DE4031093A1 - Prepn. of o-alkyl-oxime cpds. - synthetic intermediates by electrochemical oxidn. of o-alkyl hydroxylamines - Google Patents

Abstract

Prepn of 0-alkyl-oximes of formula (I) comprises electrochemical oxidn of 0-alkyl-hydroxylamines of formula (II). In the formulae R1, R2 = H or matic or aliphatic hydrocarbyl opt substd by halo, 0H, alkoxy, carboxy or CN; or R1 + R2 or R3 + R1 or R2 = (CH2)n; n = 4-7; R3 = H or 1-12C alkyl opt substd by halo, 0H or alkoxy. The pref process is carried out in an alcoholic solvent (esp Me0H or Et0H) with a (II) content of 1-50% wt and in the presence of a conducting salt (1-20% wt). USE/ADVANTAGE - (I) are intermediates in the synthesis of plant protection agents. This process does not lead to the formation of large amts of unwanted salts, nor to the formation of toxic side prods.

Description

The invention relates to a process for the preparation of O-alkyl oximes by electrochemical oxidation of O, N-dialkylhydroxylamines.

From J. Org. Chem. 49, 4969-4972 (1984) it is known that O, N-dialkylhydroxylamines with lead tetraacetate or tert-butyl hypochloride in Can oxidize triethylamine to O-.Alkyloximen. These procedures have the Disadvantage that either lead-containing residues or in considerable quantities Neutral salts are formed which have to be disposed of. Also arise at Reactions with chlorinated chlorine by-products, often are carcinogenic. It is also known that O-alkyl oximes Oxidation of O, N-dialkylhydroxylamines on silver oxide or silver carbonate can be prepared (J. Amer. Chem. Soc. 98, 7375-7379 [1976]), although no uniform product is created. It also requires the use of Silver as an oxidizing agent to avoid silver loss elaborate regeneration. Another oxidizing agent is described in J. Chem. Soc. Commun, 1984, 606-607, N-chlorosuccinimide. With this The process is disadvantageous in that the oxidation in methylene chloride, a solvent suspected of carcinogenic effects, Must be carried out, making complex security Actions are required.

It has now been found that O-alkyl oximes of the general formula

in which R¹ and R² are hydrogen atoms, aliphatic or aromatic hydrocarbon radicals which can be substituted by halogen atoms, hydroxyl, alkoxy, carboxy or nitrile groups, where R¹ or R² together with R³ or R¹ together with R² also for a - (CH₂) _n -Rest with n = 4 to 7, and R³ is a hydrogen atom or an alkyl radical with 1 to 12 C atoms, which may contain halogen atoms, hydroxyl groups or alkoxy groups, mean, R³ together with R¹ or R² for one - (CH₂ ) _n residue with n = 4 to 7, can be produced particularly advantageously in that O-alkylhydroxylamines of the general formula

in which R¹, R² and R³ have the meaning given above, electrochemically oxidized.

The reaction according to the invention is illustrated by the following reaction scheme illustrates:

The result of the method according to the invention is surprising since Tetrahedron 28, 4497-4501 (1972), or DE-PS 25 39 767 is known that the electrochemical oxidation of by N-formyl, N-benzoyl or N-acetyl-protected amino compounds in the presence of nuclephiles Solvents, such as methanol, lead to N-α-methoxylated products, such as The following reaction equation clarifies:

R = H, alkyl, aryl.

In the starting materials of formula II, the radicals R¹ and R² are z. B. for hydrogen atoms or for aliphatic or aromatic hydrocarbon radicals, which can contain halogen atoms, such as fluorine, chlorine or bromine atoms, hydroxyl groups, alkoxy groups, such as methoxy or ethoxy groups, carboxy groups or nitrile groups. Aliphatic radicals mean straight-chain, branched or ring-shaped hydrocarbon radicals, which can also contain double bonds. These are e.g. B. alkyl and alkylene radicals having 1 to 12, preferably 1 to 8, in particular 1 to 4 carbon atoms, such as methyl, ethyl, n- and iso-propyl, n-, iso- and tert-butyl , Vinyl, allyl or isopropenyl groups, furthermore cycloalkyl radicals having 3 to 8, preferably 5 and 6, carbon atoms, such as cyclopentyl or cyclohexyl groups. Aryl or alkylaryl groups having 6 to 12, preferably 6 to 8, carbon atoms, such as phenyl, benzoyl or phenylethyl radicals, can be considered as aromatic hydrocarbon radicals. The radical R¹ or R² can also together with the radical R³, and the radicals R¹ and R² can also together represent a radical of the formula - (CH₂) _n -, in which n is an integer from 4 to 7. In the first case z. B. isooxazolidines, in the second case the molecule contains z. B. cyclopentyl or cyclohexyl rings.

The rest R³ stands for a hydrogen atom or for a straight chain or branched alkyl radical having 1 to 12, preferably 1 to 8, in particular 1 to 4 carbon atoms, the halogen, such as fluorine, bromine or chlorine, Alkoxy groups, such as methoxy or ethoxy groups, or hydroxyl groups may contain. Furthermore, R³ can be part of the above-mentioned ring-shaped Be leftovers.

A solution of the is advantageously used for the electrooxidation O-alkylhydroxylamines in a solvent. Are suitable as solvents those that are sufficiently stable under the electrolysis conditions. The are z. B. ethers such as tetrahydrofuran, ketones such as acetone, nitriles such as Acetonitrile or alcohols such as alkanols with 1 to 4 carbon atoms. Particularly good methanol and ethanol are suitable.

To ensure sufficient conductivity of the electrolyte for the electrolysis ensure, the solution of the O-alkylhydroxylamine becomes a conductive salt (Auxiliary electrolyte) added. The chemical composition of the auxiliary electrolyte does not play an essential role in the invention. It can be therefore all the conductive salts or common in organic electrochemistry Use conductive salt mixtures, but it is advantageous to be cheap and good Select traceable conductive salts. Examples include halides, such as chlorides, bromides or fluorides, perchlorates, tetrafluoroborates, Hexafluorophosphates or sulfonates. The respective cations of the conductive salts can, for example, alkali, alkaline earth, ammonium or tetraalkylammonium ions be.

The composition of the electrolyte can be chosen within wide limits will. For example, the electrolyte consists of an alcoholic one Solution with an O-alkylhydroxylamine content of 1 to 50, preferably 3 to 20 wt .-% and a content of conductive salt of 0.1 to 20, preferably 0.5 to 5% by weight.

The process according to the invention can be carried out in the usual technical Electrolysis cells are carried out. Undivided ones are preferably used Flow cells that are useful to minimize cell voltage  have small electrode spacings of, for example, 0.25 to 2 mm. As anodes z. B. precious metals such as platinum, with precious metal oxides doped titanium, metal oxides such as MnO₂ and PbO₂, however preferred Graphite used. As cathode material such. B. lead, iron, steel, Nickel or precious metals like platinum are used. Preferred cathode material is also graphite.

The amounts of electricity required are in the method according to the invention unusually low. So are the O-alkylhydroxylamines in electrolysis already fully implemented with 2 to 2.5 F / mol O-alkylhydroxylamine. The Current density is not a limiting factor; B. 0.1 to 25 A / dm², preferably 3 to 15 A / dm².

The method according to the invention is carried out e.g. B. at temperatures up to 5 ° C. below the boiling point of the solvent used, preferably at 5 up to 90 ° C, especially at 10 to 70 ° C. Is used as a solvent Methanol or ethanol is conveniently electrolyzed at Temperatures from 15 to 35 ° C.

The processing of the electrolysis discharges can be done according to known Make methods. The electrolysis discharge is expediently made by distillation worked up. Excess solvent is first distilled off. The Leitsalze can z. B. by filtration or extraction separate and the oxime pure by distillation or recrystallization win. Solvents, possibly unreacted O-alkylhydroxylamine and the Conductive salts can advantageously be returned to electrolysis.

The process according to the invention can be carried out both batchwise and be carried out continuously.

The O-alkyl oximes produced by the process according to the invention Formula I are versatile intermediates for the synthesis of Pesticides.

Examples 1 to 6

The electrooxidations were carried out in an undivided electrolysis cell 9 graphite electrodes (8 columns, electrode spacing 0.5 mm) at temperatures from 20 to 25 ° C. During the electrolysis with a Current density of 5 A / dm² was rubbed, the electrolyte with the in of the composition specified in the table with 200 l / h via a heat exchanger pumped through the cell.  

After a charge of 2 to 2.5 F / mol of the starting compound Formula II has ended the electrolysis. Then the issue became Distilled off solvent at normal pressure, the precipitated conductive salt Room temperature separated by a pressure filter and the filtrate pure distilled.

The O-alkyl oximes of formula I were in at a conversion of <95% Yields between 28 and 65%, based on the starting material of formula II, receive.

Conductive salt and solvent recovered during workup can be used again in an electrooxidation.  

table

Claims (4)

1. Process for the preparation of O-alkyl oximes of the general formula in which R¹ and R² are hydrogen atoms, aliphatic or aromatic hydrocarbon radicals which can be substituted by halogen atoms, hydroxyl, alkoxy, carboxy or nitrile groups, where R¹ or R² together with R³ or R¹ together with R² also for a - (CH₂) _n - radicals with n = 4 to 7, and R³ is a hydrogen atom or an alkyl radical with 1 to 12 C atoms, which may contain halogen atoms, hydroxyl groups or alkoxy groups, where R³ together with R¹ or R² represents a - (CH₂ ) _n residue with n = 4 to 7, characterized in that O-alkylhydroxylamines of the general formula in which R¹, R² and R³ have the meaning given above, are electrochemically oxidized. 2. The method according to claim 1, characterized in that one O-alkylhydroxylamines in a solvent and in the presence of a Conductive salt is electrochemically oxidized. 3. The method according to claim 2, characterized in that one in the electrochemical oxidation as an electrolyte is an alcoholic solution with an O-alkylhydroxylamine content of 1 to 50% by weight and Conductive salt from 0.1 to 20 wt .-% is used. 4. The method according to claim 3, characterized in that one as alcohol Methanol or ethanol used.