catalysts Article Electrochemical Incorporation of Carbon Dioxide into Fluorotoluene Derivatives under Mild Conditions Silvia Mena , Jesus Bernad and Gonzalo Guirado * Departament de Química, Universitat Autònoma de Barcelona, Campus UAB, 08193 Bellaterra, Barcelona, Spain; silvi_22-22@hotmail.com (S.M.); jesus.bernad1@gmail.com (J.B.) * Correspondence: gonzalo.guirado@uab.cat; Tel.: +34-93-581-4882 Abstract: One of the main challenges to combat climate change is to eliminate or reuse Carbon dioxide (CO2 ), the largest contributor to the greenhouse gases that cause global warming. It is also important to synthesize compounds through greener technologies in order to obtain more environmentally friendly solutions. This study describes the electrocarboxylation process of α,α,α- trifluorotoluene using different working electrodes (glassy carbon, silver and copper) and electrolytes (polar aprotic solvent and ionic liquid). Carboxylated compounds were obtained in the same way in both electrolytic medias with more than 80% conversion rates, high yields, good selectivity, and moderate efficiencies using silver and copper as cathodes in organic electrolytes and ionic liquids. Keywords: ionic liquids; electrocarboxylation; CO2 valorization; α,α,α-trifluorotoluene   1. Introduction Citation: Mena, S.; Bernad, J.; Atmospheric CO2 is the main source of carbon for life on Earth. However, even though Guirado, G. Electrochemical carbon dioxide in the Earth’s atmosphere is a trace gas compared to nitrogen (78.1%) and Incorporation of Carbon Dioxide into oxygen (20.9%), due to anthropogenic activity (fossil fuel combustion and deforestation) its Fluorotoluene Derivatives under atmospheric concentration has increased by about 43% since the beginning of industrial- Mild Conditions. Catalysts 2021, 11, ization [1]. Together with other anthropogenic gases, such as methane, CO2 is one of the 880. https://doi.org/10.3390/ greenhouse gases (GHG), and the largest contributor to global warming [2]. Renewable catal11080880 (or green) energy is a term that describes energy generated from environmentally friendly primary energy sources. Their production method does not emit by-products that can Academic Editor: Francis Verpoort have a negative impact on the environment. Renewable energies include wind, hydro- electric, geothermal, tidal, solar, and biomass energies [3]. Carbon capture and storage Received: 25 June 2021 Accepted: 20 July 2021 (CCS) strategies involve several processes and materials used to sequester CO2 and store it Published: 22 July 2021 underground long-term, e.g., in gas fields or reservoirs. Examples of strategies for CO2 capture and storage based on chemical systems are the use of aqueous amines, the most Publisher’s Note: MDPI stays neutral used of which are methanolamine (MEA) and diethanolamine (DEA), which are known with regard to jurisdictional claims in to have a high affinity for CO2 [4]. Another common method is the use of MOFs [5] (with published maps and institutional affil- high potential but with less soft conditions), microalgae [6], bacteria, and ionic liquids [7]. iations. CO2 is an abundant, low-cost, and non-flammable source of carbon, making it a C1 skeleton for building bigger molecules. Thanks to these properties, CO2 can act as a reagent, and is a very interesting component both for designing capture and utilization strategies (CCU) for obtaining chemical products and for its direct use as a solvent (supercritical Copyright: © 2021 by the authors. CO2 ). Therefore, CO2 can be used in processes where it is converted into chemicals and Licensee MDPI, Basel, Switzerland. fuels [8]. This can be achieved through carboxylation reactions in which the CO2 molecule This article is an open access article is used as a precursor for organic compounds such as carbonates, acrylates, and polymers; distributed under the terms and or reduction reactions in which C=O bonds are broken to produce chemical compounds conditions of the Creative Commons such as methane, methanol, syngas, urea, and formic acid [4,9–11]. Attribution (CC BY) license (https:// The electrochemical reduction of CO2 , in both protic and aprotic solvents, begins creativecommons.org/licenses/by/ with the formation of the radical anion CO2 − . This radical anion is highly reactive and 4.0/). evolves in different ways depending on the working conditions. The main drawback Catalysts 2021, 11, 880. https://doi.org/10.3390/catal11080880 https://www.mdpi.com/journal/catalysts Catalysts 2021, 11, x FOR PEER REVIEW 2 of 13 Catalysts 2021, 11, 880 The electrochemical reduction of CO2, in both protic and aprotic solvents, begins2with of 13 the formation of the radical anion CO2 . This radical anion is highly reactive and evolves − in different ways depending on the working conditions. The main drawback associated with the direct associated with electrochemical reduction of the direct electrochemical CO2 is that reduction of COit occurs at very high reduction 2 is that it occurs at very high potentials.potentials. reduction For example, ForCO 2 is reduced beyond −2.2 V vs. SCE in aprotic solvents [12]. example, CO2 is reduced beyond −2.2 V vs. SCE in aprotic For this reason, different catalytic solvents [12]. For this reason, different pathways for reducing catalytic pathways 2 have been established, con- COfor reducing CO2 have been cluding that radical anions of aromatic esters and nitriles established, concluding that radical anions of aromatic esters and are very selective nitriles catalysts are very that selective can produce high yields of oxalate in the electrochemical reduction catalysts that can produce high yields of oxalate in the electrochemical reduction of COof CO 2 , lowering the2, potential in which it occurs [12,13]. lowering the potential in which it occurs [12,13]. Another pathway Another pathway in in which which COCO22 can can bebe electrochemically electrochemically valorized valorized within within highly highly ap- ap- plied potentials plied potentials is is the the electrocarboxylation electrocarboxylation process. process. This This reaction reaction consists consists in in the the utilization utilization of CO22 as a reagent and carbon source for for its its incorporation incorporation in in organic organic molecules, molecules, giving giving carboxylic acids or esters with one carbon carbon elongation elongation (Scheme (Scheme 1). 1). In this case, the reagent reagent incorporating CO22 is to be functionalized by incorporating is electrochemically electrochemically activated instead of the gas. process is In general, this process is carried carried out out at at potentials potentials that that are are less less negative negative than than COCO22, allowing allowing generation of the in-situ generation of organic organic anions anions(R (R−−),), which which can can potentially potentially nucleophilically attack corresponding carboxylation carbon dioxide leading to corresponding carboxylation processes. processes. Scheme 1. Electrochemical carboxylation process. There There are are different different reports reports which which described described electrocarboxylation electrocarboxylation processed processed withwith aa lot lot of of different different substrates substrates [14,15]. [14,15]. One One ofof the the most most studied studied and and mature mature strategy strategy toto synthesize synthesize carboxylated carboxylated compounds compounds are are the the electrochemical electrochemical carboxylations carboxylations of of organic organic halides, halides, where where Gennaro et al. showed that the use of silver as a working electrode improves Gennaro et al. showed that the use of silver as a working electrode improves the process the process because because ofof the the electrocatalytic electrocatalytic properties properties of of silver silver for for C-halogen C-halogen bond bond cleavage cleavage [16–19] [16–19] oror unsaturated compounds such as ketones [20], alcohols, or unsaturated compounds such as ketones [20], alcohols, or thioethers [21]. thioethers [21]. This This pathway pathway is is an an expanding expanding track track due due to to the the associated associated working working conditions (tem- conditions (tem- perature perature and atmospheric pressure), which are more favorable and have a multitude of and atmospheric pressure), which are more favorable and have a multitude of potential applications. However, the main disadvantage of performing potential applications. However, the main disadvantage of performing electrochemical electrochemical reactions reactions isis that thatprotic proticororaprotic aprotic solvents solvents areare used, used, which which are well-known are well-known hazardous hazardous sub- substances, and supporting electrolytes are also used in high concentrations. Hence, an stances, and supporting electrolytes are also used in high concentrations. Hence, an at- attractive alternative is the use of more sustainable solvents, such as ionic liquids. These tractive alternative is the use of more sustainable solvents, such as ionic liquids. These are are defined as fluids formed basically by ions, with low fusion points (less than 100 ◦ C), defined as fluids formed basically by ions, with low fusion points (less than 100 °C), and and that have unique properties, such as viscosity, density, solubility, and hydrophobicity, that have unique properties, such as viscosity, density, solubility, and hydrophobicity, which can be modified in function of the needs required. Moreover, in the second genera- which can be modified in function of the needs required. Moreover, in the second gener- tion of ionic liquids are the room temperature ionic liquids (RTILs), which are liquids at ation of ionic liquids are the room temperature ionic liquids (RTILs), which are liquids at working conditions [22]. Hence, using electrochemistry and RTILs together is an alterna- working conditions [22]. Hence, using electrochemistry and RTILs together is an alterna- tive for creating greener electrochemical routes, substituting traditional organic solvents tive for creating greener electrochemical routes, substituting traditional organic solvents employed with other solvents that are safer and more environmentally friendly [23–25]. employed with other solvents that are safer and more environmentally friendly [23–25]. This alternative route for synthesizing carboxylic acids could be employed with This alternative route for synthesizing carboxylic acids could be employed with tri- trifluoromethylated compounds [26,27]. These are an important group in the fluoro- alkyles group, andcompounds fluoromethylated its carboxylic[26,27]. acidThese are anhas derivative important group associated in thebecause interest fluoro-alkyles it is a group, and its carboxylic acid derivative has associated interest biologically active compound. In this regard, Savéant et al. [28] studied the because it is a biologically reductive active compound. mechanism In this regard, and reactivity of C–FSavéant bonds et in al. [28] studied the reductive trifluoromethylarenes, where mechanism and the reduction reactivity of C–F bonds in trifluoromethylarenes, where the reduction leads to defluorinated products in a mechanism involving the formation of mono- and leads to defluori- nated products difluorinated in a mechanism species (Scheme 2).involving This reactionthe involves formationthe ofelimination mono- and of difluorinated spe- a fluoride anion − (F ) from a radical anion that is rapidly protonated. The difference between fluorine, bromine, and chlorine species is the greater strength of the carbon–fluorine bond. Catalysts Catalysts 2021, 11, x FOR PEER REVIEW 33 of 13 Catalysts 2021, 2021, 11, 11, xx FOR FOR PEER PEER REVIEW REVIEW 3 of of 13 13 cies cies (Scheme 2). This reaction involves the elimination of a fluoride anion (F−−−)) from a rad- Catalysts 2021, 11, 880 cies (Scheme (Scheme 2). 2). This This reaction reaction involves involves the the elimination elimination of of aa fluoride fluoride anion anion (F (F ) from from aa3 of rad- 13 rad- ical ical anion anion that that is is rapidly rapidly protonated. protonated. The The difference difference between between fluorine, fluorine, bromine, bromine, and and chlo- chlo- ical anion that is rapidly protonated. The difference between fluorine, bromine, and chlo- rine rine species is the greater strength of the carbon–fluorine bond. rine species species is is the the greater greater strength strength of of the the carbon–fluorine carbon–fluorine bond. bond. Scheme 2. Electrochemical reduction mechanism of trifluoromethylarene compounds proposed Scheme 2. Scheme 2. 2. Electrochemical Electrochemical reduction reduction mechanism of trifluoromethylarene mechanism of trifluoromethylarene compounds trifluoromethylarene compounds proposed compounds proposed proposed mechanism mechanism by by Savéant Savéant et et al. al. Reprinted with permission permission form form reference reference [28]. [28]. Copyright © 1997, 1997, mechanism mechanism by by Savéant Savéant et et al. al. Reprinted Reprinted with with permission permission form form reference reference [28]. [28]. Copyright © 1997, Copyright © 1997, American American American Chemical Chemical Society. Society. AmericanChemical ChemicalSociety. Society. The standard The standard potential potential for for the the formation formation of of the the radical radical anion anion species species increases increases from from The standard standard potential potential for for the the formation formation of of the the radical radical anion anion species species increases increases from from the the mono- mono- di- di- and and trifluorinated trifluorinated species, species, so so that that the the reduction reduction of of the the three three carbon-fluorine carbon-fluorine carbon-fluorine the mono- di- and trifluorinated species, so that the reduction of the three carbon-fluorine bonds electrons. proposed above, the bonds requires bonds requires six requires sixelectrons. six electrons. According electrons. According to According to the to the reduction the reductionmechanism reduction mechanismproposed mechanism proposedabove, proposed above,the above, the the generation generation of of different organic organic anions anions from from the the reduction reduction and and breaking breaking of of the the the C-F C-F C-F bond bond bond generation of different organic anions from the reduction and breaking of the C-F bond makes priori an electrocarboxylation on the makes it makes it possible it possible to possible to design to design aaa priori design priori an priori an electrocarboxylation an electrocarboxylation product electrocarboxylation product route product route based route based on based on the on the the electrochemical electrochemical activation of fluorinated fluorinated reagents reagents under under mild mild conditions conditions (Scheme (Scheme 3). 3). electrochemical activation activation of of fluorinated fluorinated reagents reagents under under mild mild conditions conditions (Scheme (Scheme 3).3). F F F F F F F F FF Electrochemical FFF FF FF F F Electrochemical Electrochemical F Electrocarboxylation F F F F activation Electrocarboxylation CO R-Y COOR F F activation Electrocarboxylation CO2 R-Y COOR F +++ eee activation CO22 R-Y COOR CO CO2 CO22 Scheme Scheme3. Scheme 3.Proposed 3. Proposedroute Proposed routefor route forthe for theelectrochemical the electrochemicalvalorization electrochemical valorizationof valorization of CO 22 through its electrochem- Scheme 3. Proposed route for the electrochemical valorization ofofCO CO CO through 2 through its 2 through electrochem- itsits electrochemical electrochem- ical ical incorporation incorporation in in α,α,α-trifluorotoluene α,α,α-trifluorotoluene with with an an electrocarboxylation electrocarboxylation process. process. ical incorporation incorporation in α,α,α-trifluorotoluene in α,α,α-trifluorotoluene withwith an electrocarboxylation an electrocarboxylation process. process. Thus, Thus, an an attractive attractive alternative alternative toto to conventional conventional electrochemical electrochemical solvents solvents for for carrying Thus, Thus,an anattractive attractivealternative alternative conventional to conventional electrochemical electrochemicalsolvents for carrying for carrying solvents out carrying out out these these these processes processes processes would would would be be be thebe the usethe use use of use of of ionic ionic ionicofliquids.liquids. liquids. This This strategy, strategy, This strategy, which which which would would would syner- syner- out these processes would the ionic liquids. This strategy, whichsynergistically would syner- gistically gistically combine combine electrochemistry, CO 2 valorization, and green solvents, which been has not combine combine electrochemistry, gisticallyelectrochemistry, CO CO22 valorization, CO2 valorization, electrochemistry, and and green and green solvents, valorization, solvents, which green has not solvents, which which has has not studies not been been for studies studies this kind for for of this this kind kind reagents, of of reagents, reagents, would make would would it make make possible toit it possible possible obtain to to obtain obtain carboxylic carboxylic carboxylic acids from acids acids α,α,α- been studies for this kind of reagents, would make it possible to obtain carboxylic acids from α,α,α-trifluorotoluene, trifluorotoluene, from 1 (Figure 1).111 (Figure 1). from α,α,α-trifluorotoluene, α,α,α-trifluorotoluene, (Figure (Figure 1). 1). Figure Figure 1. 1. Chart Chart of of structures. structures. Compound 11 is the reactant, reactant, whereas compounds 2-7 and D1-D2 D1-D2 are Figure 1. Figure 1. Chart Chart of structures. Compound of structures. Compound 11 is Compound is the the the reactant, iselectrolysis reactant, whereas whereas whereas compounds compounds compounds 2-7 2-7 2-7 and and and D1-D2 D1-D2 are are are products products obtained obtained after after controlled controlled potential potential electrolysis under under nitrogen nitrogen or or carbon carbon dioxide dioxide atmos- atmos- productsobtained products obtainedafter aftercontrolled controlled potential potential electrolysis electrolysis under under nitrogen nitrogen or or carbon carbon dioxide dioxide atmos- atmosphere. phere. phere. phere. Catalysts 2021, 11, x FOR PEER REVIEW 4 of 13 Catalysts 2021, 11, 880 4 of 13 2. Results and Discussion 2. Results and Discussionbehavior of α,α,α-trifluorotoluene (1) was studied in different The electrochemical The and solvents electrochemical electrodes under behavior of α,α,α-trifluorotoluene an inert atmosphere in order to(1) was studied establish in different the optimal exper- solvents and electrodes imental conditions under for the an inert optimal atmosphere in electrochemical order to capture of establish CO2. the optimal experi- mental conditions for the optimal electrochemical capture of CO2 . 2.1. Electrochemical Reduction of α,α,α-trifluorotoluene under an Inert Atmosphere 2.1. Electrochemical Reduction of α,α,α-trifluorotoluene under an Inert Atmosphere 2.1.1. Electrochemical Reduction Mechanism of α,α,α-trifluorotoluene in a Polar Aprotic 2.1.1. Electrochemical Reduction Mechanism of α,α,α-trifluorotoluene in a Polar Solvent Solvent Aprotic Cyclic voltammograms Cyclic voltammograms(CVs) (CVs)were wererecorded recorded at different scanscan at different ratesrates (from 0.10 a0.10 (from 1.0 Va s −1) using − 1 glassy carbon, GC (green line), silver, Ag (red line), and 1.0 V s ) using glassy carbon, GC (green line), silver, Ag (red line), and copper, Cu copper, Cu (black line) as working (black line) electrodes as workingunder a N2 atmosphere electrodes under a N2for a 10 mL solution atmosphere for a 10 ofmL 1 insolution N,N’-dimethyl- of 1 in formamide (DMF) using 0.10 M of tetrabutylammonium hexafluorophosphate N,N’-dimethylformamide (DMF) using 0.10 M of tetrabutylammonium hexafluorophos- (TBA PF6), Figure(TBA phate 2a. The PFsame general 6 ), Figure 2a. trend was observed The same in all cases. general trend Several subsequent was observed in all cases.irreversi- Several ble multi-electron subsequent waves irreversible (~6 electrons)waves multi-electron are shown, whose electrochemical (~6 electrons) are shown, whose parameters electrochem-are summarized ical parameters in Table 1. The use of are summarized in silver Table and copper 1. The use ofas silver a cathode and seems coppertoasintroduce a cathodea small electrocatalytic seems to introduce a small effect electrocatalytic for the reduction processes effect for theperformed in an aprotic reduction processes organic performed electrolyte [29], due to the interaction between metal cathodes and in an aprotic organic electrolyte [29], due to the interaction between metal cathodes and reduction products obtained after reduction electrochemical products obtained afterreduction and/or the electrochemical intermediates. reduction and/or the intermediates. Cyclicvoltammetry Figure 2. Cyclic voltammetry (CV) (CV) of of a 5–25 a 5–25 mMmM solution solution of 1 of 1 in DMF/0.1M in DMF/0.1M TBA PF TBA PF6rate: 6. Scan . Scan 0.3 V·s . 0.3 rate: −1 Pt: V − 1 ·s . Pt: counter electrode counter(CE), saturated electrode (CE),calomel electrode saturated calomel(SCE): reference electrode (SCE):electrode reference (RE). work- electrode ing electrode (RE). working(WE). (a) Glassy electrode (WE).carbon (GC, carbon (a) Glassy green line), (GC,Ag (red line), green line), Cu Ag (black line).Cu (red line), (b)(black Electrolysis line). monitorization through CV using with GC as a WE. (b) Electrolysis monitorization through CV using with GC as a WE. Table 1. Electrochemical parameters for a solution of 5.5–15 mM of 1 in DMF/0.1 M TBA PF6, for WE Table 1. Electrochemical parameters for a solution of 5.5–15 mM of 1 in DMF/0.1 M TBA PF6, for WE GC (d = 1 mm), Ag (d = 3 mm) and Cu (d = 3 mm). GC (d = 1 mm), Ag (d = 3 mm) and Cu (d = 3 mm). WE v (V/s) Epc (V vs. SCE) ΔEp (mV) a α WE v (V/s) Epc (V vs. SCE) ∆Ep (mV) a α 0.1 −2.72 195 0.25 0.3 0.1 −2.75−2.72 195 200 0.25 0.24 GC 0.5 0.3 −2.76−2.75 200 209 0.24 0.23 GC 0.5 −2.76 209 0.23 0.7 −2.73 197 0.24 0.7 −2.73 197 0.24 1.0 1.0 −2.76−2.76 203 203 0.24 0.24 0.1 −2.70 235 0.21 0.1 −2.70 235 0.21 0.3 −2.71 241 0.20 0.3 −2.71 241 0.20 Ag Ag 0.5 0.5 −2.75−2.75 241 241 0.20 0.20 0.7 0.7 −2.78−2.78 246 246 0.20 0.20 1.0 1.0 −2.78−2.78 253 253 0.19 0.19 0.1 0.1 −2.68−2.68 208 208 0.23 0.23 0.3 0.3 −2.69−2.69 214 214 0.22 0.22 Cu Cu 0.5 0.5 −2.69−2.69 218 218 0.22 0.22 0.7 0.7 −2.70−2.70 222 222 0.22 0.22 1.0 1.0 −2.72−2.72 231 231 0.21 0.21 a ∆E (mV) = (E − E )·1000. a ΔEpp (mV) = (E pcpc − Ep1/2 p1/2)·1000. Catalysts 2021, 11, 880 5 of 13 A controlled potential electrolysis at a potential value of ca. 0.1 V more negative than the Epc (after the first reduction wave) was performed under an inert atmosphere using either carbon graphite (instead of glassy carbon), silver, or copper cathodes. The analysis of the sample after the electrolysis showed that the analogues of α,α,α-trifluorotoluene, 2, 3, and 4 lose fluoride atoms and are hydrogenated: . Table 2 summarizes conversion rates obtained, which are determined by 1 H NMR and GC chromatography of the electro- chemical crude reactions, and the Faraday efficiency of the process (reagent converted into product in function of the charge consumed). The yield of isolated products is ca. 5% less than the conversion rate values. This result is then compared to the observed quantity of product measured through another analytical method. It is possible to see that the use of Ag and Cu instead of carbon considerably increases the efficiency of the electrochemical reaction from 50% to 80%. Besides, the electrochemical processes were monitored by cyclic voltammetry (Figure 2b). Table 2. Product distribution after control potential electrolysis of 1 in DMF/0.1 M TBA PF6 with carbon graphite, silver, and copper cathodes. Eapplied Products Conversion Cathode C·mol−1 Efficiency (V vs. SCE) Obtained Rates a 2 74 C −2.9 4.7 50% 3 26 2 50 Ag −2.9 4.0 3 50 80% 4 Traces 1 Traces Cu −2.9 3.7 2 52 80% 3 48 a Abundance of specie i /Abundance of all species (through 1 H RMN and 19 F RMN). The electrochemical reduction mechanism of 1 in DMF/0.1M TBA PF6 under inert atmosphere was fully disclosed by the combined use of the electrochemical techniques mentioned above (cyclic voltammetry and controlled potential electrolysis experiments). Hence, it is possible to propose that 1 followed the electron transfer, chemical reaction, electron transfer (ECE) mechanism. Hence, in a first electrochemical step (E) the radical anion, 1, was generated. A first order chemical reaction (C) coupled to this first electron transfer led to the loss of fluoride anion and the obtention of a fluorobenzylic radical through a C–F bond cleavage reaction. Finally, the radical was reduced to an anion at the electrode surface (E), which later protonated by reacting with the solvent or the supporting electrolyte cation (Scheme 4). This was repeated to obtain fluoromethylbenzene, 3, and toluene, 4, as reported in the literature by Savéant and coworkers. [28] The chemical stability of the electrochemically generated a fluorobenzylic anion, which acts as a nucleophile leading, and opens the door to incorporating CO2 via the nucleophile–electrophile reaction through the electrochemical reduction of 1 under CO2 atmosphere. 2.1.2. Electrochemical Reduction Mechanism of α,α,α-trifluorotoluene in Ionic Liquid Once the electrochemical behavior of 1 had been analyzed in an electrolytic media based on organic electrolytes, it was changed to a greener electrolyte. The ionic liquid selected to perform the electrochemical study was BMPyr TFSI because of its hydropho- bicity, which helps in the extraction and recycling process. Moreover, it has an associated broad electrochemical window in which it is possible to see the electrochemical processes. Figure 3 shows the cyclic voltammetry response of a solution of 1 in the IL with the three working electrodes in an inert atmosphere. Different subsequent reduction irre- versible multi-electron waves (~6 electrons) are observed between the cathodic potentials Epc = −2.8 V and Epc = −2.95 V (vs. SCE). Therefore, the same general electrochemical trend was observed when DMF was replaced by BMPyr TFSI under N2 atmosphere. Catalysts Catalysts2021, 2021,11, 11,xxFOR FORPEER PEERREVIEW REVIEW 66of of13 13 Catalysts 2021, 11, 880 6 of 13 −2.8 −2.8VVand andEpc Epc==−2.95 −2.95VV(vs. (vs.SCE). SCE).Therefore, Therefore,the thesame samegeneral generalelectrochemical electrochemicaltrend trendwas was observed when DMF was replaced by BMPyr TFSI under N2 atmosphere. observed when DMF was replaced by BMPyr TFSI under N2 atmosphere. FF FF EE FF ++ ee FF FF FF 11 FF FF C FF ++ FF C FF FF FF FF EE ++ ee FF FF FF FF ++ SH SH HH FF FF 22 Scheme Scheme 4. 4. Proposed Proposed mechanism mechanism for for the the electrochemical electrochemicalreduction electrochemical reductionof reduction ofα,α,α-trifluorotoluene. of α,α,α-trifluorotoluene. α,α,α-trifluorotoluene. 3. Cyclic voltammetry Figure 3. Figure voltammetry of 24 24 mM of of 1 in BMPyr BMPyr TFSI TFSI with with WE WE GC GC (green (green line), line), Ag Ag (red (red line), line), Figure 3.Cyclic Cyclic voltammetryofof 24mM mM of11inin BMPyr −1 .TFSI with WE GC (green line), Ag (red line), Cu Cu (black line), CE Pt and RE SCE. Scan rate: 0.3 V · s Cu(black (blackline), line),CE CEPtPtand andRE RESCE. SCE.Scan Scan rate:0.3 V·s−1.. 0.3V·s −1 The electrochemical The parameters for the electrochemical reduction of 1ofare summarized The electrochemical electrochemical parameters parameters for for the the electrochemical electrochemical reduction reduction of 11 are are summa- summa- in Table rized 3, which shows how the electron transfer is faster using the ionic liquid compared rized in Table 3, which shows how the electron transfer is faster using the ionic liquid in Table 3, which shows how the electron transfer is faster using the ionic liquid with the polar compared aprotic solvent (α value ca. 0.4 vs. ca. 0.2). It seems the solvation of 1, which comparedwith withthe thepolar polaraprotic aproticsolvent solvent(α (αvalue valuec.a.c.a.0.4 0.4vs. vs.c.a. c.a.0.2). 0.2).ItItseems seemsthe thesolvation solvation is 1, of strongly isrelated with the polarity of the electrolyte, favors the favors electron transfer process, of 1,which being which faster strongly isin strongly IL than related related in with withthe DMF/0.1M thepolarity polarity TBA PF of of . the theaelectrolyte, As electrolyte, result, the favors ionic the theelectron liquidelectron can trans- acttrans- as a fer process, being faster in IL than in DMF/0.1M 6 TBA PF 6. As a result, the ionic liquid can fer process, (co)-catalyst being faster makingmaking in IL than the electrochemicalin DMF/0.1M parameters,TBA PF 6. As a result, the ionic liquid can α and ∆Ep , higher and lowerlower in IL act actasasaa(co)-catalyst (co)-catalyst making the theelectrochemical electrochemical parameters, parameters,ααand andΔE ΔEpp,,higher higherand and lower compared in with organic electrolyte, respectively. in IL compared ILThe compared number with with organic organic electrolyte, of electrons electrolyte, was obtained respectively. respectively. by functionalizing the intensity current and normalizing with a pattern of 9-fluorenone and titanocene (well-known cathodic redox probes) in the same experimental conditions. With these data it is possible to propose the same ECE mechanism proposed above (Scheme 4) as the electrochemical mechanism for 1 in BMPyr TFSI, where compound 1 is reduced and loses its fluorine atoms in order to obtain products 2, 3, and 4. Catalysts 2021, 11, 880 7 of 13 Table 3. Electrochemical parameters for a solution of 24 mM of 1 in BMPyr TFSI, using as a working electrodes (WE): GC (d = 1 mm), Ag (d = 3 mm) and Cu (d = 3 mm). WE v (V/s) Epc (V vs. SCE) ∆Ep (mV) a α nº Electrons b 0.1 −2.86 110 0.44 7.74 0.3 −2.87 109 0.44 6.55 0.5 −2.89 102 0.47 6.53 GC 0.7 −2.91 120 0.40 6.15 1 −2.92 126 0.38 5.95 113 ± 9 0.43 6.6 ± 0.7 0.1 −2.86 99 0.49 7.66 0.3 −2.87 96 0.50 7.03 0.5 −2.88 99 0.49 6.36 Ag 0.7 −2.89 107 0.45 6.02 1 −2.90 113 0.43 5.80 103 ± 7 0.47 6.6 ± 0.8 0.1 −2.79 103 0.47 7.24 0.3 −2.80 102 0.47 7.04 0.5 −2.83 123 0.39 6.83 Cu 0.7 −2.83 124 0.39 6.04 1 −2.85 136 0.35 6.08 118 ± 14 0.41 6.6 ± 0.6 a∆Ep (mV) = (Epc − Ep1/2 )·1000. b The number of electrons was obtained by functionalizing the intensity current and normalizing with a pattern of 9-fluorenone and titanocene (well-known cathodic redox probes) in the same experimental conditions. The bold data is the average of the numbers in the column, which are above them. 2.2. Electrochemical Study of α,α,α-trifluorotoluene in a Saturated CO2 Atmosphere Before studying the electrochemical behavior of 1 in CO2 saturated solutions, it is necessary to perform an electrochemical study of CO2 with the three cathodic materials and in both electrolytes. For this reason, we prepared different CO2 solutions in DMF and IL. The concentration of CO2 in solution was determined using a thermal mass flowmeter, gravimetric methods, as well as by comparison with well-known redox probes such as 9-fluorenone and titanocene. 2.2.1. CO2 Electrochemical Reduction Mechanism in DMF/0.1M TBA PF6 and BMPyr TFSI Figure 4 shows the CO2 cyclic voltammetry in both electrolytic medias using three working electrodes. Using a carbon working electrode, it is not possible to see an electro- chemical response of CO2 reduction, only a slight rise in the intensity current (Figure 4a,b). On the contrary, when using silver (Figure 4c,d) and copper (Figure 4e,f) as working electrodes there is a new peak related to the direct reduction of CO2 on their surface. Table 4 summarizes the electrochemical parameters of the electron transfer obtained in both electrolytic medias, showing a slow irreversible electron transfer in both cases. It is important to highlight how that the nature of the cathode as well as the electrolyte shifted the reduction peak potential values, making the process energetically more favorable. The combined use of silver and copper cathodes and ILs, as catalyst and cocatalyst, allows to make lower the potential in which CO2 is reduced [23–25]. Note that the CO2 cathodic peak potential diminishes in 138 mV (with Cu) and 588 mV (with Ag) when the organic electrolyte (DMF/0.1M TBA PF6 ) is replaced by the ionic liquid (BMPyr TFSI). This can be explained by considering that the IL is a pure ion solvent, which means that the concentra- tion of the counter-cation is considerably higher in IL than in DMF solution where “only” a 0.1 M concentration of tetrabutylammonium cation is present, so the formed product (1− ) would be strongly solvated in IL being the reduction potential value of the process less negative. Catalysts 11, 880 2021,2021, Catalysts 11, x FOR PEER REVIEW 8 of 813of 13 Figure 4. Cyclic Figure voltammetry 4. Cyclic voltammetryof CO 2 saturated of CO solutions 2 saturated of DMF/0.1 solutions MM of DMF/0.1 TBATBAPFPF 6 with WE: 6 with (a)(a) WE: GC (c) GC WE (c) AgWEandAg (e) and (e) WE WE Cu. Cu.voltammograms Cyclic Cyclic voltammograms of CO2 saturated of CO2 saturated solutionssolutions of BMPyrofTFSI BMPyr with WE: TFSI (b) with WE: GC (d) Ag(b) (f)GC Cu.(d) Agrate: Scan (f) Cu. V·s−rate: 0.5Scan 1. 0.5 V·s−1. Table 4 summarizes Table 4. Electrochemical the electrochemical parameters parameters for solutions of CO of the electron transfer obtained 2 in both electrolytic medias, with the use of in both electrolytic GC, Ag, and Cu cathodes). medias, showing a slow irreversible electron transfer in both cases. It is important to highlight how that the nature of the cathode as well as the electrolyte potential ∆E a Cathode shifted Epc (V) the reduction vs. SCE peak p (mV) values, αb making the process [CO2 ] more energetically (mM) favor- able. The combined use of silverDMF/0.1M and copper cathodes TBA PF6 and ILs, as catalyst and cocatalyst, allows GC to make lower the - potential in which - CO 2 is reduced [23–25]. Note that the CO2 - - cathodic Ag peak potential diminishes in 138 −2.638 244mV (with Cu) and 0.20 588 mV (with Ag) 118 when the organic Cu electrolyte (DMF/0.1M −2.676 TBA PF6)192is replaced by the0.25 ionic liquid (BMPyr 118TFSI). This can be explained by considering that the IL BuMePyr TFSI is a pure ion solvent, which means that the concentration of the counter-cation is considerably higher in IL than in DMF solution GC - - - - whereAg “only” a 0.1 − M2.050 concentration of144tetrabutylammonium0.33 cation is present, 454 so the formed Cu product (1 −) would be strongly solvated in IL being the reduction potential value −2.538 375 0.13 454 a ∆Eof(mV) the process = (E − E less negative. ). ∆E (mV) = 47.7/α. b p pc p1/2 p Table 4. Electrochemical parameters for solutions of CO2 in both electrolytic medias, with the use 2.2.2. Electrocarboxylation of α,α,α-trifluorotoluene in DMF/0.1M TBA PF6 and of GC, Ag, and Cu cathodes). BMPyr TFSI Cathode After Epc (V) characterizing electrochemically vs. SCE COΔE 2 pin(mV) α b medias botha electrolytic [CO 2] (mM) with three working electrodes, a cyclic voltammetry study TBA DMF/0.1M of 1 wasPF6 performed in a saturated CO2 atmosphere.GC Figure 5 shows how - new electron waves - appear depending - on the working - material Agemployed. Using −2.638 a carbon working electrode, 244 the same behavior 0.20 as in 118 inert the atmosphere Cu is observed: only an −2.676 irreversible, slow multielectron 192 wave, 0.25 with a slight 118rise in the current intensity (Figure 5a,b). However, when silver or copper are used as working BuMePyr TFSI electrodes, new reduction peaks appear at Epc ~ −2.6 V (vs. SCE) in DMF/0.1 M TBA PF6 , GC - - - - which overlaps the wave related to the compound 1 reduction (Figure 5c,e). In the case Ag TFSI ionic liquid, of the BMPyr −2.050a new peak appears 144at E ~ −2.0 0.33 V (vs. SCE) with 454silver pc Cu −2.538 375 0.13 (Figure 5d) as was reported in [30] and at Epc ~ −2.5 V (vs. SCE) with copper (Figure 454 5f), a ΔEp (mV) = (Epc − Ep1/2). b ΔEp (mV) = 47.7/α. which overlaps with the wave related to compound 1 reduction. These new peaks correspond with CO2 reduction on the surface of Ag and Cu, as was2.2.2. Electrocarboxylation observed above, since both of α,α,α-trifluorotoluene electrodes catalyze theindirect DMF/0.1M TBAofPF reduction CO6 and BMPyr 2 on their TFSI surface. On the other hand, compound 1 has the same electrochemical behavior as in inert After so atmosphere, electrochemically characterizing it is possible to perform CO2 in both electrolytic the electrocarboxylation medias reactions throughwiththe three working anions electrodes, obtained a cyclic in the ECE voltammetry mechanism study proposed forof 1 was performed in a saturated CO2 α,α,α-trifluorotoluene. atmosphere. Figure 5 shows how new electron waves appear depending on the working material employed. Using a carbon working electrode, the same behavior as in the inert atmosphere is observed: only an irreversible, slow multielectron wave, with a slight rise in the current intensity (Figure 5a,b). However, when silver or copper are used as working electrodes, new reduction peaks appear at Epc~−2.6 V (vs. SCE) in DMF/0.1 M TBA PF6, which overlaps the wave related to the compound 1 reduction (Figure 5c,e). In the case of the BMPyr TFSI ionic liquid, a new peak appears at Epc~−2.0 V (vs. SCE) with silver (Figure Catalysts 2021, 11, 880 9 of 13 5d) as was reported in [30] and at Epc~−2.5 V (vs. SCE) with copper (Figure 5f), which overlaps with the wave related to compound 1 reduction. Figure Figure 5. Cyclic 5. Cyclic voltammetry voltammetry of solutions of solutions of 10–25 of 10–25 mM mM of 10.1–0.4M of 1 and and 0.1–0.4M [CO2 ][CO 2] in DMF/0.1M in DMF/0.1M TBA TBA PF PF6 using 6 using as WEas (a)WE GC,(a) (c)GC, (c) Ag Ag and (e)and Cu. (e) Cu. voltammograms Cyclic Cyclic voltammograms in BMPyr in BMPyr TFSI TFSI with WEwith (b)WE GC,(b) (d)GC, (d) Ag Ag and (f) and Cu. (f) ScanCu. Scan rate: V·s− 0.5rate: 1 . V·s−1. 0.5 So,These exhaustive control new peaks potentialwith correspond electrolysis (0.1 V more CO2 reduction on thenegative than surface of Ag the andpotential Cu, as was ofobserved the cathodic peak) above, was since performed both electrodes with solution catalyze in DMF/0.1M the 1direct reduction TBA of COPF 6 and 2 on theirBMPyr surface. TFSI On ionic liquid, the other using hand, silver and compound copper 1 has because the same higher yields electrochemical were obtained behavior as in inertin an atmos- inert atmosphere. Next, the electrolysis methyl iodide phere, so it is possible to perform the electrocarboxylation (CH I) was added to improve 3 reactions through the anions the extraction obtained process in the ECEandmechanism obtain the proposed carboxylated compounds. The electrocarboxylation for α,α,α-trifluorotoluene. processesSo, and products exhaustive obtained control are summarized potential electrolysisin(0.1 Table 5. V more negative than the potential of the cathodic peak) was performed with solution 1 in DMF/0.1M TBA PF6 and BMPyr Table 5. Products obtained after TFSI the electrochemical ionic liquid, usingcarboxylation of 1 in both silver and copper electrolytic because highermedias with three yields were different obtained in an inert cathode materials. atmosphere. Next, the electrolysis methyl iodide (CH3I) was added to improve the extrac- tion process and obtain the carboxylated DMF/0.1M TBA PF6 compounds. The electrocarboxylation processes and products obtained are summarized in Table 5. Defluorinated Carboxylated Eapplied In solutions of DMF, the main product is 5 with both working electrodes, Efficiencyobtaining Cathode C·mol−1 Products Products (V) yields c.a. 74–89% and efficiencies a c.a. 31–37% for the Electrocarboxylation electrocarboxylation a process. How- (Yield%) (Yield%) ever, although after the first C-F cleavage the majority of the product of the electrocarbox- D1 (6%) 5 (82%) Ag −2.8 ylation6.2 process is obtained, D2the(5%)obtention of D1 and D2 (in the case of Ag), 31%and 3 in the 7 (7%) case of Cu, indicates that the electrocarboxylation process competes either with the hy- 5 (70%) Cu −2.8 drogenation 4.2 and dimerization3 (26%)processes in Cu and Ag, respectively. The 37% use of ionic liq- 6 (4%) uids, BMPyr TFSI, as electrolyte favors the electrocarboxylation reaction being quantita- BuMePyr TFSI tive to the electrocarboxylation reaction when Ag or Cu are used as cathodes. This fact Eapplied can be explained by Carboxylated taking in to account the greater Efficiency Cathode C·mol − 1 Yieldstability a of the fluorobenzylic anion (V) Products as well as the higher concentration of CO2 under CO2 saturated atmosphere in the IL Electrocarboxylation Ag −2.9 [25,30].6.0Finally, it is important 5 to highlight that the use of Cu as a cathode 100% 33% increases the efficiency of the electrocarboxylation 5 reaction, whereas 31% the use of silver makes it totally Cu −2.9 6.0 selective. 56% 7 69% a Abundance if species i/Abundance of all species (through CG/MS). In solutions of DMF, the main product is 5 with both working electrodes, obtaining yields ca. 74–89% and efficiencies ca. 31–37% for the electrocarboxylation process. However, although after the first C-F cleavage the majority of the product of the electrocarboxylation process is obtained, the obtention of D1 and D2 (in the case of Ag), and 3 in the case of Cu, indicates that the electrocarboxylation process competes either with the hydrogenation and dimerization processes in Cu and Ag, respectively. The use of ionic liquids, BMPyr TFSI, as electrolyte favors the electrocarboxylation reaction being quantitative to the elec- D2 (5%) 7 (7%) 5 (70%) Cu −2.8 4.2 3 (26%) 37% 6 (4%) BuMePyr TFSI Catalysts 2021, 11, 880 Eapplied Carboxylated Efficiency10 of 13 Cathode C·mol−1 Yield a (V) Products Electrocarboxylation Ag −2.9 6.0 5 100% 33% trocarboxylation reaction6.0 5 31% when Ag or Cu are used as cathodes. This fact can be explained Cu −2.9 56% by taking in to account the greater stability7 69% of the fluorobenzylic anion as well as the a Abundance if species i/Abundance of all species (through CG/MS). higher concentration of CO2 under CO2 saturated atmosphere in the IL [25,30]. Finally, it is important to highlight that the use of Cu as a cathode increases the efficiency of the Finally, with the electrocarboxylation combined reaction, use of whereas thethe usedata obtained of silver makes after cyclicselective. it totally voltammetry and control Finally, with the combined use of the data obtained after cyclic voltammetrybyand potential electrolysis, an ECE mechanism could be proposed followed an con- elec- trocarboxylation trol processan potential electrolysis, as ECE a synthetic routecould mechanism for obtaining carboxylated be proposed followed fluorinated com- by an electrocar- pounds through, boxylation process asα,α,α-trifluorotoluene in both organic a synthetic route for obtaining and BMPyr carboxylated TFSIcompounds fluorinated electrolytes (Schemeα,α,α-trifluorotoluene through, 5). in both organic and BMPyr TFSI electrolytes (Scheme 5). Scheme5.5.Proposed Scheme Proposed mechanism mechanism forfor the the electrochemical electrochemical activation activation of α,α,α-trifluorotoluene of α,α,α-trifluorotoluene fol- followed lowed by by electrochemical electrochemical carboxylation. carboxylation. 3. Materials and Methods 3.1. Materials Carbon dioxide (CO2 ) and nitrogen (N2 ) gases were purchased from Carburos Metálicos S.A. (Cornellà de Llobregat, Barcelona, Spain), with a purity of 99.9999%. All of the commer- cially available reagents, α,α,α-trifluorotoluene, iodomethane (MeI), N,N’-dimethylformamide (DMF), and tetrabutylammonium hexafluorophosphate (TBA PF6 ) were acquired from Sigma-Aldrich (Madrid, Spain) with maximum purity and used as received. 1-butyl−1- methylpyrrolidinium bis(trifluoromethylsulphonyl)imide (BMPyr TFSI) was acquired from Solvionic (Toulouse, France) and was dried with activated molecular sieves for 24 h to guarantee that the amount of water was always less than 100 ppm. 3.2. Electrochemical Experiments A three-electrode electrochemical system in a one-compartment conical cell was used for the set-up of cyclic voltammetry (CV) and controlled potential electrolysis. The electrochemical details of those techniques have been previously described [13,19,21–25]. Catalysts 2021, 11, 880 11 of 13 When either organic electrolytes and ionic liquids are used, the current values obtained were first normalized by the concentration and the scan rate (Ip/cv1/2 ) aiming the direct comparison between the cyclic voltammograms in the different cathodes (glassy carbon, silver and copper). For the electrolysis experiments, the disc working electrodes were replaced by a graphite carbon bar and silver or copper foils. Compounds were electrolyzed at a negative potential of 0.10 V more negative than the Epc potential value under nitrogen- or carbon dioxide-saturated solutions. When the reaction was completed, a methylation agent, methyl iodide (MeI or CH3 I), was added to improve the extraction process and obtain the carboxylated compounds. The mixture was extracted in two different ways depending on the electrolyte media: when it is performed in DMF solutions, the mixture was extracted with water/ether mixtures (2:1). The organic layer was dried with Na2 SO4 and evaporated to yield a residue. However, when IL is employed, the products of the electrolyzed solution were extracted with ether, making it possible to recover almost 80% of the ILs at the end of the process, after purification [25]. The organic layer was lastly washed with water and dried with Na2 SO4 and evaporated to yield a residue. In some cases, the products were isolated using column chromatography. All residues or products obtained were dissolved in deuterated chloroform CDCl3 and characterized by proton nuclear magnetic resonance (1 H-NMR), gas chromatography (GC), and gas chromatography-mass spectroscopy (GC-MS) and compared with their respective pure commercially-available analogues. 1 H-NMR and 19 F-NMR measurements were performed in a Bruker DPX250 (250 MHz) with a Quattro Nucleus Probe (QNP) (Billerica, MA, USA). Proton Chemical shifts were reported in ppm (δ) (CDCl3 , δ = 7.26). The J values are reported in Hz. Fluor Chemical shifts were reported in ppm (δ) (CDCl3 ). GC-MS analysis were performed using an Agilent Technologies 6850 GC instrument with a 5975C detector Hewlett Packard (Santa Clara, CA, USA). PhCF3 (1): 1 H RMN (CDCl3 ) δ (ppm): 7.75–7.30 (m, 5H). 19 F RMN (CDCl3 ) δ (ppm): −63.3 (s, 3F). PhCF2 H (2): 1 H RMN (CDCl3 ) δ (ppm): 7.48–7.30 (m, 5H); 6.64 (t, J = 56,5 Hz, 1H). 19 F RMN (CDCl3 ) δ (ppm): −111.1 (s, 2F). PhCFH2 (3): 1H RMN (CDCl3 ) δ (ppm): 7.55–7.25 (m, 5H) 5.37 (d, J = 47.8 Hz, 2H). PhCH3 (4): GC-MS (70 eV): m/z (%): 92.0 (78) [M+ ]; 91.0 (100) [M+ − H]; 65.0 (12) [M+ − C2 H3 ]; 39.0 (11). 1 H RMN (CDCl3 ) δ (ppm): 7.33–7.10 (m, 5H); 2.34 (s, 3H). PhCF2 COOMe (5): GC-MS (70 eV): m/z (%): 186.0 (9) [M+ ]; 127.0 (100) [M+ − C2 H3 O2 ]; 77.0 (10) [M+ − C3 H3 O2 F2 ]; 59.0 (4) [M+ − C7 H5 F2 ]. 1 H RMN (CDCl3 ) δ (ppm): 7.65–7.40 (m, 5H); 3.87 (s, 3H). 19 F RMN (CDCl3 ) δ (ppm): −104.2 (s, 2F). PhCF(COOMe)2 (6): 1 H RMN (CDCl3 ) δ (ppm): 7.45–7.25 (m, 5H); 3,80 (s, 6H). 19 F RMN (CDCl3 ) δ (ppm): −152.5 (s, 1F). PhCHFCOOMe (7): GC-MS (70 eV): m/z (%): 168.0 (25) [M+ ]; 109.0 (100) [M+ − C2 H3 O2 ]; 89.0 (5) [M+ − C2 H4 O2 F]; 83.0 (11); 77.0 (3) [M+ − C3 H4 O2 F]; 59.0 (7) [M+ − C7H6F]. 1 H RMN (CDCl3 ) δ (ppm): 7.65 – 7.40 (m, 5H); 5.82 (d, J = 47.9 Hz, 1H); 3.87 (s, 3H). 19 F RMN (CDCl3 ) δ (ppm): −180.2 (d, 1F). PhCH2 CH2 Ph (D1): GC-MS (70 eV): m/z (%): 182.1 (25) [M+ ]; 146.0 (17); 117.0 (8); 104.0 (8); 91.0 (100) [M+ − C7 H7 ]; 73.0 (9); 65.0 (14); 43.0 (14). PhCHFCH2 Ph (D2): (70 eV): m/z (%): 200.1 (60) [M+ ]; 172.1 (17); 117.0 (20); 109.0 (100) [M − C7 H7 ]; 91.0 (66) [M+ − C7 H6 F]; 82.0 (75); 65.0 (16); 54.0 (17); 41.0 (16). + 3.3. Determination of the CO2 Concentration in Solution A thermal mass flow meter (EL-FLOW® Mass Flow Meter/Controller, (Bronkhorst Hi-Tec, Ruurlo, Netherlands) was used to control CO2 concentrations in the solution. Secondary methods have been also used for verifying the CO2 concentration values. Hence, Titanocene (E0 = −1.07 V vs. SCE) was used as a one-electron redox probe in organic electrolytes, whereas a gravimetric methodology was used as also used for validating CO2 concentrations in ionic liquids. Catalysts 2021, 11, 880 12 of 13 4. Conclusions This manuscript describes a new “environmentally-friendly” electrochemical ap- proach for producing highly valuable compounds using CO2 as a building block in ILs through the electrochemical carboxylation of trifluoromethyl aromatic derivatives. The electrochemical reduction mechanism of α,α,α-trifluorotoluene (ECE) was determined with three different working electrodes: carbon, silver, and copper; and in two different electrolyte media: DMF/0.1M TBA PF6 and BMPyr TFSI ionic liquid. It was shown that the obtention of an anionic aromatic species after C-F cleavage could be used as a nu- cleophile in an electrochemical carboxylation process. Therefore, CO2 was characterized prior in both electrolytes with all the above-mentioned cathodic materials through cyclic voltammetry. Next, a “green electrochemical” was design in organic electrolytes and ILs. α,α,α-Trifluorotoluene (PhCF3 ) was carboxylated through a control potential electrolysis in saturated CO2 solutions. We obtained quantitative electrocarboxylation yields and good efficiencies when Cu or Ag cathodes were employed in ILs. Finally, the use of Ag and ILs allow to design a fully quantitative and selective electrochemical carboxylation reaction for obtaining PhCF2 COOMe from PhCF3 COOMe in mild conditions. Author Contributions: G.G. conceived and designed the experiments; S.M. and J.B. performed the experiments and analyzed the data. S.M. and G.G. wrote the paper. Funding Acquisition, G.G. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by MINECO/FEDER (project CTQ2015-65439-R) and Ministerio de Ciencia e Innovación (PID2019-106171RB-I00) of Spain. Acknowledgments: The authors thank the Ministerio de Ciencia e Innovación of Spain for financial support though the project CTQ 2015-65439-R and PID2019-106171RB-I00. S.M. is grateful to the Universitat Autònoma de Barcelona for pre-doctoral PIF fellowships. 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