Org. Synth. 1962, 42, 1
DOI: 10.15227/orgsyn.042.0001
ACETONE DIBUTYL ACETAL
[Propane, 2,2-dibutoxy-]
Submitted by N. B. Lorette and W. L. Howard
1.
Checked by Max Tishler and Stanley Nusim..
1. Procedure
A mixture of 312 g. (3 moles) of acetone dimethyl acetal (Note 1), 489 g. (6.6 moles) of butanol, 1.0 l. of benzene, and 0.2 g. of p-toluenesulfonic acid is placed in a 3-l. flask. The flask is connected to a packed fractionating column and the solution distilled until the azeotrope of benzene and methanol, boiling at 58°, is completely removed (Note 2). The contents of the boiler are then cooled below the boiling point and a solution of 0.5 g. of sodium methoxide in 20 ml. of methanol (Note 3) is added all at once with stirring. The flask is replaced for further distillation, and most of the remaining benzene is distilled at atmospheric pressure. The pressure is then reduced, and the remaining benzene and unreacted butanol are removed (Note 4). Finally, the pressure is reduced to 20 mm., the last traces of low-boiling materials are taken to the cold trap, and the product is distilled. After a small fore-run, acetone dibutyl acetal is collected at 88–90°/20 mm. The yield is 421–453 g. (74.6–80.3%), n25D 1.4105, d254 0.8315.
2. Notes
1.
Commercial acetone dimethyl acetal (2,2-dimethoxypropane) from the Dow Chemical Company was used without further treatment.
2.
About 570 ml. of this azeotrope is obtained. The
methanol produced may be estimated by washing an aliquot with about two volumes of water in a graduated cylinder. The
methanol content is approximately the difference between the initial volume and that of the residual
benzene phase, and about 230 ml. is obtained, depending on the efficiency of fractionation. Other hydrocarbons, e.g.,
hexane or
cyclohexane, can be used for the removal of
methanol.
The submitters' distillation was carried out in a 19 × 1200-mm. vacuum-jacketed silvered column fitted with a magnetically operated vapor-takeoff head controlled by a timed relay. The checkers found that a 19 × 340-mm. vacuum-jacketed column fitted with a magnetically operated liquid takeoff and packed with ¼-in. glass Raschig rings was sufficient for carrying out the distillation. The checkers, using a reflux ratio of 2.7 to 1 throughout the distillation, found the total time required to be 19 hours.
Since the required separations are not difficult, any reasonably efficient fractionating column may be used.
3.
Other soluble non-volatile bases may be used.
4.
It is best to keep the temperature of the distilland below 125–150°, because pyrolysis of the product becomes progressively more serious at higher temperatures. The pressure is reduced to a convenient value when the distilland temperature reaches 125°. For example, a pressure of 200 mm. will allow the condensation of the
benzene without resort to special cooling.
3. Discussion
Acetone dibutyl acetal has been prepared from
isopropenyl acetate and
butanol,
2 from
butanol and
isopropenyl butyl ether obtained from the reaction of
butanol with
propyne,
3 and by orthoformic ester synthesis.
4,5
4. Merits of Preparation
The preparation described here is a modification of previously used alkoxyl interchange reactions, but it is more convenient because the use of the azeotrope-forming solvent permits the virtually complete removal of the by-product alcohol under mild conditions. The method is general for most primary and secondary alcohols, including those with functional groups which are stable under the mild conditions used.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Benzene (71-43-2)
methanol (67-56-1)
cyclohexane (110-82-7)
butanol (71-36-3)
sodium methoxide (124-41-4)
isopropenyl acetate (108-22-5)
hexane (110-54-3)
Acetone dibutyl acetal,
Propane, 2,2-dibutoxy- (141-72-0)
acetone dimethyl acetal,
2,2-dimethoxypropane (77-76-9)
isopropenyl butyl ether
propyne (74-99-7)
p-toluenesulfonic acid (104-15-4)
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