Furfuryl alcohol condensation

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. 

A mixture of the alcohol with formic acid rapidly self-heated, then reacted violently [1], A stirred mixture with cyanoacetic acid exploded violently after application of heat [2], Contact with acids causes self-condensation of the alcohol, which may be explosively violent under unsuitable physical conditions. The general mechanism has been discussed [3], The explosion hazards associated with the use of acidic catalysts to polymerise furfuryl alcohol may be avoided by using as catalyst the condensation product of 1,3-phenylenediamine and l-chloro-2,3-epoxypropane [4], See Nitric acid Alcohols (reference 6)... 

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. 

Condensation, of paraldehyde with diethyl malonate, 32, 54 of a-phene thyl chloride with diphenylacetonitrile, 39, 74 of phenylacetylene with ethyl orthoformate, 39, 59 of 1-phenylbiguanide with ethyl chloroacetate, 38,1 of potassium diphenylacetonitrile with benzyl chloride, 39, 73 of potassium trithiocarbonate with potassium chloroacetate, 39, 77 of sodium acetylacetonate to tetraacetylethane, 39, 61 of sodium formylacetone with cyano-acetamide, 32, 32 of tetracyanoethylene with N,N-dimethylaniline, 39, 68 of thiophene, paraldehyde, and hydrogen chloride, 38, 86 of thiourea with furfuryl alcohol, 36,66... 

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],... 

Many industrial applications utilize the solvent properties of furfural and fur-furyl alcohol however, both chemicals also display unique features as monomers for condensation polymerization. Most of the furfuryl alcohol sold is used as monomer in the manufacture of resins for industrial application. 

Pump 11 takes the depressurized slurry into an overflow sedimentation centrifuge 12 where most of the catalyst particles are separated from the liquid phase. Removal of the solids from the bowl is effected manually at appropriate intervals. The liquid phase flows into a still 13 topped by a rectification column 14. The head vapors of the column are liquefied in condenser 15, the resulting distillate being partly returned to the column to effect rectification and partly collected in tank 16. This distillate is pure furfuryl alcohol. Vacuum pump 17 maintains a reduced pressure to permit distillation at moderate temperatures. Catalyst fines and high-boiling polymers inevitably formed in the reactor remain in the still and are discarded. 

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. 

Urea-formaldehyde resin, like phenol-, or furfuryl alcohol-formaldehyde resins, is typically thought of as resulting from simple condensation chemistry. The ultimate hardening of the resin is thought to be the result of the formation of a cross-linked network brought about by acid catalysis. Current reviews are available (1, 2) which discuss this traditional preception of UF resin chemistry. 

This occnrs by acid catalysis, but generally the immediate product, a furfuryl alcohol, reacts further 2-(2,2,2-trichloro-l-hydroxy)ethylfuran can, however, be isolated. Macrocycles known as tetraoxaqua-terenes can be obtained by condensations " with dialkyl ketones or cyclohexanone via sequences, giving prodncts exactly comparable to those described for pyrrole (16.1.1.7). 

Many efforts have been made to base polymers on furfural made from pentoses.159 The polymers may be useful, but tend to have lower thermal stability than the usual synthetic polymers. Polyesters based on furfural were mentioned earlier. The acid-catalyzed polymerization of furfuryl alcohol is used in foundry cores.160 Furfural has been condensed with cardanol (m-pentadecadienylphenol) from cashew nut shell oil in the presence of other phenols to produce polymeric resins.161 Cardanol and hydrogenated cardanol have been polymerized with horseradish peroxidase to soluble polymers in up to 85% yield.162 Plasticizers that are effective in polyvinyl chloride, such as (12.31), have been made from furfural.163... 

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... 

It is prepared by condensation of 2-bromomethyl-5-methylfuran, obtained by action of A-bromosuc-cinimide on 2,5-dimethylfuran with furfuryl alcohol (1.52). 

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 ... 

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