A process for synthesizing tetrahydrofuran-2,5-dicarboxylic acid (THFDCA), the process comprising: (a) ring closing to form a ring compound; and (b) oxidizing using a catalyst comprising platinum and bismuth to form an acid mixture; wherein step (a) may be performed before or after step (b); wherein when step (a) is performed before step (b), then step (a) comprises contacting 1,2,5,6-hexanetetrol with an acid for a time sufficient to form the ring compound, wherein the formed ring compound is tetrahydrofuran dimethanol; and step (b) comprises oxidizing the tetrahydrofuran dimethanol formed in step (a) while the tetrahydrofuran dimethanol is in contact with the catalyst such that an acid mixture is formed comprising at least one of THFDCA or 2,5-anhydro-3,4-dideoxy-hexanoic acid, and when 2,5-anhydro-3,4-dideoxy-hexanoic acid is formed as part of the acid mixture, i) recovering the 2,5-anhydro-3,4-dideoxy-hexanoic acid from the acid mixture, ii) recovering the 2,5-anhydro-3,4-dideoxy-hexanoic acid from the acid mixture and oxidizing the same while in contact with a catalyst comprising platinum and bismuth to form THFDCA, or iii) oxidizing the 2,5-anhydro-3,4-dideoxy-hexanoic acid in the acid mixture while in contact with the catalyst used in step b) to form additional THFDCA; wherein when step (b) is performed before step (a), then step (b) comprises oxidizing 1,2,5,6-hexanetetrol while the HTO is in contact with the catalyst such that an acid mixture comprising 2,5-dihydroxyadipic acid and 2-hydroxyglutaric acid is formed, wherein more 2,5-dihydroxyadipic acid is formed than 2-hydroxyglutaric acid; and step (a) comprises contacting 2,5-dihydroxyadipic acid formed in step (b) with an acid other than 2,5-dihydroxyadipic acid for a time sufficient to form the ring compound, wherein the formed ring compound is THFDCA. (a) ring closing to form a ring compound; and (b) oxidizing using a catalyst comprising platinum and bismuth to form an acid mixture; wherein step (a) may be performed before or after step (b); wherein when step (a) is performed before step (b), then step (a) comprises contacting 1,2,5,6-hexanetetrol with an acid for a time sufficient to form the ring compound, wherein the formed ring compound is tetrahydrofuran dimethanol; and step (b) comprises oxidizing the tetrahydrofuran dimethanol formed in step (a) while the tetrahydrofuran dimethanol is in contact with the catalyst such that an acid mixture is formed comprising at least one of THFDCA or 2,5-anhydro-3,4-dideoxy-hexanoic acid, and when 2,5-anhydro-3,4-dideoxy-hexanoic acid is formed as part of the acid mixture, i) recovering the 2,5-anhydro-3,4-dideoxy-hexanoic acid from the acid mixture, ii) recovering the 2,5-anhydro-3,4-dideoxy-hexanoic acid from the acid mixture and oxidizing the same while in contact with a catalyst comprising platinum and bismuth to form THFDCA, or iii) oxidizing the 2,5-anhydro-3,4-dideoxy-hexanoic acid in the acid mixture while in contact with the catalyst used in step b) to form additional THFDCA; wherein when step (b) is performed before step (a), then step (b) comprises oxidizing 1,2,5,6-hexanetetrol while the HTO is in contact with the catalyst such that an acid mixture comprising 2,5-dihydroxyadipic acid and 2-hydroxyglutaric acid is formed, wherein more 2,5-dihydroxyadipic acid is formed than 2-hydroxyglutaric acid; and step (a) comprises contacting 2,5-dihydroxyadipic acid formed in step (b) with an acid other than 2,5-dihydroxyadipic acid for a time sufficient to form the ring compound, wherein the formed ring compound is THFDCA. wherein step (a) may be performed before or after step (b); wherein when step (a) is performed before step (b), then step (a) comprises contacting 1,2,5,6-hexanetetrol with an acid for a time sufficient to form the ring compound, wherein the formed ring compound is tetrahydrofuran dimethanol; and step (b) comprises oxidizing the tetrahydrofuran dimethanol formed in step (a) while the tetrahydrofuran dimethanol is in contact with the catalyst such that an acid mixture is formed comprising at least one of THFDCA or 2,5-anhydro-3,4-dideoxy-hexanoic acid, and when 2,5-anhydro-3,4-dideoxy-hexanoic acid is formed as part of the acid mixture, i) recovering the 2,5-anhydro-3,4-dideoxy-hexanoic acid from the acid mixture, ii) recovering the 2,5-anhydro-3,4-dideoxy-hexanoic acid from the acid mixture and oxidizing the same while in contact with a catalyst comprising platinum and bismuth to form THFDCA, or iii) oxidizing the 2,5-anhydro-3,4-dideoxy-hexanoic acid in the acid mixture while in contact with the catalyst used in step b) to form additional THFDCA; wherein when step (b) is performed before step (a), then step (b) comprises oxidizing 1,2,5,6-hexanetetrol while the HTO is in contact with the catalyst such that an acid mixture comprising 2,5-dihydroxyadipic acid and 2-hydroxyglutaric acid is formed, wherein more 2,5-dihydroxyadipic acid is formed than 2-hydroxyglutaric acid; and step (a) comprises contacting 2,5-dihydroxyadipic acid formed in step (b) with an acid other than 2,5-dihydroxyadipic acid for a time sufficient to form the ring compound, wherein the formed ring compound is THFDCA.