Tetrah.&~r~ Vol. 48. No. 45. pp. 9999-10002.1992 00404020192 smo+.oo

Printed in Great Britain 0 1992 Pergmon Re.ss Ltd

Oxidation of Acetylene to Glyoxal by Dilute Hydrogen Peroxide

Francesco P. Ballistreria, Salvatore Faillab and Gaetano A. Tomase.lli*a

bipartitnento S&me Chit&be, University of Catania, V.le A. Doria 6, Catania, Italy 95125 htuto Chico, Facolth Ingegneria, University of Catania, V.le A. Doria 6, Catania, Italy 95125

(Received in UK 11 September 1992)

Absbacr: Acetylene is oxidized to glyoxal by dilate hydrogen peroxide at 25°C in the presence of bio(VI) or W(VI) salts

as catalysts and mercutic acetate as co-catalyst.

Alkynes, as compared with alkenes, are much less reactive toward oxidizing reagents. As an example, the parent

compound of the series, i.e. acetylene, is oxidized to glyoxal in the presence of catalytic amounts of nitrogen oxides

at 170-250°C’. This is unfortunate, since oxidation of acetylene to glyoxal under mild conditions would be an

attractive synthetic procedure.

Glyoxal is achemical with many industrial applications, e.g. cross-linking agent in paper, photographic or textile

industries. In addition it represents a very useful synthon for heterocyclic chemistry because the presence of two

adjacent carbonyl functionalities.

Recently we found that peroxomolybdenum and peroxotungsten complexes, either isolated or formed in situ

by addition of hydrogen peroxide to a suitable metal precursor, behave as efficient oxidants of both internal and

terminal alkynes provided that the reactions are carried out in the presence of mercuric salt~~‘~‘~. In the absence of

the mercuric catalyst no oxidation process takes place5. Usually 1,Zdicarbonyl compounds are obtained although,

in some cases, carboxylic acids resulting from the cleavage of the triple bond are also produced.

To enlarge the synthetic scope of this novel oxidizing system, e.g. Mo(VI)- or W(VI)-peroxocomplexes in the

presence of mercuric salts, we have developed the procedure described in this paper which allows the oxidation

of acetylene to glyoxal under very mild conditions.

Results and Discussion

In our method acetylene is simply bubbled at room temperature for a fixed time interval, typically 30 min,

through an aqueous solution containing dilute hydrogen peroxide, an Mo(V1) or W(V1) derivative and

Hg(OCOCHs)2.

The pertinent data, referring to a series of metal precursors, ranging from simple salts to heteropoly acids, are

reported in Table 1. The results collected in the Table indicate that the yields in oxidation products, based on the

acetylene converted, are also reasonably good.

A comment on the selectivity of the reaction is in order. Together with the desired product glyoxal, which is in

most of the experiments the major one, formic acid is produced.

We have tested the possibility that formic acid might be yielded by subsequent oxidation of the glyoxal formed

10000 F.P. BALLISTRERI~~~~.

in the reaction mixture.

Table 1. Oxidation of acetylene with dilute hydrogen peroxide in aqueous solvents at 25Ca.

Exp. Catalyst

n. (mmol)

Glyoxalb’d Formic acidcsd Hz02 consumed’ Solve&

(yields,%) (yields,%) (mmol)

1 NazMo04.2HsO (2.0) 53 35 18 HsO/Dioxane

2 NasWO4.2HzO (2.0) 62 24 20 HzO/Dioxane

3 HsPMot20m (1.0) 42 43 19 HzO/Dioxane

4 H3pw12040 (1.0) 48 48 20 HaO/Dioxane

5 NasMo04.2HzO (2.0) 60 21 18 H20

6 Na2WOe2HzO (2.0) 51 33 18 H20

7 HsPMo12040 (1.0) 63 26 20 H20

a Reaction time is 30 min for all the reactions. b Yields were determined by titration and by weighing the isolated 2,4- diaitrophenyl hydrazone derivative; the agreement, between the two determinations, is within 5%. ’ Yields were obtained detemUning the ethyl ester derivative by g.1.c. d Percentages of oxidation products are referred to 10 mmoles of converted acetylene. e In all the reactions 6 mmoles of Hg@COCH~)2 and 100 mmoles of HzOz were used throughout. f 40 ml of dioxaue and 20 ml of water or 60 ml of water.

Therefore we have oxidized glyoxal under the same conditions adopted for acetylene oxidation. The pertinent

results are shown in Table 2.

Table 2. Oxidation of glyoxal with dilute hydrogen peroxide in dioxane/water (40/20) at 25 oCa’b.

Exp.

n.

Glyoxal disappearedC

(mmol)

Formic acidd

(mmol)

8 4.0 6.9

9 4.0 7.7

10 4.3 7.8

aReaction time is 30 min. % all the reactions 10 mmoles of glyoxal, 2 mmoles of NazMoO4.2HzO. 6 mmoles of Hg(OCOCH3h and 100 mmoles of Hz02 were used throughout. CDetermined by titration. dEvaluated by determining the ethyl ester derivative

Oxidation of acetylene to glyoxal loo01

The data obtained point out that glyoxal is oxidized to formic acid according to the following stoichiometry (eq

1):

eat. H + HaOa - 2 OH (1)

Since reaction (1) seems to display a rate slower than or comparable to that of acetylene oxidation during given

time, it might be reasonable to suppose that this might be also the route leading to formic acid formation in the

process of acetylene oxidation.

In such a case an estimate of the yields of the fmal oxidation product8 with respect to the Hz02 consumed gave

values in the range 60-70%6. Blank experiments indicated that, under the adopt ed experimental conditions, Hg”

catalyzed decomposition of oxidant species may occur in some extent and may be therefore responsible of these

estimated yields.

Surprisingly enough, the yields are little affected by the nature of the metal precursor, even in the case of

heteropoly acids. This likely bears some relevance as far as the mechanism of the oxidation and, in particular, the

role of the mercuric salt is concerned.

Some work relative to the oxidation of organic sulphides to sulphoxides showed a catalytic effect by the mercuric

salt as arising from an electrophilic interaction of this salt with the oxygen atoms of the peroxometalcomplex in

the transition state7. The electrophilic catalysis taking place in the transition state might reduce the selectivity of

the different oxidant species.

However, the not very high, even if good, selectivity of the process is overcome by the great ease of the

procedure, including use of water as solvent.

Although the results presented here are not optimized and improvements are certainly possible our procedure

may be considered, to the best of our knowledge, the easiest way to obtain a dilute aqueous solution of glyoxal’.

Acknowledgements. This research was carried out in the frame of “Progetto Finalizzato Chimica Fine II”.

Financial support by CNR and also by MURST is gratefully acknowledged.

EXPERIMENTAL SECTION

Materials. Dioxane (Carlo Erba, RPE-ACS) was distilled before use, whereas Hz02 (35%) (Carlo Erba, RPE),

formic acid (Carlo Erba, RPE) and glyoxal (30 wt.% solution in water, Ega-Chemie) were used as received.

Na2Mo04.2Hz0, Na~W0~.2Hz0,12Mo0s.HsP0~.xH~0,12W0s.HsP04.xHz0, Hg(OCOCHs)2 (Aldrich, ACS)

were used without further purification. Acetylene is a highly pure commercial sample (99.99%) from SIO.

Instrumentation

GLC analysis was carried out on a Perkin-Elmer 8420 gas chromatograph equipped with a flame ionization

detector and program capability. Proton NMR spectra were recorded in CDClslDMSO with tetramethylsilane as

internal standard using a Bruker WP-80 MHz spectrometer. MS analyses were performed by using a double focus

ing Kratos MS 50s instrument equipped with the standard EI source and a DS 90 data system.

10002 F. P. BALLISTRERI er al.

Oxidation procedure

All oxidation reactions were performed under argon at room temperature. In a typical experiment acetylene was

bubbled, for a fmed time interval, in a three-necked 500 ml round bottom flask, equipped with an air liquid cold

finger, through a 60 ml aqueous solution containing hydrogen peroxide (100 mmoles), an Mo(VI) or W(V1)

derivative (2 mmoles) and Hg(GCGCH3)z (6 mmoles). The amount of acetylene taken up by the solution was

evaluated by measuring the volumes of acetylene introduced and recovered by means of a gas burette. Routinely

20 mmoles of alkyne were added over a period of 30 min and 8-10 mmoles of unreacted substrate are collected.

Thus, ca. 50-608 of the substrate, i.e. lo-12 mmoles, under our conditions, dissolve in the oxidizing solution.

The evaluation of reaction products was performed on 27 ml of solution in the following way, after destruction of

the unreacted oxidant by triphenylphosphine.

Glyoxal was determined gravimetrically as 2,4- dinitrophenylhydrazone in a 20 ml aliquot. The aliquot was

added to a 2,4-dinitrophenylhydrazine solution, obtained dissolving 1 g of 2,4-dinitrophenylhydrazine in 5 ml of

HzS04 (98%) and 30 ml of EtOH (95%); the precipitate was filtered, dried and weighed: C14HroNsOs, red crystals,

m.p. (nitrobenzene) 323-324°C; ‘H NMR, 6 (CDCl$DMSO 50/50), 7.95-8.93 (m, 6H, aromatic protons), 8.53 (s,

2H, CH), 11.9 (s, 2H, NH); MS spectrum9 (EI, 70 eV), m/z 418 (M+, 67), 236 (30), 183 (loo), 164 (55), 153 (50),

30 (60).

Glyoxal was also determined by Cannizzaro reaction” treating another aliquot of 2 ml of the reaction mixture

with a known excess of NaOH (20 ml, 0.05 N). After 10 min, 10 ml of HCI (0.1 N) were added and the excess of

HCl was back titrated by NaOH (0.05 N), using phenophtalein as indicator. The agreement between the two

determinations was within 5%.

Formic acid was determined in the last aliquot of 5 ml by addition of EtOH (5 ml) and few drops of Hz804

(98%). After 15 hrs (time needed to transform the acid into the corresponding ester completely) ethyl formate was

determined by GLC analysis, using a capillary column (DB- 1,20 m) and toluene as internal standard.

Ethyl ester was identified by comparison of the retention time with that of an authentic sample.

References and Notes

1. Guette’, J.P.; Manic&, G.; Metivier, B. L’actualitt? Chimique 1982,23. 2. Ballistreri, F.P.; Failla, S.; Tomaselli, G.A.; Corci, R Tetrahedron Len. 1986,5139.

3. BaUisueri, F.P.; Failla, S.; Tomaselli, G.A. The Role of Oxygen in Chemistry and Biochemistry, Ando, W.; Morooka, Y. Eds.; Elsevier; 1988; p. 341. 4. Ballistreri, F.P.; Failla, S.; Tomaselli, G.A. J. Org. Chem. 1988,53,830. 5. Recent work (lshii, Y.; Sakata, Y. J. Org. Chem. 1990,55,X45) showed that internal alkyaes are oxidized at reflux also without mercury salts by hydrogen peroxide in the presence of a W(VI) peroxopolyoxocomplex to a&epoxy ketones and a,&unsaturated ketones. 6. The evaluation was made on the basis of eq 1 and of tbe following stoicbiometry for acetylene oxidation:

7. Ballistreri, F.P.; Faith, S.; Spina, E.; Tomaselli, G.A. J. Mol. Catal. 1%9,50,39. 8. Glyoxal can be obtained by oxidation of acetaldehyde with nitric acid ( BASF, French Patent 1%7, 1509 259 ) or selenium dioxide ( Air Liquid, French Patent lW9.2 038 575 ) or by oxidation of ethylene glycol with air at 300-700°C ( Laporte Chemicals, French Patent 1970,2 007 925 ) or by oxidation of ethylene with nitric acid on Pd ( BASF, French Patent 1964, 1363 089 ) or with air in the presence of selenium dioxide on silica ( Costa Novella, E. Annales Quim. 1972,68,325 ). 9. Stanley, J.B.; Senn. V.J.; Brown, D.F.; Dolhr, F.G. AppL Spectrosc. 197127, 141. 10. Salomaa, P. Acta Chem Stand. 1956, IO, 306.