Method for preparing carboxylic esters from aldehydes

Abstract

A method can prepare a carboxylic ester. The method includes reacting an aldehyde in the presence of an aluminium alkoxide applied to a support material.

Claims

1. A method for preparing a carboxylic ester, the method comprising: reacting (meth)acrolein in the presence of an aluminum alkoxide applied to a support material comprising silicon dioxide.

2. The method according to claim 1, wherein the aluminum alkoxide is a compound of formula (II):
Al(OR.sup.2).sub.3(II), wherein each R.sup.2 radical is independently of one another a (C.sub.1-C.sub.12)-alkyl group or a (C.sub.2-C.sub.12)-alkenyl group and each R.sup.2 radical may independently of one another optionally be substituted by one or more substituents selected from the group consisting of (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.4-C.sub.12)-heterocycloalkyl, (C.sub.6-C.sub.20)-aryl, (C.sub.4-C.sub.20)-heteroaryl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.3-C.sub.12)-cycloalkyl, S(C.sub.1-C.sub.12)-alkyl, S(C.sub.3-C.sub.12)-cycloalkyl, COO(C.sub.1-C.sub.12)-alkyl, COO(C.sub.3-C.sub.12)-cycloalkyl, CONH(C.sub.1-C.sub.12)-alkyl, CONH(C.sub.3-C.sub.12)-cycloalkyl, N[(C.sub.1-C.sub.12)-alkyl].sub.2, OH, NH.sub.2, and a halogen atom.

3. The method according to claim 1, wherein the aluminum alkoxide is a compound of formula (III)
Al(OCH.sub.2R.sup.3).sub.3(III), wherein each of the R.sup.3 radicals corresponds to C.sub.2 alkenyl or methyl substituted C.sub.2 alkenyl.

4. The method according to claim 2, wherein each R.sup.2 group is, independently, a group selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, allyl, and 2-methylallyl.

5. The method according to claim 1, wherein said reacting is carried out at a reaction temperature of 10 to 60 C.

6. The method according to claim 1, wherein said reacting is carried out continuously.

7. The method according to claim 1, wherein said (meth)acrolein is reacted without addition of solvent.

Description

EXAMPLES

Example 1 (Comparative Example Using Homogeneous Catalyst)

(1) 1.5 g of Al(OMethallyl).sub.3 (2 mol % Al based on methacrolein) was mixed with 20 g of methacrolein at 20 C. The reaction mixture was stirred at 20 C. for 48 h. Reactant and product were then separated from the catalyst by distillation under reduced pressure and the distillates were analyzed by GC.

Example 2 (Catalyst on SiO.SUB.2 .Support)

(2) Al(OMethallyl).sub.3 (6 g) was dissolved in anhydrous cyclohexane (20 mL) and mixed with 15 g of SiO.sub.2 support (Cariact Q10, 1.18-2.36 mm from Fuji Silysia Chemical). This mixture was temperature-controlled at 60 C. for 4 h and then cooled. The solvent was removed under reduced pressure to obtain a catalyst (1).

(3) 5.25 g of this supported catalyst (1) (2 mol % Al based on methacrolein) was mixed with 20 g of methacrolein at 20 C. The reaction mixture was stirred at 20 C. for 48 h. The product mixture was then separated by filtration and analyzed by GC.

Example 3 (Catalyst on SiO.SUB.2.Al.SUB.2.O.SUB.3 .Support)

(4) Al(OMethallyl).sub.3 (6 g) was dissolved in anhydrous cyclohexane (20 mL) and mixed with 15 g of SiO.sub.2Al.sub.2O.sub.3 support (65 m powder, 7 wt % Al.sub.2O.sub.3). This mixture was temperature-controlled at 60 C. for 4 h and then cooled. The solvent was removed under reduced pressure to obtain a catalyst (2).

(5) 5.25 g of this supported catalyst (2) (2 mol % Al based on methacrolein) was mixed with 20 g of methacrolein at 20 C. The reaction mixture was stirred at 20 C. for 48 h. The product mixture was then separated by filtration and analyzed by GC.

Example 4 (Catalyst on SiO.SUB.2.Al.SUB.2.O.SUB.3.MgO Support)

(6) Al(OMethallyl).sub.3 (6 g) was dissolved in anhydrous cyclohexane (20 mL) and mixed with 15 g of SiO.sub.2Al.sub.2O.sub.3MgO support (20-100 m powder, 6.2 wt % Al.sub.2O.sub.3, 4 wt % MgO). This mixture was temperature-controlled at 60 C. for 4 h and then cooled. The solvent was removed under reduced pressure to obtain a catalyst (3).

(7) 5.25 g of this supported catalyst (3) (2 mol % Al based on methacrolein) was mixed with 20 g of methacrolein at 20 C. The reaction mixture was stirred at 20 C. for 48 h. The product mixture was then separated by filtration and analyzed by GC.

(8) The product parameters determined in Examples 1-4 are compiled in the following table.

(9) TABLE-US-00001 Methallyl Methacrolein Methallyl methacrylate Conversion methacrylate Selectivity No. Support (%) Yield (%) (%) 1 None 58.6 51.8 88.4 2 SiO.sub.2 80.2 79.6 99.3 3 SiO.sub.2Al.sub.2O.sub.3 41.1 21.7 52.8 4 SiO.sub.2Al.sub.2O.sub.3MgO 12.3 2.8 22.8

(10) These examples show that supported aluminium alkoxides are effective catalysts for the conversion of aldehydes to carboxylic esters. It is particularly shown here that the efficacy of the catalysts can be increased by selection of a suitable support material. A support material based on silicon dioxide having a low proportion of aluminium oxide and other metal oxides leads to a higher yield. The best results are achieved using pure silicon dioxide as support.

Example 5 (Recycling the Catalyst)

(11) 5.25 g of supported catalyst (1) was mixed with 20 g of methacrolein (<100 ppm water) at 20 C. The reaction mixture was stirred at 20 C. for 48 h. The product mixture was then separated by filtration and analyzed by GC (catalyst use 1). Fresh methacrolein (20 g) was added and the reaction mixture was stirred at RT for a further 48 h and analyzed by GC after filtration (catalyst use 2). Thereafter, the catalyst was again mixed with 20 g of fresh methacrolein and stirred at 30 C. for 48 h. The results of these experiments are compiled in the following table:

(12) TABLE-US-00002 Methacrolein Methallyl Methallyl Conversion methacrylate methacrylate No. (catalyst use) (%) Yield (%) Selectivity (%) 1 80.2 79.6 99.3 2 78.0 76.5 98.1 3 77.6 76.0 98.0

(13) This example shows that the method according to the invention also allows reuse of the supported aluminium alkoxide.