# Can alkyl fluorides be formed by the Hunsdiecker reaction?

We know that the Hunsdiecker reaction is

$$\ce{RCOOAg + X2 ->[CCl4] RX + AgX + CO2}.$$

This reaction is successful with chlorine and bromine. Also, we know that if $\ce{X}$ is iodine, we will get an ester.

Can we form alkyl fluorides using this reaction? If not, why?

• Are you trying to use fluorine gas? :/
– Zhe
May 2 '18 at 15:39
• Yes @Zhe. Generally we do that only... May 2 '18 at 16:46
• That was a rhetorical question........
– Zhe
May 2 '18 at 17:09
• Fluorine shows anomalous behaviour among the halogens. While chlorine, bromine and iodine produce alkyl halides with alkanes in presence of light, fluorine produces carbon and HF in a violent reaction. May 3 '18 at 13:40

The classic reaction of silver salt of fatty acid and halogen to produce alkyl halide was first studied by Alexander Boronin in 1861. But the reaction was generalized by Heinz Hunsdiecker due to which the reaction is named Hunsdiecker reaction. Hunsdiecker used bromine to make methyl bromide. Chlorine was then used to make alkyl chloride. When iodine was used, then ester was formed. This reaction was called Simmonini reaction. Fluorine was not yet discovered then and hence alkyl fluoride was not made through this reaction (fluorine was discovered in 1886 by Henry Moissan).

But there are some speculation discussed among the chemist community whether Boronin actually used some fluorine containing reagent to make alkyl fluoride. It is discussed in this forum that Boronin might have used "acidic potassium fluoride" or $\ce{KHF2}$/potassium fluoride($\ce{KF}$) to make benzoyl fluoride in 1862 but there is no report or scientific paper on this reaction making it a speculated information. (Note: fluorine was discovered by electrolyzing $\ce{KHF2}$).

Fluorine containing compounds were made through Hunsdiecker reaction though proper alkyl fluoride synthesis through this reaction is yet to be reported:

1. Perfluoroalkyl iodides were made through this reaction: $$\ce{R_fCO2Ag + I2 ->[\Delta] R_fI + CO2 + AgI}$$ This compound is used to make numerous fuctionalized fluorocarbons and first Grignard reaction of this class.

2. Perfluoroalkyl diiodides has also been prepared by heating perfluorocarboxylic acid in presence of iodine. It has been used to make diacids having ether linkage.

3. Fluorinated ester of type $\ce{RFCO2CF2RF′}$ has been was obtained from reaction of silver 3,6,9-trioxa-F-undecanoate and iodine with a diluent at 130° C. Substitution products, $\ce{RFCOY}$ (Y = nucleophile) and pyrolysis products, $\ce{RFCOF}$ and $\ce{RF′COF}$ were isolated and characterized. It appears probable that the acyl hypoiodite and the iodo-F-alkane reacted by an $\ce{S_Ei -}$ type process to give the completely fluorinated ester.

4. Fluoro-functionalized graphene oxide is made via the Hunsdiecker reaction. It is made by treating of carboxylated graphene oxide with selectfluor at 90 °C for 10 h under an atmosphere of nitrogen, using silver nitrate as a catalyst.

### References:

1. Organofluorine Chemistry: Principles and Commercial Applications edited by R.E. Banks, B.E. Smart, J.C. Tatlow - page 18
2. Well-Architectured Fluoropolymers: Synthesis, Properties and Applications By Bruno Ameduri, Bernard Boutevin - page 108
3. Brace, N. O. Some approaches to the synthesis of fluorinated alcohols and esters. I. Completely fluorinated esters from the hunsdiecker reaction of silver F-alkanoates with iodine. J. Fluorine Chem. 1981, 18 (4), 515–524. DOI: 10.1016/S0022-1139(00)82668-8.
4. Xing, R.; Li, Y.; Yu, H. Preparation of fluoro-functionalized graphene oxide via the Hunsdiecker reaction. Chem. Commun. 2016, 52 (2), 390–393. DOI: 10.1039/c5cc08252h.
• Borodin did synthesize benzoyl fluoride. But he made it by reacting benzoyl chloride with KHF2. Even then, benzoyl fluoride is not an alkyl fluoride. See chtf.stuba.sk/~szolcsanyi/education/files/…. May 3 '18 at 14:03
• See encrypted.google.com/patents/US4704484. This mentions that Hunsdiecker reaction is limited to halogens except fluorine. May 3 '18 at 14:05
• @ShoubhikRajMaiti Yes, that's the point. Borodin tried to make a fluorine compound from Hunsdiecker reaction but was unable to synthesize an alkyl fluoride. May 3 '18 at 14:24