Method of alcohol oxidation to carbonyl compounds

FIELD: chemistry.

SUBSTANCE: invention refers to electrochemical method of primary and secondary alcohol oxidation to related carbonyl compounds including preparation of mother solution at room temperature. Then salt 2,2,6,6-tetramethylpiperidine hydrochloride of general formula is added to electrolyte solution consisting of oxidised alcohol, water, methylene chloride, sodium chloride and sodium sulphate with electrolysis on platinum electrodes at current strength 1.5 A and temperature 20-25C.

EFFECT: higher technological effectiveness of process combined with reduced time for producing high-yield end product.

2 ex

 

The invention is a new electrochemical oxidation of primary and secondary alcohols to the corresponding carbonyl compounds.

There is a method of oxidation of alcohols with N-chlorosuccinimide (NCS), catalyzed 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in the two-phase system in the presence of carrier tetrabutylammonium chloride (TBACl) (J.Einhom, .Einhom, F.Ratajczak, J.-L.Pierre. J. Org. Chem., 1996, 61. No. 21. P.7452-7454). For example, at room temperature, mix a solution of 0.14 g (1 mmol) 1-phenyl-1-ethanol, 15, 6 mg (0.1 mmol) TEMPO, with 27.7 g (0.1 mmol) TBACl in 10 ml of methylene chloride and 10 ml of 0.5 M NaHCO3and 0.05 M2CO3. Then to the resulting solution with vigorous stirring, 0.16 g (1.2 mmol) of NCS. The stirring is continued for 3.5 hours. Next, the organic layer is separated, the aqueous extracted with CH2Cl2(210 ml). The organic layers are combined, dried and evaporated. The residue is purified chromatographically. Get 68% of methylvinylketone.

However, this method is time-consuming and uneconomical as catalyst requires the use of expensive nitroxyl radical, as the aqueous phase - only alkaline buffer solution, as in the acidic environment of the nitroxyl radical is restored and loses catalytic properties, as well as the use of interfacial carrier, except that secondary alcohols are oxidized in these in the circumstances is less effective i.e. with a lower output than the original.

The closest is the way of the oxidation of alcohols in the two-phase system with the assistance of N-oxopiperidine salt (Ungiven, Accused, Heikichi. WPI. Academy of Sciences. Ser. chem., 1992, No. 4, s-945).

In a cylindrical cell was placed 4.6 mmol 4-chloro-1-butanol, 0.1 mmol of 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TMPO), 50 ml of methylene chloride and 100 ml of an aqueous solution containing 25% sodium bromide and 5% sodium bicarbonate, and the electrodes (the anode is graphite, the cathode is platinum) at a distance of 5 mm from each other. Then, stirring the contents of the cell and maintaining the temperature of 20C, pass a constant electric current (current - 1 And the current density at the anode of 0.1 A/cm2) until complete conversion of the alcohol, which was controlled by GLC. At the end of the electrolysis the organic layer was separated, the aqueous was extracted with methylene chloride (275 ml), the combined extracts and organic layer was dried over anhydrous sodium sulfate, was evaporated, and the residue was analyzed to assess the output. Output 4-chlorobutanol 70%.

However, this method is also used nitroxyl radical TEBO, the receipt of which is time-consuming and unsafe, as it requires the use of 30% hydrogen peroxide and salts of heavy metals (tungstate or molybdate sodium).

The task of the image is to be placed - simplification oxidation of alcohols to carbonyl compounds in the techno-economic and environmental terms.

This object is achieved in that in contrast to the prototype and the analogous synthesis is not used interfacial carrier, as the aqueous phase is used only alkaline buffer solution, and instead of nitroxyl radical, is used as catalyst in the oxidation of alcohols - 2,2,6,6-tetramethylpiperidine-1-oxyl formula

use its predecessor - spatial-hindered amine - 2,2,6,6-tetramethylpiperidine in the form of a hydrochloride of the General formula

the oxidation is carried out electrochemically on platinum electrodes in the electrolyzer cell using the electrolyte solutions of sodium chloride and sodium sulfate in the presence of methylene chloride at room temperature. At the anode are formed oxygen and chlorine, the last chloridum in the amine solution with the formation of 1-chloro-2,2,6,6-tetramethylpiperidine. Halogenation at the cathode is restored to minilogo radical, which in reaction with oxygen forms a 2,2,6,6-tetramethylpiperidine-1-oxyl.

These conditions increase the manufacturability of the process, shorten the time for obtaining the target product, so as to exclude stage receiving the Oia, isolation and purification of the catalyst reaction - nitroxyl radical, carbonyl compounds get high yield. Nitroxyl radical, obtained directly in the reaction zone, is oxidized by chlorine to oxammonium salt, which, oxidizing the alcohol, is restored to the nitroxyl radical. Thus, the catalytic cycle is closed. In ecological terms the proposed method for the oxidation of alcohols differs from the well-known fact that the use of solid, non-volatile, stable hydrochloride 2,2,6,6-tetramethylpiperidine instead of liquid, volatile and toxic 2,2,6,6-tetramethylpiperidine.

The proposed method allows to oxidize primary and secondary alcohols in the presence of hydrochloride 2,2,6,6-tetramethylpiperidine, which is electrochemically converted into 2,2,6,6-tetramethylpiperidine-1-oxyl, which is the catalyst in the oxidation process.

Example 1. Oxidation of secondary alcohols, for example, oxidation of 2-pentanol to 2-pentanone.

In electrolyzer electrolyzer, with a capacity of 250 ml, equipped with a water jacket, thermometer and mechanical stirrer, are placed 100 ml of water and 30 ml of methylene chloride, 4.4 g (0.05 mol) of 2-pentanol, 5.9 g (0.1 mol) of sodium chloride, 5.0 g (0.1 mol) of sodium sulfate and 0.9 g (0,005 mol) of the hydrochloride 2,2,6,6-tetramethylpiperidine. The anode and the cathode, and a platinum plate 10 and 10 cm2respectively. The conditions of the electrolysis temperature 20-25C, the current is 1.5 a (current density of 0.075 A/cm2). Synthesis finish after passing 3,4 f/mol of electricity. After electrolysis the organic layer is separated, the aqueous layer was extracted with methylene chloride (250 ml). The organic layers are combined, dried and analyzed by GLC. The electrolyte composition according to GC: 82% 2-pentanone, 18.5% of 2-pentanol, 1.5% of 2,2,6,6-tetramethylpiperidine-1-oxyl. To highlight 2-pentanone methylene chloride evaporated, and the residue is distilled and collected fraction 100-102C, yield 3.2 g (75%) of cyclohexanone.

Example 2. Oxidation of primary alcohols by the example of the oxidation of benzyl alcohol to benzaldehyde.

In electrolyzer electrolyzer, with a capacity of 250 ml, equipped with a water jacket, thermometer and mechanical stirrer, are placed 100 ml of water and 30 ml of methylene chloride, 1.8 g (0.01 mol) of the hydrochloride 2,2,6,6-tetramethylpiperidine, 5.9 g (0.1 mol) of sodium chloride and carry out electrolysis for 0.5 hours. The anode and the cathode, and a platinum plate 10 and 10 cm2respectively. The conditions of the electrolysis temperature 20-25C, the current is 1.5 a (current density of 0.075 A/cm2). Then in a pot add a solution of 5.4 g (0.05 mol) of benzyl alcohol in 20 ml of methylene chloride and continue the electrolysis of 3 hours. Synthesis finish after transmission of 2.6 f/mol. After electrolysis the organic layer is separated, the aqueous layer was extracted with methylene chloride (230 ml). The organic layers are combined, dried and analyzed by GLC. The electrolyte composition according to GC: 85,0% benzaldehyde, 12,0% benzyl alcohol, 3.0% of 2,2,6,6-tetramethylpiperidine-1-oxyl. To highlight benzaldehyde methylene chloride evaporated, and the residue is distilled in vacuum. Collect the fraction 62-64C (10 mm Hg), the yield of 4.25 g (80%) of benzaldehyde.

Comparison of synthesis shows that the proposed method requires significantly less time (about 50 times on the basis of 1 mol turn compounds), chemicals and leads to a higher yield of the target product (75-80%) in comparison with the known (60-70%).

Electrochemical method for the oxidation of primary and secondary alcohols to the corresponding carbonyl compounds, comprising preparing a starting solution at room temperature, characterized in that the electrolyte solution consisting of oxidizable alcohol, water, methylene chloride, sodium chloride and sodium sulfate salt is hydrochloride 2,2,6,6-tetramethylpiperidine General formula

the electrolysis is performed on platinum electrodes with an electric current of 1.5 a and a temperature of 20-25C.



 

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