Furfural ring formation

Esters of diphenylacetic acids with derivatives of ethanol-amine show mainly the antispasmodic component of the atropine complex of biologic activities. As such they find use in treatment of the resolution of various spastic conditions such as, for example, gastrointestinal spasms. The prototype in this series, adiphenine (47), is obtained by treatment of diphenyl acetyl chloride with diethylaminoethanol. A somewhat more complex basic side chain is accessible by an interesting rearrangement. Reductive amination of furfural (42) results in reduction of the heterocyclic ring as well and formation of the aminomethyltetrahydro-furan (43). Treatment of this ether with hydrogen bromide in acetic acid leads to the hydroxypiperidine (45), possibly by the intermediacy of a carbonium ion such as 44. Acylation of the alcohol with diphenylacetyl chloride gives piperidolate (46). ... 

Ir catalysts supported on binary oxides of Ti/Si and Nb/Si were prepared and essayed for the hydrogenation of a,P-unsaturated aldehydes reactions. The results of characterization revealed that monolayers of Ti/Si and Nb/Si allow a high metal distribution with a small size crystallite of Ir. The activity test indicates that the catalytic activity of these solids is dependent on the dispersion obtained and acidity of the solids. For molecules with a ring plane such as furfural and ciimamaldehyde, the adsorption mode can iirfluence the obtained products. SMSI effect (evidenced for H2 chemisorption) favors the formation of unsaturated alcohol. 

Finally, the formation of derivatives of pyridine from 5-hydroxymethylfurfural and related compounds on treatment with ammonia 0 may be considered in this section on the furan ring. 5-Hydroxymethyl-furfural itself gives 2-hydroxymethyl-5-hydroxypyridine (XLIV) with ammonia, which is presumably formed by opening of the ring in the intermediate aldehyde-ammonia compound followed by closure to give the 6-membered ring. 

The subsequent formation of furfural from pentose involves the liberation of three molecules of water per molecule of pentose. Any such major transformation of a molecule does not take place concertedly but in steps. A plausible mechanism is illustrated in Figure 2. The initial pentose is shown in its prevalent ring form representing an intramolecular hemiac-etal. The open-chain aldehyde form in equilibrium with the ring form can be disregarded as it amounts to less than one percent of the total pentose present. The transformation steps shown consist of two 1,2-eliminations and one 1,4-elimination of water. The 1,2-eliminations must... 

Already in the thirties, copper-chromite promoted by addition of an alkaline earth oxide, was a favourite commercial catalyst for various hydrogenations. In the gas-phase hydrogenation of furfural copper catalysts have been used mainly to avoid hydrogen addition on the furan ring. However, an imdesired further reduction of the furfuryl alcohol to 2-methyl-furan can sometimes occur. Bremner et al. [9] studied in details the reaction of furfural over a number of copper catalysts. These studies showed that in the hydrogenation of furfural, high temperatures (> 300°C) or the addition of chromite to the copper catalyst favoured the formation of 2-methyl-furan, whereas low temperatures (< 200°C) or the addition of alkali-metal containing compoimds favoured the formation of furfuryl alcohol. 

Degradation of the sucrose framework Reactions or reaction cascades, including dehydration/rehydration, ring opening/closure, bond scission/ formation lead to structures being of known value from petrochemically derived compounds, but are based on the renewable feedstock sucrose, the most prominent representatives being bioethanol and 5-hydroxymethyl furfural (HMF). 

Silica gel also promotes a mild dehydrohalogenation as part of the synthesis of an important intermediate azetidinone, in the formation of the cephem ring system [81]. Fructose undergoes a catalysed dehydration to give 5-(hydroxymethyl)furfural in yields which vary depending on the reaction conditions and the catalyst used [82]. 

The ascorbic acids are weak acids as a result of the presence of the enolic groups rather than of the lactone ring 1S8, H5). They reduce Fehling solution, and the double bond is oxidized by acidic iodine solution. The reaction with iodine is used as a quantitative method to distinguish them from 2-keto acids. The action of boiling 12 % HCl causes the formation of furfural in very high yields, above 80% (see above). 

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