CS225491B1 - Increase of activity and durability of pd/c catalysts used for oxidation of the 2,3 to 4,6-diisopropylidene-sorbose to the 2,3 to 4,6 diisopropylidene-l-2-keto-l-gluconic acid - Google Patents

Description

The invention relates to a method for increasing the activity and durability of Pd / C catalysts used in the oxidation of 2,3: 4 > 6 diisopropylidene-L-sorbose to 2,3: 4,6-diisopropylidene-2-keto-1-gluconic acid.

DAS is an intermediate in the production of ascorbic acid, which is currently produced by Reichstein synthesis. An important step in the synthesis is the oxidation of 2,3: 2 / · diisopropylidene-L-sorbose to 2,3: 4, 6-diisopropylidene-2-keto-L-gluconic acid. Technologically, oxidation with sodium hypochlorite is best handled. However, the disadvantage of this process is the formation of large amounts of waste salts. Perspective method, which does not reach the level of hypochlorite method, is oxidation in NaBr - NaOBr environment. A suitable method and the most environmentally friendly method is direct oxidation 2,3:

4,6 - diisopropylidene - L - sorboses by air for the catalysis of platinum subgroup metals supported on a support which is most often activated charcoal / Belg. pat. 351 804 /. The reaction is carried out at a temperature of 80-135 ° C, an oxygen partial pressure of 2-100 kPa and an aqueous solution pH of greater than 7.5.

In the catalytic oxidation of 2,3: 4 »6 - diisopropylidene L - sorbose, the activity of the catalyst is determined by the method of preparation, the type of carrier used and the metal subgroup of platinum.

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The oxygen concentration in the reaction medium is also an important factor influencing the course of the reaction. The amount of oxygen introduced into the reaction mixture should not be in large excess relative to the amount of oxygen consumed by the organic substrate. Otherwise, the catalyst is non-lethal inactivated. Another factor is the initial concentration of the base used and 2.3 s of 4,6-diisopropylidene L-sorbose, which should be selected such that at the reaction temperature these substances do not become deposited on the surface of the catalyst and thus partially deactivate it. The purity of the starting 2,3 čist 4,6-diisopropylidene-L-sorbose is significantly influenced by the activity of the catalyst. 2,3: 4,6-diisopropylidene-L-sorbose may contain sulfur and nitrogenous substances from the previous reaction stages, namely from biological oxidation - D-sorbitol to L-sorbose and acetonization, i conversion of L-sorbose to 2,3: 4,6-diisopropylidene of L-sorbose. These additives are the leading catalysts of the platinum group and reduce their activity and lifetime.

In addition to previously known processes, 2,3: 4,6 diisopropylidene-L-sorbose can be purified by multiple crystallizations from various organic solvents, for example methanol, acetone, benzene and petroleum ether. The disadvantage of this process is the high consumption of organic solvents, energy consumption in preparation of saturated solutions at elevated temperatures, and moreover, recrystallization of 2,3: 4,6 diisopropylidene-L-sorbose is Sasha's demanding process because DAS, like other sugars, crystallizes from saturated solutions very difficult. Another disadvantage is that the impurities present therein are partially transferred from one crystallization stage to another and 2,3: 4,6-diisopropylidene-L-sorbose of suitable purity required for the catalytic oxidation process can only be obtained by repeated repetitions of purification . This is, however, associated with high losses of 2,3: 4,6-diisopropylidene-L-sorbose, which remains in the mother liquors and, at the same time, insufficient purification reduces the activity and durability of the palladium or platinum-based catalysts used.

We have found to increase the activity and lifetime of the catalysts in the oxidation of 2,3: 4> 6-diisopropylidene-L sorbose by molecular oxygen, carried out in aqueous solutions containing basic substances in amounts sufficient to maintain a pH above 8 and catalysed throughout the reaction. The process according to the invention is characterized in that 2,3: 4,6-diisopropylidene-L sorboza or a solution thereof is used for the reaction, which is purified using activated carbon as the adsorbent of the catalytic substances.

Various types of activated carbon, preferred and as large surfaces as possible, can be used to adsorb the 2,3-4,6-diisopropylidene-L sorbose. The purification process may be carried out using adsorption columns packed with granulated activated carbon of appropriate grain, or by suspending the activated carbon in a 2,3: 4,6-diisopropylidene-L sorbose solution and subsequently removing it by filtration. The size of the adsorbers, or the amount of activated carbon relative to the amount, is given by the impurity content in the coupled 2.3; 4,6 diisopropylidene-L-sorbose. Cleaning losses are very low. Thus purified or a solution thereof can be used directly for catalytic oxidation. The removal of catalytic poisons increases the activity and durability of the palladium catalyst types.

The invention is illustrated by the following examples.

Example 1

Oxidation 2,3: 4,6 - diisopropylidene - L - sorboses to 2,3:

4.6-Diisopropylidene-2-keto-L-gluconic acid air was carried out in a 250 ml stirred, semi-flow, titanium steel reactor. The reaction mixture was stirred with a 2,000 rpm propeller stirrer. The reactor was heated by hinged electrical blocks and the temperature of the reaction mixture was sensed by a platinum resistance sensor embedded in a thermowell in the reaction vessel and controlled by a TRS 12 transistor controller. and oxidizing gas flow through a calibrated rotameter. Air was introduced into the reaction mixture by a capillary extending to the bottom of the reactor.

15 g of pure technical DAS were weighed into the reactor

97.1 wt. (determined by internal standard gas chromatography), 150 ml deionized water, 1.5 g of a catalyst containing 5% Pd on specific surface activated carbon

265 m. G and 3.02 g of NaOH. After pressurizing the reactor to 0.35 MPa air and adjusting the air flow rate to 20 cm / min. The reaction mixture was monitored at regular intervals by analyzing the oxygen content of the off-gas. After stopping the oxygen consumption, the reaction was complete.

The 2,3: 4,6-diisopropylidene L-sorbose content of 2,3: 4,6-diisopropylidene-2-keto-L-gluconic acid and unreacted 2,3: 4,6-diisopropylidene was analyzed by gas chromatography after conversion to more volatile methyl derivatives with diazomethane. The internal standard method was used. The reaction product obtained under the above conditions after 5.5 hours of oxidation contained

65.6% game. 2,3: 4,6-diisopropylidene-2-keto-L-gluconic acid and 33.2% unreacted 2.3: 4.6-diisopropylidene-L-sorbose.

Example 2

The process, the amounts of reagents and the reagents used hurt, as in Example 1, but the 2,3: 4,6-diisopropyl-propylidene-1-sorbone was purified prior to the reaction so that to 15 g of the material in 100 g ml of dionized water was added 1.75 g of colerex activated carbon to _n with a specific surface area of 1,265 m. g. · The filter solution obtained 2,3: 4,6 diisopropylidene-L-sorbose was used directly for oxidation. The reaction product after 7 hours of oxidation contained 97.2 wt.

2,3% 4,6-diisopropylidene-2-keto-L-gluconic acid and 2.3% unreacted 2,3: 4,6-diisopropylidene-L-sorbose.

Example 3

The operating procedure, the amounts of reagents used and the conditions were the same as in Example 1, but 2,3,4 * 6-diisopropylidene-L-sorbose purified by triple crystallization from methanol was used for the reaction. After 7.5 hours of oxidation, the reaction product contained 90.0 wt. 2,5: 4,6-diisopropylidene-2-keto-L-gluconic acid and 9.4 unreacted 2,3: 4,6-diisopropylidene-L-sorbose.

Example 4

The operating procedure, the amounts of reactants used and the conditions were the same as in Example 1, but used for the reaction

2,3 - 4,6 - diisopropylidene - L - sorbose purified by triple crystallization from benzene. After 7.5 hours of oxidation, the reaction product contained 88.2 wt. 2,3 i 4,6-diisopropylidene-2-keto-L-gluconic acid and 11,6% unreacted

2,3: 4,6-diisopropylidene-L-sorbose.

Example 5

The procedure, the amounts of reagents used and the conditions were the same as in Example 1, except that 2,3 with 4,6-diisopropylidene-L-sorbose purified on activated carbon DB-1 with a specific surface area of 1,099 mg was used. The reaction was catalyzed using a catalyst isolated from the reaction mixture of Example 2. Oxidation which lasted for 7 hours gave 98.5 wt. 2,3: 4,6-diisopropylidene-2-keto-L-gluconic acid ·

Claims (1)

OBJECT OF THE INVENTION A method of increasing the activity and lifetime of Pd / C catalysts used in the oxidation of 2,3: 4,6-diisopropylidene-L-sorbose to 2,3: 4> 6-diisopropylidene-2 keto-L-gluconic acid in sodium solutions containing bases characterized by by using 2,3 with 4,6-diisopropylidene-L-sorbose or a solution thereof which is purified by the use of activated carbon as the adsorbent of catalytic iodides for oxidation ·