Platinum fructose oxidation

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]. 

Bioelectrocatalytic properties were obtained for FDH at carbon and gold and platinum electrodes [111,113]. The catalytic oxidation current of FDH-modified carbon paste electrodes approached a maximum value at 4-0.5 V vs. Ag/AgCl. At this potential and under optimum conditions, i.e., pH 4.5, fi uctose can be measured between 0.2 and 20 mM in fi uit juices. Most importantly the fructose sensor was insensitive to ambient oxygen. 

Weygand and Bergmann investigated the oxidation of certain derivatives (known as Amadori products) of l-amino-l-deoxy-n-fructose. The oxidation of 1-deoxy-l-p-toluidino-n-fructose in 2 V ammonium hydroxide at 50° in the presence of a platinum-on-carbon catalyst led to the degradation of the compound to n-arabinonic acid, presumably according to the following sequence. 

The electrocatal3rtic oxidation of sucrose has only been the subject of a few investigations. The chemical oxidation of sucrose was firstly mentioned in the works of Bresler (1) and Usch (2). Karabinos (3) analysed the oxidation products of fructose, glucose, glucono-y-lactone and sucrose in 0.5 M NaHCOa. The author concluded that the main reaction products were CO2 and H2O. Bockris et al. (4), investigated the electrochemical oxidation of different carbohydrates at platinum electrodes for their possible use in fuel cells. They noticed that the electroactivity was better in alkaline medium than in acidic medium, and that the reactivity of the molecule decreased with increasing molecular weights. 

The catalytic oxidation of the carbohydrates in the presence of Cu(II) for the detection of sucrose, galactose, and fructose was exploited using a Teflon-coated platinum wire plated with copper as the working electrode. Therefore, the addition of copper ions in the run buffer increased the sensitivity to an order of magnitude compared to run buffer without copper. Detection limits were 1 pmol 1 ... 

The platinum oxide catalyst converts the hexitols to the corresponding aldoses and ketoses which are carried through the above series of reactions by the oxygen. Mannitol is oxidized by Pt02 to D-mannose, isolated as methyl a-mannoside in a yield of 20%. Fructose is formed simultaneously. With a platinum-activated carbon catalyst, L-sorbose has been converted to 2-keto-L-gulonic acid, 2,3-0-isopropylidene-L-sorbose to2,3-0-isopropyl-... 

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