PROCESS FOR PREPARING DIMETHYLAMINOALKYL (METH)ACRYLATES

Abstract

The present invention relates to a process for preparing dimethylaminoalkyl (meth)acrylates from alkyl (meth)acrylate and dimethylaminoalkanol. It likewise relates to the use of a catalyst system comprising a solution of a lithium alkoxide in alcohol in the preparation of a dimethylaminoalkyl (meth)acrylate.

Claims

1-15. (canceled)

16. A process for preparing dimethylaminoalkyl (meth)acrylate, comprising reacting a mixture comprising: (a) alkyl (meth)acrylate, (b) dimethylaminoalkanol and (c) a catalyst system comprising a solution of a lithium alkoxide in alcohol to produce said dimethylaminoalkyl (meth)acrylate, wherein the catalyst system contains no alkaline earth metal compounds.

17. The process of claim 16, wherein during the reaction, additional amounts of (a) the alkyl (meth)acrylate, (b) the dimethylaminoalkanol and, optionally, (c) the catalyst system are added to the reaction mixture and the dimethylaminoalkyl (meth)acrylate which forms is removed partly or completely from the reaction mixture.

18. The process of claim 16, wherein the dimethylaminoalkanol is selected from the group consisting of: 2-dimethylamino-1-ethanol, 3-dimethylamino-1-propanol, 4-dimethylamino-1-butanol, 5-dimethylamino-1-pentanol, 6-dimethylamino-1-hexanol, 7-dimethylamino-1-heptanol, and 8-dimethylamino-1-octanol.

19. The process of claim 16, wherein the alkyl (meth)acrylate is selected from the group consisting of: methyl (meth)acrylate, ethyl(meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, and octyl (meth)acrylate.

20. The process of claim 16, wherein the dimethylaminoalkanol is 2-dimethylamino-1-ethanol and the alkyl (meth)acrylate is methyl methacrylate.

21. The process of claim 16, wherein the lithium alkoxide is selected from the group consisting of: lithium methoxide, lithium ethoxide, lithium n-propoxide, lithium iso-propoxide, lithium n-butoxide, lithium iso-butoxide and lithium tert-butoxide, and the alcohol, independently thereof, is selected from the group consisting of: methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol and tert-butanol.

22. The process according of claim 16, wherein the catalyst system consists of a solution of lithium methoxide in methanol or of a solution of lithium tert-butoxide in methanol or tert-butanol.

23. The process of claim 16, wherein the reaction mixture is heated to a temperature in the range of 100 to 140 C.

24. The process of claim 16, wherein the reaction mixture further comprises one or more inhibitors selected from the group consisting of: hydroquinone monomethyl ether and 2,4-dimethyl-6-tert-butylphenol.

25. The process of claim 16, wherein the molar ratio of (a) alkyl (meth)acrylate to (b) dimethylaminoalkanol in the reaction mixture is 3.5:1 to 1.1:1.

26. The process of claim 16, wherein the fraction of lithium alkoxide in the reaction mixture is 0.4 to 5 mol %, based on the dimethylaminoalkanol.

27. The process of claim 18, wherein the alkyl (meth)acrylate is selected from the group consisting of: methyl (meth)acrylate, ethyl(meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, and octyl (meth)acrylate.

28. The process of claim 27, wherein the lithium alkoxide is selected from the group consisting of: lithium methoxide, lithium ethoxide, lithium n-propoxide, lithium iso-propoxide, lithium n-butoxide, lithium iso-butoxide and lithium tert-butoxide, and the alcohol, independently thereof, is selected from the group consisting of: methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol and tert-butanol.

29. The process of claim 28, wherein the dimethylaminoalkanol is 2-dimethylamino-1-ethanol and the alkyl (meth)acrylate is methyl methacrylate.

30. The process according of claim 29, wherein the catalyst system consists of a solution of lithium methoxide in methanol or of a solution of lithium tert-butoxide in methanol or tert-butanol.

31. The process of claim 28, wherein the reaction mixture further comprises one or more inhibitors selected from the group consisting of: hydroquinone monomethyl ether and 2,4-dimethyl-6-tert-butylphenol.

32. The process of claim 31, wherein the dimethylaminoalkanol is 2-dimethylamino-1-ethanol and the alkyl (meth)acrylate is methyl methacrylate.

33. The process of claim 29, wherein during the reaction, additional amounts of (a) the alkyl (meth)acrylate, (b) the dimethylaminoalkanol and, optionally, (c) the catalyst system are added to the reaction mixture and the dimethylaminoalkyl (meth)acrylate which forms is removed partly or completely from the reaction mixture.

34. The process of claim 29, wherein the molar ratio of (a) alkyl (meth)acrylate to (b) dimethylaminoalkanol in the reaction mixture is 3.5:1 to 1.1:1.

35. The process of claim 29, wherein the fraction of lithium alkoxide in the reaction mixture is 0.4 to 5 mol %, based on the dimethylaminoalkanol.

Description

[0034] FIG. 1 shows sump temperatures in the preparation of dimethylaminoethyl methacrylate for a batchwise reaction regime using various catalysts.

[0035] FIG. 2 shows conversion and selectivity in the preparation of dimethylaminoethyl methacrylate for a continuous reaction regime using various catalysts and varying the quantity of catalyst.

[0036] The examples which follow serve to elucidate the present invention.

EXAMPLES

[0037] 1. Batchwise Reaction

[0038] Reaction Apparatus:

[0039] Use was made of a laboratory jack, heating stirrer with external regulation, oil bath (150 C.), 0.5-litre and 2-litre four-neck round-bottomed flasks, sump thermometer, air inlet with bubble counter, sabre stirrer, mirrored, vacuum-insulated column with length of 45 cm, packed with 88 mm Raschig rings, reflux divider, overhead thermometer, intensive condenser, product condenser, Anschutz-Thiele receiver, distillate receiver.

[0040] Distillation Apparatus (Work-Up):

[0041] Use was made of 1-litre three-neck round-bottomed flasks, boiling capillaries, sump thermometer, column with a length of 20 cm, packed with 88 mm Raschig rings, distillation bridge, Anschtz-Thiele receiver, distillate receiver, oil bath (130 C.), 0 mbar reduced pressure.

[0042] Procedure:

[0043] In all the experiments, the reactants, stabilizers and catalysts were included in the initial charge, which was subsequently heated using an oil bath (150 C.).

[0044] Comparative Examples 1 and 2 could not be completed, owing to an unexpected exothermic reaction.

[0045] Inventive Example 3 and Comparative Example 4 were regularly sampled and the theoretical conversion was determined. After the reaction, the excess methyl methacrylate was drawn off and the crude ester remaining in the sump was introduced into a distillation apparatus. The pure 2-dimethylaminoethyl methacrylate was distilled off from the top.

Comparative Example 1 (Potassium Methoxide)

[0046] Initial Mass:

[0047] 89.61 g=1 mol of dimethylaminoethanol 99.48% purity

[0048] 300.36 g=3 mol of methyl methacrylate (molar ratio 1:3)

[0049] 0.1541 g=980 ppm, based on theoretical yield, of hydroquinone monomethyl ether

[0050] 0.2358 g=1500 ppm, based on theoretical yield, of 2,4-dimethyl-6-tert-butylphenol

[0051] 5.7 g of potassium methoxide, 32% in MeOH=2.6 mol % based on alcohol

Comparative Example 2 (Sodium Methoxide)

[0052] Initial Mass:

[0053] 89.61 g=1 mol of dimethylaminoethanol 99.48% purity

[0054] 300.36 g=3 mol of methyl methacrylate (molar ratio 1:3)

[0055] 0.1541 g=980 ppm, based on theoretical yield, of hydroquinone monomethyl ether

[0056] 0.2358 g=1500 ppm, based on theoretical yield, of 2,4-dimethyl-6-tert-butylphenol

[0057] 4.7 g of sodium methoxide, 30% in MeOH=2.6 mol % based on alcohol

Inventive Example 3 (Lithium Methoxide)

[0058] Initial Mass:

[0059] 358.42 g=4 mol of dimethylaminoethanol, 99.48% purity

[0060] 1201.4 g=12 mol of methyl methacrylate (molar ratio 1:3)

[0061] 0.6163 g=980 ppm, based on theoretical yield, of hydroquinone monomethyl ether

[0062] 0.9433 g=1500 ppm, based on theoretical yield, of 2,4-dimethyl-6-tert-butylphenol

[0063] 39.49 g of lithium methoxide, 10% in MeOH=2.6 mol % based on alcohol

[0064] Theoretical yield of 2-(dimethylaminoethyl) methacrylate: 628.8 g

[0065] Theoretical yield of 2-dimethylaminoethyl methacrylate: 550.5 g, corresponding to 87.5% of theory

Comparative Example 4 (Lithium Amide)

[0066] Initial Mass:

[0067] 358.42 g=4 mol of dimethylaminoethanol, 99.48% purity

[0068] 1201.4 g=12 mol of methyl methacrylate (molar ratio 1:3)

[0069] 0.6163 g=980 ppm, based on theoretical yield, of hydroquinone monomethyl ether

[0070] 0.9433 g=1500 ppm, based on theoretical yield, of 2,4-dimethyl-6-tert-butylphenol

[0071] 2.41 g of lithium amide=2.6 mol % based on alcohol

[0072] Isolated yield of 2-dimethylaminoethyl methacrylate: 628.8 g

[0073] Theoretical yield of 2-dimethylaminoethyl methacrylate: 554.6 g, corresponding to 88.2% of theory

[0074] Evaluation:

[0075] In Comparative Examples 1 and 2, an exothermic reaction (see FIG. 1) favoured the formation of oligomers.

[0076] In Inventive Example 3 and Comparative Example 4, the transesterification was virtually identical in its course. The main difference here lies in the advantageous use of a liquid catalyst (Inventive Example 3) relative to a solid catalyst (Comparative Example 4).

[0077] 2. Continuous Reaction

[0078] Experimental Setup:

[0079] Use was made of four 100-litre stainless-steel stirring tanks with external half-shells for heating and cooling, connected as a tank cascade, 0.75 m.sup.2 thin-film evaporator, manufactured by SMS (Buss-SMS-Canzler GmbH, Germany), stainless steel column nominal width 2006 m with stainless steel Pall rings 2020 mm, 3 m.sup.3 stainless steel circulation evaporator two 3 m.sup.3 stainless steel condensers, 1 m.sup.2 stainless steel final condenser, three 1.7 m.sup.3 feed vessels for dimethylaminoalkanol, alkyl (meth)acrylate and N,N-dimethylaminoalkyl (meth)acrylate/alkyl (meth)acrylate mixture from the initial fraction of the purifying distillation, 1 Lewa H2 metering pump for dimethylaminoalkanol and alkyl (meth)acrylate, 1 Lewa HL2 metering pump for the initial alkyl (meth)acrylate/dimethylaminoalkanol fraction, powder metering device or pump for solid or liquid catalyst, stabilizing metering via Lewa HK 2 metering pump, temperature and level control circuit, two 1.2 m.sup.3 stainless steel settling vessels, 6 m.sup.3 stainless steel crude ester mixing tank, various vapour pressure reducers, temperatures displays.

[0080] Procedure:

[0081] The reaction of alkyl (meth)acrylate with dimethylaminoalkanol takes place in three cascade-connected stirred tanks at a sump temperature of 110 C., 120 C. and 130 C., respectively. The reaction product from the third stage is passed via a thin-film evaporator. The vapours pass, together with the vapours of stages 1 to 3, via a common line into the bottom third of the column. The dimethylaminoalkanol starting material and the initial fraction are likewise introduced into this column and dewatered by the vapours, which flow in the opposite direction. By rectification, a top product with around 70% of alcohol, around 29.5% of alkyl (meth)acrylate and around 0.5% of water is brought about. This distillate is free from dimethylaminoalkanol and dimethylaminoalkyl (meth)acrylate. From the column sump dewatered dimethylaminoalkanol and circulation alkyl (meth)acrylate flow into the first reaction stage. A pump conveys the catalyst solution into the first stage. Pure alkyl (meth)acrylate is metered in a further portion via a level regulation system, in accordance with the demand for conversion and alkyl (meth)acrylate content in the crude ester in the column sump. Stabilization is accomplished by dissolving hydroquinone monomethyl ether and/or 2,4-dimethyl-6-tert-butylphenol and/or 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl (TEMPOL) in alkyl (meth)acrylate and applying this stabilizer solution to the tops of the columns. By this means, the stabilizers are distributed via recycle streams into all process stages and process areas. All stages are sparged with air and operate under atmospheric pressure. The stripped crude ester is cooled to about 40 C., run through settling vessels into a mixing tank, restabilized, and pumped to the storage facility. One settling vessel in each case is in operation, and after around 10 days any solid that has deposited (e.g. lithium methacrylate) is separated off via a centrifuge. The plant permits the throughput of 50 L/h of dimethylaminoalkanol, corresponding to 0.5 kmol/h of dimethylaminoalkyl (meth)acrylate.

[0082] For start-up, all of the stages are filled with crude ester and, after heating to reaction temperature, the feeds of dimethylaminoalkanol, alkyl (meth)acrylate, initial fraction and catalyst are applied. Via the circulation evaporator, the column is heated so as to produce around 150 L/h of top product. The distillate is withdrawn only in a quantity such that the composition, with 70% alcohol and 30% alkyl (meth)acrylate remains constant. Monitoring is done by measuring the refractive index (n.sub.D 20) or the density, or by using an in situ NIR probe. At the 70/30 ratio, it is possible, relative to the 85/15 azeotrope, to remove water at a concentration of around 0.5% overhead and to ensure the required absence of water from the process stages. From the column sump, around 500 L/h of a mixture of 80% alkyl (meth)acrylate, 16% dimethylaminoalkanol and 4% dimethylaminoalkyl (meth)acrylate are run into the 1st stage. The alkyl (meth)acrylate fraction here serves as a circulation product in particular for the dewatering. The prime reason for the different volume flow rates in the column sump and at the top of the column is the difference in calorific data between alkyl (meth)acrylate and alcohol. Because the plant offers no outletother than via the crude esterfor dimethylaminoalkanol, GC analysis of the products in the column sump allows, following conversion into mol %, a good overview of conversion and selectivity. This is true both of the crude ester and of the individual reaction stages. The experiments each run over several days, with variations, respectively, in the catalyst and in the catalyst concentration. One of the factors determining the lower limit for the catalyst concentration is the performance range of the metering apparatus. Following emptying and inspection of the reaction chamber, the catalyst is changed.

[0083] Evaluation:

[0084] The results are collated in Tables 1 and 2.

[0085] LiNH.sub.2, LiOMe (solid) and LiOMe (as a 10 wt % solution in methanol) show results that are similar, and are comparable with LiOH, in terms of the conversion of aminoethanol.

[0086] In contrast to LiOH, where crystallizing lithium methacrylate diminishes the transfer of heat owing to formation of deposits, in stages 1 and particularly 2 and 3, and causes a drop in temperature and necessitates weekly cleaning and disconnection, no such deposits are observed in the reaction tanks, within the period of comparison, upon use of LiOMe or LiNH.sub.2. Nevertheless, the ester contains lithium methacrylate in dissolved and precipitated form. The undissolved fraction amounts to approximately 0.1% (relative to 1% in the case of LiOH) and can easily be filtered.

[0087] In terms of selectivity for dimethylaminoethyl methacrylate, distinct advantages are apparent relative to LiOH. As a result of formation of high boilers, LiOH exhibits a selectivity of 94% across all the reaction stages. While LiOMe and LiNH.sub.2 do also form the known high boilers in the very first stage (as a result of addition of methanol with dimethylaminoethyl methacrylate and/or of addition of the dimethylaminoethyl group onto dimethylaminoethyl methacrylate) in the same quantity, these compounds are nevertheless cleaved again in the subsequent stages, and so increase the selectivity for dimethylaminoethyl methacrylate to around 97%.

[0088] Below a catalyst concentration of 1 mol %, a drop in conversion of down to 95% is observed. In this concentration range, it becomes difficult to carry out uniform metering of the catalyst in solid form, this being so in particular for the poorly free-flowing LiOMe, and being the cause of the relatively wide scattering of the individual measurement values.

[0089] The aforesaid problems are eliminated by using a solution of 10% LiOMe in methanol. The additional methanol in the catalyst solution can be removed as an azeotrope from the first stage, without adversely affecting the overall reaction.

TABLE-US-00001 TABLE 1 Catalyst LiNH.sub.2 (mol %) 0.7% 0.8% 0.8% 0.8% 1.3% 1.3% 2.4% 2.5% Conversion 94.9 95.9 95.6 95.7 96.3 96.5 96.9 96.9 Selectivity 95.2 94.9 95.2 94.9 96.9 96.2 97.6 97.5 Catalyst LiNH.sub.2 (mol %) 2.6% 4.5% 4.8% 4.9% 5.0% 8.6% 8.6% Conversion 96.7 97 97.4 96.7 97 98.2 98.3 Selectivity 97.4 97.30 97.5 97.5 97.6 97.6 97.5 Catalyst LiOMe (solid) (mol %) 0.4% 0.8% 0.8% 0.8% 1.3% 1.4% 1.5% 1.5% 2.0% 2.1% 4.6% 4.6% Conversion 91.2 96.3 96.9 97.5 98 97.9 95.9 97.4 97 97.2 96.1 96.4 Selectivity 95.6 96.1 96 96 95.7 96.1 97.1 97.5 97.2 96.7 96 96.6 Catalyst LiOMe (solution) (mol %) 0.8% 0.8% 1.3% 1.4% 2.3% 2.3% 4.7% 4.7% Conversion 96.1 96.3 98.1 97.8 97.1 97.4 95.9 96.1 Selectivity 95.7 95.2 95.6 96 97.1 96.6 95.9 95.4 Catalyst LiOH/CaO 1:3.5 1:2.3 (mol %) 2.3% 2.3% 3.5% 3.4% Conversion 93.4 93.6 93.6 94.5 Selectivity 93.8 94.0 94.0 94.0 Catalyst LiOH (mol %) 2.1% 3.9% Conversion 96.2 97.4 Selectivity 94.2 94.0

TABLE-US-00002 TABLE 2 Catalyst LiNH.sub.2 (mol %) 0.8% 1.3% 2.5% 4.9% 8.6% (averaged) Conversion 95.5 96.4 96.8 97.0 98.3 (averaged) Selectivity 95.1 96.6 97.5 97.5 97.6 Catalyst LiOMe (solid) (mol %) 0.4% 0.8% 1.4% 2.0% 4.6% (averaged) Conversion 91.2 96.9 97.3 97.1 96.3 (averaged) Selectivity 95.6 96.0 96.6 97.0 96.3 Catalyst LiOMe (solution) (mol %) 0.8% 1.3% 2.3% 4.7% (averaged) Conversion 96.2 98.0 97.3 96.0 (averaged) Selectivity 95.5 95.8 96.9 95.7