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Barbituric acid, the precursor of barbiturates, was first produced
in 1864 by condensation of malonic acid and urea; it had no
central nervous system (CNS) effects. In 1903, diethyl barbituric
acid (barbital) was created as the first barbiturate with
CNS inhibitory effects. Barbiturates were commonly used as
sedative-hypnotics in the mid-twentieth century; meantime
they were abused by some people as sold on the street. Use of
barbiturates quickly dropped after introduction of benzodiazepines
as the safer sedative-hypnotics. However some of the
barbiturates are still used as anticonvulsants and some for
euthanasia.
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A white or almost white, crystalline powder, hygroscopic.
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Sedative, hypnoyic.
Controlled substance (depressant).
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Crystalline granules or white powder. Used as an anesthetic and sedative.
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Freely soluble in water. Aqueous solutions are unstable upon storage.
Safety Profile
Poison by ingestion,
intraperitoneal, subcutaneous, intravenous,
intraduodenal, intramuscular, intracerebral,
parented, and rectal routes. An
experimental teratogen. Other experimental
reproductive effects. Human systemic
effects by ingestion: wakefulness, change in
motor activity, ataxia, and antipsychotic
effects. Mutation data reported. When
heated to decomposition it emits toxic
fumes of NOx and Na2O.
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Routes and Pathways Relevant Physicochemicals Properties
Pentobarbital sodium, with a molecular weight of 248.3,
consists of white, crystalline granules or white powder with
a slight characteristic odor. The melting point equals 130 °C
and respective vapor pressure is 3.02 × 10
10 mmHg at 25 °C.
Pentobarbital is very soluble in water (679 mg l1), freely
soluble in alcohol, and practically insoluble in ether. pH of
a 10% solution in water is between 9.8 and 11.0. Its dissociation
constant (pK) and octanol/water partition coefficient (log
Kow) are 7.88 and 2.10, respectively. Henry’s law constant is
8.5 108 Pa m3 mol1 at 25°C.
Environmental Persistency
Due to lack of hydrolyze-prone functional groups, pentobarbital
is not expected to undergo hydrolysis in the environment.
Also, pentobarbital does not contain chromophores to absorb
wavelengths higher than 290 nm and therefore is not susceptible
to direct photolysis by sunlight.
Environmental Degradation
Pentobarbital has been positively identified (not quantified) in
a ground-water sample collected from a well 300 m from
a landfill which received wastes between 1968 and 1969 and
re-sampling 21 years later (in 1991) revealed the presence of
pentobarbital at a concentration of 1 mg l
-1 which shows
persistency of pentobarbital in the environment.
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