Catalytic oxidation of furan and hydrofuran compounds. 8. Conversions of 2(5H)-furanone by hydrogen peroxide in media of various pH

Article abstract of DOI:10.1023/A:1021240828432

The reaction of 2(5H)-furanone with aqueous hydrogen peroxide in media of pH within the range 1-8 have been studied in the absence of catalysts for the first time. It was discovered that at pH 3 to 8 2(5H)-furanone was almost quantitatively converted into succinic acid and reduction of the acidity of the medium facilities the reaction. A possible scheme is considered for the conversions of 2(5H)-furanone under the reaction conditions.

Full text of DOI:10.1023/A:1021240828432

Chemistry of Heterocyclic Compounds, Vol. 38, No. 9, 2002
CATALYTIC OXIDATION OF FURAN
AND HYDROFURAN COMPOUNDS.
8.* CONVERSIONS OF 2(5H)-FURANONE BY
HYDROGEN PEROXIDE IN MEDIA OF VARIOUS pH
R. I. Ponomarenko, L. A. Badovskaya, and V. M. Latashko
The reaction of 2(5H)-furanone with aqueous hydrogen peroxide in media of pH within the range 1-8
have been studied in the absence of catalysts for the first time. It was discovered that at pH 3 to 8
2(5H)-furanone was almost quantitatively converted into succinic acid and reduction of the acidity of
the medium facilitates the reaction. A possible scheme is considered for the conversions of
2(5H)-furanone under the reaction conditions.
Keywords: hydrogen peroxide, 2(5H)-furanone, succinic acid, buffer solutions.
In the previous paper we described the synthesis of 2(5H)-furanone (1) from furfural and some of its
reactions, including oxidation by the action of H2O2 in the presence of compounds of Mo(VI) and Cr(VI) at pH
1-2 , which proceeded with extreme difficulty [1].
Results are given in the present communication on an investigation of the interaction of furanone 1 with
aqueous hydrogen peroxide in media of pH 1-8 in the absence of compounds of variable valency metals. This
reaction, not studied systematically hitherto, is of independent interest for the chemistry of hydrofuranones,
particularly for raising the possibility of the selective synthesis of individual products.
The reaction of furanone 1 with H2O2 at various pH values was investigated in buffer solutions with
initial concentrations of reactants from 1.0 and 1.5 M respectively, and initial ionic strength of 3 M the same in
all experiments. The consumption of starting materials, the accumulation of products, and the final composition
of the reaction mixtures was followed by titrimetry, and also spectral methods, paper chromatography (PC), and
TLC. On carrying out the reaction in each of the pH intervals studied an appropriate temperature was
maintained sufficient for the complete conversion of furanone 1 after 5 h (see Table 1).
Reaction was not carried out at pH >8 due to the active decomposition of H2O2 under these conditions.
As is seen from Table 1 reduction in the acidity of the medium contributed to a more intensive
proceeding of the reaction. It was carried out at pH 7-8 with the most significant evolution of heat and most
readily. It is noteworthy that at pH ~1 and temperature of 100°C furanone 1 underwent no conversion.
The oxidation of furanone 1 in experiments 1-5 was completed almost quantitatively with the formation
of succinic acid. Organic peroxide was detected chromatographically in the intermediate stages of the reaction.
Succinic acid was isolated in ~60% yield of theoretical from the reaction systems. The losses of this product are
_______
* For Part 7 see [1].
__________________________________________________________________________________________
Kuban State Technological University, Krasnodar 350072, Russia; e-mail: k-obh@kubstu.ru. Translated
from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1204-1206, September, 2002. Original article
submitted March 12, 2002.
0009-3122/02/3809-1049$27.00©2002 Plenum Publishing Corporation
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TABLE 1. Conditions for the Complete Conversion of 2(5H)-Furanone (1)
after 5 h at Molar Ratio of 1 to H2O2 of 1.0:1.5
рН
Experiment
Temperature, °C
3-4
4-5
5-6
6-7
7-8
95-100
70-75
60-65
40-45
20-25
1*
2
3
4
5
_______
* Conversion was 50%.
related to the difficulty of separating it from the components of the buffer. Trace amounts of malic and an
unidentified hydroxy acid were also formed. It should be mentioned that maleic and fumaric acids invariably
accompanying furanone 1 on peroxide oxidation of furfural were not detected on oxidizing furanone 1 itself.
To explain the formation of succinic acid from furanone 1 we proceeded from the known data on its
isomerization to the less stable 2-hydroxyfuran 2 and 2(3H)-furanone 3 [2].
HO
HO
OH
HOOH, HOH
O
OH
O
1
O
2
O
HO
4
HOH
O
HOOH
HOO
O
O
–HOH
O
O
O
O
O
O
HO
OH
3
5
6
7
The irreversible conversion of isomer 1, 2, or 3 must lead to a shift in the equilibrium in that direction.
In the reaction being studied this is possible by the action of aqueous H2O2. It is known that an increase in pH
leads to growth of the nucleophilicity of H2O2 [3]. Among the isomers 1-3 the greatest reactivity in reaction with
nucleophilic reagents would be expected for lactones 1 and 3, since hydroxyfuran 2 has an increased ring
electron density. A possible product of the interaction of compound 1 with H2O2 is 2,3,4-trihydroxybutanoic
acid 4, which if formed by the reaction, then as mentioned above would be in insignificant amount together with
malic acid. We consider it most probable that succinic acid is formed by irreversible oxidation–hydrolytic
conversions of isomer 3, including the formation of hydroperoxide 5, which is converted into succinic anhydride
6, itself hydrolyzed in the reaction media to succinic acid 7.
EXPERIMENTAL
The TLC was carried out on Sorbfil plates, eluent was CHCl3, visualizing agent was acidic KMnO4
solution (for furanone 1 and the oxidized compounds), or KI solution (for peroxy compounds). Paper
chromatography (PC) was carried out on No. 2 paper, eluent was BuOH saturated with water and HCOOH,
visualizing agent was an alkaline solution of bromophenol blue (for acids) or acidic KMnO4 solution (for
hydroxy acids and unsaturated acids). The IR spectra were obtained on an UR 20 spectrometer in nujol. The
total acidity was determined by alkalimetric titration with thymolphthalein.
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Oxidation of 2(5H)-Furanone (1). Aqueous solution (10 ml) of furanone 1 (5.0 g, 60 mmol) was
stirred with 30% aqueous solution of H2O2 (50 ml, 10.2 g, 90 mmol), KOH (6.7 g, 120 mmol), and H3PO4
(86 wt, %; 6.8 g, 60 mmol). The reaction was carried out at pH 7-8 until complete consumption of compound 1
(TLC). To maintain the pH in the prescribed range the acid formed was neutralized periodically by adding
aqueous KOH (12 M). Test samples for the analysis of total acidity, TLC, and PC were taken directly after
mixing the reactants, then after 15, 30, 75, 150, and 300 min.
When oxidizing furanone 1 in the pH ranges 6-7, 5-6, 4-5, and 3-4 the amount of KOH was reduced to
5.9 g (105 mmol), 5.0 g (90 mmol), 4.2 g (75 mmol), and 3.4 g (60 mmol) respectively, but for establishing the
same initial ionic strength 1.1 g (15 mmol), 2.2 g (30 mmol), 3.4 g (45 mmol), and 4.5 g (60 mmol) of KCl
respectively were introduced into the solutions. When oxidizing 1 at pH ~1 KOH was not added to the buffer.
Isolation of Reaction Products. For experiments 2-5 H3PO4 was added to the oxidized mixtures to
pH 1 and water was distilled off under vacuum. The residue was treated with hot EtOH (100 ml) and insoluble
KH2PO4 was filtered off. The filtrate was evaporated under vacuum, and the residue recrystallized from water
(20 ml). Succinic acid 7 (4.1-4.3 g, 58-61% of theory) was obtained; mp 182-185°C (lit. [4] mp 185°C), Rf 0.80
(PC), which agrees with the Rf of a known sample. The IR spectrum was identical to that given previously in [5].
In the reduced oxidates traces of malic acid (Rf 0.43) and an unknown hydroxy acid (Rf 0.57), possibly
2,3,4-trihydroxybutanoic acid 4, were detected in addition to acid 7 and H3PO4 by PC.
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