Method for producing 2-substituted 4-hydroxy-4-methyl-tetrahydropyrans in a reactor cascade

Abstract

The invention relates to a method for producing 2-substituted 4-hydroxy-4-methyltetrahydropyrans.

Claims

1. A process for the preparation of a 2-substituted 4-hydroxy-4-methyltetrahydropyran of the formula (I) ##STR00009## in which R.sup.1 is a straight-chain or branched C.sub.1-C.sub.12-alkyl, straight-chain or branched C.sub.2-C.sub.12-alkenyl, unsubstituted or C.sub.1-C.sub.12-alkyl and/or C.sub.1-C.sub.12-alkoxy substituted cycloalkyl having in total 3 to 20 carbon atoms or unsubstituted or C.sub.1-C.sub.12-alkyl and/or C.sub.1-C.sub.12-alkoxy substituted aryl having in total 6 to 20 carbon atoms, comprising reacting 3-methylbut-3-en-1-ol of the formula (III) ##STR00010## with an aldehyde of the formula (IV)
R.sup.1CHO(IV) where R.sup.1 in the formula (IV) has the meaning given above, in the presence of an acidic catalyst, wherein the reaction takes place in an arrangement consisting of n reactors connected in series, n being a natural number from 2 to 8; wherein a part stream is removed between the first and last reactor in the flow direction and is fed into a reactor positioned upstream of the removal point.

2. The process according to claim 1, wherein the reaction takes place continuously.

3. The process according to claim 1, wherein the reaction takes place in the presence of a solvent.

4. The process according to claim 1, wherein a part stream is removed from the reactor discharge of the first and/or second reactor in the flow direction and is returned at least partially to the first reactor in the flow direction via an external recirculation.

5. The process according to claim 4, wherein the part stream of the reactor discharge is stripped off from the first reactor and is returned to the first reactor in the flow direction via an external circuit.

6. The process according to claim 1, wherein heat is withdrawn from the part stream before it is fed into a reactor positioned upstream of the removal point.

7. The process according to claim 1, wherein at least the first reactor in the flow direction is operated isothermally.

8. The process according to claim 1, wherein the first and second reactor in the flow direction is operated in each case isothermally.

9. The process according to claim 1, wherein the (n1)th reactor in the flow direction is operated isothermally.

10. The process according to claim 1, wherein heat is withdrawn from the reactor discharge from at least one of the first to (n1)th reactors before introducing it into the following reactor in the flow direction.

11. The process according to claim 1, wherein at least the last reactor in the flow direction is operated without recirculation of the reactor discharge.

12. The process according to claim 1, wherein n is 2 or 3.

13. The process according to claim 1, wherein the reaction at least in the last reactor in the flow direction is carried out adiabatically.

14. The process according to claim 1, wherein a reactor arrangement is used for the reaction which comprises at least one fixed-bed reactor.

15. The process according to claim 1, wherein a reactor arrangement is used for the reaction which comprises at least one reactor with an internally arranged heat exchanger.

16. The process according to claim 1, wherein R.sup.1 is isobutyl or phenyl.

17. The process according to claim 1, wherein the reaction takes place in the presence of an acidic catalyst which is selected from the group consisting of hydrochloric acid, sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid and strongly acidic cation exchangers.

18. The process according to claim 13, wherein the reaction is carried out in the presence of a strongly acidic cation exchanger.

19. The process according to claim 1, wherein the alcohol of the formula (III) and the aldehyde of the formula (IV) are used in a molar ratio in the range from 0.7:1 to 2:1.

20. The process according to claim 1, wherein the alcohol of the formula (III) and the aldehyde of the formula (IV) are reacted in the presence of 3% by weight to 15% by weight of water based on the amount of the reaction mixture consisting of the components of the formulae (III) and (IV) and water.

21. The process according to claim 1, wherein the reaction is carried out at a temperature in the range from 0 C. to 70 C.

22. The process according to claim 1, wherein the reaction is carried out at a pressure in the range from 1 bar to 15 bar.

Description

DESCRIPTION OF THE FIGURES

(1) The process according to the invention is explained in more detail by reference to FIGS. 1 to 3 below without limiting it to these embodiments.

(2) FIG. 1 shows an embodiment of the process according to the invention with a main reactor with recirculation stream and a secondary reactor.

(3) FIG. 2 shows an embodiment of the process according to the invention with a main reactor with integrated heat exchanger and a secondary reactor.

(4) FIG. 3 shows an embodiment of the process according to the invention with two reactor stages with recirculation stream and a secondary reactor.

(5) In FIGS. 1 to 3 the following reference numerals are used: 1 (Main) reactor 2 Cooling unit 3 (Secondary) reactor 4 (Intermediate) cooling unit 5 Pump 6 Reactor 7 Cooling unit 8 Separating column A Isoprenol stream B Aldehyde stream C Water D Recirculation stream E Starting material

(6) The process according to the invention can be carried out with at least one main reactor, preferably 1 to 2 main reactors, in cascade form. The main reactors can be operated in parallel or in series, preferably in series, and optionally with interim cooling. Here, the procedure can take place, for example, in the back-mixed reactor system or in isothermal mode. In the back-mixed reactor system, an of the circulation stream of the main reactor part can be back-mixed and cooled or each main reactor separately can be back-mixed and cooled by its own circulation stream and/or intermediate cooling can take place after each main reactor. The division into two or more beds, optionally also with interim cooling, can also be implemented in one apparatus.

(7) After emerging from the main reactor part of the reaction, at least one secondary reactor follows, preferably 1 to 2 secondary reactors. These can be operated in a straight pass (isothermally or back-mixed), in parallel or in series. Preferably, they are connected in series and operated in a straight pass without back-mixing.

(8) FIG. 1 shows a suitable embodiment of a suitable two-stage reactor cascade with a main reactor (1) and a secondary reactor (3).

(9) The three starting material streams isoprenol (A), aldehyde (B) and water (C) are introduced into the reactor (1) via three feeds. A discharge from the reactor (1) is removed via a line and the pump (5) and is divided into two part streams. A recirculation stream (D) is fed to the main reactor (1) via the cooling unit (2) together with the starting material streams (A), (B) and (C). A feed stream is passed via a cooling unit (4) to the second reactor (3). The starting material (E) is removed directly from the secondary reactor (3) as discharge and optionally fed to a work-up stage.

(10) In this embodiment, both reactors are preferably configured as fixed-bed reactors. The main reactor (1) is operated in loop mode, whereas the secondary reactor is operated in a straight pass. In the arrangement shown in FIG. 1, the main reactor (1) and the secondary reactor (3) are connected in series such that the temperature profile above the catalyst bed can be adjusted via a back-mixing in the main reactor system. As a result, a large temperature increase at the start of the reaction can be prevented.

(11) FIG. 2 shows an alternative embodiment of a suitable two-stage reactor cascade with a main reactor (1) and a secondary reactor (3). Instead of the recirculation, an isothermal reaction procedure is achieved via a heat exchanger integrated into the reactor (1).

(12) The three starting material streams isoprenol (A), aldehyde (B) and water (C) are introduced into the reactor (1). A discharge from the reactor (1) is removed and is supplied as feed stream to the second reactor (3) via a cooling unit (4). The starting material (E) is removed directly as discharge from the secondary reactor (3) and optionally fed to a work-up stage. The main reactor is equipped with integrated heat exchange surfaces, whereas the secondary reactor (3) is designed as a simple fixed-bed reactor. Both reactors are operated in this embodiment in a straight pass. The isothermal reaction procedure shown in FIG. 2 avoids undesired temperature peaks.

(13) FIG. 3 shows one suitable embodiment of a three-stage reactor cascade with two main reactors (1), (6) and a secondary reactor (3).

(14) The three starting material streams isoprenol (A), aldehyde (B) and water (C) are introduced into the reactor (1) via three feeds. A discharge from the reactor (1) is removed and is fed as feed stream to the second reactor (6) via a cooling unit (7). A discharge is removed from the reactor (6) via a line and the pump (5) and is divided into two part streams. A recirculation stream (D) is returned to the main reactor (1) together with the starting material streams (A), (B) and (C) via the cooling unit (2). A feed stream is fed to the third reactor (3) via a cooling unit (4). The starting material (E) is removed directly as discharge from the secondary reactor (3) and optionally fed to a work-up stage.

(15) In this embodiment, all three reactors are preferably configured as fixed-bed reactors. The main reactors (1) and (6) are operated together in loop mode, whereas the secondary reactor (3) is operated in a straight pass. In the arrangement shown in FIG. 3, the main reactors (1), (6) and the secondary reactor (3) are connected in series such that the temperature profile above the catalyst bed can be adjusted via a back-mixing in the main reactor system and an interim cooling between the first and second main reactor. As a result, temperature peaks in both reactors can be effectively prevented.

EXAMPLES

Example 1

Continuous Process

(16) An apparatus consisting of a main reactor and a secondary reactor consisting of three individual reactors was used. The main reactor used was a jacketed reactor made of RA4 without heating medium for an adiabatic procedure with a length of 150 cm and an internal diameter of 2.6 cm. The secondary reactor used was three jacketed reactors made of RA4, each with a length of 150 cm, an internal diameter of 1.0 cm and heated at respectively 30 C., 40 C. and 50 C.

(17) The apparatus was filled with a total of 328 g of the strongly acidic cation exchanger Amberlyst 131. The main reactor was in this case filled with 230 g (305 ml), the secondary reactors each with 32.5 g (44 ml), of the cation exchanger. The cation exchanger was washed prior to use firstly several times with water, then once with methanol and finally with water so as to be methanol-free. The system was conditioned by introducing a mixture of pyranol:water in a mass ratio of 95:5. The main reactor was then operated back-mixed with a recirculation stream of 2000 g/h, the recirculated stream being cooled to a temperature of 25 C. before reentering the main reactor. The secondary reactor was operated in a straight pass to complete conversion.

(18) After conditioning the cation exchanger to the stated pyranol/water mixture, a mixture of isovaleraldehyde:isoprenol:water in a mass ratio of 45:50:5 was introduced at 25 C. and in a total quantitative stream of 100 g/h. This gave a crude product with an exit temperature from the last secondary reactor of 50 C. in a yield of 76% and with a selectivity of 77.6% based in each case on isovaleraldehyde with the following composition: Isovaleraldehyde: 1.03 GC % by weight, Isoprenol: 3.6 GC % by weight, Dihydropyran isomers: 8.69 GC % by weight, 1,3-Dioxane: 5.56 GC % by weight, Acetal: 0.57 GC % by weight, trans-Pyranol: 18.26 GC % by weight, cis-Pyranol: 50.08 GC % by weight, Water: 6.8% by weight (according to Karl Fischer).