Toward green syntheses of carboxylates: Considerations of mechanisms and reactions at the electrodes for electrocarboxylation of organohalides and alkenes

doi:10.1016/S1872-2067(22)64180-9

Abstract

Abstract:

Abstract: Electrosynthesis and carbon dioxide (CO₂) utilization both have gained interest in recent years due to the efforts to alleviate the climate crisis. Significant progress in the field of electrochemical carboxylation using CO₂ or electrocarboxylation of organic substrates, particularly organohalides and alkenes, has been made in the past decade. Different components of electrocarboxylation experimental setup as well as the understandings of the mechanism play an important role in the success of the carboxylate syntheses. In this review, overview of the proposed mechanisms and the electrochemical setup are described. The significance of electrochemical components, such as the effect of different cathodes, sacrificial anode materials, and other additives, are explained. The examples of electrocarboxylation for both organohalides and olefins are provided. Lastly, the current trends in the field and future directions are discussed.

Key words: Electrocarboxylation, CO₂ utilization, Electrosynthesis, CO₂ coupling, Electrochemical method3

Teera Chantarojsiri, Tassaneewan Soisuwan, Pornwimon Kongkiatkrai. Toward green syntheses of carboxylates: Considerations of mechanisms and reactions at the electrodes for electrocarboxylation of organohalides and alkenes[J]. Chinese Journal of Catalysis, 2022, 43(12): 3046-3061.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(22)64180-9

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Figures/Tables 22

Scheme 1. Electrocarboxylation reaction mechanisms for different substrates. R represents alkyl or aryl groups. Proposed mechanisms for alkyl or aryl halides are shown in (a)?(d). Activation of alkenes are proposed and displayed in (e)?(h), while defluorinative carboxylation mechanisms of gem-difluoroalkene and α-CF3 alkenes are listed in (i)? (l).

Fig. 1. (a) Cyclic Voltammograms of o-dibromobenzne, m-dibromobenzene, p-dibromobenze, and bromobenzene with Ag electrode in 0.1 mol/L TBABF4 DMF, showed two successive reductive processes for m-dibromobenzne and p-dibromobenze, one 2-electron reduction for o-dibromobenzene, and one 1-electron reduction for bromobenzene. (b) Schematic representation of reductive debromination with m-dibromobenzene. (c) Cyclic Voltammograms of m-dibromobenzene with Ag electrode showed current enhancement upon exposure to CO2 atmosphere, compared to when CO2 was absent and background signal. (d) Cyclic voltammograms of m-dibromobenzene with different electrodes under N2. Reproduced with permission from Ref. [9], Copyright 2012, Elsevier. (e) Cyclic voltammograms of Ni-catalyzed aryl bromide electrocarboxylation. (f) Proposed catalytic cycle of carboxylation of arylbromide, catalyzed by Ni complex. Reproduced under the terms of the CC-BY 4.0 license from Ref. [15].

Scheme 2. Electrolyses experiments of 16 mmol/L 4-fluorobenzonitrile, in 0.1 mol/L TBABF4 DMF solution under N2, demonstrated the products from the protonation and the coupling of possible radical intermediates. Ag foil was used as a working electrode with Pt counter electrode and SCE reference electrode. Reprinted with permission from Ref. [12]. Copyright 2019, Elsevier

Fig. 2. Proposed reaction pathway for defluorinative carboxylation performed at the IEFPCM-M06-2X/6-311++G(d,p) level [14]. Reprinted with permission from Ref. [14]. Copyright 2020, the Royal Society of Chemistry.

Fig. 3. Three different types of electrolysis batch cell, consisting of undivided cell, quasi-divided cell and divided cell.

Fig. 4. A chart representing a direct electrochemical process without redox mediators (left), and indirect electrochemical process with a redox mediator (right).

Fig. 5. Representative mechanism of phenyl bromide electrocarboxylation. Reductive debromination of bromobenzene yields phenyl radical that can be reduced again by the cathode to form phenyl radical anion, which can react with CO2 to form carboxylate product.

Fig. 6. Representative mechanism of benzyl bromide electrocarboxylation. Reduction of benzyl bromide generate a benzyl radical and a bromide ion. The radical proceeds to be one-electron reduced by the cathode, forming a radical anion which can react with CO2 to form the carboxylate product.

Fig. 8. Cathodic sweep of 100 mmol/L benzyl chloride, bromide, and iodide, showing the onset of reduction of each substrate by different metal cathodes. The voltammograms were recorded at 50 mV/s, under Ar atmosphere, in 0.1 TBABF4 MeCN solution. Reproduced with permission from Ref. [34], Copyright 2021, Elsevier.

Scheme 3. Recently reported electrocarboxylation of aryl and benzyl halides.

Fig. 9. Cyclic voltammogram of 4-fluorobenzonitrile in 0.1 mol/L TBABF4 DMF solution at the scan rate 500 mV/s under CO2 atmosphere. (GC: glassy carbon electrode, Ag: silver electrode), Reproduced with permission from Ref. [12], Copyright 2019, Elsevier.

Scheme 4. Electrocarboxylation of olefins and conjugated substrates which are recently reported.

Fig. 12. Proposed reaction mechanism of aryl halides (a) and allylic halides (b). M, in both cases, represents Ni, Pd, Cu, and Co. Active catalysts, generally reduced species, undergo oxidative addition with aryl halides or allylic halides (step I), before being reduced by the electrode (step II). CO2 addition occurs in step III and products are released to regain active catalysts (step IV). Ligands that were used to support metal catalysts for electrochemical carboxylation (c).

Fig. 13. DFT calculations at the PW6B95-D4/def2-TZVPP+SMD(DMF) //TPSS-D3(BJ)/def2-SVP level of theory suggested the allylic C-C bond formation as the rate determining step, due to the higher reaction barrier. Reproduced with permission from Ref. [20], Copyright 2020, Wiley.

Scheme 5. (a) Stabilization of carboxylate intermediates by Mg2+, Zn2+ and Al3+. (b) The plausible formation of Grignard type reagent. (c) The reduction of CO2 by Sm(II) and the stabilization of intermediate by Sm complex.

Fig. 15. Proposed reaction mechanism and reactions at each electrode for carboxylation of benzyl ammonium salts. Reproduced with permission from Ref [19]. Copyright 2019, the American Chemical Society

Table 1 Electrocarboxylation Conditions of Aryl Halides, Benzyl Halides, Allylic Halides, and Pseudohalides.

Substrate	Cathode (-)		Anode (+)		Electrochemical setup		Solvent			Electrolyte		Catalyst/Additive	Product			Yield (%)	Ref.
Aryl halides
Aryl bromide	Ag		Mg		undivided cell		DMF			nBu₄NI		CH₃I	methyl benzyl ester			30-78	[35]
Dibromobenzene	Ag		Mg		undivided cell		DMF			Et₄NBF₄		—	benzene dicarboxylic acid			49-71	[9]
4-Iodobenzonitrile	Ag		Ag		undivided cell		DMF			nBu₄NBF₄		—	4-cyanobenzoic acid			40-90	[12]
Aryl halides	SS		Sm		undivided Cell		DMF			nBu₄NBF₄		—	benzoic acid			42-80	[18]
Bromospiropyran	GC or Ag		Pt		undivided cell		DMF			nBu₄NPF₆		CH₃I	methyl carboxylated spiropyran			35	[37]
Benzyl halides
Benzyl chloride	Ag		Al		undivided cell		MeCN			Et₄NClO₄		—	phenylacetic acid			79-95	[38]
Benzyl halides	Pt		Pt		quasi-divided cell		DMF			nBu₄NBF₄		—	N-methyl-N-(phenylac etoxy)methylforamides			69-78	[39]
Benzyl bromide	mesoporous Ag		Mg		undivided cell		DMF			Et₄NBr		CH₃I for ester formation	methyl ester			78	[40]
4-Nitrobenzyl bromide	Cu/Pd/rGO/GCE		Pt		undivided cell		CH₃CN			nBu₄NPF₆		nanoparticles/ Pd nanoparticles/ reduced graphene oxide nanocomposite	4-nitrophenylacetic acid			76	[49]
Secondary benzyl chloride	Ag foil		Ag foil		undivided cell		bis(tri-fluoromethanesulfonyl)imide (PP13 TFSI)			bis(tri-fluoromethanesulfonyl)imide (PP13 TFSI)		—	ibuprofen			83	[36]
α-Methylbenzyl bromide	Ag		Pt		divided cell		CH₃CN (cathodic side), aqueous (anodic side)			nBu₄NI (catholyte), KHCO₃ (anolyte)		paired electrolysis	phenylacetic acid			86	[41]
Secondary benzyl halide	Sm		SS		undivided Cell		CH₃CN			nBu₄NI		Sm(II) generated pre-electrolysis	carboxylic acid			42-96	[50]
Secondary benzyl bromide	Co@Ag		Mg		undivided Cell		CH₃CN			nBu₄NI		encapsulated Co(salen) (Co@Ag)	chiral carboxylic acid			58	[44]
Substrate		Cathode (-)		Anode (+)		Electrochemical setup		Solvent	Electrolyte		Catalyst/Additive			Product	Yield (%)		Ref.
Unactivated halides
Aliphatic, benzyl, and aryl halide		Ag		Pt		undivided cell		DMF	nBu₄NBr		MgBr₂ added to prevent ester formation			carboxylic acid	41‒78		[17]
Unactivated Alkyl Bromides, Unactivated aryl halides, aryl sulfonates		C felt		C or Zn		undivided and divided cell		NMP	NaI		Ni with bpy ligands, oxidative chlorination of tolene as paired oxidation reaction, KOtBu, DMAP, MgBr₂			carboxylic acid	27‒83		[16]
Allylic halides
Allylic chloride		Ni Foam		Mg		undivided cell		DMF	nBu₄NPF₆		Co(OAc)₂ PPh₃			carboxylic acid	45‒79		[20]
Allylic chloride		Ag		Mg		undivided cell		DMF	nBu₄NI		Ni(dppm)Cl₂			carboxylic acid	43‒96		[21]
Cinnamyl chloride		Cu@Ag		Mg		undivided cell		CH₃CN	nBu₄NI		encapsulated Cu(salen) (Cu@Ag)			carboxylic acid	37‒99		[29]
Pseudo halides and others
4-nitrobenzyl phenyl thioether		GC		Pt		undivided cell		DMF	nBu₄NBF₄		—			4-aminophenyl acetic acid (from C-S cleavage)	10		[51]
Homostyrenyl acetate		Pt		Mg		undivided cell		EtOH	Et₄NOTs		Pd, DPPPh, 1,2-(bis(diphenylphosphino)benzene)			carboxylic acid with 20:1 branched to linear ratio	58‒95		[26]
Cinnamyl Aacetate		Pt		Mg		undivided cell		EtOH	Et₄NOTs		Pd, (R)-MeO-BIPHME (chiral bidentate triarylphosphine)			carboxylic acid 67% ee	55‒66		[26]
Benzal diacetate		Pt		Mg		undivided cell		DMF	nBu₄NBF₄		—			mandelic acid	61‒97		[52]
Allylic acetate		C		Mg		undivided cell		DMF	nBu₄NBF₄		Ni(bpy)₂Br₂, CH₃I and K₂CO₃			unsaturated carboxylic acid	30‒71		[43]
Primary and secondary benzylic C-N bonds in benzylammonium		C		Pt		undivided cell		DMF	nBu₄PBF₄		trimethylammonia generated in situ as sacrificial reductant			carboxylic acid	25‒87		[19]
Organic sulfones		Pt		Mg		undivided cell		DMF	nBu₄NI		triethanolamine as proton source			phenylacetic acid	73‒99		[53]
N-Boc-α-amino sulfones		Pt		Mg		undivided cell		DMF	nBu₄NBF₄		—			N-boc-α-amino acids	58‒87		[54]
Aromatic alcohol		Ni		Glassy carbon		undivided cell		CH₃CN	tetraethylammonium acetate (TEAAc)		TEMPO as the redox mediator that oxidize alcohol to ketone			α-hydroxy acid	61		[48]

Table 1 Electrocarboxylation Conditions of Aryl Halides, Benzyl Halides, Allylic Halides, and Pseudohalides.

Substrate	Cathode (-)		Anode (+)		Electrochemical setup		Solvent			Electrolyte		Catalyst/Additive	Product			Yield (%)	Ref.
Aryl halides
Aryl bromide	Ag		Mg		undivided cell		DMF			nBu₄NI		CH₃I	methyl benzyl ester			30-78	[35]
Dibromobenzene	Ag		Mg		undivided cell		DMF			Et₄NBF₄		—	benzene dicarboxylic acid			49-71	[9]
4-Iodobenzonitrile	Ag		Ag		undivided cell		DMF			nBu₄NBF₄		—	4-cyanobenzoic acid			40-90	[12]
Aryl halides	SS		Sm		undivided Cell		DMF			nBu₄NBF₄		—	benzoic acid			42-80	[18]
Bromospiropyran	GC or Ag		Pt		undivided cell		DMF			nBu₄NPF₆		CH₃I	methyl carboxylated spiropyran			35	[37]
Benzyl halides
Benzyl chloride	Ag		Al		undivided cell		MeCN			Et₄NClO₄		—	phenylacetic acid			79-95	[38]
Benzyl halides	Pt		Pt		quasi-divided cell		DMF			nBu₄NBF₄		—	N-methyl-N-(phenylac etoxy)methylforamides			69-78	[39]
Benzyl bromide	mesoporous Ag		Mg		undivided cell		DMF			Et₄NBr		CH₃I for ester formation	methyl ester			78	[40]
4-Nitrobenzyl bromide	Cu/Pd/rGO/GCE		Pt		undivided cell		CH₃CN			nBu₄NPF₆		nanoparticles/ Pd nanoparticles/ reduced graphene oxide nanocomposite	4-nitrophenylacetic acid			76	[49]
Secondary benzyl chloride	Ag foil		Ag foil		undivided cell		bis(tri-fluoromethanesulfonyl)imide (PP13 TFSI)			bis(tri-fluoromethanesulfonyl)imide (PP13 TFSI)		—	ibuprofen			83	[36]
α-Methylbenzyl bromide	Ag		Pt		divided cell		CH₃CN (cathodic side), aqueous (anodic side)			nBu₄NI (catholyte), KHCO₃ (anolyte)		paired electrolysis	phenylacetic acid			86	[41]
Secondary benzyl halide	Sm		SS		undivided Cell		CH₃CN			nBu₄NI		Sm(II) generated pre-electrolysis	carboxylic acid			42-96	[50]
Secondary benzyl bromide	Co@Ag		Mg		undivided Cell		CH₃CN			nBu₄NI		encapsulated Co(salen) (Co@Ag)	chiral carboxylic acid			58	[44]
Substrate		Cathode (-)		Anode (+)		Electrochemical setup		Solvent	Electrolyte		Catalyst/Additive			Product	Yield (%)		Ref.
Unactivated halides
Aliphatic, benzyl, and aryl halide		Ag		Pt		undivided cell		DMF	nBu₄NBr		MgBr₂ added to prevent ester formation			carboxylic acid	41‒78		[17]
Unactivated Alkyl Bromides, Unactivated aryl halides, aryl sulfonates		C felt		C or Zn		undivided and divided cell		NMP	NaI		Ni with bpy ligands, oxidative chlorination of tolene as paired oxidation reaction, KOtBu, DMAP, MgBr₂			carboxylic acid	27‒83		[16]
Allylic halides
Allylic chloride		Ni Foam		Mg		undivided cell		DMF	nBu₄NPF₆		Co(OAc)₂ PPh₃			carboxylic acid	45‒79		[20]
Allylic chloride		Ag		Mg		undivided cell		DMF	nBu₄NI		Ni(dppm)Cl₂			carboxylic acid	43‒96		[21]
Cinnamyl chloride		Cu@Ag		Mg		undivided cell		CH₃CN	nBu₄NI		encapsulated Cu(salen) (Cu@Ag)			carboxylic acid	37‒99		[29]
Pseudo halides and others
4-nitrobenzyl phenyl thioether		GC		Pt		undivided cell		DMF	nBu₄NBF₄		—			4-aminophenyl acetic acid (from C-S cleavage)	10		[51]
Homostyrenyl acetate		Pt		Mg		undivided cell		EtOH	Et₄NOTs		Pd, DPPPh, 1,2-(bis(diphenylphosphino)benzene)			carboxylic acid with 20:1 branched to linear ratio	58‒95		[26]
Cinnamyl Aacetate		Pt		Mg		undivided cell		EtOH	Et₄NOTs		Pd, (R)-MeO-BIPHME (chiral bidentate triarylphosphine)			carboxylic acid 67% ee	55‒66		[26]
Benzal diacetate		Pt		Mg		undivided cell		DMF	nBu₄NBF₄		—			mandelic acid	61‒97		[52]
Allylic acetate		C		Mg		undivided cell		DMF	nBu₄NBF₄		Ni(bpy)₂Br₂, CH₃I and K₂CO₃			unsaturated carboxylic acid	30‒71		[43]
Primary and secondary benzylic C-N bonds in benzylammonium		C		Pt		undivided cell		DMF	nBu₄PBF₄		trimethylammonia generated in situ as sacrificial reductant			carboxylic acid	25‒87		[19]
Organic sulfones		Pt		Mg		undivided cell		DMF	nBu₄NI		triethanolamine as proton source			phenylacetic acid	73‒99		[53]
N-Boc-α-amino sulfones		Pt		Mg		undivided cell		DMF	nBu₄NBF₄		—			N-boc-α-amino acids	58‒87		[54]
Aromatic alcohol		Ni		Glassy carbon		undivided cell		CH₃CN	tetraethylammonium acetate (TEAAc)		TEMPO as the redox mediator that oxidize alcohol to ketone			α-hydroxy acid	61		[48]

Table 2 Electrocarboxylation Conditions of Alkenes and Derivatives.

Substrate	Cathode (-)	Anode (+)	Electrochemical Setup	Solvent	Electrolyte	Catalysts/Additives	Product	Yield (%)	Ref.
Alkenes
Aryl substituted alkenes	Ni	Al	undivided cell	DMF	nBu₄NBr	—	dicarboxylic acid (aryl succinic acid)	50-87	[22]
Cinnamate esters	Ti	Mg	undivided cell	CH₃CN	Et₄NF₄	—	mono and dicarboxylic acids	61-77	[46,55]
Alkene and alkyl bromide	Graphite	Mg	undivided cell	DMF	nBu₄NPF₆	—	carboxylic acid	38-79	[56]
Conjugated dienes and poly aromatics
Conjugated dienes	SS	C	undivided cell	DMF	Et₄NI	triethanolamine or water as proton source	α,δ-hydrocarboxylic acid	30-60	[22]
Polycyclic aromatic hydrocarbon	Ni	Al	undivided cell	DMF	nBu₄NBr	—	trans-dicarboxylic acid	55-92	[42]
Heteroaromatics	Pt	Mg	undivided cell	DMF	nBu₄NCIO₄	—	trans-oriented 2,3-dicarboxylic acids	44-98	[13]
Styrenes
Styrene	Ni	Mg	undivided cell	DMF	nBu₄NBF₄	H₂O as proton source	β-substituted carboxylic acid (major), dicarboxylic acid (minor)	27-60	[25]
Styrene	nitrogen- coordinated single-atomic Cu catalyst	Mg	undivided cell	CH₃CN	nBu₄NBr	—	dicarboxylic acid	—	[57]
trans-Stillbene	Si Nanowires	Al	undivided cell	CH₃CN	nBu₄NBr	photoelectrochemical condition	carboxylic acid	—	[58]
α,β-Unsaturated compounds
α,β-Unsaturated ester	C	C	undivided cell	DMF	Et₄NI	triethanolamine as reductant and proton source	β-carboxylated ester	23-81	[23]
α,β-Unsaturated ketone	Si nanowires	Al	undivided cell	CH₃CN	nBu₄NBr	photoelectrochemical condition	β-carboxyketone	65-98	[59]
Fluoro-substituted alkenes
Alkene with α-CF₃ group	Pt	Pt	undivided cell	DMF	nBu₄NClO₄	—	defluoronative γ-carboxylation, vinyl acetic acid	40-83	[14]
gem-difluoroalkenes	Pt	Ni	undivided cell	DMF	nBu₄NI	—	α-fluoroacrylic acid (defluorinative carboxylation)	35-76	[15]

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