RU2302410C1 - Electrochemical method for preparing 2,2,6,6-tetramethylpyperidine-1-oxyl - Google Patents

Abstract

FIELD: organic synthesis.

SUBSTANCE: preparation of 2,2,6,6-tetramethylpyperidine-1-oxyl depicted by general formula:

comprises providing a stock solution at room temperature and is characterized by that through solution comprised of sodium sulfate, methylene dichloride, and 1-chloro-2,2,6,6-tetramethylpyperidine of general formula:

in membrane-free electrolyzer with platinum electrodes, 1.5 A electric current is passed during 3 h.

EFFECT: expanded synthetic possibilities in nitroxyl compounds area and reduced process expenses.

Description

The invention can find application for a new method for producing a compound that is used in organic chemistry as a reagent in oxidation reactions and is a convenient means of studying the structure, reactivity of molecules, as well as energy and steric factors in kinetics.

A known method for producing a nitroxyl radical - di-tert-butyl nitroxyl (A.K. Hoffmann, A.T. Henderson J. Am. Chem. Soc., 1961, 83, P.4671). 25 g (0.24 mol) of tert-nitrobutane in 30 ml of ether and 5.5 g (0.25 mol) of sodium metal are mixed at room temperature. At the end of the reaction, the solvent was removed in vacuo to give 9 g of a mixture of substances, which, according to GLC, contained 22% di-tert-butyl nitroxyl and 70% di-tert-butyl hydroxylamine. In addition, small amounts of tert-nitrobutane and tert-butyl alcohol were found.

However, this method is time-consuming and unsafe, because requires the use of ether and metallic sodium; the resulting mixture of products is difficult to separate; the target product is obtained in low yield; in addition, this method is not common for the synthesis of nitroxol radicals of other series.

The closest is the method of producing the nitroxyl radical of 2,2,6,6-tetramethylpiperidin-1-oxyl from 2,2,6,6-tetramethylpiperidine (Rozantsev E.G. Free iminoxyl radicals. M: Chemistry, 1970, p. .192).

In a 500 ml flat-bottomed flask, a solution of 141 g of 2,2,6,6-TMP, 15 g of Trilon B, 800 ml of 45% methanol and 250 ml of 30% hydrogen peroxide is prepared under cooling. The mixture is left at room temperature for 10 days, diluted with a double volume of water, saturated with potassium carbonate and extracted with ether. The ether extract was dried with anhydrous magnesium sulfate, the ether was evaporated and the residue was sublimated in vacuo. The yield of radical is 95 g (61%). Dark red transparent prisms (sublimate) with a strong camphor smell, so pl. 37.8-38.1 ° С, according to the literature 35 ° С.

The chemical method is long and environmentally unsafe, because time-consuming, the use of methanol and 30% hydrogen peroxide.

The objective of the invention is to simplify the process of obtaining the known 2,2,6,6-tetramethylpiperidine-1-oxyl in the technical, economic and environmental terms.

The problem is achieved in that 2,2,6,6-tetramethylpiperidin-1oxyl of the formula

in contrast to the structural analogue, they are produced electrochemically on platinum electrodes in a diaphragmless electrolyzer using sodium sulfate and 1-chloro-2,2,6,6-tetramethylpiperidine of the general formula

in the presence of methylene chloride and water at room temperature. Oxygen is formed on the anode during the discharge of water molecules. At the cathode, 1-chloro-2,2,6,6-tetramethylpiperidine is reduced to an amine radical, which in solution with oxygen forms 2,2,6,6-tetramethylpiperidin-1-oxyl.

These conditions significantly increase the manufacturability of the process, shorten the time for obtaining the target product, its cost due to the fact that the electrolysis is carried out at room temperature and allows 4.1 F / mol of electricity to pass through, the platinum used catalyzes the reduction process and is obtained in good yield 2, 2,6,6-tetramethylpiperidin-1-oxyl.

Example. Preparation of 2,2,6,6-tetramethylpiperidin-1-oxyl from 1-chloro-2,2,6,6-tetramethylpiperidine.

The proposed method allows the electrochemical synthesis of 2,2,6,6-tetramethylpiperidin-1-oxyl, which is widely used in organic synthesis as an oxidizing agent.

In a 200 ml non-diaphragm electrolyzer equipped with a water jacket, a thermometer and a mechanical stirrer, 80 ml of water, 7.1 g of sodium sulfate (0.05 mol), 3.8 g (0.02 mol) of 1-chloro-2 are loaded 2,6,6-tetramethylpiperidine and 30 ml of methylene chloride. The anode and cathode are platinum plates with an area of 10 and 5 cm ^2, respectively. Electrolysis conditions: temperature 20-25 ° C, current strength 1.5 A. The synthesis is completed after passing 4.1 F / mol.

A 10% sodium hydroxide solution was added to the aqueous layer to a pH of 10-11 and extracted with methylene chloride (3 × 30 ml). The solvent was distilled off, and the residue was purified by sublimation in vacuo (10-15 mmHg). Yield of 2,2,6,6-tetramethylpiperidin-1-oxyl 1.4 g (40% of the starting 1-chloro-2,2,6,6-tetramethylpiperidine or 80% of the reacted 1-chloro-2,2 6,6-tetramethylpiperidine), mp. 36 ° C. 1.9 g (50%) of 1-chloro-2,2,6,6-tetramethylpiperidine (bp 61-62 ° C / 7 mm Hg) was obtained from the organic layer by vacuum distillation.

A comparison of the syntheses shows that the electrochemical requires significantly less time and leads to a higher yield of the target product (80%) compared with the chemical (61%).

Claims (1)

Electrochemical method for producing 2,2,6,6-tetramethylpiperidin-1-oxyl of the formula

comprising preparing a stock solution at room temperature, characterized in that through a solution consisting of sodium sulfate, water, methylene chloride and 1-chloro-2,2,6,6-tetramethylpiperidine of the General formula

in a diaphragmless electrolyzer with platinum electrodes, a current of 1.5 A is passed for 3 hours.