were analyzed after 24 h on an LP-70 polarograph in a thermostated cell with a dropping mercury electrode (m =
1.59 mg/s, t = 3.66 s at potential -1.0 and 25 ± 0.2 °C) with a normal calomel electrode. Half-wave reduction
potentials: Compound 2 – 0.38-0.40; compounds 5 and 6 – 0.67; compound 7 – 1.3 V.
The concentrations of the substances in the tests were determined against calibration curves. The total
content of the acids in the reaction mixtures obtained by the oxidation of furfural in expts. 1-4 was determined
by titration. To a 0.5 ml sample of the oxidate we added 4.5 ml of distilled water. The solutions were titrated
with 0.01 or 0.1 N solutions of NaOH, depending on the concentration of protons, in the presence of an alcohol
solution of phenolphthalein.
The content of peroxides in the reaction mixtures was determined by the usual methods by cerimetric
titration of the H2O2 and iodometric determination of the total amount of peroxides [5]. The content of organic
peroxides was determined from the difference in the obtained data.
The furfural was oxidized by the following methods.
Experiment 1. To a mixture of water (30.3 ml) and hydrogen peroxide (14.7 ml, 0.192 mol) with
weight fraction 38.5% we added of the distilled furfural (5.0 ml, 0.060 mol). The mixture was stirred at 60°C
until the H2O2 and organic peroxides were completely transformed.
Experiments 2-4. The experiments were carried out by the same procedure as for expt. 1 except that the
corresponding catalyst was first added to the reaction flask – V2O5 (1.5·10−4 mol) or Nb2O5 (1.5·10−3 mol), or
Nb(OAc)2 (3·10−3 mol).
Synthesis of 2(5H)-Furanone (3). A mixture of furfural (33.4 ml, 0.3 mol), Nb(OAc)2·4H2O (0.57 g,
1.5·10−3 mol), water (133 ml), and an aqueous solution of H2O2 (30.7 ml, 0.3 mol) with weight fraction 38.5%
was stirred at 60°C for 3.5 days until the peroxides were completely transformed. The product 3 was extracted
with ether, washed with NaHCO3 solution, dried with Na2SO4, and evaporated. The residue was distilled at
reduced pressure, and 16.1 g (64%) of 2(5H)-furanone (3) was obtained; bp 90-93 °С (13 mm Hg), (bp 90-92 °С
20
20
1
(12-13 mm Hg) [19]); nD 1.4650 (nD 1.4650 [19]). The H NMR spectrum agreed with the previously
obtained spectrum [19]. Found, %: С 57.14; Н 4.79. С4Н4O2. Calculated, %: С 57.33; Н 4.96.
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