Organic Syntheses, Coll. Vol. 1, p.401 (1941); Vol. 3, p.83 (1923).
To a mixture of 500 g. (5.3 moles) of chloroacetic acid
and 500 g. of cracked ice, is added, with stirring, just sufficient cold 40 per cent sodium hydroxide
solution to make the solution faintly alkaline to phenolphthalein
. About 360 cc. is required; the temperature should not rise above 20° (Note 1)
. The solution is then mixed with 365 g. (5.3 moles) of sodium nitrite
dissolved in 500 cc. of water and heated in a 3-l. round-bottomed flask
fitted with a two-holed stopper
containing a bent tube of large diameter
connecting with an efficient condenser
(set downward for distillation) and a thermometer
dipping into the liquid. The receiver
should be so arranged that it can be cooled, if necessary, by a stream of water.
The solution is heated slowly until the first appearance of bubbles of carbon dioxide
, which occurs when the temperature has reached about 80°. The flame is then removed and the reaction allowed to proceed by itself (Note 2)
. If no rise in temperature occurs, heat is very cautiously applied until the temperature rises to 85°, when the flame is again removed (Note 3)
. At this temperature the exothermic decomposition of the sodium nitroacetate
becomes so rapid that the temperature rises almost to 100° without further application of external heat. If heat is applied after the temperature of the liquid reaches 85°, violent frothing will occur, with serious loss of nitromethane
. If the reaction becomes too vigorous it may be checked by applying a wet towel to the flask. Nitromethane
starts to distil over at about 90°. During the spontaneous heating, about 120 cc. of nitromethane
distils over, accompanied by about 170 cc. of water (Note 4)
. This water is saved for redistillation.
When the mixture ceases to maintain its temperature spontaneously at 95–100°, heat is applied cautiously until the temperature reaches 110°. About 13 cc. of nitromethane
and 200 cc. of water distil over. Further distillation gives water which contains too little nitromethane
to pay for recovery. At this point enough sodium chloride
and sodium carbonate
have separated to cause serious bumping.
The water separated from the nitromethane
distillates is mixed with one-fourth of its weight of salt, and redistilled, yielding 10–12 cc. of nitromethane
and about 100 cc. of water. This water on distillation gives 3–4 cc. of nitromethane
and about 45 cc. of water (Note 5)
The total yield of moist product is 125–135 g.
; on drying with a little calcium chloride
and distilling, 115–125 g.
of pure nitromethane
, boiling at 98–101°
, is obtained (35–38
per cent of the theoretical amount). A small forerun distils over below 98°, and a little dark brown residue remains (Note 6)
The thermometer dipping in the liquid
is absolutely necessary, as the success of the preparation depends on proper temperature control. The vital point of the whole preparation is to remove all external heat as soon as the reaction is well started. This is between 80 and 85°. No frothing ever occurs when this precaution is rigidly adhered to.
Several of these distilling sets can be set up and run by one operator, if each lot is started only when the preceding one has reached 85° and external heat has been removed. The corresponding water layers from different sets can be united and distilled at once.
It has been recommended1
that use be made of a gravity separator
connected with the adapter
in order to separate the nitromethane
as fast as it condenses. It was found inadvisable to use such a separator, as the nitromethane
is so little heavier than water that a rapid separation is not possible; drops of nitromethane
remain suspended and pass over with the water. It is best to allow the distillates to stand in cylinders
for at least one-half hour before separating the nitromethane
by means of a separatory funnel
. During this standing, as much as 2
per cent more of nitromethane
sometimes settles out.
If the time consumed is an important consideration, it is well to note that the spontaneous heating from 85° to 100° gives three-fourths of all the nitromethane
obtained in the preparation. This takes less than one hour. The further heating above 100° and the distillations of the water layers take over two hours, and give only one-fourth of the total yield.
It is suggested that improved yields are obtainable when 374 g. of crystalline boric acid
is added subsequent to the sodium nitrite
and prior to the heating. In this way, carbon dioxide together with some oxides of nitrogen
are evolved at about 45°. The reason offered for the higher yields is the destruction of sodium bicarbonate
by the boric acid
, which thereby prevents alkaline hydrolysis of the sodium chloroacetate
(C. L. Tseng, private communication; 2
The yield is somewhat improved by using 625 g. of chloroacetic acid
and about 450 cc. of 40 per cent sodium hydroxide
solution instead of the 500 g. and 360 cc., respectively, now specified (H. Adkins, private communication; 2
This preparation is referenced from:
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