Charles E. Carraher, Jr. Wright State University Dayton, Ohio 45431
Synthesis of Furfuryl Alcohol and Furoic Acid
T h e followine exercise can b e conducted utilizine two 3hour l a b ~ r a t o r ~ ~ e r i aonddsis meant t o illustrate l j t h e use of t h e Cannizzaro reaction i n svnthesis.. 2). ~- r o d u c t i o nof a commercial resin a n d 3) t h e importance of several natural products i n t h e present industrial economy.
Prologue
Phenol-furfural resins are used as a quick-curing cement for bonding similar to those produced with phenol-formaldehyde (Bakelite, etc.). It is used as the bonding agent for many abrasive wheels and in plywood. They are quick curing and adhere to glass and metal as well as to wood and paper. Here we will describe the production of a plywood adhesive using furfurvl alcohol emnlovine a urea-formaldehvde hase. The use of ,~~ urea.formaldehyde resins has developed rapidly hecauaeof thecheap produrtion of synthetic urea and formaldehyde. Urea is made from carbon dioxide and ammonia while formaldehyde is synthetirally produced from carbon monoxide and hydrogen via methanol. Urea resins are utilized in the production of such molded articles as knobs, boxes, tumblers and tableware, buttans, reflectors and molded shades for indirect liehtine. The diamu&mdof furfuraldehyde is complicated by susceptibility of the furan ring tonueleophilrcattack by the haseinthe5-position. Even so the reaction prmeeds well enough giving about 60% yield of furfuryl alcohol and furoic acid. The reaction is outlined as follows. ~~
Canniuaro, luckily for the sciences, was an impassioned man, full of zeal, not fearing a strong or novel line of action. His early life was marked with w l i t i d turmoil. He was from Sicilv and in 1848 had to flee due to hisoart in an unsuccessful revolution bccurrine within the Kingdom of ~ ' a p l eof s which Sicily was a part. In 1851 heieturned to Sardinia rather than Naples. In 1853 he discovered a useful sequence for converting particular aldehydes into a mixture of an acid and alcohol. This reaction now bears his name and will be considered in greater length later. In the 1850's chemistry was in a turmoil. While the atomic theory of Dalton was widely accepted, the methods for describing chemical substances and structures were hotly contested. There was no agreement on the atomic weights of the different elements and without this there was no generally accepted formula describing chemical compounds. Kekule, in desperation, called a conference of highly regarded chemists throughout Europe to discuss this problem. The First International Chemical Congress met in 18fi0in Karlsruhe, S Rhine from France. a small town B C ~ O ~the Cannizzaro attended. In 1858he had come across Avogadro's hyoothesis which had laid in wait for nearlv. 50 . vears. In tvnical .. misslonnry npnl he introduced to the congress Avogadro's hsp~nheais, describing how it could he used to determine molecular we~ghrsof gases. Fnrm this the chemical composition and proportion of each component could he determined for a number of simplier compounds. Thus was laid an idea, which became a building block of chemistry, biology and physics. Late in his life, Cannizzaro again entered politics eventually hecoming vice- president of the Italian Senate.
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H
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Pentonana from H+ straw, rice, oat hulls, ete.
'0-C-C-0'
Furfuraldehyde
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lntroductlon Aldehydes having no alpha hydrogens (such as benzaldehyde) do not undergo aldolization when treated with base; instead they disproportionate, giving equal mounts of the corresponding alcohol and acid. This is called the Cannizzaro reaction. One molecule of aldehyde acts as the hydride-donor and another as the acceptor. The intermediate is an ester which is hydrolyzed under the reaction conditions. The averall sequence is as follows
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Furoic acid (salt)
Furfury1 alcohol
In theory, only 0.5 mole of base is required to convert one mole of aldehvde into the alcohol and acid (salt). It is customarv to use an excess of hase to sneed uo the ssoonification of the ester. In the present exwriae, furfuryl alcohol is isolatpd as the crude product and is not purified funher. Kven so it is of sufficient purity to allow its use as e hinder. The exercise is well suivd for students to work in pairs. ~
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Furfural derives much of its industrial use as an intermediate in the synthesis of adiponitrile eventually ending up in Nylon 66 and its use in resins and adhesives. It derives much of its importance in that it is obtained inexpensively by the distillation in the presence of a mineral acid of cellulosic materials such as rice and oat hulls, corncobs and straw. It is also an intermediate in the synthesis of furfuryl almhol which is also used in adhesives and resins.
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Experimental Furfuraldehyde (30 ml, 0.37 mole) is poured in a 200-ml beaker and cooled to 10°C utilizing an ice-water bath. Sodium hydroxide (25 ml of 10 M )is added slowly with stirring a t a rate such that the temperature does not rise above 25°C. Stirring is continued, with the reaction mixture maintained in the ice-water bath, for 10 min after final addition of the sodium hydroxide, The reaction mixture is alVolume 55, Number 4, April 1978 1 269
lowed to reach ambient temperature and allowed to stand for 20 m ....i.n ..~
The mixture should be clear. Ifnecessary, water isadded dropwise untd the solid (sodium furoasej is dissolved. (Avoid adding excess water.) The resulting solution isextracted once with diethvlether (30 ml) followed bv three extractiom with a 1:4benzene-etherivlv: 15-ml po;tions) soluiion. Both the organic extracts and aqueous layer are retained. (To presewe time it is advisihle to begin the section Plywood Adhesive and then go to the section Furfuryl Alcohol and then to Furoic Acid as the furfuryl alcohol-organic solution is left to evaporate.) Furfuryl Alcohol. Magnesium sulfate (about 0.2 g) is added to the organic extract from above. The mixture is shaken and filtered under s u k o n . The organic filtrate is placed in a hood and dryed to give a viaeousoil, furfuryl alcohol. (Use ofasteam bath enhances the drying process.) Fumic Acid. Hydmchloricacid (12 M )is addedto the aqueous layer from the initial steps until a pH less than 2 is achieved. The resulting suspension is cooled to 0-3% using an iee-water bath. The precipitated furoic acid is collected using suction filtration. (If the product is colored a second treatment may he necessary employing a small amount of charcoal.) Theuroduct is allowed to drv in air until the next laboratory period ;hen it is weighed and the yihd calculated. Plywood Adhesiue. An aqueous NaOH (2.5 M) solution is added to 37% aqueous formaldehyde (30g; 1.6 mole) until a pH of about 7.5 is obtained. This is added to a three necked flask fitted with a stirrer and reflux cordenser. Urea (15g,0.25 mole) is then added and stirring and heating heeun until a eentle reflux results which is maintained for 1to 1.5houis. The reflux mixture is concentrated hv distillation of 10 -~ ml of water from the mixture under water ssoira&r uressure. Celot~on.A plywood adhesive is prepared as follows. The ureaformaldehyde resin prepared directly ahwe (us? about 20g) iu added t o a three necked flask (100 rnll fitted with a condenser and stirrer. Furfuryl alcohol (5g, 0.05 mole), wood flour or sawdust (3-4G), calcium phosphate (C@PO&; 0.2 g) and triethanolamine (0.1 g) are stirred into the resin. The resulting mixture is brought to 90% slowly over 20 min (with stirrine) and maintained at 9OPCfor 15 min. The mixture is &led (slawl$and poured into alarge test tube or other container which can he sacrificed. ~~
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270 1 Journal of Chemical Education
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Addition of an aqueous solution of NHICI (0.4 gin 1 ml of water) will cause hardening. to occw pronding a working life for the adhevive uf about 5-8 hours. Prior toaddition ofthe NHKl solution, theadhesive resin is stable for 30-60 days. The adhesiveability is demonstrated by placing a thin layer of materialbetween two pieces of wood or wooden splits oermittine them . . to set until the next iiborataw oeriod. A plug is made by filling a & c h b a x or other container (or leaving the material in the test tube) with the NH&l treated adhesive and permitting it to set until the next period. Urea and formaldehyde condense giving a resin with an unknown macrostructure but somewhat known local structure. Initially monoethylol urea is formed. I t can react further eventually yielding a highly complell three-dimensional struction.
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Complex Three-Dimensional Structure
The addition of an almhol such as furfury1alcohol allows the initial production of alkyl (or aryl)-substituted monomethylol urea. The presence of the alkyl or aryl group greatly increases the oil solubility of the resin permitting the resin to also he used for coatings application. CJuestions. A number of oueations can be invited aaaoriaterl , ~~~~-...with ~.~~ the.erercise, for instance: How could furfuryl alcohol be further purified? How could you determine the purity offurfuql alcohol? How was the "recipe" utilized to produce the plywood adhesive probably arrivedat? How important is it that the recipe he followedcloselywhat would be probable limits? Why was wood dust used? Ammonium chloride acts to increase the rate of hardening. Is it then a catalyst? Why? ~
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