[7681-49-4] · FNa · Sodium Fluoride · (MW 41.99)
(halogen replacement by fluorine)
Physical Data: mp 993 °C; d 2.56 g cm-3.
Solubility: sol 42.2 g L-1 H2O; sol HF; insol EtOH.
Form Supplied in: white solid, widely available.
Handling, Storage, and Precautions: moderately toxic with LD50 = 0.18 g kg-1 in rats. People are severely affected after injesting less than one gram of NaF.
Although NaF can be used to replace other halogens with fluorine, Potassium Fluoride is the research chemist's reagent of choice because NaF is less efficient and much less soluble in commonly used solvents. This is not meant to imply that NaF is ineffective. Where the previously listed disadvantages are not critical, NaF is less hygroscopic and cheaper.2 In general, laboratory syntheses use KF and, upon scaleup to a plant procedure, NaF is substituted if possible.
Traditionally, compounds containing a reactive chlorine bonded to carbon, sulfur, or phosphorus can be converted to the corresponding fluorides with NaF in tetramethylene sulfone, MeCN, or DMF, as shown in Table 1.1 Pentachloropyridine and NaF in tetramethylene sulfone gave 3,5-dichlorotrifluoropyridine.3 In a similar way, 2,4,6-trifluoro-1,3,5-triazine can be formed from the trichloro- or a mixture of chloro- and fluoro-1,3,5-triazines.4 The rate and efficiency of the reaction can be improved by the addition of a phase-transfer catalyst. This is illustrated by the conversion of benzyl halides to benzyl fluoride or carboxylic acid halides to carboxylic acid fluorides.5
Although a halomethyl ether can be converted to a fluoromethyl ether (Table 1), an unusual reaction incorporates the use of NaF, with the reactant and product as the solvent, under supercritical reaction conditions, to displace halogen with fluoride (eqs 1 and 2). KF is equally effective.6
Generally speaking, the choice of NaF in place of KF is based on economics. There is no cited synthetic advantage of NaF over KF other than that NaF is easier to obtain and maintain in the anhydrous state.
Donald F. Halpern
Murray Hill, NJ, USA