Benzene

Benzene

“The tar deposit at the former GASCO site [on the Willamette] was created by discharges from the oil gasification facility early in the 20th century, but the contamination remains in and on top of river sediment. The tar contains high levels of total polycyclic aromatic hydrocarbon (TPAH), as well as other chemicals, most notably benzene.”

“…about 15,000 cubic yards of contaminated sediment will be dredged from the [Willamette River] followed by placement of a protective cap. The action includes a silt curtain system designed to contain contamination loosened during removal and prevent fish from entering the dredge area. The silt curtain will also be engineered to withstand boat wakes and high-river flows. Contamination will be taken by barge and then truck for disposal at the Chem Waste Subtitle C (hazardous waste) facility in Arlington, Oregon.

6/21/2005 – from the Environmental Protection Agency (EPA) website - http://www.epa.gov/

Benzene, or benzol, is an organic chemical compound and a known carcinogen with the molecular formula C6H6. It is sometimes abbreviated Ph–H. Benzene is a colorless and highly flammable liquid with a sweet smell and a relatively high melting point. Because it is a known carcinogen, its use as an additive in gasoline is now limited, but it is an important industrial solvent and precursor in the production of drugs, plastics, synthetic rubber, and dyes. Benzene is a natural constituent of crude oil, but it is usually synthesized from other compounds present in petroleum. Benzene is an aromatic hydrocarbon and the second [n]-annulene ([6]-annulene), a cyclic hydrocarbon with a continuous pi bond.

An aromatic hydrocarbon is a hydrocarbon, of which the molecular structure incorporates one or more planar sets of six carbon atoms that are connected by delocalised electrons numbering the same as if they consisted of alternating single and double covalent bonds. The term 'aromatic' was assigned before the physical mechanism determining aromaticity was discovered, and was derived from the fact that many of the compounds have a sweet scent. This sweet scent actually came from impurities in the compounds. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon, benzene.

Benzene, C6H6, is the simplest AH and was recognized as the first aromatic hydrocarbon, with the nature of its bonding first being recognized by Friedrich August Kekulé von Stradonitz in the 19th century. Each carbon atom in the hexagonal cycle has four electrons to share. One goes to the hydrogen atom, and one each to the two neighboring carbons. This leaves one to share with one of its two neighboring carbon atoms, which is why the benzene molecule is drawn with alternating single and double bonds around the hexagon.

Many chemists draw a circle around the inside of the ring to show six electrons floating around in delocalized molecular orbitals the size of the ring itself. This also accurately represents the equivalent nature of the six bonds all of bond order ~1.5.

Benzene burns with a sooty yellow flame because of the high carbon-hydrogen ratio.

- From Wikipedia 2008