Hydrogen chloride
210755
223321789
2008-07-03T15:40:12Z
72.93.68.89
{{redirect|HCl|the acid|hydrochloric acid}}
{{Chembox new
| Name = Hydrogen chloride
| ImageFile = Hydrogen-chloride-2D-dimensions.png
| ImageSize = 120px
| ImageName = Hydrogen chloride
| ImageFile1 = HCl molecule model-VdW surface.svg
| ImageSize1 = 120px
| ImageName1 = Molecular model of hydrogen chloride
| IUPACName = Hydrogen chloride<br />Chlorane
| OtherNames = Chlorohydric acid<br />Hydrochloride<br />Hydrochloric acid<br />Hydrochloric acid gas
| Section1 = {{Chembox Identifiers
| CASNo = 7647-01-0
| RTECS = MW4025000
}}
| Section2 = {{Chembox Properties
| Formula = HCl
| MolarMass = 36.4606 g/mol
| Appearance = Colorless gas, [[hygroscopic]].
| Density = 1.477 g/l, gas (25°C)
| Solubility = 72 g/100 ml (20°C)
| MeltingPt = -114.2°C (158.8 K)
| BoilingPt = -85.1°C (187.9 K)
| pKa = -4
}}
| Section3 = {{Chembox Structure
| MolShape = Linear
| Dipole = 1.05 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| MainHazards = Toxic, corrosive.
| NFPA-H = 3
| NFPA-F =
| NFPA-R = 1
| NFPA-O = OX
| FlashPt = Non-flammable.
| RPhrases = {{R23}}, {{R24}}, {{R25}}, {{R35}}<br />{{R37}}.
| SPhrases = {{S7}}, {{S9}}, {{S26}}, {{S36}},<br />{{S37}}, {{S39}}, {{S45}}.
}}
| Section8 = {{Chembox Related
| OtherAnions = [[Hydrogen fluoride]]<br />[[Hydrogen bromide]]<br />[[Hydrogen iodide]]
| OtherCations = [[Sodium chloride]]
| OtherCpds = [[Hydrochloric acid]]
}}
}}
The [[Chemical compound|compound]] '''hydrogen chloride''' has the [[chemical formula|formula]] [[Hydrogen|H]][[Chlorine|Cl]]. At room temperature, it is a colorless [[gas]], which forms white fumes of [[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 [[diatomic]] molecules, each consisting of a [[hydrogen]] [[atom]] H and a [[chlorine]] atom Cl connected by a [[covalent bond|covalent]] [[single bond]]. Since the chlorine atom is much more [[electronegative]] than the hydrogen atom, the covalent bond between the two atoms is quite polar. Consequently, the molecule has a large [[dipole moment]] with a negative [[partial charge]] δ<sup>-</sup> at the chlorine atom and a positive partial charge δ<sup>+</sup> at the hydrogen atom. In part due to its high polarity, HCl is very [[soluble]] in [[water]] (and in other polar [[solvent]]s).
Upon contact, H<sub>2</sub>O and HCl combine to form [[hydronium]] [[cation]]s H<sub>3</sub>O<sup>+</sup> and [[chloride]] [[anion]]s Cl<sup>-</sup> through a reversible [[chemical reaction]]:
:HCl + H<sub>2</sub>O → H<sub>3</sub>O<sup>+</sup> + Cl<sup>−</sup>
The resulting solution is called [[hydrochloric acid]] and is a [[strong acid]]. The [[acid dissociation constant|acid dissociation]] or ionization constant, ''K''<sub>a</sub>, is large, which means HCl dissociates or ionizes practically completely in water. Even in the absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve in certain other solvents such as [[methanol]], [[protonation|protonate]] molecules or ions, and serve as an acid-[[catalyst]] for chemical reactions where anhydrous (water-free) conditions are desired.
:HCl + CH<sub>3</sub>OH → CH<sub>3</sub>O<sup>+</sup>H<sub>2</sub> + Cl<sup>−</sup>
<small>HCl protonating a methanol (CH<sub>3</sub>OH) molecule</small>
Because of its acidic nature, hydrogen chloride is a [[corrosive]] gas, particularly in the presence of any moisture.
[[Image:Hydrochloric acid 01.jpg|thumb|200px|left|Hydrochloric acid fumes turning pH paper<!-- The orange section of the strip means it's pH paper, not litmus paper. Litmus paper is red or blue--> red showing that the fumes are acidic]]
<!-- use this to start full-width paragraph:<br style="clear:both;"> -->
==Health effects==
Hydrogen chloride forms corrosive [[hydrochloric acid]] on contact with water found in body tissue. [[Inhalation]] of the fumes can cause [[cough]]ing, [[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 [[burn (injury)|burns]]. Hydrogen chloride may cause severe burns to the [[eye]] and permanent eye damage.
==History==
[[Alchemy|Alchemists]] of the [[Middle Ages]] recognized that hydrochloric acid (then known as ''spirit of salt'' or ''acidum salis'') released vaporous hydrogen chloride, which was called ''marine acid air''. In the 17th century, [[Johann Rudolf Glauber]] used salt ([[sodium chloride]]) and [[sulfuric acid]] for the preparation of [[sodium sulfate]], releasing hydrogen chloride gas (see production, below). In 1772, [[Carl Wilhelm Scheele]] also reported this reaction and is sometimes credited with its discovery. [[Joseph Priestley]] prepared hydrogen chloride in 1772, and in 1810 [[Humphry Davy]] established that it is composed of [[hydrogen]] and [[chlorine]].<ref>{{cite journal | author = [[Harold Hartley|Hartley, Harold]] | title = The Wilkins Lecture. Sir Humphry Davy, Bt., P.R.S. 1778-1829 | journal = Proceedings of the Royal Society of London (A) | year = 1960 | volume = 255(1281) | pages = 153 – 180}}</ref>
During the [[Industrial Revolution]], demand for [[alkaline]] substances such as [[soda ash]] increased, and [[Nicolas Leblanc]] developed a new industrial-scale process for producing the soda ash. In the [[Leblanc process]], salt was converted to soda ash, using sulfuric acid, limestone, and coal, giving hydrogen chloride as by-product. Initially, this gas was vented to air, but the [[Alkali Act]] of 1863 prohibited such release, so then soda ash producers absorbed the HCl waste gas in water, producing hydrochloric acid on an industrial scale. Later, the [[Hargreaves process]] was developed, which is similar to the Leblanc process except [[sulfur dioxide]], water, and air are used instead of sulfuric acid in a reaction which is exothermic overall. In the early 20th century the Leblanc process was effectively replaced by the [[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 [[alkynes]] in producing the chlorinated [[monomer]]s [[chloroprene]] and [[vinyl chloride]], which are subsequently [[polymer]]ized to make polychloroprene ([[Neoprene]]) and [[polyvinyl chloride]] (PVC), respectively. In the production of vinyl chloride, [[acetylene]] (C<sub>2</sub>H<sub>2</sub>) is hydrochlorinated by adding the HCl across the [[triple bond]] of the C<sub>2</sub>H<sub>2</sub> molecule, turning the triple into a [[double bond]], yielding vinyl chloride.
The "acetylene process", used until the 1960s for making [[chloroprene]], starts out by joining two [[acetylene]] molecules, and then adds HCl to the joined intermediate across the [[triple bond]] to convert it to chloroprene as shown here:
[[Image:Chloroprene synthesis.png|554 px]]
This "acetylene process" has been replaced by a process which adds [[chlorine|Cl<sub>2</sub>]] to one of the double bonds in 1,3-[[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 [[chloralkali process|chlor-alkali]] industry, [[sodium chloride|salt]] solution is [[electrolysis|electrolyzed]] producing [[chlorine]] (Cl<sub>2</sub>), [[sodium hydroxide]], and [[hydrogen]] (H<sub>2</sub>). The pure chlorine gas can be re-combined in an HCl forming [[hydrogen chloride]] gas.
:Cl<sub>2</sub> + H<sub>2</sub> → 2HCl
As the reaction is [[exothermic reaction|exothermic]], the installation is called an HCl [[oven]]. The resulting hydrogen chloride gas is [[absorption (chemistry)|absorbed]] in [[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 [[chlorination|chlorinated]] and [[fluorine|fluorinated]] [[organic chemistry|organic]] compounds, e.g., [[Teflon]], [[Freon]], and other [[Chlorofluorocarbon|CFC]]s, as well as [[chloroacetic acid]], and [[polyvinyl chloride|PVC]]. Often this production of hydrochloric acid is integrated with captive use of it on-site. In the [[chemical reaction]]s, hydrogen [[atom]]s 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 + Cl<sub>2</sub> → 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:
:2NaCl + H<sub>2</sub>SO<sub>4</sub> <math>\longrightarrow</math> Na<sub>2</sub>SO<sub>4</sub> + 2HCl↑
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 [[hydrolysis]] of certain reactive chloride compounds such as [[phosphorus chlorides]], [[thionyl chloride]] (SOCl<sub>2</sub>), and [[acyl chloride]]s. Adding more water would absorb the HCl gas forming hydrochloric acid. For example, cold water can be gradually dripped onto [[phosphorus pentachloride]] (PCl<sub>5</sub>) to give HCl in this reaction:<sup>[4]</sup>
:PCl<sub>5</sub> + H<sub>2</sub>O <math>\longrightarrow</math> POCl<sub>3</sub> + 2HCl
Hot water could liberate more HCl by hydrolyzing PCl<sub>5</sub> all the way to ''ortho''-[[phosphoric acid]].<sup>[4]</sup> Reaction of water with [[phosphorus trichloride]] (PCl<sub>3</sub>) also yields HCl.<sup>[4]</sup> Reaction of thionyl chloride with water would give [[sulfur dioxide]] (SO<sub>2</sub>) gas as well as HCl. For the reactions of thionyl chloride or acyl chlorides with water, see [[thionyl chloride]] or [[acyl halide]].
HCl can also be made using sodium bisulfate and sodium chloride: NaHSO<sub>4</sub> + NaCl --> Na<sub>2</sub>SO<sub>4</sub> + HCl
==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 SiHCl<sub>3</sub> for purification of silicon
Hydrogen chloride usually comes in compressed [[gas cylinder]]s that are either red and brown or grey with a yellow band.
==See also==
* Dutch article on infrared spectrum of HCl: [[w:nl:Infraroodspectrum van zoutzuur|Infraroodspectrum van zoutzuur]]
* [[Chloride]], inorganic salts of hydrochloric acid
* [[Hydrochloride]], organic salts of hydrochloric acid
==References==
{{reflist}}
2. Thames and Kosmos Chem C2000 Experiment Manual
==External links==
*{{ICSC|0163|01}}
*[http://www.spezialgase.de/specialgasescatalog/gase/chlorwasserstoff/ Chemical and laboratory data]
*[http://www.jtbaker.com/msds/englishhtml/H3880.htm MSDS safety data]
[[Category:Hydrogen compounds]]
[[Category:Chlorides]]
[[Category:Hazardous air pollutants]]
[[Category:Nonmetal halides]]
[[ar:كلوريد هيدروجين]]
[[bg:Хлороводород]]
[[de:Chlorwasserstoff]]
[[es:Cloruro de hidrógeno]]
[[fr:Chlorure d'hydrogène]]
[[gl:Cloruro de hidróxeno]]
[[ko:염화 수소]]
[[hr:Klorovodik]]
[[hu:Hidrogén-klorid]]
[[id:Hidrogen klorida]]
[[ja:塩化水素]]
[[nds:Chlorwaterstoff]]
[[pl:Chlorowodór]]
[[pt:Cloreto de hidrogênio]]
[[ru:Хлороводород]]
[[sk:Chlorovodík]]
[[sr:Хлороводоник]]
[[sv:Väteklorid]]
[[th:ไฮโดรเจนคลอไรด์]]
[[vi:Clorua hiđrô]]
[[uk:Хлороводень]]
[[zh:氯化氢]]