A simple method for preparing difluorodiiodomethane from difluoro(fluorosulfonyl)acetyl fluoride

Article abstract of DOI:10.1135/cccc20021320

Difluorodiiodomethane is prepared in 60% yield by the reaction of difluoro(fluorosulfonyl)acetyl fluoride with I₂/KI in the presence of a catalytic amount of SiO₂ in acetonitrile at 60-65°C.

Full text of DOI:10.1135/cccc20021320

1320
Xiao et al.:
A SIMPLE METHOD FOR PREPARING DIFLUORODIIODOMETHANE
FROM DIFLUORO(FLUOROSULFONYL)ACETYL FLUORIDE
Ji-Chang XIAO, Jian-Xin DUAN, An-Rong LI, Yong GUO
1,
and Qing-Yun CHEN *
Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, PR China;
1
e-mail: chenqy@pub.sioc.ac.cn
Received May 14, 2002
Accepted Jun e 21, 2002
Dedicated to the memory of Professor Miloš Hudlický.
Difluorodiiodom eth an e is prepared in 60% yield by th e reaction of difluoro(fluorosulfo-
n yl)acetyl fluoride with I2/KI in th e presen ce of a catalytic am oun t of SiO2 in aceton itrile at
60–65 °C.
Keyw ord s: Difluorodiiodom eth an e; Difluoro(fluorosulfon yl)acetyl fluoride; Silica gel; Iodin e;
Potassium iodide; Iodin ation .
Recen tly, th e ch em istry of difluorodiiodom eth an e (CF2I2, 1) h as been de-
veloped sign ifican tly sin ce its syn th esis was im proved in our laboratory ten
years ago. Like its ph oto- or diben zoyl-peroxide-in duced reaction s with
alken es reported first by Dolbier et al.1, 1, as an difluoroiodom eth yl radical
source, can add to electron -rich olefin s in th e presen ce of [PdCl2(PPh 3)2] 2,
[Pd(PPh 3)4] 2, Na2S2O4 3, Fe 4 or un activated Zn . Lead tetraacetate5 or h igh
4
tem perature (185 °C)6 is even able to prom ote th e addition reaction of 1 to
poly- or perfluoroalken es. Com poun d 1 was also sh own to be a trifluoro-
m eth ylatin g agen t for aza-arom atic com poun ds an d en am in es wh en
irradiated in DMF 7. Differen t from CF2Br2, dieth yl (difluoroiodom eth yl)-
ph osph on ate could be readily obtain ed in n early quan titative yield by sim ple
treatm en t of 1 with trieth yl ph osph ite in dieth yl eth er8. However, th e de-
sired vin yl iodides, ICF2CH=CIR, derived from th e addition reaction of 1 to
5
alkyn es, could n ot be obtain ed th rough th e in itiation with eith er Pb(OAc)4
or aqueous h ydrogen peroxide in aceton e9. In stead, n on -fluorin ated com -
poun ds, β-iodo-α,β-un saturated carboxylic esters an d acids were form ed.
10
Un like oth er difluorocarben e precursors such as CF2Cl2 10, CF2Br2
,
Collect. Czech. Chem. Commun. (Vol. 67) (2002)
doi:10.1135/cccc20021320

Difluorodiidomethane from Difluoro(fluorosulfonyl)acetyl Fluoride
1321
CF2BrCl 10, treatm en t of 1 with ph en oxides in DMF at room tem perature
gave ArOCF2I on ly in 7–15% yields, th e diph en yl carbon ates bein g th e m a-
jor products, wh ile with ben zen eth iolates afforded difluorom eth ylen e de-
rivatives (ArSCF2I, ArSCF2SAr an d ArSCF2H) also in low yields11.
In prin ciple, 1 can be prepared by th e addition of difluorocarben e to io-
din e. However, previous m eth ods from various difluorocarben e precursors
suffered from low yields (ca 20%)12. Th e fluorin ation of CI4 with HgF2 gives
1, but th e yields are un satisfactory (27%)1. It was foun d th at usin g m eth yl
brom odifluoroacetate or potassium brom odifluoroacetate as difluorocarben e
source, 1 can be obtain ed in 50–60% yield with KI/I2 in th e presen ce of a
catalytic am oun t of CuI in DMF 13. A h igh er yield (85%) of 1 was also
reported on h eatin g 1,2-epoxyh exafluoropropan e with I2 in autoclave at
185 °C 14
.
In order to in vestigate furth er th e reaction s of 1, it seem s n ecessary to
h ave a sim pler way to syn th esize 1, because th e startin g m aterials of th e
above m en tion ed approach es are n ot readily available or a special equip-
m en t is n eeded. Fortun ately, a syn th etic m eth od for 1 from difluoro-
(fluorosulfon yl)acetyl fluoride(FSO2CF2COF, 2) was foun d to serve th e
purpose. Usin g 2, 1 can be prepared on 100 g scale in a ordin ary glassware.
We presen t h erein th e results.
EXPERIMENTAL
Difluoro(fluorosulfon yl)acetyl fluoride was obtain ed from En gin eerin g Research Cen ter in
Organ ic Syn th esis, Ch in ese Academ y of Scien ces. Aceton itrile (CH3CN) was dried over ph os-
ph orus pen toxide an d fresh ly distilled prior to use. Potassium iodide (KI) was dried over a
direct flam e. Silica gel (SiO2, 300–400 m esh ) was baked in an oven at 120 °C for 6 h . 19F NMR
spectra (δ, ppm ) were recorded on a Bruker AM-300 (282 MHz) spectrom eter usin g CFCl3 as
extern al stan dard, upfield sh ifts bein g design ated as n egative. Mass spectra were taken on a
Hewlett–Packard HP-5989A spectrom eter.
Difluorodiiodom eth an e (1)
A solution of dry KI (0.8 m ol, 132.8 g) an d I2 (0.8 m ol, 203.2 g) in CH3CN (600 m l) was
placed in a 1 000 m l th ree-n ecked flask fitted with a droppin g fun n el, a water con den ser
con n ected to a dry ice con den ser, a th erm om eter an d a m agn etic stirrer. To th e solution dry
silica gel (0.06 m ol, 3.6 g) was added durin g stirrin g. After h eatin g th e con ten t to 60–65 °C,
com poun d 2 (1.1 m ol, 198 g) was slowly added un der vigorous stirrin g durin g 8 h for fin ish -
in g th e reaction . Th en th e m ixture was kept for addition al tim e un til th e 19F NMR spectros-
copy sh owed th e en d of th e reaction (ca 2 h ). Sim ple distillation gave a solution of 1 in
CH3CN wh ich th en was poured in to H2O (2 l). Th e oil was separated, wash ed with H2O (5 ×
50 m l) an d dried over an h ydrous Na2SO4. About 171 g (0.56 m ol, 70%) of crude product 1
was obtain ed. Redistillation gave 148 g (0.49 m ol, 61%); b.p. 101 °C. MS, m/z: 304 (8.6, M+),
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

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Xiao et al.:
285 (1.1, CFI2), 254 (100, I2), 177 (30.3, CF2I), 158 (1.4, CFI), 127 (75.7, I), 50 (2.3, CF2). 19F NMR
(CDCl3): 18.6 (s)1.
RESULTS AND DISCUSSION
Difluoro(fluorosulfon yl)acetyl fluoride (2) is on e of th e startin g m aterials
for producin g th e com m ercial ion -exch an ge resin Nafion -H 15. Com poun d
2 is readily available or can be prepared by th e reaction of CF2=CF2 with
SO316. In our laboratory, a variety of its derivatives, such as HCF2SO2R [(R = F,
OC6H5, OCH2CF2CF2H, OC6F5, HCF2O, N(CH3)C6H5)]17, CH3O2CCF2SO2R
18
19
(R = F, OC6H5, HCF2CF2CF2CF2CHO)17, HCF2SO3H and FO2SCF2CO2SiMe3
were prepared as difluorocarben e precursors, wh ich can gen erate CF2: un der
n eutral, alkalin e or even stron gly acidic con dition s. In terestin gly, 2 was re-
cen tly foun d to be a difluorocarben e source, from wh ich 1 could be syn th e-
sized in th e presen ce of a catalytic am oun t of silica gel.
Slow dropwise addition of 2 to a stirred solution of I2/KI in CH3CN in th e
presen ce of 5–10 m ole % of silica gel at 60–65 °C in several h ours gave 1, af-
ter usual work-up, in 60–70% yield.
CH3CN
FSO2CF2COF + KI + I2
CF2I2
SiO2
2
1
60–65 °C
Th e presen ce of SiO2 is essen tial for th e reaction ; in its absen ce, th e acid
fluoride did n ot decom pose. A 5 – 10 m ole % of SiO2 relative to I2 is th e op-
tim um ratio. Usin g on e equivalen t or m ore results n ot on ly in dram atically
decreasin g yield but also in form ation of an un iden tified by-product (δ 42.8
ppm ). In th e absen ce of KI, th e reaction did n ot occur. It was foun d th at
both the KI/I2 ratio 1 : 1 and the concentration of I–3 in CH3CN 1.3–1.5 m ol l–1
are n ecessary, oth erwise th e reaction is eith er too fast or too slow an d th e
yields becom e lower. Th e results of th e effect of th e reactan t ratios on th e
yield are listed in Table I.
Th e exact m ech an ism is n ot com pletely un derstood yet alth ough th e
gen eration of CF2 resultin g from SiO2 in duced decom position of 2 seem s to
be beyon d doubt. Oth er silicon com poun ds, such as Si(OEt)4, silicon e an d
Al2O3 can also trigger th e sam e reaction un der sim ilar con dition s, but th e
yields are n ot better (32, 31 an d 45%, respectively).
In con clusion , we h ave developed a n ew, sim ple m eth od for th e syn th esis
of difluorodiiodom eth an e from readily available difluoro(fluorosulfon yl)-
acetyl fluoride.
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

Difluorodiidomethane from Difluoro(fluorosulfonyl)acetyl Fluoride
1323
TABLE I
Th e effects of th e reactan t ratios on th e yield of 1
En try
FSO2CF2COF
I2
KI
1
SiO2
Yield, %a
1
2
2
1.7
2.4
24
13
12
11
10
7
1
1.6
1
10
12
0
1.3
1
1.3
3
1
10
10
10
10
10
10
5
0
4
10
1
59
57
58
53
61
62b
0
5
10
10
10
10
10
10
10
1
6
1
7
1
8
1
9
1
10
11
20
11
1
0
1
0
a
b
Isolated yield based on I2; isolated yield based on FSO2CF2COF.
We thank the National Science Foundation of China for financial support of this work.
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