Furfural Condensation

When furfural is added to a xylose solution, and when this mixture is then submitted to a xylose-to-furfural catalysis, the furfural yield is smaller than without the added furfural. However, a reaction of furfural with xylose can be excluded since the addition of furfural 

However, it is also possible that two furfural molecules react with an intermediate to give difurfural xylose  

according to the laws of kinetics, the overall rate of these furfural condensation reactions should be 

Although [fNT] can be taken to be proportional to the xylose concentration, there is no known experimental way to determine ka and kb explicitly. What is possible is to measure the actual yield as a function of time, xylose concentration, acidity, and temperature, for the experimental setup chosen, and to use these yield curves, together with the known pentose disappearance rate and the known furfural reslnification rate, as a graphical interpolation basis for determining the losses by the condensation reactions. Such a procedure, reported by Root, Saeman, Harris, and Neill [18], is given in an appendix chapter, but it is usually considered too complicated and too unreliable to be used for yield prognoses. 

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Furfural condenses with acetone in the presence of sodium hydroxide solution to yield 2-furfuralacetone (compare Bemalacelone, Section IV,128) ... 

Furfural condenses with acetic anhydride and potassiuiu acetate to give furylacrylic acid (compare Perkin reaction, Cinnamic Acid, Section IV, 124) ... 

Just as most other aldehydes do, furfural condenses with compounds possessing active methylene groups such as aUphatic carboxyUc esters and anhydrides, ketones, aldehydes, nitriles, and nitroparaffins. 

Cohen66 has forwarded a hypothesis to describe the observed effects in this test. Any hypothesis must account for the specificity of the reaction for desoxyribose as contrasted to ribose, the roles of tryptophan and perchloric acid in the reaction, and the shift in absorption maximum observed between the desoxyribose and furfural condensates. (This latter observation indicates that the tryptophan reaction is not due t,o... 

Crude analyses of this material indicate a furfural condensation product. 

Hot Pressing of Felted Mats. An experiment intended to identify which of thetwo mechanisms is operative was designed and executed. The approach taken was based on the argument that each mechanism requires certain cell wall components be present and that removal of all or most of the component will be detrimental to wet-strength development. The phenol-furfural condensation mechanism requires hemicellulose as a source of furfural. The thermoplasticity of lignin mechanism requires lignin. Consequently, three pulps were prepared containing ... 

It is concluded that all of the results presented above discredit the phenol-furfural condensation mechanism and that the source of wet strength in hardboards is thermoplastic-fusion of lignin concentrated on the surfaces of the fibers. 

Treatment of the monomer with an acidic catalyst leads initially to polymers of low molecular weight and ultimately to crosslinked, black, insoluble, heat-resistant resin (17). Despite their reportedly excellent properties, virtually no commercial use of such resins exists outside the Soviet Union. The structure and polymerization mechanism of these furfural-ketone polymers are described in a recent study (18). An excellent combustion-resistant resin has been reported (19) from the addition of dialkylphosphites to bis(2-furfurylidene) ketone (6). Furfural condensates with other aliphatic and aromatic ketones have been reported (20,21) to provide photo-crosslinkable resins and hypergol components. 

The phosphorylation of phenol-furfural condensate affords a cation-exchange resin with improved thermal and chemical reristance. The heat treatment of phosphonic add resins from furfural redns, phenol-resorcinol-formaldehyde resin, and polystyrene at 100-180 °C for 10-48 h shows that the furfural-based phosphonic acid resins possess higher thermal stability than those from the other two polymers. 

Poly(iso-butyl vinyl ether)-furfural condensate obtained through the condensation of furfural with poly(iso-butyl vinyl ether) in benzene medium in presence of hydrochloric acid at 50 °C on treatment with sulfuric acid yields a carboxylic acid cation-exchange resin with a capacity of 5.8 meq/g. 

The styrene-furfural condensation product on chloromethylation followed by amination with dimethylamine affords a weak-base resin having a capacity of 1.4—1.5 meq/g. The relative affinities of this resin for anions follow the sequence, COj > NOj" > SO > HCOJ > OAc for the Cl form of the resin. The operational efficiency of this resin increases with lowering the pH of the solution to be treated. 

A reaction of furfural with an intermediate of the pentose-to-furfural conversion, this reaction being commonly called furfural condensation . 

In view of this situation, it may seem surprising that in the ampoule process , without any removal of furfural, the losses are hardly greater than in the industrial processes with their huge expense for steam stripping. The explanation lies in the simple facts that at any time the loss reactions are slower than the furfural formation, and that the principal loss, which is furfural condensation, diminishes as the xylose concentration diminishes, so that it comes to a halt when all of the xylose is consumed. 

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