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Propyne

Names
Preferred IUPAC name Propyne
Other names Methylacetylene Methyl acetylene Allylene
Identifiers
CAS Number	74-99-7
3D model (JSmol)	Interactive image
Beilstein Reference	878138
ChEBI	CHEBI:48086
ChEMBL	ChEMBL116902
ChemSpider	6095
ECHA InfoCard	100.000.754
EC Number	200-828-4
MeSH	C022030
PubChem CID	6335
UNII	086L40ET1B
CompTox Dashboard (EPA)	DTXSID0026387
InChI InChI=1S/C3H4/c1-3-2/h1H,2H3Key: MWWATHDPGQKSAR-UHFFFAOYSA-N InChI=1/C3H4/c1-3-2/h1H,2H3Key: MWWATHDPGQKSAR-UHFFFAOYAI
SMILES CC#C
Properties
Chemical formula	C3H4
Molar mass	40.0639 g/mol
Appearance	Colorless gas
Odor	Sweet
Density	0.53 g/cm
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)
Hazards
Explosive limits	1.7%-?
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 1000 ppm (1650 mg/m)
REL (Recommended)	TWA 1000 ppm (1650 mg/m)
IDLH (Immediate danger)	1700 ppm
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). N verify (what is  ?) Infobox references

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.

Production and equilibrium with propadiene

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

${\displaystyle {\ce {H3CC#CH <=> H2C=C=CH2}}}$

The coefficient of equilibrium K_eq 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. MAPD interferes with the catalytic polymerization of propene.

Laboratory methods

Propyne can also be synthesized on laboratory scale by reducing 1-propanol, allyl alcohol or acetone 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 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 cryogenic fuels that must be kept at extremely low temperatures.

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. Whereas purified propyne is expensive, MAPP gas could be used to cheaply generate large amounts of the reagent.

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

The chemical shift of an alkynyl proton and propargylic proton generally occur in the same region of the H NMR spectrum. In propyne, these two signals have almost exactly the same chemical shifts, leading to overlap of the signals, and the H 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.

In Astrophysics

Propyne has been detected in multiple astrophysical objects following its first observation in 1973 in the galactic center giant molecular cloud Sgr B2 using radio astronomy techniques. Propyne has been proposed to act as a precursor molecule to the formation of PAHs in space, such as indene.

Propyne has been detected by infrared spectroscopy in the chemically reducing atmospheres of the outer planets in our solar system, including on Jupiter in 2000 and on Saturn in 1997, both using the Infrared Space Observatory; on Titan in 1981 using Voyager's IRIS instrument; and on the ice giants Uranus in 2006 and on Neptune in 2008 using the Spitzer space telescope.

Notes

1. "Prop-1-yne" mistake fixed in the errata Archived 2019-08-01 at the Wayback Machine. The locant is omitted according to P-14.3.4.2 (d), p. 31 for propene and P-31.1.1.1, Examples, p. 374 for propyne.

References

1. "Characteristic (Functional) and Substituent Groups". Nomenclature of Organic Chemistry. IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 374. doi:10.1039/9781849733069-00372. ISBN 978-0-85404-182-4.
2. ^ NIOSH Pocket Guide to Chemical Hazards. "#0392". National Institute for Occupational Safety and Health (NIOSH).
3. ^ Peter Pässler, Werner Hefner, Klaus Buckl, Helmut Meinass, Andreas Meiswinkel, Hans-Jürgen Wernicke, Günter Ebersberg, Richard Müller, Jürgen Bässler, Hartmut Behringer, Dieter Mayer, "Acetylene" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim 2007 (doi:10.1002/14356007.a01_097.pub2).
4. Keiser, Edward & Breed, Mary (1895). "The Action of Magnesium Upon the Vapors of the Alcohols and a New Method of Preparing Allylene". Journal of the Franklin Institute. CXXXIX (4): 304–309. doi:10.1016/0016-0032(85)90206-6. Retrieved 20 February 2014.
5. Reiser, Edward II. (1896). "The preparation of Allylene, and the Action of Magnesium upon Organic Compounds". The Chemical News and Journal of Industrial Science. LXXIV: 78–80. Retrieved 20 February 2014.
6. Valentian, Dominique; Sippel, Martin; Grönland, Tor-Arne; Baker, Adam; van Den Meulen, Jaap; Fratacci, Georges; Caramelli, Fabio (2004). "Green propellants options for launchers, manned capsules and interplanetary missions" (PDF). la.dlr.de. DLR Lampoldshausen. Archived from the original (PDF) on 2006-01-10.
7. Michael J. Taschner; Terry Rosen; Clayton H. Heathcock (1990). "Ethyl Isocrotonate". Organic Syntheses; Collected Volumes, vol. 7, p. 226.
8. US patent 5744071, Philip Franklin Sims, Anne Pautard-Cooper, "Processes for preparing alkynyl ketones and precursors thereof", issued 1996-11-19 
9. 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.
10. Loudon, Marc; Parise, Jim (2015-08-26). Organic chemistry. Parise, Jim, 1978- (Sixth ed.). Greenwood Village, Colorado: W. H. Freeman. ISBN 9781936221349. OCLC 907161629.
11. Snyder, L. E.; Buhl, D. (May 1973). "Interstellar Methylacetylene and Isocyanic Acid". Nature Physical Science. 243 (125): 45–46. doi:10.1038/physci243045a0. ISSN 2058-1106.
12. Abplanalp, Matthew J.; Góbi, Sándor; Kaiser, Ralf I. (2019-03-06). "On the formation and the isomer specific detection of methylacetylene (CH3CCH), propene (CH3CHCH2), cyclopropane (c-C3H6), vinylacetylene (CH2CHCCH), and 1,3-butadiene (CH2CHCHCH2) from interstellar methane ice analogues". Physical Chemistry Chemical Physics. 21 (10): 5378–5393. doi:10.1039/C8CP03921F. ISSN 1463-9084.
13. Fouchet, T.; Lellouch, E.; Bezard, B.; Feuchtgruber, H.; Drossart, P.; Encrenaz, T. (2000), Jupiter's hydrocarbons observed with ISO-SWS: vertical profiles of C2H6 and C2H2, detection of CH3C2H, doi:10.48550/ARXIV.ASTRO-PH/0002273, retrieved 2025-01-05
14. de Graauw, T.; Feuchtgruber, H.; Bezard, B.; Drossart, P.; Encrenaz, T.; Beintema, D. A.; Griffin, M.; Heras, A.; Kessler, M.; Leech, K.; Lellouch, E.; Morris, P.; Roelfsema, P. R.; Roos-Serote, M.; Salama, A. (1997-05-01). "First results of ISO-SWS observations of Saturn: detection of CO_2_, CH_3_C_2_H, C_4_H_2_ and tropospheric H_2_O". Astronomy and Astrophysics. 321: L13 – L16. ISSN 0004-6361.
15. Maguire, W. C.; Hanel, R. A.; Jennings, D. E.; Kunde, V. G.; Samuelson, R. E. (August 1981). "C3H8 and C3H4 in Titan's atmosphere". Nature. 292 (5825): 683–686. doi:10.1038/292683a0. ISSN 1476-4687.
16. Burgdorf, Martin; Orton, Glenn; van Cleve, Jeffrey; Meadows, Victoria; Houck, James (2006-10-01). "Detection of new hydrocarbons in Uranus' atmosphere by infrared spectroscopy". Icarus. 184 (2): 634–637. doi:10.1016/j.icarus.2006.06.006. ISSN 0019-1035.
17. Meadows, Victoria S.; Orton, Glenn; Line, Michael; Liang, Mao-Chang; Yung, Yuk L.; Van Cleve, Jeffrey; Burgdorf, Martin J. (2008-10-01). "First Spitzer observations of Neptune: Detection of new hydrocarbons". Icarus. 197 (2): 585–589. doi:10.1016/j.icarus.2008.05.023. ISSN 0019-1035.

External links

• NIST Chemistry WebBook page for propyne
• German Aerospace Center
• Nova Chemicals
• CDC - NIOSH Pocket Guide to Chemical Hazards

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Deuterated molecules	Ammonia Ammonium ion Formaldehyde Formyl radical Heavy water Hydrogen cyanide Hydrogen deuteride Hydrogen isocyanide Propyne N2D Trihydrogen cation
Unconfirmed	Anthracene Dihydroxyacetone Methoxyethane Glycine Graphene Hemolithin H2NCO Linear C5 Naphthalene cation Phosphine Pyrene Silylidyne
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• Rocket fuels