Method to synthesise cyclic compounds containing urethane or urea groups

Abstract

A method of synthesising a cyclic urethane compound or cyclic urea compound including mixing a reactant of structure (I) (I) with a solvent of structure (II) (II) to form a mixture, and adding carbon dioxide to the mixture and reacting the mixture to obtain a product of structure (II), wherein in structure (I), X1 is -OH or -NHR8; and in structure (II), X2 is -O- or -NR8-; in both structures (I) and (II), n is selected from 0, 1, 2 and 3; in both structures (I) and (II), R1 to R8 is each independently selected from H, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkoxy group, and a substituted or unsubstituted arylalkyl, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure.

Description

METHOD TO SYNTHESISE CYCLIC COMPOUNDS CONTAINING URETHANE OR UREA GROUPSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Serial Number 63 / 678,297 filed August 1, 2024. The noted application is incorporated herein by reference.FIELD OF INVENTION

[0002] The present disclosure relates to a method of synthesising a cyclic urethane compound or cyclic urea compound by reacting an amino alcohol or diamine with carbon dioxide, wherein the cyclic urethane compound or cyclic urea compound product is used as the solvent in the method.BACKGROUND

[0003] Due to emphasis on green chemistry and the need to reduce carbon footprint where possible, the use of carbon dioxide as a feedstock to synthesise useful compounds has been extensively investigated. One such use of carbon dioxide is in the synthesis of commercially useful cyclic urethane compounds and cyclic urea compounds.

[0004] It is known to react carbon dioxide with an amino alcohol to form a cyclic urethane compound, or to react carbon dioxide with a diamine to form a cyclic urea compound. However, the currently known methods employ large quantities of solvent in the methods. The solvent needs to be separated from the product (cyclic urethane compound or cyclic urea compound) at the end of the method, which can be a complicated process and adds costs. There is a need for a simplified method of reacting carbon dioxide with an amino alcohol to form a cyclic urethane compound, or reacting carbon dioxide with a diamine to form a cyclic urea compound, in which the addition of the solvent does not complicate the process, does not make purification of the product more difficult, and does not add costs.

[0005] The present disclosure addresses the problems and needs mentioned above.

[0006] It has been surprisingly found that the cyclic urethane compound or cyclic urea compound may act as a solvent in the method, thereby eliminating the need altogether to add another chemical compound as the solvent to the reaction mixture. That is, the product of the reaction may be the solvent, which therefore greatly simplifies the purification process because another chemical compound is not added to the reaction mixture. This minimises the number of different chemicals added to the reactionmixture, which in turn may reduce production costs associated with making the cyclic urethane compound or cyclic urea compound.SUMMARY

[0007] In a first aspect, there is provided a method of synthesising a cyclic urethane compound or cyclic urea compound, the method comprising: step 1) mixing a reactant comprising a compound according to structure (I) with a solvent comprising a compound according to structure (II) to form a mixture, and step 2) adding carbon dioxide to the mixture and reacting the mixture to obtain a product comprising a compound according to structure (II), wherein the compound according to structure (II) is a cyclic urethane compound or cyclic urea compound: structure (I):structure (II):wherein, in structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is selected from 0, 1, 2 and 3; in both structures (I) and (II), Ri to Rs is each independently selected from H, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkoxy group, and a substituted or unsubstituted arylalkyl, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure.

[0008] When the compound according to structure (II) in the solvent and the product has the same chemical structure, the purification of the product from the crude product mixture is simpler because there are fewer chemical compounds in the crude product mixture.This simplifies the purification process and reduces production costs associated with making the cyclic urethane compound or cyclic urea compound. Moreover, using the product as the solvent avoids the typical processing costs to separate and recycle the solvent.

[0009] The embodiments described should not be read to limit or otherwise narrow the scope of any inventive concepts otherwise provided by the present disclosure. While multiple embodiments are disclosed, other embodiments will become apparent to those skilled in the art from the following description. Accordingly, the description is to be regarded as illustrative rather than restrictive.DETAILED DESCRIPTION

[0010] As used herein, the term “substituted” refers to (at least one) substituent group on the group to which it relates, e.g. a substituted alkyl group refers to an alkyl group which contains at least one substituent group.

[0011] The substituent group can be any substituent group known in the art. Examples of the substituent group include a halogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a heterocyclic group, a silyl group, an alkoxy group, an amino group, an aryloxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an acyloxy group, an acylamino group, an aminocarbonylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, an alkylthio group, an arylthio group, an alkyl sulfinyl group, an aryl sulfinyl group, an alkyl sulfonyl group, an aryl sulfonyl group, a silyloxy group, a heterocyclic oxy group, a carbamoyl group, a carbamoyloxy group, a heterocyclic thio group, a sulfamoyl group, an arylazo group, a heterocyclic azo group, an imide group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, a hydrazino group, an imino group, a cyano group, a hydroxy group, a nitro group, a mercapto group, a sulfo group, a carboxy group, a hydroxamic acid group, a sulfino group, a boronate group (-B(OH)2 ), a phosphate group (- OPO(OH)2 ), a phosphono group (-PO(OH)2 ), and a sulfate group (-OSO3 H). The group selected from the substituent group may further have a substituent. In at least one embodiment, the substituent group, if present, is a hydroxy group.

[0012] Method of synthesising a cyclic urethane compound or cyclic urea compound

[0013] The present disclosure provides a method of synthesising a cyclic urethane compound or cyclic urea compound, the method comprising: step 1) mixing a reactant comprising a compound according to structure (I) with a solvent comprising a compound accordingto structure (II) to form a mixture, and step 2) adding carbon dioxide to the mixture and reacting the mixture to obtain a product comprising a compound according to structure (II), wherein the compound according to structure (II) is a cyclic urethane compound or cyclic urea compound: structure (I):structure (II):wherein, in structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is selected from 0, 1, 2 and 3; in both structures (I) and (II), Ri to Rs is each independently selected from H, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkoxy group, and a substituted or unsubstituted arylalkyl, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure.

[0014] As used herein, the term “cyclic urethane compound” refers to a compound which is cyclic and contains a urethane group as part of the ring in the cyclic structure. Similarly, the term “cyclic urea compound” refers to a compound which is cyclic and contains a urea group as part of the ring in the cyclic structure.

[0015] The method described herein comprises at least two steps, step 1) and step 2). Further steps may be present, if needed or desired.

[0016] Step 1) involves mixing a reactant comprising a compound according to structure (I) with a solvent comprising a compound according to structure (II) to form a mixture. During this step, the reactant and solvent do not react.

[0017] The reactant may comprise further compounds other than a compound according to structure (I). In a preferred embodiment, the reactant only comprises (consists of) acompound according to structure (I). That is, the reactant is a compound according to structure (I) and contains no other compounds (besides inevitable impurities). The reactant may contain more than one compound according to structure (I).

[0018] The solvent may comprise further compounds other than a compound according to structure (II). In a preferred embodiment, the solvent only comprises (consists of) a compound according to structure (II). That is, the solvent is a compound according to structure (II) and contains no other compounds (besides inevitable impurities). The solvent may contain more than one compound according to structure (II).

[0019] In one embodiment, the compound according to structure (II) may have a dipole moment of at least 3.0 debye, or at least 3.5 debye, or at least 3.6 debye, or at least 3.7 debye, or at least 3.8 debye, or at least 3.9 debye, or at least 4.0 debye. MeOx (3- methyloxazolidin-2-one) has a dipole moment of about 4.13 and DMI (1,3- dimethylimidazolidin-2-one) has a dipole moment of about 4.05. The skilled person would be aware of suitable dipole moment values for the compound according to structure (II), so that it may suitably act as a solvent in the reaction.

[0020] Step 2) involves adding carbon dioxide to the mixture and reacting the mixture to obtain a product comprising a compound according to structure (II).

[0021] There is a relationship between the compound according to structure (I) and the compound according to structure (II). Specifically, when the compound according to structure (I) reacts with carbon dioxide, a compound according to structure (II) is formed as the product. Accordingly, the groups Ri to Rs in structures (I) and (II) correspond to one another. That is, if R2 is hydrogen in structure (I), R2 must be hydrogen in structure (II). The same applies to each of Ri to Rs. Moreover, Xi and X2 correspond to one another, such that if Xi is -OH, X2 must be -O- and if Xi is NHRs, X2 must be -NRs.

[0022] In structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is selected from 0, 1, 2 and 3; in both structures (I) and (II), Ri to Rs is each independently selected from H, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkoxy group, and a substituted or unsubstituted arylalkyl. As used herein, “alkyl group” includes both branched and linear alkyl groups.

[0023] In one embodiment, Ri to Rs is each independently selected from H, a substituted or unsubstituted alkyl group having from 1 to 20 carbon atoms, a substituted or unsubstituted aryl group having from 1 to 20 carbon atoms, a substituted orunsubstituted alkoxy group having from 1 to 20 carbon atoms, and a substituted or unsubstituted arylalkyl having from 1 to 20 carbon atoms.

[0024] In one embodiment, Ri may be a substituted or unsubstituted alkyl group having from 1 to 20 carbon atoms. In one embodiment, Ri is a substituted or unsubstituted alkyl group containing from 1 to 5 carbon atoms. In a preferred embodiment, Ri is -CH3, - CH2CH3, -CH2CH2CH3, -CH(CH3)2or -CH2CH2OH. In a most preferred embodiment, Ri is -CH3.

[0025] In one embodiment, R2 to R7 are each independently hydrogen or a substituted or unsubstituted alkyl group having from 1 to 20 carbon atoms. In one embodiment, R2 to R7 are each independently hydrogen or a substituted or unsubstituted alkyl group having from 1 to 5 carbon atoms. In one embodiment, R2 to R7 are each independently hydrogen or a substituted or unsubstituted alkyl group having from 1 to 3 carbon atoms. In one embodiment, R2 to R7 are each hydrogen.

[0026] In one embodiment, Rs may be a substituted or unsubstituted alkyl group having from 1 to 20 carbon atoms. In one embodiment, Rs is a substituted or unsubstituted alkyl group containing from 1 to 5 carbon atoms. In a preferred embodiment, Rs is -CH3, - CH2CH3, -CH2CH2CH3 or -CH(CH3)2. In a most preferred embodiment, Rs is -CH3.

[0027] In one embodiment, n is 0 or 1. In a preferred embodiment, n is 0.

[0028] When Xi is -OH and X2 is -O-, a cyclic urethane compound is present. When Xi is - NHRs and X2 is -NRs-, a cyclic urea compound is present.

[0029] In one embodiment, Ri is a substituted or unsubstituted alkyl group having from 1 to 3 carbon atoms; R2 to R7 are each independently hydrogen or a substituted or unsubstituted alkyl group having from 1 to 3 carbon atoms; Rs is - a substituted or unsubstituted alkyl group having from 1 to 3 carbon atoms; and n is 0 or 1. When the substituents of the compound according to structure (II) are defined in this way, the compound is a commercially useful chemical and is an excellent solvent for the corresponding reactant according to structure (I).

[0030] In one embodiment, Ri and Rs (if present) are -CH3; R2 to R7 are each hydrogen; and n is 0. When the substituents of the compound according to structure (II) are defined in this way, the compound is a commercially useful chemical and is an excellent solvent for the corresponding reactant according to structure (I).

[0031] In one embodiment, the weight ratio of reactant to solvent in step 1) is from about 20:80 to about 1 :99, or from about 17:83 to about 3:97, or from about 15:80 to about 5:95, or from about 12:88 to about 8:92, or preferably about 10:90.

[0032] In one embodiment, step 1) further comprises adding a catalyst to the mixture. A catalyst should assist the reaction between carbon dioxide and the compound according to structure (I). The catalyst is not particularly limited and any known catalyst in the art which works for such a reaction can be used. In one embodiment, the catalyst is a cerium-based catalyst, and is preferably cerium oxide (CeCh). The skilled person would know the amount of catalyst to use to obtain the desired outcome. In one embodiment, the mole ratio of catalyst to reactant is from about 0.01 : 1 to about 0.5: 1, or from about 0.05: 1 to about 0.25: 1, or from about 0.07: 1 to about 0.15: 1, or from about 0.075: 1 to about 0.125: 1, or from about 0.09: 1 to about 0.11 : 1, or from about 0.1 : 1.

[0033] In one embodiment, the reaction in step 2) occurs at a temperature suitable for the reaction to occur. For example, the temperature in step 2) may be from about 100°C to about 200°C, or from about 110°C to about 190°C, or from about 120°C to about 180°C, or from about 130°C to about 170°C, or from about 140°C to about 160°C, or from about 145°C to about 155°C, or about 155°C.

[0034] In one embodiment, the reaction in step 2) occurs for a time period suitable to obtain the desired conversion of reactant to product. For example, the reaction in step 2) may occur for a time period of about 1 hour to about 10 hours, or from about 1 hour to about 9 hours, or from about 1 hour to about 8 hours, or from about 1 hour to about 7 hours, or from about 2 hours to about 6 hours, or from about 3 hours to about 5 hours, or about 4 hours.

[0035] In one embodiment, in step 2), the reaction is carried out in any suitable reactor vessel. In one embodiment, the carbon dioxide is added to the mixture in step 2) at room temperature until a pressure of from about 10 bar to about 100 bar, or from about 20 bar to about 90 bar, or from about 20 bar to about 80 bar, or from about 25 bar to about 75 bar, or from about 30 bar to about 70 bar, or from about 35 bar to about 65 bar, or from about 40 bar to about 60 bar, or from about 45 bar to about 55 bar, is reached in the reactor.

[0036] In one embodiment, the method further comprises step 3) removing a portion of the product comprising a compound according to structure (II) to form a remaining stream, and reusing the remaining stream in step 1). The removing a portion of the product may involve removing the crude product mixture to another vessel and purifying the crude product mixture (e.g. by distillation) to obtain a portion of the product and the remaining stream. Reusing of the remaining stream may involve recirculating the remaining stream back to the reactor. In one embodiment, a continuous process may be carriedout, involving step 1) and step 2) followed by step 3). During the continuous process, water may be removed.

[0037] In one embodiment, the conversion of the reactant to product is above about 80%, or above about 90%, or above about 95%, or above about 98%, or above about 99%. In one embodiment, the selectivity of the reaction to form the product is above about 80%, or above about 90%, or above about 95%, or above about 98%, or above about 99%. The conversion and selectivity may be analysed by gas chromatography, as is standard in the art.

[0038] Non-limiting embodiments

[0039] In an embodiment of the present disclosure, there is provided a method of synthesising a cyclic urethane compound or cyclic urea compound, the method comprising: step 1) mixing a reactant comprising a compound according to structure (I) with a solvent comprising a compound according to structure (II) to form a mixture, and step 2) adding carbon dioxide to the mixture and reacting the mixture to obtain a product comprising a compound according to structure (II), wherein the compound according to structure (II) is a cyclic urethane compound or cyclic urea compound: structure (I):structure (II):wherein, in structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is 0 or 1; in both structures (I) and (II), Ri to Rs is each independently selected from H and a substituted or unsubstituted alkyl group havingfrom 1 to 5 carbon atoms, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure.

[0040] In an embodiment of the present disclosure, there is provided a method of synthesising a cyclic urethane compound or cyclic urea compound, the method comprising: step 1) mixing a reactant comprising a compound according to structure (I) with a solvent comprising a compound according to structure (II) to form a mixture, and step 2) adding carbon dioxide to the mixture and reacting the mixture to obtain a product comprising a compound according to structure (II), wherein the compound according to structure (II) is a cyclic urethane compound or cyclic urea compound: structure (I):structure (II):wherein, in structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is 0; in both structures (I) and (II), Ri and Rs is each independently selected from a substituted or unsubstituted alkyl group having from 1 to 5 carbon atoms; R2 to R7 is each hydrogen, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure.

[0041] In an embodiment of the present disclosure, there is provided a method of synthesising a cyclic urethane compound or cyclic urea compound, the method comprising: step 1) mixing a reactant consisting of a compound according to structure (I) with a solvent consisting of a compound according to structure (II) to form a mixture, and step 2) adding carbon dioxide to the mixture and reacting the mixture to obtain a productcomprising a compound according to structure (II), wherein the compound according to structure (II) is a cyclic urethane compound or cyclic urea compound: structure (I):structure (II):wherein, in structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is 0; in both structures (I) and (II), Ri and Rs is each independently selected from a substituted or unsubstituted alkyl group having from 1 to 5 carbon atoms; R2 to R7 is each hydrogen, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure.

[0042] In an embodiment of the present disclosure, there is provided a method of synthesising a cyclic urethane compound or cyclic urea compound, the method comprising: step 1) mixing a reactant consisting of a compound according to structure (I) and a catalyst of cerium oxide with a solvent consisting of a compound according to structure (II) to form a mixture, and step 2) adding carbon dioxide to the mixture and reacting the mixture to obtain a product comprising a compound according to structure (II), wherein the compound according to structure (II) is a cyclic urethane compound or cyclic urea compound: structure (I):structure (II):wherein, in structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is 0; in both structures (I) and (II), Ri and Rs is each -CH3; R2 to R7 is each hydrogen, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure.

[0043] In an embodiment of the present disclosure, there is provided a method of synthesising a cyclic urethane compound or cyclic urea compound, the method comprising: step 1) mixing a reactant consisting of a compound according to structure (I) and a catalyst of cerium oxide with a solvent consisting of a compound according to structure (II) to form a mixture, and step 2) adding carbon dioxide to the mixture and reacting the mixture to obtain a product comprising a compound according to structure (II), wherein the compound according to structure (II) is a cyclic urethane compound or cyclic urea compound: structure (I):structure (II):wherein, in structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is 0; in both structures (I) and (II), Ri and Rs is each -CH3; R2 to R7 is each hydrogen, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure, and wherein the weight ratio of reactant to solvent in step 1) is from about 15:85 to about 5:95.

[0044] Examples

[0045] The present disclosure will be described in more detail with reference to the Examples. The present disclosure is not limited to the following Examples.

[0046] Example 1: Synthesis of 3-methyloxazolidin-2-one (MeOx)

[0047] 180 g of 3-methyloxazolidin-2-one (MeOx, commercially available from Huntsman Corporation) and 20 g of 2-(methylamino)ethan-l-ol (MMEA, commercially available from Huntsman Corporation) were mixed and charged to a stainless steel autoclave equipped with a hollow shaft stirrer. 4.5 g of CeCh (available from PIDC) were then charged to the reactor. The reactor was sealed and inertized by 3 x 5 bar cycles of nitrogen. The head space of the autoclave containing nitrogen was then replaced with CO2 by 3 x 5 bar cycles CO2. Then, CO2 was purged into the reactor at room temperature until the pressure reached approximately 50 bar. Afterwards, the stirrer speed was increased to 1000 rpm and the mixture was stirred at a temperature of 150°C for 4 hours (4 hours from the moment it reached 150°C). After 4 hours, the reactor was cooled down and depressurized, the catalyst filtered over a Nutsche filter and the filtrate collected for analysis by gas chromatography. The analysis showed 90% conversion of MMEA and greater than 95% selectivity towards 3-methyloxazolidin-2-one (MeOx) formation. 85% yield of MeOx.

[0048] The reaction scheme above is representative of Example 1.

[0049] Example 2: Synthesis of l,3-dimethylimidazolidin-2-one (DMI)

[0050] 180 g of l,3-dimethylimidazolidin-2-one (DMI, commercially available from TCI Chemicals) and 20 g of N,N’ -dimethylethane- 1,2-diamine (DMEDA, commercially available from TCI Chemicals) were mixed and charged to a stainless steel autoclave equipped with a hollow shaft stirrer. 3.9 g of CeCh (available from PIDC) were then charged to the reactor. The reactor was sealed and inertized by 3 x 5 bar cycles of nitrogen. The head space of the autoclave containing nitrogen was then replaced with CO2 by 3 x 5 bar cycles CO2. Then, CO2 was purged into the reactor at room temperature until the pressure reached approximately 50 bar. Afterwards, the stirrer speed was increased to 1000 rpm and the mixture was stirred at a temperature of 150°C for 4 hours (4 hours from the moment it reached 150°C). After 4 hours, the reactor was cooled down and depressurized, the catalyst filtered over a Nutsche filter and the filtrate collected for analysis by gas chromatography. The analysis showed 99% conversion of DMEDA and greater than 99% selectivity towards DMEU formation. 98% yield of DMI.

[0051] The reaction scheme above is representative of Example 2.

[0052] All ranges described herein are exemplary in nature and include any and all values in between. The terms “substantially”, “approximately” and “about” used herein are interchangeable and refer to a measurement that includes the stated measurement and any measurements reasonably close to the stated measurement. Measurements that are reasonably close to the stated measurement deviate from the stated measurement by a reasonably small amount as understood and readily ascertained by individuals having ordinary skill in the relevant art. Such deviations may be attributable to measurement error, differences in measurement and / or manufacturing equipment calibrations, human error in reading and / or setting measurements, minor adjustments made to optimize performance and / or structural parameters in view of differences in measurement associated with other components, particular implementation scenarios, imprecise adjustment and / or manipulation of objects by a person or machine. In the event it is determined that individuals having ordinary skill in the relevant art would not readily ascertain values for such reasonably small differences, the terms “about” and “approximately” can be understood to mean plus or minus 10% of the stated value.

[0053] Throughout the description and claims, the terms take the meanings explicitly defined herein, unless the context clearly dictates otherwise.

[0054] The phrases “in one embodiment”, “in an embodiment” and “in some embodiments” etc. as used herein do not necessarily refer to the same embodiment s), though they may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, though they may. All embodiments of the present disclosure are intended to be combinable.

[0055] The terms “comprises” and “comprising” mean to include but not limited to, such that further features may be present. The terms may also mean to consist of or consist essentially of.

[0056] All references and test methods cited herein are incorporated by reference in their entireties.

Claims

CLAIMS1. A method of synthesising a cyclic urethane compound or cyclic urea compound, the method comprising: step 1) mixing a reactant comprising a compound according to structure (I) with a solvent comprising a compound according to structure (II) to form a mixture, and step 2) adding carbon dioxide to the mixture and reacting the mixture to obtain a product comprising a compound according to structure (II), wherein the compound according to structure (II) is a cyclic urethane compound or cyclic urea compound: structure (I):structure (II):wherein, in structure (I), Xi is -OH or -NHRs; in structure (II), X2 is -O- or -NRs-; in both structures (I) and (II), n is selected from 0, 1, 2 and 3; in both structures (I) and (II), Ri to Rs is each independently selected from H, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkoxy group, and a substituted or unsubstituted arylalkyl, and wherein the compound according to structure (II) in the solvent and the product has the same chemical structure.

2. A method according to Claim 1, wherein the weight ratio of reactant to solvent in step 1) is from about 20:80 to about 1 :99, preferably from about 15:80 to about 5:95, most preferably about 10:90.

3. A method according to Claim 1 or Claim 2, wherein the solvent consists of a compound according to structure (II).

4. A method according to any preceding claim, wherein, in structures (I) and (II), n is 0.

5. A method according to any preceding claim, wherein, in structures (I) and (II), Ri is a substituted or unsubstituted alkyl group containing from 1 to 5 carbon atoms, preferably -CH3.

6. A method according to any preceding claim, wherein, in structures (I) and (II), Rs is a substituted or unsubstituted alkyl group containing from 1 to 5 carbon atoms, preferably -CH3.

7. A method according to any preceding claim, wherein, in structures (I) and (II), R2 to R7 are each H.

8. A method according to any preceding claim, wherein the reaction in step 2) occurs at a temperature of from about 120°C to about 180°C, preferably about 140°C to about 160°C.

9. A method according to any preceding claim, wherein the reaction in step 2) occurs for a time period of about 2 hours to about 6 hours.

10. A method according to any preceding claim, wherein step 1) further comprises adding a catalyst to the mixture, preferably wherein the catalyst is cerium oxide.

11. A method according to Claim 10, wherein the mole ratio of catalyst to reactant is from about 0.01 : 1 to about 0.5: 1, preferably about 0.1 : 1.

12. A method according to any preceding claim, wherein in step 2) the reaction is carried out in a reactor, and carbon dioxide is added to the mixture in step 2) at room temperature until a pressure of about 25 bar to about 75 bar is reached in the reactor.

13. A method according to any preceding claim, wherein the conversion of the reactant to product is above about 90% and / or wherein the selectivity of the reaction to form the product is above about 90%.

14. A method according to any preceding claim, wherein the method further comprises step 3) removing a portion of the product comprising a compound according to structure (II) to form a remaining stream, and reusing the remaining stream in step 1).

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