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DESIGNATIONS
CAS No.: 110-86-1
Registry name: Pyridine
Chemical name: Pyridine
Synonyms, Trade names: Pyridinum, azine, azabenzene
Chemical name (German): Pyridin, Pyridinum
Chemical name (French): Pyridine
Appearance: colourless liquid with nauseating odour
BASIC CHEMICAL AND PHYSICAL DATA
| Empirical formula: | C5H5N |
| Rel. molecular mass: | 79.10 g |
| Density: | 0.9819 g/cm3 |
| Relative gas density: | 2.73 |
| Boiling point: | 115.5°C |
| Melting point: | -41.8°C |
| Vapour pressure: | 20.5 hPa at 20°C |
| Flash point: | 17°C |
| Ignition temperature: | 550°C |
| Explosion limits: | 1.7-10.6 vol% (56-350 g/m3) |
| Odour threshold: | 0.02 ppm (in air) |
| Solvolysis/solubility: | unlimited in water, readily soluble in alcohols, ethers, oils and benzene |
| Conversion factors: | 1 mg/m3 = 0.304 ppm |
| 1 ppm = 3.288 mg/m3 |
ORIGIN AND USE
Usage:
Technical pyridine is mixed with picolines and other substances.
It is used as denaturant for ethanol, as a solvent in
laboratories as well as for organic salts and chemicals in
industry. Pyridine is a constituent in the synthesis of a large
number of medical drugs, alkaloids, dyes, disinfectants,
herbicides and insecticides.
Origin/derivation:
Pyridine is contained in bone, coal and low-temperature tar, in
various types of pyrogenic oil, in oils obtained from bituminous
slate and in coffee oil. Technical pyridine is obtained from coal
tar by washing with diluted sulphuric acid; subsequent separation
involves alkalis.
Production figures:
Worldwide 1989 = 26,000 t/a (ULLMANN, 1993)
Toxicity
| Humans: | LD 15 g | |
| Mammals: | ||
| Mouse | LD50 891 mg/kg | acc. UBA, 1986 |
| Rat | LD50 866 mg/kg | acc. UBA, 1986 |
| Rat | LC50 4,000 ppm, 4 h, inhalation | acc. UBA, 1986 |
| Aquatic organisms: | ||
| Fish | LC 15 mg/l | acc. HOMMEL, 1993 |
| Daphnia | LC0 70 mg/l | acc. HOMMEL, 1993 |
| Daphnia | LC50 240 mg/l | acc. HOMMEL, 1993 |
| Daphnia | LC100 910 mg/l | acc. HOMMEL, 1993 |
Characteristic effects:
Humans/mammals: Pyridine is a nerve toxin and local irritant particularly for the eyes and mucous membranes. Typical symptoms of poisoning are dizziness, headaches, drowsiness, vomiting, reddening of skin and paralysis of nerves in head. Adverse effects in mammals follow long-term exposure: the ammonia metabolism in the brain, the liver and the kidneys is inhibited.
ENVIRONMENTAL BEHAVIOUR
Water:
Dissolves completely in water and forms toxic mixtures even when
considerably diluted. In warm climates, explosive mixtures may
form with air above the water's surface. Continuous pyridine
immissions may increase the metabolism of the microflora.
However, concentrations from 0.5 mg/l are already sufficient to
suppress nitrification and ammonification processes. Oxidation
processes are noticeably reduced by 5 mg/l. The compound is
stable in water since there is no hydrolysis.
Air:
Toxic, combustible liquid which readily evaporates to form
flammable vapours which are denser than air.
Soil:
Pyridine is highly mobile. Combined applications of pyridine
and phenol enhance the stability of pyridine in soil. Initial
inhibition of bacterial growth is followed by adaptation both in
soil and in aquatic systems. Concentrations of 750 mg/kg in soil
have disappeared after 4 months.
Degradation, decomposition products, half-life;
Following resorption, pyridine is rapidly distributed in the
body. Metabolic degradation takes place primarily as a result of
methylisation and oxidation involving the pair of free electrons
of the nitrogen atom. N-oxymethyl pyridine has been identified as
a metabolite. In addition, the substance is quickly excreted:
concentrations of 0.4 g/kg body weight are completely excreted
within three days.
ENVIRONMENTAL STANDARDS
| Medium/acceptor | Sector | Country/organ. | Status | Value | Cat. | Remarks | Source |
| Water: | Drinkw | SU | G |
0.2 mg/l |
acc. KOCH, 1989 | ||
| Groundw | D(HH) | G |
0.01 mg/l |
Investigation | acc. LAU-BW, 1989 | ||
| Groundw | D(HH) | G |
0.03 mg/l |
Rehabilitation | acc. LAU-BW, 1989 | ||
| Waste water | SU | G |
1 mg/l |
acc. KOCH, 1989 | |||
| Fish breeding | SU | G |
0.01 mg/l |
acc. KOCH, 1989 | |||
| Soil: | NL | G |
0.1 mg/kg AD |
Reference | acc. TERRA TECH, 6/94 | ||
| NL | L |
1 mg/kg AD |
Intervention | acc. TERRA TECH, 6/94 | |||
| Air: | Emiss. | D | L |
20 ml/m3 |
mass flow > 0.1 kg/h | acc. TA Luft, 1986 | |
| Workp | D | L |
5 ml/m3 |
MAK | Peak limit II, 1 | DFG, 1989 | |
| Workp | D | L |
15 mg/m3 |
MAK | DFG, 1989 | ||
| Workp | D | L |
0.2 ml/m3 |
MIK | 1) A | acc. BAUM, 1988 | |
| Workp | D | L |
0.7 mg/m3 |
MIK | 1) A | acc. BAUM, 1988 | |
| Workp | D | L |
0.6 mg/m3 |
MIK | 2) B | acc. BAUM, 1988 | |
| Workp | D | L |
2.1 mg/m3 |
MIK | 2) B | acc. BAUM, 1988 | |
| Workp | USA | (L) |
15 mg/m3 |
TWA | acc. SORBE, 1986 | ||
| Workp | USA | (L) |
5 ml/m3 |
TWA | acc. SORBE, 1986 | ||
| Workp | USA | (L) |
30 mg/m3 |
STEL | acc. SORBE, 1986 | ||
| Workp | USA | (L) |
10 ml/m3 |
STEL | acc. SORBE, 1986 | ||
| Workp | SU | (L) |
1.5 ml/m3 |
acc. SORBE, 1986 | |||
| Workp | SU | (L) |
5.mg/m3 |
acc. SORBE, 1986 |
Notes:
1) For drinking water treatment in each case: A =
impact limits up to which drinking water can be produced solely
by way of natural methods
2) For drinking water treatment in each case: B =
impact limits up to which drinking water can be produced with the
aid of currently tried and tested chemical/physical methods
Assessment/comments
Pyridine is considerably mobile and subject to high dispersion in the hydrosphere, pedosphere and atmosphere due to its water solubility and volatility and the only slight tendency towards bioaccumulation and accumulation in soil. Pyridine must not be dumped. Residues must be burnt in chemical incineration plants. The substance is hazardous to water.