Method for the preparation of β-hydroxyketones

Technical Field:

This invention relates to a method for the preparation of β-hydroxyketones represented by general formula (I)

(where R is an alkyl group which may have a methyl group at the a position, an alkyl group substituted by alkylthio group which may have a methyl group at the a position, an alicyclic group which may have substituents at positions other than the , β and β ' positions, a heterocyclic group which may have substituents at positions other than the a , β and β ' positions, and a phenyl group which may have an electron withdrawing group at the para position) (hereinafter refeerred to as Compound I). Compound I is extremely important as an intermediate for pharmaceuticals and agricultural chemicals.

Background Art:

Documents such as Ber. 404764 (1907), Ann. Chim. , (Paris) 6_ 406-86 (1951) describe that Compound I is conventionally synthesized by aldol type condensation of aldehyde and acetone using such a compound as NaOH as a catalyst. The yield is generally low, particularly when aldehyde with a hydrogen is used. A very excessive amount of acetone is used in many cases so that diacetone alcohol, which is a reaction product of acetone itself, is inevitably byproduced in a large amount.

In the method described in Japanese open patent No. Sho 55-141429 that aldehyde and alkaline metal salt of acetoacetic acid are reacted, triethylainine or trimethylamine, which is a water-soluble amine, is used as a catalyst. Therefore the method has industrailly big problems of odor and waste water treatment. In the

method described in Japanese open patent No. Sho 55-141429, the yield is good if aldehyde with two a hydrogen atoms is used. If aldehyde with no or one a hydrogen atom is used, the reaction is slow and yield is low. The purity is low so that the intended product must be purified by distillation if used as an industrial material.

An object of this invention is to provide methods for the preparation of β - hydroxyketones which do not use water-soluble amines having the problems of odor and waste water treatment and which are applicable if aldehyde with no or one a hydrogen atom is used.

Disclosure of Invention:

The inventors earnestly studied reactions of aldehyde with aqueous solution of alkaline metal salt of acetoacetic acid in order to accomplish the said purpose, and found as a result that the reaction smoothly proceeds only in the pH range of 9 to 10, a mole ratio of aldehyde to alkaline metal salt of acetoacetic acid is important because the reactivity greatly differs depending on the structure of aldehyde, an addition of■ an appropriate amount of water-soluble organic solvent such as methanol, ethanol, glycerol or 1, 4-dioxane makes the reaction faster, and a pH selection is needed when alkaline metal bicarbonate formed by the reaction is removed. Thus this invention has been completed.

That is, this invention is, in a method for the preparation of β - hydroxyketones represented by general formula

(where R is an alkyl group which may have a methyl group at the a position, an alkyl group substituted by alkylthio group which may have a methyl group at the a position, an alicyclic group which may have substituents at positions other than the a , β and β ' positions, a heterocyclic group which may have substituents at

positions other than the a , β and β ' positions, and a phenyl group which may have an electron withdrawing group at the para position), by reacting aldehydes represented by general formula

RCHO (A)

(where R is as defined above) with aqueous solution of alkaline metal salt of scetoacetic acid represented by general formula . CH ₃ CCH-C00©M© (B)

II o

(where M© is an alkaline metal ion), a method for the preparation of the said - hydroxyketones which comprises reacting (A) and (B) when a mole ratio of (A) to (B) is 1.0 to 1.5 if (A) has two a hydrogen atoms, 1.5 to 2.0 if one a hydrogen atom, 2.0 to 2.5 if no a hydrogen atom and 1.1 to 1.5 if R is a phenyl group with electron withdrawing group at the para position even if with no a hydrogen atom, at Pli of 9 to 10.

Best Mode for Carrying Out the Invention:

The reaction in this invention smoothly proceeds only in a specific pH range: Good pH during the reaction is 9 to 10. If pH is lower than it, the reaction becomes slow and the decomposition of alkaline metal salt of acetoacetic acid becomes relatively faster and hence the yield is low. If pH exceeds 10, the yield of the intended product is low because of such reasons that a , /3-unsaturated ketones repesented by general formula

(where R is as defined above), which are dehydrated products of the intended product of β-hydroxyketones, are byproduced.

In the method of this invention, pH is adjusted with mineral acid or hydroxide alkaline aqueous solution, with no problems of waste water treatment.

The reaction of this invention is a two-step reaction represented by

COO Θ M ©

RCHO + CIIβ CCHjCOO Θ M © > RCHCHCCH ₃

!ι I II

0 OH 0

C00©M© RCHCHCCHβ + H ₂ 0 > RCHCH2CCH3 + M© CH0 ₃ ©

I II I II

OH 0 OH 0

The reaction of the first step is an equilibrium reaction. When aldehyde with 2 a hydrogen atoms is used, the reaction of the first step smoothly prceeds and the reaction of the second step is rate-determining. However, in the case of aldehyde branched at the a position, the reaction of the first step is slow because of its steric hindrance, and the equilibrium is shifted to the material side when compared with that of aldehyde _. not branched at theα position. Under the conditions that the reaction of the second step smoothly proceeds, decomposition of alkaline metal salt of acetoacetic acid into acetone and alkaline metal bicarbonate is accelerated. Therefore the yield is low. A mole ratio of aldehyde to alkaline metal salt of acetoacetic acid is an important factor in order to solve those problems. For instance, a mole ratio of alkaline metal salt of acetoacetic acid can be small when aldehyde with two a hydrogen atoms such as 2-ethylthiobutanal is used. In the case of aldehyde with great steric hindrance such as 3-tetrahydrothiopyrane carbaldehyde, the reaction does not proceed smoothly if a mole ratio of alkaline metal salt of acetoacetic acid is small, and the yield is low. It is therefore necessary to use an appropriate amount of alkaline metal salt of acetoacetic acid according to the steric structure of aldehyde.

In other words, a mole ratio of aldehydes represented by general formula (A) to alkaline metal salt of acetoacetic acid represented by general formula (B) is 1.0 to 1.5 if aldehydes represented by general formula (A) have two hydrogen atoms, 1.5 to 2.0 if one a hydrogen atom, 2.0 to 2.5 if no hydrogen atom and 1.1 to 1.5 if R is a phenyl group with electron withdrawing group at the para position even if with no hydrogen atom. It goes without saying that use of excessive amount

of alkaline metal salt of acetoacetic acid is not preferable in economy, because the excessive portion is decomposed into acetone and alkaline metal bicarbonate, though there is no effect on the yield or purity.

In the method of this invention, an addition of appropriate amount of water- soluble organic solvent such as methanol, ethanol, glycerol or 1, 4-dioxane makes the reaction faster. An addition of excessive amount greatly reduces the polarity of the reaction system, resulting in accelerated decomposition of alkaline metal salt of acetoacetic acid and low yield. A preferable addition of water-soluble organic solvent such as methanol is less than 300ml to a mole of aldehyde.

In this invention, alkaline metal bicarbonate is formed by the reaction and deposited as crystal. In Japanese open patent No. Sho 55-141429, the bicarbonate crystal deposited after the reaction is decomposed by using a mineral acid such as concentrated hydrochloric acid to make the pH 4. When -hydroxyketone branched at the r position is used, if the reaction solution is made acidic, the remaining material aldehyde reacts with formed /3-hydroxyketone to form byproducts. Hence the yield becomes extremely low. Becuase of this, after the reaction is completed, the crystal of alkaline metal bicarbonate which is formed by the reaction must be removed by filtration or by adding water to dissolve without making the reaction solution acidic. If the intended /3-hydroxyketone is not branched at the γ position, or if the remaining material aldehyde is small in amount, the formed bicarbonate crystal may be decomposed with mineral acid such as concentrated hydrochloric acid.

Aldehydes, a material, represented by general formula (A) and which are used in this invention include alkylaldehydes with two a hydrogen atoms and of straight chain or with side chains such as ethanal, propanal, n-butanal, n-caprylaldehyde, 3- methylbutanal, 3-methylhexanal and 3, 4-dimethylpeptanal; aldehydes substituted by alkylthio group and with two hydrogen atoms such as methylthioethanal, ethylthioethanal and 3-ethylthiobutanal; alkylaldehydes with methyl group at the a position such as isobutanal; alicyclic aldehydes which may have substituents at

positions other than the a , β and β ' positions such as cyclohexane carbaldehyde, 3-methylcyclohexane carbaldehyde and 4-methylcyclohexane carbaldehyde; heterocyclic aldehydes which may have substituents at positions other than the a , β and β ' positions such as 3-tetrahydropyran carbaldehyde, 4-tetrahydroρyran carbaldehyde and 3-tetrahydrothioρyran carbaldehyde; and benzaldehydes which may have electron withdrawing groups at the para position such as benzaldehyde, p-nitrobenzaldehyde and p-cyanobenzaldehyde.

The other material, the aqueous solution of alkaline metal salt of acetoacetic acid represented by general formula (B), are aqueous solutions of sodium acetoacetate, potassium acetoacetate and lithium acetoacetate. An aqueous solution of alkaline metal salt of acetoacetic acid is easily obtained by hydrolyzing diketene or acetoacetates with aqueous solution of caustic alkali such as sodium hydroxide or potassium hydroxide.

A way of implementing the preparation method of this invention is described in detail in the following.

An aqueous solution containing alkaline metal salt of acetoacetic acid of the aforementioned mole ratio to a mole of aldehyde is adjusted the pH to 9 to 10 with mineral acid such as hydrochloric acid or an aqueous solution of caustic alkali, and then aldehyde is added. At this time less than 300ml, to a mole of aldehyde, of water-soluble organic solvent such as methanol may be added. The reaction is carried out with stirring at a reaction temperature of 20 to 70 °C, preferably 40 to 60 °C, for 1 to 9 hours, while keeping the pH to 9 to 10 with aqueous solution of caustic alkali. Organic acids and amines may be used as a base and acid to adjust the pH. Industrially mineral acids or aqueous solutions of caustic alkalis are better. After the reaction is completed, a water-insoluble organic solvent such as chloroform or toluene is added to the obtained reaction mixture, the deposited alkaline metal bicarbonate is filtrated, and the filtrate is separaated into an aqueous and organic layers according to an ordinary method. The deposited bicarbonate, if small in amount, may be dissolved by adding water. The obtained

organic layer is concentrated and distilled under vacuum to give the intended β- hydroxyketone.

This invention is further described in detail by reference to the following examples. The range of this invention is not limited at all by the following examples.

Example 1

Into a reaction vessel of 1_2 in inside volume were placed 232.2g (2.0 moles) of methyl acetoacetate and 200.4g of water, to which 293.8g (2.1 moles as NaOH) of 28.6% NaOH aqueous solution was dropped over an hour with stirring while cooling with water and keeping the inside temperature to below 35°C. The resulting solution was stirred at 35 to 36 °C for 5 hours for hydrolysis. Part of the content in the reaction vessel was collected to titrate for pH with IN HC1 standard aqueous solution. From the results, the obtained aqueous solution of sodium acetoacetate was 32.95. in concentration and the yield was 97.1% to methyl acetoacetate.

678.9g (1.8 moles as sodium acetoacetate) of the aqueous solution of sodium acetoacetate was placed in a reaction vessel of 2_2 in inside volume and the pH was adjusted to 10.0 with concentrated hydrochloric acid. Into the vessel were added 198.3g (1.5 moles) of 3-ethylthiobutanal and 300ml of methanol to react with stirring at 50°C for 4 hours. The pH was maintained to 9 to 10 with 28.6% NaOH aqueous solution during the reaction.

After the reaction was completed, the solution was cooled down to room temperature, 750ml of chloroform was added, and the solution was filtrated by aspiration to remove deposited NaHC0 ₂ . The filtrate was separated into an organic and aqueous layers. The solvent in the obtained organic layer was distilled under reduced pressure. The remaining oily product was distilled under reduced pressure to give 267.2g of colorless oily product with boiling point of 84 to 86°C at 0.2mmHg and n ² * = 1.4850. (Crude yield: 93.6%) The obtained product was analyzed

by gas chroma tography to f ind tha t the intended p roduc t, 6-e thy l th io-4- hydroxyheptane-2-one was 95.0% in purity. (Yield : 88. 9%)

Examples 2 to 8

Example 1 was repeated except using different aldehyde under the conditions shown in Table 1.

The results are shown in Table 1 including that of Example 1.

Example 9

758.9g (2.0 moles as sodium acetoacetaate) of 32.7% aqueous solution of sodium acetoacetate, which was synthesized under the same conditions as those used in Example 1, was placed in a reaction vessel of 2£ in inside volume and the pH was adjusted to 9.8 with concentrated hydrochloric acid. Into the vessel were added 130.2g (1.0 mole) of 3-tetrahydrothiopyran carbaldehyde and 200ml of methanol to react at 50°C with stirring for 7 hours. The pH was maintained to 9 to 10 with 28.6% NaOH aqueous solution during the reaction.

After the reaction was completed, the solution was cooled down to room temperature, 500ml of chloroform was added, and the solution was filtrated by aspiration to remove deposited NaHC0 ₃ . The filtrate was separated into an organic and aqueous layers. The solvent in the obtained organic layer was distilled under reduced pressure. The residue was distilled under reduced pressure to give 177.2g of colorless oily product with boiling point of 98 to 104 °C at 0.2mmHg and n ²³ = 1.5223. (Crude yield: 94.1%) The obtained product was analyzed by gas chromatography to find that the intended product, 4-hydroxy-4-(3-te trahydrothiopyranyl)-butane-2-one was 95.4% in purity. (Yield: 89.8%)

Example 10

Into a reaction vessel of li in inside volume were placed 232.2g (2.0 moles) of methyl acetoacetate and 300.3g of water, to which 392.7g (2.1 moles as KOH) of

30% KOH aqueous solution was dropped over 1.5 hours with stirring while cooling with water and keeping the inside temperature to below 35°C. The resulting solution was stirred at 33 to 35 °C for 4 hours for hydrolysis. Part of the content in the reaction vessel was collected to titrate for pH with IN HC1 standard aqueous solution. From the results, the obtained aqueous solution of potassium acetoacetate was 30.8% in concentration and the yield was 96.8% to methyl acetoacetate.

728.2g (1.6 moles as potassium acetoacetate) of the aqueous solution of potassium acetoacetate was placed in a reaction vessel of 2£ in inside volume and the pH was adjusted to 9.8 with concentrated hydrochloric acid. Into the vessel were added 130.2g (1.0 moles) of 3-tetrahydrothiopyran carbaldehyde and 200ml of methanol to react with stirring at 40 °C for 9 hours. The pH was maintained to 9 to 10 with 30% KOH aqueous solution during the reaction.

After the reaction was completed, the solution was cooled down to room temperature. 200ml of water was added to dissolve the deposited KHC0 ₃ . The liberated oily product was extracted with chloroform, the solvent was distilled under reduced pressure, and the residue was distilled under reduced pressure to give 181.7g of colorless oily product with boiling point of 97 to 104 °C at 0. OlmmHg and n ² ^ = 1.5216. (Crude yield: 96.5%) The obtained product was analyzed by gas chromatography to find that the intended product, 4-hydroxy-4-(3- tetrahydrothiopyranyl)-butane-2-one was 94.8% in purity. (Yield: 91.5%)

Example 11

After the reaction was carried out in the same manner as that used in Example 1, the solution was cooled down to room temperature. Concentrated hydrochloric acid was slowly dropped to make the pH 4.0 to decompose the formed NaHC0 ₃ . Methanol was distilled until reaching to distillation temperature of 100 °C. The remaining solution was cooled. The liberated oily product was extracted with 750ml of chloroform, the solvent was distilled under reduced pressure, and the residue was

distilled under reduced pressure to give 272.9g of colorless oily product with boiling point of 87 to 93 °C at 0.3mn_Hg and n ² _D ⁴ = 1.4838. (Crude yield: 95.6%) The obtained product was analyzed by gas chromatography to find that the intended product, 6-ethylthio-4-hydroxyheptane-2-one was 94.4% in purity. (Yield: 90.2%)

Comparative Example 1

Example 11 was repeated except using isobutylaldehyde as the aldehyde. The intended product, 4-hydroxy-5-methyl-2-hexanone was 78.3% in yield.

Comparative Example 2

91.3g (0.24 moles as sodium acetoacetaate) of 32.6% aqueous solution of sodium acetoacetate, which was synthesized under the same conditions as those used in Example 1, was placed in a 300ml reaction vessel and the pH was adjusted to 9.8 with 10% HCI aqueous solution. Into the vessel were added 40ml of methanol and 26. Og (0.20 mole) of 3-tetrahydrothioρyran carbaldehyde to react at 50 °C with stirring for 6 hours. The pH was maintained to 9 to 10 with 10% NaOH aqueous solution during the reaction.

After the reaction was completed, the solution ^' was cooled down to room temperature. Concentrated hydrochloric acid was slowly dropped to make the pH 4.0 to decompose the formed NaHC0 ₃ . Methanol was distilled until reaching to distillation temperature of 100°C. The remaining solution was cooled. The liberated oily product was extracted with 100ml of chloroform. The obtained extract was analyzed by gas chromatography to find that it contained 26.2g of the intended product, 4-hydroxy-4-(3-tetrahydrothiopyranyl)-butane-2-one. This is equivalent to 70.4% of standard yield of 3-tetrahydrothiopyrane carbaldehyde.

Comparative Examples 3 to 6

Example 1 was repeated except using 3-tetrahydrothioρyran carbaldehyde as the aldehyde under the conditions shown in Table 2.

The results are shown in Table 2 including those for Comparative Examples 1 and 2.

Table 1 Examples

Table 2 Comparative Examples

* The intended product in the organic layer was analyzed by gas chromatography

Industrial Applicabi l i ty:

According to the method of this invent ion, intended β -hydroxyketones (Compound I) can be prepared under mild conditions, safely and easi ly, and with good yield. This invention is thus extremely signif icant in industry, particularly in manufacturing of pharmaceuticals and agricultural chemicals.