Organic solvent free 5-hydroxymethylfurfural (HMF) oxidation into 2,5-furandicarboxylic acid (FDCA) with hydrogen peroxide using quaternary ammonium octamolybdate and quaternary ammonium dectungstate was studied. Tetra-1-ethyl-3-methylimidazolium octamolybdate ([EMIM]4Mo8O26), tetra-hexadecyltrimethyl ammonium octamolybdate ([CTAB]4Mo8O26) and tetra-ethylpyridinium octamolybdate ([EPy]4Mo8O26) displayed high activity for the selective oxidation of HMF to FDCA, and the selectivity of FDCA could reach 100% with a 99.5% conversion of HMF in the presence of [EMIM]4Mo8O26. The byproduct formed in competition with FDCA was identified as the intermediate 5-hydroxymethyl-2-furan carboxylic acid (HMFCA) and 5-formyl-2-furan carboxylic acid (FFCA), and neither 2,5-diformyl furan (DFF) nor any other byproducts from the oxidative cleavage of the HMF furan ring were detected during the oxidation process, which indicated that the aldehyde group of HMF oxidizes first, followed by the oxidation of the hydroxymethyl group in this reaction system. Although the quaternary ammonium salts, such as [EMIM]Br, EPyBr and CTAB, prevented FDCA formation from the HMFCA advanced oxidation, they could eliminate the oxidative cleavage of the furan ring and improve the affinity of HMF and catalysts, to make the catalytic active centers readily accessible to HMF molecules. However, tetra-1-ethyl-3-methylimidazolium dectungstate ([EMIM]4W10O32), tetra-hexadecyltrimethyl ammonium dectungstate ([CTAB]4W10O32) and tetra-ethylpyridinium dectungstate ([EPy]4W10O32) were unfavorable for FDCA formation. The great difference in performance of quaternary ammonium octamolybdate and quaternary ammonium dectungstate in HMF oxidation with H2O2 was attributed to their different structure.

New co-polyesters of poly(butylene-co-1,4-cyclohexanedimethylene-2,5-furandicarboxylic acid) (PBCFs) were synthesized from 2,5-furandicarboxylic acid (FDCA), 1,4-butanediol (BDO) and 1,4-cyclohexanedimethanol (CHDM) via a two-step esterification–polycondensation procedure. The structure of the synthesized polymers were characterized by 1H NMR, and the characterization results revealed that the co-polymers had triad components in a random sequential structure. The average sequence length and monomer percentages in the co-polymer could be adjusted by changing the feed molar ratio of BDO to CHDM, however, the easy removal of BDO during the polycondensation procedure facilitates the formation of long chain links containing CHDM units. Co-polyester composition could be calculated from the quantitative 13C NMR spectra which are well consistent with the elemental analysis results. The incorporation of CHDM units into poly(butylene-2,5-furandicarboxylate) (PBF) can significantly influence the thermal transition behavior, thermal stability and crystallinity of PBCFs. PBCFs showed Tg monotonously increasing with CHDM content, and the characterized Tg by DSC method is consistent with the calculated value from the Fox equation. As the molar percent of CHDM unit in co-polymers increases from 20 to 70%, Tg changes from 45.7 to 74.4 °C, Tm from 140.1 to 251.9 °C and decomposition temperature from 380.6 to 388.0 °C. XRD results indicated that the crystallinity and crystal structure of the polyester was significantly changed by CHDM incorporation. When the content of CF units increases to 31%, PBC31F is almost amorphous and it is difficult to form long regular segments to form micro-crystals, and this co-polymer shows neither cold-crystallization nor melting behavior. However, multiple melting behaviors are observed in the DSC heating traces of PBC52F, PBC61F, PBC70F and PCF with a shoulder peak on the side of the main melting peak because of partial melting–recrystallization and final melting process taking place successively during the heating scan.

•Glycosidic bond hydrolysis couples with fructose dehydration to promote reaction.•1,2-Glycosidic bond was more difficult cleavage than 1,4-glycosidic bond.•Amino group plays a great role in the rate-determining step of glucose isomerization.•COOH well catalyzes sucrose hydrolysis and fructose dehydration.•Tyrosine displays the best activity in sucrose conversion to 5-HMF.In this study, the synthesis of 5-hydroxymethylfurfural (5-HMF) from sucrose was carried out in ionic liquids 1-ethyl-3-methylimidazolium bromide ([Emim]Br) catalyzed by amino acids, and tyrosine displays the best activity. Under the optimal reaction conditions, 76.0% yield of 5-HMF from sucrose was obtained at 160 °C for 4 h. The uniquely effective activity of tyrosine for sucrose conversion into 5-HMF in [Emim]Br is mainly attributed to its two types of active sites, free base NH2 and dissociated H+ sites. The former one plays a crucial role in the isomerization of glucose to fructose, and the latter one is active in the hydrolysis of sucrose into monosaccharides and dehydration of generated fructose to 5-HMF. Furthermore, the presence of acidic phenol group in tyrosine also has the synergic catalytic effect on sucrose conversion. In addition, with the use of tyrosine catalyst, other carbohydrates to form 5-HMF were also tested, and the effects of solvent, reaction temperature and reaction time on sucrose conversion into 5-HMF were investigated in detail. A possible mechanism for this catalytic process has been proposed.