Chemistry Reference
In-Depth Information
For the registration of the spectra or for the HPLC analysis (see next
section) it is essential to filter the solution because arcing causes the forma-
tion of very small carbon particles which remain in suspension. The crude
reaction mixtures were always filtered prior to analysis with a syringe fitted
with PVDF filtering membrane having a pore size of 0.45
10
6
m. By
using different current intensities and different solvents the growth of
certain absorption bands of the electronic absorption spectra was studied as
function of the arcing time.
8.2.2 HPLC A
NALYSIS OF THE
P
OLYYNES
The high-performance liquid chromatographic analysis (HPLC) was per-
formed on an Agilent Technologies model 1100, equipped with a diode-
array detector that was set at wavelengths of 225, 250, 274, 295, and 350 nm.
The solution containing the crude mixture of products, after filtration, was
injected into a 4.6
150mm HPLC column (Zorbax Eclipse XDB-C8). A
mobile phase of CH
3
CN/H
2
O 80/20 (v/v) was used under isocratic condi-
tions at a flow rate of 1.5 ml/min and 151 bar. The polyynes eluted from the
column were identified by a diode-array detector through their typical
spectra, which are given in the literature [23,24,41].
8.2.3 S
TUDY OF THE
E
ND
-C
APPING OF THE
P
OLYYNE
C
HAINS
The crude polyyne mixture obtained by the submerged electric arc between
graphite electrodes in n-hexane or n-dodecane or decahydronaphthalene
were treated with an excess of Ilosvay's reagent. The reagent was prepared
by dissolving 1.5 g of CuI and 1.3 g of NH
2
OH
HCl (hydroxylamine hydro-
chloride) in 55ml of distilled water together with 33ml of 33% aqueous NH
3
.
It was sufficient to shake the organic solution with the aqueous reagent and
immediately a brown precipitate is obtained due to the formation of the
copper acetylide derivatives. The formation of the copper acetylides was
abundant in solutions prepared by prolonged arcing and the acetylides can
be even collected by filtration (WARNING! Acetylides are all explosive when
they are dry. Always keep them humid and destroy them by treatment with
conc. HCl).
The detection of the polyynes end groups can be done by FT-IR spec-
troscopy on concentrated solutions of polyynes using an FT-IR model
IR300 from Thermo-Optek and an IR cell for liquids. The concentrated
solution of polyynes can be prepared by prolonged arcing in dodecane or
in decahydronaphthalene.
8.2.4 T
HE
E
LECTRIC
A
RC
B
ETWEEN
G
RAPHITE
E
LECTRODES
IN
n-H
EXANE
This section describes the search for products other than polyynes and pres-
ents the evidence for the formation of polycyclic aromatic hydrocarbons
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