Aromatic hydrocarbons

Benzene, the simplest uncharged aromatic hydrocarbon

Mesomerism of Benzene. The delocalized π electrons are energetically more favorable

The aromatic hydrocarbons or benzoid hydrocarbons , called arenes according to IUPAC , are cyclic, planar hydrocarbons with an aromatic system . Due to their delocalized π-electron system , they are energetically more favorable than their non-aromatic mesomers and therefore more chemically stable. Aromatic hydrocarbons can be divided into mono- (mAh) or polycyclic aromatic hydrocarbons (PAH).

Like all pure hydrocarbons, aromatic hydrocarbons are non-polar , lipophilic compounds. Since aromatic compounds are compared to the aliphatic carbon compounds and are thus defined by a negation, this means that all non-aliphatic organic compounds are aromatic. The classification of organic compounds into aliphatics and aromatics is based on the aromaticity criteria .

history

The first discovered was the aromatic 1825 by Michael Faraday in coal gas found benzene (C ₆ H ₆ ). Soon substances with similar properties were discovered that showed a different structure. It quickly became apparent that these formally unsaturated compounds, in spite of the double bonds, were not easy to induce into addition reactions .

Examples

Examples of aromatic hydrocarbons
Parent compound benzene	alkylated arenes ( Alkylbenzenes )	Arenes with multiple phenyl groups (Polyarylalkanes)	fused arenas (PAK)
≡ benzene	Toluene xylenes ( o -, m -, p -xylene) ethylbenzene cumene	Biphenyl Diphenyl methane triphenyl methane	Naphthalene anthracene phenanthrene pyrene
Note: The structural formulas of aromatic compounds are usually shown in just one mesomeric form .

Annulenes , i.e. cyclic hydrocarbons with conjugated double bonds, can have aromaticity. After benzene, [14] -annulene is the smallest aromatic annulene, and annulenes with 18 and 22 carbon atoms are also aromatic.

Occurrence and extraction

Aromatic hydrocarbons are found in petroleum . There arenes can be found which have the structural elements of indane , tetrahydronaphthalene , fluorene , biphenyl and acenaphthene , as well as arenes with an isoprenoid structure. The majority of the technically important compounds are synthesized using petrochemical processes . In the coking plant , aromatics are a by-product and can be found in coal tar and coke oven gas . Important mass products are benzene, toluene, xylenes and ethylbenzene ( BTEX aromatics). They are themselves the raw materials for plastics and for other bulk chemicals. Important PAHs are naphthalene and anthracene, which are obtained from coal tar and petroleum.

The most important processes for the production of aromatics

Procedure	Objective of the procedure	Process conditions				Other characteristics
		Pressure (bar)	Temperature (T °)	catalyst	Encore
Refining process
Hydrogenation of pyrolysis gasoline	Hydrogenation of diolefins and desulfurization	40-60	200-250	Co , Mo , Ni , Pd	H 2	Two-step process
Benzene pressure refining	Hydrogenation of crude benzene coking plant	20-50	350	Co, Mon	H 2	Sulfur reduction below 0.5 ppm; Removal of unsaturated hydrocarbons which make it difficult to obtain benzene by distillation
Dealkylation processes
Houdry -Litol	Benzene production from toluene	50	600	Co, Mon	H 2	Hydrogenation of unsaturates; hydrocracking cleavage of non-aromatics; Desulfurization, dealkylation and dehydrogenation of naphthenes lead to high benzene yields
Houdry dealkylation (HDA)	Benzene production from toluene	45	Max. 750		H 2	Benzene yield up to 99%
Isomerization processes
Octafining	Increased proportion of p -xylene	10-30	425-480	Pt / zeolite	H 2	Comparable to the Isomar ( UOP ), Isoforming ( Exxon ) and Isarom ( IFP ) processes
Transalkylation
Arco	Production of benzene and C 8 aromatics from toluene	2	480-520	Al 2 O 3 / SiO 2		Fluidized bed process in the gas phase
Tatoray	Production of benzene and C 8 aromatics from toluene	10-50	350-530	Zeolite	H 2	adiabatic process
Mobil LTD	Production of benzene and C 8 aromatics from toluene	46	260-315	Zeolite		Contact life approx. 1.5 years

Derivatives

Aromatic hydrocarbons can form derivatives with organic or non-organic substituents.

literature

• Cornelsen: Chemistry Upper Level - Organic Chemistry , 1st Edition, ISBN 978-3-06-011174-9 .

Individual evidence

1. ↑ Entry on arenes . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.A00435 Version: 2.3.3.
2. ↑ Entry on aromatic . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.A00441 Version: 2.3.3.
3. ^ FA Carey, RJ Sundberg: Organische Chemie , VCH, Weinheim 1995.
4. ↑ Hans-Dieter Jakubke, Ruth Karcher (Ed.): Lexicon of Chemistry , Spectrum Academic Publishing House, Heidelberg, 2001.
5. ^ Heinz-Gerhard Franck, Jürgen Walter Stadelhofer: Industrial Aromatic Chemistry: Raw Materials · Processes · Products . Springer, 1987, ISBN 978-3-662-07876-1 , pp. 135 .