WO1997041088A1

WO1997041088A1 - Process for preparing monoesters of 1,3-diols

Info

Publication number: WO1997041088A1
Application number: PCT/FI1997/000263
Authority: WO
Inventors: Kalevi Heinola; Esko Karvinen; Lars-Peter Lindfors; Kari Kulmala; Hannele Hakanpää-Laitinen; Lea Rintala; Eija Kuisma; Lea Parkkinen
Original assignee: Neste Oyj
Priority date: 1996-04-29
Filing date: 1997-04-29
Publication date: 1997-11-06
Also published as: AU2639697A; DE19781729C2; FI961827A; FI961827A0; GB2327421A8; GB2327421A; GB9821987D0; DE19781729T1; FI101472B; GB2327421B; FI101472B1

Abstract

The invention relates to a process for preparing monoesters of 1,3-diols. The invention relates to a process for preparing in particular 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, according to which process isobutyraldehyde is brought into contact with an alkalihydroxide catalyst. The alkali hydroxide catalyst used according to the invention is a dilute solution of lithium hydroxide, in which the concentration of lithium hydroxide is about 1 - 12 % by weight. An aqueous solution containing about 2 - 10 % by weight of sodium hydroxide and about 0.1 - 6 % by weight of lithium hydroxide, is used preferably. This enhances selectivity with respect to 1,3-diols, with an increased conversion of the aldehyde into a monoester and a subsequent decrease in recirculation volumes in the preparation process.

Description

Process for Preparing Monoesters of 1 ,3-diols

The present invention relates to a process according to the preamble of claim 1 for preparing monoesters of 1,3-diols.

According to such a process an aldehyde, containing an hydrogen atom in an alpha position, is brought into contact with a basic catalyst to prepare monoesters of general formulae I

H - C - C - C - CH, - 0 - C - C - H

I I I π i ^ω

R₂ OH R₂ 0 R-,

and II, respectively,

! I !

H - C - C - C - CH₂-0H

I I !

(ID

C = 0

R₁ - CH - R.

and the corresponding 1,3-diols. In formulae I and II substituents R, and R₂ are identical or different from each other and denote lower alkyls.

It is known in the art that there are several processes for preparing 1 ,3-glycols and monoesters thereof from aldehydes. The reaction usually takes place at an elevated temperature in the range from about 40 °C to about 180 °C in the presence of catalysts. After the reaction unreacted aldehyde is separated from the reaction mixture and recycled in the process. The product is typically purified by vacuum distillation. The processes described above can be either continuous or batch processes.

US Patents Nos. 3,291,821 and 4,225,726 and DE Patent Applications Nos. 3,833,033, 3,024,496 and 3,447,029 can be cited as examples of technical solutions representative of known art. For example, sodium hydroxide, a hydroxide of an alkaline earth metal, metallic tin or tin oxide are used as catalysts in these known processes.

There are considerable disadvantages associated with the known technical solutions. Therefore, the reaction heat generated in an exothermic reaction complicates the control of the reaction in many processes. Another significant problem is caused by the fact that the basic catalysts like sodium hydroxide, for example, are used as dilute aqueous solutions, which results in a low degree of conversion of the starting material (for example, processes according to US Patents Nos. 3,291,821 and 4,225,726). On the other hand, the known methods have disadvantages relating to the conversion of the process into a continuous process (DE Patent Application No. 3,024,496).

A process that is quite advantageous as such has been described in EP Patent Application

0 367 743, in which process a two-component catalyst solution (15 to 40 % NaOH + a phase-transfer catalyst) and isobutyraldehyde (isobutanal, IBAL) are added to a reactor simultaneously. Said process can be applied to batch reactors and to reactors designed to operate continuously. However, the degree of conversion is rather low, which causes the recycling volumes to be large. Moreover, the use of two catalysts complicates purification of the reaction solution.

A one-step method, according to which isobutyraldehyde is added to a hydroxide of an alkali metal, after which the reaction is allowed to proceed for an hour before separating the product from the reaction mixture, for preparing 2,2,4-trimethyl-l ,3-pentanediol monoisobutyrate is described in GB Patent Application No. 2,008,097. In said application, cited here as a reference, an alkali metal hydroxide is used in the form of a solid, concentrated aqueous solution with a concentration of at least 20 % (usually 20 to 60 %) or a mixture of a solid substance and a concentrated aqueous solution of a solid substance. According to this method the amount of water contained in the reaction medium can be reduced. However, the use of a concentrated catalyst also raises the temperature of the reaction medium rapidly at the beginning of the reaction and renders control of the reaction more difficult. The concentrated catalyst also breaks down the desired monoester yielded as the final product into the corresponding undesirable diol.

In the GB Patent Application No. 2,008,097 the alkali metal hydroxides described are sodium hydroxide, potassium hydroxide and lithium hydroxide. According to the application sodium hydroxide is catalytically the most active and economically preferable of these hydroxides.

It is an object of the present invention to overcome the disadvantages of the known art and to provide a novel process for preparing 1 ,3-glycol monoesters.

The present invention is based on the unexpected observation that - contrary to what has been stated in GB Patent Application No. 2,008,097 - lithium hydroxide, when used as a catalyst, is very active when an aldehyde is reacted with itself if used as a dilute aqueous solution. The term "dilute aqueous solution" is used to denote an aqueous solution or an aqueous suspension, in which the concentration of lithium hydroxide expressed in terms of mass percentage is less than 20 %, preferably less than 15 % and in particular less than about 12 %. Lithium hydroxide has been found to be so active that in a dilute catalyst mixture there is no need for using phase-transfer catalysts, but lithium hydroxide can form the essential catalytic component of the solution alone or as a mixture with at least one other hydroxide of another alkali metal or hydroxide of an alkaline earth metal.

More specifically, the invention is characterized by what is stated in the characterizing part of claim 1.

The invention provides considerable advantages. The heat produced by the reaction can be controlled, which improves the safety of the process. The invention increases selectivity of the process with respect to the 1,3-glycol monoester, or in other words it improves the conversion to the monoester, which in turn reduces recycling volumes. This is mostly due to the fact that lithium hydroxide is catalytically very active. Additionally, because the basic catalyst mixture containing hydroxyl ions is dilute, the monoester does not break down to the diol to any significant extent. When lithium hydroxide is used as a mixture with one other or some other hydroxides, sufficient conversion can be achieved with reasonable cost of the catalyst(s). A phase-transfer catalyst is not needed.

The present invention is described in more detail in the following and with the aid of some working examples.

This invention relates to the preparation of monoesters of general formulae I

H - C - C - C - CH-, - 0 - C - C - H

(I)

OH

and of II, respectively,

R₁ H

! I

H - C - C - CH₂-0H

2 ° ^K2 (ID

C = 0

R„ - CH - R.

and the corresponding diols of general formula III R ₁ H R ₁

H - C - C - C - C H - OH (HI)

R ₂ OH R ₂

in which formulae I - III R, and R₂ are identical or different and denote a lower alkyl.

For the purpose of the present invention, the term "lower alkyl" means an alkyl group of preferably 1 - 4 carbon atoms with a straight or branched chain, such as methyl, ethyl, n- propyl, /-propyl, rc-butyl, /-butyl or /-butyl.

In particular, it is preferred to prepare the mono-isobutyrate of 2,2,4-trimethyl-l,3- pentanediol (TMPDMIB), which is a mixture of monoesters, the components of which are represented by the monoesters of general formulae I and II. In these formulae both R, and R₂ denote methyl groups. Thus, the described product is usually a mixture of two isomers, namely, a mixture of l-hydroxy-2,2,4-trimethylpentyl-3-isobutyrate and 3-hydroxy-2,2,4- trirnethylpentyl-1-isobutyrate. The product typically contains some 2,2,4-trimethy 1-1,3 - pentadiol as a by-product. The amounts of this by-product are, however, smaller than in the products yielded by methods known in the art.

1,3-glycol monoester is prepared by contacting an aldehyde of formula IV

2

I

H C - C = 0 ( IV )

I j

R . H

with a catalyst while stirring. In formula IV R, and R₂ have the same meaning as above. Depending on the desired final product several different aldehydes with one hydrogen atom in the alpha-position can be used as starting materials. The examples include isobutyraldehyde (IBAL), 2-methylbutyraldehyde, 2-ethylbutyraldehyde, 2- ethylpentaldehyde, 2-ethylhexaldehyde, 2-propylpentaldehyde, 2-propylhexaldehyde and 2-butylhexaldehyde. When TMPDMIB is prepared, isobutyraldehyde is used. Other aldehydes yield the corresponding esters, respectively. Thus, to give an example, 2- methylbutyraldehyde reacts to yield 3-hydroxy-2-ethyl-2,4-dimethylhexyl-2- methylbutyrate and 1 -hydroxy-2-ethyl-2,4-dimethylhexyl-3-(2-methyl)-butyrate.

The present invention is based on the reaction of an aldehyde with itself, during which a proton is removed from the alpha-position of the aldehyde by the action of a basic catalyst, whereafter the enolate ion, thus formed, reacts with the carbonyl group of another aldehyde molecule. This yields an aldol (aldehyde-alcohol) which is capable of reacting with a third aldehyde molecule, when a trimer of the aldehyde used as the starting material is formed. This trimer yields the desired monoester and the corresponding diol as a by- product.

The process of the present invention is a one-step reaction, which means that the reaction is carried out without isolating intermediate products. The final product is typically formed without any essential changes in the reaction conditions, such as changing of the catalyst, during the reaction. However, the temperature can vary to some extent.

In the following, the method is described as a semibatch process, but the present invention can also be carried out as a batch process or a continuous process with changes that are self-evident to those expert in the art. A batch reactor is equipped with efficient means for stirring and it is possible to place the input line of the aldehyde close to the bottom of the reactor, in order to ensure that the organic material that is lighter than water, could be mixed as efficiently as possible with the water phase.

According to a preferred embodiment of the present method an aqueous solution of the catalyst, the temperature of which is adjusted to a desired value, is added to the reactor first, whereafter an aldehyde of general formula IV is added to the stirred solution while keeping the rate of addition constant. After completion of the addition the mixture can be allowed to react further. After the reaction step, phases are allowed to separate and the aqueous phase is decanted away. The reaction product is washed 1 - 5 times with water. The reaction product is further purified by breaking down the IBAL trimer into IBAL and distilling away IBAL and possible light by-products. The desired monoester is collected by means of distillation as the final product and the corresponding diol as a by-product.

According to this invention the catalyst used comprises an aqueous mixture of lithium hydroxide with a lithium hydroxide concentration of about 0.1 to 19.9 percent by weight, preferably about 0.2 to 15 percent by weight, in particular about 0.4 to 12 percent by weight. The amount of lithium hydroxide expressed as mass ratio in comparison to the amount of die aldehyde is typically about 0.1 :100 - 20:100, preferably about 0.2:100 - 10: 100. Because the concentration of a saturated aqueous solution of lithium hydroxide is typically about 12 percent by weight, more concentrated lithium hydroxide-water mixtures contain an aqueous suspension (slurry) of water and lithium hydroxide. Lithium hydroxide used as a catalyst is so active that the concentration of its aqueous mixture does not need to be increased to more than 10 percent by weight, at which value all the lithium hydroxide used is still soluble.

Lithium hydroxide can be added to the aqueous phase of the catalyst in the form of the monohydrate of lithium hydroxide (LiOH H₂O). In the following examples a solution of

LiOH monohydrate with a concentration of 3 to 10 percent by weight was used, corresponding to a concentration of about 1.7 to 5.5 percent by weight of lithium hydroxide. Compared to sodium hydroxide solutions of the same concentration lithium hydroxide gives rise to even over 20 percentage units higher yields of TMPDMIB. In the case of other 1,3-glycol esters the improvements in the degree of conversion are of the same order of magnitude.

The aqueous mixture of lithium hydroxide can contain a hydroxide of another alkali metal, in practice sodium hydroxide and/or potassium hydroxide, when the total concentration of hydroxide compounds is less than 50 % by weight, preferably less than 20 % by weight.

This is due to the fact that even a small addition of lithium hydroxide improves the activity of an alkali metal hydroxide solution. Aqueous solutions of NaOH/LiOH, with a mass ratio NaOH/LiOH 1 : 100 to 100: 1, preferably 1 :50 to 50:1, in particular 1 : 10 to 10: 1, are particularly advantageous. According to one preferable embodiment an aqueous solution containing about 2 to 10 % by weight of sodium hydroxide and about 0.1 to 6 % by weight of lithium hydroxide, when an aqueous solution containing about 3 to 6 % by weight of sodium hydroxide and 0.2 to 2 % by weight of lithium hydroxide, is regarded particularly suitable. All the percentages described above have been calculated from the weight of the aqueous mixture/solution.

Mixtures of potassium hydroxide and lithium hydroxide can be used in the weight ratios described above. Additionally, mixtures of potassium hydroxide, sodium hydroxide and lithium hydroxide, with weight proportions of the alkalimetal hydroxides being essentially 1 to 100 : 1 to 100 : 1 to 100, preferably 10 to 100 : 10 to 100 : 1 to 10, can be used when desired.

In addition to the alkali metal hydroxides described above alkaline earth metal hydroxides, such as calcium, barium or strontium hydroxide, can be used. The amounts of the these hydroxides are typically about 0.1 to 5 % by weight, preferably about 0.5 to 3 % by weight of the aqueous mixture.

The reaction temperature of the one-step condensation reaction of the present invention can be about 40 to 150 °C, preferably about 20 to 80 °C, in particular about 40 to 75 °C. Because aqueous solutions of a catalyst are used in the reaction, pressures in excess of the atmospheric pressure are required to reach temperatures above 100 °C. Therefore, the absolute operating pressures are typically in the range of about 0.8 to 4 atm, normal atmospheric pressure being regarded as preferable. The reaction temperature is preferably kept during the addition of the aldehyde and the subsequent reaction at a constant value, typically with an accuracy of ±2 to ±10 degrees (°C). The boiling point of isobutyr¬ aldehyde is about 64.5 °C, whence follows that it is advantageous to add IBAL to a catalytic mixture, the temperature of which is about 60 °C. After the reaction the organic phase and the aqueous phase are allowed to separate, whereafter the aqueous phase containing base and possibly alkali metal salts and/or alkaline earth metal salts of isobutyric acid is removed by decanting.

After the reaction step the organic phase is washed with water (1 to 5 times). IBAL trimer is broken down to IBAL by heating and the product is purified by distillation.

The following examples for preparing monoisobutyrate of 2,2,4-trimethyl-l,3-pentanediol are given to illustrate the invention. In all of the following examples a standard procedure was used, according to which

- a catalytic mixture was added to the reactor first,

- the temperature was set at 20 to 80 °C,

- isobutyraldehyde was added at a constant rate of addition to the reactor while stirring, - after the addition was complete the mixture was allowed to react further and

- after the reaction step the phases were allowed to separate and

- the aqueous phase was decanted off.

Examples 1 and 2 are reference examples, in which only sodium hydroxide was used as the catalyst, examples 3 - 8 are illustrative of this invention. A mixture of sodium hydroxide and lithium hydroxide was used in examples 3 - 5, and only lithium hydroxide was used in examples 6 - 8.

The following examples are given only for the purpose of illustrating the invention and are not to be understood as restrictive of the invention in any way whatsoever.

Example 1 (reference)

A 1,3-glycolester was prepared according to the standard procedure described above with the following amounts of substance and conditions described below:

Catalyst: 10 % (by weight) NaOH solution, 50 g IBAL: 80 g

Temperature: 60 °C

Time of addition: 2.5 hours

Total reaction time: 5.5 hours

A typical distribution of products was the following: 12 % by weight IBAL, 14 % by weight IBAL trimer, 54 % by weight TMPDMIB, 14 % by weight 2,2,4-trimethyI-l,3- pentanediol, 6 % by weight of other products.

Example 2 (reference)

Catalyst: 5 % (by weight) NaOH solution, 50 g

IBAL: 80 g

Temperature: 45 - 70 °C

Time of addition : 2.5 hours

Total reaction time: 4 hours

A typical distribution of products was the following: 22 % by weight IBAL, 26 % by weight IBAL trimer, 41 % by weight TMPDMIB, 4 % by weight 2,2,4-trimethyl-l,3- pentanediol, 7 % by weight of other products.

Example 3

A 1 ,3-glycolester was prepared according to the standard procedure described above in accordance with this invention:

Catalyst: 5 % (by weight) NaOH solution, with 1.4 % (by weight)

LiOH monohydrate, 250 g (corresponds to about 2 g LiOH) IBAL: 400 g Temperature: 60 °C

Time of addition: 2 hours Total reaction time: 5 hours

A typical distribution of products was the following: 12 % by weight IBAL, 14 % by weight IBAL trimer, 61 % by weight TMPDMIB, 7 % by weight 2,2,4-trimethyl-l,3- pentanediol, 6 % by weight of other products.

Example 4

A 1,3 -glycol ester was prepared according to the standard procedure described above in accordance with this invention:

Catalyst: 4 % (by weight) NaOH solution, with 1.1 % (by weight) LiOH monohydrate, 250 g (corresponds to about 1.5 g LiOH)

IBAL: 400 g

Temperature: 50 -65 °C

Time of addition: 2.5 hours

Total reaction time: 4.5 hours

A typical distribution of products was the following: 20 % by weight IBAL, 28 % by weight IBAL trimer, 44 % by weight TMPDMIB, 2 % by weight 2,2,4-trimethyl-l,3- pentanediol, 6 % by weight of other products.

Example 5

Catalyst: 5 % (by weight) NaOH solution, with 0.8 % (by weight)

LiOH monohydrate, 250 g (corresponds to about 1.1 g LiOH) IBAL: 400 g Temperature: 50 - 70 °C

Time of addition: 1 hour 45 minutes

Total reaction time: 5 hours 15 minutes

A typical distribution of products was the following: 18 % by weight IBAL, 15 % by weight IBAL trimer, 54 % by weight TMPDMIB, 5 % by weight 2,2,4-trimethy 1-1,3 - pentanediol, 8 % by weight of other products.

Example 6

A 1,3-glycol ester was prepared according to the standard procedure described above in accordance with this invention:

Catalyst: 3 % (by weight) LiOH monohydrate solution, 50 g (=0.84 g LiOH)

IBAL: 80 g

Temperature: 60 °C

Time of addition: 2 hours

Total reaction time: 5.5 hours

A typical distribution of products was the following: 16 % by weight IBAL, 29 % by weight IBAL trimer, 48 % by weight TMPDMIB, 2 % by weight 2,2,4-trimethyl-l,3- pentanediol, 5 % by weight of other products.

Example 7

A 1 ,3-glycol ester was prepared according to the standard procedure described above in accordance with this invention:

Catalyst: 5 % (by weight) LiOH monohydrate solution, 50 g (=1.4 g

LiOH) IBAL: 80 g Temperature: 55 °C

Time of addition: 2 hours

Total reaction time: 5 hours

A typical distribution of products was the following: 10 % by weight IBAL, 17 % by weight IBAL trimer, 63 % by weight TMPDMIB, 5 % by weight 2,2,4-trimethyl-l,3- pentanediol, 5 % by weight of other products.

Example 8

Catalyst: 10 % (by weight) LiOH monohydrate solution, 50 g (=2.8 g LiOH)

IBAL: 80 g

Temperature: 55 °C

Time of addition: 2 hours

Total reaction time: 5 hours

A typical distribution of products was the following: 6 % by weight IBAL, 3 % by weight IBAL trimer, 71 % by weight TMPDMIB, 16 % by weight 2,2,4-trimethyl-l,3- pentanediol, 4 % by weight of other products.

By comparing the examples described above it can be stated that

- a small addition of LiOH into a NaOH solution increases the yield of 1,3-glycol ester by 20 percentage units (Example 3/Reference example 2) and that

- when equal or smaller amounts are used, in the case of LiOH conversion into products is better than for NaOH by more than 20 percentage units (Example 8/Reference example 2).

Claims

1. A process for preparing monoesters of general formulae I

H - C - C - C - CH-, - 0 - C - C - H QΛ

OH

and of II, respectively,

R₁ H R₁

H - C - C - - CH₂-0H

I I I

(II)

R, - CH - R.

and/or diols of the general formula III

_Rl H R₁

I I I - H - C - C - C - CH₂-0H

I I | (Ki)

R₂ OH R₂

in which formulae R, and R₂ are identical or different and denote a lower alkyl, according to which process an aldehyde of general formula IV ^R2

I

H C - C = 0 ( IV )

I j

R ₁ H

is contacted with an alkali hydroxide catalyst, c h a r a c t e r i z e d in that the alkali hydroxide catalyst used comprises a dilute aqueous solution of lithium hydroxide.

2. The process according to claim 1, wherein the concentration of lithium hydroxide is less than 20 % by weight.

3. The process according to claim 2, wherein the concentration of lithium hydroxide is about 1 - 12 % by weight.

4. The process according to claim 1, wherein the aqueous solution of lithium hydroxide contains also another alkali metal hydroxide, with a total concentration of the hydroxide compounds being less than 50 % by weight, preferably less than 20 % by weight.

5. The process according to claim 4, wherein the aqueous solution of lithium hydroxide contains sodium hydroxide and/or potassium hydroxide, with the weight ration of LiOH to the other hydroxide(s) being 1 :100 to 100:1.

6. The process according to claim 4, wherein a dilute aqueous solution of about 2 to 10 % by weight of sodiumhydroxide and about 0.1 to 6 % by weight of lithium hydroxide, is used as the alkali metal hydroxide catalyst.

7. The process according to claim 6, wherein a dilute aqueous solution of about 3 to 6 % by weight of sodium hydroxide and 0.5 to 2 % by weight of lithium hydroxide is used.

8. The process according to any preceding claim, wherein the compound of general formula IV is added gradually to an aqueous solution containing lithium hydroxide, while stirring the said solution during the addition of the said compound.

9. The process according to any preceding claim, wherein the aqueous mixture of lithium hydroxide also contains a hydroxide of an alkaline earth metal, preferably a hydroxide of calcium, barium and/or strontium.

10. The process according to any preceding claim, wherein the reaction is carried out in a batch reactor.

1 1. The process according to any preceding claim, wherein monoisobutyrate of 2,2,4- trimethyl-l,3-pentanediol is prepared.