Org. Synth. 1952, 32, 57
DOI: 10.15227/orgsyn.032.0057
4,6-DIMETHYLCOUMALIN
[Sorbic acid, 5-hydroxy-3-methyl, δ-lactone]
Submitted by Newton R. Smith and Richard H. Wiley
1,2.
Checked by R. S. Schreiber and H. H. Fall.
1. Procedure
In a
125-ml. Claisen flask, equipped with a capillary for vacuum distillation and a
thermometer, are placed
50 g. (0.3 mole) of isodehydroacetic acid (p. 549) and
2 g. of copper powder (Note 1). A 125-ml. simple distilling flask, cooled by a
water jet, is used as a vacuum receiver and is attached to a
water aspirator. The Claisen flask is heated at atmospheric pressure in an
oil bath at 230–235° for 45 minutes or until the decarboxylation has ceased. The pressure on the system is then slowly reduced, and the
dimethylcoumalin is distilled directly from the reaction flask
(Note 2). The crude
dimethylcoumalin (
34–35 g.,
92–95%) is redistilled from a Claisen flask. The yield of
4,6-dimethylcoumalin is
30–32 g. (
81–87%); b.p.
140–142°/35 mm. (Note 3); m.p.
50–51°.
2. Notes
1.
Copper chromite catalyst may be substituted.
2.
The submitters recommend 3 hours for decarboxylation. At 45-minute intervals the pressure on the system is reduced and the
dimethylcoumalin distilled directly from the reaction flask. After the distillation slackens, the pressure is returned to atmospheric and the decarboxylation is continued. However, the checkers found that the decarboxylation is virtually completed during the first 45-minute period.
3.
The checkers observed a boiling point of
134–136°/35 mm. for 4,6-dimethylcoumalin. The melting point, however, was identical with that reported by the submitters.
3. Discussion
4,6-Dimethylcoumalin has been prepared by the decarboxylation of
isodehydroacetic acid in
sulfuric acid or by heating,
3 and by the distillation of
4-methyl-2-pyrone-6-acetic acid.
4
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
4,6-Dimethylcoumalin
Isodehydroacetic acid
sulfuric acid (7664-93-9)
copper powder (7440-50-8)
COPPER CHROMITE
Sorbic acid, 5-hydroxy-3-methyl, δ-lactone (675-09-2)
dimethylcoumalin
4-methyl-2-pyrone-6-acetic acid
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