2-Ethynyl-1,4-dimethylbenzene: Properties, Handling & Lab Use

2-Ethynyl-1,4-dimethylbenzene is a terminal alkyne-bearing aromatic reagent widely used as a building block in metal-catalyzed cross-coupling reactions, click chemistry, and the synthesis of functionalized arylacetylene derivatives.

Chemical Name

2-Ethynyl-1,4-dimethylbenzene

Common Synonym

2-Ethynyl-p-xylene

SKU / Catalog Number

E469623

Functional Group

Terminal alkyne (C≡CH) on a dimethyl-substituted benzene ring

Primary Applications

Sonogashira coupling, CuAAC click chemistry, material science building block

Storage Recommendation

Store in a cool, dry, well-ventilated area away from heat and ignition sources; keep container tightly sealed

Reference Standard

Sigma-Aldrich No. 521116

Chemical Identity and Physical Properties

2-Ethynyl-1,4-dimethylbenzene (synonym: 2-ethynyl-p-xylene) is an aromatic terminal alkyne in which an ethynyl group (–C≡CH) is positioned at carbon-2 of a 1,4-dimethylbenzene (p-xylene) scaffold. The combination of the electron-donating methyl substituents with the reactive terminal alkyne creates a versatile reagent for diverse synthetic transformations.

As a terminal alkyne, the compound possesses an acidic C–H bond (pKa approximately 25 in DMSO for simple arylacetylenes), making it amenable to metalation and subsequent nucleophilic addition. The aromatic ring contributes to conjugation with the triple bond, slightly activating the alkyne toward electrophilic and transition-metal-mediated reactions. The compound is expected to be a colourless to pale yellow liquid at room temperature; however, researchers should consult the certificate of analysis (CoA) supplied with SKU E469623 for confirmed physicochemical data.

Synthesis and Key Reaction Applications

Sonogashira Cross-Coupling: The most prominent application of 2-ethynyl-1,4-dimethylbenzene is as an alkyne coupling partner in Pd/Cu-catalysed Sonogashira reactions. The terminal alkyne couples efficiently with aryl or vinyl halides under mild conditions to furnish internal diarylacetylenes or enyne products, which are valuable intermediates in pharmaceutical and materials chemistry.

Copper-Catalysed Azide–Alkyne Cycloaddition (CuAAC): As a terminal alkyne, this reagent participates in CuAAC click chemistry to afford 1,4-disubstituted 1,2,3-triazoles with high regioselectivity. This approach is useful for bioconjugation, polymer functionalisation, and the construction of heterocyclic libraries.

Nucleophilic Addition and Metalation: Deprotonation with strong bases (e.g., n-BuLi, NaH) generates the corresponding lithium or sodium acetylide, which can add to carbonyl compounds, epoxides, or electrophilic heterocycles to yield propargylic alcohols and related structures.

Material Science: Arylacetylene units derived from this reagent are incorporated into conjugated oligomers, liquid-crystal precursors, and porous organic frameworks, owing to the rigid, linear geometry of the alkyne spacer.

Safety, Handling, and Storage Guidelines

General Hazard Awareness: 2-Ethynyl-1,4-dimethylbenzene is an organic aromatic compound and should be treated as potentially flammable and an irritant. Researchers must consult the current Safety Data Sheet (SDS) prior to use, as specific GHS classification, flash point, and toxicity data should be obtained from the official SDS for SKU E469623.

Personal Protective Equipment (PPE): Wear appropriate chemical-splash goggles, nitrile gloves, and a laboratory coat. Work in a fume hood when weighing or transferring the neat compound to minimise inhalation exposure.

Storage: Store in a tightly sealed container in a cool, dry, well-ventilated area, away from heat sources, open flames, and incompatible oxidising agents. Refrigerated storage (2–8 °C) may help preserve reagent quality over extended periods; consult the product label for the recommended storage temperature.

Waste Disposal: Dispose of residues and contaminated materials in accordance with local, institutional, and national regulations for organic solvent waste. Do not pour down the drain.

Quality, Purity, and Ordering Information

Aladdin Scientific supplies 2-Ethynyl-1,4-dimethylbenzene under SKU E469623. The product corresponds to the reference compound listed as Sigma-Aldrich No. 521116. Purity specification and analytical data (NMR, GC purity, or HPLC) are provided on the Certificate of Analysis (CoA) accompanying each lot; researchers are strongly encouraged to verify the CoA upon receipt.

For applications requiring high purity — such as pharmaceutical intermediate synthesis or quantitative click-chemistry studies — researchers should confirm that the purity grade meets their experimental threshold before use. Contact Aladdin Scientific technical support for bulk quantities, custom purity tiers, or special packaging requirements.

Frequently asked questions

What is the main difference between 2-Ethynyl-1,4-dimethylbenzene and phenylacetylene in coupling reactions?

2-Ethynyl-1,4-dimethylbenzene carries two electron-donating methyl groups on the aryl ring, which can subtly influence the electronic density at the alkyne and affect reaction rates and selectivity compared with unsubstituted phenylacetylene. The steric profile of the 2-methyl group adjacent to the alkyne may also influence catalyst coordination in Sonogashira reactions. Researchers should optimise catalyst loading and base conditions accordingly.

How should I handle 2-Ethynyl-1,4-dimethylbenzene to avoid degradation?

Store the compound in a tightly sealed vial under an inert atmosphere (nitrogen or argon) in a cool, dark location. Avoid prolonged exposure to air, moisture, and light. Always work in a fume hood and use fresh solvent when preparing solutions to prevent oxidative coupling or polymerisation of the terminal alkyne.

Can 2-Ethynyl-1,4-dimethylbenzene be used in CuAAC click chemistry without modification?

Yes. As a terminal alkyne, 2-Ethynyl-1,4-dimethylbenzene is directly suitable for copper(I)-catalysed azide–alkyne cycloaddition (CuAAC) without prior activation or protection. It reacts with organic azides in the presence of a Cu(I) catalyst and a suitable base or reducing agent to furnish 1,4-disubstituted 1,2,3-triazoles regioselectively.

What solvents are compatible with 2-Ethynyl-1,4-dimethylbenzene in typical reactions?

Common compatible solvents include THF, DMF, DMSO, acetonitrile, toluene, and diethyl ether. Solvent choice depends on the specific reaction type and catalyst system. For Sonogashira couplings, triethylamine often serves both as base and co-solvent. Always check reagent and catalyst solubility before selecting the solvent system.

References

1. Sonogashira, K.; Tohda, Y.; Hagihara, N. A convenient synthesis of acetylenes: catalytic substitutions of acetylenic hydrogen with bromoalkenes, iodoarenes and bromopyridines. Tetrahedron Letters, 1975.
2. Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. A stepwise Huisgen cycloaddition process: copper(I)-catalyzed regioselective ligation of azides and terminal alkynes. Angewandte Chemie International Edition, 2002.
3. Sigma-Aldrich Product Reference No. 521116 — 2-Ethynyl-p-xylene. Sigma-Aldrich/MilliporeSigma catalogue.

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.