WO1998024752A1

WO1998024752A1 - Process for preparing 2,2,4-trimethyl-1,3-pentanediol isobutyrate

Info

Publication number: WO1998024752A1
Application number: PCT/FI1997/000754
Authority: WO
Inventors: Kalevi Heinola; Kari Kulmala; Lars-Peter Lindfors; Hannele Hakanpää-Laitinen; Lea Rintala; Lea Parkkinen; Vesa-Matti Lehtinen
Original assignee: Neste Oy
Priority date: 1996-12-03
Filing date: 1997-12-03
Publication date: 1998-06-11
Also published as: AU5190298A; FI964829A; FI964829A0; FI104819B

Abstract

A two-step process for preparing 2,2,4-trimethyl-1,3-pentanediol isobutyrate. The process comprises subjecting isobutyraldehyde to a first reaction in the presence of an alkali metal hydroxide to produce a first reaction mixture containing 2,6-diisopropyl-5,5-dimethyl-1,3-dioxan-4-ol, and then subjecting the reaction mixture to a second reaction in the presence of an alkaline earth metal hydroxide to produce a second reaction mixture containing 2,2,4-trimethyl-1,3-pentanediol isobutyrate. The 2,2,4-trimethyl-1,3-pentanediol isobutyrate is recovered from the second reaction mixture and purified. By means of the invention, the desired product can be obtained at high yields and with a minimum of side products.

Description

Process for preparing 2,2,4-trimethyl-l,3-pentanediol isobutyrate

The present invention relates to a process according to the preamble of claim 1 for preparing 2,2, 4-trimethyl-l,3-pentanediol isobutyrate.

2,2,4-trimethyl-l,3-pentanediol isobutyrate is a known substance which has numerous technical applications. In particular, in view of its good hydrolysis resistance, it is being used for preparing insecticides, lubricant esters, polymer additives and plasticizers. It is also an excellent additive for certain adhesives and coatings.

A large number of methods are known in the art for preparing 1,3-glycols and their monoesters from the corresponding aldehydes. These methods are mostly based on a self-reaction or condensation reaction of the aldehydes in the presence of a base, whereby a proton in alfa-position of the aldehyde is removed by the alkaline catalyst, whereinafter the ion formed reacts with the carbonyl group of another aldehyde molecule. The resulting aldol (aldehyde-alcohol) is capable of reacting with a third aldehyde molecule, which gives rise to a trimer of the aldehyde. The desired monoester and a diol, which is a side -product, are obtained from said trimer.

Usually the reaction takes place at increased temperature, i.e. at about 40 to about 180 °C. Unreacted aldehyde is separated from the reaction mixture and recycled. The product is purified by vacuum distillation. The process can be continuous or carried out batchwise.

Typical prior art processes are disclosed in the following publications: US Patents Nos. 3,291,821 and 4 225 726 and German Published Patent Applications 3,833,033, 3,024,496 and 3,447,029. The catalysts used in these known processes include sodium hydroxide, alkaline earth metal hydroxides, metallic tin and stannous oxide.

The afore-mentioned processes are all based on one-step condensation reactions. In the present context this means that the desired end product is obtained essentially without altering the reaction conditions.

However, also processes which are carried out in two-steps are known in the art. Thus, DE Patent No. 3,403,696 discloses a process, wherein the aldehyde reaction to form a trimer is carried out in the presence of an alkaline catalyst, whereas the final conversion of the trimer to the corresponding diol and the monoester thereof is achieved by hydrogenation of the intermediate reaction mixture in the presence of a nickel catalyst. JP Patent Laid-Open No. 39,420/1973 teaches a two-step process wherein the reaction product of the aldehyde reaction is carried out in the presence of an alcoholate catalyst.

There are several disadvantages related to these prior art processes. In particular, the process according to DE Patent No. 3,403,696 is hampered by a low conversion of the isobutyraldehyde (i.e. the reacted amount of the aldehyde), generally the conversion varies between 50 and 70 % . The yield of the desired product is only about 40 % . Furthermore significant amounts of undesired sideproducts are formed. The known two- step process is rather complicated, it involves the use of high pressures (50 - 150 bar) and two quite different kinds of catalyst systems. The selectivity of the process is also poor; the yield of the ester product (Esterol) is less than 50 %. As regards the process according to JP Patent Laid-Open No. 39,420/1973 it should be pointed out that the use of a soluble catalyst increases the amount of side reactions, i.e. the formation of TMPD and isobutyric acid.

It is an object of the present invention to eliminate the problems relating to the prior art and to provide a novel process for preparing 1 ,3-glycol monoesters. and in particular 2,2,4-trimethyl-l,3-pentanediol isobutyrate.

The present invention is based a two-step process, whereby isobutyraldehyde (in the following abbreviated "Ibal") is first converted to 2, 6-diisop ropy 1-5, 5 -dimethyl- 1,3- dioxan-4-ol (in the following: "Aldoxan") and Aldoxan is then converted to 2,2,4- trimethyl-l,3-pentanediol isobutyrate ("Esterol"). Both reactions are catalytic. In the first step, the catalyst is an alkali metal hydroxide, such as sodium hydroxide, and in the next step an alkaline earth metal hydroxide (e.g. calcium hydroxide) is used. More specifically, the process according to the present invention is mainly characterized by what is stated in the characterizing part of claim 1.

The invention provides considerable advantages. Thus, the yield of the Esterol produced by the present invention is about 70 to 80 % . Both reactions of the two-step process take place under controlled conditions and the heat evolution can easily be controlled by adjustment of the Ibal dosing rate. By carrying out the first step at somewhat lower temperatures than required in a one-step process, the amounts of side-products can be minimized. The first step from Ibal to Aldoxan produces essentially all of the heat released during the reaction. Therefore, since practically no heat is generated during the reaction of the Aldoxan to form the Esterol, all of the alkaline earth metal catalyst can be added in one portion. Furthermore, as the catalyst is not an alcoholate, the Aldoxan does not have to be isolated from the reaction mixture by, e.g. distillation as taught in JP Patent Laid-Open No. 39,420/1973, before the second reaction step.

According to a preferred embodiment, Ca(OH)₂ in solid form or slurried or dissolved in water is used as catalyst and because its solubility in the reaction medium is low, the reaction product, i.e. the Esterol, does not essentially decompose to form TMPD and isobutyric acid.

Next, the invention will be examined in more closely with the aid of the following detailed description and with reference the attached drawing which in a schematic fashion depict the various stages and intermediates of the present two-step process.

Generally speaking, as indicated above, the invention relates the preparation of monoesters of formulas I H - C - C - C - CH₂ - 0 - C - C - H

OH

and II

c - c - c CH--OH

(II)

C = 0

- CH - R.

wherein R and R₂ are identical or different and stand for lower alkyl.

"Lower alkyl" means preferably a straight or branched, 1 to 4 carbon atoms containing alkyl group, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl or t-butyl.

In particular, the invention relates to the preparation of 2,2,4-trimethyl-l,3-pentanediol monoisobutyrate (TMPDMIB) which is a monoester mixture, the components of which are the monoesters of formulas I and II. In said formulas, substituents R, and R₂ both stand for methyl. As shown in the attached figure, said product thus generally comprises the mixture of two isomers. namely l-hydroxy-2,2,4-trimethylpentyl-3-isobutyrate and 3-hydroxy-2,2,4-trimetylpentyl-l-isobutyrate. The ratio between the isomers is from 1:6 to 6:1, preferably about 1:4 to 4:1. Typically, the product contains as a side product also minor amounts of 2,2,4-trimethyl-l,3-pentadiol. The amounts of this product are, however, smaller than in the products prepared according to known methods. The following description is based on working of the invention in a batch reactor as a semi-batch process. The process is characterized as a "semi-batch" process, because the reactant of at least the first reaction step, i.e. the aldehyde, is pumped over a period of time into the batch reactor. However, as obvious to a person skilled in the art, the process can just as well be carried out as a conventional batch process or as a continuous process. In the present case, the batch reactor is provided with efficient agitation and, if desired, the aldehyde can be fed close to the bottom of the reactor so as to achieve proper mixing of the water and the organic material which is lighter than water. If the process is operated as a continuos process, the reactor preferably comprises a plug-flow reactor or a similar reactor which is continuously charged with a mixture of alkaline catalyst solution and aldehyde.

An overall description of chemical conversions involved with the process, in the present context called "the aldoxan route", is given in the attached drawing. It should be noticed that the catalysts mentioned in the figure, sodium hydroxide and calcium hydroxide, only represent exemplifying (but preferred) embodiments, as the following description will show.

During the first step isobutyraldehyde is pumped into an aqueous solution of an alkali metal hydroxide. When isobutyraldehyde is dosed into the sodium hydroxid solution, it reacts immediately to isobutyraldoxan (Aldoxan). The reaction involves the forming of an intermediate, Ibal-aldol, which reacts with another Ibal molecule to the Aldoxan.

The momentary heat evolution is directly proportional to the Ibal dosing rate. Thus, the feed rate is mainly limited by the cooling capacity of the reactor. Efficient mixing is necessary for ensuring that mass-transfer phenomena do not limit the reaction rate.

The catalyst, the alkali metal hydroxide, is employed in the form of a diluent aqueous solution having a concentration of up to 20 wt-% , preferably about 0.5 to 16 wt-% , and in particular about 1 to 12 wt-%. Already a very dilute caustic can effect the reaction.

Higher concentrations favors Esterol formation. The alkali metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide. It is preferred to use sodium hydroxide. However, the aqueous alkali metal hydroxide solution can contain a mixture of two or more alkali metal hydroxides. Thus, the following combinations are possible: sodium hydroxide and potassium hydroxide, sodium hydroxide and lithium hydroxide, potassium hydroxide and lithium hydroxide and sodium hydroxide, potassium hydroxide and lithium hydroxide. It has been shown that even a small addition of lithium hydroxide improves the activity of an aqueous solution of sodium and/or potassium hydroxide. Particularly preferred mixed alkali metal hydroxide solutions are aqueous solutions of NaOH and LiOH having a weight ratio of - NaOH to LiOH in the range of 1:100 to 100:1, preferably 1:50 to 50:1, in particular about 1 : 10 to 10: 1. A suitable aqueous solution can, for instance, contain about 0.5 to 16 wt-% sodium hydroxide and about 0.1 to 6 wt-% lithium hydroxide. All the above mentioned percentages have been calculated from the weight of the aqueous solution.

In addition to the above mentioned alkali metal hydroxide catalyst it is also possible to use other catalysts, such as phase-transfer catalyst. These catalyst are described in more detail in EP Patent Specification No. 0 367 743. Suitable phase-transfer catalysts comprise onium catalyst containing at least 8 carbon atoms in their structure. Particularly preferred phase-transfer catalysts are the straight chained polyethers, such as polyglycolethers having a mean molecular weight of 200 to 400 (e.g. poly(ethylene glycol) (PEG).

The reaction temperature of the first step is about 20 to 150 °C, preferably about 20 to 70 °C, in particular about 20 to 65 °C. The boiling point of isobutyraldehyde is about 64.5 °C. It is therefore preferred to feed Ibal to the catalyst solution at a temperature below approx. 65 °C. The conversion and the selectivity to aldoxan are improved when the temperature is decreased from 60 to 20 °C. At 60 °C, approximately 25 % of Ibal remains unreacted, whereas the figure at 50 and 40 °C is 15 and 8 %, respectively. However, the majority of Ibal unreacted in the first step, reacts further to Esterol in the second step. The selectivity to Esterol and Aldoxan is roughly at least 70 %, preferably at least 80 % and in particular at least 90 % (and even up to 99 %) in the first step.

Small or minute quantities of TMPD are often observed. The tempera re is kept constant during the addition of the aldehyde and during the following reaction. A temperature variation of about ±2 to ± 10 °C is, however, generally acceptable.

The conversion of Ibal during the first step is from 75 to 95 % depending of process conditions. The yield of Aldoxan varies accordingly between 50 - 90 % .

When the first reaction is over (when pumping of Ibal stopped), the phases of the reaction mixture are allowed to separate. The lower caustic layer, which contains the alkaline agent and possibly alkali metal salts of isobutyric acid, is decanted from the reactor leaving the Aldoxan behind. Aldoxan is washed in the reactor with water to remove extra caustic.

To convert Aldoxan to Esterol, an alkaline earth metal hydroxide is added to the organic phase, which is agitated. The alkaline earth metal hydroxide catalyses the ring-opening of the Aldoxan. During the reaction two esterol isomers are formed, as indicated in formulas I and II and in the figure.

As mentioned above, the intermediate product (raw product) of the first reaction step does not have to be purified before the second reaction step.

The alkaline earth metal hydroxide is selected from the group consisting of magnesium hydroxide, calcium hydroxide, strontium hydroxide and barium hydroxide, calcium hydrodroxide being particularly preferred. The concentration of the alkaline earth metal hydroxide (calculated from the weight of the organic phase) is generally 0.1 to 10 wt-%, preferably 1 to 6 wt- % . The temperature of the second step is somewhat higher than during the first step.

Using Ca(OH)₂ as an example, the dosage of the hydroxide is, for example, 0.5 to 2 wt-% calculated from the weight of the organic phase. This amount is charged into the reactor, and the temperature is adjusted to the desired value. Since calcium hydroxide as many of the other alkaline earth metal hydroxides has very limited solubility in solvents, such as water, it is preferred to feed said hydroxide either as a solid (a powder) or in the form of an aqueous slurry. The typical reaction temperature range is about 40 to 80 °C, preferably about 60 to 70 °C. Higher temperatures favor formation of Esterol from Aldoxan.

After the second reaction step and a reaction time of about 10 hours at 70 °C or about 15 hours at 60 °C, the conversion level of Ibal was 96 - 97 % and the selectivity to Esterol above 90 % . At long reaction times, TMPD is formed in larger quantities (up to 4 % at 60 °C and 20 h).

When the reaction is completed (about 5 to 24 hours), the alkaline earth metal hydroxide is filtered off and Esterol is washed with water. The crude product is purified by distillation. The yield from Aldoxan to Esterol i.s about 80 % . The total yield from Ibal to Esterol is about 70 - 80 % .

Based on the above, a particularly preferred embodiment of the invention comprises the following reaction steps:

Step A: Conversion of Ibal to Aldoxan: - reaction temperature: 20 to 65 °C, in particular about 50 °C;

- catalyst: diluent aqueous solution of NaOH;

- stirring: sufficiently efficient to prevent mass-transfer limitations and dead zones;

- recipe: 2.55 1 of 2 wt-% NaOH solution loaded into the reactor + 4.3 1 of Ibal dosed into the reactor during six hours; - phase separation/removal of water phase/ washing of organic phase.

Step B: Conversion of Aldoxan to Esterol:

- reaction temperature: 40 to 75 °C, in particular about 70 °C;

- reaction time: 10 hours; - stirring: sufficiently efficient to prevent mass-transfer limitations and dead zones;

- recipe: reaction mixture from step 1 ( ~ 4.3 1 organic mixture containing ~ 85 % Aldoxan/Esterol, 15 % Ibal saturated with ~ 5 wt-% water) + 0.5 wt-% Ca(OH)₂ (solid or as a slurry) added to the reactor;

- filtration of Ca(OH)₂;

- distillation of crude product to obtain an end product having a purity of more than 98 % .

The following non-limiting working examples clarify the invention.

Example 1

Conversion of isobutyraldehyde to Aldoxane

A laboratory reactor was charged under nitrogen atmospere with 700 g of a 5 wt-% NaOH solution containing 1.6 g PEG 400 (phase-transfer catalyst). The abbreviation PEG 400 stands for polyethylene glycol having a molar mass of 400. The mixmre was agitated and about 790 g isobutyraldehyde was added, using different feed rates, at a temperature of 33 °C.

After the reaction, the product composition was (in wt-%) typically:

Conversion (Ibal) 95 % Selectivity (Esterol) 12.7 %

Selectivity (Aldoxan) 87.7 %

Selectivity (TMPD) 0.3 %

Example 2 Conversion of isobutyraldehyde to Aldoxan

A laboratory reactor was charged under nitrogen atmospere with 700 g of a 2 wt-% NaOH solution containing 1.6 g PEG 400. The mixmre was agitated and about 790 g isobutyraldehyde was added at a temperature of 60 °C within about 4 hours.

After the reaction, the product composition was (in wt-%) typically: Conversion (Ibal) 83 %

Selectivity (Esterol) 21 %

Selectivity (Aldoxan) 78 %

Selectivity (TMPD) 1 %

Examples 3 to 6

Conversion of Aldoxane to Esterol

The organic phase of the first reaction step was washed with water. The reaction was continued by feeding about 2 wt-% (of the weight of the organic phase) of Ca(OH)₂ to the reaction mixmre at different temperamres. Typical results obtained are listed below:

Example 3

Temperature 60 °C

Ca(OH)₂ 2 wt-%

Reaction time 20 hours

Conversion (Aldoxan) 97 %

Selectivity (Esterol) 90 %

Selectivity (Aldoxan) 2.5 %

Selectivity (TMPD) 4.4 %

Example 4

Temperature 60 °C

Ca(OH)₂ 2 wt-%

Reaction time 3 hours

Conversion (Aldoxan) 96 %

Selectivity (Esterol) 53 %

Selectivity (Aldoxan) 46.7 % Selectivity (TMPD) 0.3 %

Example 5

Temperamre 70 °C

Ca(OH)₂ 2 wt-% Reaction time 5 hours

Conversion (Aldoxan) 96 % Selectivity (Esterol) 81 %

Selectivity (Aldoxan) 16.3 % Selectivity (TMPD) 2.4 %

Example 6

Temperamre 70 °C

Ca(OH)₂ 0.5 wt-%

Reaction time 5 hours

Conversion (Aldoxan) 96 %

Selectivity (Esterol) 63 %

Selectivity (Aldoxan) 35 %

Selectivity (TMPD) 1.5 %

Example 7

Two-step process for preparing esterol

A laboratory reactor was kept under nitrogen atmosphere and charged with 200 g of a 2 wt-% NaOH solution. The solution was kept under agitation and 500 g isobutyraldehyde was added to the solution with a time period of about 4.5 hours at a temperamre of 50

°C. After the termination of the feed, the phases were allowed to separate and the aqueous phase was decanted and discarded. The organic phase was washed once with water. The composition of the organic phase was (in wt-%):

Isobutyraldhyde 16 %

Aldoxan 75 % Esterol 9 %

The reaction was continued by heating the reaction mixmre to 60 °C and by adding 9.2 g Ca(OH)₂ as a catalyst. After about 14 hours the composition of the reaction mixmre was:

Isobutyraldhyde 8 %

TMPD 1 %

Aldoxan 7 %

Esterol 84 %

The catalyst was filtered off, the crude product was washed with water and the product was separated by distilling.

Example 8

Two-step process for preparing esterol

A laboratory reactor was kept under nitrogen atmosphere and charged with 200 g of a 2 wt-% NaOH solution. The solution was kept under agitation and 500 g isobutyraldehyde was added to the solution with a time period of about 4.5 hours at a temperamre of 60 °C. After the termination of the feed, the phases were allowed to separate and the aqueous phase was decanted and discarded. The organic phase was washed once with water. The composition of the organic phase was (in wt-%):

Isobutyraldl αyde 30 %

Aldoxan 60 %

Esterol 9 %

The reaction was continued by heating the reaction mixture to 70 °C and by adding 9.6 g Ca(OH)₂ as a catalyst. After about 9 hours the composition of the reaction mixmre was:

Isobutyraldhyde 7 %

TMPD 5 %

Aldoxan 4 %

Esterol 84 %

Claims

Claims:

1. A process for preparing 2,2,4-trimethyl-l,3-pentanediol isobutyrate, comprising the steps of - subjecting isobutyraldehyde to a first reaction in the presence of an alkali metal hydroxide to produce a first reaction mixmre containing 2,6-diisopropyl-5,5-dimethyl- l,3-dioxan-4-ol,

- subjecting said reaction mixmre to a second reaction in the presence of an alkaline earth metal hydroxide in order to produce a second reaction mixmre containing 2,2,4- trimethyl-l,3-pentandiol isobutyrate, and

- recovering said 2,2,4-trimethyl-l,3-pentandiol isobutyrate from said second reaction mixmre.

2. The process according to claim 1, wherein said alkali metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide.

3. The process according to claim 2, wherein said alkali metal hydroxide is employed in the form of a diluent aqueous solution having a alkali metal hydroxide concentration of up to 20 wt-% .

4. The process according to any one of the preceding claims, wherein the first reaction is carried out in the presence of an alkali metal hydroxide with a phase-transfer catalyst.

5. The process according to claim 1 , wherein said alkaline earth metal hydroxide is selected from the group consisting of magnesium hydroxide, calcium hydroxide, strontium hydroxide and barium hydroxide.

6. The process according to claim 5, wherein said alkaline earth metal hydroxide is employed in the solid form or in aqueous slurry or solution.

7. The process according to any one of the preceding claims, wherein said first reaction is carried out at a temperamre of 20 to 70 °C and said second reaction is carried out at a temperamre of 40 to 80 °C.

8. The process according to any one of the preceding claims, comprising - mixing isobutyraldehyd with a diluent aqueous solution of sodium hydroxide and subjected to said first reaction at 20 to 65 °C to form a reaction mixmre containing an aqueous phase and a first organic phase,

- separating said first organic phase from said aqueous phase,

- mixing calcium hydroxide with said organic phase, - subjecting said first organic phase to said second condensation reaction at 40 to 75 °C to form a reaction mixmre with a second organic phase containing crude 2,2,4- trimethy 1- 1 , 3 -pentanediol isobutyrate ,

- separating said calcium hydroxide from said 2,2,4-trimethyl-l ,3 -pentanediol isobutyrate and - purifying said 2, 2, 4-trimethy 1-1, 3 -pentanediol isobutyrate.

9. The process according to claim 8, wherein said calcium hydroxide is mixed with said organic phase in solid form or in a slurry.

10. The process according to claim 8 or 9, wherein said first organic phase is washed with an aqueous solution in order to remove remaining sodium hydroxide.

11. The process according to any one of claims 8 to 10, wherein said 2,2,4-trimethyl- 1,3 -pentanediol isobutyrate is purified by subjecting said second organic phase to distillation.

12. The process according to any one of claims 8 to 11, wherein said calcium hydroxide is mixed with said first organic phase in a concentration of 0.1 to 10 wt-%, preferably 1 to 6 wt-% .

13. The process according to any of the preceding claims, wherein said second organic phase containing crude 2,2,4-trimethyl-l, 3-pentanediol isobutyrate contains a maximum of 10 % TMPD.

14. The process according to any one of the preceding claims, wherein the conversion of isobutyraldehyde in said first reaction is 60 to 95 % , and the conversion of 2,6- diisopropyl-5,5-dimethyl-l ,3-dioxan-4-ol in said second reaction is 70 to 95 % .