Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/44—Preparation of carboxylic acid esters by oxidation-reduction of aldehydes, e.g. Tishchenko reaction

Definitions

• 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.
• 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.
• 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.
• 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.
• 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 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.
• 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.
• 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.
• 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.
• the invention relates the preparation of monoesters of formulas I H - C - C - C - CH 2 - 0 - C - C - H
• R and R 2 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.
• 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.
• substituents R, and R 2 both stand for methyl.
• 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.
• 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.
• the process can just as well be carried out as a conventional batch process or as a continuous process.
• 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.
• 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.
• isobutyraldehyde is pumped into an aqueous solution of an alkali metal hydroxide.
• isobutyraldehyde When isobutyraldehyde is dosed into the sodium hydroxid solution, it reacts immediately to isobutyraldoxan (Aldoxan).
• Aldoxan isobutyraldoxan
• 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.
• 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 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-%.
• a very dilute caustic can effect the reaction.
• 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.
• 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.
• phase-transfer catalyst 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.
• 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 % .
• 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.
• 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.
• two esterol isomers are formed, as indicated in formulas I and II and in the figure.
• 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.
• 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.
• the conversion level of Ibal was 96 - 97 % and the selectivity to Esterol above 90 % .
• TMPD is formed in larger quantities (up to 4 % at 60 °C and 20 h).
• 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;
• reaction temperature 40 to 75 °C, in particular about 70 °C;
• 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;
• PEG 400 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.
• the product composition was (in wt-%) typically:
• 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.
• the product composition was (in wt-%) typically: Conversion (Ibal) 83 %
• 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:
• 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
• reaction mixmre was heated 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:
• the catalyst was filtered off, the crude product was washed with water and the product was separated by distilling.
• 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.
• 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-%):
• 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:
• the catalyst was filtered off, the crude product was washed with water and the product was separated by distilling.

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• Chemical & Material Sciences (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Cited By (5)

Citations (3)

• 1996
  • 1996-12-03 FI FI964829A patent/FI104819B/fi active
• 1997
  • 1997-12-03 WO PCT/FI1997/000754 patent/WO1998024752A1/en active Application Filing
  • 1997-12-03 AU AU51902/98A patent/AU5190298A/en not_active Abandoned

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