pentafluorobenzoic acid
{{Chembox
| Name = Pentafluorobenzoic acid
| ImageFile =Pentafluorobenzoic acid.svg
| ImageFile2 =Pentafluorobenzoic acid-3D-balls.png
| ImageSize =
| ImageAlt =
| PIN = Pentafluorobenzoic acid
| OtherNames = perfluorobenzoic acid
|Section1={{Chembox Identifiers
| CASNo = 602-94-8
| CASNo_Ref =
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = B4JCP8R5GJ
| PubChem = 11770
| RTECS=
| Beilstein = 2054395
| Gmelin = 2054395
| ChemSpiderID = 11277
| SMILES = Fc1c(c(F)c(F)c(F)c1F)C(=O)O
| InChI = 1/C7HF5O2/c8-2-1(7(13)14)3(9)5(11)6(12)4(2)10/h(H,13,14)
| InChIKey = YZERDTREOUSUHF-UHFFFAOYAQ
| StdInChI = 1S/C7HF5O2/c8-2-1(7(13)14)3(9)5(11)6(12)4(2)10/h(H,13,14)
| StdInChIKey = YZERDTREOUSUHF-UHFFFAOYSA-N }}
|Section2={{Chembox Properties
| C=7 | H=1 | F=5 | O=2
| Appearance = White crystalline powder
| Density = 1.942 g/cm3
| MeltingPtC = 100-102
| BoilingPtC = 220
| HenryConstant =
| pKa =1.60
| LogP = 2.06
| VaporPressure =
| Solubility = Very soluble }}
|Section3={{Chembox Hazards
| MainHazards =
| NFPA-H = 2
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S =
| FlashPtC = 87
| AutoignitionPtC = }}
|Section4={{Chembox Related
| OtherAnions =
| OtherCations =
| OtherFunction = benzoic acids,
Nitrobenzoic acids
| OtherFunction_label = carboxylic acids
| OtherCompounds = }}
}}
Pentafluorobenzoic acid (PFBA) is an organofluorine compound with the formula C6F5CO2H. It is a white crystalline powder that has a high solubility in water. Its pKa of 1.48 indicates that it is a strong acid.Prakash, G. K. S.; Hu, J. "Pentafluorobenzoic Acid" in e-EROS Encyclopedia of Reagents for Organic Synthesis, 2005. {{doi|10.1002/047084289X.rn00682}}
Preparation
Pentafluorobenzoic acid is prepared by treating pentafluorophenyllithium (or pentafluorophenyl Grignard reagent) with carbon dioxide. These reagents are usually prepared in situ from pentafluorobenzene and bromopentafluorobenzene.{{cite journal | last1 = Harper | first1 = R. J. Jr. | last2 = Soloski | first2 = E. J. | last3 = Tamborski | first3 = C. | year = 1964 | title = Reactions of Organometallics with Fluoroaromatic Compounds | journal = J. Org. Chem. | volume = 29 | issue = 8| page = 2385 | doi = 10.1021/jo01031a067 }}
It arises via the reaction of perfluorotoluene with trifluoroacetic acid and antimony pentafluoride.{{cite journal | doi = 10.1016/j.jfluchem.2007.05.020| title = Transformation of perfluorinated benzocycloalkenes and alkylbenzenes to their carbonyl derivatives under the action of CF3COOH/SbF5| journal = Journal of Fluorine Chemistry| volume = 128| issue = 9| pages = 1058–1064| year = 2007| last1 = Zonov| first1 = Yaroslav V.| last2 = Karpov| first2 = Victor M.| last3 = Platonov| first3 = Vyacheslav E.}}
Substitution reactions
Substitution of fluoride occurs typically at the para position. This reaction has been used to anchor the −C6F4CO2H group to surfaces. Magnesium methoxide results in ortho methoxylation. Cleavage of this ether gives tetrafluorosalicylic acid. Via similar ortho-directed reactivity, nickel complexes catalyse the defluoridation of 2 and 5 positions. Without nickel, defluoridation occurs with para-selectivity.