Furfural

Description

Furfural is a colourless to amber-like oily liquid with an almond-like odour. On exposure to light and air, it turns reddish brown. Furfural is used in making chemicals, as a solvent in petroleum refining, a fungicide, and a weed killer. It is incompatible with strong acids, oxidisers, and strong alkalis. It undergoes polymerisation on contact with strong acids or strong alkalis. Furfural is produced commercially by the acid hydrolysis of pentosan polysaccharides from non-food residues of food crops and wood wastes. It is used widely as a solvent in petroleum refining, in the production of phenolic resins, and in a variety of other applications. Human exposure to furfural occurs during its production and use, as a result of its natural occurrence in many foods and from the combustion of coal and wood.

Description

Furfural, or furan-2-carbaldehyde, is an oily liquid formed when sugars from lignocellulosic biomasses such as corncobs, sawdust, and oat hulls dehydrate. This is a natural process that is the basis of the commercial production of furfural.
In the first half of the 19th century, chemists such as Johann W. D?bereiner at the University of Jena (Germany) and John Stenhouse at Glasgow University discovered furfural in the distillation products of various biomaterials. It did not become an industrial product until Quaker Oats (Chicago) began to produce it on a large scale from oat hulls.
Furfural, one of the earliest sustainable chemical feedstocks, is used to synthesize a wide range of industrial chemicals, including solvents, resins, plastics, and furan derivatives. As the hazard information table shows, it must be handled with an abundance of caution.
Furfural is one of several five-carbon oxygenated hydrocarbons that make up the aroma of canned pumpkin you might use to make your Thanksgiving pumpkin pie. Oddly, this odor differs significantly from that of the six-carbon compounds, such as former Molecule of the Week cis-3-hexen-1-ol, that emanates from freshly cut pumpkins.
Happy Thanksgiving from the MOTW team!

Chemical properties

Furfural is a colorless to yellow aromatic het erocyclic aldehyde with an almond-like odor. Turns amber on exposure to light and air.

Chemical properties

Furfural has a characteristic penetrating odor typical of cyclic aldehydes. Furfural is prepared industrially from pentosans that are contained in cereal straws and brans; these materials are previously digested with diluted H2S04, and the formed furfural steam is distilled.

Physical properties

Colorless to yellow liquid with an almond-like odor. Turns reddish brown on exposure to light and air. Odor and taste thresholds are 0.4 and 4 ppm, respectively (quoted, Keith and Walters, 1992). Shaw et al. (1970) reported a taste threshold in water of 80 ppm.

Occurrence

Reported found in several essential oils from plants of the Pinaceae family, in the essential oil from Cajenne linaloe, in the oil from leaves of Trifolium pratense and Trifolium incarnatum, in the distillation waters of several essential oils, such as ambrettee and angelica seeds, in Ceylon cinnamon essential oil, in petitgrain oil, ylang-ylang, lavender, lemongrass, calamus, eucalyptus, neroli, sandalwood, tobacco leaves and others Also reported found in many foods including apple, apricot, citrus peel oils and juices, berries, guava, grapes, pineapple, asparagus, kohlrabi, celery, onion, leek, potato, tomato, cinnamon, mustard, bread, cheeses, meats, fsh, cognac, rum, whiskies, cider, grape wine, cocoa, coffee, tea, barley, peanuts, popcorn, pecans, oats, honey, soybeans, passion fruit, plums, mushroom, mango, tamarind, fruit brandies, whiskey malt, white bread, rum, bourbon, cardamom, coriander seed, calamus, corn oil, malt, wort and other sources

The Uses of Furfural

In the manufacture of furfural-phenol plastics such as Durite; in solvent refining of petroleum oils; in the preparation of pyromucic acid. As a solvent for nitrated cotton, cellulose acetate, and gums; in the manufacture of varnishes; for accelerating vulcanization; as insecticide, fungicide, germicide; as reagent in analytical chemistry. In the synthesis of furan derivatives.

The Uses of Furfural

Solvent refining of lubricating oils, resins, and other organic materials; as insecticide, fungicide, germicide; an intermediate for tetrahydrofuran, furfural alcohol, phenolic and furan polymers

The Uses of Furfural

Commercially, furfural is produced through hydrolysis of pentosan in agricultural byproducts (e.g., crop wastes). It has a diverse applications which include as a solvent in various manufacturing industries (e.g., petroleum and automotive products), accelerant for vulcanization of rubber, raw material for manufacturing furan derivatives (e.g., tetrahydrofurfuryl alcohol) and synthetic resins, wetting agent, flavoring ingredient for foods (e.g., roasted coffee), fragrance in consumer and personal care products (e.g., fragrance cream, bath products, toiletries), and pesticides for controlling unwanted microorganisms, fungi, weeds, insects, and nematodes. The application methods for pesticidal use include drip irritation, spray boom, sprinkler, and low-pressure back-pack spray.

Definition

ChEBI: An aldehyde that is furan with the hydrogen at position 2 substituted by a formyl group.

Definition

furfural: A colourless liquid,C₅H₄O₂, b.p. 162°C, which darkenson standing in air. It is the aldehydederivative of furan and occurs invarious essential oils and in fuseloil. It is used as a solvent for extractingmineral oils and natural resinsand itself forms resins with somearomatic compounds.

Preparation

Industrially prepared from pentosans that are contained in cereal straws and brans; these materials are previously digested with diluted H2SO4, and the formed furfural steam is distilled.

Production Methods

Furfural is obtained commercially by treating pentosan-rich agricultural residues (corncobs, oat hulls, cottonseed hulls, bagasse, rice hulls) with a dilute acid and removing the furfural by steam distillation. Major industrial uses of furfuraldehyde include: (1) the production of furans and tetrahydrofurans where the compound is an intermediate; (2) the solvent refining of petroleum and rosin products; (3) the solvent binding of bonded phenolic products; and (4) the extractive distillation of butadiene from other C4 hydrocarbons.
When pentoses, e.g., arabinose, xylose, are heated with dilute HCl, furfuraldehyde is formed, recognizable by deep red coloration with phloroglucinol, or by the formation, with phenylhydrazine, of furfuraldehyde phenylhydrazone C4H3O·CH : NNHC6H5, solid, mp 97 °C.

Reactions

Aside from a darkening in color, furfural is relatively stable thermally and does not exhibit changes in physical properties after prolonged heating up to 230°C. The reactions of furfural are typical of those of the aromatic aldehydes, although some complex side reactions occur because of the reactive ring. Furfural yields acetals, condenses with active methylene compounds, reacts with Grignard reagents, and provides a bisulfite complex. Upon reduction, furfural yields furfural alcohol; upon oxidation, it yields furoic acid. It can be decarbonylated to furan.

Taste threshold values

Taste characteristics at 30 ppm: brown, sweet, woody, bready, nutty, caramellic with a burnt astringent nuance.

Synthesis Reference(s)

The Journal of Organic Chemistry, 45, p. 3449, 1980 DOI: 10.1021/jo01305a015

General Description

Colorless or reddish-brown mobile liquids with a penetrating odor. Flash points 140°F. Denser than water and soluble in water. Vapors heavier than air. May be toxic by ingestion, skin absorption or inhalation.

Air & Water Reactions

Flammable. Furfural is sensitive to light and air. Soluble in water, with mixing.

Reactivity Profile

Furfural reacts with sodium hydrogen carbonate. Furfural also can react with strong oxidizers. An exothermic resinification of almost explosive violence can occur upon contact with strong mineral acids or alkalis. Furfural forms condensation products with many types of compounds, including phenol, amines and urea. .

Hazard

Absorbed by skin; irritant to eyes, skin, and mucous membranes. Toxic by skin absorption; questionable carcinogen.

Health Hazard

Vapor may irritate eyes and respiratory system. Liquid irritates skin and may cause dermatitis.

Fire Hazard

Special Hazards of Combustion Products: Irritating vapors are generated when heated

Flammability and Explosibility

Non flammable

Industrial uses

Also known as furfuraldehyde, furol, and pyromuclealdehyde,furfural is a yellowish liquidwith an aromatic odor, soluble in water and inalcohol, but not in petroleum hydrocarbons. Onexposure, it darkens and gradually decomposes.Furfural occurs in different forms in variousplant life and is obtained from complex carbohydratesknown as pentosans, which occur insuch agricultural wastes as cornstalks, corncobs,straw, oat husks, peanut shells, bagasse,and rice. Furfural is used for making syntheticplastics, as a plasticizer in other synthetic resins,as a preservative in weed killers, and as aselective solvent especially for removing aromaticand sulfur compounds from lubricatingoils. It is also used for the making of butadiene,adiponitrile, and other chemicals.
Various derivatives of furfural are not used,and these, known collectively as furans, are nowmade synthetically from formaldehyde andacetylene, which react to form butyl nedole.

Safety Profile

Confirmed carcinogen. Poison by ingestion, intraperitoneal, subcutaneous, intravenous, and intramuscular routes. Moderately toxic by inhalation and sktn contact. Human mutation data reported. A skin and eye irritant. Mutation data reported. The liquid is dangerous to the eyes. The vapor is irritating to mucous membranes and is a central nervous system poison. However, its low volatility reduces its toxicity effect. Ingestion of furfural has produced cirrhosis of the liver in rats. In industry there is a tendency to minimize the danger of acute effects resulting from exposure to it. This is particularly true because of its low volathty. Flammable liquid when exposed to heat or flame; can react with oxidizing materials. Moderate explosion hazard when exposed to heat or flame or by chemical reaction. An exothermic polymerization of almost explosive violence can occur upon contact with strong mineral acids or alkalies. Keep away from heat and open flames. Mixture with sodium hydrogen carbonate ignites spontaneously. To fight fire, use alcohol foam, CO2, dry chemical. When heated to decomposition it emits acrid smoke and irritating fumes.

Potential Exposure

Furfural is used for lube oil refining and butadiene extraction; as a solvent for wood resin, nitrated cotton, cellulose acetate, and gums; in the produc tion of phenolic plastics, thermosetting resins, refined petroleum oils, dyes, and varnishes; in the manufacture of pyromucic acid, vulcanized rubber, insecticides, fungicides, herbicides, germicides, furan derivatives, polymers, and other organic chemicals.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.

Carcinogenicity

The IARC evaluated furfural and determined that there was inadequate evidence in humans for the carcinogenicity of furfural. There is limited evidence in experimental animals for the carcinogenicity of furfural.

Source

Furfural occurs naturally in many plants including rice (90,000–100,000 ppm), lovage roots (2 to 20 ppm), caraway, strawberry leaves, cilantro, java cintronella, cassia, ylang-ylang, sweetflag, Japanese mint, oat husks (100,000 ppm), anise, broad-leaved lavender, myrtle flowers (0–1 ppm), lemon verbena, Karaya gum (123,000 ppm), nutmeg seeds (15,000 ppm), West Indian lemongrass, licorice roots (2 ppm), cinnamon bark (3 to 12 ppm), Hyssop shoots (1–2 ppm), periwinkle leaves, rockrose leaves, and garden dill (Duke, 1992).
Identified as one of 140 volatile constituents in used soybean oils collected from a processing plant that fried various beef, chicken, and veal products (Takeoka et al., 1996).
The gas-phase tailpipe emission rate from California Phase II reformulated gasoline-powered automobile without a catalytic converter was 1.70 mg/km (Schauer et al., 2002).

Environmental Fate

Biological. Under nitrate-reducing and methanogenic conditions, furfural biodegraded to methane and carbon dioxide (Knight et al., 1990). In activated sludge inoculum, following a 20-d adaptation period, 96.3% COD removal was achieved. The average rate of biodegradation was 37.0 mg COD/g?h (Pitter, 1976).
Photolytic. Atkinson (1985) reported an estimated photooxidation half-life of 10.5 h for the reaction of furfural with OH radicals in the atmosphere.
Chemical/Physical. Slowly resinifies at room temperature (Windholz et al., 1983). May polymerize on contact with strong acids or strong alkalies (NIOSH, 1997).

storage

Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Furfural must be stored to avoidcontact with oxidizing materials (such as perchlorates, peroxides, chlorates, nitrates, and permanganates) and strongacids because violent reactions occur. Store in tightly closedcontainers in a cool, well-ventilated area away from heat.Sources of ignition, such as smoking and open flames areprohibited where furfural is used, handled, or stored in amanner that could create a potential fire or explosion hazard. Before entering confined space where this chemicalmay be present, check to make sure that an explosive concentration does not exist.

Shipping

UN1199 Furaldehyde, Hazard class: 6.1; Labels: 6.1-Poisonous materials, 3-Flammable liquid.

Purification Methods

Furfural is unstable to air, light and acids. Impurities include formic acid, .-formylacrylic acid and furan-2-carboxylic acid. Distil it in an oil bath from 7% (w/w) Na2CO3 (added to neutralise acids, especially pyromucic acid). Redistil it from 2% (w/w) Na2CO3, and then, finally fractionally distil it under vacuum. It is stored in the dark. [Evans & Aylesworth Ind Eng Chem (Anal ed) 18 24 1926.] Impurities resulting from storage can be removed by passage through chromatographic grade alumina. Furfural can be separated from impurities other than carbonyl compounds by the bisulfite addition compound. The aldehyde is steam volatile. It has been purified by distillation (using a Claisen head) under reduced pressure. This is essential as is the use of an oil bath with temperatures of no higher than 130o which is highly recommended. When furfural is distilled at atmospheric pressure (in a stream of N2), or under reduced pressure with a free flame (caution: because the aldehyde is flammable), an almost colourless oil is obtained. After a few days and sometimes a few hours, the oil gradually darkens and finally becomes black. This change is accelerated by light and occurs more slowly when it is kept in a brown bottle. However, when the aldehyde is distilled under vacuum and the bath temperature kept below 130o during the distillation, the oil develops only a slight colour when exposed to direct sunlight during several days. The distillation of very impure material should NOT be attempted at atmospheric pressure; otherwise the product darkens very rapidly. After one distillation under vacuum, a distillation at atmospheric pressure can be carried out without too much decomposition and darkening. The liquid irritates mucous membranes. Store it in dark containers under N2, preferably in sealed ampoules. [Adams & Voorhees Org Synth Coll Vol I 280 1941, Beilstein 17/9 V 292.]

Toxicity evaluation

The limited data in animals are insufficient for deriving a plausible mechanism of toxicity. Nevertheless, aldehyde functional group is intrinsically reactive and low molecular weight aldehydes such as formaldehyde are known to interact with biologically important macromolecules such as DNA, structural proteins, and enzymes. This supposition is consistent with the toxic effects observed at multiple sites, i.e., respiratory system, nervous system, liver, and kidneys.

Incompatibilities

May form explosive mixture with air. Acids and bases can cause polymerization, causing fire or explosion hazard. Reacts violently with oxidants. Incompatible with strong acids; caustics, ammonia, ali phatic amines; alkanolamines, alromatic amines; oxidizers. Attacks many plastics.

Waste Disposal

Dissolve or mix the material with a combustible solvent and burn in a chemical incinera tor equipped with an afterburner and scrubber. All federal, state, and local environmental regulations must be observed. Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transpor tation, treatment, and waste disposal.