Fructose dehydration

Fourteen DFAs and some oligomers were identified in caramel obtained by thermal treatment of inufin. - Monosaccharides (glucose, fructose), dehydration products (1,6-anhydro-p-D-glucopyranose, 1,6-anhydro-p-D-glucofuranose), disaccharides (gentiobiose and isomaltose), and oligosaccharides were also found in glucose and sucrose caramel. ... 

Furan Derivatives Catalytic processes used to obtain furan derivatives from carbohydrates and the catalytic routes from furan intermediates to chemicals and polymers have been reviewed by Moreau et al. [27]. Some of the main reactions are summarized in Fig. 3.2. From fructose or carbohydrates based on fructose (sucrose, inulin), the first transformation step is dehydration to 5-hydroxy methylfur-fural (HMF). Fructose dehydration at 165 °C was performed in the presence of... 

Carlini, C., Patrono, P, Galletti, A. M. R., and Sbrana, G., Heterogeneous catalysts based on vanadyl phosphate for fructose dehydration to 5-hydroxymethyl-2-furaldehyde. Appl Catalysis A-Generul 2004,275 (l-2), 111-118. 

The interest in FDA arises from its possible application as a renewable-derived replacement for terephthalic acid in the manufacture of polyesters. A multitude of oxidation techniques has been applied to the conversion of HMF into FDA but, on account of the green aspect, platinum-catalyzed aerobic oxidation (see Fig. 8.35), which is fast and quantitative [191], is to be preferred over all other options. The deactivation of the platinum catalyst by oxygen, which is a major obstacle in large-scale applications, has been remedied by using a mixed catalyst, such as platinum-lead [192]. Integration of the latter reaction with fructose dehydration would seem attractive in view of the very limited stability of HMF, but has not yet resulted in an improved overall yield [193]. 

Fructose, one of the most common ketohexoses, readily dehydrates to afford HMF in the presence of Br0nsted acids in polar solvents. A variety of aprotic polar solvents, including DMSO, DMF, N,N-dimethylacetamide (DMA), and sulfolane, are used for these liquid-phase reaction because of the solubility of carbohydrates. A variety of solid acids, such as ion-exchange resins [156], zeolites [157, 158], metal oxides, and heteropoly acid salts, have been examined for HMF production from fructose [159,160]. Niobic acid, niobium phosphate, vanadium phosphate, sulfated zirconia, Amberlyst-15, and acid-functionalized mesoporous silicas are also found to exhibit high catalytic activity for fructose dehydration [161-167]. Moreover, soHd acid catalysts have also been examined in ionic liquids [168-175]. 

Sanda K, Rigal L, Gaset A (1992) Optimisation of the synthesis of 5-chloromethyl-2-furancarboxaldehyde from D-fructose dehydration and in-situ chlorination of 5-hydroxymethyl-2-furancarboxaldehyde. J Chem Technol Biotechnol 55 139-145... 

Armaroli, T., Busca, G., Carlini, C., et al (2000). Acid sites characterization of niobium phosphate catalysts and their activity in fructose dehydration to 5-hydroxymethyl-2-furaldehyde, J. Mol Catal, 151, pp. 233-243. 

Table 14. Yield of 5-hydroxy methyl furfural (HMF) from fructose dehydration after recycling of IL l-H-3-methyl imidazolium chloride...

We tested this reaction scheme in meat. Ten percent D-glucose was added to a beef extract and the pH was adjusted widi a 6 N hydrochloric acid or sodium hydroxide solution. Figure 4 shows the pH-dependence of M-1 and M-3 after 15 min heating at 121°C. As expected, 1,2-enolization and M-3 formation predominates below pH 4. Above pH 5 there is little M-3 formation, which explains why we never observed M-3 from heated meats (pH 5.4). There is a sharp decline in the M-1 yield above pH 10. This observation is consistent with the base-catalyzed fructose dehydration Shaw et al. investigated at pH 11.5 (45). They reported that M-1 was not formed at pH 11.5 however, if the alkalinity was not constantly maintained, M-1 was formed as the pH decreased. Similarly, when 1% D-ribose was added to the beef extract, formation of 2-furaldehyde dominated at low pH and M-2 formation became more impotant at pH above 4.5, which again explains why 2-furaldehyde was never observed in heated meats. The general reaction pathways for formation of the markers are summarized in Figure 5. 

Sucrose is unstable at temperatures albO C (320T) and thermolyzes to the brown candy that we appreciate as caramel. Caramel contains a myriad of decomposition products formed by simultaneous cleavage of sucrose to glucose and fructose, dehydrations, fragmentations (such as retroaldol additions), isomerizations through enols (apply the last three reactions to glucose and see what you get), and polymerizations. Two of the odorants that have been identified in the mixture are shown below. 

Kruger JS, Choudhary V, Nikolakis V, Vlachos DG. Elucidating the roles of zeolite H-BEA in aqueous-phase fructose dehydration and HMF rehydration. ACS Catal 2013 3 1279-91. 

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