Propyne (methylacetylene) is an

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 ...

with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

. It is a component of MAPD gas—along with its

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Is ...

propadiene (allene), which was commonly used in gas welding. Unlike

acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . 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 ...

, propyne can be safely condensed.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 ().

Production and equilibrium with propadiene

Propyne exists in equilibrium with propadiene, the mixture of propyne and propadiene being called MAPD: :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 Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as ...

to produce

propene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petrol ...

, an important

feedstock A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials that are feedstock for future finished products. As feeds ...

in the

chemical industry The chemical industry comprises the companies that produce industrial chemicals. Central to the modern world economy, it converts raw materials ( oil, natural gas, air, water, metals, and minerals) into more than 70,000 different products. ...

. MAPD interferes with the catalytic

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many f ...

of propene.

Laboratory methods

Propyne can also be synthesized on laboratory scale by reducing

1-propanol Propan-1-ol (also propanol, n-propyl alcohol) is a primary alcohol with the formula and sometimes represented as PrOH or ''n''-PrOH. It is a colorless liquid and an isomer of 2-propanol. It is formed naturally in small amounts during many fer ...

allyl alcohol Allyl alcohol ( IUPAC name: prop-2-en-1-ol) is an organic compound with the structural formula . Like many alcohols, it is a water-soluble, colourless liquid. It is more toxic than typical small alcohols. Allyl alcohol is used as a raw material ...

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscibl ...

vapors over magnesium.

Use as a rocket fuel

European space companies have researched using light

hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

with

liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an app ...

, a relatively high performing liquid rocket propellant combination that would also be less toxic than the commonly used MMH/NTO (

monomethylhydrazine Monomethylhydrazine (mono-methyl hydrazine, MMH) is a highly toxic, volatile hydrazine derivative with the chemical formula . It is used as a rocket propellant in bipropellant rocket engines because it is hypergolic with various oxidizers such as ...

/ nitrogen tetroxide). Their research showed that propyne would be highly advantageous as a rocket fuel for craft intended for

low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never m ...

al operations. They reached this conclusion based upon a specific impulse expected to reach 370 s with oxygen as the oxidizer, a high

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

and

power density Power density is the amount of power (time rate of energy transfer) per unit volume. In energy transformers including batteries, fuel cells, motors, power supply A power supply is an electrical device that supplies electric power to a ...

—and the moderate

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding env ...

, which makes the chemical easier to store than

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy b ...

s that must be kept at extremely low temperatures. (See ''

cryogenics In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “c ...

''.)

Organic chemistry

Propyne is a convenient three-carbon building block for

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. Deprotonation with ''n''-butyllithium gives propynyllithium. This nucleophilic reagent adds to

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containi ...

groups, producing

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

s and

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

s. 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

hydroquinone Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. It has two hydroxyl groups bonded to a benzene ring in a ''pa ...

s in the total synthesis of

vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vi ...

. 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.

Notes

References

External links

NIST Chemistry WebBook page for propyne

German Aerospace Center

Nova Chemicals

{{Authority control Alkynes Fuel gas Rocket fuels