DE4017575A1 - Prepn. of alpha-hydroxy-methyl-aryl-ketal(s) - by electrochemical oxidation of an aryl-methyl ketone with an alkanol in the presence of a small amt. of water - Google Patents

Abstract

The prepn. of alpha-hydroxymethyl arylketals of formula (I) comprises electrochemical oxidation of an arylmethylketone of formula (II) with an alkanol of formula R2OH (III) in the presence of an auxiliary electrode and 0-5 wt.% water R1 = H, 1-20C alkyl, 2-20C alkenyl, 2-20C alkynyl, 2-20C alkoxyalkyl, 4-20C alkenyloxyalkyl, 3-12C cycloalkyl or 4-20C cycloalkylalkyl, R2 = 1-8C alkyl; R3-R7 = each H, 1-8C alkyl, 1-8C alkoxy, 2-8C alkenyl, 3-8C alkenyloxy, 2-8C alkynyl, 3-8C alkynyloxy, halogen, CN, Ph, PhO, halophenyl, halophenoxy, carboxy, 2-8C alkoxycarbonyl, 3-8C alkenyloxycarbonyl, 3-8C alkynyloxycarbonyl; or R3 and R4 or R4 and R5 together form -(CH2)-n or -(CH=CH)-m opt. substd. mono- or di- substd. by 1-8C alkyl, 1-8C alkoxy and/or halogen n = 1-10 m = 1-3. USE/ADVANTAGE - (I) are intermediates in the prepn. of hydroxyphenones and can therefore be used in the prepn. of plant protecting agents photoinitiators and pharmaceuticals. The process overcomes the disadvantages (e.g. poor yields, multi-stage reactions, rearrangement instead of substitution, long reaction times) associated with previous processes.

Description

The present invention relates to a method for producing α-Hydroxymethylaryl ketals by electrochemical oxidation of aryl methyl ketones with alkanols in the presence of an auxiliary electrolyte and 0 to 5% by weight water.

From Tetrahedron Letters 25, 691-694 (1984) and from J. Org. Chem., 51, 130-135 (1986) is the preparation of α-hydroxymethylaryl ketals from difficult to access starting compounds under basic conditions in known multi-stage reactions with long reaction times.

The electrochemical oxidation of aliphatic aldehydes and ketones with anodically generated "J⁺" in the presence of an alcohol under basic conditions for the corresponding α-hydroxyacetals and ketals is in J. Chem. Soc., Perk. I, 73-77 (1986). The oxidation under neutral conditions only give low yields (JP-A-57/188 684). The The formation of α-hydroxy compounds from aromatic ketones is not described. Rather, it is known from Tetrahedron Letters 30, 371-374 (1989) that aryl ketones under similar conditions, i.e. H. in alcoholic Solution, but either with iodine / lithium perchlorate as auxiliary electrolyte not be oxidized or only react to the ketals. In the presence of Orthoesters under otherwise unchanged conditions will not find any 2-hydroxylation but a 1,2-rearrangement of the aryl radical to 2-alkyl-2- arylacetic acid esters instead.

The invention was therefore based on the object of a method for the production of α-hydroxymethylaryl ketals and the previously available remedied disadvantages.

Accordingly, there has been a process for producing α-hydroxymethylaryl ketals of the general formula I

in which the substituents
R¹ is hydrogen, C₁ to C₂₀ alkyl, C₂ to C₂₀ alkenyl, C₂ to C₂₀ alkynyl, C₂ to C₂₀ alkoxyalkyl, C₄ to C₂₀ alkenyloxyalkyl, C₃ to C₁₂ cycloalkyl or C₄ to C₂₀- Cycloalkyl-alkyl,
R² is C₁ to C₈ alkyl and
R³, R⁴, R⁵, R⁶, R⁷ independently of one another hydrogen, C₁ to C₈ alkyl, C₁ to C₈ alkoxy, C₂ to C₈ alkenyl, C₃ to C₈ alkenyloxy, C₂ to C₈ alkynyl, C₃- to C₈-alkynyloxy, halogen, cyano, phenyl, phenoxy, halophenyl, halophenoxy, carboxy, C₂- to C₈-alkoxycarbonyl, C₃- to C₈-alkenyloxycarbonyl, C₃- to C₈-alkynyloxycarbonyl or R³ and R⁴ or R⁴ and R⁵ together an optionally by C₁ to C₈ alkyl, C₁ to C₈ alkoxy and / or halogen monosubstituted or disubstituted (CH ₂ ) _n - or (CH = CH) _m group, in which n for 1 to 10 and m for 1 up to 3,
found, which is characterized in that an aryl methyl ketone of the general formula II

in which Ar and R¹ have the meanings given above, with an alkanol of the general formula III

R²-OH (III)

in which R² has the meanings given above, in the presence of an auxiliary electrolyte and 0 to 5% by weight of water electrochemically oxidized.

In principle, all aryl methyl ketones come as starting compounds Formula II which is inert under the electrolysis conditions Bear substituents.  

The substituents in the formulas I, II and III have the following meanings:
R¹ is hydrogen,
unbranched or branched C₁ to C₂₀ alkyl, preferably C₁ to C₁₂ alkyl, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec.-butyl, tert.-butyl, n -Pentyl, iso-pentyl, sec.- Pentyl, tert.-pentyl, neo-pentyl, 1,2-dimethylpropyl, n-hexyl, iso-hexyl, sec.-Heyl, n-heptyl, iso-heptyl, n- Octyl, n-nonyl, iso-nonyl, n-decyl, iso-decyl, n-undecyl, iso-undecyl, n-dodecyl and iso-dodecyl, particularly preferred unbranched or branched C₁- to C₈-alkyl such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec.-butyl, tert.-butyl, n-pentyl, iso-pentyl, sec.-pentyl, tert.-pentyl, neo-pentyl, 1, 2-dimethylpropyl, n-hexyl, iso-hexyl, sec.-hexyl, n-heptyl, iso-heptyl, n-octyl,
unbranched or branched C₂ to C₂₀ alkenyl, preferably unbranched or branched C₂ to C₈ alkenyl, such as vinyl, allyl, buten-1-yl, buten-2-yl, buten-2-yl, penten-1-yl, Penten-2-yl, penten-3-yl, penten-4-yl, hexen-1-yl, hexen-2-yl, hexen-3-yl and hexen-4-yl,
unbranched or branched C₂ to C₂₀ alkynyl, preferably unbranched or branched C₂ to C₈ alkynyl, such as ethynyl, 1-propin-3-yl, 1-butyn-3-yl, 1-pentyn-3-yl, 1- Hexin-5-yl, 1-heptin-6-yl and 1-octin-7-yl,
unbranched or branched C₂ to C₂₀ alkoxyalkyl, preferably unbranched or branched C₂ to C₈ alkoxyalkyl, such as methoxymethyl, ethoxymethyl, n-propoxymethyl, iso-propoxymethyl, n-butoxymethyl, iso-butoxymethyl, sec.-butoxymethyl, tert.- Butoxymethyl, n-pentoxymethyl, iso-pentoxymethyl, sec.-pentoxymethyl, tert.-pentoxymethyl, neo-pentoxymethyl, 1,2-dimethylpropoxymethyl, n-hexoxymethyl, iso-hexoxymethyl, sec.-hexoxymethyl, n-heptoxymethyl, iso-heptoxymethyl , Methoxy-1-ethyl, ethoxy-1-ethyl, n-propoxy-1-ethyl, iso-propoxy-1-ethyl, n-butoxy-1-ethyl, iso-butoxy-1-ethyl, sec.-butoxy- 1-ethyl, tert-butoxy-1-ethyl, n-pentoxy-1-ethyl, iso-pentoxy-1-ethyl, sec-pentoxy-1-ethyl, tert-pentoxy-1-ethyl, neo-pentoxy -1-ethyl, 1,2-dimethylpropoxy-1-ethyl, n-hexoxy-1-ethyl, iso-hexoxyl-ethyl, sec.-hexoxy-1-ethyl, methoxy-2-ethyl, ethoxy-2-ethyl, n-propoxy-2-ethyl, iso-propoxy-2-ethyl, n-butoxy-2-ethyl, iso-butoxy-2-ethyl, sec.-butoxy-2-ethyl, tert.-butoxy-2-ethyl, n-pentox y-2-ethyl, iso-pentoxy-2-ethyl, sec.-pentoxy-2-ethyl, tert.-pentoxy-2-ethyl, neo-pentoxy-2-ethyl, 1,2-dimethyl-propoxy-2- ethyl, n-hexoxy-2-ethyl, iso-hexoxy-2-ethyl and sec.-hexoxy-2-ethyl,
unbranched or branched C₄ to C₂₀ alkenyloxyalkyl, preferably unbranched or branched C₄ to C₈ alkenyloxyalkyl, such as allyloxymethyl, allyloxy-1-ethyl, allyloxy-2-ethyl, allyloxy-1-propyl and allyloxy-2-propyl,
C₃- to C₁₂-cycloalkyl, preferably C₃- to C₈-cycloalkyl, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl,
C₄ to C₂₀ cycloalkyl-alkyl, preferably C₄ to C₈-cycloalkylalkyl, such as cyclopentyl-alkyl, 2-cyclopentyl-ethyl, 1-cyclopentyl-ethyl, cycloalkyl-methyl, 1-cyclohexylethyl and 2-cyclohexylethyl,
C₁ to C₈ alkyl, preferably unbranched C₁ to C₈ alkyl such as methyl, ethyl, propyl, butyl, n-pentyl, n-hexyl, n-heptyl or n-octyl, particularly preferably unbranched C₁ to C₄ alkyl such as Methyl, ethyl, n-propyl or n-butyl,
R³, R⁴, R⁵, R⁶, R⁷ independently of one another
Hydrogen,
C₁ to C₈ alkyl, preferably C₁ to C₄ alkyl, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl or tert-butyl, particularly preferably methyl or ethyl ,
C₁- to C₈-alkoxy, preferably C₁- to C₄-alkoxy such as methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, iso-butoxy, sec-butoxy or tert-butoxy, particularly preferably methoxy or ethoxy ,
C₂ to C₈ alkenyl, preferably C₂ to C₄ alkenyl such as vinyl, allyl, 3-buten-1-yl, 2-buten-1-yl and 1-buten-1-yl,
C₃- to C₈-alkenyloxy, preferably C₃- to C₆-alkenyloxy such as allyloxy, buten-1-yloxy, buten-1-yloxy, penten-1-yloxy, penten-1-yloxy, penten-2-yloxy, penten-3 -yloxy, penten-4-yloxy, hexen-1-yloxy and hexen-2-yloxy,
C₂ to C₈ alkynyl, preferably C₂ to C₄ alkynyl such as ethynyl, 2-propn-1-yl and 3-butyn-1-yl,
C₃- to C₈-alkynyloxy, preferably C₃- to C₄-alkynyloxy such as propynoxy and butynoxy,
Halogen such as fluorine, chlorine, bromine or iodine, preferably fluorine, chlorine and bromine,
Cyano,
Phenyl,
Phenoxy,
Halophenyl, preferably chlorophenyl such as 2-chlorophenyl and 4-chlorophenyl,
Halophenoxy, preferably chlorophenoxy such as 2-chlorophenoxy and 4-chlorophenoxy,
Carboxy,
C₂ to C₈ alkoxycarbonyl, preferably C₂ to C₄ alkoxycarbonyl such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, n-butoxycarbonyl, isobutoxycarbonyl and tert.-butoxycarbonyl,
C₃- to C₈-alkenyloxycarbonyl, preferably C₃- to C₆-alkenyloxycarbonyl such as allyloxycarbonyl, buten-1-yloxycarbonyl, penten-1-yloxycarbonyl and hexen-1-yloxycarbonyl,
C₃- to C₈-alkynyloxycarbonyl, preferably C₃- to C₅-alkynyloxycarbonyl such as propynyloxycarbonyl and butynyloxycarbonyl,
R³ and R⁴ or R⁴ and R⁵ together
(CH ₂ ) _n , such as CH ₂ , (CH ₂ ) ₂ , (CH ₂ ) ₃ , (CH ₂ ) ₄ , (CH ₂ ) ₅ and (CH₂) ₆, preferably (CH₂) ₃, (CH₂) ₄, (CH₂) ₅; (CH₂) ₆, particularly preferably (CH₂) ₃ and (CH₂) ₄,
(CH = CH) _m , such as (CH = CH), (CH = CH) ₂ , (CH = CH) ₃ , preferably (CH = CH) ₂), (CH = CH) ₃ particularly preferably (CH = CH) ₂,
1 to 10, preferably 3 to 6, particularly preferably 3 and 4,
1 to 3, preferably 2 and 3, particularly preferably 2.

All radicals R³ to R⁷ may not be hydrogen, 0 are preferred to 3 not equal to hydrogen, 0 to 2 to not equal are particularly preferred Hydrogen.

To ensure sufficient conductivity of the electrolyte for the electrolysis ensure, the electrolysis mixture is preferably a halogen-containing Auxiliary electrolyte added. Examples of auxiliary electrolytes are: elemental halogen, alkyl halide and hydrogen halide, preferred iodides or bromides are used, such as ammonium halides, e.g. B. Ammonium bromide, ammonium iodide and tetrabutylammonium iodide and especially  preferably metal halides such as sodium bromide, sodium iodide, potassium iodide and potassium bromide.

The composition of the electrolyte can be chosen within wide limits. The electrolyte generally contains 0 to 5% by weight of water. The electrolytes can have the following compositions, for example
1 to 49, preferably 5 to 30% by weight of ketone of the formula II,
50 to 98.9, preferably 70 to 95% by weight alkanol R²-OH,
0.1 to 5, preferably 0.5 to 3 wt .-% auxiliary electrolyte and
0.1 to 5, preferably 0.5 to 3 wt .-% water.

The electrochemical oxidation is preferably taken at current densities of 0.5 to 25 A / dm² and at temperatures from (-20) to 60 ° C, especially 0 up to 40 ° C. Higher temperatures are possible, but generally bring no advantages. The reaction can be reduced or increased, but preferably at normal pressure (atmospheric pressure) and in itself usual electrolysis cells are carried out. One preferably works with undivided flow cells.

Suitable anode materials are, for example, noble metals such as platinum or oxides such as ruthenium and chromium oxide or RuO _x TiO _x mixed oxides and preferably graphite.

Iron, steel, nickel and Precious metals such as platinum and preferably graphite.

Working up is carried out in a manner known per se, preferably the compounds I according to the invention worked up by distillation.

The hydroxymethylaryl ketals I are important precursors for Hydroxyphenones are and can be used as pesticides, photoinitiators and pharmaceutical products.

Examples 1 to 5

The starting compounds II were in an undivided cell with 11 bipolar electrodes in an electrolyte containing 45 g of potassium iodide Contained auxiliary electrolytes, subjected to electrolysis. Anode as well The cathode consisted of graphite. The current density was 3.3 A / dm² and the Electrolysis temperature 25 ° C. The electrolyte was flowed through 200 l / h pumped through the cell. The exact composition of the electrolyte as well as further details of the examples are in the table compiled:  

table

Claims (5)

1. Process for the preparation of α-hydroxymethylaryl ketals of the general formula I in which the substituents
R¹ is hydrogen, C₁ to C₂₀ alkyl, C₂ to C₂₀ alkenyl, C₂ to C₂₀ alkynyl, C₂ to C₂₀ alkoxyalkyl, C₄ to C₂₀ alkenyloxyalkyl, C₃ to C₁₂ cycloalkyl or C₄ to C₂₀- Cycloalkyl-alkyl,
R² is C₁ to C₈ alkyl and
R³, R⁴, R⁵, R⁶, R⁷ independently of one another hydrogen, C₁- to C₈- alkyl, C₁- to C₈-alkoxy, C₂- to C₈-alkenyl, C₃- to C₈-alkenyloxy, C₂- to C₈-alkynyl, C₃- to C₈-alkynyloxy, halogen, cyano, phenyl, phenoxy, halophenyl, halophenoxy, carboxy, C₂- to C₈-alkoxycarbonyl, C₃- to C₈-alkenyloxycarbonyl, C₃- to C₈-alkynyloxycarbonyl or R³ and R⁴ or R⁴ and R⁵ together an optionally by C₁ to C₈ alkyl, C₁ to C₈ alkoxy and / or halogen monosubstituted or disubstituted (CH ₂ ) _n - or (CH = CH) _m group, in which n for 1 to 10 and m for 1 up to 3,
characterized in that an aryl methyl ketone of the general formula II in which Ar and R¹ have the meanings given above, with an alkanol of the general formula IIIR²-OH (III) in which R² has the meanings mentioned above, in the presence of an auxiliary electrolyte and 0 to 5% by weight of water, electrochemically oxidized. 2. The method according to claim 1, characterized in that for the electrochemical oxidation an electrolyte of the composition
1 to 49% by weight of ketone of the formula II,
50 to 98.8% by weight of alkanol R²-OH,
0.1 to 5 wt .-% auxiliary electrolyte and
0.1 to 5% by weight of water
used. 3. The method according to claim 1, characterized in that the performs electrochemical oxidation on graphite electrodes. 4. The method according to claim 1, characterized in that the electrochemical oxidation at temperatures from (-20) to 60 ° C and at Current densities from 0.5 to 25 A / dm². 5. The method according to claim 1, characterized in that as Auxiliary electrolyte uses iodide or bromide.