Patent Application
20150225861
The present application is a utility application based on, and claiming benefit to, German Application No. 102014202502.8, filed on Feb. 12, 2014.
Not Applicable.
Not Applicable.
Not Applicable.
1. Field of the Invention
The invention relates the electrochemical production of 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid by electrochemical oxidative ring cleavage of a mixture of cis- and trans-3,3,5-trimethylcyclohexanol.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
According to the current state of the art, the production of 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid (TMAS) from a mixture of cis- and trans-3,3,5-trimethylcyclohexanol (TMCol) is effected by oxidative ring cleavage using nitric acid.
Disadvantages of this process due to the use of nitric acid are, inter alia, corrosion, safety issues, and the formation of nitrous components.
It is mentioned in Hans-Jürgen Schäfer, Oxidation of organic compounds at the nickel hydroxide electrode, Topics in Current Chemistry, Vol. 142, pp. 101-129, 1987, Johannes Kaulen, Hans-Jürgen Schäfer, Oxidation of alcohols by electrochemically regenerated nickel oxide hydroxide. Selective oxidation of hydroxysteroids, Tetrahedron Vol. 38 No. 22 pp. 3299-3308, 1982, and Johannes Kaulen: Oxidation of diols and secondary alcohols at the nickel hydroxide electrode. Use for selective oxidation of hydroxysteroids [in German], dissertation at the University of Münster 1981, that the electrochemical oxidation of cyclohexanol at relatively high temperatures proceeds, to some extent, with adipic acid being formed by ring cleavage. The reaction is effected using nickel hydroxide electrodes. Yields of adipic acid of 16% and 24% at 25° C. and of 42% at 80° C. were obtained.
B. V. Lyalin, V. A. Petrosyan, Electrosynthesis of adipic acid by undivided cell electrolysis, Russian Chemical Bulletin, International Edition, Vol. 53 No. 3 pp. 688-692, March, 2004, likewise addresses electrochemical oxidative ring cleavage of cyclohexanol to give adipic acid at nickel hydroxide electrodes. This paper reports a maximum yield of adipic acid of 46.7% at a simultaneous current yield of 11.5%. By-products in the reaction are succinic acid and glutaric acid formed in a yield of 6.3% and 11.5%, respectively. These components are formed by oxidative elimination of CH2 groups from the C6 core structure of cyclohexanol.
Adipic acid is formed as the disodium salt in the above publications. The salt can be converted into the H acid form by simple acidification with hydrochloric acid, for example.
The solubility of cyclohexanol in water is 40 g/l at 20° C. The solubility of the trimethylated cyclohexanol, TMCol, in water is only 1.8 g/l at 20° C.
It was found that, surprisingly, TMCol may be converted into 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid (TMAS) by electrochemical oxidative ring cleavage under alkaline conditions despite the low solubility in water. The conversion proceeds via the intermediate 3,3,5-trimethylcyclohexanone (TMCon).
Advantages of this process compared to the process mentioned above due to the use of nitric acid being avoided are: avoidance of corrosivity, no formation of nitrous gases.
These and other objects are achieved by the present invention, which electrochemically produces 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid by electrochemical oxidative ring cleavage of a mixture of cis- and trans-3,3,5-trimethylcyclohexanol in an aqueous alkaline solution.
a: A cross-section of a Swiss-roll continuous flow electrolytic cell.
b: Section through sandwich construction of a Swiss-roll continuous flow electrolytic cell.
c: Rolled-up sandwich construction of a Swiss-roll continuous flow electrolytic cell.
a: An empty electrolytic cell.
b: An electrolytic cell filled with nickel pellets.
In this specification, the words “a” and “an” and the like carry the meaning of “one or more.” The phrases “selected from the group consisting of,” “chosen from,” and the like include mixtures of the specified materials. Terms such as “contain(s)” and the like are open terms meaning ‘including at least’ unless otherwise specifically noted. Where a numerical limit or range is stated, the endpoints are included. Also, all values and subranges within a numerical limit or range are specifically included as if explicitly written out.
The invention provides a process for the electrochemical production of 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid by electrochemical oxidative ring cleavage of a mixture of cis- and trans-3,3,5-trimethylcyclohexanol in aqueous alkaline solution.
The electrochemical conversion of TMCol into TMAS is effected in an electrolytic cell. The process is in principle not limited to a particular type of electrolytic cell.
The reaction is performed in aqueous alkaline solution. Useful alkalis include in principle all known inorganic bases. Alkali metal hydroxides, such as LiOH, NaOH, KOH, and soluble alkaline earth metal hydroxides are preferred. In accordance with the invention, it is particularly preferable to use aqueous sodium hydroxide solution or aqueous potassium hydroxide solution.
Materials useful in principle as anode material include transition metals. It is preferable to use nickel.
Materials useful in principle as cathode material include transition metals. It is preferable to use stainless steel.
Preference for use as the anode is given to electrode types having a large specific surface area. Gauzes, pellet beds, and foams are particularly preferred.
The electrolysis may be effected batchwise or continuously.
The electrolysis may be carried out in a batch electrolytic cell and also in a continuous flow electrolytic cell. It is preferable to carry out the electrolysis in a continuous flow electrolytic cell.
The electrolysis is preferably run at an elevated temperature. A temperature of from 60° C. to 100° C. is preferred. A temperature of from 70° C. to 90° C. is particularly preferred.
Preferred variants of the process are described hereinbelow.
The electrochemical conversion of TMCol into TMAS may be effected in the electrolysis batch apparatus shown in
The electrochemical conversion of TMCol into TMAS may alternatively be effected in the electrolysis apparatus shown in
The electrolytic cell is a continuous flow electrolytic cell with a stainless steel cathode and a nickel anode.
Various pump types may be used as pumps for the electrolysis apparatus shown in
The continuous flow electrolytic cell employed may specifically be a Swiss-roll cell (see “Peter. M. Robertson, F. Schwager, A new cell for electrochemical processes, Journal of Electroanalytical Chemistry Vol. 65 pp. 883-900, 1975”, “Peter Seiler, Peter M. Robertson, The anodic oxidation of diacetone-L-sorbose on an industrial scale [in German], Chimia Vol. 36 No. 7/8 pp. 305-312, 1982”). The Swiss-roll cell is shown in
It was found that it is likewise possible to use an electrolytic cell made of a stainless steel housing, a central nickel rod and nickel pellets introduced into the cell. The cell type is shown in
The nickel pellets are electrically insulated from the stainless steel housing by a polypropylene fabric disposed on the inside of the stainless steel housing.
It was further found that the cell type shown in
Prior to TMAS electrosynthesis, the nickel anode surface may be conditioned in order to electrochemically deposit a thin multilayered nickel oxide hydroxide top layer onto the nickel anode surface.
This may, for example, be carried out as follows:
280 ml of a conditioning solution comprising 0.1 mol/l of NiSO4×6H2O, 0.1 mol/l of NaOAc×3H2O, and 0.005 mol/l of NaOH in distilled water was introduced into the electrolysis. In the case of the electrolysis apparatus of
To carry out electrosynthesis of TMAS, the electrolytic cell was filled with water and also sodium hydroxide and TMCol dissolved therein. The recirculated solution was then brought to the desired temperature. The electrolysis was carried out by passing electrical current through the cell galvanostatically for several hours.
Upon completion of the electrolysis, the solution was completely discharged from the electrolysis apparatus and the electrolysis apparatus was then rinsed out with DM water. The electrolysis apparatus was left dry between experiments. The combined solution from the electrolysis apparatus was worked up in order to isolate TMCol, TMCon, TMAS, and any by-products upon completion of the electrolysis.
The electrolysis was carried out as described above in the electrolysis batch apparatus shown in
260 ml of water, 11.2 g of sodium hydroxide, and 5.73 g of TMCol were charged to the electrolytic cell.
The electrolysis was carried out by passing 2 A through the cell for 6 hours. The temperature was 80° C.
2.45 g of TMCol, 2.34 g of TMCon, and 1.06 g of TMAS were isolated following work-up. The yield of TMAS based on the TMCol employed was 14%.
The electrolysis was carried out as described above in the electrolysis apparatus shown in
260 ml of water, 11.2 g of sodium hydroxide, and 5.93 g of TMCol were charged to the electrolysis apparatus. A peripheral pump was used.
The electrolysis was carried out by passing 2 A through the cell for 24 hours. The temperature was 80° C.
0.05 g of TMCol, 0.03 g of TMCon, and 2.70 g of TMAS were isolated following work-up. The yield of TMAS based on the TMCol employed was 34%.
The electrolysis was carried out as described above in the electrolysis apparatus shown in
264 ml of water, 11.2 g of sodium hydroxide, and 5.93 g of TMCol were charged to the electrolytic cell. A peripheral pump was used.
The electrolysis was carried out by passing 2 A through the cell for 24 hours. The temperature was 80° C.
0.06 g of TMCol, 0.04 g of TMCon, and 2.52 g of TMAS were isolated following work-up. The yield of TMAS based on the TMCol employed was 32%.
The electrolysis was carried out as described above in the electrolysis apparatus shown in
264 ml of water, 11.2 g of sodium hydroxide, and 5.93 g of TMCol were charged to the electrolytic cell. A peripheral pump was used.
The electrolysis was carried out by passing 2 A through the cell for 17 hours. The temperature was 80° C.
0.09 g of TMCol, 0.14 g of TMCon, and 2.06 g of TMAS were isolated following work-up. The yield of TMAS based on the TMCol employed was 26%.
The purpose of the work-up of the electrolysis solution described hereinbelow was to isolate TMCol, TMCon, TMAS, and any by-products upon completion of the electrolysis and to subsequently determine conversion, yield, and selectivity.
50 g of sodium chloride were added to the aqueous solution poured out of the electrolysis apparatus.
The alkali aqueous phase was extracted with methyl tert-butyl ether (analytical grade) to remove remaining TMCol and TMCon by repeated (at least 4-fold) extraction in a separating funnel.
The ether phase was dried with anhydrous magnesium sulphate. To this end, magnesium sulphate was added to the ether phase until newly added magnesium sulphate remained in the liquid in the form of fine grains in that clumping no longer occurred. The magnesium sulphate was subsequently filtered off.
The ether was removed by rotary evaporation. The rotary evaporator was initially operated at atmospheric pressure. The boiling point of the solution increased significantly towards the end of the distillative removal. Accordingly, a slight vacuum was applied and the underpressure was increased as the concentration of MTBE in the solution was reduced in order always to achieve a sufficient distillation rate (up to 300 mbar at 90° C.). The distillation at 300 mbar and 90° C. was continued until the head temperature in the rotary evaporator fell to and remained constant at room temperature.
Unreacted TMCol and TMCon were left behind in a residual amount of MTBE. These compounds were analysed by gas chromatography to determine purity and quantity.
TMAS was isolated by perforation. A relatively large liquid volume was required for the perforator. The mixture was diluted with water accordingly.
The alkaline aqueous phase was subsequently acidified with concentrated hydrochloric acid to a pH of 1.
The acidified aqueous phase was perforated with MTBE (analytical grade) for 48 h.
The ether phase was subsequently dried with anhydrous magnesium sulphate. To this end, magnesium sulphate was added to the ether phase until newly added magnesium sulphate remained in the liquid in the form of fine grains in that clumping no longer occurred. The magnesium sulphate was subsequently filtered off.
The MTBE was removed by rotary evaporation. The rotary evaporator was initially operated at atmospheric pressure. The boiling point of the solution increased significantly towards the end of the distillative removal. Accordingly, a slight vacuum was applied and the underpressure was increased as the concentration of MTBE in the solution was reduced in order always to achieve a sufficient distillation rate (up to 300 mbar at 90° C. but not sufficient for quantitative removal of MTBE). The distillation at 300 mbar and 90° C. was continued until the head temperature in the rotary evaporator fell to and remained constant at room temperature.
TMAS and by-products were left behind in a residual amount of MTBE after the distillative removal and were quantitatively determined by gas chromatography following etherification with diazomethane.
The above description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, this invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. In this regard, certain embodiments within the invention may not show every benefit of the invention, considered broadly.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102014202502.8 | Feb 2014 | DE | national |
