Methylacetylene
Encyclopedia
Methylacetylene is an alkyne
with the chemical formula
H
3C≡CH. It is a component of MAPP gas
along with its isomer
1,2-propadiene (allene), which is commonly used in gas welding. Unlike acetylene
, methylacetylene can be safely condensed.
, the mixture of methylacetylene and propadiene
being called MAPD:
Keq = 0.22 (270 °C), 0.1 K (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.
as a relatively high performing liquid rocket propellant combination which would also be less toxic than the commonly used MMH/NTO (monomethylhydrazine
/nitrogen tetroxide) systems, showed that propyne would be highly advantageous as a rocket fuel for craft intended for low Earth orbit
al operations. This conclusion was reached based upon a specific impulse
expected to reach 370 s
if oxygen is used as oxidizer, a high density
and power density
, and the moderate boiling point
, which causes the chemical to present fewer problems in storage than for example a fuel
that needs to be kept at extremely low temperatures. (See cryogenics
.)
. Deprotonation with n-butyllithium
gives propynyllithium. This nucleophilic reagent adds to carbonyl
groups, producing alcohol
s and ester
s. Whereas purified propyne is expensive, MAPP gas can be used to cheaply generate large amounts of the reagent.
Alkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...
with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
3C≡CH. It is a component of MAPP gas
MAPP gas
MAPP gas is a trademarked name belonging to Linde Group, previously to Dow, for a fuel gas based on a stabilized mixture of methylacetylene and propadiene. The name comes from the original chemical composition: methylacetylene-propadiene propane...
along with its isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
1,2-propadiene (allene), which is commonly used in gas welding. Unlike acetylene
Acetylene
Acetylene is the chemical compound with the formula C2H2. 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 pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
, methylacetylene can be safely condensed.
Production and equilibrium with allene
Methylacetylene exists in equilibrium with alleneAllene
An allene is a compound in which one carbon atom has double bonds with each of its two adjacent carbon centres. Allenes are classified as polyenes with cumulated dienes. The parent compound of allene is propadiene. Compounds with an allene-type structure but with more than three carbon atoms are...
, the mixture of methylacetylene and propadiene
Propadiene
Propadiene is the organic compound with the formula H2C=C=CH2. It is the simplest allene, a compound with conjoined C=C double bonds. Propadiene's common name is allene...
being called MAPD:
- H3CC≡CH H2C=C=CH2
Keq = 0.22 (270 °C), 0.1 K (5 °C)
MAPD is produced as a side product, often an undesirable one, by cracking
Cracking (chemistry)
In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products...
propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...
to produce propene, an important feedstock in the chemical industry
Chemical industry
The chemical industry comprises the companies that produce industrial chemicals. Central to the modern world economy, it converts raw materials into more than 70,000 different products.-Products:...
. MAPD interferes with the catalytic
Ziegler-Natta catalyst
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes . Three types of Ziegler–Natta catalysts are currently employed:* Solid and supported catalysts based on titanium compounds...
polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
of propene.
Use as a rocket fuel
Research by European space concerns into using light hydrocarbons with liquid oxygenLiquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
as a relatively high performing liquid rocket propellant combination which would also be less toxic than the commonly used MMH/NTO (monomethylhydrazine
Monomethylhydrazine
Monomethylhydrazine is a volatile hydrazine chemical with the chemical formula CH3 NH2. It is used as a rocket propellant in bipropellant rocket engines because it is hypergolic with various oxidizers such as nitrogen tetroxide and nitric acid...
/nitrogen tetroxide) systems, showed that propyne would be highly advantageous as a rocket fuel for craft intended for low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
al operations. This conclusion was reached based upon a specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
expected to reach 370 s
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
if oxygen is used as oxidizer, a high density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
and power density
Power density
Power density is the amount of power per unit volume....
, and the moderate boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
, which causes the chemical to present fewer problems in storage than for example a fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
that needs to be kept at extremely low temperatures. (See cryogenics
Cryogenics
In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...
.)
Organic chemistry
Propyne is a convenient three-carbon building block for organic synthesisOrganic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
. Deprotonation with n-butyllithium
N-Butyllithium
n-Butyllithium is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene...
gives propynyllithium. This nucleophilic reagent adds to carbonyl
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....
groups, producing alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s and ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s. Whereas purified propyne is expensive, MAPP gas can be used to cheaply generate large amounts of the reagent.