Organic Syntheses, Coll. Vol. 2, p.414 (1943); Vol. 10, p.78 (1930).
In a 500-cc. Pyrex flask
, fitted with a cork
which loosely carries a glass mechanical stirrer
and a separatory funnel
, are placed 90 g. (1 mole) of anhydrous oxalic acid (Org. Syn. Coll. Vol. I, 1941, 421)
and 100 cc. (79 g., 2.5 moles) of methanol (Note 1)
. Then, while the mixture is rapidly stirred, 35 cc. of pure concentrated sulfuric acid (Note 2)
is slowly added through the separatory funnel. The mixture is heated, if necessary (Note 3)
, nearly to boiling, then filtered as rapidly as possible through a 15-cm. filter paper
placed in a slightly heated glass funnel
, the filtrate being collected in a 500-cc. wide-mouthed Erlenmeyer flask
. The first flask is rinsed with 40 cc. of hot methanol
, which is poured through the filter paper. After twenty-four hours at 15° (Note 4)
the crystals are filtered with suction, sucked as dry as possible, pressed between filter paper, and air-dried for a few minutes. The filtrate, after cooling to about −10°, is filtered rapidly and the product dried as before. A total of 100–115 g.
of material, slightly moist with sulfuric acid
and melting at 50–52°
, is obtained.
For purification, the crude product is dissolved in 100 cc. of redistilled methanol
, filtered through a warm funnel
, and allowed to crystallize. After several hours the crystals are filtered, and the filtrate is chilled and filtered as before. A total of 80–90 g.
per cent of the theoretical amount) of methyl oxalate
, melting at 52.5–53.5° (Note 5)
, is obtained.
used is the commercial (almost acetone-free) grade known as Columbian Spirits. This material is redistilled for recrystallizing the methyl oxalate
Less sulfuric acid
than that employed gives a smaller yield; larger quantities sometimes result in a product that causes difficulty in filtration. It is essential that the acid be added slowly and with vigorous stirring to prevent local superheating and darkening of the solution and product. Some commercial grades of methanol
become quite dark in contact with sulfuric acid
. The grade of methanol
used here does not discolor, the filtrates being only light yellow.
Solution of the oxalic acid
causes a sharp drop in temperature whereas solution of the sulfuric acid
raises the temperature.
The major portion of the reaction is complete within a few minutes, but several hours are necessary for complete crystallization.
Larger batches give the same percentage yield as the one described. When several batches are to be run, the alcohol from the first recrystallization becomes the starting alcohol for the second batch, etc. This increases the yield somewhat.
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