C(C1[CH2:8][CH:7](CCC)[O:6][C:5]1=[O:12])(=O)C.[CH2:13](O)[CH:14]([OH:16])[CH3:15].[CH2:18]1[CH2:23][CH2:22][CH2:21][CH2:20]C1.C(O)C>S([O-])(O)(=O)=O.[Na+].S(=O)(=O)(O)O.[OH-].[Na+].O>[CH2:22]([CH:21]1[CH2:20][C:13]([C:5]([O:6][CH2:7][CH3:8])=[O:12])=[C:14]([CH3:15])[O:16]1)[CH2:23][CH3:18]
A mixture of 201.3 grams of crude 3-acetyl-5-propyl-dihydro-2 (3H)-furanone (1.18 mols), 90.0 grams of propylene glycol (1.18 mols), 50.3 grams of cyclohexane and 1.16 grams of sodium hydrogen sulfate were heated and refluxed for four hours. The water produced by reaction was collected in a Dean Stark trap. After refluxing for 4 hours, the cyclohexane was stripped from the reaction mixture at 80° C. and a vacuum which increased up to 20 inches vacuum. To the residue was added 271.4 grams of anhydrous ethanol (5.9 mols) and 2.8 grams of concentrated sulfuric acid. The mixture was heated to 110° C. in an autoclave for 2.5 hours. The mixture was cooled and neutralized with 2.6 grams of sodium hydroxide and stripped under 15 inches of vacuum at a temperature up to 100° C. The residue was washed with water and the organic layer separated and distilled to yield 150.2 grams of 2 -propyl-4-carbethoxy-5-methyl-2,3-dihydrofuran for a yield of 64.3 percent based on a 92.8% conversion of the Ketal. As shown in the examples, the process of the present invention provides for a high yield of the dihydrofuran product without the use of large excesses of alcohol and the formation of large amounts of by-products formed by the processes of the prior art.
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