CS246341B1 - Method of citronellal's alkoxydihydroderivatives production - Google Patents

Description

The present invention relates to a process for the preparation of the alkoxydihydroderivatives of citronellal of the formula I

R-O CHO

where

R is methyl or methyl. Said compounds have applications in the cosmetic industry c. In the manufacture of certain non-monoid hormones. Their preparation is described in DOS 2,262,740. According to said patent, the preparation consists in reacting cilronellel with dimethyl or diethylarains to form the corresponding enamines, addition of an alcohol to the enamine double bond in the presence of sulfuric acid and finally decomposition of the enamine by addition of an alkalizing agent such as NaOH into an acidic reaction mixture. The desired alkoxydihydrocitronellal is isolated by distillation.

The disadvantages of this process are the following: dimethyl- and diethylamines are high vapor pressure substances and odor nuisance to the working environment, neutralization of the acidic reaction mixture by the addition of an alkalizing agent leads to the formation of relatively large amounts of undesirable acetals and the crude product thus obtained contains then make distillation more difficult. In addition, in this neutralization process it is difficult to keep the temperature of the reaction mixture low and the precipitated sodium sulphate greatly impaired miscibility.

It has now been found that better results in terms of effect are obtained when diethanolamine is used for the preparation of the enamine, the tension of which is absolutely minimal. A reduction in the formation of undesired acetals is achieved by the step of adding the acidic reaction mixture to a mixture of an organic solvent, preferably toluene or hexane, water and ice, and an excess of an alkalizing agent so as to maintain a pH of > 8.

A process for the preparation of aloxydibydroderivatives of citronellal of the formula I

where

R is methyl or ethyl, according to the invention is the reaction of citronellal with Ν, Ν-diethanolamine to form the enamine of formula II

CH ^ Ch _? OH

CH ^CH ^OH (reacted with a mixture of 96-100% sulfuric acid and an alcohol R —OH, where R is as defined above and the resulting enamine of the alkoxydihydrocitronellal is decomposed to the alkoxydihydrocitronellal of formula I by successively adding the acidic reaction mixture while cooling to a temperature in the range of 0 to 30 degrees Celsius into a mixture of an organic solvent, preferably hexane or toluene, water and an alkalizing agent in an amount ensuring the pH of the reaction mixture >

Removal of a significant amount of side substances is achieved by converting the alkoxydihydrocitronellal contained in the crude reaction product by treatment with sodium bisulfite to an addition compound of formula III

Well-OH

where

R is as previously defined. The non-aldehyde side-substances are extracted into an organic solvent, preferably toluene or hexane, and the alkoxydihydrocitronellal-free side-substances are decomposed in the presence of an organic solvent by treatment with a strong alkali, preferably sodium hydroxide. This procedure yields a product which, according to gas chromatography, contains 90 to 95% of alkoxydihydrocitronellal.

In the following example, the process of the invention is illustrated, parts refer to parts by weight, percent by weight.

Example

18.6 d of diethanolamine are mixed with 10 d of anhydrous potassium carbonate. 25 d of Citricellal are added at 45-50 ° C, then the mixture is stirred for 2 hours. The resulting enamine is freed from wet potassium carbonate by filtration. The residual solid was stirred with 20 d toluene and filtered again. The combined filtrates were added to a mixture of 90 d methanol and 55 d 100% sulfuric acid at a temperature below 5 ° C. The mixture was allowed to stir for 15 hours. Then the reaction mixture was added to a mixture of ice (100 µl, 50 d toluene and 25 d 50% sodium hydroxide).

The pH of the mixture was then adjusted to 9 by adding 50 ^l % sulfuric acid. After separating the layers, the lower, aqueous layer is drained, to the upper is added 60 d of water and 10 d of 50% sulfuric acid. After stirring, the mixture is allowed to settle and the bottom layer is drained. 60 d of water and 64 d of 30% sodium bisulfite solution were added to the upper layer. The mixture was allowed to stir for 30 minutes, then allowed to stand and the bottom layer transferred to another reaction vessel. 100 d of toluene and 19 kg of 50% sodium hydroxide are added, the pH must be higher than 11. The mixture is stirred for 30 minutes, then left to stand and the lower layer is drained.

The upper layer was extracted 2x with 50 d 10% sodium chloride and finally the toluene solution of the product was dried over 5 d anhydrous sodium sulfate and the toluene was evaporated. 20 d of crude product is obtained which, as determined by gas chromatography, contains 90% of methoxydihydrocitronellal.

The major impurity is hydro-dihydrocitronellal, (8%). After rectification, 13.5 d of methoxydihydrocitronellal having a purity of greater than 96% is obtained. The yield of the isolated product is 42.8% of theory, calculated on citronellal.

Toluene is evaporated from the toluene solution after separation of the bisulfite adduct III. 4 d of a mixture containing 15% methoxydihydrocitronellal and 20 other substances are obtained.

24S341

Claims (1)

A process for the preparation of alkoxydihydroderivatives of citricellal of the general formula I wherein R is methyl or ethyl, characterized by reacting citronellal with Ν, Ν-diethanolamine to form an enamine of formula II (II), which is reacted with a mixture of 96 to 100% sulfuric acid and an alcohol R-OH, where R has and the resulting enamine alkoxydihydrocitronellal is decomposed to the alkoxydihydrocitronellal of formula (I) by successively adding the acidic reaction mixture to 0 to 30 ° C with cooling to a mixture of organic solvent, preferably hexane or toluene, water and an alkalizing agent a mixture of> 8, whereby cooling can be carried out by direct introduction of ice into the alkaline reaction mixture and the resulting crude alkoxydihydrocitronellal in an organic solvent solution is optionally treated with an aqueous sodium bisulfite solution to form a water-soluble bisulfite adduct of formula III R is as previously defined, the organic solvent with the non-aldehyde impurities is separated, pure organic solvent is added, and the adduct III is decomposed by treatment with an alkalizing agent, preferably sodium hydroxide, at an aqueous pH> 10 to an alkoxydihydroditroinellial which is extracted into the organic solvent .