JPS648638B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing 2-keto-L-gulonic acid by oxidation of L-sorbose. Conventionally, in order to produce 2-keto-L-gulonic acid by oxidizing L-sorbose, 2-keto-L-gulonic acid and acetone were reacted to form diacetone-L-sorbose, which was then mixed with hypochlorous acid. Diacetone-2-keto-L-gulonic acid was produced by oxidation using a salt or permanganate, and this was produced through a multi-step process of deacetonization. This conventional method requires multi-stage reaction operations, is complicated, and has the drawback of consuming expensive permanganate or hypochlorite as an oxidizing agent.
An object of the present invention is to provide a method for producing 2-keto-L-gulonic acid that does not have the drawbacks of conventional methods. As a result of various research into a method for oxidizing L-sorbose that does not have the drawbacks of conventional methods, the inventors of the present invention found that the pH of the reaction aqueous solution was maintained at an appropriate level by using a catalyst consisting of platinum or palladium with lead or bismuth added as a second component. If oxidized in air, 2-keto-L
-We have discovered that gulonic acid can be produced with the same yield as conventional methods, and have completed the present invention. That is, in the method of the present invention, L-sorbose is treated in an aqueous solution in the presence of a catalyst containing lead and/or bismuth in platinum or/and palladium, while maintaining the pH of the reaction solution at 6 to 10 and using an oxygen-containing gas. This method produces oxidized 2-keto-L-gulonic acid. According to the method of the present invention, it is not necessary to react L-sorbose with acetone to derive diacetone-L-sorbose and then oxidize it, and the reaction that required three steps in the conventional method can be carried out in one step. In addition, 2-keto-L-gulonic acid can be produced industrially advantageously without the need for expensive oxidizing agents such as hypochlorite or permanganate, and without any post-treatment process for waste oxidants. You can. The catalyst used in the process of the invention is platinum or/and palladium with lead or/and bismuth added, and is usually supported by a suitable carrier.
For example, it is used by being supported on activated carbon or alumina. Platinum and palladium are metallic or oxides, and lead and bismuth are metallic, hydroxides, oxides, chlorides, carbonates, organic acid salts or nitrates. The amount of palladium or/and platinum supported on the carrier is 0.1 to 10 wt%, preferably 0.5
~5 wt%, and lead or/and bismuth in the range of 0.5 to 10 wt%, preferably 1 to 5 wt%. The catalyst can be prepared by a conventional method, for example, immersing activated carbon powder in an aqueous solution of chloroplatinic acid and lead nitrate, followed by reduction treatment with an aqueous formalin solution. In addition, commercially available precious metal-supported carbon powder catalysts were mixed with lead or /
It can also be prepared by methods such as immersion in an aqueous solution of a soluble salt of bismuth and drying. The method of the present invention is carried out in a solvent, and water is frequently used as the solvent. The concentration of the raw material L-sorbose to be added to the aqueous solution is 2 to 20 wt%, preferably 5
~15wt% range. The amount of catalyst used is, for example, when the reaction is carried out in batches, 5 to 100 g, usually 10 to 50 g, of catalyst per reaction solution 1. As the reaction progresses, the pH of the reaction solution shifts from around 7 to the acidic side due to the acid of the target product produced by oxidation. Since the rate of oxidation reaction rapidly decreases when the pH of the reaction solution is acidic, it is preferable to maintain the pH of the reaction solution near neutrality. For this purpose, an alkaline substance is added to the reaction solution one after another in synchronization with the progress of the reaction, and the pH of the reaction solution is maintained at 6 to 10. The alkaline substance used is a caustic alkali, an alkali metal carbonate or bicarbonate, etc., and is usually added to the reaction solution in the form of an aqueous solution thereof. Reverse the PH of the reaction solution
If the pH is made more basic than 10, the rate of oxidation reaction will increase, but this is not preferable because it increases the amount of polymers and tar-like by-products. Therefore, the pH of the reaction solution is 6~
The reaction is carried out while maintaining the molecular weight within the range of 10, more preferably 7 to 9. The oxidizing agent used in the method of the present invention is an oxygen-containing gas, and oxygen or air is often used. In particular, it is preferable to use air. The pressure of the oxygen-containing gas during the reaction is often from normal pressure to 5 kg/cm ² . Regarding the mixed state of the oxygen-containing gas and the reaction liquid, it is necessary to maintain good gas-liquid dispersion by, for example, blowing gas into the reaction liquid and stirring well. The reaction temperature is preferably in the range of room temperature to 100°C, particularly 40 to 70°C. The time required for the reaction is 1 to 20 hours when reacting in batches, usually 2 hours.
In the range of ~10 hours. The type of reactor is usually a completely mixed suspended bed, stirred tank type or bubble column type reactor.
A fixed bed reactor using a granular catalyst may also be used. The reaction tank can be used in a single stage or in a multistage type.
After the reaction is complete, the aqueous solution from which the catalyst has been removed is concentrated under reduced pressure, and when a lower alcohol such as methanol or a solvent such as acetone is added and stirred, crystals of the sodium salt of the target product precipitate, and these are washed separately, etc. It can be isolated by the following means. 2-keto-L-gulonic acid obtained by the method of the present invention is an extremely useful compound as a precursor of ascorbic acid (vitamin C). The present invention will be explained below with reference to Examples. Example 1 A stainless steel cylindrical container with an inner diameter of 20 cm and a full plate,
A turbine blade type stirrer and an air blowing tube were used in the reactor. 30 g of a catalyst consisting of an 8 wt % L-sorbose aqueous solution 1.2 wt % pt, 3 wt % PBCO ₃ supported on activated carbon powder was charged, and the temperature was raised to 50°C. The reaction was carried out at normal pressure with air blown in at 200 ml/min and stirring at 500 rpm. As the reaction progressed, an aqueous sodium hydroxide solution was added at intervals to maintain the pH of the reaction solution at 7 to 8. The consumption of the aqueous sodium hydroxide solution stopped 2.5 hours after the start of the reaction, so the reaction was terminated and the catalyst was separated from the reaction solution. As a result of analyzing and quantifying the reaction solution using high performance liquid chromatography, 2-
The sodium salt of keto-L-gulonic acid was produced in 87% yield. Example 2 A reaction was carried out in the same manner as in Example-1, except that the catalyst used was changed. The results obtained are shown in Table-1. 【table】

Claims (1)

[Claims] 1. When oxidizing L-sorbose to produce 2-keto-L-gulonic acid, the process is characterized by oxidizing with an oxygen-containing gas in the presence of a catalyst containing lead or/and bismuth in platinum or/and palladium. Method for producing 2-keto-L-gulonic acid.