Acetone is the
organic
compound with the
formula
OC(CH
3)
2. This colorless, mobile, flammable
liquid is the simplest example of the
ketones. Owing to the fact that acetone is
miscible with
water
it serves as an important
solvent in its own
right, typically as the solvent of choice for cleaning purposes in
the laboratory. More than 3 million tonnes are produced annually,
mainly as a precursor to polymers. Familiar household uses of
acetone are as the active ingredient in
nail polish remover and as paint thinner
and sanitary cleaner/nail polish remover base. It is a common
building block in organic chemistry. In addition to being
manufactured, acetone also occurs naturally, even being
biosynthesized in small amounts in the human body.
Production
Acetone is produced directly or indirectly from propene. Most
commonly, in the
cumene process,
benzene is alkylated with propene and the resulting
cumene (isopropylbenzene) is oxidized to give
phenol and acetone:
- C6H5CH(CH3)2 +
O2 → C6H5OH +
OC(CH3)2
This conversion entails the intermediacy of cumene hydroperoxide,
C
6H
5C(OOH)(CH
3)
2.
Acetone is also produced by the direct oxidation of propene with a
Pd(II)/Cu(II) catalyst, akin to the
Wacker process.
Older production methods
Previously, acetone was produced by the
dry distillation of
acetates, for example
calcium acetate.
During World War I acetone was produced via bacterial fermentation, as developed by
Chaim Weizmann (later the first
president of Israel
) in order to
help the British war effort. This
Acetone Butanol Ethanol process
was abandoned due to the small yields.
Biosynthesis
Small amounts of acetone are produced in the body by the
decarboxylation of
ketone bodies.
Uses
About half of the world's production of acetone is consumed as a
precursor to
methyl
methacrylate. This application begins with the initial
conversion of acetone to its
cyanohydrin:
- (CH3)2CO + HCN →
(CH3)2C(OH)CN
In a subsequent step, the nitrile is
hydrolyzed to the unsaturated
amide, which is esterified:
- (CH3)2C(OH)CN + CH3OH →
CH2=(CH3)CCO2CH3 +
NH3
The second major use of acetone entails its condensation with
phenol to give
bisphenol A:
- (CH3)2CO + 2 C6H5OH
→
(CH3)2C(C6H4OH)2
+ H2O
Bisphenol-A is a component of many polymers such as
polycarbonates,
polyurethanes, and
epoxy
resins.
Combustion
(CH
3)
2CO + 4O
2 → 3CO
2 +
3H
2O
As a solvent
Acetone is a good solvent for most plastics and synthetic fibres
including those used in laboratory bottles made of polystyrene,
polycarbonate and some types of polypropylene. It is ideal for
thinning fiberglass resin, cleaning fiberglass tools and dissolving
two-part
epoxies and
superglue before hardening. It is used as a
volatile component of some
paints and
varnishes. As a heavy-duty degreaser, it is useful
in the preparation of metal prior to painting; it also thins
polyester resins, vinyl and adhesives.
Many millions of kilograms of acetone are consumed in the
production of the solvents methyl isobutyl alcohol and
methyl isobutyl ketone. These
products arise via an initial
aldol
condensation to give
diacetone
alcohol.
- 2 (CH3)2CO →
(CH3)2C(OH)CH2C(O)CH3
Acetone is used as a solvent by the pharmaceutical industry and as
a denaturation agent in denatured alcohol. Acetone is also present
as an
excipient in some pharmaceutical
products.
Storage of acetylene
Although flammable itself, acetone is also used extensively as a
solvent for the safe transporting and storing of
acetylene, which cannot be safely pressurized as a
pure compound. Vessels containing a porous material are first
filled with acetone followed by acetylene, which dissolves into the
acetone. One liter of acetone can dissolve around 250 liters of
acetylene.
Laboratory uses
In the laboratory, acetone is used as a
polar aprotic
solvent in a variety of
organic
reactions, such as
SN2
reactions. The use of acetone solvent is also critical for the
Jones oxidation. It is a common
solvent for rinsing
laboratory
glassware because of its low cost, volatility, and ability to
form a low boiling temperature
azeotrope
with water. For similar reasons, acetone is also used as a
drying agent. Acetone can be cooled with
dry ice to -78 °C without freezing; acetone/dry ice
baths are commonly used to conduct reactions at low temperatures.
Acetone is fluorescent under ultraviolet light, and its vapor may
be used as a fluorescent tracer in fluid flow experiments. Acetone
should never be used in
ultrasonic
cleaning applications due to dangers associated with flash
point ignition and health concerns.
Domestic and other niche uses
Acetone is often the primary component in cleaning agents such as
nail polish remover.
Ethyl acetate, another organic solvent, is
sometimes used as well. Acetone is a component of
superglue remover and it easily removes residues
from glass and porcelain.
It can be used as an artistic agent; when rubbed on the back of a
laser print or photocopy placed face-down on another surface and
burnished firmly, the toner of the image
transfers to the destination surface.
Some automotive enthusiasts add acetone at around 1 part in 500 to
their fuel, following claims of improvement in fuel economy and
engine life. Systematic testing has determined that acetone has no
measurable effect on fuel economy or may in fact reduce engine life
by adversely affecting fuel system parts. The effect of acetone on
fuel economy was addressed on the popular American TV show
MythBusters in 2006, in which they observed a
decrease on fuel economy.
Safety
Flammability
The most common hazard associated with acetone is its extreme
flammability. It
auto-ignites at a temperature of
465 °C (869 °F). At temperatures greater than acetone's
flash point of −20 °C (−4 °F), air mixtures of
between 2.5% and 12.8% acetone, by volume, may explode or cause a
flash fire. Vapors can flow along surfaces to distant ignition
sources and flash back. Static discharge may also ignite acetone
vapors.
Acetone peroxide
When oxidized, acetone forms acetone
peroxide as a byproduct, which is a highly unstable
compound. It may be formed accidentally, e.g. when waste
hydrogen peroxide is poured into waste
solvent containing acetone. Acetone peroxide is more than ten times
as friction and shock sensitive as
nitroglycerin. Due to its instability, it is
rarely used, despite its easy chemical synthesis.
Toxicology
Acetone is believed to exhibit only slight toxicity in normal use,
and there is no strong evidence of chronic health effects if basic
precautions are followed.
At very high vapor concentrations, acetone is irritating and, like
many other solvents, may depress the
central nervous system. It is also a
severe irritant on contact with eyes, and a potential
pulmonary aspiration risk. In one
documented case, ingestion of a substantial amount of acetone led
to systemic toxicity, although the patient eventually fully
recovered. Some sources estimate
LD50 for human ingestion at
1.159 g/kg; LD
50 inhalation by mice is given as 44 g per
cubic meter, over 4 hours.
Interestingly, acetone has been shown to have
anticonvulsant effects in animal models of
epilepsy, in the absence of toxicity, when
administered in millimolar concentrations. It has been hypothesized
that the high-fat low-carbohydrate
ketogenic diet used clinically to control
drug-resistant epilepsy in children works by elevating acetone in
the brain.
Environmental effects
Acetone evaporates rapidly, even from water and soil. Once in the
atmosphere, it is degraded by UV light with a 22-day half-life.
Acetone dissipates slowly in soil, animals, or waterways since it
is sometimes consumed by microorganisms, but it is a significant
groundwater contaminant due to its high
solubility in water. The
LD50 of acetone for fish is
8.3 g/l of water (or about 0.8%) over 96 hours, and its
environmental half-life is about 1 to 10 days. Acetone may pose a
significant risk of oxygen depletion in aquatic systems due to the
microbial activity consuming it.
References
- Stylianos Sifniades, Alan B. Levy, “Acetone” in Ullmann’s
Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim,
2005.
- NALGENE Labware - Technical Data
- http://www.accessdata.fda.gov/scripts/cder/iig/index.cfm
- Mine Safety and Health Administration (MSHA) -
Safety Hazard Information - Special Hazards of Acetylene
- History - Acetylene dissolved in acetone
- Acetone MSDS
- MythBusters
(Season 4, Episode
53)
- Acetone MSDS
-
http://ccohs.ca/oshanswers/chemicals/chem_profiles/acetone/basic_ace.html
- Safety (MSDS) data for propanone
- tf21
- http://jmloveridge.com/cosh/Acetone.pdf
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