5-Ethyl-2-Hydroxybenzaldehyde: Properties, Uses & Handling

5-Ethyl-2-hydroxybenzaldehyde is a substituted salicylaldehyde bearing an ethyl group at the 5-position, making it a valuable aromatic aldehyde building block widely employed in organic synthesis, coordination chemistry, and the preparation of Schiff base ligands.

Chemical Name

5-Ethyl-2-hydroxybenzaldehyde

Aladdin SKU

E344459

Functional Groups

Aldehyde (–CHO) and phenolic hydroxyl (–OH) on an ethyl-substituted benzene ring

Key Reactivity

Condenses with primary amines to form Schiff bases; acts as a bidentate O,N-donor precursor in metal coordination

Structural Class

Ortho-hydroxy aromatic aldehyde (salicylaldehyde derivative)

Typical Physical State

Liquid or low-melting solid with a characteristic aldehyde odor (exact mp/bp: see SDS)

Chemical Identity and Structure

5-Ethyl-2-hydroxybenzaldehyde belongs to the salicylaldehyde family of compounds. Its core structure consists of a benzene ring carrying three substituents: a formyl group (–CHO) at C-1, a hydroxyl group (–OH) at C-2 (ortho to the aldehyde), and an ethyl group (–CH₂CH₃) at C-5 (para to the hydroxyl). The ortho relationship between the phenolic –OH and the aldehyde –CHO is of particular chemical significance: the two groups can participate in intramolecular hydrogen bonding, influencing the compound's spectroscopic properties, reactivity, and tautomeric behavior.

The ethyl substituent at C-5 increases the lipophilicity of the molecule relative to unsubstituted salicylaldehyde and can modulate the electronic density of the aromatic ring via a weak inductive effect. This balance of polarity and hydrophobicity makes the compound useful when intermediate lipophilicity is required in a target molecule.

Applications in Research and Synthesis

Schiff Base and Ligand Synthesis: The most widely exploited reaction of 5-ethyl-2-hydroxybenzaldehyde is condensation with primary amines to generate Schiff bases (imines). When the amine partner itself bears donor atoms (e.g., amino acids, hydrazides, aminothiols), the resulting Schiff base adopts a polydentate geometry capable of chelating transition metals. Such metal complexes are of interest in bioinorganic model chemistry, catalysis, and materials science.

Organic Building Block: The aldehyde functionality participates in a broad range of classical organic reactions, including Knoevenagel condensations, Wittig olefinations, nucleophilic additions (Grignard, organolithium), and reductive aminations. The ortho-OH group can additionally be exploited in intramolecular cyclization reactions to form benzofuran or chromene scaffolds.

Sensor and Dye Research: Ortho-hydroxy aromatic aldehydes and their Schiff base derivatives are used as fluorescent chemosensors for metal ions. The ethyl group can fine-tune photophysical properties compared with simpler analogues, providing researchers with a means to optimize emission wavelength and quantum yield.

Safety, Handling, and Storage

General Precautions: As with most aromatic aldehydes, 5-ethyl-2-hydroxybenzaldehyde should be handled in a well-ventilated fume hood. Personal protective equipment including chemical-resistant gloves, safety glasses, and a laboratory coat is recommended. Avoid inhalation of vapors and contact with skin or eyes.

Storage: Store in a tightly sealed container in a cool, dry place away from strong oxidizers, bases, and ignition sources. Refrigerated storage (2–8 °C) is typically recommended to minimize oxidation of the aldehyde group and maintain long-term purity. Always consult the current Safety Data Sheet (SDS) for the definitive hazard classification, GHS pictograms, first-aid measures, and disposal guidance.

Waste Disposal: Dispose of residues in accordance with applicable local, regional, and national regulations. Do not pour aldehyde-containing waste down the drain.

Reagent Specifications and Quality

Aladdin Scientific offers 5-Ethyl-2-hydroxybenzaldehyde under SKU E344459. Researchers should consult the product page or contact technical support for the current lot-specific certificate of analysis (CoA), which details purity (typically assessed by GC or HPLC), appearance, and water content. Consistent high purity is critical when using this compound as a synthetic building block, since aldehyde impurities or water can interfere with condensation and organometallic reactions.

When comparing suppliers, key specification parameters to evaluate include: assay (% purity by GC), refractive index (for liquid form), color (APHA scale), and residual solvent content. Request a CoA for each lot to confirm compliance with your experimental requirements.

Frequently asked questions

What is the primary use of 5-Ethyl-2-hydroxybenzaldehyde in organic chemistry?

It is principally used as a building block for Schiff base synthesis via condensation with primary amines. The resulting imines, bearing the phenolic –OH group, function as bidentate or polydentate ligands for transition-metal complexation and are also explored as fluorescent chemosensors. Beyond ligand chemistry, the aldehyde group participates in Knoevenagel condensations, Wittig reactions, and nucleophilic additions.

How should 5-Ethyl-2-hydroxybenzaldehyde be stored to maintain purity?

The compound should be stored in a tightly sealed container under cool, dry conditions, preferably at 2–8 °C and away from light, moisture, oxidizers, and ignition sources. Refrigerated storage slows oxidation of the aldehyde functionality. Always check the current SDS and CoA for lot-specific recommendations.

What is the Aladdin SKU for 5-Ethyl-2-hydroxybenzaldehyde?

5-Ethyl-2-hydroxybenzaldehyde is available from Aladdin Scientific under SKU E344459. Contact Aladdin's technical support or visit the product page for current pricing, pack sizes, and the latest certificate of analysis.

How does the ethyl substituent affect the reactivity of this compound compared with salicylaldehyde?

The ethyl group at C-5 is an electron-donating alkyl substituent that modestly increases the electron density of the ring via hyperconjugation and induction. This can slightly enhance nucleophilic character at the carbonyl carbon relative to electron-withdrawing substituted analogues. More practically, the ethyl group raises lipophilicity, improving solubility in organic solvents and influencing the partition coefficient of derived products.

Is 5-Ethyl-2-hydroxybenzaldehyde the same as 3-ethylsalicylaldehyde?

No. Salicylaldehyde numbering places the –CHO at C-1 and –OH at C-2. '3-Ethylsalicylaldehyde' would carry the ethyl at C-3 (ortho to the –OH), whereas 5-ethyl-2-hydroxybenzaldehyde carries it at C-5 (para to the –OH). These are distinct regioisomers with different physical and chemical properties. Always confirm the CAS number and structure on the certificate of analysis before use.

References

1. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 4th ed.; Wiley-Interscience: New York, 1992. (General aldehyde reactivity and Schiff base formation.)
2. Hobza, P.; Havlas, Z. Blue-shifting hydrogen bonds. Chem. Rev. 2000, 100, 4253–4264. (Background on intramolecular hydrogen bonding in ortho-hydroxy aldehydes.) doi:10.1021/cr990050q
3. Anacona, J. R.; Rodriguez, A. Synthesis and antibacterial activity of metal complexes of Schiff bases derived from salicylaldehyde. J. Coord. Chem. 2004. (Representative use of salicylaldehyde derivatives in Schiff base metal complexes.)

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