660
N. Ilayaraja et al. / Journal of Fluorine Chemistry 130 (2009) 656–661
Table 5
19F and GC/MS data of cleaved perfluoro products obtained during ECPF of aromatic and cyclic carboxylic acid chlorides [15–21].
Compound
19F Chemical shift (
d
, ppm)
MS m/z (rel. int.)
a = +39.76 (1F, m)
416 ([M]+, C8F16O, 0.7%); 397 ([MꢁF]+, C8F15O, 3.5%); 331([MꢁOꢁCF3]+, C7F13, 3.5%);
281 ([C6F11]+, 7.1%); 269 ([C5F11]+, 1.8%); 219 ([C4F9]+, 14.3%); 200 ([C4F8].+, 10.7%);
197 ([C4F7O]+, 3.6%); 181 ([C4F7]+, 57.1%); 150 ([C3F6]+, 14.3%); 131 ([C3F5]+, 71.4%);
119 ([C2F5]+, 21.4%); 100 ([C2F4].+, 27.1%); 97 ([C2F3O]+, 2.8%); 69 ([CF3]+, 100%);
50 ([CF2]+, 4.3%); 47 ([COF]+, 10.7%); 31 ([CF]+, 7.1%)
b = ꢁ115.39 (2F, m)
c = ꢁ118.75 (2F, m)
d = ꢁ120.94 (2F, m)
e = ꢁ180.13 (1F, m)
f = ꢁ125.64 (2F, m)
g = ꢁ81.42 (3F, m)
h = ꢁ71.73 (3F, m)
a = ꢁ80.36 (6F, m)
b = ꢁ120.31 (4F, m)
c = ꢁ117.81 (4F, m)
338 ([M]+, C6F14, 0.1%); 319 ([MꢁF]+, C6F13, 1.1%); 269 ([MꢁCF3]+, C5F11, 4.8%);
219 ([C4F9]+, 7.1%); 169 ([C3F7]+, 35.7%); 119 ([C2F5]+, 76.1%); 100 ([C2F4]+, 45.2%);
69 ([CF3]+, 100%); 50 ([CF2]+, 7.1%)
a = +40.15 (1F, m)
b = ꢁ115.71 (2F, m)
c = ꢁ117.03 (2F, m)
366 ([M]+, C7F14O, 0.1%); 347 ([MꢁF]+, C7F13O, 2.5%); 297 ([MꢁCF3]+, C6F11O, 1.3%);
281 ([C6F11]+, 1.9%); 269 ([C5F11]+, 1.2%); 247 ([C5F9O]+, 2.5%); 231 ([C5F9]+, 6.3%);
219 ([C4F9]+, 3.1%); 181 ([C4F7]+, 18.7%); 131 ([C3F5]+, 41.2%); 119 ([C2F5]+, 21.2%);
100 ([C2F4]+, 22.5%); 69 ([CF3]+, 100%); 50 ([CF2]+, 3.1%); 47 ([COF]+, 12.5%);
31 ([CF]+, 8.7%); 28 ([CO]+, 1.9%)
d,e = ꢁ117.63 (4F, m)
f = ꢁ119.53 (2F, m)
g = ꢁ85.17 (3F, m)
a = +40.24 (1F, m)
b = ꢁ115.65 (2F, m)
c = ꢁ119.50 (2F, m)
d = ꢁ122.87 (2F, m)
e = ꢁ179.70 (1F, m)
f = ꢁ123.21 (2F, m)
g = ꢁ84.76 (3F, m)
h = ꢁ53.69 (3F, m)
432 ([M]+, C8F16O2, 0.1%); 413 ([MꢁF]+, C8F15O2, 0.1%); 347 ([MꢁOCF3]+, C7F13O, 2.1%);
297 ([C6F11O]+, 1.4%); 278 ([C6F10O]+, 1.5%); 197 ([C4F7O]+, 2.2%); 181 ([C4F7]+, 14.1%);
147 ([C3F5O]+, 2.8%); 131 ([C3F5]+, 29.6%); 119 ([C2F5]+, 16.9%); 100 ([C2F4]+, 21.1%);
97 ([C2F3O]+, 2.1%); 81 ([C2F3]+, 2.3%); 69 ([CF3]+, 100%); 50 ([CF2]+, 4.2%);
47 ([COF]+, 15.5%); 28 ([CO]+, 1.5%)
selectivity to 60%. The proportion of aliphatic acid fluoride
(6) formed by cleavage of the ring was found to be in the
4. Experiments
a
range of 25%. In the case of (1e), the cleavage was more
significant and compounds 5 and 6 were formed in almost
equal proportion.
In the case of compounds 1b and 1c which contained –CH3 and
–OCH3 groups in the p-position, the major products still contained
–CF3 and –OCF3 groups. The selectivity of 2b and 2c was found to
be around 40–45%. The aliphatic analogue with COF group
4.1. General experimental procedures
An Aplab (India) DC power supply was used for the electrolysis.
19F NMR spectra were recorded with 376.5 MHz (400 MHz for 1H)
Bruker NMR Spectrometer using CDCl3 as solvent. CFCl3 was used
as internal reference for 19F NMR spectra, respectively. The
products were subjected to GC/MS analysis using Agilent 5975C
GC/MSD (70 eV) coupled with Triple-Axis HED-EM detector and
7890A GC.
Synthetic grade (>98%) benzoyl chloride (1a), 4-methylbenzoyl
chloride (1b), 4-methoxybenzoyl chloride (1c), 4-fluorobenzoyl
chloride (1d) and cyclo-hexane carboxylic acid chloride (1e) were
purchased from M/s Merck, Germany and used as received.
Anhydrous hydrogen fluoride (AHF) >99.9% was supplied by M/s
TANFAC, Cudalore, Tamilnadu, India.
obtained by
a cleavage (compounds 3b and 3c) and the alicyclic
analogue without RF substitution (compound 5) were the other
major products. The perfluorocarbons (4,7,8) obtained in all these
experiments due to the cleavage of –COF group was relatively
lower especially in the case of aromatic starting materials. During
the ECPF of 1b, a small fraction of compound (8a) was obtained.
This may be due to the conversion of –COF group in 1a to –CF3
group.
3. Conclusion
4.2. Electrochemical cell
Oxidative polymerisation of aromatic compounds on the
anode surface leads to the electrode fouling during electro-
chemical perfluorination of aromatic carboxylic acid chlorides.
This can be prevented by adding 1% dimethyl sulfide (w/v) in
the initial stage of electrochemical fluorination. The perfluori-
nated sulfur compounds adsorbed on the electrode surface
sustain the electrode activity by preventing polymeric film
formation. It is important to ensure that the total concentration
of reactants and partially fluorinated intermediates should not
be too high. This is to ensure that these reactants and
intermediates do not couple among themselves leading to
the formation of oligomers and polymers. Under these condi-
tions, the perfluorinated alicyclic and aliphatic carboxylic acids
are the main products. Substituents in the p-position of the
benzene ring improve the selectivity of acid fluorides. The exact
nature of the product formed from the DMS additive on
the electrode surface and the influence of this product requires
further investigation.
A double walled 200 ml capacity stainless steel cell with
alternate nickel anodes and cathodes was employed (effective
anode area = 230 cm2) for the electrolysis. The temperature of the
cell and the condenser was maintained at
5
and ꢁ30 8C,
respectively, using cryostats. Liquid products from the cell were
drained through a ball valve fixed at the bottom of the electrolysis
cell.
4.3. ECPF of substituted aromatic and cyclo-hexane carboxylic acid
chlorides
Prior to each galvanostatic experiments, the electrolyte (AHF)
was initially subjected to pre-electrolysis in the same electro-
chemical cell setup at a constant cell voltage V to ensure removal of
trace level of moisture present in the AHF. During pre-electrolysis
the nickel electrode is also anodically polarized and electroche-
mically activated. Pre-electrolysis was carried out for about 36–
48 h until initial current of 4 A was reduced to 0.2 A (current drop