Isobutane, also known as ''i''-butane, 2-methylpropane or methylpropane, is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with

molecular formula 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, such as paren ...

HC(CH₃)₃. It is an

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

butane Butane () is an alkane with the formula C4H10. Butane exists as two isomers, ''n''-butane with connectivity and iso-butane with the formula . Both isomers are highly flammable, colorless, easily liquefied gases that quickly vaporize at ro ...

. Isobutane is a colorless, odorless gas. It is the simplest

alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...

with a tertiary carbon atom. Isobutane is used as a precursor molecule in the

petrochemical industry file:Jampilen Petrochemical Co. 02.jpg, 300px, Jampilen Petrochemical co., Asaluyeh, Iran The petrochemical industry is concerned with the production and trade of petrochemicals. A major part is constituted by the plastics industry, plastics (poly ...

, for example in the synthesis of

isooctane 2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH3)3CCH2CH(CH3)2. It is one of several isomers of octane (C8H18). This particular isomer is the standard 100 point on the octane rating scal ...

Production

Isobutane is obtained by

isomerization In chemistry, isomerization or isomerisation is the process in which a molecule, polyatomic ion or molecular fragment is transformed into an isomer with a different chemical structure. Enolization is an example of isomerization, as is tautomer ...

Uses

Isobutane is the principal feedstock in alkylation units of refineries. Using isobutane, gasoline-grade "blendstocks" are generated with high branching for good combustion characteristics. Typical products created with isobutane are 2,4-dimethylpentane and especially

2,2,4-trimethylpentane 2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH3)3CCH2CH(CH3)2. It is one of several isomers of octane (C8H18). This particular isomer is the standard 100 point on the octane rating scale ...

Solvent

In the Chevron Phillips slurry process for making

high-density polyethylene High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or " polythene" when used for HDPE pipes. With a high strength-to-density rati ...

, isobutane is used as a diluent. As the slurried polyethylene is removed, isobutane is "flashed" off, and condensed, and recycled back into the loop reactor for this purpose.

Precursor to ''tert''-butyl hydroperoxide

Isobutane is oxidized to ''tert''-butyl hydroperoxide, which is subsequently reacted with

propylene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula . 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 petroleum-like o ...

to yield

propylene oxide Propylene oxide is an epoxide with the molecular formula C3H6O. This colourless volatile liquid with an odour similar to ether, is produced on a large scale industrially. Its major application is its use for the production of polyether polyols f ...

. The

tert-butanol ''tert''-Butyl alcohol is the simplest tertiary alcohol, with a formula of (CH3)3COH (sometimes represented as ''t''-BuOH). Its isomers are 1-butanol, isobutanol, and butan-2-ol. ''tert''-Butyl alcohol is a colorless solid, which melts nea ...

that results as a by-product is typically used to make gasoline additives such as

methyl tert-butyl ether Methyl ''tert''-butyl ether (MTBE), also known as ''tert''-butyl methyl ether, is an organic compound with a structural formula (CH3)3COCH3. MTBE is a volatile, flammable, and colorless liquid that is sparingly soluble in water. Primarily used a ...

(MTBE).

Miscellaneous uses

Isobutane is also used as a propellant for aerosol spray cans. Isobutane is used as part of blended fuels, especially common in fuel canisters used for

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Refrigerant

Isobutane is used as a

refrigerant A refrigerant is a working fluid used in the cooling, heating, or reverse cooling/heating cycles of air conditioning systems and heat pumps, where they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are ...

. Use in refrigerators started in 1993 when

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presented the Greenfreeze project with the former East German company . In this regard, blends of pure, dry "isobutane" (R-600a) (that is, isobutane mixtures) have negligible

ozone depletion potential The ozone depletion potential (ODP) of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane (R-11 or CFC-11) being fixed at an ODP of 1.0. Chlorodifluoromethane (R-22), for examp ...

and very low

global warming potential Global warming potential (GWP) is a measure of how much heat a greenhouse gas traps in the atmosphere over a specific time period, relative to carbon dioxide (). It is expressed as a multiple of warming caused by the same mass of carbon dioxide ( ...

(having a value of 3.3 times the GWP of carbon dioxide) and can serve as a functional replacement for R-12, R-22 (both of these being commonly known by the trademark

Freon Freon ( ) is a registered trademark of the Chemours Company and generic descriptor for a number of halocarbon products. They are stable, nonflammable, low toxicity gases or liquids which have generally been used as refrigerants and as aerosol p ...

), R-134a, and other

chlorofluorocarbon Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly Halogenation, halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F). They are produced as volatility (chemistry), volat ...

hydrofluorocarbon Hydrofluorocarbons (HFCs) are synthetic organic compounds that contain fluorine and hydrogen atoms, and are the most common type of organofluorine compounds. Most are gases at room temperature and pressure. They are frequently used in air condit ...

s in conventional stationary refrigeration and air conditioning systems. As a refrigerant, isobutane poses a fire and explosion risk in addition to the hazards associated with non-flammable CFC refrigerants. Substitution of this refrigerant for motor vehicle air conditioning systems not originally designed for isobutane is widely prohibited or discouraged. Vendors and advocates of hydrocarbon refrigerants argue against such bans on the grounds that there have been very few such incidents relative to the number of vehicle air conditioning systems filled with hydrocarbons. A leak of isobutane in the refrigerant system of a fridge initiated the 2024 Valencia residential complex fire in

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, that claimed 10 lives.

Nomenclature

The traditional name isobutane was still retained in the 1993

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

recommendations, https://www.acdlabs.com/iupac/nomenclature/93/r93_679.htm but is no longer recommended according to the 2013 recommendations. Since the longest continuous chain in isobutane contains only three carbon atoms, the

preferred IUPAC name In chemical nomenclature, a preferred IUPAC name (PIN) is a unique name, assigned to a chemical substance and preferred among all possible names generated by IUPAC nomenclature. The "preferred IUPAC nomenclature" provides a set of rules for choo ...

is 2-methylpropane but the locant (2-) is typically omitted in general nomenclature as redundant; C2 is the only position on a propane chain where a methyl substituent can be located without altering the main chain and forming the constitutional isomer ''n''-butane.

References

External links

International Chemical Safety Card 0901
{{Authority control Alkanes Butane E-number additives Propellants Refrigerants