We have studied the oxidation of furfural by hydrogen peroxide in the presence of sodium molybdate in detail for the first time. The reactions of furfural with hydrogen peroxide under the conditions of autocatalysis by the acids that accumulate [2][3][4][5][6][7] and catalysis by compounds of selenium and vanadium [8, 9] were reported earlier. The authors of these papers isolated ~-formylacrylic acid (I) or its esters [8, 9] and 2(5H)-furanone (II) and succinic acid (III) [6, 7] as the main products. It was assumed that oxidation took place either according to the classical Baeyer-Villiger mechanism [2, 7] or by hydroxylation [9], depending on the conditions. It was reported that compound (I), maleic acid (IV), and fumarie acid (V) and also a certain amount of malic acid (VI) were formed during the oxidation of furfural by a 5 % solution of hydrogen peroxide in the presence of NaHMoO 4 [10]. The authors consider that the reaction in the presence of sodium hydromolybdate takes place similarly to the reaction in the furfural-hydrogen peroxide-selenium compound system.As seen from the published literature, in papers on the peroxide oxidation of furfural [2-10] the possibility of using the peroxo complexes of molybdenum, which are easily formed in the aqueous hydrogen peroxide-molybdenum vl system, has not been realized [11]. In the light of known data on the epoxidizing ability of such ~umplexes [11][12][13][14][15][16][17][18][19][20] and in order to discover new synthetic possibilities in the reaction of furfural with hydrogen peroxide we studied its characteristics in the presence of sodium molybdate.The oxidation of furfural was conducted at 60~ with a 30% aqueous solution of hydrogen peroxide in the presence of catalytic amounts of Na2MoO 4 (Table 1, version 1). The pH of the initial reaction mixture was 5 on account of the stabilizer contained in the hydrogen peroxide. In the first 5-10 min its color changed from red-brown to lemon-yellow, which remained to the end of the process.The end of the reaction was detected by the transformation of the initial reagents and the formation of the initial and final compounds by means of a set of analytical methods, i.e., chromatography with authentic samples (GLC, HPLC, TLC, and paper chromatography), polarography, and titrimetric analysis (for analysis of the acidic and peroxide compounds). Kinetic curves for the consumption of furfural and hydrogen peroxide and the accumulation of furanone (II) and acids were obtained (Fig. 1).As seen from the obtained results (Table 1, version 1, and Fig. 1), the furanone (II) is mainly formed in the investigated system together with tartaric acid (VII), malic acid (VI), and succinic acid (III). A distinctive feature of the process *For Communication 3, see [1].