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1,4-Pentadiyne

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1,4-Pentadiyne
Chemical structure of 1,4-pentadiyne
Names
IUPAC name
Penta-1,4-diyne
Identifiers
3D model (JSmol)
ChemSpider
  • InChI=1S/C5H4/c1-3-5-4-2/h1-2H,5H2
    Key: MDROPVLMRLHTDK-UHFFFAOYSA-N
  • C#CCC#C
Properties
C5H4
Molar mass 64.087 g·mol−1
Appearance colorless liquid[1]
Melting point −21 – −19 °C (−6 – −2 °F; 252–254 K)[1]
Boiling point 61–64 °C (142–147 °F; 334–337 K)[2]
1.4283 (23 °C)[2]
Structure[3]
0.516 D
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

1,4-Pentadiyne (penta-1,4-diyne) is a chemical compound belonging to the alkynes. The compound is the structural isomer to 1,3-pentadiyne.

Preparation

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Until the late 1960s, no successful synthesis of this seemingly simply preparable molecule was described. Although long-chain and more complex 1,4-diynes had been synthesized successfully before,[4] synthesis approaches starting from sodium acetylide or the acetylene Grignard reagent and propargyl bromide or methylene chloride failed, even with the inclusion of copper(I) chloride.[5][1] Mostly 1,3-pentadiyne was obtained as rearrangement product.[1]

The first successful isolation reacted propargyl bromide and ethynylmagnesium bromide, with a copper(I) chloride catalyst in THF. This gave a 70% yield in solution, but the product was difficult to separate from the solvent. Compared to previous attempts, the successful approach included an additional round of flash distillation and gas-liquid chromatography of the distillate.[1][2]

An improved synthesis method was published by Verkruijsse and Hasselaar in 1979. Copper chloride was substituted by copper(I) bromide as well as propargyl bromide by propargyl tosylate. At lower reaction temperatures and fewer by-products, the alkiyne was obtained after multistep extraction. According to the publication’s authors, this circumvented the problem that the solvent THF and the main compound share similar boiling points.[2]

Preparation of 1,4-pentadiyne by Verkruijsse and Hasselaar

Moreover, a flash vacuum pyrolysis starting from 3-ethynylcycloprop-1-ene at 550 °C yields the compound and penta-1,2-dien-4-yne as sideproduct.[6]

Pyrolytic or photochemical decomposition of 3‑ethynyl­cyclo­prop-1‑ene gives 5:1 1,4‑penta­diyne and a dienyne sideproduct.[6]

Alternatively, a photolytic decomposition of cyclopentadienylidene via UV radiation is possible.[7]

The compounds forms also during the exothermic reaction of allene and the ethynyl radical. This reaction is mainly of interest for astrochemistry.[8][9][10]

Properties

[edit]

At room temperature the substance discolors from a colorless to a yellowish liquid, however, storage in diluted solutions at 0 °C is possible for multiple weeks.[1]

While for 1,4-pentadiene the sp2-hybridization leads to a bond angle of 120° between the single and double bond, in 1,4-pentadiyne it is a 180° angle due to the sp-hybrid orbital. Both triple bonds in 1,4-position destabilize each other according to another study by 3.9 kcal · mol−1, a repulsion between the p orbital lobes close to the sp3-hybridized carbon has been postulated.[11] According to a QCSID(T) calculation, the alkiyne is destabilized relative to 1,3-pentadiyne by 25 kcal · mol−1.[12]

Although microwave spectroscopy revealed besides a dipole moment of 0.516 D no significant distortions compared to an ideal tetrahedron, three different ionization energies are reported for the π-system.[3]

Usage

[edit]

1,4-pentadiyne is a common starting material for the synthesis of heterobenzenes such as stiba-, arsa- and phosphabenzene and their substituted derivates.[13][14]

1,4-Pentadiin is used in the preparation of heterobenzenes

References

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  1. ^ a b c d e f D. A. Ben-Efraim; F. Sondheimer (1969). "The synthesis and some reactions of a series of "skipped" polyacetylenes containing terminal acetylene groups". Tetrahedron. 25 (14): 2823–2835. doi:10.1016/0040-4020(69)80026-8.
  2. ^ a b c d H. D. Verkruijsse; M. Hasselaar (1974). "An Improved Synthesis of 1,4-Diynes". Synthesis. 4 (4): 292–293. doi:10.1055/s-1979-28653. S2CID 95166709.
  3. ^ a b Robert L. Kuczkowski; Frank J. Lovas; R. D. Suenram (1981). "The microwave spectrum, structure and dipole moment of 1,4-pentadyine". J. Mol. Struct. 72: 143–152. Bibcode:1981JMoSt..72..143K. doi:10.1016/0022-2860(81)85014-4. hdl:2027.42/24440.
  4. ^ H. Taniguchi; I. M. Mathai; S. I. Miller (1966). "Synthesis and spectral properties of 1,4- and 1,3-pentadiynes". Tetrahedron. 22 (3): 867–878. doi:10.1016/0040-4020(66)80058-3.
  5. ^ J. M. Todd (1961). Attempted preparation of 1, 4-pentadiyne (MA). Boston University. hdl:2144/18627.
  6. ^ a b Michael M. Haley; Bluegrass Biggs; Will A. Looney; Robert D. Gilbertson (1995). "Synthesis of Alkenyl- and Alkynylcyclopropenes". Tetrahedron Lett. 36 (20): 3457–3460. doi:10.1016/0040-4039(95)00634-O.
  7. ^ G. Maier; J. Endres (2000). "Photochemistry of matrix-isolated cyclopentadienylidene revisited". J. Mol. Struct. 556 (1–3): 179–187. Bibcode:2000JMoSt.556..179M. doi:10.1016/S0022-2860(00)00631-1.
  8. ^ Fangtong Zhang; Seol Kim; Ralf I. Kaiser (2009). "A crossed molecular beams study of the reaction of the ethynyl radical (C2H(X2Σ+)) with allene (H2CCCH2(X1A1))". Phys. Chem. Chem. Phys. 11 (23): 4707–4714. Bibcode:2009PCCP...11.4707Z. doi:10.1039/B822366A. PMID 19492123.
  9. ^ F. Stahl; P. v. R. Schleyer; H. F. Schaefer III; R. I. Kaiser (2002). "Reactions of ethynyl radicals as a source of C4 and C5 hydrocarbons in Titan's atmosphere". Planet. Space Sci. 50 (7–8): 685–692. Bibcode:2002P&SS...50..685S. doi:10.1016/S0032-0633(02)00014-4.
  10. ^ Fabien Goulay; Satchin Soorkia; Giovanni Meloni; David L. Osborn; Craig A. Taatjes; Stephen R. Leone (2011). "Detection of pentatetraene by reaction of the ethynyl radical (C2H) with allene (CH2=C=CH2) at room temperature". Phys. Chem. Chem. Phys. 13 (46): 20820–20827. doi:10.1039/C1CP22609F. PMID 22002654.
  11. ^ Donald W. Rogers; Nikita Matsunaga; Frank J. McLafferty; Andreas A. Zavitsas; Joel F. Liebman (2004). "On the Lack of Conjugation Stabilization in Polyynes (Polyacetylenes)". J. Org. Chem. 69 (21): 7143–7147. doi:10.1021/jo049390o. PMID 15471463.
  12. ^ Nils Hansen; Stephen J. Klippenstein; James A. Miller; Juan Wang; Terrill A. Cool; Matthew E. Law; Phillip R. Westmoreland; Tina Kasper; Katharina Kohse-Höinghaus (2006). "Identification of C5Hx Isomers in Fuel-Rich Flames by Photoionization Mass Spectrometry and Electronic Structure Calculations". J. Phys. Chem. A. 110 (13): 4276–4388. Bibcode:2006JPCA..110.4376H. doi:10.1021/jp0569685. PMID 16571041.
  13. ^ Arthur J. Ashe III (1978). "The group 5 heterobenzenes". Acc. Chem. Res. 11 (4): 153–157. doi:10.1021/ar50124a005.
  14. ^ Arthur J. Ashe III; Woon-Tung Chan (1979). "Preparation of 2-substituted arsabenzes". J. Org. Chem. 44 (9): 1409–1413. doi:10.1021/jo01323a010.
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