Organic Syntheses, Coll. Vol. 1, p.358 (1941); Vol. 1, p.57 (1921).
One kilogram (2.5 moles) of iodoform (Note 1)
is placed in a 5-l. round-bottomed flask fitted with a rubber stopper holding a mechanical stirrer (Note 2)
, a reflux condenser
, a separatory funnel
, and a thermometer with bulb immersed in the liquid
. To this is added 500 cc. of the sodium arsenite
solution [prepared from 274 g. (1.38 moles) of c. p. arsenious oxide, 532 g. (13.3 moles) of sodium hydroxide
, and 2600 cc. of water] (Note 3)
. Stirring is started, and heat is applied until the temperature of the thermometer reaches 60–65°, where it is held constant during the whole reaction (Note 4)
. If the temperature is allowed to go much higher, especially at the beginning of the experiment, the reaction becomes too vigorous, and at the same time a little methyl iodide
is formed. The remainder of the sodium arsenite
solution is added gradually during the course of one-half hour. The whole mixture is then kept one hour at 60–65° to make sure that the reaction is completed.
The reaction mixture is allowed to cool somewhat (to about 40°) and is filtered with suction in order to remove the mechanical impurities which have come from the technical arsenious oxide
and sodium hydroxide
. The filtrate consists of a clear water solution with a pale yellow oil underneath. It is better not to allow the reaction mixture to cool completely before filtering or else a precipitate of sodium arsenate
will gradually separate and this will tend to make an emulsion of the methylene iodide
and hinder filtration and separation. The methylene iodide
is now separated from the filtrate, dried with a little calcium chloride
, and then distilled under reduced pressure. Practically all of it (Note 5)
comes over as a light straw-colored oil between 106° and 107°/70 mm. (Note 6)
, the bath being kept at 130–135°. The yield of crude product is 610–660 g.
per cent of the theoretical amount). On redistillation not more than 10–20 g. is lost. The crude product is quite satisfactory for most purposes.
Experiments were made on 100-g. lots of iodoform
, using varying amounts (between 1 mole and 2 moles) of sodium arsenite
. The yield is, in general, best when only a very slight excess over 1 mole of arsenious oxide is used. In every case the amount of sodium hydroxide
employed was that called for by the theory.
In making methylene iodide
from 100-g. or even 200-g. lots of iodoform
, the sodium arsenite
solution may be added all at once. When the runs become larger, however, it is inadvisable to do this, and directions similar to those described above in running 1 kg. of iodoform
must be used.
Mechanical stirring is quite necessary in order to get the best yields in the shortest time.
The dilution of the solution makes very little difference, the yields remaining about the same. It is, therefore, better to use as concentrated a solution as possible so that large runs may be made in a comparatively small apparatus. A more concentrated solution, however, than the one advised above is not satisfactory, since too much sodium arsenate
tends to separate out during the cooling after the methylene iodide
has formed and causes some trouble in the purification. If sodium arsenate
does separate, the methylene iodide
is obtained either by distilling with steam, or by diluting and boiling to dissolve the crystals, this last to be followed by filtering and separating.
If the reaction is carried out at refluxing temperature instead of at 60–65°, the yield of product is diminished by 5–10 per cent, the formation of a little methyl iodide
accounting for the loss.
After distillation under reduced pressure, a residue of 1 to 2 g. is left in the flask. When air is admitted to the flask, a single flash of light sometimes occurs. In one case, the thermometer and stopper were even blown out of the flask. The cause was not determined.
The methylene iodide
obtained after distillation under reduced pressure melts at 6°.
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