Process for preparing organic esters

Abstract

The present invention relates to a process for preparing an ester having formula RCOOR (I), wherein R represents a group selected from: (i) a linear or branched alkyl, containing from 1 to 20 carbon atoms, (ii) an aryl containing from 6 to 12 carbon atoms, (iii) a heterocycle with 4 to 12 carbon atoms containing at least one heteroatom selected from O, N, P and S, R represents a linear or branched alkyl containing from 1 to 12 carbon atoms, said process comprising at least a phase of reacting a reaction mixture comprising at least one aldehyde having formula RCHO (II), wherein R has the meanings defined above, and at least one alcohol having general formula ROH (III), wherein R has the meanings defined above, in the presence of at least one solid basic catalyst, at a temperature within the range of 120 C.-300 C., obtaining said ester having formula (I).

Claims

1. A process for preparing an ester of formula (I):
RCOOR(I), the process comprising: reacting a reaction mixture comprising at least one aldehyde having formula (II): RCHO (II) and at least one alcohol having formula (III): ROH (III) in the presence of at least one solid basic catalyst, at a temperature T.sub.H of higher than or equal to 120 C. and lower than 300 C., in an inert atmosphere, to obtain the ester of the formula (I) with a selectivity ranging from 20 to 100% with respect to the at least one aldehyde having the formula (II), wherein in the formulae (I), (II), and (III), R represents a group selected from the group consisting of: i) a linear or branched C.sub.1-C.sub.20 alkyl, (ii) a C.sub.6-C.sub.12 aryl, and (iii) a heterocycle having 4 to 12 carbon atoms and at least one heteroatom selected from the group consisting of O, N, P and S, and R represents a linear or branched C.sub.1-C.sub.12 alkyl; and the at least one solid basic catalyst is selected from the group consisting of an oxide of one or more alkaline or alkaline earth metals, a hydrotalcite of formula (M.sup.2+).sub.n(M.sup.3+).sub.2(OH).sub.16X.mH.sub.2O, where M.sup.2+ is a bivalent metallic cation selected from the group consisting of Mg.sup.2+, Fe.sup.2+, Ni.sup.2+, Zn.sup.2+, Cd.sup.2+, and Co.sup.2+, M.sup.3+ is a trivalent metallic cation selected from the group consisting of Al.sup.3+, Fe.sup.3+, Ga.sup.3+, Cr.sup.3+, Mn.sup.3+, and Co.sup.3+, X is an anion selected from the group consisting of CO.sub.3.sup.2, OH.sup., and NO.sub.3.sup., n is an integer ranging from 4 to 10, and m is an integer lower than or equal to 10, a zeolite prevalently or completely exchanged with one or more alkaline and/or alkaline-earth metals, and a fluoride of an alkaline metal supported on a solid substrate of alumina, silica, or a mixture thereof.

2. The process according to claim 1, wherein R is a linear C.sub.1-C.sub.10 alkyl.

3. The process according to claim 1, wherein R is a C.sub.6-C.sub.12 aryl, optionally substituted with at least a linear or branched C.sub.1-C.sub.4 alkyl, saturated or unsaturated.

4. The process according to claim 1, wherein R is a C.sub.1-C.sub.10 alkyl.

5. The process according to claim 4, wherein the reacting at the temperature T.sub.H has a duration ranging from 15 minutes to 10 hours.

6. The process according to claim 1, wherein the reacting at the temperature T.sub.H is carried out at a pressure ranging from 1 atm to 100 atm.

7. The process according to claim 1, wherein a molar ratio between the alcohol and the aldehyde in the reaction mixture ranges from 1:1 to 30:1.

8. The process according to claim 1, further comprising: before the reacting at the temperature T.sub.H, reacting the reaction mixture in the presence of the at least one solid basic catalyst at a temperature T.sub.L higher than 50 C. and lower than or equal to 120 C., wherein the temperature T.sub.L is lower than the temperature T.sub.H.

9. The process according to claim 8, wherein the reaction mixture is kept at the temperature T.sub.L for a time ranging from 10 minutes to 10 hours.

10. The process according to claim 8, wherein the reaction mixture is kept at the temperature T.sub.H for a time ranging from 10 minutes to 6 hours.

11. The process according to claim 1, wherein R is a linear C.sub.1-C.sub.8 alkyl.

12. The process according to claim 1, wherein R is a linear C.sub.1-C.sub.8 alkyl.

13. The process according to claim 4, wherein the reacting at the temperature T.sub.H has a duration ranging from 30 minutes to 8 hours.

14. The process according to claim 1, wherein the reacting at the temperature T.sub.H is carried out at a pressure ranging from 40 to 60 atm.

15. The process according to claim 1, wherein a molar ratio between the alcohol and the aldehyde in the reaction mixture ranges from 1.5:1 to 20:1.

16. The process according to claim 8, wherein the reaction mixture is kept at the temperature T.sub.L for a time ranging from 1 to 3 hours.

17. The process according to claim 8, wherein the reaction mixture is kept at the temperature T.sub.H for a time ranging from 1 to 2 hours.

Description

EXAMPLE 1

(1) A magnesium oxide catalyst was prepared as follows. A solution of Mg(NO.sub.3).sub.2 1 M was added dropwise to a solution of sodium carbonate 1 M maintained at a temperature of 50-60 C., under stirring. The total volumes of the two solutions used were the same. The pH of the final suspension of magnesium hydroxide was maintained at 9.5: in the case of deviation from said value, the pH was adjusted by the addition of a suitable quantity of nitric acid or sodium hydroxide.

(2) At the end of the addition of Mg(NO.sub.3).sub.2, the suspension was kept under stirring for 45 minutes, always at 60 C.

(3) The suspension was then filtered and the product collected was washed with distilled water, in a ratio equal to 330 ml of water per gram of product collected.

(4) The magnesium hydroxide thus obtained was dried at 120 C. for 4 hours.

(5) The magnesium hydroxide was then calcined at 450 C. for 5 hours in air, transforming it into the corresponding oxide (surface area equal to 150 m.sup.2/g).

EXAMPLE 2

(6) 60 ml of anhydrous methanol were charged into an autoclave having a capacity of 150 ml. 1 g of furfural and 2 g of magnesium oxide prepared as described in Example 1, were added to this.

(7) The autoclave was closed and purged with nitrogen to eliminate the air present in its interior. The reaction mixture was heated in the presence of the catalyst to two different temperatures (T.sub.L=100 C. and T.sub.H=160 C.) under the following conditions.

(8) The reaction mixture was heated to 100 C. for 1 hour under stirring (1,000 rpm). The temperature was then raised from 100 C. to 160 C. and the mixture was heated to this temperature for 2 hours in autogenous pressure, equal to 60 bar, under stirring (1,000 rpm).

(9) The autoclave containing the reaction mixture was then cooled to room temperature and then opened. The reaction mixture extracted from the autoclave was filtered to separate the magnesium oxide. The mixture was subsequently subjected to HPLC analysis to determine its composition.

(10) The analyses indicated a conversion of furfural equal to 50% and a selectivity to the methyl furfurate ester equal to 80%, the remaining 20% of the converted furfural consisting of furfuryl alcohol.

EXAMPLE 3

(11) A reaction mixture prepared according to Example 2 and containing anhydrous methanol, furfural and magnesium oxide (prepared according to what is described in Example 1) was subjected to two heating steps to temperatures T.sub.L=100 C. and T.sub.H=160 C. under the following conditions.

(12) The reaction mixture was heated to 100 C. for 2 hours under stirring (1,000 rpm). The temperature was then raised from 100 C. to 160 C. and the mixture was heated to this temperature for 3 hours in autogenous pressure, equal to 60 bar, under stirring (1,000 rpm).

(13) The autoclave containing the reaction mixture was then cooled to room temperature and then opened. The reaction mixture extracted from the autoclave was filtered to separate the magnesium oxide. The mixture was subsequently subjected to HPLC analysis to determine its composition.

(14) The analyses indicated a conversion of furfural equal to 75% and a selectivity to the methyl furfurate ester equal to 90%, the remaining 10% of the converted furfural consisting of furfuryl alcohol.

EXAMPLE 4

(15) A reaction mixture prepared according to Example 2 and containing anhydrous methanol, furfural and magnesium oxide (prepared according to what is described in Example 1) was subjected to two heating steps at temperatures T.sub.L=100 C. and T.sub.H=200 C. under the following conditions.

(16) The reaction mixture was heated to 100 C. for 2 hours under stirring (1,000 rpm). The temperature was then raised from 100 C. to 200 C. and the mixture was heated to this temperature for 3 hours in autogenous pressure, equal to 85 bar, under stirring (1,000 rpm).

(17) The autoclave containing the reaction mixture was then cooled to room temperature and then opened. The reaction mixture extracted from the autoclave was filtered to separate the magnesium oxide. The mixture was subsequently subjected to HPLC analysis to determine its composition.

(18) The analyses indicated a conversion of furfural equal to 100% and a selectivity to the methyl furfurate ester equal to 80%, the remaining 20% of the converted furfural consisting of furfuryl alcohol.

EXAMPLE 5

(19) 60 ml of anhydrous ethanol were charged into an autoclave having a capacity of 150 ml. 2 g of benzaldehyde and 2.5 g of magnesium oxide prepared according to what is described in Example 1, were added to this.

(20) The autoclave was closed and purged with nitrogen to eliminate the air present in its interior. The reaction mixture was heated in the presence of the catalyst to two different temperatures (T.sub.L=100 C. and T.sub.H=160 C.) under the following conditions.

(21) The reaction mixture was heated to 100 C. for 1 hour under stirring (1,000 rpm). The temperature was then raised from 100 C. to 160 C. and the mixture was heated to this temperature for 2 hours in autogenous pressure, equal to 60 bar, under stirring (1,000 rpm).

(22) The autoclave containing the reaction mixture was then cooled to room temperature and then opened. The reaction mixture extracted from the autoclave was filtered to separate the magnesium oxide. The mixture was subsequently subjected to HPLC analysis to determine its composition.

(23) The analyses indicated a conversion of benzaldehyde equal to 70% and a selectivity to the ethyl benzoate ester equal to 85%, the remaining 15% of the converted benzaldehyde consisting of benzylic alcohol.