2-Hexynoic Acid: Handling, Storage & Lab Protocol Guide

2-Hexynoic Acid is a short-chain alpha,beta-acetylenic carboxylic acid widely employed as a building block in organic synthesis, medicinal chemistry, and materials science research.

CAS Number

53293-00-8

Molecular Formula

C6H8O2

Molecular Weight

112.13 g/mol

Appearance

Colorless to pale yellow liquid or low-melting solid

Recommended Storage

Store at 2–8 °C, under inert atmosphere, away from light and moisture

Primary Applications

Organic synthesis building block, coupling reactions, pharmaceutical intermediates

Chemical Overview and Properties

2-Hexynoic Acid (CAS 53293-00-8) is a six-carbon alpha,beta-acetylenic carboxylic acid with the triple bond positioned between C-2 and C-3. Its molecular formula is C₆H₈O₂ and molecular weight is 112.13 g/mol. The compound exists as a colorless to pale yellow liquid or low-melting solid at room temperature.

The combination of an activated carboxylic acid and an internal alkyne functionality makes 2-Hexynoic Acid a versatile electrophilic synthon. The conjugated system renders the beta-carbon susceptible to nucleophilic addition (Michael-type reactions), while the carboxylic acid moiety can undergo standard esterification, amidation, and coupling reactions. These dual reactive handles are exploited in the preparation of complex heterocycles, natural product analogues, and bioactive molecules.

Solubility: 2-Hexynoic Acid is miscible with common polar organic solvents including ethanol, methanol, acetone, ethyl acetate, and dimethyl sulfoxide (DMSO). It has limited miscibility with water and non-polar hydrocarbons. Always verify solubility in your specific solvent system prior to large-scale use.

Safety and Handling Precautions

Before working with 2-Hexynoic Acid, consult the current Safety Data Sheet (SDS) provided by Aladdin Scientific. Key hazard considerations for alpha,beta-unsaturated carboxylic acids include potential irritation to skin, eyes, and the respiratory tract.

• Personal Protective Equipment (PPE): Wear chemical-resistant gloves (nitrile or neoprene), a laboratory coat, and safety goggles. When handling larger quantities or in poorly ventilated areas, use a half-face respirator with organic vapor cartridges.
• Ventilation: All manipulations should be carried out in a certified chemical fume hood.
• Skin/Eye Contact: In the event of skin contact, wash immediately with soap and water for at least 15 minutes. For eye contact, irrigate with copious amounts of water and seek medical attention promptly.
• Incompatibilities: Keep away from strong oxidizing agents, strong bases, and reactive metals. The compound should not be exposed to open flames due to its organic nature.
• Waste Disposal: Dispose of waste in accordance with local, regional, and national regulations for organic acid waste. Do not pour down the drain without treatment.

Stock Solution Preparation Protocol

The following protocol describes preparation of a 100 mM stock solution of 2-Hexynoic Acid in DMSO for use in biological or synthetic screening assays. Adjust scale and solvent as required by your application.

Materials Required

• 2-Hexynoic Acid (SKU: H157077, Aladdin Scientific)
• Anhydrous DMSO (molecular biology grade or better)
• Analytical balance (±0.1 mg precision)
• Amber glass vials with PTFE-lined caps
• Inert gas line (nitrogen or argon)
• Vortex mixer or magnetic stir plate

Procedure

1. Equilibrate the vial of 2-Hexynoic Acid to room temperature inside a desiccator for approximately 15 minutes before opening to avoid condensation.
2. Tare an amber glass vial on the analytical balance. Weigh out 11.2 mg of 2-Hexynoic Acid (MW = 112.13 g/mol) to yield 1 mL of a 100 mM solution.
3. Add 900 µL of anhydrous DMSO and mix thoroughly by vortexing or magnetic stirring until the compound is completely dissolved.
4. Bring the total volume to 1.00 mL with additional DMSO. Verify complete dissolution — the solution should be clear and colorless to faintly yellow.
5. Purge the headspace of the vial with a gentle stream of dry nitrogen or argon, then cap tightly.
6. Label the vial with compound name, SKU, concentration, solvent, date of preparation, and preparer's initials.
7. Store stock solution at –20 °C for long-term stability. Avoid repeated freeze-thaw cycles; prepare single-use aliquots where feasible.

Note: For aqueous buffer systems, prepare a concentrated stock in DMSO first, then dilute into buffer such that the final DMSO concentration does not exceed 0.1–1% (v/v) to minimize solvent effects in biological assays.

Storage Conditions and Stability

Proper storage is critical to maintaining the integrity and purity of 2-Hexynoic Acid over time.

• Recommended temperature: 2–8 °C (refrigerator) for short- to medium-term storage. For extended periods, –20 °C freezer storage under inert atmosphere is preferred.
• Atmosphere: Store under dry nitrogen or argon to prevent moisture absorption and potential hydrolysis or oxidative degradation.
• Light sensitivity: Protect from light. Use amber glass vials or wrap containers in aluminum foil.
• Container integrity: Ensure containers are tightly sealed after each use. Use PTFE-lined caps to prevent solvent-cap interactions.
• Shelf life: When stored correctly, 2-Hexynoic Acid is expected to remain stable for at least 24 months from date of manufacture. Verify purity by NMR or HPLC if the material has been stored for extended periods or if discoloration is observed.

If significant yellowing, polymerization, or unusual odor is detected, do not use the material. Contact Aladdin Scientific technical support for guidance.

Typical Research Applications

2-Hexynoic Acid serves multiple roles across synthetic and applied chemistry research:

• Organic synthesis building block: The carboxylic acid group can be activated as an acid chloride, mixed anhydride, or NHS ester for subsequent coupling to amines, alcohols, or other nucleophiles. The alkyne moiety is compatible with click chemistry (CuAAC) conditions after appropriate functionalization.
• Michael addition substrate: The alpha,beta-unsaturated system accepts soft nucleophiles (thiols, amines, carbon nucleophiles) in conjugate addition reactions, providing access to gamma-substituted hexanoic acid derivatives.
• Pharmaceutical intermediate synthesis: Alpha,beta-acetylenic acids are established intermediates in the synthesis of antifungal agents, antibiotics, and enzyme inhibitors. 2-Hexynoic Acid may serve as a structural analogue or precursor in medicinal chemistry programs.
• Polymer and materials chemistry: Ynoic acids have been explored as monomers or cross-linkers in the synthesis of functional polymers and coatings.

Note: Specific published applications referencing 2-Hexynoic Acid directly should be confirmed by a literature search (e.g., SciFinder, Reaxys) prior to use in a new application context.

Frequently asked questions

What solvents are recommended for dissolving 2-Hexynoic Acid?

2-Hexynoic Acid dissolves readily in polar organic solvents such as DMSO, ethanol, methanol, acetone, and ethyl acetate. Aqueous solubility is limited; prepare a concentrated stock in DMSO and dilute into aqueous buffer as needed, keeping the final DMSO content below 1% (v/v) for biological assays.

How should 2-Hexynoic Acid be stored to maintain purity?

Store 2-Hexynoic Acid at 2–8 °C for routine use, or at –20 °C for long-term storage. Keep the container sealed under an inert atmosphere (nitrogen or argon) and protected from light and moisture. Verify purity by NMR or HPLC if the material has been stored for an extended period or shows any discoloration.

Is 2-Hexynoic Acid compatible with click chemistry reactions?

2-Hexynoic Acid contains an internal alkyne rather than a terminal alkyne, which means it is generally less reactive in standard copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reactions compared to terminal alkynes. Researchers wishing to use it in click chemistry contexts typically need to first convert it to a terminal alkyne derivative or use strain-promoted cycloaddition strategies. Confirm reactivity empirically for your specific system.

What personal protective equipment is required when handling 2-Hexynoic Acid?

Wear chemical-resistant gloves (nitrile or neoprene), a laboratory coat, and safety goggles at all times. Conduct all handling in a certified fume hood. When working with larger quantities, consider a half-face respirator equipped with organic vapor cartridges. Always consult the current SDS before use.

How do I calculate the amount of 2-Hexynoic Acid needed for a specific molar concentration?

Use the formula: mass (g) = target concentration (mol/L) × volume (L) × molecular weight (g/mol). For 2-Hexynoic Acid (MW = 112.13 g/mol), to prepare 10 mL of a 50 mM solution: mass = 0.05 mol/L × 0.01 L × 112.13 g/mol = 0.056 g (56.1 mg). Always weigh on a calibrated analytical balance.

References

1. Aladdin Scientific Product Page: 2-Hexynoic Acid, SKU H157077. Aladdin Scientific Corp.
2. Safety Data Sheet: 2-Hexynoic Acid. Aladdin Scientific Corp. (consult current version on supplier website).
3. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. 4th ed. Wiley-Interscience, 1992. (General reference for alpha,beta-unsaturated carbonyl reactivity and Michael additions.)
4. Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angew. Chem. Int. Ed. 2001, 40, 2004–2021. doi:10.1002/1521-3773(20010601)40:11<2004::AID-ANIE2004>3.0.CO;2-5

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