. In this way, the hydrogen escapes rapidly and little reduction of the chloroform takes place.
Orthoformic ester can be prepared by the treatment of a mixture of chloroform
and alcohol with sodium
by the action of dry sodium ethoxide
or on an ether
solution of chloroform
by the action of alcoholic sodium hydroxide
and by the action of alcoholic hydrochloric acid
on ethyl formimido ester6
or its mercuric chloride double salt
has been published for the preparation of orthoformic ester, in which sodium
are added alternately to the absolute alcohol
. A few runs were made according to its directions but the results were not so satisfactory as those obtained by
the procedure described.
This preparation is referenced from:
- Org. Syn. Coll. Vol. 1, 237
- Org. Syn. Coll. Vol. 1, 248
- Org. Syn. Coll. Vol. 1, 272
- Org. Syn. Coll. Vol. 2, 126
- Org. Syn. Coll. Vol. 2, 137
- Org. Syn. Coll. Vol. 2, 262
- Org. Syn. Coll. Vol. 2, 287
- Org. Syn. Coll. Vol. 2, 323
- Org. Syn. Coll. Vol. 4, 291
- Org. Syn. Coll. Vol. 4, 630
Chemical Abstracts Nomenclature (Collective Index Number);
mercuric chloride double salt
hydrochloric acid (7647-01-0)
sodium hydroxide (1310-73-2)
sodium chloride (7647-14-5)
sodium ethoxide (141-52-6)
Orthoformic acid, triethyl ester (122-51-0)
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