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Microanalytical Redox Tetrations.

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(DTA). Correlation of the two sets of data often is difficult,
since the instruments used normally d o not employ the same
experimental conditions. A Stanton HT-D thermobalance
was therefore modified to enable simultaneous DTA and TGA
measurements to be made.
With this instrument, the thermal decompositions of numerous chromates and dichromates were investigated, where the
following reactions occur (among others):
MxCr04.n H20 (s) + M ~ C r 0 4(s)
[x = 1 or 21
+ n H20 (9)
An acetamido group in the meta position of styrene increases
the thermal stability of the resultant homopolymers (4) and (5)
to a lesser degree than an amino group does, whereas the acetylated copolymer (6) has a thermal stability similar to that of
the acetylated homopolymers (4)and (5) but shows enhanced
thermal stability over the amino copolymer (3). The molecular weight apparently has no effect upon the thermal stability.
On pyrolysis in nitrogen, practically n o difference was found
for the polymers ( I ) , ( 5 ) , and (6) from the pyrolysis in air.
(1)
Thermogravimetric Analysis of Oxides
This reaction may be multi-stage.
H . Uwenfs, Drogenlos (Belgium)
MxCr04 (s)
+
2 MxCr04 ( s )
+ 2 MxOCrzO3 (s)
MxCr04 (1)
2 MxO-Crz03(s) +
2 MxO-Cr203(s) +
(24
+ 3/2 0 2 (g)
MxOCr203 (s) + MxO (s)
2 MxO (s) + Cr203 (s)
(2b)
(3a)
(3b)
These reactions may be simultaneous to or even precede
reaction 2(b)
MIIOCrrO3 (s)
+ MO (s)
- + M2ICr204 (s)
+ 1/2 0 2 (g)
(4)
Thermal Analysis of Inorganic Azides
H . Rosenwasser and 0.F. Kezer, Fort Belvoir, Virginia (U.S.A.)
The reaction of rare earth sesquioxides with hydrazoic acid
yields basic azides. These compounds containing the elements
from lanthanum through dysprosium in the lanthanide series
have a metal to nitrogen ratio of 1 : 6 and may be formulated
as Ln(0H) (N3)2.1.5 H20, whereas the heavier lanthanide elements (and yttrium) formcompounds with lower azidecontents,
which fit the formula L ~ z ( O H ) ~ N ~ . HInfrared
~O.
spectra,
however, indicate that the compounds have a n 0x0-structure.
These compounds were studied by means of differential thermal analysis. In general, the thermograms show the endothermic peaks caused by loss of water, and exothermic peaks due
to the conversion of azide groups to nitrogen molecules. Both
processes sometimes occur simultaneously. From thermogravimetric analyses, an oxyazide and an oxyhydroxide are
postulated as intermediates in the decompositions.
Although the thermal decomposition of the basic azides of
lanthanum and praseodymium proceeds smoothly in air, the
reactions taking place in vacuum often lead to explosions.
Studies with a DuPont micro-DTA unit show the effect of
heating rate as a factor in determining whether or not the
samples will explode. Information recorded on the thermograms includes crystalline phase transitions, melting points,
and decomposition of the azide ions. In the case of thallium
azide, a crystal structure change has been indicated for the
first time.
Thermal Analysis of Poly-(m-Aminostyrene) and
Related Polymers
R . H. Still and C. J . Keuttcli, Hatfield and Boreham Wood
(England)
m-Aminostyrene was homopolymerized using two different
concentrations of cc,a’-azobisisobutyronitrileto yield two homopolymers ( I ) and (2) of differing molecular weight. Copolymerization with styrene yielded a 2:1 copolymer (3) (2 moles
styrene : 1 mole m-aminostyrene). Acetylation of these polymers yielded poly-(m-acetamidostyrene) (4) and ( 5 ) , and the
corresponding 2:l copolymer (6). These substances were
studied by TGA in static air. The homopolymers ( I ) and (2),
owing to the presence of amino groups, are thermally more
stable than polystyrene, but the copolymer ( 3 ) showed no
enhanced thermal stability.
602
The reduction of simple oxides in a hydrogen atmosphere or
hydrogen stream using a thermobalance allows their stoichiometry to be determined.
This method was extended to mixtures of a non-volatile
(AmO,) and a volatile (BnOy) oxide. After preparation under
conditions (calcination at high temperature) where partial
evaporation of the volatile compound could be expected, the
composition of the final product was determined by the following procedure: The weight loss on reduction gave the total
amount of oxygen bound in the mixture. From the weight of
the residue the total quantity of metal (A+B) became known.
In a separate run the volatile oxide BnOy was evaporated at
high temperature under vacuum. The subsequent reduction of
the residue gave the amount of the metal A. The quantity of
the metal B was calculated by difference.
When the oxides form a solid compound (ApBqO,), a n excess of the volatile oxide can be removed at high temperature
and atmospheric pressure. Subsequent reduction of the residue
gives the amount of the combined metallic components
(ApBq). The oxygen content of the combination ApBqO, is
obtalned by the weight loss during reduction. Finally the
amount of component A is determined as decribed above.
German version: Angew.
[VB 922/229 IE]
Chem. 77, 592 (1965)
Microanalytical Redox Titrations
J . Z$ka, Prague (Czechoslovakia)
Suitable solutions for redox microtitrations include lead(1V)
acetate in glacial acetic as an oxidizing agent and hydrazine
sulfate or hydroquinone as reducing agents. The redox
potentials of other solutions can be shifted by combining the
oxidized or reduced form of the reagent in a complex or
sparingly soluble product. Examples of this are titrations
with iron(I1) sulfate in triethanolamine [l]. Under alkaline
conditions and in the presence of triethanolamine, iron(I1)
sulfate is a strong reducing agent. Compounds of trivalent
manganese, copper(I1) and bismuth(II1) salts, as well as
dichromates and tellurates can be titrated directly. The
titration of dichromate by this method is more sensitive
than in acid solution. It is suitable for the microdetermination
of dichromate in the presence of vanadate(V) which is not
reduced under these conditions. Tellurates can be determined
in the presence of tellurites and compounds of four- and
six-valent selenium. The method can also be used for the
potentiometric microdetermination of aromatic nitro groups
(reduction to NHz groups) and of nitroso and azo compounds.
[Osterreichische Gesellschaft fur Mikrochemie und
Analytische Chemie, Leoben (Austria),
January 29th and 30th, 19651
[VB 912p20 IEJ
German version: Angew. Chem. 77, 626 (1965)
[ I ] J . Doleial, E. Lukfyte, V . RybaCek, and J. Z+ka, Coll. czechoslov. chem. Commun. 29, 2597 (1964).
Angew. Chem. internat. Edit. 1 Vol. 4 (1965) 1 NO. 7
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