Tetrachloroethylene

Liquid Tetrachloroethylene in a clear glass bottle.

Tetrachloroethylene is a pleasant-smelling colourless liquid that is used for dry-cleaning. It is also known as perchloroethylene and perc for short. It has the chemical formula C
2Cl
4 and it is composed of carbon and twice the chlorine. It was first made in 1839 in France.

Properties

Perchloroethylene is a colourless liquid at room temperature. It has a mild, sweet odour that most people can smell even in small amounts. It is much heavier than water and it does not mix with water, because Perc is nonpolar while water is polar. It can mix with many other solvents. Perc boils at 121 degrees Celsius and freezes at –22 degrees Celsius.

3D model of tetrachloroethylene's molecular structure. Green balls represent chlorine atoms and black balls represent carbon atoms.

Its molecule is very similar to ethylene but with chlorines instead of hydrogens in ethylene.

Uses

A freight train car carrying Tetrachloroethylene

Perc has been used in dry cleaning since the 1930s. It was introduced as a safe alternative to carbon tetrachloride (extremely poisonous to the liver) and flammable solvents like gasoline.

Years ago, dry cleaners used to throw away dirty perc after a few uses. The modern dry cleaning machines have mechanism to distill (boiling and condensing again) the perc for re-use.

Perchloroethylene was previously used as a parasite medication for animals.

Dangers

Perc has low toxicity but people who inhale it for a long time can become unconscious. Perc's ability to remove oils is very strong and can hurt the skin. It is not inflammable or explosive.

Similar compounds

• trichloroethylene
• carbon tetrachloride