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Kinetics of the Thermal Decomposition of Magnesium and Calcium Carbonates.

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glohin consists of > 95 % HhA, 2 % HbA2, and 0.5 % HbF.
This composition is altered by anomaly of the a- or @-chains
in HbA, since as a replacement for the defective chains, 6
(HbA2) and y (HbF) chains are incorporated. Pathological
manifestations can he associated with definite changes in the
composition of the haemoglobin.
Biochemistry and Pathogenesis of Hereditary
Haemolytic Anaemias with Enzyme
Defects in the Hexose Monophosphate Cycle
G . W . Lohr and H. D . Waller, Tiibingen (Germany)
There are two haemolytic anaemias that are caused by
enzyme deficiencies in the hexose monophosphate cycle:
1. Glucose-6-phosphate dehydrogenase deficiency, the most
frequent hereditary disease. The life-span of the erythrocytes
is shortened. In general, haemolysis only occurs after ad.
a derivative of 8ministration of drugs ( e . ~primaquine,
2. Glutathione reductase deficiency, first observed 1961/1962.
The haemolytic crises appear spontaneously.
Metabolism in Hereditary Enzymopathies
F. Linnewelz, MarburgILahn (Germany)
The following diseases due to enzyme defects were discussed :
1. Phenylketonuria: Blocking of the breakdown of phenylalanine to tyrosine leads to excrction of phenylpyruvic acid.
Since the amino acid pool becomes unbalanced as a result
of an excess of intact phenylalanine, resorption in the gut is
decreased. For this reason, the supply of essential amino
acids to the brain is reduced, this in turn leading to mental
deficiency if it occurs during the phase of brain differentiation
in the infant. By administration of a diet low in phenylalanine in the first year of life, such children could develop
normal intelligence.
2. Cystinosis is due to disturbance of the breakdown of
cysteine to taurine and the toxic: effect of the intermediate
product o n the kidney.
3. Leucinosis: The lack of a decarboxylase prevents catabolism of leucine, isoleucine, and valine.
4. Glycogenosis: There is a deticiency of glucose-dphosphatase.
[VB 687/79 IE]
Kinetics of the Thermal Decomposition
of Magnesium and Calcium Carbonates
The pressure dependence of k can be written:
E. Cremer, Innsbruck (Austria)
This relationship can be deduced from the same factors as with
the decomposition of CaC03, but with the assumption of
stronger COz adsorption.
[GDCh-01 tsverband Frankfurt/Main (Germany),
February 7tb, 19631
[VB 685/75 IE]
The rates of decomposition of MgC03 [l] and CaCO3 [2]
are strongly dependent o n the COz pressure, even in a temperature and a pressure range in which the reverse reaction
could certainly not yet be observable. The oxides had to be
decomposed at constant pressure in order to determine the
“order” of the reaction. The concept of order in heterogeneous reactions, however, poses certain problems. What
one measures here is generally the change of percentage
conversion (u) with time, and the equation
k = k’ (1 + bPC0z)/PC02
Unimolecular Reactions in
Photochemical Systems
G. B. Porter, Frankfurt/Main (Germany) [4]
= k(100-u)”
applies formally, just as for gas reactions. For a gas reaction
however, (100-u) is proportional to the concentration in the
entire reaction volume, whereas for the heterogeneous
reaction, generally only a fraction of (100-u) % may have
the opportunity of reacting simultaneously. If the reaction
rate is proportional to the surface area of the starting
material, as is the case with CaCO3 prepared from CaO and
COz [2], then n = 2/3 in the above reaction. The data from
measurements of the decomposition of MgC03 are better
evaluated by a diffusion formula (for low conversion u2 =
kt) [l]. However, the diffusion through the oxide film formed
is certainly not rate determining [3]. The rate coefficient k,
which is independent of the degree of decomposition, can he
used to evaluate the pressure and temperature dependence of
the reaction. The induction period due to the formation of
reaction nuclei observed in the decomposition of CaC03 can
be eliminated by preforming the nuclei during preparation.
For the pressure dependence of the CaO formation reaction
a t 800-85OOC we have,
k = k* (l/Pcoz-~/Px)
This relationship can be derived theoretically if the estahlishCaO* + COz is
ment of a surface equilibrium CaC03
assumed, where px denotes the equilibrium pressure above
the reacting mass. The equilibrium pressure with MgC03 is
so high at 500-600°C that the term l/px can be neglected.
[I] E. Cremer, K . Allgeuer, and W. .4schenbrenner, Radex-Rundschau 1953,494.
[2] W. Nitsch, Ph. D. thesis, Universitat Innsbruck 1959; E. Cremer and W. Nitsch, Z. Elektrochem., Ber. Bunsenges. physik.
Chem. 66,697 (1962).
[3] L. Bachmann and E . Cremer, Z. anorg. allg. Chem. 6 5 , 309
Angew. Chem. internat. Edit. 1 Vol. 2 (1963)
1 No. 5
Our studies of the dependence of pressure, temperature, and
wave length of the quantum yields of photolysis of gaseous
hexafluoroacetone show that there are two alternative
primary processes. One involves monomolecular dissociation
of excited singlet state molecules, which are formed with
vibrational energy considerably in excess of the equilibrium
energy during the excitation process with light. The fact that
the quantum yields decrease with increasing pressure can be
interpreted in terms of competition between dissociation and
collisional degradation. The quantum yields also decrease at
long wave lengths, because the excited singlet molecules are
formed with low vibrational energy. The temperature of the
system has little effect on this primary process, since it affects
only the equilibrium vibrational energy of molecules.
The second primary process entails unimolecular dissociation
of triplet state molecules formed from excited singlet state
molecules by intersystem crossing in a radiationless transition. Since the triplet state has a relatively long lifetime
(ca. 10-4 sec) there is ample time for vibrational equilibrium
to be established. Thus, this primary process is essentially a
thermal unimolecular reaction. As such, its rate constant
depends strongly on temperature, hut not on the wavelength
of excitation. Added biacetyl accepts energy efficiently from
hexafluoracetone triplet state molecules, completely deactivating them to the ground state. Even traces of biacetyl eliminate
the second mode of dissociation almost completely, which
permits the two primary processes to be studied independently.
[GDCh-Ortsverband Freiburg-Stidbaden (Germany),
[VB 686174 E l
February 8th, 19631
[4] Present address: lnstitut fur physikalische Chemie der Universivat Frankfurt/Main. Work carried out in collaboration with
P . Bowers, University of British Columbia, Vancouver (Canada).
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decompositions, thermal, carbonates, magnesium, kinetics, calcium
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