2099
RAJ, BERyL., Orient. J. Chem., Vol. 34(4), 2098-2105 (2018)
fluorine gas, anhydrous HF has been widely used
Reagents
for the synthesis of organofluorine compounds.
However, anhydrous HF is volatile and highly
corrosive and hence they are very difficult to handle.
The trifluoromethylated compounds have been
widely used in pharamaceutical and medicinal
applications particularly as tuberculation agent.
In view of importance of heterocyclic compounds,
isonicotinicacid hydrazide (INAH) is taken as
substrates for electrochemical trifluoromethylation.
The most of the works related to the electro organic
synthesis of trifluoromethylated compounds has used
trifluoroacetic acid (TFA) and sodium trifluoroacetate
(NaTFA) as sources of trifluoromethyl group and
pyridine (Py) used for increasing the conductivity
of the medium for electrolysis.[5-12] To the best of our
knowledge, electrochemical trifluoromethylation of
INAH has not been reported elsewhere.
All chemicals were of analytical grade.
Potassium ferrocyanide, Sodium bicarbonate,
pyridine, isonicotinicacid hydrazide, Trifluoroacetic
acid, Triethylamine, Acetonitrile and Acetone were
purchased from Merck, Germany.
Cyclic voltammetric studies
An undivided glass cell with the capacity of
15 cm3 was used for cyclic voltammetric experiment.
Thecellhadprovisionforgasinletandoutlet.Nitrogen
gas was used for the deaeration. Remi magnetic
stirrer with the Teflon glad paddle was used to stir
the electrolyte. High purity platinum (area 0.06cm2)
and glassy carbon electrodes (GCE, area 0.07cm2)
were used as working electrodes throughout the
present study. Silver electrode was used as quasi
reference electrode. A platinum foil was used as a
counter electrode. GCE was sufficiently polished
with emery sheets starting from 1/0, 2/0, 3/0 and
4/0 (John Oakey, England), followed by washing
with triple distilled water and trichloroethylene to
get reproducible voltammograms. The GCE was
activated by electrochemical cycling as described in
the literature. The electrode activity was frequently
checked with the ferricyanide/ferrocyanide redox
system13 until to get the ΔEp value very close to
60mV. All the experiments were carried out at
25 1oC. Cyclic voltammetric (CV) measurements
were recorded using an Eco Chemie Autolab
Potentiostat system under computer control.
The aim of the present work is to investigate
trifluoromethylation of isonicotinicacid hydrazide in
trifluoroacetic acid containing pyridine, triethylamine
and sodium trifluoroacetate dissolved in acetonitrile
onplatinumandglassycarbonelectrodesusingcyclic
voltammetry.Galvanostatic electrolysis of isonicotinic
acid hydrazide was done on platinum in the same
media and the products were characterized by
GC-MS. It is also aimed to analyze the voltammetric
parameters such as oxidation peak current and
peak potential of INAH using CV on glassy carbon
and Pt electrodes in different electrolyte media as
well as Galvanostatic electrolysis of INAH on Pt
and optimisation of different parameters such as
faradic charge, current density and different mole
ratios of supporting electrolyte on the selectivity of
trifluoromethyl derivative of INAH.
Glavanostatic electrolysis
An undivided cell with 25 ml capacity of
polypropylene tube served as preparative cell for
trifluoromethylation of INAH. The anode was a
rectangular platinum foil (3.5 cm2) and the cathode
was stainless steel (3.5cm2). Acetonitrile (25 ml)
containing 0.1 mol/L(0.342 g) of isonicotinic acid
hydrazide, 0.25 mol/L(0.712 g) of trifluoroacetic acid
and 0.1mol/L(0.197 g) of pyridine was introduced into
the cell.Electrolysis was carried out galvanostatically
at room temperature. After completion of the
electrolysis, the electrolyte was distilled out and the
product mixture was identified by GC-MS.
EXpERIMENTAL
preparation of sodium trifluoroacetate
The conversion of trifluoroacetic acid into
corresponding acetate salt is usually achieved by
stirring the acid with sodium bicarbonate under cold
condition. 50 ml of trifluoroacetic acid was taken in
a 100 ml round bottom flask and neutralized with
54.6 g of sodium bicarbonate with constant stirring
under cold condition.After completion of this reaction
(pH 7), the solution was evaporated to dryness using
vacuum evaporator. Finally, the salts of sodium
trifluoroactetate were obtained.
RESULTS AND DISCUSSION
Cyclic voltammetric (CV) studies
Cyclic voltammetric studies were done
in different solvent-supporting electrolyte media