A method for producing a fluorinated organic compound, comprising the steps of A) fluorinating an organic compound by reaction with a fluorine source of the formula MF n, wherein M is H, or a metal of Group 1 or 2 of the periodic table; and n is 1 or 2; in the presence of - a hypervalent iodine aromatic ring compound, or - an iodine aromatic ring compound and an oxidant; and B) separating the iodine aromatic ring compound from a reaction liquid after step A is started wherein the compound is a compound of formula (2a1), and the compound is a compound of formula (2b1): wherein, each independently at each occurrence Ar is an aromatic ring, R p1 is a carboxylic acid group; -O-(CH 2) q -NR 3 X or -(CH 2) q -NR 3 X, wherein q is a number of ≥ 1; R is H or C 1 - 20 -alkyl; and X is halogen, arylsulfonyloxy or alkylsulfonyloxy; or -O-(CH 2) q -A or -(CH 2) q -A, wherein A is -SO 3 Y or -COOY; Y each independently is H, a metal atom, or NR 5 4 wherein R 5 each independently is H or an organic group; R p2 is alkyl, alkoxy, halogen, cyano, nitro, a carboxylic acid group, a sulfonic acid group, hydroxy, phosphoryloxy; -O-(CH 2) q -NR 3 X or -(CH 2) q -NR 3 X as defined for R p1, or two R p2 bonded to one iodine atom may together form =O; n1 is a number of > 0; n2 is a number of ≥ 1; and (n1+n2) is ≤11. A) fluorinating an organic compound by reaction with a fluorine source of the formula MF n, wherein M is H, or a metal of Group 1 or 2 of the periodic table; and n is 1 or 2; in the presence of - a hypervalent iodine aromatic ring compound, or - an iodine aromatic ring compound and an oxidant; and - a hypervalent iodine aromatic ring compound, or - an iodine aromatic ring compound and an oxidant; and B) separating the iodine aromatic ring compound from a reaction liquid after step A is started wherein the compound is a compound of formula (2a1), and the compound is a compound of formula (2b1): wherein, each independently at each occurrence Ar is an aromatic ring, R p1 is a carboxylic acid group; -O-(CH 2) q -NR 3 X or -(CH 2) q -NR 3 X, wherein q is a number of ≥ 1; R is H or C 1 - 20 -alkyl; and X is halogen, arylsulfonyloxy or alkylsulfonyloxy; or -O-(CH 2) q -A or -(CH 2) q -A, wherein A is -SO 3 Y or -COOY; Y each independently is H, a metal atom, or NR 5 4 wherein R 5 each independently is H or an organic group; R p2 is alkyl, alkoxy, halogen, cyano, nitro, a carboxylic acid group, a sulfonic acid group, hydroxy, phosphoryloxy; -O-(CH 2) q -NR 3 X or -(CH 2) q -NR 3 X as defined for R p1, or two R p2 bonded to one iodine atom may together form =O; n1 is a number of > 0; n2 is a number of ≥ 1; and (n1+n2) is ≤11. wherein the compound is a compound of formula (2a1), and the compound is a compound of formula (2b1): wherein, each independently at each occurrence Ar is an aromatic ring, R p1 is a carboxylic acid group; -O-(CH 2) q -NR 3 X or -(CH 2) q -NR 3 X, wherein q is a number of ≥ 1; R is H or C 1 - 20 -alkyl; and X is halogen, arylsulfonyloxy or alkylsulfonyloxy; or -O-(CH 2) q -A or -(CH 2) q -A, wherein A is -SO 3 Y or -COOY; Y each independently is H, a metal atom, or NR 5 4 wherein R 5 each independently is H or an organic group; R p2 is alkyl, alkoxy, halogen, cyano, nitro, a carboxylic acid group, a sulfonic acid group, hydroxy, phosphoryloxy; -O-(CH 2) q -NR 3 X or -(CH 2) q -NR 3 X as defined for R p1, or two R p2 bonded to one iodine atom may together form =O; n1 is a number of > 0; n2 is a number of ≥ 1; and (n1+n2) is ≤11. Ar is an aromatic ring, R p1 is a carboxylic acid group; -O-(CH 2) q -NR 3 X or -(CH 2) q -NR 3 X, wherein q is a number of ≥ 1; R is H or C 1 - 20 -alkyl; and X is halogen, arylsulfonyloxy or alkylsulfonyloxy; or -O-(CH 2) q -A or -(CH 2) q -A, wherein A is -SO 3 Y or -COOY; Y each independently is H, a metal atom, or NR 5 4 wherein R 5 each independently is H or an organic group; R p2 is alkyl, alkoxy, halogen, cyano, nitro, a carboxylic acid group, a sulfonic acid group, hydroxy, phosphoryloxy; -O-(CH 2) q -NR 3 X or -(CH 2) q -NR 3 X as defined for R p1, or two R p2 bonded to one iodine atom may together form =O; n1 is a number of > 0; n2 is a number of ≥ 1; and (n1+n2) is ≤11.