Benzene, Toluene, Xylene

 

Benzene

Benzene is an organic chemical compound with the molecular formula C6H6. Its molecule is composed of 6 carbon atoms joined in a ring, with 1 hydrogen atom attached to each carbon atom. Because its molecules contain only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.



Benzene is a natural constituent of crude oil, and is one of the most basic petrochemicals. Benzene is an aromatic hydrocarbon and the second [n]-annulene ([6]-annulene), a cyclic hydrocarbon with a continuous pi bond. It is sometimes abbreviated Ph–H. Benzene is a colourless and highly flammable liquid with a sweet smell. It is mainly used as a precursor to heavy chemicals, such as ethylbenzene and cumene, which are produced on a billion kilogram scale. Because it has a high octane number, it is an important component of gasoline, composing a few percent of its mass. Most non-industrial applications have been limited by benzene's carcinogenicity.

Health Effects: Benzene increases the risk of cancer and other illnesses. Benzene is a notorious cause of bone marrow failure. Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, and bone marrow abnormalities. The specific hematologic malignancies that benzene is associated with include: acute myeloid leukemia (AML), aplastic anemia, myleodysplastic syndrome (MDS), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML).

Toluene

Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from a group of six atoms from the benzene molecule has been replaced by a univalent group, in this case CH3.



It is an aromatic hydrocarbon that is widely used as an industrial feedstock and as a solvent. Like other solvents, toluene is sometimes also used as an inhalant drug for its intoxicating properties; however, inhaling toluene has potential to cause severe neurological harm. Toluene is an important organic solvent, but is also capable of dissolving a number of notable inorganic chemicals such as sulfur, iodine, bromine, phosphorus. and other non-polar covalent substances.

Heath Effects:Inhaling high levels of toluene can cause death or unconsciousness. Repeatedly breathing toluene over long periods of time at work, or through deliberately "sniffing" or "huffing" glue or paint, can cause death, permanent brain damage, or depression. If you are pregnant, repeated exposure to toluene may increase the risk of damage to the fetus.

Exposure to high levels of toluene may affect your kidneys, nervous system, liver, brain, and heart. Direct, prolonged contact with liquid toluene or vapor can irritate the eyes and cause dry skin and skin rashes. Ingesting toluene can cause vomiting, diarrhea, and difficult breathing.

Exposure to low to moderate levels of toluene can cause confusion, light-headedness, dizziness, headache, fatigue, weakness, memory loss, nausea, appetite loss, coughing, wheezing, and hearing and color vision loss.

Xylene

Xylenes are aromatic hydrocarbons consisting of a benzene ring with two methyl substituents. It is a major petrochemical, produced by catalytic reforming. Xylenes are also produced from coal carbonisation in the manufacture of coke fuel. Representing about 0.5–1% of crude oil, depending on the source, xylenes are hence found in small amounts in gasoline and airplane fuels. Xylene is mainly produced as part of the BTX aromatics (benzene, toluene and xylenes) extracted from the product of catalytic reforming known as "reformate". The mixture is a slightly greasy, colourless liquid commonly encountered as a solvent. It was named in 1851, having been discovered as a constituent of wood tar.



Heath Effects:

The main effect of inhaling xylene vapour is depression of the central nervous system (CNS), with symptoms such as headache, dizziness, nausea and vomiting. Volunteers have tolerated 100 ppm, but higher concentrations become objectionable. Irritation of the nose and throat can occur at approximately 200 ppm after 3 to 5 minutes. Exposures estimated at 700 ppm have caused nausea and vomiting. Extremely high concentrations (approximately 10000 ppm) could cause incoordination, loss of consciousness, respiratory failure and death. In some cases, a potentially fatal accumulation of fluid in the lungs (pulmonary edema) may result. Symptoms of pulmonary edema, such as shortness of breath and difficulty breathing, may be delayed several hours after exposure. However, these effects are rarely seen since xylene is irritating and identifiable by odour at much lower concentrations.

The only reported death resulted from exposure to xylenes (unspecified isomer composition and unknown concentration) in a confined space. Reversible liver and kidney damage has been reported in cases of severe xylene exposure. Results of short-term studies on human volunteers indicate that xylenes can cause neurobehavioural effects such as impaired short-term memory and reaction time (300 ppm xylene, with exercise) and alterations in body balance (65 to 400 ppm m-xylene). Exposure to 300 or 400 ppm xylene or 65 to 150 ppm p-xylene have not had similar effects. This variation in results is probably due to differences in the effects being studied, exposure conditions, development of tolerance and total xylene uptake (which increases during exercise).