2-Mercapto-4-methoxybenzaldehyde 294674-98-9 98% Light Yellow to Pale Brown Solid Aromatic Aldehyde Intermediate

1. Product Overview

2-Mercapto-4-methoxybenzaldehyde (CAS 294674-98-9) is a uniquely functionalized aromatic building block featuring both a nucleophilic thiol group at the ortho-position and an electrophilic aldehyde group, complemented by a para-methoxy electron-donating substituent. This specific arrangement facilitates intramolecular cyclization reactions, making it an indispensable precursor for constructing benzothiophene and benzothiazole scaffolds. It is extensively utilized in medicinal chemistry for the synthesis of sulfur-containing heterocycles that serve as core structures in pharmaceuticals targeting oncology, inflammation, and infectious diseases.

2. Key Features and Benefits

• Orthogonal Reactivity: The thiol (–SH) and aldehyde (–CHO) groups offer distinct reaction pathways. The thiol readily participates in oxidative coupling, Michael additions, or nucleophilic substitutions, while the aldehyde is ideal for condensation reactions (e.g., Schiff bases, Wittig reactions).

• Facile Heterocycle Formation: Under mild acidic or basic conditions, it readily undergoes cyclization with various reagents (e.g., phenacyl bromides, α-halo ketones, or cyanamides) to yield highly substituted benzo[b]thiophenes or 2-aminobenzothiazoles.

• Synthetic Versatility: The methoxy group enhances the electron density of the aromatic ring, influencing regioselectivity in electrophilic substitution reactions and serving as a synthetic handle for further derivatization (e.g., demethylation to phenols).

• High Purity: Supplied at ≥98% purity (HPLC), ensuring minimal interference from oxidized disulfide impurities in sensitive coupling reactions.

3. Major Applications

• Pharmaceutical Synthesis: A critical intermediate in the synthesis of bioactive molecules, including tyrosine kinase inhibitors and antimicrobial agents. It is specifically documented in the synthesis of 2-arylbenzo[b]thiophene derivatives.

• Organic Synthesis: Used as a starting material for the preparation of fluorescent dyes and photoactive materials based on the benzothiophene chromophore.

• Agrochemical Research: Serves as a precursor for developing novel pesticides or fungicides containing sulfur heterocycles.

• Material Science: Incorporated into conductive polymers or organic electronic materials where sulfur-containing aromatic systems are required.

4. Technical Specifications

Item Description
Product Name 2-Mercapto-4-methoxybenzaldehyde
Synonyms 4-Methoxy-2-sulfanylbenzaldehyde; 4-Methoxy-2-mercaptobenzaldehyde; 2-Mercapto-p-anisaldehyde
CAS Number 294674-98-9
Molecular Formula C₈H₈O₂S
Molecular Weight 168.21 g/mol
MDL Number MFCD03426877
Assay (Purity) ≥98% (HPLC)
Appearance Light yellow to pale brown crystalline solid or powder
Melting Point 78–82 °C (Literature value)
Boiling Point ~276.6 °C (Predicted)
Density ~1.23 g/cm³ (Predicted)
pKa ~3.87 (Predicted, Phenolic SH)
Solubility Soluble: DMSO (>50 mg/mL), Methanol, Ethanol, DMF, Dichloromethane (DCM), Chloroform, THF.
Slightly Soluble:Water, Ether.
Insoluble:Hexane.
Spectral Data ¹H NMR (CDCl₃, 400 MHz): δ 3.85 (s, 3H, OCH₃), 6.95 (dd, J=8.5, 2.5 Hz, 1H, Ar-H), 7.45 (d, J=2.5 Hz, 1H, Ar-H), 7.80 (d, J=8.5 Hz, 1H, Ar-H), 9.85 (s, 1H, CHO), 11.20 (s, 1H, SH).
¹³C NMR (CDCl₃):δ 55.5 (OCH₃), 113.5, 124.0, 129.5, 131.0, 160.5, 190.5 (CHO).
SMILES COC1=CC(=C(C=C1)C=O)S
InChI Key UQZJZKXJQKZQKU-UHFFFAOYSA-N
Storage (Powder) 2–8 °C, sealed under inert atmosphere (N₂/Ar), protected from light; stable ≥12–18 months
Sensitivity Air & Light Sensitive (prone to oxidation to disulfide); Moisture Sensitive
HS Code 2930.90.90

5. Storage and Handling

• Storage Conditions: Store in a tightly sealed container under an inert gas atmosphere (Nitrogen or Argon) at 2–8 °C. Protect rigorously from light, air, and moisture to prevent oxidation of the thiol group to the corresponding disulfide.

• Handling: Allow the container to warm to room temperature in a dry, inert environment (e.g., glovebox) before opening to prevent condensation. Handle quickly and reseal promptly. Use anhydrous solvents for dissolution.

• Stability Note: The free thiol group is susceptible to aerial oxidation. If discoloration (darkening) occurs, the material may have partially oxidized; purification via recrystallization or column chromatography may be required for critical applications.

• Solution Prep: Prepare stock solutions in degassed anhydrous DMSO or DMF. Avoid prolonged storage of solutions; use immediately after preparation.

6. Safety Summary

• GHS Classification: GHS07 – Warning

• Hazard Statements: H302 (Harmful if swallowed); H315 (Causes skin irritation); H319 (Causes serious eye irritation); H335 (May cause respiratory irritation).

• Precautionary Statements: P261 (Avoid breathing dust/mist); P264 (Wash thoroughly after handling); P271 (Use only outdoors or in a well-ventilated area); P280 (Wear protective gloves/eye protection); P301+P312 (If swallowed: Call a physician if you feel unwell); P302+P352 (If on skin: Wash with plenty of soap and water); P305+P351+P338 (If in eyes: Rinse cautiously with water for several minutes; remove contact lenses if present); P337+P313 (If eye irritation persists: Get medical advice).

• Special Handling: As a thiol-containing compound, it may emit a characteristic unpleasant odor. Always handle in a certified fume hood.

• Intended Use: For laboratory research and development ONLY. Not for human or veterinary therapeutic, diagnostic, or food use.

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