DE19904929A1 - Process for the preparation of 2,2,3,3-tetramethoxypropanol - Google Patents

Abstract

The invention relates to a method of producing 2,2,3,3-tetramethoxypropyl alcohol by way of an electrochemical oxidation of methylglyoxaldimethylacetal using a mixture of methanol, water and an auxiliary electrolyte as medium for the electrolysis and an iron, steel, platinum or zinc cathode.

Description

The present invention relates to a method for manufacturing of 2,2,3,3-tetramethoxypropanol by electrochemical oxidation of methylglyoxaldimethylacetal using a Mi containing methanol and water as electrolysis medium and a cathode made of iron, steel, platinum or zinc.

From EP-A-460 451 it is known to use α-hydroxymethyl ketals electrochemical oxidation of carbonyl compound with alcohols to manufacture. As part of a list, the appropriate α-hydroxymes 2,2,3,3-Tetramethoxypropanol is also called thylketale guided. This document uses, among other things, as cathode material graphite recommended. It has been shown that the Use of such cathodes in the case of many α-hydroxyethyls tals for good results, especially yields and selectivities acts. In the case of the production of 2,2,3,3-tetramethoxy However, propanol proved that only certain of those in this Scripture mentioned cathode materials to satisfactory yields to lead.

The invention was therefore based on the object of a method that the manufacture of 2,2,3,3-tetramethoxypropa nol with high selectivity, conversion and yield.

The electrolysis liquid contains in addition to the starting compounds Methanol and methoxyglyoxaldimethylacetal water, preferably in Amounts from 0.1 to 5% by weight.

So that the electrolysis liquid has sufficient conductivity has, it is mixed with an auxiliary electrolyte. As Auxiliary electrolytes are preferably halogen-containing compounds gene, for example elemental halogen, alkyl halides, halo genhydrogen and preferably salts of halides, especially be prefers iodides and bromides. Among the salts of the halides are especially ammonium halides, e.g. B. ammonium bromide or ammo nium iodide or tetrabutylammonium iodide or metal halides, be preferably alkali metal halides such as sodium bromide, sodium iodide, Potassium iodide or potassium bromide is preferred.

The electrolysis liquid preferably has the following composition:

• - 1 to 49, preferably 5 to 30 wt .-% methylglyoxaldimethyl acetal  
• - 50 to 98.8, preferably 70 to 95 wt .-% methanol
• - 0.1 to 5, preferably 0.5 to 3 wt .-% of an auxiliary electrode lyten and
• - 0.1 to 5, preferably 0.5 to 3 wt .-% water.

The reaction according to the invention is preferably carried out at current densities of 0.5 to 25 A / dm ² and at temperatures from -20 to 60 ° C., preferably 0 to 40 ° C.

The choice of pressure is generally not critical. In general The process at pressures of 0.1 to 10 bar is preferred exercised at normal pressure. High pressures are particularly suitable at high reaction temperatures.

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

Those made of iron, steel, platinum or zinc are used as cathodes. The steel can be both unalloyed steel and higher-alloy steel with additives such as chrome, manganese, boron or stainless steel. The term iron is not only elemental iron but also the well-known types of iron, which are more or less Si, Mn, S, P and further additions of Al, Cr, Mn, Mo, Ni, Ta, Ti, Vn, Si , Co, and other common alloy components. V ₂ A, V ₄ A stainless steel is particularly preferred.

The process according to the invention can be carried out in the generally customary manner Electrolysis cells are carried out, for example in un divided flow cells, e.g. B. undivided plate-frame-cell len.

In general, the electrolysis is stopped when sales of approximately 100% is reached. Processing the electroly Sea liquid is made according to the general principles in organic chemistry my usual process, for example by distillation.

Experimental part Preparation of 2,2,3,3-tetramethoxypropanol Example 1 (comparative example)

Undivided bipolar plate stack cell
10 gaps, 0.5 mm gap distance
Anode: graphite
Cathode: graphite
Total electrode area: 29.2 dm ²

Approach:
450 g of methylglyoxal dimethyl acetal
45 g of potassium iodide
15 g water
2490 g of methanol
Current: 5 A.
Duration: 5 hours
Temperature: approx. 30 ° C
Turnover: <99%
Yield: 24.6

Example 2

Undivided plate-frame cell
6 mm electrode gap
Anode: Sigraflex
Cathode: Type 1.4301 steel
Total electrode area: 2.56 dm ²

Approach:
75 g of methylglyoxal dimethyl acetal
7.5 g potassium iodide
0.5 g water
417 g of methanol
Current: 6.4 A
Duration: 6.8 h
Temperature: approx. 20 ° C
Sales: 98.1%
Yield: 69.9

Claims (5)

1. Process for the preparation of 2,2,3,3-tetramethoxypropanol by electrochemical oxidation of methylglyoxaldimethyl acetal using a mixture containing metha nol, water and an auxiliary electrolyte as the electrolysis medium and a cathode made of iron, steel, platinum or zinc. 2. The method according to claim 1, characterized in that the Electrolysis medium contains 0.1 to 5 wt .-% water. 3. The method according to claim 1 or 2, characterized in that the electrolysis medium contains a halogen-containing auxiliary electrolyte contains. 4. The method according to claims 1 to 3, characterized in net that one as an auxiliary electrolyte iodides or bromides puts. 5. The method according to claims 1 to 4, characterized in that the electrolysis medium has the following composition:

• - 1 to 49 wt .-% methylglyoxaldimethylacetal
• - 50 to 98.8 wt: - methanol
• - 0.1 to 5 wt .-% auxiliary electrolyte and
• - 0.1 to 5% water.