Hydrogen chloride



Hydrogen chloride
IUPAC name Hydrogen chloride
Chlorane
Other names Chlorohydric acid
Hydrochloride
Hydrochloric acid
Hydrochloric acid gas
Identifiers
CAS number 7647-01-0
RTECS number MW4025000
Properties
Molecular formula HCl
Molar mass 36.4606 g/mol
Appearance Colorless gas, hygroscopic.
Density 1.477 g/l, gas (25°C)
Melting point

-114.2°C (158.8 K)

Boiling point

-85.1°C (187.9 K)

Solubility in water 72 g/100 ml (20°C)
Acidity (pKa) -4
Structure
Molecular shape Linear
Dipole moment 1.05 D
Hazards
Main hazards Toxic, corrosive.
NFPA 704
0
3
1
 
R-phrases R23, R24, R25, R35
R37.
S-phrases S45.
Flash point Non-flammable.
Related Compounds
Other anions Hydrogen iodide
Other cations Sodium chloride
Related compounds Hydrochloric acid
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

The hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. The formula HCl is often used to refer, somewhat misleadingly, to hydrochloric acid, an aqueous solution derived from hydrogen chloride.

Chemistry

Hydrogen chloride is composed of solvents).

Upon contact, H2O and HCl combine to form chloride anions Cl- through a reversible chemical reaction:

HCl + H2O → H3O+ + Cl−

The resulting solution is called catalyst for chemical reactions where anhydrous (water-free) conditions are desired.

HCl + CH3OH → CH3O+H2 + Cl−

HCl protonating a methanol (CH3OH) molecule

Because of its acidic nature, hydrogen chloride is a corrosive gas, particularly in the presence of any moisture.

 

Health effects

Hydrogen chloride forms corrosive hydrochloric acid on contact with water found in body tissue. Inhalation of the fumes can cause coughing, choking, inflammation of the nose, throat, and upper respiratory tract, and in severe cases, pulmonary edema, circulatory system failure, and death. Skin contact can cause redness, pain, and severe skin burns. Hydrogen chloride may cause severe burns to the eye and permanent eye damage.

History

chlorine.[1]

During the Industrial Revolution, demand for Solvay process, which did not produce HCl. However, hydrogen chloride production continued as a step in hydrochloric acid production.

Historical uses of hydrogen chloride in the 20th century include hydrochlorinations of double bond, yielding vinyl chloride.

The "acetylene process", used until the 1960s for making triple bond to convert it to chloroprene as shown here:


This "acetylene process" has been replaced by a process which adds butadiene instead, and subsequent elimination produces HCl instead, as well as chloroprene.

Production

Most hydrogen chloride produced on an industrial scale is used for hydrochloric acid production.

Direct synthesis

In the hydrogen (H2). The pure chlorine gas can be re-combined in an HCl forming hydrogen chloride gas.

Cl2 + H2 → 2HCl

As the reaction is deionized water, resulting in chemically pure hydrochloric acid. This reaction can give a very pure product, e.g. for use in the food industry.

Organic synthesis

The largest production of hydrochloric acid is integrated with the formation of atoms on the hydrocarbon are replaced by chlorine atoms, whereupon the released hydrogen atom recombines with the spare atom from the chlorine molecule, forming hydrogen chloride. Fluorination is a subsequent chlorine-replacement reaction, producing again hydrogen chloride.

R-H + Cl2 → R-Cl + HCl
R-Cl + HF → R-F + HCl

The resulting hydrogen chloride gas is either reused directly, or absorbed in water, resulting in hydrochloric acid of technical or industrial grade.

Laboratory methods

Small amounts of HCl gas for laboratory use can be generated in a HCl generator by dehydrating hydrochloric acid in two ways:

  • Liberation from concentrated hydrochloric acid by the addition of sulfuric acid.
  • Liberation from concentrated hydrochloric acid by the addition of anhydrous calcium chloride.

Alternatively, HCl can be generated by the reaction of sulfuric acid with sodium chloride:

NaCl + H2SO4 → NaHSO4 + HCl↑

Clandestine laboratories commonly use HCl gas generated in this way to convert a freebase drugs into the corresponding hydrochloride salts which are more conveniently distributed.

HCl can also be prepared by the phosphorus pentachloride (PCl5) to give HCl in this reaction:[4]

PCl5 + H2O → POCl3 + 2HCl

Hot water could liberate more HCl by hydrolyzing PCl5 all the way to ortho-acyl halide.

Applications

These are some of the uses for hydrogen chloride gas:

  • Most hydrogen chloride is used in the production of hydrochloric acid.
  • Hydrochlorination of rubber
  • Production of vinyl and alkyl chlorides
  • Chemical intermediate in other chemical production
  • Used in toilet bowl cleaner(The Works)
  • Use as babbitting flux
  • Treatment of cotton
    • Delinting
    • Separation from wool
  • Used in semiconductor industry (in pure grade)
    • Etching semiconductor crystals
    • Converting silicon to SiHCl3 for purification of silicon

Hydrogen chloride usually comes in compressed gas cylinders that are either red and brown or grey with a yellow band.

See also

  • Dutch article on infrared spectrum of HCl: Infraroodspectrum van zoutzuur
  • Chloride, inorganic salts of hydrochloric acid
  • Hydrochloride, organic salts of hydrochloric acid

References

  1. ^ Hartley, Harold (1960). "The Wilkins Lecture. Sir Humphry Davy, Bt., P.R.S. 1778-1829". Proceedings of the Royal Society of London (A) 255(1281): 153 – 180.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hydrogen_chloride". A list of authors is available in Wikipedia.