Hydrogen iodide

Structural formula
General
Surname	Hydrogen iodide
other names	Hydrogen iodide Hydrogen iodide Hydrogen iodide Iodane
Molecular formula	HI
Brief description	colorless, pungent smelling gas
External identifiers / databases
CAS number 10034-85-2 EC number 233-109-9 ECHA InfoCard 100.030.087 PubChem 24841 Wikidata Q2462
properties
Molar mass	127.91 g mol −1
Physical state	gaseous
density	5.79 kg m −3 (0 ° C)
Melting point	−50.7 ° C
boiling point	−35.4 ° C
Vapor pressure	0.73 M Pa (20 ° C)
pK s value	−10 (at 25 ° C)
solubility	easily in water (425 g l −1 at 20 ° C)
Dipole moment	0.448 (1) D (1.49 * 10 -30  C  *  m )
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 314 P: 260-280-303 + 361 + 353-304 + 340 + 310-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Hydrogen iodide ( empirical formula HI), also known as hydrogen iodide or hydrogen iodide , is a colorless, pungent-smelling, corrosive gas that dissolves very well in water to form the very strong hydriodic acid . The bond length between the iodine and hydrogen atoms is 160.9 pm .

history

The formation and decomposition reaction:

${\displaystyle \mathrm {H_{2}+I_{2}\ \leftrightharpoons \ 2\,HI} }$

was examined in detail and with high accuracy by the physico-chemist Max Bodenstein as early as 1894 . It came into the focus of researchers at the end of the 19th century because it made it possible to observe molecular equilibrium reactions. In addition to the oxyhydrogen reaction and the formation of sulfur trioxide , the hydrogen iodide reaction formed an experimental basis for a theory of the kinetics of gas reactions.

Extraction and presentation

The industrial production takes place through the catalytic reaction of the gaseous elements using a platinum sponge heated to 500 ° C as a catalyst :

${\displaystyle \mathrm {H_{2}+I_{2}\longrightarrow 2\ HI} }$

Hydrogen and iodine react to form hydrogen iodide.

The reaction of iodine with hydrazine is also occasionally used:

${\displaystyle \mathrm {N_{2}H_{4}+2\ I_{2}\longrightarrow 4\ HI+N_{2}} }$

Hydrazine and iodine react to form hydrogen iodide and nitrogen .

In addition, water from phosphorus triiodide can release hydrogen iodide:

${\displaystyle \mathrm {PI_{3}+3\ H_{2}O\longrightarrow H_{3}PO_{3}+3\ HI} }$

However, this reaction is unsuitable for driving off really dry hydrogen iodide.

The following possibility is available as a laboratory synthesis for hydrogen iodide:

${\displaystyle \mathrm {C_{10}H_{18}+3\ I_{2}\longrightarrow 6\ HI\uparrow +C_{10}H_{12}} }$

Decalin and iodine react to form hydrogen iodide and tetralin .

Furthermore, it is advisable in the laboratory to extract hydrogen iodide from conc. Obtaining hydriodic acid , although this is not an actual representation.

${\displaystyle \mathrm {HI(aq)+\ P_{2}O_{5}\longrightarrow \ HI(g)\uparrow +2\ H_{3}PO_{4}} }$

properties

Hydrogen iodide with a pK _S value of -10 one of the strongest known acids. It is stable in the absence of air. Oxidation to iodine occurs in air :

${\displaystyle \mathrm {4\,HI+O_{2}\longrightarrow 2\,H_{2}O+2\,I_{2}} }$

Oxidizing agents such as bromine and chlorine oxidize hydrogen iodide with the formation of the corresponding hydrogen halide to elemental iodine. When heated, hydrogen iodide splits into the elements hydrogen and iodine ( reverse reaction of the formation reaction ).

use

Hydrogen iodide is used for the production of iodides, organic iodine compounds and as a catalyst. In the analysis by chemical degradation it played a not insignificant role as a reducing agent.

safety instructions

Due to its acidic properties, hydrogen iodide irritates the eyes and the respiratory tract; in high concentrations it is even toxic due to the release of iodine ions in the body and the corrosive effects on the respiratory tract. Due to its high solubility in water, however, it forms fog and precipitates in air, and it is slowly decomposed by the oxygen in the air. Poisoning with the gas is therefore very rare. The level of danger therefore corresponds roughly to that of hydriodic acid.

Individual evidence

1. ↑ ^{a b c d e f g} Entry on hydrogen iodide, anhydrous in the GESTIS substance database of the IFA , accessed on February 18, 2017(JavaScript required) .
2. ↑ ^{a b} chem.wisc.edu: pKa Data , Compiled by R. Williams (PDF, 78 kB).
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Dipole Moments, pp. 9-51.
4. ↑ Entry on Hydrogen iodide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
5. ↑ Hydriodic acid data sheet from Sigma-Aldrich , accessed on July 9, 2019 ( PDF ).
6. ^ Entry on hydrogen iodide. In: Römpp Online . Georg Thieme Verlag, accessed on November 12, 2014.