Organic Syntheses, Coll. Vol. 1, p.42 (1941); Vol. 1, p.15 (1921).
In a 5-l. round-bottomed flask
are placed 2 kg. (1587 cc., 21.7 moles) of glycerol
and 700 g. (585 cc., 12.9 moles) of technical 85 per cent formic acid (Note 1)
. The flask is connected with a condenser
set for downward distillation and the temperature within the reaction mixture is indicated by a thermometer
, the bulb of which is immersed in the liquid. It is advisable to use as a receiver
a distilling flask
attached tightly to the lower end of the condenser. A tube is then run from the side arm of the distilling flask to a bottle of strong caustic soda
to dissolve and decompose any acrolein
which may be formed; a few pieces of clay plate
are added to the distillation flask containing the reactants in order to prevent bumping, and it is then heated rapidly
over a good ring burner (Note 2)
. The first runnings should come over within fifteen minutes and a temperature of 195° should be reached in thirty to forty-five minutes. Slow heating causes charring and formation of much acrolein
, and thus gives a very low yield of allyl alcohol
. The distillate collected up to the point where the thermometer registers 195° is saved separately (Note 3)
. Heating is continued until the temperature reaches 260°, the main reaction taking place between 225° and 235°. At 260°, when the heating should be stopped, a white smoke appears and decomposition apparently begins. The distillate (about 750 cc.) coming over between the thermometer readings between 195° and 260° is saved. For this operation about four hours are required.
The contents of the flask are now allowed to cool to a temperature between 100° and 125°, and 500 g. (9.2 moles) more of the technical 85 per cent formic acid
is added. The distillation is then repeated in exactly the same manner as described above and 500 cc. of distillate is collected between the temperatures from 195–260°. The reaction mixture is allowed to cool again and a third portion of 500 g. of formic acid
is added. This distillation yields not more than 350 cc. of the desired fraction, indicating that the glycerol
is used up and that further addition of formic acid
is unnecessary; moreover, the residue left behind is now small, amounting only to 100–200 cc. The three distillations require from one to one and one-half days.
The alcohol may be made practically anhydrous by refluxing with successive portions of fused potassium carbonate
until no further action is observed. The carbonate
will remain finely divided and will not become sticky when water is absent. A considerable amount of allyl alcohol
is lost mechanically during the drying in this way, so that the potassium carbonate
which is used here should be employed for the salting out of fresh portions of allyl alcohol
in the first part of subsequent preparations. The allyl alcohol
thus produced is dry enough for all practical purposes (98–99 per cent), and it is unnecessary to dry with lime or barium oxide
as advised in the literature in order to remove all the water. The allyl alcohol
obtained by this process boils at 94–97°
The checkers have used the following method with success for obtaining a completely anhydrous product. The allyl alcohol
obtained after one salting out with potassium carbonate
is distilled as indicated above to give a product of about 70 per cent purity and then mixed with one-quarter of its volume of carbon tetrachloride (Note 6)
. The mixture is then slowly distilled from a round-bottomed flask fitted with a fractionating column at least 80 cm. long
, collecting the low-boiling mixture of carbon tetrachloride
, water, and allyl alcohol
, drying it with potassium carbonate
, and returning it to the flask (Note 7)
. This process is repeated several times, until only very little water passes over. The mixture is then completely distilled, taking the following cuts: Up to 80°, 80–90°, 90–95°, 95.5–97°, the last being alcohol
which titrates 100 per cent pure. The lower fractions are dried separately and refractionated, thus giving an additional portion boiling at 95.5–97°
Unless heating is rapid, the yields are very unsatisfactory.
The lower fraction which distils up to the point where the thermometer registers 195° contains a considerable amount of formic acid
, and in large-scale production it would undoubtedly pay to recover it.
When the crude allyl alcohol
is distilled from a steam bath
under reduced pressure, the distillate is considerably richer in allyl alcohol
(sometimes up to 90 per cent). The strength can be readily determined by measuring the specific gravity and comparing with the following figures:
Per cent allyl alcohol..
Density at 20°.......
The best results are obtained when working at a pressure of 200–300 mm. Some boiling points of the watery alcohol are: 60°/200 mm., 70°/300 mm., and 78°/500 mm.
A large amount of work was carried out upon the oxalic acid
method for the production of allyl alcohol
. The results were not satisfactory and therefore are not included here. It might be said, however, that, when oxalic acid
is used in place of formic acid
, the reaction requires a longer time for completion and is not nearly so smooth. There is a much greater tendency toward foaming and the reaction must be continually watched in order to prevent this, especially after the first distillation with oxalic acid
, when more oxalic acid
is added and heating is continued. Another disadvantage is that large amounts of acrolein
are produced when oxalic acid
is used. In general, the yield by this method amounts to not over 20–30
per cent, whereas with formic acid
a yield of 45–47
per cent is easily obtained. As far as the preparation of allyl alcohol
is concerned, in amounts such as are used in the above experiments, the formic acid
method is greatly to be preferred. The method of employing anhydrous oxalic acid
, which has been reported as giving particularly good yields, did not give satisfactory results when tried.
The apparatus described on p. 262
may be used for these operations.
The two most practical methods for the preparation of allyl alcohol
are by the action of either formic1
or oxalic acid2
. Both methods have been studied, and the formic acid
method has been shown to be much the superior. Improved yields are obtainable3
by reworking the fractions obtained in accordance with the procedure described in this volume, but such improvement was found to be only 2 per cent in an experiment carried out by one of the editors.
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