Fluorosulfonic acid

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  • Identifiers

    CAS number
    7789-21-1

    Molecular formula
    FHO3S

    SMILES
    OS(=O)(=O)F

    Safety labels

    Corrosive
    Corrosive

    Irritant
    Irritant

  • Odor profile

    Fragrance
    Odorless 90.64%
    Sulfurous 19.41%
    Pungent 16.04%
    Cooked 15.87%
    Savory 15.52%
    Clean 11.96%
    Burnt 11.71%
    Roasted 11.64%
    Sharp 11.52%
    Sour 11.06%

     

    Flavor
    Bitter 71.85%
    Odorless 39.82%
    Bland 25.62%
    Formyl 21.21%
    Nitrile 20.03%
    Rotten 19.77%
    Mousy 19.24%
    Urine 18.72%
    Sulfur 18.41%
    Decomposing cabbage 18.26%

     

    Odor impact est.
    Low

  • Properties

    XLogP3-AA
    -0.3

    pKa est.
    4.82 (weak acid)

    Molecular weight
    100.07 g/mol

    Melting point expt.

    • -125.1 °F (USCG, 1999)
    • -89 °C

    Boiling point

    • 324.9 °F at 760 mmHg (USCG, 1999)
    • 163 °C @ 760 MM HG
    • FORMS STABLE SALTS WHICH ARE LITTLE HYDROLYZED BY WATER & WHICH MAY BE RECRYSTALLIZED FROM WATER; BP: 110 °C AT 120 MM HG; 77.0 °C @ 18 MM HG
    • 163 °C

    Flash point

    • 103.14 ˚C est.

    Solubility expt.

    • SOL IN NITROBENZENE
    • Solubility in water: reaction

  • Synonyms

    • Fluorosulfonic acid
    • Fluorosulfuric acid
    • 7789-21-1
    • sulfurofluoridic acid
    • FLUOSULFONIC ACID
    • Fluorosulphuric acid
    • Monofluorosulfuric acid
    • HSDB 467
    • EINECS 232-149-4
    • UN1777
    • Perfluorosulfonic acid
    • DTXSID3033511
    • UNII-PPX0648643
    • CHEMBL1207889
    • DTXCID1013511
    • FLUOROSULFONIC ACID [MI]
    • FLUOSULFONIC ACID [HSDB]
    • EC 232-149-4
    • Fluosulfuric acid
    • PPX0648643
    • Fluorosulphonic acid
    • Fluorosulfuric acid (HSO3F)
    • sulfofluoran
    • Fluorosulfuric-acid-
    • MFCD00066174
    • FSO3H
    • DTXSID00175883
    • CHEBI:193136
    • Tox21_202147
    • BDBM50147628
    • NCGC00091007-01
    • NCGC00091007-02
    • NCGC00259696-01
    • CAS-7789-21-1
    • DS-002588
    • Fluorosulfonic acid [UN1777] [Corrosive]
    • NS00080889
    • Q411017
    • Fluorosulfonic acid, purified by triple-distillation

  • Applications

    Fluorosulfonic acid (CAS 7789-21-1) is an extremely strong Brønsted acid widely used as a catalyst and reaction medium in anhydrous organic synthesis, enabling acid-catalyzed transformations such as esterification, alkylation, and isomerization in industrial manufacturing; it is employed as a dehydrating solvent and activator in polymer and specialty-chemical processes, often allowing reactions to proceed under highly water-sensitive conditions; in pharmaceutical intermediate synthesis it is used to promote selective, high-activity reactions under tight control; in coatings and inks formulations it serves as a processing catalyst to drive resin curing and surface-chemistry modifications; these applications reflect its role as a non-nucleophilic superacid in demanding chemical routes, with handling governed by strict safety and regulatory requirements.

    gpt-5-nano

  • Solubility @25˚C

    Solvent Solubility (g/L)
    ethanol 147.68
    methanol 265.62
    isopropanol 108.61
    water 373.08
    ethyl acetate 32.58
    n-propanol 88.06
    acetone 151.36
    n-butanol 66.88
    acetonitrile 82.03
    DMF 641.32
    toluene 15.56
    isobutanol 53.94
    1,4-dioxane 110.96
    methyl acetate 50.92
    THF 146.42
    2-butanone 63.97
    n-pentanol 43.97
    sec-butanol 62.7
    n-hexane 7.46
    ethylene glycol 147.81
    NMP 307.81
    cyclohexane 9.21
    DMSO 669.35
    n-butyl acetate 22.48
    n-octanol 23.31
    chloroform 11.76
    n-propyl acetate 27.68
    acetic acid 86.72
    dichloromethane 26.67
    cyclohexanone 57.03
    propylene glycol 89.79
    isopropyl acetate 23.84
    DMAc 364.82
    2-ethoxyethanol 140.8
    isopentanol 48.7
    n-heptane 7.87
    ethyl formate 61.88
    1,2-dichloroethane 34.83
    n-hexanol 30.52
    2-methoxyethanol 263.87
    isobutyl acetate 12.64
    tetrachloromethane 4.06
    n-pentyl acetate 20.54
    transcutol 110.19
    n-heptanol 24.99
    ethylbenzene 8.95
    MIBK 31.02
    2-propoxyethanol 101.73
    tert-butanol 95.93
    MTBE 37.62
    2-butoxyethanol 66.52
    propionic acid 54.2
    o-xylene 16.93
    formic acid 162.58
    diethyl ether 51.26
    m-xylene 13.46
    p-xylene 10.27
    chlorobenzene 8.3
    dimethyl carbonate 58.92
    n-octane 3.64
    formamide 260.28
    cyclopentanone 86.91
    2-pentanone 51.09
    anisole 29.72
    cyclopentyl methyl ether 50.49
    gamma-butyrolactone 100.39
    1-methoxy-2-propanol 171.85
    pyridine 56.86
    3-pentanone 39.99
    furfural 118.73
    n-dodecane 2.65
    diethylene glycol 133.6
    diisopropyl ether 14.18
    tert-amyl alcohol 58.65
    acetylacetone 58.38
    n-hexadecane 2.8
    acetophenone 31.04
    methyl propionate 49.28
    isopentyl acetate 16.07
    trichloroethylene 23.99
    n-nonanol 21.16
    cyclohexanol 39.21
    benzyl alcohol 35.19
    2-ethylhexanol 15.41
    isooctanol 16.9
    dipropyl ether 30.49
    1,2-dichlorobenzene 8.16
    ethyl lactate 36.52
    propylene carbonate 42.44
    n-methylformamide 253.54
    2-pentanol 42.38
    n-pentane 11.83
    1-propoxy-2-propanol 64.72
    1-methoxy-2-propyl acetate 34.79
    2-(2-methoxypropoxy) propanol 56.84
    mesitylene 11.1
    ε-caprolactone 47.82
    p-cymene 8.04
    epichlorohydrin 81.96
    1,1,1-trichloroethane 9.46
    2-aminoethanol 154.06
    morpholine-4-carbaldehyde 248.34
    sulfolane 162.48
    2,2,4-trimethylpentane 3.27
    2-methyltetrahydrofuran 60.1
    n-hexyl acetate 21.91
    isooctane 2.59
    2-(2-butoxyethoxy)ethanol 68.28
    sec-butyl acetate 14.59
    tert-butyl acetate 23.91
    decalin 3.2
    glycerin 147.35
    diglyme 121.05
    acrylic acid 62.06
    isopropyl myristate 12.45
    n-butyric acid 43.32
    acetyl acetate 21.01
    di(2-ethylhexyl) phthalate 17.0
    ethyl propionate 28.42
    nitromethane 170.01
    1,2-diethoxyethane 38.8
    benzonitrile 23.23
    trioctyl phosphate 14.33
    1-bromopropane 18.99
    gamma-valerolactone 132.05
    n-decanol 17.73
    triethyl phosphate 16.88
    4-methyl-2-pentanol 23.04
    propionitrile 46.36
    vinylene carbonate 43.09
    1,1,2-trichlorotrifluoroethane 70.87
    DMS 23.48
    cumene 7.78
    2-octanol 17.08
    2-hexanone 31.74
    octyl acetate 17.46
    limonene 10.57
    1,2-dimethoxyethane 204.38
    ethyl orthosilicate 15.93
    tributyl phosphate 14.55
    diacetone alcohol 51.18
    N,N-dimethylaniline 37.42
    acrylonitrile 66.94
    aniline 34.72
    1,3-propanediol 126.06
    bromobenzene 5.58
    dibromomethane 18.05
    1,1,2,2-tetrachloroethane 24.15
    2-methyl-cyclohexyl acetate 16.82
    tetrabutyl urea 31.77
    diisobutyl methanol 12.22
    2-phenylethanol 24.85
    styrene 10.31
    dioctyl adipate 20.42
    dimethyl sulfate 96.99
    ethyl butyrate 23.42
    methyl lactate 69.48
    butyl lactate 29.18
    diethyl carbonate 17.92
    propanediol butyl ether 57.7
    triethyl orthoformate 20.75
    p-tert-butyltoluene 8.3
    methyl 4-tert-butylbenzoate 37.86
    morpholine 132.71
    tert-butylamine 52.0
    n-dodecanol 14.61
    dimethoxymethane 243.19
    ethylene carbonate 38.81
    cyrene 59.94
    2-ethoxyethyl acetate 28.12
    2-ethylhexyl acetate 12.66
    1,2,4-trichlorobenzene 9.64
    4-methylpyridine 53.01
    dibutyl ether 16.7
    2,6-dimethyl-4-heptanol 12.22
    DEF 101.45
    dimethyl isosorbide 68.5
    tetrachloroethylene 17.93
    eugenol 48.56
    triacetin 27.34
    span 80 40.48
    1,4-butanediol 70.12
    1,1-dichloroethane 17.22
    2-methyl-1-pentanol 27.77
    methyl formate 180.35
    2-methyl-1-butanol 42.68
    n-decane 3.79
    butyronitrile 40.6
    3,7-dimethyl-1-octanol 15.44
    1-chlorooctane 7.55
    1-chlorotetradecane 4.59
    n-nonane 3.93
    undecane 3.09
    tert-butylcyclohexane 2.62
    cyclooctane 4.86
    cyclopentanol 59.37
    tetrahydropyran 53.95
    tert-amyl methyl ether 32.43
    2,5,8-trioxanonane 101.0
    1-hexene 14.19
    2-isopropoxyethanol 74.61
    2,2,2-trifluoroethanol 61.95
    methyl butyrate 38.73

    Scent© AI

1 4

IFRA standard 51

Recommendation
No restriction
Maximum acceptable concentrations in the finished product (%)
Category 1
Products applied to the lips
 No restriction Category 7A
Rinse-off products applied to the hair with some hand contact
 No restriction
Category 2
Products applied to the axillae
 No restriction Category 7B
Leave-on products applied to the hair with some hand contact
 No restriction
Category 3
Products applied to the face/body using fingertips
 No restriction Category 8
Products with significant anogenital exposure
 No restriction
Category 4
Products related to fine fragrance
 No restriction Category 9
Products with body and hand exposure, primarily rinse off
 No restriction
Category 5A
Body lotion products applied to the body using the hands (palms), primarily leave on
 No restriction Category 10A
Household care products with mostly hand contact
 No restriction
Category 5B
Face moisturizer products applied to the face using the hands (palms), primarily leave on
 No restriction Category 10B
Household care products with mostly hand contact, including aerosol/spray products (with potential leave-on skin contact)
 No restriction
Category 5C
Hand cream products applied to the hands using the hands (palms), primarily leave on
 No restriction Category 11A
Products with intended skin contact but minimal transfer of fragrance to skin from inert substrate without UV exposure
 No restriction
Category 5D
Baby Creams, baby Oils and baby talc
 No restriction Category 11B
Products with intended skin contact but minimal transfer of fragrance to skin from inert substrate with potential UV exposure
 No restriction
Category 6
Products with oral and lip exposure
 No restriction Category 12
Products not intended for direct skin contact, minimal or insignificant transfer to skin
 No restriction