Boiling Point Range
Name: Amit S.
Date: Summer 2009
Why does petroleum ether have a range of boiling points
35-60 degrees Celsius? Why is it not one constant value?
Petroleum ether is a horribly misleading name. For starters it is not an
ether (R-O-R'), it is a mixture of saturated hydrocarbons (CnH2n+2) taken
as a fraction from the distillation of crude oil. So it does not have a fixed
boiling point as it is not a pure substance.
It is generally used as it is cheaper than a pure hydrocarbon, but behaves in
a predictable way as a solvent or fuel. It is not generally used as a reagent
as it is not a pure substance so it would give a mixture of products in a
chemical reaction. The exact composition will vary depending on the boiling
range you buy and on the source it was extracted from, but can be expected to
contain almost entirely alkanes, some straight and some branched.
First, "petroleum ether" is not an ether. An ether contains ---CH2-O-CH2---
somewhere in its molecular structure. Second, "petroleum ether" is a mixture
of hydrocarbons tapped off to have a desired boiling point range during the
distillation of hydrocarbons. The hydrocarbons are typically alkanes (no double
bonds or ringed substances. So the term "petroleum ether" is misleading. I am
guessing but I think the name derives from the boiling range that is similar to
diethyl ether, and the term "petroleum" derives from its source.
Petroleum is a mixture of hydrocarbons and the reported boiling point range
describe the lowest and highest boiling points of the substances within that
Greg (Roberto Gregorius)
Petroleum ether is not a single pure compound. It is a mixture of hydrocarbons,
which have different boiling points when pure.
Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
Petroleum ether is actually a mixture of hydrocarbons. That is to say, it is a
mixture of different length alkanes. An alkane is a molecule that is a chain of
carbon atoms. The longer the chain, the more energy it takes to make it boil, and
therefore the higher the boiling point. You can find petroleum ether which has a
much higher boiling point than the one you describe below, and would therefore
have longer hydrocarbon chains.
Hope this helps.
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Update: June 2012