RU2127738C1 - Method of synthesis of 2,3:4,6-di-o-isopropylidene-2-keto-l- -gulonic acid sodium salt - Google Patents

Abstract

FIELD: organic chemistry and chemical technology. SUBSTANCE: invention relates to a method of synthesis of 2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid by electrochemical oxidation of 2,3:4,6-di-O-isopropyli- -dene-α-L-sorbofuranose on metallic anodes in the presence of nickel sulfate in an aqueous solution of sodium hydroxide at heating. Process is carried out in the presence of sodium sulfate or potassium sulfate, or sodium phosphate taken at concentration 3-20% at current density 6-8 A/dm². Method ensures to increase the conversion degree to 95-96% and yield to 90%. EFFECT: improved method of synthesis, increased yield, decreased energy consumption. 3 ex

Description

 The invention relates to organic chemistry, and in particular to a method for producing sodium salt of 2,3; 4, 6-di-O-isopropylidene-2-keto-L-gulonic acid (I), an intermediate in the synthesis of ascorbic acid (vitamin C), and can be used in medicine, agriculture and food industry.

 A known method for producing (I) by oxidation of 2,3; 4,6-di-O-isopropylidene-2-keto-α-L-sorbofuranose (II) graphite anodes in an alkaline medium, the initial alkali concentration of 40 g / l, in the presence of catalyst - nickel hydroxide, loading P-150 g / l [1] - (Miller E.A., Seleznev L.G., Luknitsky F.I. et al. Abstracts of the 8th All-Union Meeting on the Electrochemistry of Organic Compounds ( ECHO-73) - Riga 1973, p. 22 - 23).

 This method has several disadvantages. These disadvantages are with low mechanical and corrosion resistance of graphite anodes. In addition, the fragility of graphite leads to the need to increase the minimum thickness of a graphite electrode, which cannot be less than 50 mm, which leads to a low fill factor of the electrolyzer, and therefore a low utilization rate of working areas. Graphite anodes have poor resistance in alkaline environments. In the process of exploitation, graphite is oxidized in the pores and then graphite grains are chipped [2] - (Yakimenko LM Electrode materials in applied electrochemistry, M., 1977).

Graphite anodes can be operated normally at currents of not more than 4 - 6 A / dm ² and are characterized by low productivity in terms of quantity 1, obtained from a unit of electrode surface area per hour, not more than 4 g / dm ² hours.

 There is also known a method for producing I by electrochemical oxidation of II on metal anodes [3] - (US Pat. No. 3,453,191 class. 204-78. Electrochemical method for producing diacetone-2-ketogulonic acid. (3)).

 Nickel, various grades of steel, nickel-plated iron, copper-nickel alloys, platinum, etc. are used as a substrate for the anode. An anode is an activated layer of nickel hydroxide deposited on a conductive substrate. To stabilize the activity of nickel hydroxide, a certain amount of nickel salts from 0.01 to 0.5 moles of nickel salt per mole P is formed in the reaction mixture, which form a suspension of nickel hydroxide when alkali is added. The optimal amount of alkali introduced into the reaction mixture is 1.8 - 2.1 moles of alkali per mole P.

The process is carried out at a temperature of from 25 to 85 ^o C. The current density and can vary up to 15 A / DM ² . The optimal value of the current density is 6 A / dm ² . To activate the process, it is recommended to conduct preliminary electrolysis in the absence of P for up to three days at a current density of 0.4 A / dm ² .

Yield 1 is 90% with a conversion of 90%. Productivity for a better example was 9 g / dm ² hours with a yield of 1 - 91.5%. The output stream 54%. Electricity consumption is about 31 kW / h.

 The disadvantage of this method is the relatively low degree of conversion of the original P - not higher than 90% and high energy consumption.

 The objective of the present invention is to increase the degree of conversion and reduce energy consumption.

This is achieved by carrying out the process of electrochemical oxidation of P on metal anodes in alkaline solutions in the presence of nickel salts from 0.005 to 0.03 mol per liter at a temperature of 40 - 55 ^o C, the hallmark of which is the addition of sodium sulfate or sodium phosphate or potassium sulfate to the reaction medium concentration of 3 to 20% and a current density of 6 to 8 A / dm ² .

 The process of electrochemical oxidation of P in the presence of these salts can significantly increase the conductivity of the solution and thus reduce energy consumption by reducing ohmic losses. However, the decrease in energy consumption was significantly higher than expected, which can be explained by the displacement of the anion P from the anode layer, and this increased the driving force of the process. When salts were introduced in the reaction mass in an amount of 3%, the energy consumption decreased to 2.5 kW / h per 1 kg P. Compared to the process in the absence of salts, 3.8 kW / hour per 1 kg P. When 20% salts were introduced, the consumption electric power was 0.8 kW / h per 1 kg P.

 A further increase in salt concentration leads to a substantial increase in corrosion. In addition, the introduction of sodium sulfate or phosphate or potassium sulfate into the reaction medium increased the oxidation rate of P at the anode, which increased the degree of conversion.

 The essence of the method is as follows.

For the synthesis of 1 from P, an alkaline solution of P is added with nickel sulfate in a concentration of from 0.005 to 0.03 M and salt in a concentration of from 3 to 20%, then electrolysis is carried out at current densities of 6 to 8 A / dm ² and a temperature of 40 to 55 ^o C.

The method is illustrated by the following examples:
Example 1

40 ml of a solution with a concentration of components: 2,3,4,6-di-O-isopropylidene - sorbofuranose (P) -0.462 M, nickel sulfate - 0.025 M, sodium hydroxide - 0.7 M, sodium sulfate - 30 g / l (3%) is poured into the electrolyzer (anode area of 0.05 dm ² ) and at a temperature of 40 ^o C, the process of electrochemical oxidation of P is conducted at a current density of 6 A / dm ² .

 The voltage at the terminals is 5.3 V, the electrolysis time is 8 hours, the conversion rate is 95%, the yield of sodium salt is 2.3; 4,6-di-O-isopropylidene-2-keto-L-gulonic acid (1) is 5.15 g power consumption is 2.5 kW • hour / kg.

 Example 2

Carried out analogously to example 1, using potassium sulfate - 100 g / l (10%) at a temperature of 50 ^o C, a current density of 8 A / DM ² . The voltage at the terminals is 2.6 V, the electrolysis time is 6 hours, the degree of conversion is 96%, output 1 is 5.16 g, the energy consumption is 1.2 kW • h / kg.

 Example 3

Carried out analogously to example 1, using sodium phosphate - 200 g / l (20%), at a temperature of 55 ^o C, a current density of 8 A / DM ² . The voltage at the terminals is 1.1 V, the electrolysis time is 6 hours, the conversion rate is 96%, the output is 15.11 g, the energy consumption is 0.8 kW • h / kg.

 The use of the invention allows to significantly reduce energy consumption and makes it possible to increase production per unit of energy used. With increasing process productivity, the degree of conversion increases, reaching a value of 95 - 96%, as well as yield 1, which is 90%.

Claims (1)

The method of obtaining the sodium salt of 2,3: 4,6-di-O-isopropylylene-2-keto-L-gulonic acid by electrochemical oxidation of 2,3: 4,6-di-O-isopropylidene-α-L-sorbofuranose on metal anodes in the presence of nickel sulfate in an aqueous solution of sodium hydroxide when heated, characterized in that the process is carried out in the presence of sodium sulfate, or potassium sulfate, or sodium phosphate, taken in a concentration of 3 - 20% at a current density of 6 - 8 A / dm ² .