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IAQ UK is an independent organisation with the aim of 'raising the agenda of indoor air quality within the home and workplace'

IAQUK Resources - Benzene

History and Production


Benzene is formed from natural processes, such as volcanoes and forest fires, which effectively is the burning of fossil oil.  The compound was first discovered by 1825 by English chemist Michael Faraday, the inventor of the early Bunsen burner and he established the field theory of electro-magnetism.  Faraday discovered Benzene when he was distilling crude oil and analysing the oil gas. He realised that by setting the oil gas alight, it burnt. 

 

The process of fractional distillation of crude oil is still taught within GCSE science today, using a Bunsen burner as the method for heating. 

 

Faraday conducted a series of complex experiments to establish the compound had 12 atoms, an equal number of carbon and hydrogens, so Faraday called the compound ‘bi-carburted hydrogen’.  Carburted meaning to combine or mix with carbon or hydrogen.  During this time he was unable to understand how the atoms were connected.

 

Benzene continued to be distilled from other products.  In 1833, Mitscherlich produced it via the distillation of benzoic acid (from gum benzoin) and lime, which was a fragrant medical ointment. Benzoic was renamed ‘benzol’ based on the German word for oil, öl. English and French chemists eventually changed the ending to ene, resulting in the name benzene; Laurent named the substance ‘phene’ in 1837, the Latin to mean ‘to illuminate’, although this was never formally adopted it is sometimes used.

 

For many years, the benefits of what Faraday called bi-carburet of hydrogen were unknown.  Only two years before Faraday's death in 1836, Charles Mansfield isolated benzene from coal tar and began the first industrial scale production of benzene, but he was unfortunately killed when a pot of boiling benzene liquid boiled over and caused a fire.

 

The unique structure of the compound suggested a new family of molecules had been synthesized, it was only in 1865, German scientist Friedrich August Kekulé von Stradonitz suggested that the structure of benzene was a regular hexagon with hydrogen at each corner.  This flash of inspiration was due to a visual concept by Kekulé of a snake that had ‘seized hold of its own tail’.  And so the hexagonal structure, sometimes called the Kekulé Structure, was developed and assisting in developing new compounds, such as Toluene, Xylene, Ethylbenzene, Mesitylene, the list is not exhaustive.

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Benzene is an organic chemical compound with the molecular formula C6H6. It is sometimes abbreviated Ph–H.

Benzene is both an anthropogenically produced and naturally occurring chemical from processes that include: volcanic eruptions, wild fires, synthesis of chemicals such as phenol, production of synthetic fibers and fabrication of rubbers, lubricants, pesticides, medications, and dyes.  The most common route of benzene exposure is through inhalation of air emissions from tobacco smoke and motor vehicle exhaust; however, ingestion and dermal absorption of benzene can also occur through contact with contaminated water. Benzene is hepatically metabolized and excreted in the urine. Measurement of air and water levels of benzene is accomplished through collection via activated charcoal tubes, which are then analyzed with a gas chromatograph.


The measurement of Benzene in humans can be accomplished via urine, blood, and breath tests; however, all of these have their limitations because benzene is rapidly metabolized in the human body into by-products called metabolites. Benzene is a colourless and highly flammable liquid with a sweet smell and a relatively high melting point.   It is a known carcinogen and is used in important industrial solvent and precursor in the production of drugs, plastics, synthetic rubber, and dyes.Benzene is a natural constituent of crude oil, and may be synthesized from other compounds present in petroleum.


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Health effects

 

Health effects from Benzene vary according to concentrations and exposure period from irritation to eyes and nasal passage to cancer causing and genetic damage. 

 

Typically the most common method for entry into the body is via inhalation and absorption through the skin. 

 

As an inhaled pollutant short term exposure can cause headaches, dizziness, and nausea.

 

Benzene is absorbed into the blood stream and rapidly distributed throughout the body.  

 

Benzene is readily absorbed by inhalation or ingestion and is rapidly distributed throughout the body, particularly in fatty tissues.

 

Metabolism occurs primarily in the liver and to a lesser extent in the bone marrow, producing intermediates which account for the toxicity of Benzene.

 

In humans, the half life is 1 to 2 days. Accumulation is not expected for Benzene or its metabolites.

 

Benzene is primarily exhaled unchanged through the lungs or excreted as metabolites in the urine.
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Source of Pollution


Background levels of Benzene normally present in the air range from 2.8 to 20 parts per billion (ppb). Most exposure to benzene is from inhalation.

 

Prior to World War One, the primary application of benzene was in gasoline blending, and as a rubber solvent. The hazards of benzene were acknowledge during this time, in 1909 three young workers sealing tin cans in an American factory using benzene as a solvent were exposed to vapours over a 4-5 month period, all three workers died within a month.  In the UK in 1920, two men died from chronic poisoning whilst spreading rubber onto balloon fabric.  Thomas Legge, the first Medical Factory Inspector, recorded the first measurements of Benzene levels.  Legge concluded that exposure levels were measured to range from 210-800 ppm, however with no ventilation in the rubber spreading rooms the concentrations were probably as high as 16,800 ppm.

 

The Second World War increased the use of benzene within explosives.  By this time it was already being extensively used as a solvent in printing, rubber and leather products. Due to the high use of Benzene, chronic occupational health cases also increased, which encouraged further research to substitute Benzene with other solvents.  Despite the hazardous occupational health effects and the pollution to the environment, Benzene has an important role as the building block in organic chemistry and the development of many synthetic compounds.  Products that contain Benzene include paint, varnishes, solvents, detergents, thinners, inks, rubbers, pesticides, dyes, lubricants, degreasing products and even medication such as paracetamol.  It is also used in dry cleaning, petroleum processing, rubber tyre manufacturing, forms of rubber and plastic manufacturing such as shoes.  It is also created as an emission from vehicle and smoking. 


Technical - Benzene - C 6 H 6 


  • 6 carbon atoms and 6 hydrogen atoms attached to each other by alternating single and double covalent bonds in a hexagonal geometry structur
  • Colourless gas
  • Sweet smell
  • CAS Number: 71-43-2
  • LTEL - 1ppm (3.25 mg/m³)
  • STEL - N/A (N/A mg/m³)
  • Risk Phrases: R45, 46, 11, 36, 48, 23, 24, 25, 65
  • Safety Phrases: S33, 45
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