Synthesis Of 2,5-Furandicarboxylic Acid From 2-Furancarboxylic Acid Via Pd-Catalyzed Bromination-Hydroxycarbonylation Tandem Reaction

The bio-based 2,5-furandicarboxylic acid(2,5-FDCA)has attract much attention in recent decades due to its versatility as an important bio-based platform chemical as well as the concern to decrease the dependence on fossil feedback to produce chemicals.Synthesizing 2,5-FDCA from 2-furancarboxylic acid(furoic acid,2-FCA)via bromination-hydroxycarbonylation/alkoxycarbonylation multi-step reaction provides a novel route to produce 2,5-FDCA.Such synthesis route is composed of several reaction-steps including bromination of 2-FCA,esterification of5-bromofuran-2-carboxylicacid,alkoxycarbonylationofethyl5-bromofuran-2-carboxylate,and hydrolysis of diethyl 5-bromofuran-2-carboxylate as well as bromination of 2-FCA,and hydroxycarbonylation of5-bromofuran-2-carboxylic acid.In the involved multiple reactions,the carbonylation of2-FCAderivatives(ethyl5-bromofuran-2-carboxylateor5-bromofuran-2-carboxylic acid)is the most important step in the whole process.In this thesis,the following work was carried out for synthesizing 2,5-FDCA with 2-FCA as the starting material via significantly important carbonylation..(1)Alkoxycarbonylation for 2,5-furandicarboxylate from methyl5-bromofuran-2-carboxylate over P,N,S-hybrid ligand modified Pd-catalystsIn this part,several as-synthesized P,N,S-hybrid ligands and commercially available phosphine ligands were applied to Pd-catalyzed alkoxycarbonylation of methyl 5-bromofuran-2-carboxylate.The results showed that the presence of bidentate phosphine ligand Xantphos modified Pd(OAc)₂-catalysts improved the efficiency of the alkoxycarbonylation of methyl 5-Bromo-2-furancarboxylate dramatically.The maximum yield of dimethyl 2,5-furandicarboxylate reached 98%under 0.5 MPa CO,100?,with 1 mol%Pd(OAc)₂ in 6 hours when methanol was used dually as nucleophile and solvent.In comparison,the presence of P,N,S-hybrid ligands modified Pd-catalysts nearly shut down the reaction.The base required as the scavenger for alkoxycarbonylation of methyl 5-bromofuran-2-carboxylate had a significant effect on it.The use of base with strong nucleophilicity was found to lead to the side-reaction of aminocarbonylation.Additionally,the presence of strong base resulted in the unrequired hydrolysis of methyl 5-bromofuran-2-carboxylate.(2)One-pot synthesis of 2,5-furandicarboxylic acid from 2-furancarboxylic acid via Pd-catalyzed bromination-hydroxycarbonylation tandem reaction in HOAc-NaOAc bufferIn the Pd-catalyzed bromination-hydroxycarbonylation tandem reaction for sysnthsis of 2,5-FDCA from 2-FCA,the bromination of 2-FCA by Br₂ goes by electrophilic aromatic substitution mechanism over acid-catalyst whereas the hydroxycarbonylation of 5-bromofuran-2-carboxylic acid occurs over a phosphine-modified Pd-catalyst with presence of base(as a scavenger).Evidently,in this one-pot sequence,the acid is required for the first-step bromination and the base is required for the second-step carbonylation,which are totally conflicting conditions.The use of the buffer solution composed of HOAc and NaOAc with p H value of3.58 successfully solved the problem of such conflicting conditions in the bromination-hydroxycarbonylation tandem reaction for 2,5-FDCA from 2-FCA.And the subsequent acidification was no longer required.It was found that the Xantphos-modified Pd-catalyst and HOAc-NaOAc buffer solution played significant role for each individual reaction whereas CO(as the carbon source)was a poison for the first-step bromination,and Br₂(as the brominating reagent)had negative effect on the second-step hydroxycarbonylation.Hence,in this practical one-pot synthesis,gaseous N₂ was used in the first-step bromination,and CO(1.0 MPa)is charged in the second-step carbonylation.Br₂ should be consumed in the first-step bromination as completely as possible.Under the optimal reaction conditions(DMF as solvent,5 mol%PdCl₂,5 mol%Xantphos,2 equiv.Br₂,2.5 equiv.H₂O,0.1 MPa N₂,90?,10 hours,then 1.0 MPa CO,90?,2 hours),the maximum yield of 2,5-FDCA reached 57%.