1,4-Pentadiyne (penta-1,4-diyne) is a chemical compound belonging to the

alkyne \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...

s. The compound is the

structural isomer In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a chemical compound, compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct chemical bond, b ...

to 1,3-pentadiyne.

Preparation

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, synthesis approaches starting from sodium acetylide and

propargyl bromide Propargyl bromide, also known as 3-bromo-prop-1-yne, is an organic compound with the chemical formula HC≡CCH2Br. A colorless liquid, it is a halogenated organic compound consisting of propyne with a bromine substituent on the methyl group. It h ...

or from the acetylene Grignard reagent with propargyl bromide and copper(I) chloride failed and mostly 1,3-pentadiyne was obtained as rearrangement product. The successful isolation in small amounts succeeded by reacting propargyl bromide and to the respective Normant cuprate converted acetylene grignard (usage of copper(I) chloride) in

THF Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...

and an, compared to previous attempts additional,

flash distillation Flash evaporation (or partial evaporation) is the partial vapor that occurs when a Boiling point#Saturation temperature and pressure, saturated liquid stream undergoes a reduction in pressure by passing through a thermal expansion valve, throttling ...

and GLC of the distillate. 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 Extraction may refer to: Science and technology Biology and medicine * Comedo extraction, a method of acne treatment * Dental extraction, the surgical removal of a tooth from the mouth Computing and information science * Data extraction, the pro ...

. According to the publication’s authors, this circumvented the problem that the solvent THF and the main compound share similar boiling points. Synthese 1,4-Pentadiin

Moreover, a

flash vacuum pyrolysis Flash vacuum pyrolysis (FVP) is a technique in organic synthesis. It entails heating a precursor molecule intensely and briefly. Two key parameters are the temperature and duration (or residence time), which are adjusted to optimize yield, convers ...

starting from 3-ethynylcycloprop-1-ene at 550 °C yields the compound and penta-1,2-dien-4-yne as sideproduct. Alternatively, a photolytic decomposition of cyclopentadienylidene via UV radiation is possible. Pyrolyse 3-Ethynylcycloprop-1-en

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

Properties

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. While for 1,4-pentadiene the sp²-

hybridization Hybridization (or hybridisation) may refer to: *Hybridization (biology), the process of combining different varieties of organisms to create a hybrid *Orbital hybridization, in chemistry, the mixing of atomic orbitals into new hybrid orbitals *Nu ...

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. According to a QCSID(T) calcuation, the alkiyne is destabilized relative to 1,3-pentadiyne by 25 kcal · mol⁻¹. 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.

Usage

1,4-pentadiyne is a common starting material for the synthesis of heterobenzenes such as stiba-, arsa- and

phosphabenzene Phosphorine (IUPAC name: phosphinine) is a heavier element analog of pyridine, containing a phosphorus atom instead of an aza- moiety. It is also called phosphabenzene and belongs to the phosphaalkene class. It is a colorless liquid that is m ...

and their substituted derivates. Darstellung Heterobenzole

References

{{DEFAULTSORT:Pentadiyne, 1,4- Diynes