Furfuryl alcohol condensation reactions

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

In conclusion, the self-condensation of 2-furaldehyde promoted by heat occurs with the formation of di- and trifurylic intermediates. The functionality of the growing chain increases after each oligomerization step until gelation and precipitation of the resin occurs. Thus, the process is non-linear from the onset since the condensation product 4 possesses three sites for further attack, namely the free C-5 position and the two formyl groups. It is interestering to note that while the polycondensation of 2-furfuryl alcohol is essentially linear and cross-linking is due to side reactions, the thermal resinification of 2-furaldehyde is intrinsically non-linear and gel formation occurs at earlier conversions. 

SF4 (31 mmol) was condensed into a glass reaction tube containing furfuryl alcohol or 2-phcnylcthunol (31 mmol), Ft3N or pyridine (31 mmol), and cyclohexane (5 mL) at —196 C and the tube sealed. Reaction occurred on warming to —50 C within 5 min to give two layers. Separation of the brown bottom layer by GC gave pure product. 

An interesting group of composite membranes with very good properties is produced by condensation of furfuryl alcohol with sulfuric acid. The first membrane of this type was made by Cadotte at North Star Research and was known as the NS200 membrane [32], These membranes are not made by the interfacial composite process rather a polysulfone microporous support membrane is contacted first with an aqueous solution of furfuryl alcohol and then with sulfuric acid. The coated support is then heated to 140 °C. The furfuryl alcohol forms a polymerized, crosslinked layer on the polysulfone support the membrane is completely black. The chemistry of condensation and reaction is complex, but a possible polymerization scheme is shown in Figure 5.10. 

However, the most important furan resins are those produced with 2-furfuryl alcohol, for example, the 2-furfuryl alcohol-formaldehyde-based resins, which are normally synthesized by a condensation reaction catalyzed by acidic sites and promoted by heat [224] or the poly(furfuryl alcohol) thermosetting resin that is usually synthesized by the cationic condensation of its monomer 2-furfuryl alcohol, which polymerizes exothermically in the presence of a catalyst such as acid and iodine in methylene chloride, producing black, amorphous, and branched and/or cross-linked structures [225],... 

Some polymers containing heterocycles can be included in resins following further condensation. This is possible, for example, for poly(furfuryl alcohol), which can condense with formaldehyde, phenol, melamine and urea. Furfuryl alcohol-formaldehyde copolymer can be synthesized in the reaction of furfuryl alcohol with formaldehyde in the presence of oxalic acid as catalyst. 

A major development in the use of tannins in macromolecular materials has taken place in the last few years and again this original contribution comes from Pizzi s laboratory. Condensed tannins were found to crosslink in polycondensation reactions with furfuryl alcohol and small amounts of formaldehyde, thus... 

Furaldehyde is a colourless, poisonous, water-soluble liquid, bp 162°C, which slowly turns brown in air. Like benzaldehyde, it undergoes the Cannizzaro reaction, the Perkin reaction, the Knoevenagel condensation and the acyloin condensation. The catalytic hydrogenation of 2-furaldehyde yields 2-(hydroxymethyl)oxolane 23 (tetrahydro-2-furfuryl alcohol). This compound undergoes a nucleophilic 1,2-rearrangement to give 3,4-dihydro-2/7-pyran 24 by the action of acid catalysts ... 

The Brimble group reported the synthesis of acortatarin A 20 in 2012. As in the first synthesis of acortatarin A 20 by Sudhakar et al. a traditional acid-catalyzed dehydrative spiroketalization was used as one of the final steps. However, instead of performing the previously used disconnection between CIO and N9, as several other groups have reporteda Maillard-type condensation reaction between amino alcohol 50 and the sugar surrogate 51 would be used to give 49. The amine 50 would come from D-mannitol and 51 would be prepared from furfuryl alcohol on a gram scale (Scheme l )" ... 

The principles of forming furan polymers from the condensation of furfuryl alcohol have become attractive for modifying wood, when ways of controlling the polymerization in dilute systems were discovered. There are several competing reactions condensation and cross-linking reactions of furfuryl alcohol with itself and also the reaction between furfuryl alcohol and lignin units is supposed (Scheme 9.4.10). ... 

Thermal properties can also be influenced by a furan ring in the para position of a phenolic ring. A phenolic novolac was prepared by reaction of phenol with methanal using oxalic acid as catalyst, and the furfuryl alcohol was added in a proportion of 0.5 mole furfuryl alcohol per mole phenol. The reaction steps in Scheme 11 show that the condensation of furfuryl alcohol at the para position of the phenolic rings is accompanied by the self-condensation of furfuryl alcohol. 

Synonyms include Furyl Carbinol, 2-Hydroxy Methyl Furan, 2-Furan Methanol, Furfuryl alcohol resin. Furan resin, FA resin, Poly(furfuryl alcohol). Prepolymers of FA. It is a raw material for organic synthesis, producing levulic acid, resin of various furane kinds in different properties, furfuryl alcohol urea formal resin and phenolic resin. It is a fine solvent for furane resin and oil varnish and pigment as well as used in rocket fuel. It is also used in the production of synthetic fibers, rubber, agricultural chemicals and foundry products. Furfuryl alcohol resins are derivatives of agricultural waste products and complex polymers that are formed in a condensation reaction that occurs when the furfuryl alcohol is acidified. The resins have low viscosity with an odor of furfuryl alcohol. The resin systems are highly reactive and can be catalyzed using a variety of active and latent acidic catalysts. When thermoset, the resins produce polymers that are heat resistant and extremely corrosion resistant to acids, bases and solvents. 

A special case of an oxidation-reduction (redox) reaction catalysed typically by alkahs (in some cases the reaction also takes place in acidic solutions) is a Cannizzaro reaction. It occurs in aldehydes that do not have a hydrogen atom on the carbon, which means that the usual aldol condensation cannot take place. One molecule of aldehyde is oxidised with the simultaneous reduction of the second molecule and the reaction product is a mixture of acid and primary alcohol (Figure 4.68). A Cannizzaro reaction of formaldehyde yields formic acid and methanol furan-2-carbaldehyde gives rise to furan-2-carboxyHc acid (also known as 2-furoic acid or pyromucic acid) and 2-furfuryl alcohol (2-furyhnethanol or 2-hydroxymethylfuran). 

Aldehydes that lack an a-hydrogen and therefore cannot undergo an aldol condensation undergo the Cannizzaro reaction in the presence of a strong base, giving the alcohol and the corresponding carboxylic acid. Furfural in the presence of sodium hydroxide yields 72-76% furfuryl alcohol and 73-76% furoic acid upon acidifying [7]. 

N-Bromosuccinimide added during 1.5 hrs. with stirring to a mixture of tetra-hydrofurfuryl alcohol and triphenylphosphine under a reflux condenser due to the exothermic reaction, then distilled under reduced pressure tetrahydro-furfuryl bromide. Y 92%. E. E. Schweizer et al., J. Org. Chem. 34, 212 (1969). 

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