DD289516A5 - PROCESS FOR THE PREPARATION OF AROMATIC ALDEHYDE - Google Patents

Abstract

The invention relates to a process for the preparation of aromatic aldehydes, for example vanillin or ethylvanillin. These compounds obtained in a chemical process are used in the production of food products and in the cosmetics industry. The method is characterized in that Arylglykolsaeure reacted with copper sulfate in an alkaline solution and the resulting in the reaction of copper I-oxide with the addition of atmospheric oxygen, a renewed oxidation of Arylglykolsaeure allows. {Aromatic aldehydes; vanillin; ethyl vanillin; Arylglykolsaeure; alpha-keto acid; Copper compounds; caustic soda; oxidation by air}

Description

Field of application of the invention

The invention relates to a process for the preparation of aromatic aldehydes, such as Ethylvaniliin or vanillin, which are used both in the food industry as well as in the cosmetics industry.

Characteristic of the known state of the art

Ethylvaniliin or vanillin is fully synthetic preferably by condensation of guar gum or guaiaco 'with formaldehyde in the presence of o-hi'ydroxyaminobenzolsulfonsäure or p-Nitrosodimethylanilin produced (Houben / Wey, Methods of Organic Chemistry, Volume VII, Part 1 {1954] , P.39 to 42).

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

Thus, on the one hand must be treated with oleum, on the other hand with the carcinogenic p-Nitrosodimethylanilin Pt, formaldehyde is generally needed.

In the search for better processes with a higher selectivity, Boedecker and Volk (US Pat. No. 2,062,205) have already developed a process in which first the corresponding arylglycolic acids are prepared by reacting reactive phenols with sodium glyoxylate.

ONa ONa

- R Il ^ "N - R

+ H-C-GOONa ^

H-C-OH O = C-ONa

The oxidation to alpha-keto acid is then carried out with fresh from copper sulfate / sodium hydroxide or sodium chloride or sodium chloride and sodium hydroxide precipitated copper li-oxide (US Patent 2,640,083).

-R

ONa

+ 2GuO> IH + Cu ₂ O + H ₂ O

• H-C-OH

I i

COONa COONa

The aldehyde synthesis is then easily by acidolytic decarboxylation.

In the synthesis of vanillin and ethylvanillin a 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 is a large excess of copper-ll-oxide ei required, up to ten times the stoichiometric amount. On the one hand, this leads to secondary reactions, but on the other hand especially to oir.or high heavy metal salt contamination and problems of separation of the copper oxide mixture after the reaction.

As an alternative, therefore Maggioni and Minisci (DE-OS 2930 222) oxidized the corresponding arylglycolic acid with oxygen or air in the presence of cupric chloride in an acidic medium. However, during processing it was found that even with considerably longer reaction times, 20 hours instead of 6 hours, only yields below 30% are achieved. In addition, significant amounts of tarry condensates were formed, apparently as a result of secondary reactions.

Object of the invention

The object of the invention is a process for the preparation of aromatic aldehydes, which is characterized by simple and environmentally friendly handling.

Explanation of the essence of the invention

The object of the invention is, while maintaining and optimizing the starting reaction, ie the reaction of arylglycolic acid with CuSO ₄ ZNaOH, to synthesize a copper compound which serves as a carrier of atmospheric oxygen in the oxidation in subsequent reactions and allows multiple synthesis.

For this purpose, according to the invention in a reaction vessel with stirrer, heater, reflux condenser and air blower, the Arylglykolsäurelösung submitted, as usual by reaction of e.g. Sodium glutathate was obtained with sodium glyoxylate. This solution is heated to boiling temperature and preceded in parallel with 5 moles of sodium hydroxide solution and 2.1 moles of copper sulfate per mole of arylglycolic acid. Under this reaction regime bbi only 5% excess copper sulfate is replaced by an almost complete, by-product-free synthesis and a well-settling copper-l-oxide as the final oxidation product. After completion of the reaction, the above clear reaction solution is separated and the Kupferoxidniederschlag washed once with water. Acidification of the reaction solution with sulfuric acid to pH 1 and extraction with toluene gives 96 to 101% crude Ethylvanillin that at least 98% from the p-component uno. 12% consists of the o-component.

In the reaction vessel is now further promoted Arylglykolsäurelösung, wherein the 0.5 to 2 times the amount of the starting reaction is most suitable. With the addition of 1.5 mol of sodium hydroxide solution and 0.05 mol of copper sulfate per mole of arylglycolic acid, the arylglycolic acid is then oxidized in boiling heat with the introduction of an air stream. The reaction is generally completed after 5 to 15 hours, preferably after about 10 hours. The klaie, aqueous solution, which is obtained after discontinuation of the copper l-oxides, is separated as usual and further processed by acidification and extraction. The yields thus obtained are 90 to 98% crude ethyl vanillin, the content of the p-component between 98 and 99%.

The remaining in the reaction vessel copper-l-oxide precipitate can be used for a further 5 to 10 reactions without significant yield losses occur.

It was found that a separate Cu-I oxidation to Cu-ll-oxide and subsequent reaction with arylglycolic acids is much more protracted and leads to the formation of considerable amounts of tarry hub products in addition to the desired reaction, so that no yields of more than 50% could be achieved ,

The advantages of the method described here are:

1. A high conversion rate in the starting reaction at almost equimolar amounts of CuSO ₄ by optimizing the reaction and preparing a reusable for Luftoxydation copper-l-oxide catalyst.

2. For the following Luftoxydationen only minor amounts of copper sulfate and caustic soda are required. This results in an excellent material economy.

3. Only about every ten reactions, a separation and workup of copper-l-oxide is necessary.

4. The process is extremely environmentally friendly. As organic auxiliary chemical only toluene is needed. Heavy metal pollution is low.

5. The high stereoselectivity of the process leads to a nearly isomererifreien raw product with only about 2% o-component. The workup to pure product is therefore simple and straightforward.

embodiments

example 1

Synthesis of ethyl vanelin

A 4-hydroxy-3-ethoxy-mandelic acid solution obtained from the reaction of sodium glutathate and sodium glyoxylate, which has been freed from unreacted guar and is adjusted to 0.5 molar, is used for oxidation. For this purpose, 11 solution in a sulphonation with reflux condenser before, heated to about 8O ⁰ C and are 40g 50% sodium hydroxide solution. Thereafter, it is heated to boiling heat and sets in parallel within one hour 1000g copper sulfate solution (263g CuSO ₄ x 5 H ₂ O and 737g water) and 160g 50% sodium hydroxide solution. After the addition is boiled for a further 3 hours at boiling heat. Now it is cooled and leaves the copper oxide settle. The solution obtained above is decanted off, the Cu ₂ O is washed with 500 ml of water and, after renewed settling of the Cu ₂ O, is separated off again.

The combined aqueous solution is acidified with 40% sulfuric acid to pH = 1 and extracted exhaustively with 1.51 toluene. After concentration i.r, vacuum gives 83g of crude ethylvanillin, which are 100% of theory. The fine cleaning is carried out by vacuum distillation and subsequent recrystallization from toluene / gasoline.

110.5 molar mandelic acid solution are then added to the reaction vessel and 30 g of sodium hydroxide are added. The mixture is heated with stirring to 100 ⁰ C and rinsed for 4 hours intensively with air. Thereafter, without interruption of the l.uftoxydation 7g copper sulfate dissolved in 3C ml of water added and oxidized for a further 6 hours with air. After completion of the reaction, the copper-1-oxide is allowed to settle as usual, decanted the reaction solution and washed with water. After the usual acidolytic decarboxylation with sulfuric acid and extraction with toluene, one obtains 81 g of crude ethyl vanillin, which is 97.5% of theory.

Further workup is as described.

This process of Luftoxydation is repeated eight times with the same amount of substance copper-l-oxide. For the work-up of the finally occurring copper oxide, oxidation to Cu-II-oxide and a subsequent conversion into copper sulfate with subsequent reuse has proved successful.

Example 2

vanillin

A solution of 4-hydroxy-3-methoxymandelic acid solution obtained from the reaction of sodium guaiacolate and sodium glyoxylate, which is 0.5 molar and has been freed of unreacted guaiacol, is used for the oxidation.

The first oxidation is carried out as described in Example 1 with 200 g of 50% sodium hydroxide solution and 1000 ml of copper sulfate solution containing 1.05 moles of copper sulfate. After the analogue reaction, decarboxylation and work-up, 70 g of crude vanillin are obtained. That's 98.5% of the theory.

In the following Luftoxydationen the resulting in this approach copper-l-oxide is used. The procedure is as described in Example 1.

This gives 68 g of crude vanillin, which is 96% of theory. The copper I oxide is used 10 times.

Example 3

Synthesis of 4-hydroxybenzaldehyde

A solution of 4-hydroxymandelic acid obtained by reaction of sodium phenolate and sodium glyoxylate and containing 1 mol and freed from unreacted phenol is used for the oxidation.

To this end, 111 molar solution with a total of 400 g of 50% sodium hydroxide solution and 2000 g of CuS '/ ₄ solution (525 g CuSO ₄ x 5 H ₂ O, 2.1 mol) are reacted by boiling for 3 hours.

The work-up is carried out analogously to Example 1.

The yield is 118g, which is 97% of theory. In the subsequent Luftoxydationen the resulting in this approach copper-l-oxide is used. The procedure is analogous to Example 1. On average, 115 g (95% of theory) of 4-hydroxybenzaldehyde.

Claims (9)

1. A process for the preparation of aromatic aldehydes by oxidation of arylglycolic acid in the presence of copper compounds zumalpha-keto acid, characterized in that reacted in a startup reaction aryiglycolic acid with sodium hydroxide and copper sulfate, after removal of the crude solution in a subsequent reaction to the copper-l-oxide added fresh arylglycolic acid reacted with sodium hydroxide while introducing oxygen in the air, after removal de ^r in the reaction solution reacted further subsequent reactions Arylglykolsäure and the reaction solution is worked up by acidolysis in manner known per se. 2. The method according to claim 1, characterized in that the arylglycolic acid is reacted in the boiling heat. 3. Process according to claims 1 and 2, characterized in that for the starting reaction per mole of arylglycolic acid concentric sodium hydroxide solution with 5 moles of NaOH and 2.1 moles of copper sulfate are used in parallel at boiling temperature. 4. Process according to claims 1 to 3, characterized in that 0.5 to 2 times the amount of arylglycolic acid of the starting reaction is used for the subsequent reaction. 5. Process according to claims 1 to 3, characterized in that for the subsequent reaction concentrated sodium hydroxide solution with 1.5 moles of NaOH and 0.05 moles of copper sulfate, based on one mole of arylglycolic acid, are used. 6. Process according to dt η claims 1,2,4 and 5, dadurcli characterized in that the subsequent reaction is carried out in a period of 5 to 15 hours, preferably 10 hours. 7. The method according to claims 1,2 'ind 4 to 6, characterized in that 10 subsequent reactions are carried out. 8. Process according to claims 1 to 7, characterized in that the copper-l-oxide is washed with water and the washing water is combined with the reaction solution. 9. Process according to claims 1 to 8, characterized in that the reaction solution is acidified with sulfuric acid to a pH of 1 and extracted with toluene of the aromatic aldehyde.