Fact-checked by Grok 2 weeks ago

1-Butyne

1-Butyne, chemically known as but-1-yne or ethylacetylene, is a terminal with the molecular formula C₄H₆ and CH₃CH₂C≡CH. It features a carbon-carbon between the first and second carbon atoms, rendering the attached terminal hydrogen acidic and enabling distinctive reactivity typical of terminal alkynes. This compound appears as a colorless gas with a characteristic and exhibits key physical properties including a of 8 °C, a of -126 °C, and a of 0.678 g/cm³ at 0 °C. Its molecular weight is 54.09 g/mol, and it has a CAS number of 107-00-6. Due to the , 1-butyne is highly reactive, participating in reactions such as , metathesis, and condensations, which underpin its utility in chemical processes. 1-Butyne serves as a versatile starting material in , particularly for constructing larger molecules in the pharmaceutical and chemical industries, and as a specialty gas for . However, it presents significant hazards: it is an extremely flammable gas that may explode if heated under pressure, with vapors capable of causing , asphyxiation, or irritation upon inhalation or contact. Proper handling requires ventilation, protective equipment, and avoidance of ignition sources.

Properties

Physical properties

1-Butyne has the molecular formula C₄H₆ and the HC≡C-CH₂-CH₃, consisting of a linear carbon chain with a terminal between the first and second carbon atoms. At , 1-butyne exists as a colorless gas with a characteristic acetylenic .
PropertyValueConditions/Notes
Boiling point8.1 °CNormal boiling point
Melting point-125.7 °CNormal melting point
Density0.678 g/cm³At boiling point
Vapor pressure1.65 barAt 20 °C
Critical temperature191 °CEstimated critical point
1-Butyne exhibits low in (approximately 2.87 g/L at 25 °C), rendering it effectively insoluble for most practical purposes, but it is readily soluble in solvents such as and acetone.

Chemical properties

1-Butyne features a characteristic carbon-carbon with a of approximately 1.20 , arising from the sp hybridization of the involved carbon atoms, which results in a linear geometry around the . The terminal C-H is about 1.06 , shorter than typical sp³ C-H bonds due to the higher s-character (50%) in the sp hybrid orbital. The terminal hydrogen imparts acidity to 1-butyne, with a of approximately 25, significantly lower than that of alkanes (pKa ~50) because the resulting acetylide anion is stabilized by the sp-hybridized carbon. This acidity facilitates under basic conditions. The for 1-butyne is -2596.8 kJ/mol in the gas phase, reflecting its high energy content from the strained . Infrared spectroscopy reveals characteristic absorptions for 1-butyne at approximately 3300 cm⁻¹ (strong, ≡C-H stretch) and 2100–2260 cm⁻¹ (weak, C≡C stretch), diagnostic of the terminal functionality. Proton NMR shows the terminal ≡C-H proton as a around 2.5 , deshielded relative to protons but upfield compared to vinylic hydrogens; the adjacent CH₂ protons appear near 2.2 (multiplet), and the CH₃ protons at about 1.0 (triplet). Due to the sp hybridization, 1-butyne exhibits reactivity at the , particularly toward and , but remains stable under inert atmospheric conditions away from oxidants or strong acids/bases.

Synthesis

Laboratory preparation

One common laboratory method for preparing 1-butyne involves the of , leveraging the relative acidity of its terminal hydrogen to generate an acetylide anion. is first deprotonated using (NaNH₂) in liquid to form the sodium acetylide intermediate. \ce{HC#CH + NaNH2 -> HC#CNa + NH3} This acetylide anion then undergoes nucleophilic substitution with ethyl bromide (CH₃CH₂Br) in an Sₙ2 reaction, yielding 1-butyne after workup. \ce{HC#CNa + CH3CH2Br -> HC#CCH2CH3 + NaBr} The reaction is typically conducted under anhydrous conditions to prevent side reactions, with yields of 70-80% achieved after purification by fractional distillation under reduced pressure. An alternative laboratory route employs double of 1,2-dibromobutane, a vicinal dihalide precursor obtained from the bromination of . Treatment with excess in liquid promotes two successive E2 eliminations, removing HBr to form the . \ce{BrCH2CHBrCH2CH3 + 2 NaNH2 -> HC#CCH2CH3 + 2 NaBr + 2 NH3} This method requires careful control of temperature and excess base to drive the reaction to completion and minimize over-deprotonation of the product .

Industrial production

1-Butyne is produced on a small industrial scale as a specialty chemical, with output limited by its niche demand in and calibration gases; due to being a gas at room temperature, it is challenging to handle quantitatively in processes like alkyne metathesis. Due to low volume, it is often synthesized using methods scaled up slightly. 1-Butyne occurs as a minor in C4 unsaturated fractions from pyrolysis processes, such as of , but is typically removed (e.g., via ) during refining to produce olefins like , rather than isolated as a product. An alternative route starts from industrially abundant , which is brominated to 1,2-dibromobutane and undergoes double with alcoholic KOH to produce 1-butyne. Industrial processes achieve greater than 95% purity for 1-butyne through to remove byproducts like , which arises from over-alkylation or . Yields are optimized for cost-effectiveness in low-volume operations.

Reactions

Addition reactions

1-Butyne, like other alkynes, undergoes reactions at the carbon-carbon , which can be sequentially reduced to alkenes or fully saturated to alkanes. These additions are driven by the high reactivity of the π-bonds in the , converting it to a double or while releasing . The reactions typically follow for in unsymmetrical cases, with the alkyne's C-H bond influencing the orientation. Hydrogenation of 1-butyne with hydrogen gas can be controlled to achieve partial or complete . Using Lindlar's (palladium on calcium carbonate poisoned with lead and ), one equivalent of H₂ adds across the triple bond to yield as the major product: \ce{HC#CCH2CH3 + H2 ->[Lindlar's][cat.] H2C=CHCH2CH3} This selective partial stops at the stage due to the catalyst's deactivation, preventing over-. For complete to , a more active like (Pd/C) is employed with excess H₂: \ce{HC#CCH2CH3 + 2 H2 ->[Pd/C] CH3CH2CH2CH3} This process fully saturates the triple bond to a single bond. Halogenation involves the addition of halogens such as bromine (Br₂) to the triple bond, proceeding stepwise. With one equivalent of Br₂ in an inert solvent like dichloromethane, 1-butyne forms a mixture of (E)- and (Z)-1,2-dibromobut-1-ene via trans addition: \ce{HC#CCH2CH3 + Br2 -> BrHC=CBrCH2CH3} The trans predominates due to the involving a bridged halonium . Excess Br₂ leads to further , yielding 1,1,2,2-tetrabromobutane: \ce{BrHC=CBrCH2CH3 + Br2 -> Br2HC-CBr2CH2CH3} This tetrabromide results from the second to the vinyl dibromide. Hydration of 1-butyne, catalyzed by mercuric sulfate (HgSO₄) in (H₂SO₄), adds water across the following , initially forming an that tautomerizes to a . The reaction produces butan-2-one as the major product: \ce{HC#CCH2CH3 + H2O ->[HgSO4][H2SO4] CH3CH2C(O)CH3} The mercury catalyst facilitates the addition by forming a vinyl mercurinium intermediate, ensuring regioselectivity where the OH adds to the internal carbon, leading to the enol CH₃CH₂C(OH)=CH₂, which rapidly tautomerizes to the methyl ketone. This method is specific for terminal alkynes to yield methyl ketones. These addition reactions are exothermic, with the conversion of the (bond energy approximately 839 kJ/) to a (631 kJ/) or (347 kJ/) releasing significant heat—more so than analogous additions due to the higher π-electron density and energy in the . For instance, the of alkynes liberates about 240-300 kJ/ per reduction, establishing the thermodynamic favorability.

Deprotonation and substitution

The terminal alkyne proton in 1-butyne exhibits sufficient acidity (pK_a ≈ 25) to undergo with strong bases, generating a nucleophilic acetylide anion that enables subsequent reactions. Treatment with (NaNH₂) in liquid is a standard method, yielding sodium 1-butynide and , as shown in the equation: \mathrm{HC \equiv CCH_2CH_3 + NaNH_2 \rightarrow Na^+ \, ^- \mathrm{C \equiv CCH_2CH_3 + NH_3} Grignard reagents, such as ethylmagnesium bromide, can also deprotonate 1-butyne to form the corresponding magnesium acetylide, though this approach is less common due to potential side reactions with the organomagnesium species. The resulting acetylide anion serves as a potent nucleophile in SN2 alkylations with primary alkyl halides, facilitating carbon-carbon bond formation and the synthesis of longer-chain internal alkynes. For instance, sodium 1-butynide reacts with methyl iodide to produce 2-pentyne and sodium iodide: \mathrm{Na^+ \, ^- \mathrm{C \equiv CCH_2CH_3 + CH_3I \rightarrow CH_3C \equiv CCH_2CH_3 + NaI} This reaction is highly efficient for unhindered primary halides and is widely employed in organic synthesis to extend the carbon skeleton of terminal alkynes. Under basic conditions, the acetylide derived from 1-butyne can condense with to form propargylic derivatives, incorporating a at the terminal carbon. This base-catalyzed reaction proceeds via to the carbonyl, followed by , yielding pent-2-yn-1-ol (HOCH₂C≡CCH₂CH₃) as the product. Such condensations are valuable for introducing oxygen functionality adjacent to the , though yields may vary with catalyst choice and conditions. 1-Butyne participates in alkyne metathesis reactions catalyzed by alkylidyne complexes, allowing the exchange of its with those from other s to form new internal alkynes. These catalysts, often featuring tripodal silanolate or ligands, operate under mild conditions (e.g., in ) with low loadings (1 %) and enable selective redistribution without significant of the terminal alkyne. This process has emerged as a powerful tool for alkyne remodeling in complex molecule synthesis.

Applications

Organic synthesis

1-Butyne serves as a versatile terminal building block in , enabling the construction of enynes and extended carbon chains essential for pharmaceuticals, materials, and fragrances. Its reactivity stems from the acidic terminal hydrogen, which facilitates metal-catalyzed couplings and nucleophilic additions. A primary application is the , where 1-butyne undergoes Pd/Cu-catalyzed reaction with aryl halides to form conjugated internal alkynes. Longer alkynes are prepared through iterative of 1-butyne, involving with a strong base like to generate the acetylide anion, followed by reaction with primary alkyl halides; for example, treatment with ethyl bromide affords 1-hexyne, which can be extended further for precursors or analogs such as pheromones. In pharmaceutical synthesis, 1-butyne acts as an intermediate for active pharmaceutical ingredients. A representative example in fragrance production involves deprotonation of 1-butyne and reaction with to form 3-hexyn-1-ol, which is selectively hydrogenated to , a green leafy note used in perfumes and flavors.

Analytical uses

1-Butyne is employed as a reference standard in for establishing retention times of C4 alkynes during the analysis of samples, where its elution behavior helps identify unsaturated hydrocarbons in complex mixtures. In , it provides a molecular at m/z 54, along with distinctive fragmentation patterns that enable the and of compounds in analytical workflows. As an reference, 1-butyne exhibits characteristic absorption bands for terminal alkynes, such as the ≡C-H stretch near 3300 cm⁻¹ (strong) and the C≡C stretch in the 2100–2260 cm⁻¹ range (weak to variable), which are used to detect and quantify terminal alkynes in mixtures. These analytical applications occur predominantly on a laboratory scale in research settings for instrument validation and trace alkyne detection in fuels, with limited adoption in industrial processes due to its specialized role.

Safety and hazards

Health and flammability risks

1-Butyne is classified as an extremely flammable gas under GHS criteria, posing significant fire and explosion risks due to its low flash point of -61 °C and ability to form explosive vapor-air mixtures. The lower and upper explosive limits in air are 2.5% and 80% by volume, respectively, indicating a wide range where ignition can occur. Heating may lead to explosive polymerization or container rupture, exacerbating these hazards. As a simple asphyxiant in its gaseous state, 1-butyne can displace oxygen in confined spaces, leading to symptoms such as , , and of consciousness at high concentrations. may also cause respiratory , while contact with the liquefied form can result in , skin , or serious eye damage. Acute toxicity data indicate low overall hazard, with no classification for carcinogenicity, mutagenicity, or .

Handling and storage

1-Butyne, a flammable compressed gas, requires careful handling in and settings to prevent ignition, , or exposure risks. It should be manipulated in well-ventilated areas, such as fume hoods, using explosion-proof equipment and non-sparking tools to minimize static discharge and spark hazards. (PPE) including safety goggles, chemical-resistant gloves, and flame-retardant clothing is essential to protect against skin contact, eye irritation, and potential ignition of clothing. all equipment and transfer lines to prevent static sparks during handling. For storage, 1-butyne is typically kept in pressurized cylinders secured upright with protection caps in place, in a cool, dry, well-ventilated area away from direct sunlight, heat sources, oxidizers, and ignition sources. Cylinder temperatures should not exceed 52 °C, and storage at 2-8 °C is recommended to maintain stability. Cylinders must be stored in approved, segregated areas in accordance with local regulations, ensuring they are firmly secured to prevent falling or damage. In case of fire involving 1-butyne, use dry chemical, (CO₂), or alcohol-resistant foam extinguishers; do not use jets unless the leak can be safely stopped, as it may spread the . For spills or leaks, evacuate the area, eliminate ignition sources, ventilate thoroughly, and stop the leak if safe using spark-proof tools; contain large spills with dikes for disposal. First aid measures include moving exposed individuals to for incidents, rinsing or eyes with , and warming frostbitten areas gradually with lukewarm while seeking medical attention. Regulatory classification designates 1-butyne as a UN 2452 (ethylacetylene, stabilized) hazardous material under hazard class 2.1 (flammable gas), requiring compliance with transportation and storage regulations for compressed flammable gases.

References

  1. [1]
    1-Butyne | C4H6 | CID 7846 - PubChem - NIH
    But-1-yne is a terminal acetylenic compound that is butane carrying a triple bond at position 1. It is an alkyne and a terminal acetylenic compound.
  2. [2]
  3. [3]
    107-00-6(1-BUTYNE) Product Description - ChemicalBook
    1-BUTYNE Property ; Melting point: -126°C ; Boiling point: 8°C ; Density, 0.678 ; refractive index, 1.3962 ; Flash point: -0.15°C.Missing: physical | Show results with:physical
  4. [4]
  5. [5]
    1-BUTYNE | 107-00-6 - ChemicalBook
    It is a specialty gas mixture used in organic synthesis of compounds and instrument calibration; it has no specifi c or signifi cant industrial ...
  6. [6]
    Chemical info for 1-Butyne
    1-BUTYNE 107-00-6 by Aldrich · Hazard statements. Contains gas under pressure; may explode if heated. Extremely flammable gas · Precautions. Keep away from heat, ...
  7. [7]
    Ethyl Acetylene Supplier - AGT International
    Ethyl Acetylene (1-butyne). C4H6. Ethyl acetylene is filled from bulk raw ... Vapour Pressure (bar.a @ 20°C), 1.65. Valve Outlet, CGA 510. Address. Head ...<|separator|>
  8. [8]
    1-butyne - Stenutz
    1-butyne, also known as 1-butine, has the formula C4H6, a density of 0.668 g/mL, a melting point of -123 °C, and a boiling point of 18 °C.
  9. [9]
    Structure and Properties of 1-Butyne in Organic Chemistry Studies
    Dec 4, 2024 · With the molecular formula C₄H₆, 1-butyne is a linear alkyne and serves as a fundamental building block in various chemical synthesis processes.
  10. [10]
  11. [11]
    [PDF] Alkynes
    Compounds with triple bonds at the end of a molecule are called terminal alkynes. ... The C-H bond length in ethyne is 1.06Е which is also shorter than in ethane ...
  12. [12]
    10.8: Alkynes - Chemistry LibreTexts
    Dec 15, 2021 · Design the synthesis route of 1-butyne from 1-butene. Approach: Use retro-synthetic analysis: "". That analysis can be translated to the ...Missing: applications | Show results with:applications
  13. [13]
    1-Butyne - the NIST WebBook
    Chemical structure: C4H6 This structure is also available as a 2d Mol file or as a computed 3d SD file · View 3d structure (requires JavaScript / HTML 5) ...
  14. [14]
    6.3: IR Spectrum and Characteristic Absorption Bands
    Dec 15, 2021 · C=C stretching. ~ 1600 and 1500 – 1430 (strong to weak) alkyne. C≡C stretching. 2100 – 2250 (weak). terminal ≡C-H stretching. 3250 – 3350 ...
  15. [15]
    Spectroscopy of the Alkynes - Chemistry LibreTexts
    Jan 22, 2023 · The H-NMR spectrum of 3,3-dimethyl-1-butyne shows a high field signal due to the alkynyl hydrogen on the terminal alkyne. This high field ...NMR Absorptions of Alkyne... · Alkynes and Infrared...
  16. [16]
    Properties and Bonding in the Alkynes - Chemistry LibreTexts
    Jan 22, 2023 · What is the carbon-carbon, carbon-hydrogen bond length for alkyne? Is it shorter or longer than alkane and alkene? Which is the most acidic ...
  17. [17]
    9.8 Alkylation of Acetylide Anions - Organic Chemistry | OpenStax
    Sep 20, 2023 · A terminal alkyne can be prepared by alkylation of acetylene itself, and an internal alkyne can be prepared by further alkylation of a terminal ...Missing: laboratory butyne
  18. [18]
    9.2 Preparation of Alkynes: Elimination Reactions of Dihalides
    Sep 20, 2023 · ... NaNH2 results in a twofold elimination of HX and formation of an alkyne. As with the elimination of HX to form an alkene, we'll defer a full ...
  19. [19]
    Catalytic Reactions of Acetylene: A Feedstock for the Chemical ...
    With the start of the industrial production of acetaldehyde by acetylene hydration in 1916, acetylene became one of the most important raw materials for ...Production and Use of Acetylene · Handling of Acetylene · Reactivity of Acetylene
  20. [20]
    CN103896712A - Preparation method of butyne - Google Patents
    The present invention relates to a kind of preparation method of butine, particularly adopting 1-butylene and halogen, butyraldehyde and phosphorus tribromide.Missing: procedure | Show results with:procedure
  21. [21]
    1-Butyne - Wikipedia
    1-Butyne is an organic compound with the formula CH 3 CH 2 C≡CH. It is a terminal alkyne. The compound is a common terminal alkyne substrate in diverse studies ...
  22. [22]
    9.4: Hydration of Alkynes - Chemistry LibreTexts
    Mar 18, 2024 · As with alkenes, hydration (addition of water) of alkynes requires a strong acid, usually sulfuric acid, and is facilitated by the mercuric ion (Hg 2 + ).
  23. [23]
    9.5: Reduction of Alkynes - Chemistry LibreTexts
    Mar 18, 2024 · Lindlar's Catalyst transforms an alkyne to a cis-alkene because both hydrogen atoms are added to the same side of the alkyne (syn) as shown in ...
  24. [24]
    Partial Reduction of Alkynes With Lindlar's Catalyst
    Aug 19, 2011 · Lindlar's catalyst is a "poisoned" metal catalyst that performs hydrogenations of alkynes in the presence of hydrogen gas (H2).
  25. [25]
    Halogenation of Alkynes: Bromination, Chlorination & Iodination of ...
    May 29, 2013 · Halogenation of alkynes with Br2 and Cl2 produces trans-dihaloalkenes, and a second halogenation gives tetrahaloalkanes. The reaction proceeds ...
  26. [26]
    Alkyne Reactivity - MSU chemistry
    1. Catalytic Hydrogenation. The catalytic addition of hydrogen to 2-butyne not only serves as an example of such an addition reaction, but also provides heat ...
  27. [27]
  28. [28]
    Deprotonation of a Terminal Alkyne - Ambeed.com
    Terminal alkynes are remarkably acidic, strong bases like sodium amide in liquid ammonia, alkyllithiums, and Grignard reagents can deprotonate terminal alkynes.Missing: butyne | Show results with:butyne
  29. [29]
    The Applications of (Para)formaldehyde in Metal‐Catalyzed Organic ...
    Nov 6, 2015 · The alkynylation of formaldehyde is an important but still challenging reaction for the synthesis of primary propargylic alcohols, which are ...
  30. [30]
    Alkyne Metathesis with Molybdenum Alkylidyne Complexes ...
    (16) The catalytic reactions were carried out in toluene solution at room temperature with a catalyst loading of 1 mol %, and activated molecular sieves (MS 5 Å) ...
  31. [31]
    Palladium(II) complex for catalyzing sonogashira coupling reactions ...
    The Sonogashira coupling of aryl halides with aryl and alkyl alkynes ... 1-butyne, 5-phenyl-1-pentyne, 5-chloro-1-pentyne, 5-hexynenitrile, 3,3 ...
  32. [32]
    A comparative study of the synthetic paths from 1-butyne to 2E,4Z ...
    2E,4Z-Heptadien-1-ol (1), the key intermediate in the synthesis of the grapevine moth sex pheromone, was obtained from 1-butyne by a number of alternative.
  33. [33]
    Exploring the Chemical Properties and Applications of 1-Butyne in ...
    Aug 14, 2024 · 1-Butyne, a member of the alkyne family, is an organic compound with the molecular formula C₄H₆. This hydrocarbon is notable for its triple bond ...
  34. [34]
    3-Hexenol | C6H12O | CID 5281167 - PubChem
    A stereospecific synthesis for cis-3-hexen-1-ol starts with the ethylation of sodium acetylide to 1-butyne, which is reacted with ethylene oxide to give 3-hexyn ...
  35. [35]
    kinetic study of 1-butene, 1,3-butadiene and 1-butyne hydrogenation ...
    The hydrogenation of 1-butene and 1,3-butadiene is compatible with a simple Langmuir-Hinshelwood kinetic equation, whereas the hydrogenation of 1-butyne is not ...
  36. [36]
    [PDF] Relative Retention Times of C₂ to C, Saturated and Unsatu
    * The data of 1-butyne and 1-pentyne were omitted in the calculation. ** The data of some C, hydrocarbons, not included in Tables 1--6, were also used in the ...
  37. [37]
  38. [38]
    1-Butyne - the NIST WebBook
    IR Spectrum · Gas Chromatography. Data at other public NIST sites: Microwave spectra (on physics lab web site) · Gas Phase Kinetics Database.
  39. [39]
    1-Butyne - the NIST WebBook
    1-Butyne. Formula: C4H6; Molecular weight: 54.0904. IUPAC Standard InChI ... GAS IN SOLUTION (CCl4 FOR 3800-1330, CS2 FOR 1330-450 CM-1). Instrument, DOW ...<|separator|>
  40. [40]
    [PDF] How to Interpret an Infrared (IR) Spectrum - XULA Digital Commons
    The nitrile peak is usually stronger than alkyne. If a terminal alkyne is present the sp C-H ( ≡C-H) bond will show an additional absorbance around 3300cm-1.
  41. [41]
    1-Butyne | C4H6 | CID 7846 - PubChem
    8.1.4 Health Hazards ... Vapors may cause dizziness or asphyxiation without warning, especially when in closed or confined areas. ... Some may be toxic if inhaled ...
  42. [42]
    None
    ### Summary of Hazards, Flammability, and Toxicity for 1-Butyne (CAS No: 107-00-6)
  43. [43]
    [PDF] Hazards Identification - Wiley Companies
    Contains no substances with occupational exposure limit values. Ingredient name. Exposure limits. 1-Butyne. No data available. 8.2 Appropriate ...
  44. [44]
    ETHYL ACETYLENE, STABILIZED - CAMEO Chemicals - NOAA
    Autoignition Temperature: data unavailable. Melting Point: data unavailable ... Ethyl acetylene; [1-Butyne], 107-00-6, 1.00 %, 10000 pounds, flammable. (CISA ...
  45. [45]
  46. [46]
  47. [47]
    [PDF] Ethyl Acetylene - SAFETY DATA SHEET
    Aug 19, 2019 · Cylinder temperatures should not exceed 52 °C (125 °F). Keep container tightly closed and sealed until ready for use. See Section 10 for ...
  48. [48]
    None
    ### Summary for 1-Butyne (Aldrich - 633755) from SDS
  49. [49]
    Advances and Challenges in User-friendly Alkyne Metathesis Catalysts
    Peer-reviewed article published in Trends in Chemistry (2022) discussing challenges in handling gaseous alkynes like 1-butyne in alkyne metathesis processes.