PROCESS FOR THE ELECTROCHEMICAL PRODUCTION OF 2,2,4-TRIMETHYLADIPIC ACID AND 2,4,4-TRIMETHYLADIPIC ACID

Abstract

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a utility application based on, and claiming benefit to, German Application No. 102014202502.8, filed on Feb. 12, 2014.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF THE MATERIAL ON THE COMPACT DISC

Not Applicable.

BACKGROUND OF THE INVENTION

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.

BRIEF SUMMARY OF THE INVENTION

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.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1: Electrolysis batch apparatus for conversion of TMCol into TMAS.

FIG. 2: Electrolysis batch apparatus for conversion of TMCol into TMAS.

FIG. 3a: A cross-section of a Swiss-roll continuous flow electrolytic cell.

FIG. 3b: Section through sandwich construction of a Swiss-roll continuous flow electrolytic cell.

FIG. 3c: Rolled-up sandwich construction of a Swiss-roll continuous flow electrolytic cell.

FIG. 4a: An empty electrolytic cell.

FIG. 4b: An electrolytic cell filled with nickel pellets.

DETAILED DESCRIPTION OF THE INVENTION

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.

Variant 1

The electrochemical conversion of TMCol into TMAS may be effected in the electrolysis batch apparatus shown in FIG. 1. The cathode is a stainless steel plunger and the anode is a cylindrical nickel gauze. The solution introduced into the apparatus is stirred by a magnetic stirrer bar and heated using a thermostat. A pump facilitates additional external circulation of the solution in order to further enhance commixing.

Variant 2

The electrochemical conversion of TMCol into TMAS may alternatively be effected in the electrolysis apparatus shown in FIG. 2. Said apparatus comprises an electrolytic cell, a temperature-controllable receiver, a pump, and a cooler.

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 FIG. 2. Pumps which in addition to the conveying effect achieve dispersion of the organic substrate in the alkaline aqueous solution are particularly suitable, for example peripheral pumps.

Variant 3

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 FIG. 3. This electrolytic cell type comprises a nickel gauze and a stainless steel gauze, one above the other, separated by a polypropylene fabric and wound around a central nickel rod. Here, the nickel rod contacts only the nickel gauze. The cell housing consists of stainless steel which contacts only the stainless steel gauze.

Variant 4a

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 FIG. 4. Here, the nickel pellets are in electrical contact with the central nickel rod.

The nickel pellets are electrically insulated from the stainless steel housing by a polypropylene fabric disposed on the inside of the stainless steel housing.

Variant 4b

It was further found that the cell type shown in FIG. 4 may be furnished with a flat-ply nickel foam and a stainless steel gauze instead of with nickel pellets. Said foam and gauze are wound around the central nickel rod, one above the other, with a polypropylene fabric separating them. Here, the nickel rod contacts only the nickel foam. The cell housing consists of stainless steel which contacts only the stainless steel gauze.

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 FIG. 2, the conditioning solution was additionally recirculated. The nickel gauze was alternately polarised as the anode or the cathode for a short time (10 s) by automatic electrode polarisation switching until a black surface layer was formed (current 150 mA, charge 100 C). The conditioning solution was subsequently discharged from the entire apparatus. The entire apparatus was then thoroughly rinsed with distilled water. The freshly activated electrolytic cell was then immediately used for electrolysis.

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.

EXAMPLES

Example 1

The electrolysis was carried out as described above in the electrolysis batch apparatus shown in FIG. 1 using a wound 100 mesh nickel gauze of 0.1 mm nickel wire having an area of 10 cm*25 cm and an interiorly disposed round stainless steel plunger of 7 cm in diameter.

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%.

Example 2

The electrolysis was carried out as described above in the electrolysis apparatus shown in FIG. 2 using a Swiss-roll electrolytic cell shown in FIG. 3 comprising a wound 100 mesh nickel gauze of 0.1 mm nickel wire having an area of 6.5 cm*24.5 cm, a polypropylene fabric, and a wound 100 mesh stainless steel gauze of 0.114 mm stainless steel wire having an area of 6.5 cm*26.5 cm.

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%.

Example 3

The electrolysis was carried out as described above in the electrolysis apparatus shown in FIG. 2 using an electrolytic cell shown in FIGS. 4a and 4b comprising nickel pellets (bed volume 60 cm³).

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%.

Example 4

The electrolysis was carried out as described above in the electrolysis apparatus shown in FIG. 2 using an electrolytic cell shown in FIG. 3a comprising a wound flat-ply nickel foam having an area of 6.5 cm*19 cm, a polypropylene fabric, and a wound 100 mesh stainless steel gauze of 0.114 mm stainless steel wire.

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%.

Example Work-Up

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.

Claims

1. A process, comprising:

electrochemically producing 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid by electrochemical oxidative ring cleavage of a mixture comprising cis- and trans-3,3,5-trimethylcyclohexanol in an aqueous alkaline solution.

2. The process of claim 1, wherein the aqueous alkaline solution is an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.

3. The process of claim 1, wherein the electrochemical oxidative ring cleavage is performed by electrolysis in an electrolytic cell comprising a cathode and an anode, wherein the electrolytic cell is a batch electrolytic cell or a continuous flow electrolytic cell.

4. The process of claim 3, wherein the electrolysis is carried out in a continuous flow electrolytic cell.

5. The process of claim 3, wherein the anode is a nickel anode.

6. The process of claim 3, wherein the cathode is a stainless steel anode.

7. The process of claim 3, wherein the anode is in the form of a gauze, a pellet bed, or a foam.

8. The process of claim 3, wherein anode is a nickel gauze, a nickel pellet bed, or a nickel foam.

9. The process of claim 5, further comprising:

electrochemically depositing a thin multilayered nickel oxide hydroxide top layer onto a surface of the nickel anode.

10. The process of claim 3, wherein the electrolysis is run at elevated temperature.

11. The process of claim 3, wherein the electrolysis is carried out at temperature from 60° C. to 100° C.

12. The process of claim 3, wherein the electrolysis is carried out at temperature from 70° C. to 90° C.