2-Ethynyl-1,4-dimethylbenzene: Properties, Uses & FAQs

2-Ethynyl-1,4-dimethylbenzene is a terminal alkyne bearing a para-xylene scaffold, widely used as a versatile building block in palladium-catalyzed cross-coupling reactions, copper-catalyzed azide–alkyne cycloaddition (CuAAC) click chemistry, and the construction of conjugated organic frameworks.

IUPAC Name

2-Ethynyl-1,4-dimethylbenzene

Also Known As

2-Ethynyl-p-xylene; 2-Ethynyl-4-methyltoluene

Molecular Formula

C₁₀H₁₀

Molecular Weight

130.19 g/mol

Functional Group

Terminal alkyne (≡C–H)

Reference Standard

Sigma-Aldrich No. 521116

Aladdin SKU

E469623

What Is 2-Ethynyl-1,4-dimethylbenzene?

2-Ethynyl-1,4-dimethylbenzene (molecular formula C₁₀H₁₀, MW 130.19 g/mol) is an aryl terminal alkyne derived from the para-xylene (1,4-dimethylbenzene) scaffold with an ethynyl substituent at the 2-position. The compound features a reactive terminal C≡C–H moiety attached directly to an electron-rich dimethyl-substituted benzene ring. This structural combination makes it a valuable synthon in modern organic and medicinal chemistry, enabling its participation in a broad range of C–C bond-forming reactions. It is catalogued under Sigma-Aldrich reference number 521116 and is available from Aladdin Scientific as SKU E469623.

Key Chemical Properties and Handling

As a terminal alkyne, 2-Ethynyl-1,4-dimethylbenzene possesses a mildly acidic terminal proton (pKa ~25 in DMSO), which can be deprotonated by strong bases such as n-BuLi or NaH to form reactive alkynyl anions suitable for nucleophilic additions. The compound is a colorless to pale yellow liquid at room temperature. It should be stored in a cool, dry, well-ventilated location away from strong oxidizers, strong bases, and ignition sources. Handling under an inert atmosphere (nitrogen or argon) is recommended to prevent oxidative oligomerization of the terminal alkyne. Personal protective equipment including gloves, eye protection, and a lab coat should be worn when working with this compound. Consult the Safety Data Sheet (SDS) before use.

Applications in Organic Synthesis

Sonogashira Cross-Coupling: 2-Ethynyl-1,4-dimethylbenzene serves as an alkyne coupling partner with aryl or vinyl halides under palladium/copper catalysis to construct internal diarylalkynes and enyne systems useful in pharmaceutical and materials research.

CuAAC Click Chemistry: The terminal alkyne reacts regioselectively with organic azides under copper(I) catalysis to produce 1,4-disubstituted 1,2,3-triazoles. This reaction is highly efficient, bioorthogonal-compatible, and widely employed in bioconjugation, drug discovery, and polymer functionalization.

Glaser Coupling and Dimerization: Under oxidative copper catalysis, two equivalents of the terminal alkyne can be coupled homolytically to form symmetric 1,3-diynes, building blocks for conjugated organic materials.

Cycloaddition and Heterocycle Synthesis: The compound participates in thermal or metal-catalyzed [2+2] and [4+2] cycloadditions to access carbocyclic and heterocyclic ring systems.

Purity, Specifications and Quality

Research-grade 2-Ethynyl-1,4-dimethylbenzene is typically supplied at high purity suitable for synthetic applications. Aladdin Scientific's E469623 is referenced against the Sigma-Aldrich standard (No. 521116). Purity is routinely verified by GC analysis. Researchers requiring NMR spectral data, GC purity certificates, or lot-specific Certificates of Analysis (CoA) should contact Aladdin Scientific's technical support team or download the CoA directly from the product page. Always verify the specifications match your experimental requirements before use, particularly for high-sensitivity applications such as asymmetric catalysis or polymer synthesis where trace metal or moisture contamination can affect outcomes.

Storage, Stability and Safety Overview

Store 2-Ethynyl-1,4-dimethylbenzene in a tightly sealed container under inert gas at 2–8 °C or at room temperature as indicated on the product label. Terminal alkynes are susceptible to slow oxidative polymerization upon prolonged exposure to air and light; therefore, aliquoting into amber vials under argon is recommended for long-term stock management. The compound is flammable and should be kept away from open flames and heat sources. Dispose of waste in accordance with local, regional, and national regulations for flammable organic solvents. Always refer to the current SDS for complete hazard, first-aid, and disposal information specific to this compound.

Frequently asked questions

What is 2-Ethynyl-1,4-dimethylbenzene used for in organic chemistry?

2-Ethynyl-1,4-dimethylbenzene is primarily used as a terminal alkyne building block in Sonogashira cross-coupling reactions, CuAAC click chemistry with organic azides to form 1,2,3-triazoles, Glaser homocoupling to produce symmetric 1,3-diynes, and various cycloaddition reactions. Its electron-rich dimethylbenzene scaffold makes it useful for constructing conjugated aromatic systems in pharmaceutical, agrochemical, and materials research.

How should 2-Ethynyl-1,4-dimethylbenzene be stored to maintain stability?

Store the compound in a tightly sealed container under an inert atmosphere (nitrogen or argon) at 2–8 °C or at room temperature as specified on the product label. Protect from light and air to prevent oxidative oligomerization. For long-term storage, aliquot into small amber vials backfilled with argon and avoid repeated freeze–thaw cycles.

What is the molecular weight and molecular formula of 2-Ethynyl-1,4-dimethylbenzene?

2-Ethynyl-1,4-dimethylbenzene has the molecular formula C₁₀H₁₀ and a molecular weight of 130.19 g/mol. It consists of a 1,4-dimethylbenzene (para-xylene) ring with an ethynyl group at the 2-position.

What is the Aladdin Scientific product SKU for 2-Ethynyl-1,4-dimethylbenzene?

2-Ethynyl-1,4-dimethylbenzene is available from Aladdin Scientific under SKU E469623. This product is referenced against Sigma-Aldrich catalogue number 521116. For pricing, availability, and Certificate of Analysis, visit the Aladdin Scientific product page or contact customer service.

Is 2-Ethynyl-1,4-dimethylbenzene compatible with CuAAC click chemistry conditions?

Yes, as a terminal alkyne, 2-Ethynyl-1,4-dimethylbenzene is fully compatible with standard CuAAC (copper-catalyzed azide–alkyne cycloaddition) conditions. Under Cu(I) catalysis in aqueous or mixed organic solvents, it reacts with organic azides to regioselectively produce 1,4-disubstituted 1,2,3-triazoles. This makes it useful for bioconjugation and drug discovery applications.

What safety precautions should be taken when handling 2-Ethynyl-1,4-dimethylbenzene?

Wear appropriate personal protective equipment including chemical-resistant gloves, safety goggles, and a lab coat. Work in a well-ventilated fume hood as the compound is flammable and may produce irritating vapors. Keep away from open flames, heat sources, and strong oxidizers. Consult the current Safety Data Sheet (SDS) for full hazard information, first-aid measures, and disposal guidance before use.

References

1. Sigma-Aldrich product catalogue entry for 2-Ethynyl-1,4-dimethylbenzene, catalogue number 521116.
2. Chinchilla, R.; Nájera, C. The Sonogashira Reaction: A Booming Methodology in Synthetic Organic Chemistry. Chemical Reviews, 2007, 107(3), 874–922. doi:10.1021/cr050992x
3. Rostovtsev, V. V. et al. A Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed Regioselective Ligation of Azides and Terminal Alkynes. Angewandte Chemie International Edition, 2002, 41(14), 2596–2599. doi:10.1002/1521-3773(20020715)41:14<2596::AID-ANIE2596>3.0.CO;2-4

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