Ammonium bifluoride

Ammonium bifluoride
Space fill model of the ammonium cation
Space fill model of the ammonium cation
Space fill model of the bifluoride anion
Space fill model of the bifluoride anion
Sample of Ammonium bifluoride
Names
IUPAC name
Ammonium bifluoride
Other names
  • Ammonium acid fluoride
  • Ammonium hydrofluoride
  • Ammonium difluoride
  • Ammonium hydrogendifluoride
  • Ammonium hydrogen difluoride
Identifiers
CAS Number
  • 1341-49-7 checkY
3D model (JSmol)
  • Interactive image
  • Interactive image
ChemSpider
  • 21241205 ☒N
ECHA InfoCard 100.014.252 Edit this at Wikidata
EC Number
  • 215-676-4
PubChem CID
  • 14935
UNII
  • C2M215358O
UN number 1727
CompTox Dashboard (EPA)
  • DTXSID9029645 Edit this at Wikidata
InChI
  • InChI=1S/F2H.H3N/c1-3-2;/h;1H3/q-1;/p+1 ☒N
    Key: XIONBZYFLSJNBW-UHFFFAOYSA-O ☒N
  • InChI=1/2FH.H3N/h2*1H;1H3
    Key: KVBCYCWRDBDGBG-UHFFFAOYAG
  • [NH4+].F[H-]F
  • [F-].F.[NH4+]
Properties
Chemical formula
[NH4][HF2]
Molar mass 57.044 g·mol−1
Appearance Colourless crystals
Density 1.50 g cm−3
Melting point 126 °C (259 °F; 399 K)
Boiling point 240 °C (464 °F; 513 K)(decomposes)
Solubility in water
63g/(100 ml) (20 °C)
Solubility in alcohol slightly soluble
Refractive index (nD)
1.390
Structure
Crystal structure
Cubic, related to the CsCl structure
[NH4]+ cation: tetrahedral
[HF2] anion: linear
Hazards
GHS labelling:
GHS05: CorrosiveGHS06: Toxic[1]
H301, H314[1]
P280, P301+P310, P305+P351+P338, P310[1]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
0
0
Related compounds
Other cations
potassium bifluoride
Related compounds
ammonium fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Infobox references
Chemical compound

Ammonium bifluoride is the inorganic compound with the formula [NH4][HF2] or [NH4]F·HF. It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass-etchant and an intermediate in a once-contemplated route to hydrofluoric acid.

Structure

Ammonium bifluoride, as its name indicates, contains an ammonium cation ([NH4]+), and a bifluoride or hydrogen(difluoride) anion ([HF2]). The centrosymmetric triatomic bifluoride anion features the strongest known hydrogen bond, with a FH length of 114 pm.[2] and a bond energy greater than 155 kJ/mol.[3]

In solid [NH4][HF2], each ammonium cation is surrounded by four fluoride centers in a tetrahedron, with hydrogen-fluorine hydrogen bonds present between the hydrogen atoms of the ammonium ion and the fluorine atoms.[4][5] Solutions contain tetrahedral [NH4]+ cations and linear [HF2] anions.

Production and applications

Ammonium bifluoride is a component of some etchants. It attacks silica component of glass:

SiO2 + 4 [NH4][HF2] → SiF4 + 4 [NH4]F + 2 H2O

Potassium bifluoride is a related more commonly used etchant.

Ammonium bifluoride has been considered as an intermediate in the production of hydrofluoric acid from hexafluorosilicic acid. Thus, hexafluorosilicic acid is hydrolyzed to give ammonium fluoride, which thermally decomposes to give the bifluoride:

H2[SiF6] + 6 NH3 + 2 H2O → SiO2 + 6 [NH4]F
2 [NH4]F → NH3 + [NH4][HF2]

The resulting ammonium bifluoride is converted to sodium bifluoride, which thermally decomposes to release HF.[6]

Ammonium bifluoride is also used as an additive in tin-nickel plating processes as the fluoride ion acts as a complexing agent with the tin, allowing for greater control over the resulting composition and finish.

Toxicity

Ammonium bifluoride is toxic to consume and a skin corrosion agent. Upon exposure to skin, rinsing with water followed by a treatment of calcium gluconate is required.[1] In water, ammonium bifluoride exists in chemical equilibrium with hydrofluoric acid and heating releases hydrogen fluoride gas.[7] Consequently, there is an equivalent toxicological risk as is present with hydrofluoric acid, and the same safety precautions apply.[8][7]

Ammonium bifluoride is used in some automotive wheel cleaning products. Many injuries have resulted in users not being aware of the risks posed by the products.[9] Ammonium bifluoride based products are often considered a safer alternative to hydrofluoric acid, yet still pose clear risks to the handler.[8] Ammonium bifluoride, ammonium fluoride, and hydrofluoric acid have been described as "too dangerous for any use in a car wash environment" by Professional Car Washing and Detailing magazine,[10] advice that accords with a 2015 report from the U.S. Centers for Disease Control and Prevention.[11]

References

  1. ^ a b c d Sigma-Aldrich Co., Ammonium bifluoride. Retrieved on 2013-07-20.
  2. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  3. ^ Emsley, J. (1980) Very Strong Hydrogen Bonds, Chemical Society Reviews, 9, 91–124. doi:10.1039/CS9800900091
  4. ^ McDonald, T. R. R. (1960). "The electron-density distribution in ammonium bifluoride". Acta Crystallogr. 13 (2): 113–124. Bibcode:1960AcCry..13..113M. doi:10.1107/S0365110X60000261.
  5. ^ "ICSD Entry: 14140". Cambridge Structural Database: Access Structures. Cambridge Crystallographic Data Centre. Retrieved 2022-06-25.
  6. ^ Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307. ISBN 978-3527306732.
  7. ^ a b National Industrial Chemicals Notification and Assessment Scheme (April 17, 2020). "Bifluorides: Human health tier II assessment" (PDF). Department of Health (Australia). Retrieved February 8, 2023.
  8. ^ a b Genuino, Homer C.; Opembe, Naftali N.; Njagi, Eric C.; McClain, Skye; Suib, Steven L. (2012). "A review of hydrofluoric acid and its use in the car wash industry". Journal of Industrial and Engineering Chemistry. 18 (5): 1529–1539. doi:10.1016/j.jiec.2012.03.001. ISSN 1226-086X.
  9. ^ Gormley, James (May 29, 2001). "The truth about ammonium bifluoride". Professional Car Washing and Detailing. Archived from the original on 2001-05-29.
  10. ^ Cook, Ryan (October 9, 2013). "The Five Factors of Clean: Chemistry, Part 1". Professional Car Washing and Detailing. Retrieved February 8, 2023.
  11. ^ Woodie, Maria (December 1, 2015). "OSHA gives employees the right to know". Professional Car Washing and Detailing. Retrieved February 8, 2023.
  • v
  • t
  • e
HF He
LiF BeF2 BF
BF3
B2F4
CF4
CxFy
NF3
N2F4
OF
OF2
O2F2
O2F
F Ne
NaF MgF2 AlF
AlF3
SiF4 P2F4
PF3
PF5
S2F2
SF2
S2F4
SF4
S2F10
SF6
ClF
ClF3
ClF5
HArF
ArF2
KF CaF2 ScF3 TiF3
TiF4
VF2
VF3
VF4
VF5
CrF2
CrF3
CrF4
CrF5
CrF6
MnF2
MnF3
MnF4
FeF2
FeF3
CoF2
CoF3
NiF2
NiF3
CuF
CuF2
ZnF2 GaF3 GeF4 AsF3
AsF5
SeF4
SeF6
BrF
BrF3
BrF5
KrF2
KrF4
KrF6
RbF SrF2 YF3 ZrF4 NbF4
NbF5
MoF4
MoF5
MoF6
TcF6 RuF3
RuF4
RuF5
RuF6
RhF3
RhF5
RhF6
PdF2
Pd[PdF6]
PdF4
PdF6
AgF
AgF2
AgF3
Ag2F
CdF2 InF3 SnF2
SnF4
SbF3
SbF5
TeF4
TeF6
IF
IF3
IF5
IF7
XeF2
XeF4
XeF6
XeF8
CsF BaF2 * LuF3 HfF4 TaF5 WF4
WF6
ReF6
ReF7
OsF4
OsF5
OsF6
OsF
7

OsF8
IrF3
IrF5
IrF6
PtF2
Pt[PtF6]
PtF4
PtF5
PtF6
AuF
AuF3
Au2F10
AuF5·F2
HgF2
Hg2F2
HgF4
TlF
TlF3
PbF2
PbF4
BiF3
BiF5
PoF4
PoF6
At RnF2
RnF6
Fr RaF2 ** Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
* LaF3 CeF3
CeF4
PrF3
PrF4
NdF3 PmF3 SmF2
SmF3
EuF2
EuF3
GdF3 TbF3
TbF4
DyF3 HoF3 ErF3 TmF2
TmF3
YbF2
YbF3
** AcF3 ThF4 PaF4
PaF5
UF3
UF4
UF5
UF6
NpF3
NpF4
NpF5
NpF6
PuF3
PuF4
PuF5
PuF6
AmF3
AmF4
AmF6
CmF3 Bk Cf Es Fm Md No
PF6, AsF6, SbF6 compounds
  • AgPF6
  • KAsF6
  • LiAsF6
  • NaAsF6
  • HPF6
  • HSbF6
  • NH4PF6
  • KPF6
  • KSbF6
  • LiPF6
  • NaPF6
  • NaSbF6
  • TlPF6
AlF6 compounds
  • Cs2AlF5
  • K3AlF6
  • Na3AlF6
chlorides, bromides, iodides
and pseudohalogenidesSiF62-, GeF62- compounds
  • BaSiF6
  • BaGeF6
  • (NH4)2SiF6
  • Na2[SiF6]
  • K2[SiF6]
Oxyfluorides
  • BrOF3
  • BrO2F
  • BrO3F
  • LaOF
  • ThOF2
  • VOF
    3
  • TcO
    3
    F
  • WOF
    4
  • YOF
  • ClOF3
  • ClO2F3
Organofluorides
  • CBrF3
  • CBr2F2
  • CBr3F
  • CClF3
  • CCl2F2
  • CCl3F
  • CF2O
  • CF3I
  • CHF3
  • CH2F2
  • CH3F
  • C2Cl3F3
  • C2H3F
  • C6H5F
  • C7H5F3
  • C15F33N
  • C3H5F
  • C6H11F
with transition metal,
lanthanide, actinide, ammonium
  • VOF3
  • CrOF4
  • CrF2O2
  • NH4F
  • (NH4)2ZrF6
  • CsXeF7
  • Li2TiF6
  • Li2ZrF6
  • K2TiF6
  • Rb2TiF6
  • Na2TiF6
  • Na2ZrF6
  • K2NbF7
  • K2TaF7
  • K2ZrF6
  • UO2F2
nitric acids
bifluorides
  • KHF2
  • NaHF2
  • NH4HF2
thionyl, phosphoryl,
and iodosyl
  • F2OS
  • F3OP
  • PSF3
  • IOF3
  • IO3F
  • IOF5
  • IO2F
  • IO2F3
  • v
  • t
  • e
Ammonium salts
Inorganic salts
monatomic anions
  • NH4F
  • (NH4)2S
  • NH4Cl
  • (NH4)2Se
  • NH4Br
  • NH4I
oxyanions
  • NH4NO2
  • NH4NO3
  • (NH4)2CO3
  • (NH4)4UO2(CO3)2
  • (NH4)HCO3
  • NH4OCN
  • (NH4)3PO4
  • (NH4)2HPO4
  • (NH4)H2PO4
  • (NH4PO4)n(OH)2
  • NH4NaHPO4
  • (NH4)2SO3
  • (NH4)2SO4
  • (NH4)Al(SO4)2·12H2O
  • (NH4)2Fe(SO4)2·6H2O
  • NH4Fe(SO4)2·12H2O
  • NH4SO3NH2
  • (NH4)HSO4
  • (NH4)2S2O8
  • (NH4)2S2O3
  • NH4ClO3
  • NH4ClO4
  • NH4VO3
  • (NH4)2CrO4
  • (NH4)2Cr2O7
  • NH4MnO4
  • (NH4)3AsO4
  • (NH4)2MoO4
  • (NH4)6Mo7O24
  • (NH4)3Mo12PO40
  • NH4IO3
  • (NH4)2Ce(NO3)6
  • (NH4)8Ce2(SO4)8·4H2O
  • (NH4)10H2W12O42·4H2O
  • NH4ReO4
other anions
  • NH4BF4
  • NH4N3
  • NH4CN
  • (NH4)HF2
  • (NH4)3AlF6
  • (NH4)SiF6
  • (NH4)HS
  • NH4SCN
  • (NH4)2ZnCl4
  • (NH4)2MoS4
  • NH4I3
  • (NH4)2TeCl6
  • (NH4)2IrCl6
  • (NH4)2PtCl6
Organic salts