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MethanolAir Fuel Cells.

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Bonding in Intermetallic Phases of the Ni-As Type
If. Wever, Berlin (Germany)
Among intermetallic phases, thc N i Ah typc represents a
transition between mainly metallic and essentially nonmetallic phases. The B atoms occupy a close-packed hexagonal unit cell with a c/a ratio of 1.633. Chains of A atoms
fit into the octahedral voids. With increasing metallic character of the €3 partner, both the cfa ratio and the heteropolar
forces between the A and B partners decrease. Homopolar
forces due to coupling between d-electrons of the A atom are
superimposed. The electrical conductivity behavior suggests
discrete d-levels for c/a > 1.633, and bands for c/a < 1.633.
If the c/a ratio is less than 1 . 3 3 , then the tetrahedral voids of
the hexagonal unit cell can also be filled with A atoms, i.e.
the structure tends towards A2B. In this way, new coordination and bonding relationships result. Further information
can be gained from studies of the electrical and magnetic
properties of the phases as wcll as from electrolytic transport
phenomena.
The Ni-Sn and Nikln systems were also studied. Both
phases have a considerable range of homogeneity. Definite
compositions (cs) corresponding to the temperature maximum in the phase diagram can be obtained by zone melting.
Electrical and magnetic properties are dependent on composition, such that the electrical conductivity of the Ni-Sn
phase shows a marked minimum at composition cs. The
electrolytic transport shows that for the Ni-Sn phase the
field force, and for the Ni-In phase the interaction force,
is the essential driving force.
A discussion of the experimental results suggests that the
d-band is filled increasingly from Ni-In to Ni-Sn to Ni-Sb.
The electrical properties can be understood if an atomic
bond between the Ni atoms in the tetrahedral voids and the
neighboring B atoms is assumed, for this would lead to a
bonding triple band. In the case of the Ni-Sn phase, the
band would be completely filled at the composition c,.
[GDCh-Ortsverband Nord-Wiirttemberg, Stuttgart
(Germany), January 23rd, 19641
[VB 786/127 IE]
G e r m a n version: Ancew. Chem. 76, 353 (1964)
Acetylation Reactions of Chlorins, a Contribution
to the Munich Chlorophyll Chemistry
H. H. Inhojfeti, Braunschweig (Germany)
By heating the Cu complex of 2-devinylisochlorin ec-dimethyl ester f l u ) with SnC12(.2HzO) and acetic anhydride at
100°C for 10 min, H . Fischer et al. [I] obtained the corresponding 2,6-diacetyl derivative ( I b ) . When the copper was
(fa): l t l
= I i Z = 11
( l b ) : K’ = R 2 = COCkI,
( , c ) : l i ’ = C O ~ ~ 1 lI3i 2; = li
//([I:
I t 1 = 1 1 . It?=
(‘O(’1l3
removed from (16) and the chlorin residue was allowed to
stand at room temperature in pyridine with benzoyl chloride,
the Cu-free 2-monoacetyl compound ( I r ) was isolated in 5
yield. From this Fischer concluded that partial dcacetylation
in the 6-position can bc achieved. Compound ( l r ) is an
important intermediate in SrreN’s synthetic reactions for
chlorophyll a. On checking these reports, it turned out that
acetylation of ( l o ) under Fischer’s conditions actually gave
a mixture of (Jb) and ( I c ) in the ratio of 4: 1. Pure ( I b ) ,
i.r. free of (Jr), could not be partially deacetylated in the
6-position by Fisrlier’s method. Moreover, considerably
more vigorous conditions, e.g. conc. aqueous HCI at room
temperature or at IOO“C, were also without effect upon the
6-acetyl group in (Ib).
If ( I n ) is acetylated at 0 ° C (60 min), a new monoacetyl
compound can be isolated in 70 ”4 yield. The product
obtained from this by removal of its copper with conc.
HCl/glacial acetic acid can be regarded on the basis of
extensive .deuterdtion experiments together with nuclear
magnetic resonance measurements as being the 6-monoacetyl compound ( I d ) (without Cu). Compound ( I d ) is
acetylated under Fischer’s conditions to give the known
mixture of ( I b ) and ( I c ) .
If ( l a ) is acetylated at 100°C with subsequent addition
of water (1 mole of H2O to 1 mole of AczO), f J r ) is obtained
in 90 ”/, yield.
The Cu-free chlorins were also made from ( I b ) , ( l c ) , and
(Id).
[GDCh-Ortsverband Braunschweig (Germany),
[VB 793/132 I€]
January 27th, 19641
G e r m a n version: Angew. Cheni. 76 (1964). in the press.
MethanoliAir Fuel Cells
W. T/ielstich, Bonn (Germany)
Apart from glycol and glycerin, methanol - including its
conversion products -- is especially suitable as liquid fuel for
galvanic fuel cells. Such cells are particularly useful for
maintenance-free energy supplies to signal devices, telegraph
stations, emergency power generators, :’rc.
The operating voltage varies between 0.5 and 0.8 V at room
temperature. Up to 145 ampere-hours were obtained per
mole of methanol (theoretical value for conversion to carbonate about 160 3mp.h). It is thus possible to store up to
1000 amp.h per 1 of fuel/electrolyte mixture. For practical
purposes, a “hard discharge curve”, i . r . a flat curve for
the voltage as a function of time or the concentration of
methanol, is of importance. This may be attained between
10 and +3OoC by suitable choice of catalysts and electrolyte composition.
Information about the individual reaction steps was obtained
by means of the potentiostatic triangular voltage method.
On anodic oxidation of formic acid on platinum (acid
electrolyte), formate radicals are formed in the potential
range between +300 and +600 mV (relative to hydrogen).
They passivate the electrode by adsorption on the surface.
It was shown that formation of oxalate or carbon monoxide
does not occur.
On passing CO? over a platiiiuni electrode in the potential
range 0 < ‘2 < + 300 mV against hydrogen, Giner [21 observed deposition of an oxidizable reaction product o n the
electrode. Now it has been shown that, here again, this
product is adsorbed formate radicals and not CO.
~
[GDCh-Ortsverband Bonn (Germany),
January 28th, 19641
[ I ] H . Fischer, f. Gemer, W . Sclinielz, and F. E d a i , Liebigs
Ann. Chem. 557, 134 (1944).
322
[VB 792/134 IE]
G e r m a n version: Angew. Chem. 76 (1964). in the press.
~
..
121 J . Ginel, Electrochim. Acta 8, 857 (1963); 9, 6 3 (1964).
Angew. Cliem. internat. Edit. 1 V d . 3 (1964)
No. 4
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