Org. Synth. 1925, 5, 23
DOI: 10.15227/orgsyn.005.0023
n-BUTYL n-BUTYRATE
[Butyric acid, butyl ester]
Submitted by G. Ross Robertson
Checked by Henry Gilman and J. E. Kirby.
1. Procedure
In a 2-l. flask fitted with a mechanical stirrer, a thermometer, and a separatory funnel, are placed a cool solution of 240 cc. (4.3 moles) of commercial sulfuric acid (sp. gr. 1.84) in 240 cc. of water, and 240 g. (296 cc., 3.24 moles) of technical n-butyl alcohol (Note 1). The whole is placed in a large, efficient ice-salt bath.
A solution of 320 g. (1.07 moles) of crystalline sodium dichromate (350 g. of the ordinary moist technical hydrated salt is also suitable) in 200 cc. of water is dropped from the funnel into the vigorously stirred alcohol mixture as rapidly as can be done without running the temperature above 20°. When most of the dichromate has been added, the viscosity of the reaction mixture becomes so great that the stirring is rendered inefficient. The temperature is now allowed to rise to 35° if necessary (Note 2), to accelerate the reaction.
The resulting green sirupy emulsion is diluted with an equal volume of water, whereupon 220–225 cc. of an oil containing the desired ester (Note 3), slowly separates. This oil is washed three times with water, separated, and treated with a few grams of anhydrous sodium sulfate in order to remove most of the water. It is now distilled slowly through a large, efficient fractionating column. The fraction boiling at 150–170° is collected, and should amount to 170–175 cc. It is washed with five 15-cc. portions of 60 per cent sulfuric acid (sp. gr. about 1.5) (Note 4), is then washed free of acids with dilute sodium hydroxide, and finally washed free of alkali with cold water. It is rapidly dried, as before, with sodium sulfate, and fractionated through the same distilling column. The fraction boiling at 162–166° (uncorr.) consists of n-butyl n-butyrate, containing a small percentage of residual butyl alcohol. The yield is 96–110 g. (41–47 per cent of the theoretical amount).
If higher purity is desired, the fractionation must be repeated. An additional yield may be secured by further fractionation of the lower-boiling fractions (Note 5) and (Note 6).
2. Notes
1.
When
n-butyl alcohol is oxidized to
butyric acid in the presence of a high concentration of
sulfuric acid, esterification takes place at once, even in the cold, as long as an excess of the
alcohol is present.
2.
If the temperature of the reaction mixture is allowed to rise much above 35°, considerable material escapes in the form of
butyraldehyde (b.p.
74°).
3.
The oil obtained as the first crude product contains, in addition to the desired ester, much unchanged
butyl alcohol, a little
butyraldehyde, and a little free
butyric acid.
4.
The
60 per cent sulfuric acid is chosen as a wash liquid because it is miscible with
butyl alcohol but not with the ester. The volatile aldehyde disappears in the two fractionations, while the
butyric acid is removed by the alkali.
5.
The low-boiling fractions could no doubt be returned to a new batch if this process were carried out repeatedly in quantity production. About 25 per cent of the original
butyl alcohol can be recovered if desired. The very small fractions boiling above 166° may contain esters of other alcohols occurring in the technical product used, and possibly
butyl succinate and related by-products.
6.
It is suggested that improved yields are obtainable when
2 moles of n-butyl alcohol
are added to
0.62 mole of crystallized sodium dichromate and
5.1 moles of concentrated sulfuric acid. The temperature is kept between 30° and 40° during the addition, and then the mixture is heated on the steam bath (90–100°) for two to six hours until the supernatant liquid is practically colorless. The mixture is then worked up as described (W. J. Hickinbottom, private communication;
1).
3. Discussion
n-Butyl n-butyrate can be prepared by the interaction of
n-butyl alcohol and
n-butyric acid in the presence of
sulfuric acid;
2 by the action of
aluminum butoxide on
butyraldehyde;
3 by oxidizing
n-butyl alcohol with
sodium dichromate and concentrated
sulfuric acid;
1 and by oxidizing
n-butyl alcohol with
sodium chlorate and dilute
sulfuric acid with
vanadium pentoxide as a catalyst,
4 a reaction which may lead to violent explosions if the
sodium chlorate is replaced by
potassium chlorate and if the temperature is not carefully controlled.
5 A number of catalytic procedures, more suitable for industrial than laboratory operation, have been described for preparing
n-butyl n-butyrate by esterification,
6 or from
butyric acid and
hydrogen,
7 or from
n-butyl alcohol alone.
8
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
alcohol (64-17-5)
sulfuric acid (7664-93-9)
hydrogen (1333-74-0)
sodium hydroxide (1310-73-2)
dichromate
sodium sulfate (7757-82-6)
vanadium pentoxide
butyl alcohol,
n-butyl alcohol (71-36-3)
Butyric acid, butyl ester,
n-BUTYL n-BUTYRATE (109-21-7)
sodium dichromate (7789-12-0)
butyric acid,
n-butyric acid (107-92-6)
butyraldehyde (123-72-8)
butyl succinate (925-21-3)
aluminum butoxide
sodium chlorate (7775-09-9)
potassium chlorate (3811-04-9)
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