Key Chemical Properties and Uses of Furfural Explained
Furfural is an organic compound obtained during the dehydration of sugars. Its IUPAC name is furan-2-carbaldehyde. The word, furfural comes from the Latin word furfur that stands for bran, its usual source. Sugars present in a variety of agricultural byproducts such as corn cobs, oats, wheat bran, and sawdust are used to produce furfural. It is commonly used in many processed foods and beverages.
Furfural is a colourless liquid that darkens on exposure to air. It is the best-known member of the furan family. Furfural meaning is furfuraldehyde or also called 2-furaldehyde. It is also an important source of other furans. The boiling point of furfuraldehyde is 161.70C. The furfural structure is given below:
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Furfuraldehyde
The chemical formula for furfuraldehyde or furfural aldehyde is C4H3O-CHO. In 1922, Quaker Oats company started producing furfural from oat hulls for commercial use much after its discovery by a German scientist Johann Wolfgang in 1821. The industrial development of the production of furfural is a great example of how industries utilize agricultural residues. The major raw material source of furfural such as corncobs, oat hulls, cottonseed hulls, rice hulls, and bagasse are replenished annually ensuring a constant supply of raw material for the production of furfural.
In large rotary digesters, lots of raw material and dilute sulphuric acid are steamed under pressure. The furfural form is continuously removed with steam and then concentrated with the help of distillation. The furfural obtained by distillation separates into two layers of condensation and the wet furfural at the bottom is dried with the help of vaccum distillation to obtain furfural with a minimum of 99% purity. Given below is the dehydration reaction of pentoses under an acid catalyst.
C5H10O5 → C5H10O2 + 3H2O
The furfural price remains stable in the market and is readily available at Furfural sigma Aldrich. Global demands of furfural remain high with China as its leading production capacity of 85% and consumption of 75%.
Properties of Furfural
Furfural has a molecular weight of 96.08 g/mol. It is denser than water and water-soluble. Its vapours are heavier than air. It has a distinct caramel taste and smells somewhat like benzaldehyde. It has a boiling point of 161.70C. It is considered a major platform chemical that is used in the production of various other chemicals.
Furfural strongly resembles benzaldehyde in its reactions as an aldehyde. In the presence of strong aqueous alkali, it undergoes a Cannizaro reaction. It dimerizes furoin under the influence of potassium cyanide and by the action of ammonia is converted into hydro furamide (C4H3O-CH)3N2.
On exposure to air at room temperature, furfural degrades into formic acid and formerly acrylic acid. Furoic or furfural acid is a crystalline solid, white in colour, and is used as a bactericide and a preservative. Its esters are fragrant liquids commonly used in perfumes and flavourings.
Methyl Furfural
5-methyl 2-furaldehyde is an arenecarbaldehyde that is slightly soluble in water and is used as a food flavouring agent. It is also used as a fragrance agent for in-home products or similar industrial products.
Hydroxymethyl Furfuraldehyde
5-hydroxy methyl furfural is an organic compound obtained upon dehydration of sugars, which is highly soluble in water and organic solvents. It is used as an additive agent in the food industry and also in the production of various fuels and chemicals. It is absent in fresh food but is naturally generated upon heating of sugar-containing food items.
Conclusion
Furfural is one of the furan derivatives from hemicellulose present in lignocellulosic. It is naturally obtained upon dehydration of xylose, which is a pentose sugar. This heterocyclic and aromatic aldehyde consists of an aldehyde side group and a furan ring. It is a colourless liquid and has an oily appearance with an almond-like odour. Furfural has various industrial purposes being a platform chemical that is used in the production of various other chemical compounds. It is also used in the production of furan compounds.
FAQs on Furfural: Structure, Properties, and Applications
1. What is the chemical structure and IUPAC name of furfural?
Furfural consists of a five-membered aromatic ring, known as a furan ring, with an aldehyde group (-CHO) attached at the second position. The furan ring contains one oxygen atom and four carbon atoms. Its chemical formula is C₅H₄O₂. According to IUPAC nomenclature, furfural is named Furan-2-carbaldehyde.
2. What are the key physical and chemical properties of furfural?
Furfural is a colourless to amber-coloured oily liquid with a characteristic almond-like odour. Its key properties include:
- Molecular Weight: 96.08 g/mol
- Boiling Point: 161.7 °C
- Solubility: It is miscible with most polar organic solvents but only slightly soluble in water.
- Reactivity: As a heterocyclic aldehyde, it exhibits reactions typical of both aldehydes (e.g., oxidation, reduction, condensation) and aromatic furan rings (e.g., substitution, hydrogenation).
3. What are the major industrial applications and uses of furfural?
Furfural is a versatile industrial chemical with numerous applications. Its primary uses include:
- Solvent: It is used as a selective solvent in the refining of lubricating oils to separate saturated from unsaturated compounds.
- Chemical Intermediate: It serves as a precursor for synthesizing other important chemicals like furfuryl alcohol, tetrahydrofuran (THF), and furoic acid.
- Resin Production: Furfural is used to manufacture furan resins, which are known for their high thermal stability and corrosion resistance, used in making abrasive wheels and cements.
- Nylon Production: It is a key source for producing hexamethylenediamine, a monomer required for manufacturing nylon.
- Fungicide and Nematicide: In agriculture, it and its derivatives are used to control fungi and nematodes.
4. What are the main types of chemical reactions that furfural undergoes?
Furfural's reactivity is defined by its two functional components: the aldehyde group and the furan ring. Key reactions include:
- Aldehyde Group Reactions: It undergoes oxidation to form furoic acid, reduction to yield furfuryl alcohol, and condensation reactions like the Cannizzaro reaction.
- Furan Ring Reactions: The ring can be hydrogenated to produce tetrahydrofuran (THF), a valuable solvent. It can also undergo decarbonylation to form furan.
- Reductive Amination: It reacts with ammonia and hydrogen to form furfurylamine.
5. How is furfural produced, and why is it considered a renewable chemical?
Furfural is produced from the acid-catalysed dehydration of pentose sugars, particularly xylose. These sugars are abundant in lignocellulosic biomass, which includes agricultural residues like corn cobs, sugarcane bagasse, and oat hulls. Because its feedstock is derived from plant matter, which can be replenished annually, furfural is considered a renewable chemical and a key component of biorefineries, offering a sustainable alternative to petroleum-based chemicals.
6. How does the furan ring in furfural influence its reactivity compared to a simple aromatic aldehyde like benzaldehyde?
The furan ring in furfural makes it significantly different from benzaldehyde. The oxygen heteroatom in the furan ring makes it more electron-rich and more susceptible to electrophilic attack and ring-opening reactions under harsh acidic conditions than the stable benzene ring. While both have an aldehyde group that directs substitution, the furan ring's lower aromatic stability means it can undergo reactions like hydrogenation more readily than the benzene ring in benzaldehyde. This unique combination of an aldehyde and a reactive heterocyclic ring gives furfural its versatile chemical nature.
7. Why is furfural often referred to as a "platform chemical"?
Furfural is called a platform chemical because it is a bio-based molecule that can be converted into a wide range of high-value chemicals and fuels. Its versatile structure, featuring both an aldehyde and a furan ring, allows it to be a starting point (a 'platform') for synthesising various derivatives like alcohols (furfuryl alcohol), solvents (THF), acids (furoic acid), and polymers. Its role as a bridge between renewable biomass and the chemical industry makes it a cornerstone of sustainable chemistry.
8. What are the specific products when furfural undergoes oxidation and reduction?
The reactions of furfural's aldehyde group are central to its chemistry:
- Oxidation: When furfural is oxidised, the aldehyde group (-CHO) is converted into a carboxylic acid group (-COOH). The resulting product is furoic acid (furan-2-carboxylic acid).
- Reduction: When furfural is reduced, typically through catalytic hydrogenation, the aldehyde group is converted into an alcohol group (-CH₂OH). This reaction yields furfuryl alcohol, which is a major industrial derivative.
