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Pyridine

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: 115.5C
Melting point: -41.8C
Vapour pressure: 20.5 hPa at 20C
Flash point: 17C
Ignition temperature: 550C
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.


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