Petroleum ether is the petroleum fraction
consisting of aliphatic hydrocarbons and boiling in
the range 35‒60 °C; commonly used as a laboratory solvent.[4] The term ether is used only figuratively, signifying extreme lightness and
volatility.
Detailed description
Properties
The very lightest, most volatile liquid hydrocarbon
solvents that can be bought from laboratory chemical suppliers may also be
offered under the name petroleum ether. Petroleum ether consists mainly of aliphatic hydrocarbons and is
usually low on aromatics. It is commonly hydrodesulfurized and may be hydrogenated to reduce the
amount of aromatic and other unsaturated hydrocarbons.
Petroleum ether bears normally a descriptive suffix giving the boiling range.
Thus, from the leading international laboratory chemical suppliers it is
possible to buy various petroleum ethers with boiling ranges such as
30-50 °C, 40-60 °C, 50-70 °C, 60-80 °C, etc. In the United
States, laboratory grade aliphatic hydrocarbon solvents with boiling ranges as
high as 100-140 °C may be called petroleum ether, rather than petroleum
spirit.[5]
It is not advisable to employ a fraction with a
wider boiling point range than 20 °C, because of possible loss of the more
volatile portion during its use in recrystallisation, etc. and consequent
different solubility relations of the higher boiling residue.[6]
Most of the unsaturated hydrocarbons may be removed
by shaking two or three times with 10 % of the volume of concentrated sulfuric
acid; vigorous shaking is then continued with successive
portions of a concentrated solution of potassium permanganate in 10 %
sulfuric acid until the color of the permanganate remains unchanged. The
solvent is then thoroughly washed with sodium
carbonate solution and then with water, dried over anhydrous calcium
chloride, and distilled. If required perfectly dry, it
should be allowed to stand over sodium wire, or calcium
hydride.[6]
Standards
Ligroin is assigned the CAS
Registry Number 8032-32-4, which is also applied to many other products,
particularly the lower boiling ones, called petroleum spirit,
petroleum ether, and petroleum
benzine. "Naphtha" has the CAS Registry Number 8030-30-6, which also covers
petroleum benzine and petroleum ether: that is, the lower boiling point
non-aromatic hydrocarbon solvents.[5]
DIN 51630 provides for petroleum spirit (also called
spezialbenzine or petrolether) which is described as "a special
boiling-point spirit commonly used in laboratory applications, having high
volatility and low aromatics content." Its initial boiling point is above
25 °C, its final boiling point up to 80 °C.[5]
Safety
Petroleum ethers are extremely volatile, have very
low flash
points, and present a significant fire hazard.[5] Fires should be
fought with foam, carbon
dioxide, dry chemical or carbon tetrachloride.[2]
The naphtha mixtures that are distilled at a lower
boiling temperature have a higher volatility and, generally speaking, a higher
degree of toxicity than the higher boiling fractions.[7]
Exposure to petroleum ether occurs most commonly by
either inhalation or through skin contact. Petroleum ether is metabolized by
the liver with a biological half-life of 46–48 h.[3]
Inhalation overexposure causes primarily central
nervous system (CNS) effects (headaches, dizzines, nausea, fatigue, and
incoordination). In general, the toxicity is more pronounced with petroleum
ethers containing higher concentrations of aromatic compounds. n-Hexane is known to cause
axonal damage in peripheral nerves.[3]
Skin contact can cause allergic contact dermatitis.[3]
Oral ingestion of hydrocarbons often is associated
with symptoms of mucous membrane irritation, vomiting, and central nervous
system depression. Cyanosis, tachycardia, and tachypnea may appear as a result
of aspiration, with subsequent development of chemical pneumonitis. Other clinical findings include albuminuria, hematuria,
hepatic enzyme derangement, and cardiac arrhythmias. Doses as low as 10 ml
orally have been reported to be potentially fatal, whereas some patients have
survived the ingestion of 60 ml of petroleum distillates. A history of coughing
or choking in association with vomiting strongly suggests aspiration and
hydrocarbon pneumonia. Hydrocarbon pneumonia is an acute
hemorrhagic necrotizing disease that can develop within 24 h after the
ingestion. Pneumonia may require several weeks for complete resolution.[8]
Intravenous administration produces fever and local
tissue damage.[9]
Petroleum-derived distillates have not been shown to
be carcinogenic in humans.[7] Petroleum ether
degrades rapidly in soil and water.
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