Electrochemical method of oxidising of alcohols to carbonyl compounds

FIELD: chemistry.

SUBSTANCE: method involves preparation of a reaction mixture at room temperature consisting of the alcohol to be oxidised, sodium bicarbonate, an organic solvent and a nitroxyl radical. Electrolysis is carried out on platinum electrodes with current of 1 A and temperature of 20-25°C. Potassium iodide is added to the reaction mixture. The organic solvent used is dichloromethane and the nitroxyl radical used is 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl of formula: with ratio of alcohol to nitroxyl radical equal to 10:1.

EFFECT: invention ensures high output of end products a within short period of time and less expenses on electricity using a high-technology method.

2 ex

 

The invention can find application as a General method for the oxidation of alcohols to carbonyl compounds and can be used in the pharmaceutical industry.

Known electrochemical method for the oxidation of alcohols in the system KJ-water-co-solvent (Tetrahedron Letters, 1979, No. 2, pp.165-168, .Shono, Y.Matsumura, J.Hayashi and .Mizoguchi). The primary alcohols are oxidized to esters of the acids, and secondary - to ketones.

For example, in a cell equipped with a stirrer and a cooling jacket and a platinum electrode was placed a solution 2,49 g (0.015 mol) of potassium iodide in 15 ml of water, 0.06 mol of 2-methylcyclohexanol and 15-20 ml of co-solvent (tert-butyl alcohol or hexane). The process is conducted at a constant current (current density of 0.02 A/cm2and finish after missing 20 f/mol of electricity. The organic layer is separated and the aqueous layer extracted three times with ether; the organic extracts are combined, washed with water and aqueous sodium thiosulfate. Then the solvent is removed and the product purified by distillation and identified by comparing with a deliberate pattern. The yield of 2-methylcyclohexanone series - 52% substance and 6% for current.

The disadvantage of this method is the high specific consumption of electricity, because on one mol of the final product have to skip to 20 f/mol of electricity, in addition to primary alcohols in these conditions is not oxidized to aldehydes, and esters of the acids.

The closest is the way of the oxidation of alcohols in the two-phase system water-toluene in the presence of crystalline iodine and nitroxyl radical. (Ross A. Miller and R Scott Hoerrer. Organic Letters, 2003, V.5, No. 3, pp 285-287).

For example, in a flask with a capacity of 100 ml, equipped with a magnetic stirrer, was placed 0.75 g (3,98 mmol) cynomologus alcohol, 10 ml of toluene and a solution of 1 g (11,94 mmol) of sodium bicarbonate in 10 ml of distilled water. Then added with stirring 0.06 g (0,398 mmol) 2,2,6,6-tetramethylpiperidine-1-oxyl and 2.02 g (of 7.96 mmol) of crystalline iodine. The mixture is stirred for 16 hours at 20°C. the mixture is Then cooled to 5°C., treated with ethyl acetate (10 ml) and added aqueous solution of sodium sulfate (0,501 g Na2SO4in 5 ml of distilled water). The mixture is then transferred into a separating funnel and the aqueous layer was separated. The organic layer is washed with 10 ml of a solution of potassium bicarbonate, dried with anhydrous sodium sulfate and evaporated in vacuo to a volume of 10 ml, and then inert gas to volume of 10 ml of the precipitation is filtered off, washed with toluene (3 ml) and dried in vacuum. As a result, there 0,69 g (85%) of the corresponding aldehyde.

The disadvantage of the above method is the high consumption of iodine (1 mol alcohol requires 2 mol of iodine), which is quite expensive, as well as the formation of by - product-potassium iodide.

The problem is Soberania - the improvement of the oxidation of alcohols to carbonyl compounds in energy saving.

The task is achieved by preparing the reaction mixture at room temperature, consisting of oxidizable alcohol, water, sodium bicarbonate, organic solvent and nitroxyl radicals as the organic solvent used methylene chloride, and as a nitroxyl radical use - 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl formula:

when the ratio of alcohol and nitroxyl radical 10:1, add potassium iodide, and the electrolysis is performed on platinum electrodes with an electric current of 1 a and a temperature of 20-25°C. While the cost of electric energy for oxidation of 1 mol of alcohol 5 times less. Also unlike the prototype and the analogous synthesis instead of crystalline iodine is potassium iodide, in which the oxidation process is not consumed, which allows for the oxidation of 1 mole of the alcohol in 8 times less potassium iodide than crystalline iodine. And the primary alcohols are oxidized only to aldehydes, and not acid, which is very important because to stop the process at this stage is not always possible. In addition, in the proposed method uses a catalytic amount of nitroxyl radical is 4-acetylamino-2,2,6,-tetramethylpiperidine-1-oxyl (100 times less than the equivalent), which, however, does not prevent to carry out the process with a high yield of the substance and current.

The process is carried out in the electrolyzer electrolysis on platinum electrodes in a two-phase system methylene chloride - water solution of potassium iodide, in the presence of a nitroxyl radical. At the anode is formed iodine oxidizing nitroxyl radical to oxammonium salt, which acts as a one-electron oxidant alcohol to the corresponding carbonyl compounds. When this salt examone turns into a hydroxylamine, which is easily oxidized to the original nitroxyl radical, thus the catalytic cycle is closed. In this case on 1 mol of the target product requires from 2 to 4 f electricity.

These conditions increase the manufacturability of the process, shorten the time for obtaining the target product, because the oxidation is much faster and requires less amount of electricity.

The proposed method allows to oxidize primary and secondary alcohols electrogenerated iodine in the presence of 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl, which is the mediator of the oxidation process. Electroenergy iodine has the advantage over other reagents, as in the process of oxidation they are not affected other legkookisljajushchiesja group.

Example 1

Oxidation of secondary alcohols at p is the iMER oxidation of cyclohexanol to cyclohexanone

In electrolyzer electrolyzer capacity 150 ml, equipped with a mechanical stirrer, a water cooling jacket and two platinum electrodes (plates, the area of the anode 20 cm2the cathode - 15 cm2), place a 4.5 ml (0,042 mol) of cyclohexanol, which is dissolved in 30 ml of methylene chloride. Then add 5 g (0.06 mol) Panso3and 2 g (0.01 mol) KJ dissolved in 70 ml of distilled water. Last added 1.1 g (0,005 mol) of 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl. The conditions of the electrolysis temperature 20-25°C, the current is 1 a (density of 0.05 A/cm2). Synthesis finish after transmission 4 f/mol of electricity. After electrolysis the contents of the cell is drained, excess iodine is neutralized with alkali solution or by addition of crystalline Na2S2O3after which separated the organic layer. The aqueous layer was extracted with methylene chloride (2×50 ml), the organic extracts are combined and dried with anhydrous sodium sulfate. According to TLC, the reaction mixture contains two substances - the original alcohol and the product. The content of cyclohexanone and cyclohexanol determined by GLC. The degree of conversion of cyclohexanol to ketone according to GC was 85%. To highlight ketone methylene chloride was removed and the residue is distilled in vacuum, collecting the fraction at 48°C (7 mm Hg). The yield of cyclohexanone 3,05 g (78%)./p>

Example 2

Oxidation of primary alcohols, for example, oxidation phenethyl alcohol to α-Truelove aldehyde.

In electrolyzer electrolyzer capacity 150 ml, equipped with a mechanical stirrer, a water cooling jacket and two platinum electrodes (plate area: anode - 20 cm2the cathode - 15 cm2), place a 4.5 ml (0,042 mole) of phenethyl alcohol, dissolved in 30 ml of methylene chloride. Then add 5 g (0.06 mol) NaHCO3and 2 g (0.01 mol) KJ dissolved in 70 ml of distilled water. Last added 1.1 g (0,005 mol) of 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl. The conditions of the electrolysis temperature 20-25°C, the current is 1 a (density of 0.05 A/cm2), intensive mixing. Synthesis finish after transmission 4 f/mol of electricity. After electrolysis the contents of the cell is drained, excess iodine restore crystalline Na2S2O3after which separated the organic layer. The aqueous layer was extracted with methylene chloride (2×50 ml), the organic extracts are combined and dried with anhydrous sodium sulfate. According to TLC, the reaction mixture contains two substances - the original alcohol and the product. The content of α-Truelove aldehyde and phenethyl alcohol determined by GLC. The conversion of phenethyl alcohol to α-Truelove aldehyde according to GC with the put 90%. To highlight aldehyde methylene chloride was removed and the residue is distilled in vacuum, collecting the fraction 41-42°C (7 mm Hg). The yield of α-Truelove aldehyde 4,01 g (80%).

Electrochemical method for the oxidation of alcohols to carbonyl compounds, includes the preparation of the reaction mixture at room temperature, consisting of oxidizable alcohol, water, sodium bicarbonate, organic solvent and nitroxyl radical, characterized in that the electrolysis is performed on platinum electrodes with an electric current of 1A and a temperature of 20-25°C, the reaction mixture was added potassium iodide, as the organic solvent used methylene chloride, and as a nitroxyl radical is 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl formula:

when the ratio of alcohol and nitroxyl radical of 10:1.



 

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,

,

in which M denotes a metal ion, or a combination of metal ions, corresponding to the elements belonging to group IB-VIIB or VIII of the Periodic table (CAS version), including the lanthanides; m is an integer from 1 to 6; p denotes an integer from 0 to 4; q represents an integer from 1 to 4; X represents an anion

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