Org. Synth. 1952, 32, 79
DOI: 10.15227/orgsyn.032.0079
β-KETOISOÖCTALDEHYDE DIMETHYL ACETAL
[Heptanal, 6-methyl-3-oxo-, 1-dimethyl acetal]
Submitted by Charles C. Price and Joseph A. Pappalardo
1.
Checked by R. S. Schreiber, Wm. Bradley Reid, Jr., and R. W. Jackson.
1. Procedure
A dry
1-l. three-necked flask fitted with a
mercury-sealed stirrer, a
calcium chloride drying tube, and a
500-ml. dropping funnel, protected by a calcium chloride drying tube, is surrounded by an ice-salt mixture at −11°. Anhydrous
methanol (130 ml.) (Note 1) and
(Note 2) and
161 g. (1 mole) of β-chlorovinyl isoamyl ketone (
p. 186) are poured into the flask
(Note 3). A solution of
43 g. (1.04 moles) of sodium hydroxide (97%) and
350 ml. of absolute methanol (Note 4) is added dropwise with stirring over a period of 2 hours, during which time the bath temperature is kept between −11° and −8°.
The reaction mixture is poured, with stirring, into 1 kg. of a saturated sodium chloride solution (Note 5). The mixture is extracted with four 100-ml. portions of low-boiling petroleum ether. The extracts are combined and dried over anhydrous potassium carbonate. The liquid is decanted, the potassium carbonate is washed with 25 ml. of low-boiling petroleum ether, and the solution is added to the main fraction. A pinch of anhydrous potassium carbonate is added to the petroleum ether solution, and the solution is then distilled from a Claisen flask to give a colorless liquid; yield 151–169 g. (80–90%); b.p. 122–125°/25 mm.; nD25 1.4260; d425 0.932 (Note 6).
2. Notes
1.
Absolute methanol (C.P. grade) was used.
2.
The checkers ran this preparation at one-third the scale described here and obtained equivalent results.
3.
When this procedure is used to make the
dimethyl acetal of
β-ketobutyraldehyde, the
methanol and
β-chlorovinyl methyl ketone must be mixed quickly and cooled well. If these two liquids are placed in the same flask without immediate cooling and mixing, the ketone may decompose rapidly with the evolution of heat and large amounts of
hydrogen chloride.
4.
It takes about 1 hour of shaking to dissolve the
sodium hydroxide pellets.
5.
If this reaction is used to prepare the water-soluble
dimethyl acetal of
β-ketobutyraldehyde, the product of the reaction is not poured into the saturated
sodium chloride solution. Instead, the
methanol solution is filtered from the
sodium chloride and distilled.
6.
The product darkens a little on standing but undergoes no change in refractive index.
3. Discussion
The preparation described
2 has been used by Nelles
3 to make a variety of β-ketoacetals.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
petroleum ether
dimethyl acetal
potassium carbonate (584-08-7)
hydrogen chloride (7647-01-0)
methanol (67-56-1)
sodium hydroxide (1310-73-2)
sodium chloride (7647-14-5)
β-ketobutyraldehyde
β-Chlorovinyl isoamyl ketone (18378-90-0)
β-chlorovinyl methyl ketone
Heptanal, 6-methyl-3-oxo-, 1-dimethyl acetal
β-Ketoisooctaldehyde dimethyl acetal (53684-58-5)
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