Electrochemical oxidation of 1,2-cyclohexanediol

Abstract

A method of oxidizing 1,2-cyclohexanediol includes containing a reaction solution that includes the 1,2-cyclohexanediol with an electrochemical cell to form a reaction product solution that includes an oxidation product of the 1,2-cyclohexanediol.

Description

ELECTROCHEMICAL OXIDATION OF 1,2-CYCLOHEXANEDIOLCLAIM OF PRIORITY

[0001] This patent application claims the benefit of priority to U.S. Provisional Application Serial No. 63 / 643,440, filed May 7, 2024, which is incorporated by reference herein in its entirety.BACKGROUND

[0002] Hexamethylene diamine (HMD) is an industrial chemical used in the production of nylon, adhesives, coatings, and resins. For example, HMD is used in the production of nylon 6,6, which is used in fibers for textiles, molded parts, and various other applications. HMD synthesis can involve hydrocyanation of 1,4-butadiene to form adiponitrile, which is then hydrogenated to produce HMD. Alternatively, HMD can be synthesized from the product of the oxidation of 1,2-cyclohexanediol.SUMMARY

[0003] This document describes a technique related to the field of organic chemistry and, more specifically, to the electrochemical oxidation of 1,2-cyclohexanediol. Certain approaches to oxidizing diols, such as 1,2-cyclohexanediol, often involve the use of oxidizing agents that can be costly or otherwise undesirable. These methods may also suffer from a relatively low selectivity, resulting in a mixture of products that can involve further purification steps.

[0004] The present inventors have developed an approach to oxidizing 1,2- cyclohexanediol using an electrochemical cell. The method can involve contacting a reaction solution containing 1,2-cyclohexanediol with the electrochemical cell to form a reaction product solution comprising an oxidation product of the 1,2-cyclohexanediol. The electrochemical cell can be an electrolytic cell comprising a cathode, an anode, and an ionconducting membrane situated between the cathode and the anode. The anode and cathode are made of materials such as graphite, glassy carbon, or a titanium mesh (TiMesh) doped with metals like iridium, cobalt, lead, cadmium, or nickel.

[0005] The reaction solution can further include a solvent, which can be an alcohol, a diol, a polyol, or a combination thereof, with a concentration ranging from 30 vol% to 99 vol%of the reaction solution. The presence of an electrolyte support, such as tetraethyl ammonium p-toluenesulfonate or lithium perchlorate, can increase an efficiency of the electrochemical process. The ion-conducting membrane can include materials such as a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer.

[0006] Such a technique can facilitate precise control over the reaction conditions, such as the voltage applied across the anode and cathode, which can be between 15 V and 25 V, and the current, which can range from 0.10 A to 0.50 A. The duration of the electrochemical oxidation process can be maintained between 2 hours and 4 hours, ensuring optimal yield and selectivity. The oxidation product of the 1,2-cyclohexanediol can be formed at a relatively high yield, such as 75% to 95%.

[0007] Each of the non-limiting examples described herein can stand on its own or can be combined in various permutations or combinations with one or more of the other examples.

[0008] This Summary is intended to provide an overview of the subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information.BRIEF DESCRIPTION OF THE FIGURES

[0009] In the drawings, which are not necessarily drawn to scale, like numerals can describe similar components in different views. Like numerals having different letter suffixes can represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects.

[0010] FIG. 1 illustrates an electrochemical system for flowing a reactant solution through an electrochemical flow cell for electrochemical oxidation, in accordance with various aspects.

[0011] FIG. 2A illustrates the electrochemical system, in accordance with various aspects.

[0012] FIG. 2B is an exploded view of the electrochemical flow cell of the electrochemical system shown in FIG. 1 and FIG. 2A, in accordance with various aspects.

[0013] FIG. 3 illustrates yield versus time for electrochemical oxidation performed under various current conditions, in accordance with various aspects.

[0014] FIG. 4 is a flowchart showing a method for flowing oxidizing a reactant solution via an electrochemical flow cell.DETAILED DESCRIPTION

[0015] One approach to synthesis of hexamethylene diamine (HMD) involves converting 1,4-butadiene to adiponitrile (e.g., via hydrocyanation). Such a reaction generally must be carried out on a relatively large scale and may consume significant energy, and may require significant capital and materials expenses.

[0016] Another approach to synthesis of HMD involves oxidation of 1,2- cyclohexanediol to form adipaldehyde. 1,2-Cyclohexanediol is a derivative of cyclohexane that can be readily synthesized from several sources, such as from glucose via hydrolysis and subsequent dehydration, from cyclohexene via dihydroxylation, or from benzene via cyclohexane oxidation. Certain techniques for oxidation of 1,2-cyclohexanediol to produce HMD involve a multi-step chemical process, such as a multi-stage oxidation and partial reduction process. These oxidation processes may be relatively expensive or may involve relatively harsh conditions that can produce significant waste material (e.g., unsaturated impurities) or may require a significant consumption of air, oxygen, hydrogen, or other reagents. Additional purification of the extracted material may involve additional energy costs and capital expenses, and result in significant production waste from purification processes. Further, it can be difficult or unfeasible to perform such techniques at a relatively small scale (e.g., in laboratory or mini -plant settings), which can be desirable for early research or for developing process techniques.

[0017] This document describes an electrochemical technique for oxidation of 1,2- cyclohexanediol. Such a technique can provide relatively high yields (e.g., > about 80%) of an adipaldehyde derivative (e.g., 1,1,6,6-tetramethoxyhexane), which can in turn be used to produce HMD or other target products. Such an electrochemical technique does not require use of an external oxidizing agent such as oxygen (O2) or hydrogen peroxide (H2O2). The present technique can also help enable selective oxidation of specific functional groups of 1,2- cyclohexanediol, which can lead to improved selectivity and reduced formation of by-products. Additionally, this technique involves electrochemical reactions which can be carried out under relatively mild conditions with regard to energy consumption and as compared to other approaches.

[0018] FIG. 1 illustrates an electrochemical system for flowing a reactant solution through an electrolytic cell for electrochemical oxidation. In an example, an electrochemical system 100 can include or use a reactant solution 102, a pump 104, an electrochemical flow cell 106, and one or more collection vessels 108 and 110. The reactant solution 102 can becontacted with the electrochemical flow cell 106 to form a reaction product solution including an oxidation product of the reactant solution 102.

[0019] The reactant solution 102 can include 1,2-cyclohexanediol, such as at a concentration between about 0.2 moles per liter (mol / L) and about 0.5 mol / L, or between about 0.3 mol / L and about 0.4 mol / L, or between about 0.34mol / L and about 0.36 mol / L, such as at a concentration of about 0.35 mol / L. The reactant solution 102 can also include a solvent, such as methanol, an alcohol, a diol, a polyol, propanol, ethanol, ethylene glycol, propylene glycol, acetonitrile, or a combination thereof. The solvent can be at a concentration within the reactant solution 102 between about 20 weight percent (wt %) and about 99 wt %, or between about 50 wt % and about 95 wt %, or between about 70 wt % and about 90 wt %, including limits and ranges therebetween. The reaction solution 102 can also include an electrolyte support including at least one of tetraethylammonium p-toluenesulfonate, tetraethylammonium hexafluorophosphate, tetraethylammonium hexafluoroarsenate, tetraethylammonium perchlorate, tetrabutylammonium tetrafluoroborate, lithium perchlorate, or a combination thereof. In an example, the electrolyte support can include tetraethylammonium p- toluenesulfonate, e.g., at a concentration between about 0.08 mol / L and about 0.12 mol / L, such as a concentration of about 0.1 mol / L. The reaction solution can be substantially free of oxidizing agents or oxidants, including without limitation air, oxygen, hydrogen peroxide, chlorine, sodium hypochlorite, or potassium permanganate.

[0020] The electrochemical system 100 can also include a pump 104 for flowing the reaction solution 102 toward the electrochemical flow cell 106. The pump 104 can be a positive displacement pump, such as a piston pump, or another pump, such as a centrifugal pump, a suction pump, a gear pump, or a peristaltic pump. In an example, the pump 104 can be chosen or adapted to provide a controlled electrochemical flow through the electrochemical flow cell 106, suitably including a flow rate between about 0.1 milliliters per minute (mL / min) and about 10 mL / min, such as between about 0.2 mL / min and about 5 mL / min. The pump 104 can be designed and operated to provide sufficient discharge pressure head to overcome the downstream pressure drops across the various steps, including the pressure needed for recirculation flow. Alternatively, the recirculation flow can have its own circulation pump unit (not shown).

[0021] The electrochemical flow cell 106 can be formed at least in part from an electrolytic cell, e.g., including an anode and a cathode. The anode and the cathode can be arranged adjacent each other and separated by an electrolyte gap. Other arrangements orelectrode geometries, such as 3-sided, 4-sided, cylindrical, or tubular geometries, and / or different electrode materials may be used. The anode and the cathode can be arranged, and a flow path can be positioned between the anode and the cathode including a volume for containing a portion of the reaction solution between the anode and the cathode, the flow path including combinations of channels, flow restrictors, or nozzles. The electrochemical flow cell 106 can include a channel or collection of channels, plate or container collection, or other combination that can provide a three-dimensional volume for receiving and containing the reaction solution. The cathode and the anode can each individually include a strip, a rod, a plate, or a combination thereof. One or both of the cathode and the anode can include at least one of graphite, glassy carbon, vitreous carbon, glass-like carbon, reticulated vitreous carbon (RVC), or fullerene. One or both of the cathode and the anode can also include a titanium mesh (TiMesh) doped with at least one of iridium, cobalt, lead, cadmium, or nickel. Alternatively or additionally, the anode, the cathode, or both can be chemically modified via a carbon paste or glassy carbon paste. Also, one of both of the cathode and the anode can include at least one of aluminum, boron-doped diamond, cobalt, copper, gold, lead, lead bronze, magnesium, nickel, nickel foam, niobium, platinum, silver, stainless steel, tin, titanium, tungsten, zinc, or graphite V2100. In an example, the cathode and the anode can each include a different composition, e.g., a glassy carbon cathode and a graphite anode or various other subcombinations of materials indicated above. For example, the anode can include a different composition than the cathode, and the anode can include at least one of platinum, magnetite, platinized titanium, carbon steel, Society of Automotive Engineers (SAE) 304 stainless steel, SAE 316 stainless steel, or nickel. Additional details about the electrochemical flow cell 106 are described with respect to FIG. 2B.

[0022] The electrochemical system 100 can include one or more collection vessels 108 and 110, such as a flask, beaker, tube, or other container. The collection vessel or vessels can contain the reaction product solution (or another composition generated via the electrochemical flow cell) after reaction within the flow path. The collection vessel or vessels can be stored at ambient pressure, for example for delivery to a synthesis process where the solution can be further processed using, e.g., electrolysis or chemical distillation. In an example, as shown with respect to a first collection vessel 108, the reaction product solution can be generated via a single pass through the electrochemical flow cell 106. Alternatively or additionally, as shown with respect to a second collection vessel 110, the reaction product solution can be generated via multiple passes of the same reactant solution 102 through the electrochemical flow cell 106,e.g., by recirculating the same solution through the electrochemical flow cell 106 multiple times.

[0023] In an example, the reaction product solution can include a reactant having a structure of (R1O)(R2O)CH-(CH2)4-CH(OR3)(OR4). Here, R1, R2, R3, and R4can be independently chosen from (Ci-Cio)hydrocarbyl. Also, R1and R2can together be a (C2- Csjhydrocarbylene that forms a cyclic acetal and R3and R4can be independently chosen from (Ci-Cio)hydrocarbyl such as methyl. For example, the (Ci-Cio)hydrocarbyl can be a (Ci- C4)hydrocarbyl. Also, R3and R4can together be a (C2-Cs)hydrocarbylene (e.g., ethylene) that forms a cyclic acetal and R1and R2can be independently chosen from (Ci-Cio)hydrocarbyl. Also, R1and R2together and R3and R4together can each be a (C2-Cs)hydrocarbylene and that each form a cyclic acetal. In an example, the reaction product solution can include a reactant having a structure of (CH3O)2CH-(CH2)4-CH(OCH3). In an example, the oxidation product of the 1,2-cyclohexanediol can be formed at a yield between about 1% and about 100% from the 1,2-cyclohexanediol, such as between about 75% and about 95% yield. Also, the percentage conversion of the 1,2-cyclohexanediol can be between about 1% and 100%, such as between about 80% and 100%.

[0024] FIG. 2A is another depiction of the electrochemical system that can be used, e.g., as a small-scale system. The electrochemical system 100 can include the pump 104, the electrochemical flow cell 106, a continuously adjustable power supply 212, and a carrying case 214. The carrying case 214 can provide an enclosure for the various other components (the pump 104, the electrochemical flow cell 106, the power supply 212, etc.) and can also house additional components such as replacement electrodes or half cells. In an example, the pump 104 includes a peristaltic pump with tubing connecting to each of the reactant solution and the electrochemical flow cell 106, respectively. The peristaltic pump can be capable of supplying a flow rate of about 0.01 mL / min to about 0.61 mL / min, such as to supply an overall flow rate of 0.02 mL / min to about 1.22 mL / min. In an example, the tubing connected to the pump 104 can have a diameter between about 0.10 mm and about 1 mm, such as between about 0.20 mm and about 0.30 mm or a diameter of about 0.25 mm. In an example, the peristaltic pump can supply a flow rate of about 5 mL / min or at a flow rate of about 0.17 mL / min.

[0025] The power supply 212 can also be connected to the electrochemical flow cell 106, such as via electrical leads. In an example, the continuously adjustable power supply can be capable of supplying a voltage, for application across the cathode and the anode of the electrochemical flow cell 106, between 0 volts (V) and about 35 V and at a current betweenabout 0 A and about 1 A. In an example, the power supply 212 can regulate a constant electrical direct current (DC) across the anode and the cathode. In an example, the constant electrical current applied across the anode and the cathode can be between about 0.1 A and about 1.0 A, such as at a constant current of about 0.10 A, about 0.50 A, and about 0.75 A. In an example, the system 100 can flow the reactant solution through the flow cell 106, at the constant electrical current in the flow cell 106, for an interval between about 0.5 hours and about 8 hours, between about 2 hours and about 4 hours, or at an interval of about 6 hours. The term “A” is an abbreviated term for amperes, a measurement unit of electrical current. For example, the term “0.5 A" means 0.5 amperes electrical current, and so on.

[0026] FIG. 2B is an exploded view of the electrochemical flow cell of the electrochemical system shown in FIG. 1 and FIG. 2 A. The electrochemical flow cell 106 can include an anode 216 a cathode 218, one or more gaskets or spacers 220 disposed between the anode 216 and cathode 218, an ion-conducting membrane 222, and one or more electrical contacts 224, and one or more stainless steel plates 226. The electrochemical flow cell 106 can be arranged as a divided cell (e.g., where the anode and cathode can be arranged in different chambers and separated from each other by a membrane), or alternatively can be arranged as an undivided cell (e.g., where the anode and cathode are arranged in the same chamber and not separated by a membrane). In an example, the reaction solution can flow through both the anode and the cathode.

[0027] The anode 216 and the cathode 218 can be arranged within the electrochemical flow cell such as to define a gap therebetween, e.g., the gap being between about 0.1 millimeters (mm) and about 5 mm or between about 0.5 mm and about 1 mm. In an example, the cathode and anode can be disposed within the electrochemical flow cell such that they are free of physical contact with one another. In an example, each of the anode 216 and the cathode 218 include a respective gasket 220 disposed between an electrode surface and the ionconducting membrane 222. In an example, each of the anode 216 and the cathode 218 can be attached to respective electrical contacts 224 for coupling with the power supply 214 (as depicted in FIG. 2A). In an example, the ion-conducting membrane 222 can include Nafion® (e.g., Nafion® 115, 117, or 212) or a sulfonated tetrafluoroethylene-based fluoropolymercopolymer (e.g., tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid copolymer).

[0028] FIG. 3 is a chart showing yield versus time for electrochemical oxidation performed under various current conditions, in accordance with various aspects. As shown inFIG. 3, varying the constant current from 0.10 A- 1.0 A with flow rate of 5 ml / min with recirculation of the reaction solution can affect a yield of the reaction. In an example, a preferred constant current can be at about 0.50 A and can produce a yield greater than 90%. The chart shows a progressive increase in yields with length of time in the electrochemical flow cell until a peak of about 3 hours (for I = 0.5 A, represented by the dashed line) and about 2.5 hours (for I = 0.75 A, represented by the solid line). Without being bound by theory, overoxidation of the reaction solution can occur when reaction time is longer than ideal and can contribute to progressively lower yields and formation of byproducts.

[0029] FIG. 4 is a flowchart showing a technique for flowing oxidizing a reactant solution via an electrochemical cell.

[0030] At 410, the technique involves the preparation of a reactant solution containing 1,2-cyclohexanediol. The electrochemical cell can be configured to facilitate the oxidation of the reactant solution. In an example, benzene can be oxidized to form the 1,2-cyclohexanediol used in the reactant solution.

[0031] At 420, once the reactant solution is flowing, the current can be regulated such as to maintain a constant value between 0.4 Amps (A) and 0.8 A. This precise control of the current can enhance efficiency and effectiveness of the oxidation reaction.

[0032] At 430, the reactant solution can be recirculated through the electrochemical cell. During the recirculation, a reaction solution is produced. Such a reaction solution can later be removed from the system within a specified electrochemical oxidation duration. Such a duration (e.g., between about 1.5 hours and about 3 hours of recirculation or otherwise being contacted with the electrochemical cell) can be determined based on factors such as the composition of the reactant solution, the regulated current, and real-time monitoring of the reaction solution during recirculation. In various aspects, the reaction solution can be recovered at yield greater than 90%. This high yield can be indicative of the process's efficiency and the quality of the oxidized products obtained. In an example, starting from a reactant solution containing 1,2-cyclohexanediol, the recovered reaction solution may include valuable chemical compounds such as adipaldehyde, adipaldehyde diacetal, adipic acid, or a combination thereof. These compounds have significant industrial applications, making their efficient production highly desirable.Examples

[0033] Various aspects of the present disclosure can be better understood by reference to the following Examples which are offered by way of illustration. The present disclosure is not limited to the Examples given herein.

[0034] Materials. 1,2-Cyclohexanediol, tetraethylammonium p-toluenesulfonate, 1,1,6,6-tetraethoxyhexane, and methanol were obtained from Millipore sigma. Electrochemical measurements such as cyclic voltammetry were performed using Pine Research Wave Driver 200 (Model: AFP3). The electrochemical flow cell electrochemical oxidation was performed using an IKA ElectraSyn flow system. The electrode surface area for each bulk electrolysis experiment was 12.6 cm2. The undivided electrochemical flow cell had 1 mm gap between anode and cathode. FIG. 2A illustrates the electrochemical oxidation flow system. FIG. 2B illustrates an electrochemical cell of the electrochemical oxidation flow system shown in FIG. 2A.

[0035] Gas chromatography (GC) analysis. The samples were charged with an internal standard (sec-butylbenzene) and analyzed by gas chromatography. The samples were analyzed on an Agilent 7890A GC equipped with a phenyl arylene polymer that was virtually equivalent to a (5%-phenyl)-methylpolysiloxanecapillary column (DB-5MS) with a 0.5 pm film. The column carrier gas was 1.6 cc / min of He (constant pressure mode) and 0.5 pL injection volume. The heating profile was 50 °C at injection, 9 °C per minute until 100 °C, 1.9 °C per minute until 120 °C, 7.3 °C per minute until 165 °C, 1.7 °C per minute until 201 °C, 20 °C per minute until 280 °C, hold for 30 minutes. The GC detector was a flame ionization detector (FID).

[0036] NMR Analysis: NMR spectra were recorded in thin walled NMR tubes on a Bruker NMR 600 MHz (1 H) spectrometer.XH and13C chemical shifts were referenced to residual proton resonances in deuterated solvent. For the determination of product yield by ’H NMR spectroscopy, 1,3,5- trimethoxybenzene was used as internal integration standard.Examples 1-4, Electrochemical oxidation of 1.2-cyclohexanediol with recirculation.

[0037] A solution of 1,2-cyclohexanediol in methanol (20 ml, 7 mmol) containing 0.1 M tetraethylammonium p-toluenesulfonate was pumped through an electrochemical flow cell equipped with an appropriate anode and cathode with a flow rate of 5 mL min-1. The reactor outlet was returned to the reaction solution to recirculate the solution. A constant current ranging from 0.1 A to 1.0 A was applied during the reaction. The reaction progress was monitored using gas chromatography.Example 5, Single-pass flow electrochemical oxidation of 1,2,-cyclohexanediol.

[0038] A solution of 1,2-cyclohexanediol in methanol (20 mL, 7 mmol) containing 0.1 M tetraethylammonium p-toluenesulfonate was pumped through an electrochemical flow cell equipped with an appropriate anode and cathode with a flow rate of 0.17 mL min-1. A constant current of 0.75 A was applied during the reaction. The reaction mixture was collected in a round-bottom flask as the reactor output. This procedure was repeated four additional times in cascade. During each pass through the cell, an aliquot amount of the reaction mixture was collected and analyzed by GC.Example 6, Analysis of Examples 1-5,

[0039] Table 1 illustrates details of Examples 1-5.

[0040] Table 1.* Electrode material (black particles) observed in the product solution. ’Reaction solution was passed through the cell 5 times.Yield = % yield of 1, 1, 6, 6 - tetramethoxyhexane

[0041] The recirculating reactions were performed at varying constant current from 0.10 A- 1.0 A with flow rate of 5 ml / min with recirculation of the reaction solution and formation of product was monitored using GC. When graphite electrodes were used in Example 1 as both anode and cathode, graphite particles were observed in the product. Use of glassy carbon electrodes as both anode and cathode worked well and was chosen for further experiments, namely, Examples 2 through 5. The optimum constant current was found to be 0.50 A under these reaction conditions with a high yield of 91.8%, as illustrated in Example 3.

[0042] Other products can be formed when the current was is high, or the reaction is performed for longer period of time. FIG. 2 illustrates yield versus time for recirculatingelectrochemical oxidation reactions performed at constant current of 0.5 A or 0.75 A. The yield of a desired product, e.g., adipaldehyde diacetal(s), increased initially, reached the maximum, and then decreased. It is believed that overoxidation of the product occurs when the reaction time is longer than needed, which caused the yield to drop. When the reaction was performed using a single pass, the yield was lower than that observed for the recirculation mode.Example 7, Electrochemical oxidation of 1,2-cyclohexanediol to adipaldehyde

[0043] A solution of 1,2-cyclohexanediol in methanol and electrolyte is electrochemically oxidized as described in Example 1-4 using recirculation. The solution is pumped through an electrochemical flow cell equipped with an appropriate anode and cathode with a flow rate of 5 mL min-1. The reactor outlet is returned to the reaction solution to recirculate the solution. A constant current ranging from 0.1 A to 1.0 A is applied during the reaction. The reaction progress is monitored using gas chromatography. The product analysis shows a conversion of the feed diol to its corresponding dialdehyde, namely, adipaldehyde, in appreciable yield.Example 8, Electrochemical oxidation of E2-cyclohexanediol to adipic acid

[0044] The Example 7 procedure is continued for a longer time. The resulting product obtained is mainly adipic acid, with some adipaldehyde. Adipic acid is recovered from the effluent in good yield.Example 9, Electrochemical oxidation of cyclododecenediol

[0045] Cyclododecenediol is electrochemically oxidized according to the procedure described in Example 1-4. Good yield of linear C12 diacid is obtained along with some linear C12 dialdehyde.Example 10. Electrochemical oxidation of cyclopentenediol

[0046] Cyclopentenediol is electrochemically oxidized according to the procedure described in Example 1-4. Good yield of 1,5-pentanediacid is obtained along with some 1,5- pentanedialdehyde.Example 11. Electrochemical oxidation of E2-cyclohexanediol to a product mixture

[0047] A product mixture comprising useful intermediates is obtained when 1,2- cyclohexanediol is electrochemically oxidized as described in Example 1-4. The overall electrochemical reaction time is varied from 10 minutes to 5 hours. GC analysis shows the product mixture containing 1,1,6,6-tetramethoxyhexane, dialdehyde diacetal, adipaldehyde, half-aldehyde-half-acid, adipic acid, and other by-products in small quantities.Example 12, Electrochemical oxidation of E2-cyclohexanediol to adipic acid ester

[0048] In Examples 1-4, the alcohol present as a solvent further reacts with adipic acid under the electrochemical conditions and produces an ester of adipic acid in good yield.Example 13, Electrochemical oxidation of E6-hexanediol to adipaldehyde diacetal

[0049] 1, 6-Hexanediol is electrochemically oxidized according to the procedure described in Examples 1-4. Good yield adipaldehyde diacetal is obtained.Example 14, Electrochemical oxidation of E6-hexanediol to adipic acid

[0050] The Example 13 procedure is continued for a longer time. The resulting product obtained is mainly adipic acid, with some adipaldehyde as an intermediate product. Adipic acid is recovered from the effluent in good yield.Example 15, Electrochemical oxidative coupling of E6-cyclohexanediol with ammonia

[0051] 1,6 -Cyclohexanediol is electrochemically oxidized as described in Examples1-4 in the presence of ammonia source. The overall electrochemical reaction time is varied from 20 minutes to 10 hours. 1,6-Hexanediimine is recovered in good yield.Example 16, Electrochemical oxidative coupling of E6-cyclohexanediol with benzyl amine

[0052] 1,6 -Cyclohexanediol is electrochemically oxidized as described in Example 1-4 in the presence of about 2 to 100 equivalents of benzyl amine. The overall electrochemical reaction time is varied from 20 min to about 10 hrs. N,N'-1,6- Hexanediylidenebis[benzenemethanamine] is recovered in good yield.

[0053] Reference will now be made in detail to certain aspects of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with theenumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

[0054] Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “about 0.1% to about 5%” or “about 0.1% to 5%” should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise. A statement describing a range as “between X and Y” includes X and Y as being a part of the stated range.

[0055] In this document, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. The statement “at least one of A and B” or “at least one of A or B” has the same meaning as “A, B, or A and B.” In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

[0056] In the methods described herein, the acts can be carried out in a specific order as recited herein. Alternatively, in any aspect(s) disclosed herein, specific acts may be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately or the plain meaning of the claims would require it. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

[0057] The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range, and includes the exact stated value or range.

[0058] The term “substantially” as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%. The term “substantially free of’ as used herein can mean having none or having a trivial amount of, such that the amount of material present does not affect the material properties of the composition including the material, such that about 0 wt% to about 5 wt% of the composition is the material, or about 0 wt% to about 1 wt%, or about 5 wt% or less, or less than, equal to, or greater than about 4.5 wt%, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or about 0.001 wt% or less, or about 0 wt%.

[0059] The term “hydrocarbon” or “hydrocarbyl” as used herein refers to a molecule or functional group that includes carbon and hydrogen atoms. The term can also refer to a molecule or functional group that normally includes both carbon and hydrogen atoms but wherein all the hydrogen atoms are substituted with other functional groups.

[0060] As used herein, the term “hydrocarbyl” refers to a functional group derived from a straight chain, branched, or cyclic hydrocarbon, and can be alkyl, alkenyl, alkynyl, aryl, cycloalkyl, acyl, or any combination thereof. Hydrocarbyl groups can be shown as (Ca- Cbjhydrocarbyl, wherein a and b are integers and mean having any of a to b number of carbon atoms. For example, (Cl-C4)hydrocarbyl means the hydrocarbyl group can be methyl (Cl), ethyl (C2), propyl (C3), or butyl (C4), and (CO-Cb)hydrocarbyl means in certain aspects there is no hydrocarbyl group.

[0061] As used herein, the term “polymer” refers to a molecule having at least one repeating unit and can include copolymers.

[0062] The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the aspects of the present disclosure. Thus, it should be understood that although the present disclosure has been specifically disclosed by specific aspects and optional features, modification and variation of the concepts herein disclosed may be resorted to by those of ordinary skill in the art, and that such modifications and variations are considered to be within the scope of aspects of the present disclosure.Exemplary Aspects.

[0063] The following exemplary aspects are provided, the numbering of which is not to be construed as designating levels of importance:

[0064] Aspect 1 can include a method of oxidizing 1,2-cyclohexanediol, such as can include contacting a reaction solution comprising the 1,2-cyclohexanediol with an electrochemical cell to form a reaction product solution comprising an oxidation product of the 1,2-cyclohexanediol.

[0065] Aspect 2 can include, or can optionally be combined with the subject matter of Aspect 1, to optionally include where the 1,2-cyclohexanediol has a concentration between 0.2 moles per liter (mol / L) and 0.5 mol / L of the reaction solution.

[0066] Aspect 3 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 or 2 to optionally include where the 1,2-cyclohexanediol has a concentration between 0.34 moles per liter (mol / L) and 0.36 mol / L of the reaction solution.

[0067] Aspect 4 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 3 to optionally include where the reaction solution further comprises a solvent.

[0068] Aspect 5 can include, or can optionally be combined with the subject matter of Aspect 4 to optionally include where the solvent has a concentration between 30 volumetric percent (vol%) and 99 vol % of the reaction solution.

[0069] Aspect 6 can include, or can optionally be combined with the subject matter of Aspect 4 to optionally include where the solvent has a concentration between 70 volumetric percent (vol%) and 90 vol % of the reaction solution.

[0070] Aspect 7 can include, or can optionally be combined with the subject matter of Aspect 4 to optionally include where the solvent comprises an alcohol, a diol, a polyol, propanol, ethanol, methanol, ethylene glycol, propylene glycol, acetonitrile, or a combination thereof.

[0071] Aspect 8 can include, or can optionally be combined with the subject matter of Aspect 4 to optionally include where the solvent comprises methanol.

[0072] Aspect 9 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 8 to optionally include where the reaction solution further comprises an electrolyte support.

[0073] Aspect 10 can include, or can optionally be combined with the subject matter of Aspect 9 to optionally include where the electrolyte support comprises tetraethylammonium p-toluenesulfonate, tetraethylammonium hexafluorophosphate, tetraethylammonium hexafluoroarsenate, tetraethylammonium perchlorate, tetrabutylammonium tetrafluoroborate, lithium perchlorate, or a combination thereof.

[0074] Aspect 11 can include, or can optionally be combined with the subject matter of Aspect 9 to optionally include where the electrolyte support comprises tetraethylammonium p-toluenesulfonate.

[0075] Aspect 12 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 11 to optionally include where the reaction solution is substantially free of oxidants.

[0076] Aspect 13 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 12 to optionally include where the electrochemical cell is an electrolytic cell.

[0077] Aspect 14 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 13 to optionally include where the electrochemical cell comprises a cathode, an anode, and an ion-conducting membrane between the cathode and the anode.

[0078] Aspect 15 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where the anode and the cathode each comprises graphite, glassy carbon, a titanium mesh (TiMesh) doped with at least one of iridium, cobalt, lead, cadmium, or nickel, or a combination thereof.

[0079] Aspect 16 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where the anode and the cathode are glassy carbon electrodes.

[0080] Aspect 17 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where at least the anode comprises at least one of platinum, magnetite, platinized titanium, carbon steel, Society of Automotive Engineers (SAE) 304 stainless steel, SAE 316 stainless steel, or nickel.

[0081] Aspect 18 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where the ion-conducting membrane comprises , a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer, or a combination thereof.

[0082] Aspect 19 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where the ion-conducting membrane comprises a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer.

[0083] Aspect 20 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where the ion-conducting membrane comprises tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid copolymer.

[0084] Aspect 21 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where the anode and the cathode each comprise a strip, a rod, a plate or a combination thereof.

[0085] Aspect 22 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where the anode and the cathode comprise plates arranged parallel to one another.

[0086] Aspect 23 can include, or can optionally be combined with the subject matter of Aspect 14 to optionally include where the anode and the cathode comprise a gap therebetween.

[0087] Aspect 24 can include, or can optionally be combined with the subject matter of Aspect 23 to optionally include where the gap between the anode and the cathode is 0.1 mm to 5 mm.

[0088] Aspect 25 can include, or can optionally be combined with the subject matter of Aspect 23 to optionally include where the gap between the anode and the cathode is 0.5 mm to 1 mm.

[0089] Aspect 26 can include, or can optionally be combined with the subject matter of Aspect 23 to optionally include where the anode and cathode are free of physical contact with one another.

[0090] Aspect 27 can include, or can optionally be combined with the subject matter of Aspect 23 to optionally include where the electrochemical cell comprises anode gasket between the membrane and the anode and / or a cathode gasket between the membrane and the cathode.

[0091] Aspect 28 can include, or can optionally be combined with the subject matter of Aspect 23 to optionally include where the electrochemical cell is a divided cell.

[0092] Aspect 29 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 28 to optionally include where the contactingof the reaction solution with the electrochemical cell comprises applying a constant electrical potential across the anode and cathode.

[0093] Aspect 30 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 29 to optionally include where the contacting of the reaction solution with the electrochemical cell comprises applying a constant electrical current across the anode and cathode.

[0094] Aspect 31 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 30 to optionally include where the contacting of the reaction solution with the electrochemical cell comprises applying a voltage between 0 volts (V) and 35 V across the anode and the cathode.

[0095] Aspect 32 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 31 to optionally include where the contacting of the reaction solution with the electrochemical cell comprises applying a voltage between 15 V and 25 V across the anode and the cathode.

[0096] Aspect 33 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 32 to optionally include where the contacting of the reaction solution with the electrochemical cell comprises applying a current between .1 Amp (A) and 1 A across the anode and the cathode.

[0097] Aspect 34 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 33 to optionally include where the contacting of the reaction solution with the electrochemical cell comprises applying a current between .10 A and 0.50 A across the anode and the cathode.

[0098] Aspect 35 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 34 to optionally include where the contacting of the reaction solution with the electrochemical cell is performed for a duration between 0.5 hours and 8 hours.

[0099] Aspect 36 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 35 to optionally include where the contacting of the reaction solution with the electrochemical cell is performed for a duration between 2 hours and 4 hours.

[0100] Aspect 37 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 36 to optionally include where the contactingof the reaction solution with the electrochemical cell is performed at a temperature between 15°C and 25°C.

[0101] Aspect 38 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 37 to optionally include where the contacting of the reaction solution with the electrochemical cell is performed at a temperature of 18°C and 22°C.

[0102] Aspect 39 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 38 to optionally include where the contacting of the reaction solution with the electrochemical cell comprises recirculating the reaction solution to contact the electrochemical cell more than one time, to form the reaction product solution.

[0103] Aspect 40 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 39 to optionally include where the method is free of recontacting the reaction solution with the electrochemical cell more than one time.

[0104] Aspect 41 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 40 to optionally include where the reaction product solution is the product of a single pass of the reaction solution through the electrochemical cell.

[0105] Aspect 42 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 43 to optionally include where the oxidation product of the 1,2-cyclohexanediol is (R1O)(R2O)CH-(CH2)4-CH(OR3)(OR4), wherein R1, R2, R3, and R4are independently chosen from (Ci-Cio)hydrocarbyl, or R1and R2together are a (C2-Cs)hydrocarbylene that forms a cyclic acetal and R3and R4are independently chosen from (Ci-Cio)hydrocarbyl, R3and R4together are a (C2-Cs)hydrocarbylene that forms a cyclic acetal and R1and R2are independently chosen from (Ci-Cio)hydrocarbyl, or R1and R2together and R3and R4together are each a (C2-Cs)hydrocarbylene and that each form a cyclic acetal.

[0106] Aspect 43 can include, or can optionally be combined with the subject matter Aspect 42 to optionally include where R1, R2, R3, and R4are independently chosen from (Ci- Ciojhydrocarbyl.

[0107] Aspect 44 can include, or can optionally be combined with the subject matter Aspect 42 to optionally include where the (Ci-Cio)hydrocarbyl is a (Ci-C4)hydrocarbyl.

[0108] Aspect 45 can include, or can optionally be combined with the subject matter Aspect 42 to optionally include where the (Ci-Cio)hydrocarbyl is a methyl.

[0109] Aspect 46 can include, or can optionally be combined with the subject matter Aspect 42 to optionally include where the oxidation product of the 1,2-cyclohexanediol is (CH3O)2CH-(CH2)4-CH(OCH3).

[0110] Aspect 47 can include, or can optionally be combined with the subject matter Aspect 42 to optionally include where R1and R2together and R3and R4together are each a (C2-Cs)hydrocarbylene and that each form a cyclic acetal.

[0111] Aspect 48 can include, or can optionally be combined with the subject matter Aspect 42 to optionally include where the (C2-Cs)hydrocarbylene is ethylene.

[0112] Aspect 49 can include, or can optionally be combined with the subject matter Aspect 42 to optionally include where the oxidation product of the 1,2-cyclohexanediol has the following structure:

[0114] Aspect 50 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 49 to optionally include where the oxidation product of the 1,2-cyclohexanediol is formed at 1% to 100% yield from the 1,2- cyclohexanediol.

[0115] Aspect 51 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 50 to optionally include where the oxidation product of the 1,2-cyclohexanediol is formed at 75% to 95% yield from the 1,2- cyclohexanediol.

[0116] Aspect 52 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 51 to optionally include where a percentage conversion of the 1,2-cyclohexanediol is 1% to 100%.

[0117] Aspect 53 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 52 to optionally include where a percentage conversion of the 1,2-cyclohexanediol is 80% to 100%.

[0118] Aspect 54 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 53 to optionally include where the method further comprises oxidizing benzene to form the 1,2-cyclohexanediol.

[0119] Aspect 55 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 54 to optionally include oxidizing the oxidationproduct of the 1,2-cyclohexanediol to form adipaldehyde, adipic acid, a diacetal derivative of adipaldehyde, or a combination thereof.

[0120] Aspect 56 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 1 through 55 to optionally include oxidizing the oxidation product of the 1,2-cyclohexanediol to form adipaldehyde.

[0121] Aspect 57 can include a method for flowing oxidizing a reactant solution via an electrochemical cell, the method comprising flowing a reactant solution including 1,2- cyclohexanediol through an electrochemical cell, regulating a constant current of the electrochemical cell between 0.4 Amps (A) and 0.8 A, and recirculating the flowed reaction solution again through the electrochemical cell.

[0122] Aspect 58 can include, or can optionally be combined with the subject matter of Aspect 57, to optionally include removing a reaction solution, produced via the recirculating of the reactant solution through the electrochemical cell, from the reaction solution within a specified ideal electrochemical oxidation duration.

[0123] Aspect 59 can include, or can optionally be combined with the subject matter of Aspect 58 to optionally include predicting the ideal electrochemical oxidation duration based on at least one of the reactant solution, the current, or monitoring of the reaction solution during the recirculating.

[0124] Aspect 60 can include, or can optionally be combined with the subject matter of Aspect 58 to optionally include where the removed reaction solution has a yield greater than 90%.

[0125] Aspect 61 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 57 through 60 to optionally include where the removed reaction solution includes at least one of adipaldehyde, adipic acid, adipaldehyde diacetal, or a combination thereof.

[0126] Aspect 62 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 57 through 61 to optionally facilitating oxidation of benzene to form the 1,2-cyclohexanediol of the reactant solution.

[0127] Aspect 63 can include a method for flowing oxidizing a reactant solution via an electrochemical cell, the method comprising flowing a reactant solution including at least one of 1,2-cyclohexanediol, cyclododecenediol, cyclopentenediol, 1,6-hexanediol, or 1,6- cyclohexanediol through an electrochemical cell, regulating a constant current of theelectrochemical cell between 0.1 Amps (A) and 1 A, and recirculating the flowed reaction solution again through the electrochemical cell.

[0128] Aspect 64 can include, or can optionally be combined with the subject matter of Aspect 63, to optionally include removing a reaction solution, produced via the recirculating of the reactant solution through the electrochemical cell, from the reaction solution within a specified ideal electrochemical oxidation duration.

[0129] Aspect 65 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 63 through 64 to optionally include where the removed reaction solution includes at least one of adipaldehyde, adipic acid, adipaldehyde diacetal, or a combination thereof.

[0130] Aspect 66 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 63 through 65 to optionally include where the removed reaction solution includes at least one of a diacid, a dialdehyde, 1,1,6,6-tetramethoxyhexane, half-aldehyde-half-acid, an ester of adipic acid, 1,6-hexanediimine, benzenemethanamine, or a combination thereof.

[0131] Aspect 67 can include, or can optionally be combined with the subject matter of one or any combination of Aspects 63 through 66 to optionally include where regulating a constant current of the electrochemical cell comprises regulating the current between 0.4 A and 0.8 A.

[0132] Aspect 68 provides the apparatus, method, composition, or system of any one or any combination of Aspects 1 through 67 optionally configured such that all elements or options recited are available to use or select from.

Claims

CLAIMSWhat is claimed is:

1. A method of oxidizing 1,2-cyclohexanediol: contacting a reaction solution comprising the 1,2-cyclohexanediol with an electrochemical cell to form a reaction product solution comprising an oxidation product of the 1,2-cyclohexanediol.

2. The method of claim 1, wherein the reaction solution further comprises a solvent having a concentration between 30 volumetric percent (vol%) and 99 vol % of the reaction solution.

3. The method of claim 2, wherein the solvent comprises an alcohol, a diol, a polyol, propanol, ethanol, methanol, ethylene glycol, propylene glycol, acetonitrile, or a combination thereof.

4. The method of claim 1, wherein the reaction solution further comprises an electrolyte support comprising tetraethylammonium p-toluenesulfonate, tetraethylammonium hexafluorophosphate, tetraethyl ammonium hexafluoroarsenate, tetraethylammonium perchlorate, tetrabutylammonium tetrafluoroborate, lithium perchlorate, or a combination thereof.

5. The method of claim 1, wherein the electrochemical cell is an electrolytic cell comprising a cathode, an anode, and an ion-conducting membrane between the cathode and the anode; wherein the anode and the cathode each comprises graphite, glassy carbon, a titanium mesh (TiMesh) doped with at least one of iridium, cobalt, lead, cadmium, or nickel, or a combination thereof.

6. The method of claim 5, wherein the ion-conducting membrane comprises a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer, or a combination thereof.

7. The method of claim 5, wherein the anode and the cathode comprise plates arranged parallel to one another, including a gap there between within a range of 0.1 mm to 5 mm.

8. The method of claim 1, wherein the contacting of the reaction solution with the electrochemical cell comprises applying a voltage between 15 V and 25 V across the anode and the cathode.

9. The method of claim 1, wherein the contacting of the reaction solution with the electrochemical cell comprises applying a current between 0.10 A and 0.50 A across the anode and the cathode.

10. The method of claim 1, wherein the contacting of the reaction solution with the electrochemical cell is performed for a duration between 2 hours and 4 hours.

11. The method of claim 1, wherein the oxidation product of the 1,2-cyclohexanediol is formed at 75% to 95% yield from the 1,2-cyclohexanediol.

12. The method of claim 1, further comprising oxidizing the oxidation product of the 1,2- cyclohexanediol to form adipaldehyde, adipic acid, a diacetal derivative of adipaldehyde, or a combination thereof.

13. The method of claim 1, further comprising oxidizing the oxidation product of the 1,2- cyclohexanediol to form adipaldehyde.

14. A method of oxidizing 1,2-cyclohexanediol: contacting a reaction solution comprising the 1,2-cyclohexanediol with an electrochemical cell to form a reaction product solution comprising an oxidation product of the 1,2-cyclohexanediol; wherein the oxidation product of the 1,2-cyclohexanediol is (R1O)(R2O)CH-(CH2)4- CH(OR3)(OR4), whereinR1, R2, R3, and R4are independently chosen from (Ci-Cio)hydrocarbyl, orR1and R2together are a (C2-Cs)hydrocarbylene that forms a cyclic acetal and R3and R4are independently chosen from (Ci-Cio)hydrocarbyl,R3and R4together are a (C2-Cs)hydrocarbylene that forms a cyclic acetal and R1and R2are independently chosen from (Ci-Cio)hydrocarbyl, orR1and R2together and R3and R4together are each a (C2-Cs)hydrocarbylene and that each form a cyclic acetal.

15. The method of claim 14, wherein the oxidation product of the 1,2-cyclohexanediol is (CH3O)2CH-(CH2)4-CH(OCH3).

16. The method of claim 14, wherein R1and R2together and R3and R4together are each a (C2-Cs)hydrocarbylene and that each form a cyclic acetal.

17. The method of claim 14, wherein the (C2-Cs)hydrocarbylene is ethylene.

18. A method for oxidizing a reactant solution via an electrochemical cell, the method comprising: flowing a reactant solution including at least one of 1,2-cyclohexanediol, cyclododecenediol, cyclopentenediol, 1,6-hexanediol, or 1,6-cyclohexanediol through an electrochemical cell; regulating a constant current of the electrochemical cell between 0.1 Amps (A) and 1 A; and recirculating the flowed reaction solution again through the electrochemical cell.

19. The method of claim 18, comprising removing a reaction solution, produced via the recirculating of the reactant solution through the electrochemical cell, from the reaction solution within a specified ideal electrochemical oxidation duration.

20. The method of claim 18, wherein the removed reaction solution includes at least one of adipaldehyde, adipic acid, adipaldehyde diacetal, or a combination thereof.

21. The method of claim 18, wherein the removed reaction solution includes at least one of a diacid, a dialdehyde, 1,1, 6, 6-tetram ethoxy hexane, half-aldehyde-half-acid, an ester of adipic acid, 1,6-hexanediimine, or benzenem ethanamine, or a combination thereof.

22. The method of claim 18, wherein regulating a constant current of the electrochemical cell comprises regulating the current between 0.4 A and 0.8 A.

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