Last updated
Preferred IUPAC name
Propyne [1] [note 1]
Other names
Methyl acetylene
3D model (JSmol)
ECHA InfoCard 100.000.754 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 200-828-4
MeSH C022030
PubChem CID
  • InChI=1S/C3H4/c1-3-2/h1H,2H3
  • InChI=1/C3H4/c1-3-2/h1H,2H3
  • CC#C
Molar mass 40.0639 g/mol
AppearanceColorless gas [2]
Odor Sweet [2]
Density 0.53 g/cm3
Melting point −102.7 °C (−152.9 °F; 170.5 K)
Boiling point −23.2 °C (−9.8 °F; 250.0 K)
Vapor pressure 5.2 atm (20°C) [2]
Explosive limits 1.7%-? [2]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 1000 ppm (1650 mg/m3) [2]
REL (Recommended)
TWA 1000 ppm (1650 mg/m3) [2]
IDLH (Immediate danger)
1700 ppm [2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Propyne (methylacetylene) is an alkyne with the chemical formula CH3C≡CH. It is a component of MAPD gas—along with its isomer propadiene (allene), which was commonly used in gas welding. Unlike acetylene, propyne can be safely condensed. [3]


Production and equilibrium with propadiene

Propyne exists in equilibrium with propadiene, the mixture of propyne and propadiene being called MAPD:

The coefficient of equilibrium Keq is 0.22 at 270 °C or 0.1 at 5 °C. MAPD is produced as a side product, often an undesirable one, by cracking propane to produce propene, an important feedstock in the chemical industry. [3] MAPD interferes with the catalytic polymerization of propene.

Laboratory methods

Propyne can also be synthesized on laboratory scale by reducing 1-propanol, [4] allyl alcohol or acetone [5] vapors over magnesium.

Use as a rocket fuel

European space companies have researched using light hydrocarbons with liquid oxygen, a relatively high performing liquid rocket propellant combination that would also be less toxic than the commonly used MMH/NTO (monomethylhydrazine/nitrogen tetroxide). Their research showed[ citation needed ] that propyne would be highly advantageous as a rocket fuel for craft intended for low Earth orbital operations. They reached this conclusion based upon a specific impulse expected to reach 370 s with oxygen as the oxidizer, a high density and power density—and the moderate boiling point, which makes the chemical easier to store than fuels that must be kept at extremely low temperatures. (See cryogenics .)

Organic chemistry

Propyne is a convenient three-carbon building block for organic synthesis. Deprotonation with n-butyllithium gives propynyllithium. This nucleophilic reagent adds to carbonyl groups, producing alcohols and esters. [6] Whereas purified propyne is expensive, MAPP gas could be used to cheaply generate large amounts of the reagent. [7]

Propyne, along with 2-butyne, is also used to synthesize alkylated hydroquinones in the total synthesis of vitamin E. [8]

The chemical shift of an alkynyl proton and propargylic proton generally occur in the same region of the 1H NMR spectrum. In propyne, these two signals have almost exactly the same chemical shifts, leading to overlap of the signals, and the 1H NMR spectrum of propyne, when recorded in deuteriochloroform on a 300 MHz instrument, consists of a single signal, a sharp singlet resonating at 1.8 ppm. [9]


  1. "Prop-1-yne" mistake fixed in the errata Archived 2019-08-01 at the Wayback Machine . The locant is omitted according to P- (d), p. 31.

Related Research Articles

<span class="mw-page-title-main">Acetylene</span> Hydrocarbon compound (HC≡CH)

Acetylene is the chemical compound with the formula C2H2 and structure H−C≡C−H. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution. Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities such as divinyl sulfide and phosphine.

<span class="mw-page-title-main">Allenes</span> Any organic compound containing a C=C=C group

In organic chemistry, allenes are organic compounds in which one carbon atom has double bonds with each of its two adjacent carbon centres. Allenes are classified as cumulated dienes. The parent compound of this class is propadiene, which is itself also called allene. Compounds with an allene-type structure but with more than three carbon atoms are members of a larger class of compounds called cumulenes with X=C=Y bonding.

<span class="mw-page-title-main">Aldehyde</span> Organic compound containing the functional group R−CH=O

In organic chemistry, an aldehyde is an organic compound containing a functional group with the structure R−CH=O. The functional group itself can be referred to as an aldehyde but can also be classified as a formyl group. Aldehydes are common and play important roles in the technology and biological spheres.

<span class="mw-page-title-main">1,2-Dibromoethane</span> Chemical compound

1,2-Dibromoethane, also known as ethylene dibromide (EDB), is an organobromine compound with the chemical formula C
. Although trace amounts occur naturally in the ocean, where it is formed probably by algae and kelp, it is mainly synthetic. It is a dense colorless liquid with a faint sweet odor, detectable at 10 ppm, is a widely used and sometimes-controversial fumigant. The combustion of 1,2-dibromoethane produces hydrogen bromide gas that is significantly corrosive.

<span class="mw-page-title-main">Iodoform</span> Chemical compound

Iodoform (also known as triiodomethane and, inaccurately, as carbon triiodide) is the organoiodine compound with the chemical formula CHI3. A pale yellow, crystalline, volatile substance, it has a penetrating and distinctive odor (in older chemistry texts, the smell is sometimes referred to as that of hospitals, where the compound is still commonly used) and, analogous to chloroform, sweetish taste. It is occasionally used as a disinfectant.

The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of chromic acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the molecular species, H2CrO4 of which the trioxide is the anhydride. Chromic acid features chromium in an oxidation state of +6 (or VI). It is a strong and corrosive oxidising agent.

Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenzene (hemimellitene). All three compounds have the formula C6H3(CH3)3, which is commonly abbreviated C6H3Me3. Mesitylene is a colorless liquid with sweet aromatic odor. It is a component of coal tar, which is its traditional source. It is a precursor to diverse fine chemicals. The mesityl group (Mes) is a substituent with the formula C6H2Me3 and is found in various other compounds.

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<span class="mw-page-title-main">Acetic anhydride</span> Chemical compound

Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a colorless liquid that smells strongly of acetic acid, which is formed by its reaction with moisture in the air.

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Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moisture-sensitive solid, although commercial samples can be yellowish and contaminated with hydrogen chloride.

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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 has a lachrymatory effect, like related compounds. The compound is used as a reagent in organic synthesis.

In organic chemistry, alkynylation is an addition reaction in which a terminal alkyne is added to a carbonyl group to form an α-alkynyl alcohol.

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  7. USpatent 5744071,Philip Franklin Sims, Anne Pautard-Cooper,"Processes for preparing alkynyl ketones and precursors thereof",issued 1996-11-19
  8. Reppe, Walter; Kutepow, N & Magin, A (1969). "Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in English. 8 (10): 727–733. doi:10.1002/anie.196907271.
  9. Marc., Loudon, G. (2015-08-26). Organic chemistry. Parise, Jim, 1978- (Sixth ed.). Greenwood Village, Colorado. ISBN   9781936221349. OCLC   907161629.