Structure and Reactivity of Furan Compounds: How Substituents, Ring Fusion, and Degree of Hydrogenation Affect Reaction Sites and Application Directions
Structure and Reactivity of Furan Compounds: How Substituents, Ring Fusion, and Degree of Hydrogenation Affect Reaction Sites and Application Directions
1 Why Do Compounds Containing the Same Furan Ring Exhibit Different Reactions and Uses?
Furan, furfural, 5-hydroxymethylfurfural, 2,5-furandicarboxylic acid, furanboronic acids, benzofuran, and tetrahydrofuran all contain a five-membered oxygen-containing ring, yet they play different roles in chemical reactions. Furfural is commonly used as an intermediate for multiple transformation pathways, furanboronic acids are used in cross-coupling reactions, 2,5-furandicarboxylic acid is used in polycondensation, benzofuran can serve as a rigid fused heterocyclic scaffold, and tetrahydrofuran primarily behaves as a saturated cyclic ether.
These differences are determined by the complete molecular structure and mainly involve three aspects:
1. The type and position of substituents alter the electron distribution on the ring and introduce additional reaction centers;
2. The mode of ring fusion changes the extent of conjugation, skeletal rigidity, and planarity;
3. The degree of hydrogenation determines whether the ring system retains an aromatic conjugated structure.
Reagents and catalysts further select specific sites, such as carbon atoms on the ring, side-chain functional groups, or carbon–halogen bonds. Consequently, compounds containing the same furan ring may undergo different reaction pathways and enter distinct areas of research, including organic synthesis, polymers, energy, biological activity, and analytical testing.
2 Common Electronic Structure of the Furan Ring
2.1 A Five-Membered Oxygen-Containing Heteroaromatic Ring
Furan consists of a five-membered ring containing four carbon atoms and one oxygen atom, with two carbon–carbon double bonds in the ring. One lone pair on the oxygen atom occupies a p orbital perpendicular to the plane of the ring and forms a continuous π-conjugated system with the two double bonds. The other lone pair lies primarily in the plane of the ring and does not directly participate in this six-π-electron system.
The ring system contains six delocalized π electrons and satisfies Hückel’s (4n + 2) rule, and is therefore classified as a heteroaromatic compound. According to ring-numbering conventions, the oxygen atom occupies position 1. Positions 2 and 5, adjacent to oxygen, are commonly referred to as the α positions, whereas positions 3 and 4 are referred to as the β positions.[1]
Furanoses and aromatic furans are not the same type of structure. A furanose is a five-membered cyclic hemiacetal formed by a monosaccharide. Its ring skeleton is a saturated, tetrahydrofuran-type oxygen-containing ring and does not possess the continuous π conjugation of an aromatic furan.[2]
2.2 How the Oxygen Atom Affects Electron Distribution on the Ring
The oxygen atom in the ring exerts both inductive and conjugative effects.
Through the σ-bond framework, the relatively high electronegativity of oxygen draws electron density from adjacent bonds. Within the π system, however, a lone pair on oxygen can delocalize into the ring, causing furan to behave as a relatively electron-rich heteroaromatic ring. As a result of these two effects, furan generally undergoes electrophilic substitution more readily than benzene, but it is also more susceptible to strong acids, strong oxidants, and highly reactive electrophiles.
When unsubstituted furan undergoes electrophilic substitution, reaction usually occurs preferentially at position 2. The σ-complex formed after electrophilic attack at position 2 can distribute the positive charge over several resonance structures, whereas the intermediate resulting from attack at position 3 has more limited charge delocalization. The position-2 pathway therefore generally has a lower energy requirement.
This positional preference can be altered by existing substituents. Electron-withdrawing groups, electron-donating groups, steric hindrance, metal coordination, and reaction reversibility may all affect regioselectivity. Therefore, “preference for position 2” should not be regarded as a fixed outcome for all substituted furans.[3]
2.3 Dual Reactivity as an Aromatic Heterocycle and a Conjugated Diene
Furan is aromatic, but under suitable conditions its two double bonds can still act as a four-π-electron conjugated diene in a Diels–Alder reaction. The Diels–Alder reaction is a [4+2] cycloaddition in which furan provides the four-π-electron component and an alkene or maleimide compound provides the two-π-electron component.[1]
The reaction may be summarized as follows:
Furan group + dieneophile ⇌ oxygen-bridged cyclohexene-type adduct
Using a maleimide as an example:
Furan group + maleimide group ⇌ 7-oxanorbornene-type adduct
Substituents on furan alter its highest occupied molecular orbital energy, steric environment, and adduct stability, thereby affecting reaction rate, regioselectivity, and the ratio of endo and exo products. An electron-withdrawing aldehyde group generally reduces the diene reactivity of furan. Nevertheless, suitable reaction media, temperatures, and dieneophiles can still enable furfural derivatives to undergo direct Diels–Alder reactions.[4,5]
3 How Three Types of Structural Change Alter Reaction Modes
3.1 Substituents: Altering Electron Distribution and Introducing Additional Reaction Centers
Substituents can change the electronic properties of the furan ring and may also participate directly in reactions. The principal effects of different substituent types are summarized below.
Substituent type | Principal effect on molecular structure | Main reaction modes | Representative research directions |
Alkyl groups | Regulate electron density, hydrophobicity, volatility, and carbon-to-hydrogen ratio | Oxidation, hydrogenation, combustion reactions, and ring functionalization | Fuel molecules and reactivity studies |
Aryl groups | Extend the conjugated system and increase skeletal rigidity | Coupling, substitution, photochemical reactions, and electron transfer | Conjugated molecules and functional materials |
Aldehyde and ketone groups | Form electron-deficient carbonyl centers | Nucleophilic addition, condensation, reduction, and oxidation | Fine-chemical synthesis and multistep transformations |
Hydroxymethyl groups | Provide alcohol hydroxyl reaction sites | Oxidation, esterification, etherification, and polycondensation | Monomers, resins, and intermediates |
Carboxyl and dicarboxyl groups | Provide salt-forming and acyl-conversion capabilities | Esterification, amidation, and polycondensation | Polyester and polyamide research |
Halogens | Form carbon–halogen bonds capable of oxidative addition or substitution | Cross-coupling, nucleophilic substitution, and metalation | Building blocks for organic synthesis |
Boronic acid groups and boronate esters | Provide transferable furanyl carbon fragments | Suzuki–Miyaura coupling | Heteroaryl connection and construction of conjugated molecules |
Nitro groups and nitrogen-containing side chains | Alter electronic properties and biological reduction processes | Reduction, bioactivation, salt formation, and acylation | Medicinal chemistry and enzymatic transformations |
3.1.1 Aldehyde and Hydroxymethyl Groups: Formation of Multiple Redox Pathways
Furfural is formed by attaching an aldehyde group to position 2 of furan. Its molecule contains both an electron-rich heteroaromatic ring and an electron-deficient aldehyde carbonyl group. Electrophilic and nucleophilic reactions can therefore occur at different sites.
Two representative side-chain transformations are:
Furan-2-carbaldehyde + H₂ → furan-2-methanol
Furan-2-carbaldehyde + [O] → furan-2-carboxylic acid
The first pathway reduces the aldehyde group while retaining the furan ring, producing furfuryl alcohol. The second pathway oxidizes the aldehyde group to produce furan-2-carboxylic acid. If the hydrogenation severity is increased or the catalyst is changed, the furan ring itself may undergo further hydrogenation. Product selectivity therefore depends on the relative rates of carbonyl hydrogenation and ring hydrogenation.
5-Hydroxymethylfurfural (HMF) contains both an aldehyde group and a hydroxymethyl group. These two side chains are at different oxidation states and can be converted into 2,5-furandicarboxylic acid (FDCA) through two principal oxidation sequences:
HMF → 5-hydroxymethyl-2-furancarboxylic acid → 5-formyl-2-furancarboxylic acid → FDCA or:
HMF → 2,5-furandicarboxaldehyde → 5-formyl-2-furancarboxylic acid → FDCA
In the first pathway, the aldehyde group is oxidized first. In the second pathway, the hydroxymethyl group is oxidized first. Both pathways converge at 5-formyl-2-furancarboxylic acid, which is subsequently oxidized to FDCA. Catalyst type and active-site environment, reaction medium, pH, oxidant, and temperature can alter the distribution of intermediates.[6,7]
3.1.2 Carboxyl and Dicarboxyl Groups: From Small-Molecule Transformations to Chain-Growth Processes
Furancarboxylic acid contains only one carboxyl group and is mainly used in salt formation, esterification, amidation, and structural modification. FDCA contains one carboxyl group at each of positions 2 and 5 of the furan ring and can undergo step-growth polycondensation with diols or diamines.
Using polycondensation with ethylene glycol as an example, the reaction may be simplified as follows:
n HOOC—furan—COOH + n HO—CH₂CH₂—OH
→ [—OC—furan—COO—CH₂CH₂—O—]ₙ + water
The product is poly(ethylene furanoate) (PEF). During polycondensation, one molecule of water is eliminated for each ester bond formed. The actual amount of water generated depends on the degree of polymerization and the composition of the end groups.
FDCA can function as a polycondensation monomer because of the following structural combination:
① Two carboxyl groups provide bidirectional chain-extension sites;
② The 2,5-disubstituted structure gives the molecule relatively high symmetry;
③ The furan ring introduces rigidity and polarity into the polymer backbone.
FDCA can be prepared from fructose through HMF oxidation and has been investigated in polymers such as PEF. The renewability of the feedstock and the environmental performance of a specific process must be evaluated separately. Acid and base consumption, catalysts, solvent recovery, separation, and energy requirements all influence the overall process assessment.[7]
3.1.3 Halogens and Organoboron Groups: Controlling the Connection Position of Furan Fragments
The carbon–halogen bond in a halogenated furan can participate in metal-catalyzed oxidative addition, whereas a furanboronic acid or boronate ester can undergo transmetalation in the presence of a base. These two types of structures can be used to connect different aryl or heteroaryl groups through Suzuki–Miyaura reactions.
The reaction may be summarized as follows:
Heteroaryl—X + furanyl—B(OH)₂
under a palladium catalyst and base → heteroaryl—furan
X is commonly bromine, iodine, or a suitably activated chlorine atom. The value of this reaction arises from the selective conversion of carbon–halogen and carbon–boron bonds.
5-Formylfuran-2-boronic acid contains both a boronic acid group and an aldehyde group. The boronic acid group can first undergo cross-coupling, after which the aldehyde group can participate in Wittig olefination, reductive amination, or condensation. This enables the stepwise construction of conjugated heteroaromatic molecules.[8]
3.1.4 Nitro Groups and Nitrogen-Containing Side Chains: The Complete Molecule Determines Biological Reactions
Some 5-nitrofuran compounds can undergo reductive activation by nitroreductases. In Escherichia coli, for example, enzymes including NfsA, NfsB, and AhpF may participate in electron-transfer processes involving 5-nitrofurans, generating nitroso, hydroxylamine, or radical-related intermediates. The activation efficiency, cellular uptake, and site of action of different compounds are also affected by their side-chain structures.
These biological effects are not general properties of the furan ring, and the specific activity of a compound cannot be inferred solely from the presence of a nitrofuran group. The furan ring, nitro group, side-chain structure, metabolic enzymes, and cellular environment collectively determine the final outcome.[9]
3.2 Ring Fusion: Changing the Extent of Conjugation and Skeletal Rigidity
Benzofuran is formed when a benzene ring and a furan ring share a carbon–carbon bond. After fusion, the two rings no longer behave as separate phenyl and furanyl groups but instead constitute a continuous fused π system.
Compared with monocyclic furan, benzofuran generally has the following structural characteristics:
① The fused skeleton is relatively rigid, with reduced conformational freedom;
② The extent of conjugation is increased, and electron distribution across the ring system is rearranged;
③ The available substitution sites extend from the four carbon positions of monocyclic furan to the complete fused-ring system;
④ The aromatic surface area is increased, potentially strengthening intermolecular π interactions and hydrophobic interactions.
Further fusion with additional aromatic rings can produce dibenzofuran and other polycyclic structures. Increased conjugation and rigidity may favor certain optical, electronic, or molecular-recognition properties, but may also reduce solubility and strengthen molecular packing. Ring fusion does not mean that hardness, stability, biological activity, and solubility all increase simultaneously; these properties often involve trade-offs.
The benzofuran scaffold also occurs in certain natural products. For example, the total synthesis of propolisbenzofuran B employed a cascade cyclization to construct its benzofuran core, demonstrating that fused furans can serve as structural units in the synthesis of complex natural products.[10]
3.3 Hydrogenation: Conversion from an Aromatic Heterocycle to a Cyclic Ether
Hydrogenation of the furan ring progressively disrupts continuous π conjugation. Although dihydrofuran and tetrahydrofuran retain a five-membered oxygen-containing ring, their reaction properties are substantially different.
Ring system | Aromaticity | Principal structural characteristics | Typical reactions |
Furan | Present | Two conjugated double bonds and one oxygen lone pair participating in π conjugation | Electrophilic substitution, Diels–Alder reactions, selective oxidation, and hydrogenation |
Dihydrofuran | Absent | Retains one carbon–carbon double bond and is an unsaturated cyclic ether | Addition, oxidation, ring opening, and further hydrogenation |
Tetrahydrofuran | Absent | Contains no carbon–carbon double bonds and is a saturated cyclic ether | Coordination, solvation, and cationic ring-opening polymerization |
The principal reaction center of a dihydrofuran is the remaining double bond. Whether the double bond is adjacent to the oxygen atom affects its enol ether character, the direction of addition, and its tendency to undergo ring opening.
The oxygen lone pairs in tetrahydrofuran (THF) do not participate in aromatic conjugation and can coordinate with organolithium reagents, Grignard reagents, and metal centers. THF can also undergo cationic ring-opening polymerization to produce polytetrahydrofuran segments. In one reported gold(I)-catalyzed glycosylation system, a glycosyl active species generated in situ initiated the cationic ring-opening polymerization of THF, demonstrating that the reaction logic of a saturated cyclic ether differs from that of aromatic furan.[11]
The principal changes associated with an increasing degree of hydrogenation can be summarized as follows:
Aromatic furan reactions → unsaturated cyclic ether reactions → saturated cyclic ether reactions
4 How Reaction Sites Are Selected within the Same Molecule
4.1 Reagent Properties Determine the Site of Preferential Attack
Furan compounds containing multiple functional groups often possess two or more possible reaction sites.
Using furfural as an example:
① Nucleophiles generally attack the aldehyde carbonyl group;
② Electrophiles may attack the furan ring;
③ Hydrogenation catalysts may selectively reduce the aldehyde group, but may also continue to reduce the double bonds in the ring;
④ Oxidation catalysts may convert the aldehyde group into a carboxylic acid, but under stronger conditions may also degrade the furan ring.
Reaction selectivity arises from the electronic properties, spatial accessibility, and catalyst adsorption modes of the different reaction sites.
4.2 Catalysts Alter the Relative Rates of Different Reaction Pathways
HMF oxidation may begin at either the aldehyde group or the hydroxymethyl group. Some catalysts preferentially produce 5-hydroxymethyl-2-furancarboxylic acid, whereas other systems preferentially form 2,5-furandicarboxaldehyde. Whether FDCA is ultimately obtained depends on the rates at which the intermediates undergo further oxidation and on whether the furan ring remains stable.[6]
In cross-coupling reactions, palladium catalysts preferentially activate carbon–halogen bonds, causing carbon–carbon bond formation to outcompete ordinary electrophilic reactions on the ring. In Diels–Alder reactions, the structure of the dieneophile and the electronic effects of substituents determine whether the furan acts as an effective diene.[4,8]
4.3 Reaction Conditions Determine Whether the Furan Ring Is Retained
Mild and selective redox conditions can primarily transform the side chain. When temperature, pressure, acidity, or oxidizing strength is increased, the furan ring may undergo hydrogenation, ring opening, condensation, or polymerization.
The following points should be examined simultaneously during experimental evaluation:
Item to be examined | Question to be answered |
Transformation of the target functional group | Do the aldehyde, alcohol hydroxyl, carboxyl, or carbon–halogen groups react as expected? |
Integrity of the ring skeleton | Does the furan ring undergo hydrogenation, ring opening, oxidation, or polymerization? |
Regioselectivity | Does the reaction occur at position 2, position 3, or on the side chain? |
Chemoselectivity | Which of the multiple functional groups reacts first? |
Side reactions | Are resinous condensation products, overoxidation products, or isomers formed? |
5 How Structural Differences Correspond to Different Applications
Research direction | Key structure | Principal chemical basis | Representative compounds |
Multipath organic transformations | Coexistence of an aldehyde group, hydroxymethyl group, and furan ring | Separate oxidation, reduction, condensation, and ring transformations | Furfural, HMF |
Polymers and resins | Dicarboxyl groups, dihydroxyl groups, or furan sites capable of cycloaddition | Polycondensation, cross-linking, and Diels–Alder reactions | FDCA, 2,5-bis(hydroxymethyl)furan, furfuryl alcohol |
Building blocks for organic synthesis | Halogens, boronic acid groups, aldehyde groups, or amino groups | Cross-coupling, substitution, and subsequent functionalization | Halogenated furans, furanboronic acids |
Thermoresponsive cross-linking | Furan diene and maleimide dieneophile | Reversible [4+2] cycloaddition | Furan-terminated polymers, bismaleimides |
Fused-heterocycle research | Benzofuran or polycyclic furan skeletons | Rigid, conjugated, and planar molecular structures | Benzofuran, dibenzofuran |
Biological activity research | Nitrofurans and specific nitrogen-containing side chains | Enzymatic reductive activation and whole-molecule recognition | Nitrofuran derivatives |
Fuel-molecule research | Alkyl-substituted furans | Carbon-to-hydrogen ratio, volatility, and hydrodeoxygenation behavior | 2-Methylfuran, 2,5-dimethylfuran |
Solvent and polyether research | Saturated five-membered cyclic ethers | Oxygen coordination capability and ring-opening polymerization | THF |
Analysis and quality control | Defined structure, purity, and assigned reference values | Chromatographic retention, mass-spectrometric response, and quantitative calibration | Reference standards, isotope-labeled compounds |
Furan–maleimide systems can be used in thermoresponsive cross-linked materials. Bond formation produces an oxygen-bridged bicyclic structure. Upon heating, some systems can undergo a retro-Diels–Alder reaction, causing the cross-linking points to dissociate. The actual degree of reversibility is affected by substituents, cross-link density, heating time, side reactions, and diffusion processes within the material. In one study of 2,5-bis(hydroxymethyl)furan (BHMF)-based polyesters, bismaleimides were used for reversible cross-linking, and the rheological and thermal behavior of the resulting materials was evaluated.[12]
6 Selection and Safe Use of Furan Compounds
6.1 First Determine the Required Ring System
When selecting a compound, the electronic structure of the ring required for the study should first be considered:
① When aromatic heterocyclic substitution, conjugation, or Diels–Alder reactions are required, an unhydrogenated furan should be selected;
② When enol ether addition, oxidation, or ring opening is required, an appropriate dihydrofuran should be selected;
③ When a saturated cyclic ether solvent, coordinating medium, or polyether precursor is required, THF or one of its derivatives should be selected;
④ When a rigid fused conjugated scaffold is required, benzofuran or another fused furan should be selected.
6.2 Then Determine the Required Reactive Functional Group
Target reaction | Corresponding structure |
Nucleophilic addition, condensation, and reductive amination | Furan aldehydes and furan ketones |
Oxidation, esterification, and etherification | Furan alcohols and hydroxymethylfurans |
Esterification, amidation, and polycondensation | Furancarboxylic acids and furandicarboxylic acids |
Cross-coupling | Halogenated furans, furanboronic acids, or boronate esters |
Reversible cycloaddition | Furans retaining an intact diene structure in the ring |
Biological reduction studies | Nitrofurans with defined nitro and side-chain structures |
The substitution position must also be matched to the synthetic route. The remaining reaction sites, spatial orientation, molecular symmetry, and polymerization connectivity may differ among 2-substituted, 3-substituted, and 2,5-disubstituted structures.
6.3 Stability and Safety Considerations
Furan compounds differ substantially in volatility, flammability, oxidative stability, and toxicological properties, and each compound should therefore be evaluated individually.
Furan is volatile and flammable and presents an acute inhalation exposure risk that requires appropriate control.[13] THF is also flammable and may form peroxides during prolonged exposure to air.[14] Furfural, halogenated furans, nitrofurans, and polycyclic fused furans have their own distinct irritancy, reactivity, or toxicological characteristics. Storage and handling conditions should be determined according to the safety data sheet, stabilizer information, and experimental scale of the specific product.
A biomass-derived origin indicates only the source of the feedstock or carbon. It does not directly mean that the compound is nontoxic, readily degradable, or associated with a low environmental burden during synthesis. Feedstock pretreatment, catalysts, solvents, energy consumption, yield, and separation processes all affect the overall assessment.
7 Classification and Research Applications of Representative Chemicals Related to Structural Modulation, Functional Group Transformations, and Reaction Applications of Furan Compounds
Table 1. Furan Parent Ring and Alkyl- and Aryl-Substituted Compounds
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
Furan parent ring | 110-00-9 | F116393 | Furan | Chemically pure (CP), ≥98%, stabilized with 0.025% BHT | Used in studies of the electronic structure, electrophilic substitution, cycloaddition, selective hydrogenation, and fundamental reactivity of five-membered oxygen-containing heteroaromatic rings. |
α-Monoalkyl-substituted furan | 534-22-5 | 2-Methylfuran | ≥98% | Used in studies of α-alkyl substitution effects, ring oxidation, hydrogenation transformations, combustion properties, and biomass-derived fuel molecules. | |
β-Monoalkyl-substituted furan | 930-27-8 | 3-Methylfuran | ≥98% (GC), contains HQ as stabilizer | Used in comparative studies of β-alkyl substitution, positional isomer effects, electron distribution on the ring, and regioselectivity. | |
2,5-Dialkyl-substituted furan | 625-86-5 | 2,5-Dimethylfuran | ≥99% | Used in studies of symmetrical dialkyl substitution, oxidative stability, catalytic hydrogenation, combustion reactions, and candidate fuel molecules. | |
α-Ethyl-substituted furan | 3208-16-0 | 2-Ethylfuran | ≥99% | Used to investigate the effects of an ethyl side chain on volatility, hydrophobicity, oxidation pathways, and combustion reactions. | |
Long-chain alkyl-substituted furan | 3777-69-3 | 2-Pentylfuran | ≥98% (GC) | Used to investigate the effects of long-chain alkyl substitution on hydrophobicity, volatility, aroma characteristics, and gas chromatographic behavior. | |
Aryl-substituted furan | 17113-33-6 | 2-Phenylfuran | ≥95% | Used in studies of aryl–furan conjugation, molecular planarity, spectroscopic properties, and reference comparisons of heteroaryl coupling products. |
Table 2. Furan Aldehydes, Ketones, Alcohols, Amines, Ethers, and Reactive Derivatives
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
Furan methanol | 98-00-0 | Furfuryl alcohol | Chemically pure (CP), ≥97% | Used in studies of selective furfural reduction, furan resin formation, etherification, esterification, and construction of furan end groups. | |
Furan aldehyde | 98-01-1 | Furfural | Standard for GC, ≥99.5% (GC) | Used for qualitative and quantitative gas chromatographic analysis of furfural, retention-time confirmation, purity evaluation, and reference comparison of products from aldehyde redox reactions. | |
Hydroxymethylfuran aldehyde | 67-47-0 | 5-Hydroxymethylfurfural | Moligand™, refined grade, ≥99.5% | Used in studies of selective transformation of aldehyde and hydroxymethyl groups, oxidation-intermediate tracking, preparation of furandicarboxylic acid, and biomass-derived monomers. | |
Furanyl methyl ketone | 1192-62-7 | 2-Acetylfuran | ≥99% | Used in studies of nucleophilic addition, condensation, and reduction of furanyl ketones, as well as the electronic effects of carbonyl groups and the furan ring. | |
β-Furan aldehyde | 498-60-2 | Furan-3-carbaldehyde | ≥98% | Used in comparative studies of aldehyde substitution at position 3, positional isomer effects, carbonyl reactivity, and regioselectivity. | |
Alkyl-substituted furfural | 620-02-0 | 5-Methylfurfural | ≥98% | Used in studies of combined methyl and aldehyde substitution, carbonyl transformations, ring oxidation, and analysis of volatile furan aldehydes. | |
Dialdehyde furan | 823-82-5 | Furan-2,5-dicarboxaldehyde | ≥98% (GC) | Used in studies of 5-hydroxymethylfurfural oxidation intermediates, dialdehyde condensation, reductive amination, and construction of bifunctional molecules. | |
Hydroxymethyl-protected furfural | 10551-58-3 | 5-(Acetoxymethyl)furfural | ≥98% (GC) | Used in studies of hydroxymethyl ester protection, selective aldehyde transformation, protecting-group removal, and stability comparisons. | |
Furan dimethanol | 1883-75-6 | 2,5-Furandimethanol (FDM) | ≥98% | Used in studies of the double-reduction product of 5-hydroxymethylfurfural, diol polycondensation, polyesters, polyurethanes, and reversible cycloaddition materials. | |
Furan methylamine | 617-89-0 | Furfurylamine | ≥99% | Used in studies of furfural reductive amination, primary-amine acylation, nitrogen-containing furan intermediates, and construction of polymer end groups. | |
Bifunctional furan diamine | 2213-51-6 | 2,5-Bis(aminomethyl)furan | ≥97% | Used as a diprimary-amine monomer in studies of polyamides, polyureas, epoxy curing, and biomass-derived nitrogen-containing materials. | |
Furfuryl alcohol ester | 623-17-6 | Furfuryl acetate | ≥99% | Used in studies of furfuryl alcohol esterification, hydroxyl protection, ester hydrolysis, volatility, and aroma-component analysis. | |
Bis(furanyl) ether | 4437-22-3 | 2,2′-[Oxybis(methylene)]difuran | ≥98% | Used in studies of bifuran structures, ether-bond stability, multisite cycloaddition, and construction of cross-linked networks. | |
Furanyl epoxy compound | 5380-87-0 | Furfuryl glycidyl ether | ≥96% | Used in studies of epoxy ring opening, amine curing, furanyl grafting, and the combined use of epoxy reactions and furan-ring cycloaddition. | |
Furfuryl methacrylate monomer | 3454-28-2 | Furfuryl methacrylate | ≥95%, contains 200 ppm monomethyl ether hydroquinone as inhibitor | Used in studies of free-radical polymerization, side-chain furan functionalization, reversible cycloaddition cross-linking, and thermoresponsive polymers. | |
Furfuryl mercaptan | 98-02-2 | Furfuryl mercaptan | ≥98% | Used in studies of sulfur-containing volatile furans, thiol reactions, food aroma composition, and gas chromatographic analysis. | |
Furfuryl thioester | 13678-68-7 | Furfuryl thioacetate | ≥99% | Used in studies of sulfur-containing furan thioesters, thioester hydrolysis, thermally generated aromas, and analysis of volatile components. |
Table 3. Furan Carboxylic Acids, Esters, Amides, Acyl Chlorides, and Nitriles
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
α-Furancarboxylic acid | 88-14-2 | Furoic acid | ≥98% | Used in studies of carboxyl-group acid–base properties, esterification, amidation, decarboxylation, and furfural oxidation products. | |
β-Furancarboxylic acid | 488-93-7 | Furan-3-carboxylic acid | ≥98% (T) | Used in comparative studies of carboxyl substitution at position 3, positional isomer effects, acidity, and derivatization reactions. | |
Hydroxymethylfurancarboxylic acid | 6338-41-6 | 5-Hydroxymethyl-2-furancarboxylic acid | ≥98% | Used in studies of the HMF oxidation pathway in which the aldehyde group is oxidized first, intermediate quantification, and subsequent oxidation reactions. | |
Formylfurancarboxylic acid | 13529-17-4 | 5-Formyl-2-furancarboxylic acid | ≥98% | Used in studies of the convergent intermediate in HMF oxidation pathways, further aldehyde oxidation, and reaction-pathway analysis. | |
Furandicarboxylic acid monomer | 3238-40-2 | 2,5-Furandicarboxylic acid (FDCA) | ≥98% | Used in studies of dicarboxyl-group esterification, polycondensation, preparation of furan-based polyesters, and structural comparison with aromatic diacids. | |
Methyl furancarboxylate | 611-13-2 | Methyl furoate | ≥99% | Used in studies of furancarboxylic acid esterification, ester hydrolysis, transesterification, and analysis of carboxylic acid derivatives. | |
Dimethyl furandicarboxylate | 4282-32-0 | Dimethyl furan-2,5-dicarboxylate | ≥98% | Used in studies of transesterification polycondensation of furandicarboxylates, polyester-monomer purification, and comparison of methyl ester routes. | |
Diethyl furandicarboxylate | 53662-83-2 | Diethyl furan-2,5-dicarboxylate | ≥98% | Used in studies of diester hydrolysis, transesterification polymerization, ethyl ester routes, and furandicarboxylate structures. | |
α-Furancarboxamide | 609-38-1 | Furan-2-carboxamide | ≥98% | Used in studies of carboxylic acid amidation, hydrogen-bonding interactions, amide hydrolysis, and the effects of amide substitution at position 2. | |
β-Furancarboxamide | 609-35-8 | Furan-3-carboxamide | ≥98% | Used in comparative studies of amide substitution at position 3, positional isomerism, hydrogen-bonding networks, and amide reactivity. | |
Furan carbonyl chloride | 527-69-5 | Furoyl chloride | ≥97% | Used in highly reactive acylation, preparation of esters and amides, interfacial reactions, and introduction of furoyl groups. | |
Furan dicarbonyl dichloride | 10375-34-5 | Furan-2,5-dicarbonyl dichloride | ≥98% (GC) | Used in studies of double acylation, polyamides, polyesters, interfacial polycondensation, and bifunctional furan monomers. | |
α-Furan nitrile | 617-90-3 | 2-Cyanofuran | ≥98% (GC) | Used in studies of the electron-withdrawing effect of a nitrile group at position 2, nitrile hydrolysis and reduction, and synthesis of nitrogen-containing heterocycles. | |
β-Furan nitrile | 30078-65-0 | 3-Cyanofuran | ≥97% | Used in studies of nitrile substitution at position 3, positional isomer effects, nitrile transformations, and comparison of ring electronic structures. | |
Dinitrile furan | 58491-62-6 | 2,5-Dicyanofuran | ≥98% (GC) | Used in studies of substitution by two electron-withdrawing groups, nitrile hydrolysis and reduction, conjugated electronic structures, and bifunctional intermediates. |
Table 4. Halogenated Furans, Organoboron Compounds, and Bifunctional Coupling Building Blocks
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
α-Chlorofuran | 3187-94-8 | 2-Chlorofuran | ≥95% | Used in studies of carbon–chlorine bond reactivity, nucleophilic substitution, metal-catalyzed coupling, and reaction-condition screening for halogenated furans. | |
α-Bromofuran | 584-12-3 | 2-Bromofuran | ≥93% | Used in studies of selective cross-coupling at position 2, metalation, heteroaryl connection, and construction of furan building blocks. | |
β-Bromofuran | 22037-28-1 | 3-Bromofuran | ≥97% | Used in studies of selective coupling at position 3, positional-isomer routes, carbon–carbon bond construction, and regioselectivity. | |
Dibromofuran | 32460-00-7 | 2,5-Dibromofuran (contains MgO as stabilizer) | ≥97% (GC) | Used in studies of two-site cross-coupling, stepwise functionalization, construction of symmetrical conjugated molecules, and polymer monomers. | |
α-Iodofuran | 54829-48-0 | 2-Iodofuran | ≥95% | Used in studies of highly reactive carbon–iodine bond coupling, metal–halogen exchange, and rapid connection of furan fragments. | |
Side-chain bromomethyl furan | 4437-18-7 | 2-(Bromomethyl)furan | — | Used in studies of side-chain nucleophilic substitution, furfurylation reactions, quaternary ammonium salt preparation, and comparison with ring-halogenated furan reactivity. | |
Bromofurfural bifunctional building block | 1899-24-7 | 5-Bromo-2-furaldehyde | ≥98% | Used in studies of carbon–bromine bond cross-coupling, aldehyde condensation and reduction, chemoselectivity, and stepwise functionalization. | |
α-Furanboronic acid | 13331-23-2 | Furan-2-boronic acid (contains varying amounts of anhydride) | ≥98% | Used in studies of furan-fragment transfer at position 2, cross-coupling, heteroaryl connection, and coupling conditions. | |
β-Furanboronic acid | 55552-70-0 | Furan-3-boronic acid (contains an undetermined amount of anhydride) | ≥95% | Used in studies of furan-fragment coupling at position 3, construction of positional isomers, and heteroaryl connection routes. | |
β-Furan boronate ester | 248924-59-6 | Furan-3-boronic acid pinacol ester | ≥98% | Used as a stable organoboron building block in studies of selective cross-coupling at position 3 and multistep synthetic routes. | |
Alkyl-substituted furan boronate ester | 338998-93-9 | 2-Methylfuran-5-boronic acid pinacol ester | ≥97% | Used in studies of methyl-substituted furan coupling, substituent electronic effects, and construction of multiply substituted heteroaromatic molecules. | |
Formylfuranboronic acid | 27329-70-0 | 5-Formylfuran-2-boronic acid (contains varying amounts of anhydride) | ≥97% | Used in studies of boronic-acid cross-coupling, subsequent aldehyde condensation and reduction, and control of the reaction sequence between two reactive sites. | |
Bis-boronate furan | 476004-83-8 | Furan-2,5-diboronic acid pinacol ester | ≥97% | Used in bidirectional cross-coupling and in the construction of symmetrical disubstituted furans, conjugated oligomers, and polymer backbones. | |
Benzofuran boronic acid | 98437-24-2 | Benzofuran-2-boronic acid (contains varying amounts of anhydride) | ≥98% | Used in coupling of fused-furan fragments, synthesis of benzofuran derivatives, and construction of rigid conjugated scaffolds. |
Table 5. Benzofurans, Polycyclic Fused Furans, and Furocoumarins
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
Benzofuran parent ring | 271-89-6 | Benzofuran | ≥99% | Used to investigate the effects of benzene-ring fusion on conjugation range, skeletal rigidity, ring substitution, and heteroaromatic reactivity. | |
Partially hydrogenated benzofuran | 496-16-2 | 2,3-Dihydrobenzofuran | ≥98% | Used in comparative studies of partial hydrogenation of the five-membered oxygen-containing ring in benzofuran, saturated-ring conformations, and changes in the aromaticity of the fused five-membered ring. | |
Dibenzofuran parent ring | 132-64-9 | Dibenzofuran | ≥98% | Used in studies of polycyclic fused conjugation, molecular rigidity, thermal properties, spectroscopic properties, and environmental analysis. | |
Furocoumarin parent ring | 66-97-7 | Psoralen | ≥98% | Used in studies of fused furocoumarin structures, photochemical cycloaddition, natural-product identification, and analytical reference comparisons. | |
5-Methoxyfurocoumarin | 484-20-8 | Bergapten | Moligand™, ≥98% (GC) | Used in studies of methoxy-substituted furocoumarins, photochemical properties, natural-product quantification, and quality evaluation. | |
8-Methoxyfurocoumarin | 298-81-7 | 8-Methoxypsoralen | Moligand™, ≥98% | Used in studies of the effects of methoxy substitution at position 8, furocoumarin photoreactions, positional isomers, and analytical detection. |
Table 6. Dihydrofurans, Tetrahydrofurans, and Polyether Material-Related Compounds
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
2,3-Dihydrofuran cyclic ether | 1191-99-7 | 2,3-Dihydrofuran | ≥99% | Used in studies of partially hydrogenated furans, addition, oxidation and ring opening of unsaturated cyclic ethers, and double-bond positional effects. | |
2,5-Dihydrofuran cyclic ether | 1708-29-8 | 2,5-Dihydrofuran | ≥97% | Used in studies of nonconjugated unsaturated cyclic ethers, double-bond positional isomerism, addition, ring opening, and further hydrogenation. | |
Tetrahydrofuran parent compound | 109-99-9 | T1491789 | Tetrahydrofuran (THF) | Anhydrous grade, ≥99.9%, unstabilized, H₂O ≤30 ppm | Used as an anhydrous reaction medium and in studies of coordination with organometallic reagents, solvation effects, and cationic ring-opening polymerization. |
2-Methyltetrahydrofuran | 96-47-9 | 2-Methyltetrahydrofuran | Anhydrous grade, ≥99%, unstabilized | Used as a hydrophobic ether solvent and in extraction, organometallic reaction media, and comparative studies of solvent properties. | |
3-Methyltetrahydrofuran | 13423-15-9 | 3-Methyltetrahydrofuran | ≥95% (GC) | Used to investigate the effects of methyl substitution position on cyclic-ether polarity, conformation, solvation, and reaction-medium properties. | |
Tetrahydrofuran methanol | 97-99-4 | Tetrahydrofurfuryl alcohol | ≥99% | Used in studies of the ring-hydrogenation product of furfuryl alcohol, alcohol esterification, etherification, solvents, and saturated cyclic-ether derivatives. | |
Tetrahydrofuran methylamine | 4795-29-3 | (±)-Tetrahydrofurfurylamine | ≥97% | Used in studies of saturated cyclic-ether primary amines, acylation, salt formation, reductive amination products, and nitrogen-containing intermediates. | |
Tetrahydrofuran carboxylic acid | 16874-33-2 | Tetrahydrofuran-2-carboxylic acid | ≥98% (GC) (T) | Used in studies of saturated cyclic-ether carboxylic acids, esterification, amidation, and structural comparison with aromatic furancarboxylic acids. | |
Tetrahydrofurfuryl acrylate monomer | 2399-48-6 | Tetrahydrofurfuryl acrylate | ≥98%, contains 500 ppm MEHQ as stabilizer | Used in studies of free-radical polymerization, introduction of saturated cyclic-ether side groups, coating monomers, and polarity control. | |
Tetrahydrofurfuryl methacrylate monomer | 2455-24-5 | Tetrahydrofurfuryl methacrylate | ≥97%, contains 900 ppm MEHQ as stabilizer | Used in methacrylate polymerization, tetrahydrofuran side-group functionalization, cross-linking systems, and material-property studies. | |
Polyether polyol | 25190-06-1 | Polytetrahydrofuran (PTHF) | Average Mₙ ~2900 | Used in studies of polyether segments, polyurethane elastomers, block copolymers, flexible segments, and molecular-weight effects. |
Table 7. Nitrofurans and Compounds Related to Metabolite-Marker Analysis
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
Oxazolidinone-side-chain nitrofuran | 67-45-8 | Furazolidone | Moligand™, ≥98% | Used in studies of 5-nitrofuran side-chain structures, reductive bioactivation, structure–activity relationships, and metabolite markers. | |
Hydantoin-side-chain nitrofuran | 67-20-9 | Nitrofurantoin | Moligand™, ≥98% | Used to investigate the effects of the hydantoin side chain on nitro reduction, molecular recognition, metabolic transformation, and analytical response. | |
Semicarbazone-type nitrofuran | 59-87-0 | Nitrofurazone | Moligand™, ≥98% | Used in studies of nitrofuran semicarbazone structures, reductive activation, degradation products, and residue analysis. | |
Aroylhydrazone-type nitrofuran | 965-52-6 | Nifuroxazide | Moligand™, ≥98% | Used in studies of aroylhydrazone side chains, nitro reduction, structure–activity relationships, purity evaluation, and analytical methods. | |
Morpholine-side-chain nitrofuran | 139-91-3 | Furaltadone | Analytical standard | Used for qualitative and quantitative analysis of nitrofurans, studies of morpholine-side-chain metabolism, residue analysis, and instrumental-method calibration. | |
Semicarbazide metabolite marker | 57-56-7 | Semicarbazide | 6 wt. % (on silica gel) | Used in studies of nitrofurazone metabolite markers, carbonyl derivatization, and nitrofuran residue detection. | |
Semicarbazide hydrochloride | 563-41-7 | Semicarbazide hydrochloride | ≥99% | Used in studies of semicarbazide salt forms, carbonyl derivatization, nitrofurazone metabolite analysis, and method development. | |
Nitrofurantoin metabolite marker | 2827-56-7 | 1-Aminohydantoin hydrochloride | ≥98% | Used in studies of nitrofurantoin metabolite residues, derivatization reactions, liquid chromatography–mass spectrometry quantification, and method validation. | |
Furazolidone metabolite marker | 80-65-9 | 3-Amino-2-oxazolidinone (AOZ) | ≥97% | Used in studies of furazolidone metabolite residues, derivatization-based detection, mass-spectrometric quantification, and analytical-method evaluation. | |
Furaltadone metabolite marker | 43056-63-9 | AMOZ | Analytical standard | Used for qualitative and quantitative analysis of furaltadone metabolite residues, instrument calibration, and analytical-method confirmation. |
Table 8. Supporting Reagents for Furan [4+2] Cycloaddition and Reversible Cross-Linking
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
Parent maleimide dieneophile | 541-59-3 | Maleimide | ≥98% | Used in studies of furan [4+2] cycloaddition, fundamental dieneophile reactivity, addition kinetics, and product stability. | |
N-Methylmaleimide | 930-88-1 | N-Methylmaleimide | ≥98% (GC) | Used to investigate the effects of N-methyl substitution on dieneophile electronic properties, cycloaddition rate, and reversibility. | |
N-Phenylmaleimide | 941-69-5 | N-Phenylmaleimide | ≥98% (GC) | Used in studies of aryl-substituted maleimides, furan cycloaddition, endo/exo selectivity, and thermally reversible behavior. | |
Hydroxyl-functionalized maleimide | 1585-90-6 | N-(2-Hydroxyethyl)maleimide (HEMI) | ≥97% | Used in hydroxyl grafting, polymer end-group functionalization, furan cycloaddition, and construction of thermoresponsive networks. | |
Bifunctional maleimide cross-linker | 13676-54-5 | 4,4′-Bismaleimidodiphenylmethane | ≥96% | Used in studies of cross-linking between two furan sites, reversible-network formation, cross-link density, thermal response, and rheological properties. | |
Anhydride-type dieneophile | 108-31-6 | Maleic anhydride | AR, ≥99% (GC) | Used in studies of furan [4+2] cycloaddition, preparation of anhydride adducts, comparison of dieneophile structures, and subsequent ring-opening reactions. |
Note: The products listed above are representative Aladdin research products. Additional product specifications, grades, and certificate-of-analysis information can be retrieved from the Aladdin website using the product name, CAS number, or catalog number.
References
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