CS272741B1 - Method of 2, 3 to 4, 6-diisopropylidene-2-keto-l-gulonic acid preparation - Google Patents

Abstract

The invention concerns a method of preparation of 2,3 : 4, 6-diisopropylidene-2-keto-L-gulonic acid which is an intermediate product in the production of ascorbic acid - vitamin C. 2,3 : 4,6-diisopropylidene-2-keto-L-gulonic acid is prepared by oxidation of 2,3 : 4,6-diisopropylidene-L-sorbose with dioxygen at 80 to 135 degrees C and oxygen partial pressure of 2 to 100 kPa in the presence of a catalyst. The principle of the invention is that the reaction occurs in a water-alkaline environment with a pH higher than 7.5 in the presence of a heterogeneous catalyst on a base of palladium coated on active charcoal with a content of palladium of 1 to 20 % by weight, based on the weight of the carrier in a quantity of 0.2 to 1 % by weight of palladium related to the weight of 2,3 : 4,6-diisopropylidene-L-sorbose, activated by compounds of cobalt or manganese in dissoluble form in the water-alkaline environment in a molar ration to palladium of 0.2 to 1.1.

Description

The present invention relates to an eposobic oxidation of 2/3: 4/6-diisopropylidene-1-sorbose to 2/3: 4/6-diisopropylidene-2-keto-L-gulonic acid in the presence of catalysts »

2/3: 4,6-Diisopropylidene L-sorbose (OAS) is an intermediate in the production of ascorbic acid by Reichstein synthesis * Oxidation of OAS to 2/3: 4/6-diisapropylldene-2-keto-L.-gulonic acid (DKG) can be performed essentially three poatupmates by oxidation with sodium hypochlorite / sodium bromate; or by oxidation with air / oxygen with catalysis or co = _Kiev sub platinum. From the environmental point of view, the most preferred is direct oxidation of OAS to DKG by air / or oxygen-enriching gas. Disadvantage of hypochloritehoreep. The bromate oxidation process consists in the formation of a large amount of waste salts.

In the oxidation of DaS to DKG catalyzed by platinum Pt metal subgroups, the metal is used in the form of metallic black / as the Adams type catalyst (Tetraheron 9/67 (1960)) or carrier type (Oap.pat. 76/113 376 / Belg. Pat. 851). 804). Platinum or palladium and activated carbon are used most often. The catalyst is prepared by reducing the metal salts adsorbed on the support with formaldehyde in an alkaline medium. Other reducing agents are hydrogen / boron hydride / hydrazine or formate in an alkaline environment.

According to the prior art, in the preparation of aldonic acids by catalytic oxidation, oxygen or air is bubbled through an aqueous sugar solution having a pH of more than 7/5 in the presence of a Pt / C or Pd / C catalyst.

Although high yields are achieved, the catalysts used are rapidly deactivated and the catalyst has to be regenerated practically _x after each batch or at least partially replaced by new ones. The concentration of oxygen in the reaction gas / initial concentration of the base used and the DAS and the purity of the DAs also influence the priabsh of the reaction. The initial concentration of the base to be used and the DAs must be chosen such that, at the reaction temperature, these substances do not become salted out on the surface of the catalyst and thus do not partially deactivate it. Oxygen fed to the reaction mixture (cannot be in large excess to dmo) because it irreversibly deactivates the catalyst (NSR Pat. 2,123,621), an important factor in terms of catalyst deactivation and OAS purity (which may contain sulfur and nitrogen compounds from previous reaction stages of synthesis) (U.S. Pat. No. 225491).

The above-mentioned deficiencies are largely eliminated by the preparation of 2/3: 4/6-diisopropylidene-2-keto-L-gulonic acid by oxidation of 2/3: 4/6-diisopropylidene-L-sorbose with molecular oxygen at 80 to 135 ° C and an oxygen partial pressure of 2 to 100 kPa in the presence of a catalyst / substance characterized in that the reaction is carried out in an aqueous-alkaline medium having a pH greater than 7/5 in the presence of Pd / C catalysts containing Pd 1 to 20% w / w Co or Mn (used at 0/2: 1 to 1 * 1 molar ratio to Pd) optionally in combination with Cd compounds (used at 0 / 1.1 to 0/2: 1 molar ratio to Pd). This achieves a significant increase in catalyst activity and lifetime / dried stored catalyst is not deactivated by air oxygen and retains flood activity even after multiple uses. Catalysts are used in an amount / corresponding to 0/2 to 1% by weight. % Pd to DAs / preferably 0/3 to 0/6 wt. To prepare the catalysts, an aqueous solution of the respective salts (nitrates / sulfates / chlorides) acidified with acetic acid and water-insoluble Co (Mn) compounds, respectively, is added to the reduced Pd / C catalyst. Cd precipitates on the catalyst surface by impregnating aqueous solutions of sodium and / or potassium hydroxide and / or potassium carbonate to pH 12.

The invention is illustrated by the following examples.

Example 1

Oxidation of 2/3: 4/6-diisopropylidene-L-sorbose to 2 / 3,4 / 5-diisopropylidene-2-keto-L-gulonic acid by air was performed in a 250 cm ³ stirred titanium steel reactor. The reaction mixture was stirred with a propeller stirrer at 2000 rpm. The reactor was heated

I

CS 272 741 B1 was flipped by the electric 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 regulator. Air was introduced into the reaction mixture by a capillary extending to the bottom of the reactor *

The reactor OO was weighed with 15 g of OAS treated with Colorex K addition, with a specific surface area of? 1

1265 mg (Cs. Pat. 225,491)? 1.5 g of freshly prepared Pd-Co-Cd / C catalyst containing 4.85 wt. Pd, 1.96 wt. Co and 0.7 wt. Cd? 150 cm ^{3 of} delonized water and 3.0 g of NaOH. After pressurizing the reactor with air to 50 psi and adjusting the air flow at 4 cm to 20 cm, the reaction mixture was driven to 130 ° C and stirred vigorously. The progress of the reaction was checked at regular intervals by analyzing the oxygen content of the off-gas. After stopping the oxygen uptake, the reaction was complete.

The contents of 2: 3: 4-6-diisopropylidene-2-keto-L-gulonic acid and unreacted 2: 3: 4; 6-diisopropylidene-L-sorbose were analyzed by gas chromatography after their conversion to the more volatile rathiated derivatives with diazomethane. The internal standard method was used. The reaction product obtained under the above conditions contained 99.9 wt.

2,384,6-diisopropylidene-2-kto-L-gulenic acid.

Example 2

The reactor described in Example 1 was weighed with 15 g of purified OaS, 150 cm of deionized water. 3.0 g of NaOH and 1.5 g of the Pd-Co-Cd / C catalyst ionized from the experiment in Example 1 were obtained from the reaction conditions of Example 1 after 5.5 hours. containing 99-8 wt. 2: 3: 4S-diisopropylidene-2-keto-L-gulonic acid at 100% conversion! 2,3,4,6-diisopropylidene-L-sorbose (OAS).

Example 3

Workflow? the amounts of reactants used and the conditions were the same as in Examples 1 and 2, except that the oxidation was catalyzed by a 1.5 Pd-Co-Cd / C catalyst isolated by filtration from the experiment described in Example 2. At 100% conversion 2; 6-dipropylidene-L-sorbose (DAS) containing a reaction product of 99.7 wt. 23: 4,6-diisopropylidene-2-keto-L-gulonic acid.

Example 4

The reactor was weighed with 15 g of purified OAS, 150 cm of delonized water? 3.0 g of NaOH and 1.5 g of dried Pd-Co-Cd / C? Catalyst? % containing 4-8% wt. Pd, 1.96 wt.

% Co and 0.7 wt. Cd, stored for 2 months in the air. Under the same operating procedure and reaction conditions as in Example 1, the reaction product contained 99.9 wt. 2-3: 4-6-diisopropylidene-2-keto-L-gulonic acid.

Example 5 15 g of purified OAS were weighed out of the reactor. 150 cm of delonized water? 3.0 g of NaOH and 1.5 g of dried Pd-Co-Cd / C? Catalyst? containing 3.5% by weight iPd? 1? 1 wt. Co and 0.4 wt. Cd? stored for 1 month in the presence of air. Under the same operating procedure and reaction conditions as in Example 1, the reaction product contained 99.7 wt. 2; 3: 4,6-diisopropylidene-2-keto-L-gulns acid at 100% conversion! YOU GIVE.

Example 6

Workflow; the amounts of reactants used and the conditions were the same as in Example 1 except that the oxidation was catalyzed by 1.5 g of dried catalyst.

Pd-Mn-Cd / C 3 containing 4 ^,; 86% by weight, Pd, 1.96% by weight; % Mn and 0.7 wt. Cd? stored 2 me

IN

CS 272 741 B1 in air · Reaction product at conversion! OaS 100%, contained 99% w / w 2/3: 4/6-diisopropylidene-2-kato-L-gulonic acid ·

Example 7

Procedure / Amounts of reactants used and conditions as in Example 1 β except that the reaction was catalyzed with 1.5 g of freshly prepared Pd / C catalyst with a Pd content of 5% by weight. After 6 hours of reaction, the reaction product contained 94.4 wt. % 2,3: 4/6-diisopropylidene-2-kato-L-gulonic acid; unreacted OAS.

Example 8

Procedure / Amounts of reactants used and conditions as in Example 1 with the difference; that the reaction was catalyzed by 1/5 g of dried Pd / C catalyst containing 5 wt. Pd / stored 1 week from air inlet. A reaction product containing 51/8 wt. % Of 2 / 3s4 / 6Tiisopropylidene-2-kato-L-gulonic acid and 47/7 wt. nezraagovanaj OAS.

Example 9

The operating procedure (amounts of reactants used and conditions as in Example 1, except that the reaction aa catalyzed 1.5 g of dried Pd / C catalyst containing 5 wt. Pd / stored for 1 month with air inlet. After a 7/5 hour reaction, a reaction product containing only 6/9 wt. 2/3: 4/6-diisopropylidene-2-keto-L-gulonic acid and 92.8 wt. unreacted OAS.

Claims (2)

1. Method of preparation of 2/3: 4; 6-diisopropylidene-1-keto-L-gulonic acid by oxidation of 2/3: 4; 6-diisopropylidene-L-aorbose with molecular oxygen at a temperature of 80 to 135 ° C and partial oxygen pressure 2 to 100 kPa in the presence of a catalyst, characterized in that the reaction is carried out in an aqueous-alkaline medium and at a pH of greater than 7/5 in the presence of a palladium-based haterogenous catalyst on active carbon with a palladium content of 1 to 20% by weight. based on the weight of the carrier in an amount of 0.2 to 1 wt. palladium, based on the weight of 2: 3: 4/6-diisopropyidone-L-8-glucose, activated by cobalt or manganese compounds in soluble form in an aqueous-alkaline medium in a molar ratio to palladium 0/2 to 1: 1. 2. The process according to claim 1, wherein the catalyst is activated by catalysis in a molar ratio to the palladium of 0/1 to 0/2: 1.