[2] Among the many preparations, a typical one involves the reaction of sodium formate with benzoyl fluoride (generated in situ from KHF2 and benzoyl chloride):[3] The molecule is planar; C-O and C-F distances are 1.18 and 1.34 A, respectively.

[1] HC(O)F decomposes autocatalytically near room temperature to carbon monoxide and hydrogen fluoride: Because of the compound's sensitivity, reactions are conducted at low temperatures and samples are often stored over anhydrous alkali metal fluorides, e.g. potassium fluoride which absorbs HF.

Benzene (and other arenes) react with formyl fluoride in the presence of boron trifluoride to give benzaldehyde.

Formylation of benzene with a mixture of CO and hexafluoroantimonic acid however, exhibits no isotope effect (C6H6 and C6D6 react at the same rate), indicating that this reaction involves a more reactive formylating agent, possibly CHO+.

[3] Formyl fluoride undergoes the reactions expected of an acyl halide: alcohols and carboxylic acids are converted to formate esters and mixed acid anhydrides, respectively.