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Arsabenzene is an organoarsenic compound with the chemical formula C5H5As. It belongs to a group of compounds called heteroarenes that have the general formula C5H5E (E= N, P, As, Sb, Bi).

This air sensitive liquid has an onion odor, and it decomposes on heating. Arsabenzene is also an ambidentate ligand, and it prefers to coordinate using η1(P)- or η6(π)-routes.

The study of arsabenzene and related compounds was an important step in the understanding of compounds that contain multiple bonds between carbon and heavier elements.

The study of heteroarenes was begun by Märkl, with the synthesis of 2, 4, 6-triphenlphosphabenzene. This is achieved by treating 2, 4, 6-trisubstituted pyrylium salt with phosphanes. The first derivative of arsabenzene was 9-arsaanthracene prepared by Jutzi and Bickelhaupt.

Synthesis
Arsabenzene is synthesized in a two step process from 1,4-pentadiyne. The diyne reacts with dibutylstannane to give 1,1-dibutylstannacyclohexa-2,5-diene. The organotin compound undergoes As/Sn exchange with arsenic trichloride to give 1-chloroacyclohexadiene, which loses a HCl upon heating, forming the arsabenzene. CH2(CHCH)2SnBu2 + AsCl3 → CH2(CHCH)2AsCl + Bu2SnCl2 CH2(CHCH)2AsCl → C5H5As + HCl

Reactions
Arsabenzene undergoes electrophilic aromatic substitution at its ortho and para positions. It is also capable of undergoing Friedel Crafts acylation.

While pyridine cannot undergo a Diels-Alder reaction, arsabenzene does behave as a diene and will readily react with hexafluoro-2-butyne at room temperature, in contrast phosphabenzene will only undergo this reaction at 100 oC and benzene has to be forced (200 oC) to undergo a Diels Alder reaction with hexafluorobut-2-yne. Thus the ability of these heterobenzenes to undergo the Diels Alder reaction with this electrophile increases down the periodic table. Bismabenzene is so reactive that it is capable of dimerizing with itself and it exists in equilibrium with its dimer.

Arsabenzene is far less basic than pyridine and unreactive with Lewis acids. There is no detectable protonation of the molecule even with trifluoroacetic or other strong acids.

Strucure
Arsabenzene is planar. The C-C bond distances of 1.39 Å, the As-C bond has a length of 1.85 Å, this is 6.6% shorter than the normal As-C single bond.

NMR spectroscopy carried out on arsabenzene indicates that it has a diamagnetic ring current.