Ind. Eng. Chem. Res. 2006, 45, 1849-1852
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APPLIED CHEMISTRY Oxidation of Glyoxal with Hydroperoxide Compounds Prepared from Maleic Acid by Ozonation To Produce Glyoxylic Acid Z. C. Sun,*,†,‡ W. Eli,† T. Y. Xu,†,‡ and Y. G. Zhang† Xinjiang Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences, Urumqi 830011, People’s Republic of China, and Graduate UniVersity of the Chinese Academy of Sciences, Beijing, People’s Republic of China
A novel process has been discovered for the production of glyoxylic acid. When the ozonolysis of maleic acid was conducted in solvents that contained methanol, acetic acid, or formic acid at approximately -5 °C, hydroperoxide compounds and glyoxylic acid hemiacetal were formed in high yield (>95%). The prepared mixture then was dropped into a glyoxal solution (the molar ratio of maleic acid and glyoxal was slightly greater than 1:1) that had been warmed to ∼38 °C. Glyoxal was oxidized by the hydroperoxides in the mixture via a Baeyer-Villiger rearrangement. When the reaction ended, some water was added to the solution and organic solvents were distilled off at reduced pressure at 50 °C. An aqueous solution of glyoxylic acid was obtained. Through this procedure, both maleic acid and glyoxal were converted to glyoxylic acid. Introduction Glyoxylic acid has two functional groups in such a basically small unit structure that it has a very important role in chemical synthesis, such as the preparation of drug modifiers, cosmetics, perfumes, and agricultural chemicals.1,2 Various processes are known to have been used in the preparation process of glyoxylic acid; however, all of them have some serious disadvantages that remain unresolved, such that glyoxylic acid has always been an expensive fine chemical. For instance, the oxidation of glyoxal with nitric acid was one of the earliest methods for production of glyoxylic acid at the industrial level. In this process, the yield of glyoxylic acid to the consumed glyoxal can reach ∼75%. However, a large quantity of nitric acid was consumed, which was caustic to the apparatus, and as a result, a large quantity of nitrogen oxides (NOX) was generated, which are seriously harmful to the environment.3 Therefore, chemists shifted their attention to using oxygen as a clean oxidant, instead of nitric acid, but the ability to find an efficient catalyst was a sticking point. It was reported in the literature4-6 that, even at room temperature, the selectivity of glyoxylic acid can reach >95% using a noble-metal catalyst, such as platinum or palladium. The problem was that the conversion of glyoxal was generally low, and no very satisfactory results were observed until recently. Biocatalytic methods were also studied and are fascinating; however, the separation of glyoxylic acid from the reaction mixture in these processes was rather difficult and complex.7-9 An alternative process was the anodic oxidation of glyoxal in a two-compartment electrolytic cell in the presence of Cl- ions. This process was energyconsuming, and it was difficult to obtain highly concentrated products.10,11 * To whom correspondence should be addressed. Tel.: (086) 09913662249. Fax: (086) 0991-3838957. E-mail:
[email protected]. † Xinjiang Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences. ‡ Graduate University of the Chinese Academy of Sciences.
The ozonolysis of maleic acid and its derivatives was another industrialized process for the manufacture of glyoxylic acid. In 1966, Black and Cook12 prepared glyoxylic acid by treating an aqueous solution of maleic acid at 15-25 °C. With a slight excess over the stoichiometric quantity of ozone, the reaction was essentially quantitative. However, in the authors’ experiment, only half of the maleic acid was converted to glyoxylic acid, and the other half was transformed to formic acid and carbon dioxide. Since then, various methods have been developed to get full use of the maleic acid, and a series of patents have been issued. One such example is the ozonolysis of maleic acid or methyl maleate in methanol at low temperature (down to -50 °C) and then reduction of the hydroperoxides with trialkyl phosphate or dimethyl sulfide, or another is the ozonolysis of maleic acid in ethyl acetate at ∼5 °C and then the reduction of the formed ozonides with sulfur dioxide.13 The yield of glyoxylic acid in these processes can reach ∼90%; however, glyoxylic acid was difficult or unable to be separated from the end-products. The most successful method should be the ozonization-catalytic hydrogenation process, which had been industrialized.14 In this process, the reaction of maleic acid or its ester derivatives with ozone was performed in methanol at temperatures between -5 °C and ∼0 °C, and a methoxy hydroperoxide compound was obtained almost quantitatively, which was then reduced by hydrogen gas at ∼15 °C, using Pd/SiO2, Pt/C, nickel, etc. as a catalyst. The use of expensive noble-metal catalysts, which are easily poisoned, and hydrogen gas, which is hazardous (because of its explosive sensitivity), was the main disadvantage of this process. We were astonished to discover that the hydroperoxide compounds generated from maleic acid by ozonation can be reduced by glyoxal efficiently and thoroughly under acid conditions.9 Therefore, a novel process was devised, in which full use of both maleic acid and glyoxal were made and glyoxylic acid was obtained at high yield with good quality. Furthermore, in this process, no expensive metallic catalyst was
10.1021/ie051172d CCC: $33.50 © 2006 American Chemical Society Published on Web 02/11/2006
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Ind. Eng. Chem. Res., Vol. 45, No. 6, 2006
necessary, no complex separating procedure was needed, and no malignant waste was released into the environment. Experimental Section Materials. Maleic acid with a purity of >99.8 wt % was purchased commercially. Glyoxal aqueous solution (analytically pure, 40 wt %) was also purchased from the commercial market. Ozone was prepared in situ, using an ozone generator. All the solvents used in experiments were analytically pure. Ozonolysis of Maleic Acid. A quantity (36.0 g, 0.31 mol) of maleic acid was diluted with 400 mL of ethyl acetate. Then, 50 mL of the participating solvent (such as methanol, acetic acid, or formic acid) was added into the solution, which was then transferred into a reactor, and cooled in an ice-saltwater bath (-5 °C). With vigorously stirring, 3.3 wt % of ozone in oxygen was sparged with the solution at a flow rate of ∼0.08 m3/h for 2 h, 40 min. The ozone absorption was not quantitative, and ∼0.34 mol of ozone passed into the solution. After the solution was swept with oxygen for 5 min, the ozonolysis of maleic acid was performed. The concentration and quantity of hydroperoxides in the solution were determined using the iodometry method.15,16 Oxidation of Glyoxal. A quantity (43.5 g, 0.30 mol) of 40.05% glyoxal aqueous solution was diluted with ∼100 mL of solvent, which corresponded to step 1; this sampling was warmed to 35-40 °C. The ozonolysis mixture that was prepared in the first step then was added dropwise into the solution over a time span of ∼2 h, after which point the reaction was conducted until the reactants gave a negative test for peroxides (using starch-iodide paper). Approximately 100 mL of water was added into the solution. Organic solvents and partial water were removed on a rotary evaporator at reduced pressure at 50 °C. A colorless or flavescent glyoxylic acid aqueous solution, with a concentration of 40%-90% (rested with the evaporating time), was obtained. All the organic solvents were reused after distillation. The concentration and yield of glyoxylic acid were determined using high-pressure liquid chromatography (HPLC).17,18 Preparation of Glyoxylic Acid Monohydrate Crystals.12 A batch of glyoxylic acid aqueous solutions with a concentration of ∼40 wt % was prepared. A small amount of oxalic acid was precipitated with calcuim oxide and filtered. Most of the water then was removed using a rotary evaporator at reduced pressure at 50 °C. When no more water could be removed using this process, some ethyl acetate was added and the extraction process was continued to remove the remaining water. A very sticky syrup was obtained. The syrup was cooled to -10 °C. The resulting solid was partially melted at ∼30 °C and then cooled to ∼20 °C. The mixture was stirred occasionally at 20 °C. Crystals were forming and growing; within 30 h, most of the syrup changed to a mass of crystals.19,20 Results and Discussion Peroxides and hydroperoxides are two common types of products in the ozonolysis process, and the latter can be generated at especially high yield when nucleophilic solvents
Figure 1. Ozonolysis of maleic acid.
are used.21,22 At the same time, hydroperoxides are commonly used oxidants in Baeyer-Villiger oxidation reactions.23,24 Therefore, hydroperoxides can be prepared in situ by ozonation and then used as Baeyer-Villiger oxidants of aldehydes and ketones to produce useable carboxylic acids or esters.25 The mechanism of ozonation in solvents can be described by the Criegee mechanism.26-28 The carbonyl oxide intermediate (1) is trapped quickly by nucleophilic solvents, as shown in Figure 1.29 An alkyloxy hydroperoxide (2) and glyoxylic acid hemiacetal (3) are obtained. As shown in Table 1, the reaction was quantitatively conducted in methanol. Even when the compound solvents contain methanol, acetic acid, or formic acid, the yield of hydroperoxides is still very high. Because hydroperoxides are unstable at higher temperature in the presence of ozone,12,14,30 the ozonolysis temperature should not exceed 10 °C. Low temperatures (down to approximately -50 °C) can be used, but they offered no particular advantage.14 The preferred temperature was within a range of -5 °C to 0 °C, which can be easily attained from an ice-saltwater bath. The choice of solvents was a challenge throughout the entire process. All the organic solvents used in the process must be easily removed at temperatures
