DD301512A7 - PROCESS FOR PREPARING AROMATIC HYDROXYALDEHYDE - Google Patents

Abstract

The invention relates to a process for the preparation of aromatic hydroxyaldehydes, for example vanillin or ethylvanillin. These compounds, which are shown in a chemical process, are used in the production of foodstuffs and in the cosmetics industry. The process is characterized in that arylglycolic acid is subjected to air oxidation with a supported copper-I-oxide supported catalyst in alkaline solution. {Aromatic hydroxyaldehydes; ethyl vanillin; vanillin; Arylglykolsäure; Alpha-keto acid; Cuprous oxide catalyst; Supported catalyst; Fixed bed process; air oxidation; aqueous-alkaline medium}

Description

Field of application of the invention

The invention relates to a process for the preparation of aromatic hydroxy aldehydes, such as ethyl vanillin or vanillin, which are widely used as taste, aroma or odor substances in the food and cosmetics industry and serve as raw materials in pharmacy.

Characteristic of the known state of the art

The industrially important compounds ethylvanillin and vanillin are prepared fully synthetically preferably by condensation of guarhol or guaiacol with formaldehyde in the presence of o-hydroxyaminobenzenesulfonic acid or p-nitrosodimethylaniline. Explanations can be found in Houben-Weyl, Methods of Organic Chemistry, Vol. VII, Part 1 (1954), pp. 39-42.

Due to their high isomer content, these processes are uneconomical, labor-intensive and also highly polluting.

So you have to work on the one hand with oleum, on the other hand with the carcinogenic p-Nitrosodimethylanilin. Formaldehyde is generally needed.

In search of better processes with higher selectivity, Boedecker and Volk (U.S. Patent 2,062,205) have developed a process which first produces the corresponding arylglycolic acids by reacting reactive phenols with sodium glyoxylate.

ONa rs ONa

- R

Il

H-G-COONa

O = O-ONa

The oxidation to alpha-keto acid is then carried out with copper-ll-oxide precipitated freshly from copper sulfate / sodium hydroxide solution or copper-II-chloride and sodium hydroxide solution (US Pat. No. 2,640,083).

ONa ONa

+ 2 CuO -s * IJ + Ou ₂ O + H ₂ O

H-C-OH

COONa COONa

The aldehyde synthesis is then easily by aeidolytic decarboxylation.

According to the already mentioned US Pat. No. 2,062,205, the preparation of aromatic aldehydes or of vanillin takes place in an aqueous alkaline medium with the addition of copper sulfate or copper II oxide.

No. 2,544,999 describes the preparation of vanillin by alkaline oxidation of lignocellulose solutions of the spent sulphite liquor in the presence of a copper catalyst, with special consideration of oxygen as oxidant, its dispersion in the reaction mixture and the alkalinity of the solution. The resulting in the first reaction sludge contains the added copper in the form of a mixture of different copper oxides and possibly metallic copper. This copper-containing catalyst slurry is repeatedly used and increases the vanillin yield.

In the synthesis of ethyl vanillin and vanillin high selectivity is ensured by a preferred attack in the p-position.

Problems in industrial use but the unsatisfactory course of oxidation. To achieve a high degree of conversion, a large excess of copper-ll-oxide is required, up to ten times the stoichiometric amount. On the one hand, this leads to secondary reactions, but on the other hand, above all, to a heavy metal salt load and to large problems in the separation of the copper oxide mixture after the reaction.

As an alternative Maggioni and Minisci (DE-OS 2930222) oxidized the entsorechenden arylglycolic acids with oxygen or air in the presence of cupric chloride in an acidic medium. In the production of ethyl vanillin pure oxygen is needed to achieve high yields. In addition, there are a number of secondary reactions with a total of unsatisfactory isomer distribution. /

Comparable with this are the statements in DE-AS 2804063, where in the preparation of the 3-alkoxy-4-hydroxybenzaldehyde in the second stage, the oxidation of Arylglykolsäurederivate u.a. by means of oxygen-containing gas in the presence of copper-lloxid in aqueous-alkaline solution, but with better selectivity and yield. Bauer and Steuer (DE-OS 2115551) oxidized the arylglycolic acids by adding polyvalent Nebengruppenrr.etallsalzen in an aqueous-acidic medium. They obtained satisfactory yields, but it was found that the high stereoselectivity of Arylglykolsäuresynthese was repealed by a Friesian shift in the aromatic in the oxidation. Thus, undesired o-levels of 5 to 10% were found. Another disadvantage is the high heavy metal salt pollution.

In another solution variant, the repeated use of the obtained in the oxidation of arylglycolic acid with copper-ll-oxide copper-l-oxide precipitate for a catalytic Luftoxydation is proposed. This leads to a crude product with high yield and good selectivity. However, this does not solve the technological problem of separating off the solid in the reaction mixture in large quantities.

Object of the invention

The aim of the invention is a process for the preparation of aromatic hydroxyaldehydes, wherein the oxidation step is selectively carried out by catalytic air oxidation. For this purpose, the catalysts used in a small amount should be easy to handle, highly effective and easily separable in order to enable a technical realization without problems.

Explanation of the essence of the invention

The object of the invention is to carry out the oxidation of the arylglycolic acids to the alpha-keto acid while maintaining the high stereoselectivity without using larger amounts of heavy metal salts.

The catalytic air oxidation of the arylglycolic acids in an aqueous-alkaline medium is carried out in a known manner in the presence of an oxidation catalyst. The catalyst used is copper 1-oxide.

For practicing the reaction, the arylglycolic acid solution having a content of 0.1 to 1.0 mol / l, preferably 0.2 to 0.4 mol / l, has a free alkalinity of 0.1 to 2.0 mol / l, preferably 0.5 to 1.2 mol / l, adjusted with sodium hydroxide solution and with 0.05 to 2.0 parts by mass in% copper-l-oxide catalyst, preferably 0.2 to 1.0 mass parts in% , based on arylglycolic acid, added. For oxidation, it is then gassed intensively with air for 6 to 15 hours to 353 to 373 K.

According to the invention, the technical implementation of the oxidation of the arylglycolic acids takes place in a fixed-bed process with a fixed supported catalyst.

For this purpose, copper-l-oxide is applied to different substances, for example silicon dioxide, titanium dioxide or aluminum oxide and pressed.

Thus, the compression of copper l-oxide with silica sol leads to an active, bound to silica supported catalyst.

Another possibility is the superficial oxidation of elemental copper to copper-ll-oxide and its subsequent reduction to the catalytically active copper-l-oxide in or outside the approach.

Copper l-oxide proves to be a reactive catalyst. Diesel is obtained in finely dispersed form advantageously by reacting the arylglycolic acid with equimolar amounts of copper sulfate and sodium hydroxide solution at boiling heat. It is then filtered off, washed with water and dried in an oven under inert gas to 393 K.

The acidolytic cleavage to the aldehyde is then carried out without difficulty by acidification to a pH of 1 to 3, preferably with 40% sulfuric acid. The resulting aldehyde can be separated by filtration or centrifugation or preferably obtained by extraction with a water-insoluble organic solvent such as toluene, benzene, ethyl acetate or other solvents.

The yields of crude product obtained are usually 90 to 100% of theory. A high stereoselectivity is achieved in the production of the industrially important aldehydes ethylvanillin and vanillin. The content of the desired p-component is greater than 99% m-ethylvanillin is not detected, and the content of the o-component is only 0.2 to 1% For purification, therefore, vacuum distillation with subsequent recrystallization is sufficient.

The advantages of the method described here are manifold.

1. It is only necessary to use a small amount of heavy metal catalyst. This leads to a convenient separability deo catalyst, for example by filtration or to a general saving of this technological stage by a fixed bed catalysis.

-3- 301 ο.2

2. Only the use of less auxiliary chemicals is required. This results in an excellent economy of the process.

3. The method has excellent stereoselectivity. The desired content of the p-component is greater than 99%. This greatly facilitates a clean presentation.

4. The process is very environmentally friendly. As the organic solvent, only toluene is needed for extraction. The heavy metal salt load is extremely low.

embodiments

Example 1a

The general preparation procedure of the arylglycolic acid derivatives is first described using the example of a 4-hydroxy-3-ethoxymandelic acid solution (as starting material for ethyl vanillin).

138g Guäthol werd'jr. dissolved in 400 g of 2.5 molar sodium hydroxide solution. Separately apply 59.2 g of glyoxylic acid (100%) as a 25% solution with 400 g of 2.0 molar sodium hydroxide solution so neutralized that the temperature does not exceed 303K. Both solutions are combined and allowed to stand for 24 hours at about 293K.

The unreacted Guathol is liberated by neutralization with 40% sulfuric acid until pH6-8 and exhaustively extracted with toluene.

The conversion rate is calculated from the amount of recovered Guäthols. In the example described, it is 90 to 93%, based on the glyoxylic acid used.

Example 1b

Preparation of the dispersed copper-l-oxide catalyst.

150 ml of 40% sodium hydroxide solution are added at room temperature to 150 ml of 40% strength sodium hydroxide solution, heated to about 353K with stirring and in portions within 1 hour alternately with 1000 g of 25% copper sulfate solution (25OgCuSO ₄ χ 5H ₂ O and 750 g of water) and another 150g40% sodium hydroxide added.

The mixture is refluxed for 2 hours. It is then cooled. The reaction solution, from which ethylvanillin can be obtained by acidification, is filtered off with suction and the separated ruby red copper l-oxide precipitate is washed twice with 250 ml of water. Subsequently, the precipitate is dried in a drying oven at 393 K under nitrogen and homogenized. This copper-l-oxide catalyst is durable and active under exclusion of air for a long time.

Example 1c

Preparation of a Cu ₂ O / SiO ₂ Catalyst.

2 kg of CuSO ₄ × 5 H ₂ O are dissolved in 101 of water and heated to 323K. Thereafter, 620 g of caustic soda are dissolved in 5.81 g of water and 406 ml of 15.8% hydrazine are added and the mixture is boiled for one hour. It is then cooled, decanted, slurried with 101 of water and filtered with suction. The copper I-oxic is then dried at 423K.

550 g of dried mass are kneaded with 300 g of 30% silica sol, extruded and dried at 393K.

Example 2

Preparation of ethyl vanillin.

1000 ml of a 0.5 molar 4-hydroxy-3-ethoxy-mandelic acid salt solution are mixed with 500 g of 12% sodium hydroxide solution and 500 mg copper-l-oxide catalyst and gassed under reflux for 9 hours at 363 K internal temperature with air intensively.

Then it is cooled, filtered from the catalyst, covered with 300 ml of toluene and acidified with about 260 g of 40% sulfuric acid to pH = 1 at. Then it is extracted twice with 200 ml toluene. The combined toluene extracts are concentrated in vacuo.

Yield: 80.5 g of crude ethylvanillin (97% of theory), content of p-ethylvanillin: 99%.

Example 3

Vanillin.

1000 ml of a 0.5 molar 4-hydroxy-3-methoxy-mandelic acid salt solution are reacted and worked up analogously to Example 2.

Yield: 72.2 g of crude vanillin (95% of theory), content of p-vanillin: 99%.

The purification is carried out by vacuum distillation and subsequent recrystallization from water, toluene or toluene / gasoline.

Example 4

Preparation of 4-hydroxybenzaldehyde.

1 000 ml of an O, 5molaren4-Hydroxymandelsäuresalzlösung, 500g 10% sodium hydroxide solution, 1.5 g of copper-l-oxide catalyst are initially charged and reacted as in Example 2 and worked up.

Yield: 56.1 g (92% of theory).

Example 5

Preparation of ethyl vanillin.

2Ol of 0.5 molar 4-hydroxy-3-ethoxy-mandelic acid salt solution are mixed with 10 kg of 12% sodium hydroxide solution, 10 g of copper-l-oxide catalyst and 2 g of tetradecyl alcohol and reacted for 8 hours in 363 to 368K Tauchstrahlbegasungsreaktor. Condensate losses are compensated from time to time.

It is then cooled and separated from the catalyst. The batch is transferred to a suitable suspension vessel and acidified with 5.1 kg of 40% sulfuric acid. The Ethylvanillin resulting gas evolution is extracted once with 151 toluene and twice with 101 toluene. The toluene extracts are concentrated in vacuo. Yield: 1.628 kg crude ethyl vanillin (98% of theory), content of p-ethyl vanillin: about 99%.

Example 6

Production of vanillin.

20 l of a 0.5 molar 4-hydroxy-3-methoxymandelic acid salt solution are mixed with 10 kg of 12% sodium hydroxide solution, 20 g of 50% copper 1-oxide on SiO ₂ as catalyst and 3 g of tetradecyl alcohol and in an agitator 9 hours with stirring at 363K fumigated with air. The work-up is carried out analogously to Example 5.

Yield: 1.444 kg crude vanillin (95% of theory), content of p-vanillin: greater than 98.5%.

The preparation of the catalyst is carried out by reaction of copper-ll-oxide in an alkaline medium with equimolar amounts of hydrazine hydrate. After separation, the copper-l-oxide is mixed with silica sol, dried and then extruded.

Example 7

Preparation of ethyl vanillin.

20 μl of a 0.5 molar 4-hydroxy-3-ethoxy-mandelic acid salt solution are mixed with 10 kg of 12% strength sodium hydroxide solution and 10 g of Cu ₂ O catalyst on silica and gassed intensively with air for 8 hours. Condensation losses are supplemented with water from time to time. To prevent the formation of foam, 2 g of tetradecyl alcohol are added.

Thereafter, the mixture is cooled and acidified in the suspension vessel with 5 kg of 40% sulfuric acid to pH = 1 at.

The Ethylvanillin incurred under gas evolution is extracted once with 15IToluen and twice with 101 toluene each time. The

combined toluene phases are concentrated in vacuo. /

Yield: 1.61 kg crude ethyl vanillin (97% of theory), p-ethyl vanillin content: 98.8%.

Documents contemplated: DD 289516 DE-AS 2804063 US 2062205 US 2544999

Claims (3)

1. A process for the preparation of aromatic hydroxyaldehydes by oxidation of arylglycolic acid in the presence of copper compounds to alpha-keto acid, characterized in that the oxidation is carried out in the fixed bed process with copper-l-oxide-containing, fixed supported catalyst or copper-l-oxide carrying elemental copper , 2. The method according to claim 1, characterized in that copper-l-oxide with carriers, such as silica, titania or alumina, is processed. 3. The method according to claim 1, characterized in that copper-l-oxide is prepared by oxidation of elemental copper to copper! L-oxide and subsequent reduction to copper-l-oxide.