DE2225243A1 - - Google Patents

Description

P 4807
R / P

Daicel Ltd.

ITo «8, 3-ch.ome, Kawara-ciio,

Higashi-ku, Osaka, Japan

Process for the preparation of βjcf-dioxocaproaldehyde dialkyl acetals

The invention relates to a process for the preparation of ßjcf-dioxocaproaldehyde dialkyl acetals of the general
formula

(R ¹ O) ₂ CHCH ₂ COCH ₂ CH

in which R is a low molecular weight alkyl group with 1 to 4 Carbon atoms, through a dealkanolic condensation of lower alkyl-βjβ-dialkoxypropionates of the general formula

(R ¹ O) ₂ CHCH ₂ COOR ² II

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1 1

in which R is the same alkyl group as above and R and

ρ
R are the same or different low molecular weight alkyl groups, each having 1 to 4 carbon atoms, with acetone under conditions suitable for a Claisen condensation.

The reaction can be illustrated by the following reaction scheme will:

(R ¹ OJ ₂ CHCH ₂ COOR ² + CPUCOCH, -> (R ¹ O) ₂ CHCH ₂ COCh ₂ COCH ₃ + R ² OH

The lower alkyl ß, ß-dialkoxypropionates of the general formula (R ¹ O) ₂ CHCH ₂ COOR ² , in which R ¹ and R ^{2 are} methyl or ethyl groups, and methods for their preparation are already known. For example, they can easily be prepared by reacting acetic acid esters and formic acid esters under the conditions suitable for the Claisen condensation, and then the acetals can be prepared from the Pormylderivaten obtained with a corresponding alkanol using a strong acid as a catalyst or by reacting between o-formic acid esters and Bromoacetic acid esters can be produced using zinc.

The Claisen condensation for the production of compounds of general formula I from acetone and lower alkyl-ß, ß ~> dialkoxypropionates, in which the low molecular weight alkyl group is preferably methyl or ethyl, in the presence of one basic condensing agent carried out. The preferred basic condensing agent is metallic sodium, Sodium methoxide or sodium ethoxide used, however, can other basic condensing agents such as sodium amide and sodium hydride can also be used. The reaction medium is preferably an anhydrous low molecular weight alkanol or another relatively low-boiling inert one

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Solvents such as diethyl ether or benzene are used. The amounts, molar ratios and mixing methods of the reactants as well as solvents and basic condensing agents are not of essential importance - and can. can easily be chosen so that the ß ^ cf-Dioxoeaproaldehyddialkylacetat is obtained in an economical manner. The reaction temperature will usually be in the range of -10 to 8o ° C is selected, but is also not of ■ essential. After the reaction, the basic components of the reaction mixture are expediently careful with an acidic neutralizing agent such as formic acid, acetic acid, hydrochloric acid, phosphoric acid or sulfuric acid neutralized, whereby it must be avoided that the mixture becomes too acidic to produce the desired β ^ cf-dioxocaproaldehyde dialkyl acetal is obtained.

The above process for the preparation of β ^ -dioxocaproaldehyde dialkyl acetals (I) by dealkanolic condensation of the specified starting compounds, i.e. lower alkyl-ß, ß-dialk-oxypropionates (II) and acetone in the presence of a basic condensing agent is described in DT-OS 19 51 294.

It has been found, however, that there is often a substantial amount of starting β, β-dialkoxypropionic acid ester in the in this process formed condensation mixture remains. In addition, this starting compound is easily hydrolyzed. if for example, the liquid condensation mixture is neutralized with aqueous sulfuric acid solution, the major part hydrolyzed the unreacted starting compound to the corresponding ß, ß-dialkoxypropionic acid. The so educated ß, ß-Dialkoxypropionic acid has about the same boiling point as the ßjif-Dioxocaproaldehyd-Dialkyläcetal and is therefore often present as an impurity in the product obtained by distillation of the liquid reaction mixture and

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deteriorates its quality. The product of the above procedure can be used as an intermediate for the synthesis of various valuable organic compounds, such as maltol (j5 ~ Hydroxy - 2-methyl "4-pyrone) j can be used. Impurities like the ß, ß-dialkoxypropionic acids mentioned, however, impair the conversion of the ß, <i -dioxocaproaldehyde ~ dialkylacetals with other organic or inorganic compounds. Maltol can be obtained by reacting ß, c / -Dioxocaproalde-hyd-dialkyl acetal (I) with lead tetraacetate to an oxidatively acetoxylated product, which is then either a thermal Decomposition (pyrolysis) or a treatment with an acidic condensation agent and a simultaneous or subsequent one Hydrolysis of the 5-acetoxy-2-methyl-4-pyrone formed Maltol can be obtained. Maltol is a valuable odoriferous substance and is used in particular as a flavoring for food. If that as described above, get ßjcf-dioxocaproaldehyde dialkyl acetal with the ß, ß-dialkoxypropionic acids contained therein as impurities for the production of maltol, such as described above is used, the yield of maltol is considerably reduced.

It has now been found that the ß, ß-dialkoxypropionic acid remaining in the product obtained can be separated off. by taking the product as it is, or in the form of a solution in an organic sparingly soluble in water Solvent so carefully mixed with an aqueous alkali solution that only the ß, ß-dialkoxypropionic acid in it is water-soluble Salt is transferred and the salt passes into the aqueous layer. So purity came through this measure of βjcT-dioxocaproaldehyde derivative can be increased. These However, the method has the disadvantage that the regeneration of the salt of ß, ß-dialkoxypropionic acid in the aqueous layer

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to the starting ß, ß-dialkoxypropionic acid ester by esterification is not always easy and the use of a troublesome requires a multi-step process. There is therefore a demand for a method of recovering the above indicated in your product remaining starting material in easier way, as this leads to a considerable increase in the Yield in the product, an improvement in the quality of the product and an increase in its value for organic Syntheses would lead. ...

The invention relates to a process for the preparation of a ß ^ cf-dioxocaproaldehyde dialkyl acetal of the general formula I, (R ¹ O) ₂ CHCh ₂ COCH ₂ COCH- ,, in which R ^{1 is} a low molecular weight alkyl group with 1 to 4 carbon atoms, with conversion of a lower alkyl dialkoxypropionate of the general formula II, (R ¹ O) ₀ CHCH ₀ COOR ² , in which R ^{1 has} the meaning given above and R ^c 'is a low molecular weight alkyl group with 1 to h carbon atoms, which are the same as R or R can be different, with acetone in the presence of a basic condensation agent and subsequent neutralization of the reaction mixture formed with an acidic neutralization agent, which is characterized in that the neutralization is carried out in the anhydrous state.

The fact that the neutralization of the liquid condensation mixture with an acidic neutralizing agent in one Mixture which contains practically no water is carried out, a decomposition of the starting compound II is prevented, and you can get the ß, ß-Dialkyloxypropionsäurees.ter II and the ß, V-Dioxocaproaldehyddsrivat I from the liquid Separate the condensation mixture and the recovered Recycle β, β-dialkoxypropionic acid ester II into the reaction system, to increase the yield of the product (I).

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In the method according to the invention, the unreacted can Starting compound (II) can be separated off easily and in high yield without seeing the above-mentioned decomposition product forms.

In general, when a β, β-dialkoxypropionic acid ester is reacted with acetone in the presence of a basic catalyst, the selectivity of the reaction with regard to the formation of the desired β, tf-dioxocaproaldehyde derivative is reduced as the β, β-dlalkoxypropionic acid ester continues to react. When carrying out the process according to the invention, it is therefore often advantageous to interrupt the dealkanolic condensation at the appropriate time, to recover the unreacted starting compound (II) and then to continue the reaction with better conversion of the starting compound. The time at which the reaction is to be interrupted, must, of course taking into account the quality of the end product, the process conditions, process costs, etc., are determined. In the process according to the invention, the dealkanolic condensation takes place in a practically anhydrous system, so that no alkali salt of β, β-dialkoxypropionic acid is formed. In addition, if the neutralization was carried out with an aqueous acidic neutralizing agent, the formation of β, β-dialkoxypropionic acid was not to be expected because the neutralization of the liquid condensation mixture and the subsequent separation are generally carried out within a very short time. It has been found, however, that the yield and quality of the end product are actually considerably reduced by the formation of β, β-dialkoxypropionic acid. In the process according to the invention, the neutralization is carried out with an acidic neutralizing agent under practically anhydrous conditions, so that a mixture of the end product and the unreacted starting compound is obtained and the formation of a decomposition

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Product is avoided.

The acidic neutralizing agent used in the method according to the invention can be anhydrous acidic compounds, such as ant, acid, acetic acid, phosphoric acid, sulfuric acid and hydrochloric acid, which do not contain water can be used. These acidic compounds can be used as such or in the form of a solution in an anhydrous organic solvent such as a low molecular weight alkanol, ether or benzene. The amount of neutralizing agent used is, of course, preferably the equivalent of the alkali used. The neutralization temperature is not particularly critical. Preferably, a temperature in the range of 0 to J50 ° C applied. Also for the type of neutralization or separation there are no specific limits. The neutralization of the liquid reaction mixture can be achieved by adding the anhydrous acidic neutralizing agent to the liquid reaction mixture with stirring or vice versa by additions the liquid reaction mixture to the acidic neutralizing agent take place with stirring. Generally divorces the salt formed from in crystal form and can be filtered off, after which the solvent is distilled off and the remaining Liquid is subjected to fractional distillation to obtain the starting compound (II) without decomposition to recover the product (I) from the distillation residue in high purity and free from β, β-dialkoxypropionic acid is obtained. The recovered starting compound (II) can be returned to the reaction system to improve the yield of the final product. The Claisen condensation for the production of ß, cf-dioxocaproaldehyde dialkyl acetals (I) according to the invention can also be carried out as described in the above-mentioned DT-OS 19 51 294.

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mm ^ Λ - »

These compounds (I) exist as keto / Snol tautomers. They contain ßicf-Dioxocaproaldehyd-Dimethylacctal and -diethylacetal, which are themselves chelating agents and also more valuable as intermediates for synthesis organic compounds such as maltol (3 - Kydroxy-2-methylethyl ™ 4-pyrone), can be used. In the process according to the invention, the compounds (I) can be used in high yield and can be obtained in a technically advantageous manner.

The following examples illustrate the invention. Details in parts relate to weight.

example 1

A mixture of 58 parts of acetone and 170 parts of dry diethyl ether was added dropwise to a mixture of 330 parts of dry diethyl ether and 52 parts of 50% sodium hydride in oil at 5 ° C. in the course of 20 minutes, after which the resulting mixture was stirred and allowed to react for 10 minutes became. The liquid reaction mixture was introduced into a reaction vessel which contained a mixture of 178 parts of methyl β, β-dimethoxypropionate and 670 parts of dry benzene, and the entire mixture was ^{stirred at 20 °} C. for 4 hours in order to cause condensation. The condensation mixture thus obtained was neutralized with 700 parts of dry diethyl ether containing 55 parts of hydrogen chloride. The precipitated crystalline sodium chloride was filtered off. The solvent was evaporated from the crude liquid reaction mixture thus obtained and the residue was further distilled in vacuo. To give 23 parts of methyl-ß-dimethoxypropionate, b.p. 60 to 63 ⁰ C (10 mm Hg) and 101 parts ßjcf-Dioxocaproaldehyd dimethyl acetal of bp 75-76 ⁰ C '(3 mm Hg). The β, (f-dioxocaproaldehyde dimethylacetal obtained did not contain any β, β-dimethoxypropionic acid. The yield was 68% of theory, calculated from the reverse

am . ^

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put methyl ~ ß, ß-dimethoxypropionate. The recovered Methyl ß., Ss-dimethoxypropionate was recycled and again used in the implementation.

In contrast, ß., Cf-Dloxccaproaldehyd-dimethylacetal, which was obtained by neutralizing the above condensation gerriiscnes with aqueous sulfuric acid, 12 'wt. -% ß, ß-D.imethoxypropionic acid, and no starting methyl ~ .B, ß-dimethoxypropionate could be recovered.

Example 2

A mixture of 58 parts of acetone and 148 parts of methyl β, β-dimethoxypropionate was gradually added dropwise to a mixture of 150 parts of dry diethyl ether and 23 parts of finely granulated metallic sodium at the reflux temperature of the diethyl ether. After the addition was complete, the reaction was allowed to ^{proceed at 5 to 10 °} C. for 2 hours, after which the reaction mixture was neutralized by slowly adding a mixture of 49 parts of sulfuric acid and 100 parts of methanol. The formed precipitate of sodium sulfate was filtered off. After the solvent had been distilled off from the filtrate, the residue was distilled in vacuo. To give 31 parts of methyl-ß, ß-dimethoxypropionate, bp 60 to 6yz (10 mm Hg) and 88 parts β, ίί-Dioxocaproaldehyd dimethyl acetal of bp 75-76 ⁰ C (j5 -mm Hg). The yield of βjtf-dioxocaproaldehyde dimethylacetal was 64% of theory, based on converted methyl β, β-dimethoxypropionate.

Example 3

The procedure of Example Ά was repeated with the difference that 190 parts of ethyl ß, ß-diethoxypropionate were used instead of methylß, ß-dirnethoxypropionate * 85 parts were obtained

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~ 10 -

ßjcS-Dioxooaproaldehyd-Diethylacetal from Bp 97 bis (4 mm Hg) which are free from ß, i3-diethoxypropionic acid v.'arsn.

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Claims (2)

aten ta η s ρ odors 1 «y process for the preparation of ß, o ~ dioxocaproaldehydüialkylacetal the general formula in which R is a low molecular weight alkyl group with 1 to 4 Carbon atoms., Wherein a low molecular weight alkyl · dialkoxypropionate of the general formula (R ¹ O) ₂ CHCH ₂ COOR ² II 1 2 in which R has the meaning given above and R is a low molecular weight alkyl group with 1 to 4 carbon atoms, 1 · 1
which can be the same as R or different from R, is reacted with acetone in the presence of a basic condensing agent and the reaction mixture formed is then neutralized with an acidic neutralizing agent, characterized in that the neutralization is carried out in an anhydrous state, after which unreacted low .Alkyl-ß, ßdialkoxypropionat is distilled off from the mixture and, if desired, returned to the reaction system and the desired ß, ß-Dioxocaproaldehyd-dialkyl acetal is distilled off from the residue. 2. The method according to claim 1, characterized in that the low molecular weight alkyl group is one ethyl or methyl group is. 209851/1240 ; 5. The method according to claim 1, characterized in that neutralization is carried out at a temperature of 0 to 150 ° C performs. ***> ? \ ■■■ '* ■■ "■ £ U 'Ö ύ O, ä ί