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Dehydration of Hydroxides.

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much more slowly than would be expected according t o
theory. The reason is that the growth of crystalline precipitates at concentrations close to saturation is generally not
diffusion-controlled.
A third example is the kinetics of phase separation in quenched supersaturated metal alloys, such as Ag-Pb. An interpretation of this separation as ripening of the clusters formed
on quenching is suggested. The change in particle number and
size may be traced by resistance measurements and with a n
electron microscope. Measurements have so far shown
qualitative agreement with theory. Independent measurements of the diffusion coefficient in heterogeneous crystals
are necessary, however, for reliable evaluation, especially
with regard to a calculation of the interfacial tension between
two solid phases.
[GDCh-Ortsverband Gottingen (Germany),
December I7th, 19641
[VB 8991204 IE]
German version: Angew. Chem. 77, 431 (1965)
Dehydration of Hydroxides
F. F r e u d , Gottingen (Germany)
A mechanism for the dehydration of Mg(0H)z and similar
compounds has been suggested by Taylor [I], in which
protons and cations are assumed to diffuse in opposite
directions. Due to the high activation energy for the lattice
diffusion of cations, this mechanism is, however, improbable
or limited to special cases. More likely, the hydroxy groups
must be assumed to be stationary, and water molecules to be
formed at OH lattice positions by transfer of protons:
OH-
+
OH-
*
+
H20
02-
+
f
H2O gas
D. Frenzel, Gottingen (Germany)
Single crystals were prepared by the Bridgman method from
lead which had been purified by zone melting. All samples
were handled in VNCUO and irradiated at 22 O C and at pressures
below 10-8 mm Hg with a 3 curie polonium-210 source.
Platinum-shadowed carbon matrices were prepared from the
surfaces for electron microphotography. The linear magnification was 40000.
The single-crystal surfaces, even before irradiation, proved
to be relatively smooth. Apart from numerous small and
irregularly occurring discontinuities [*I, grooves separated
by an average distance of about 500 A were observed in the
majority of samples. The samples were then irradiated with
total doses of between 1014 and 1016 cc-particles/cmz, i . e .
each surface atom, on the average, was hit by one a-particle.
Surprisingly, the surfaces were levelled to a large extent, the
degree of levelling being about SO%, for the largest dose.
This corresponds to a rearrangement of about 5 lead atoms
per incident a-particle.
It is reasonable to assume a diffusion mechanism for the
movement of the atoms. Surface tension may be regarded as
the driving force. It can be shown, with the aid of models
permitting the calculation of these effects, that volume
diffusion is negligible compared to surface diffusion, for a
surface roughness with a periodicity of about 500 A.
[GDCh-Ortsverband Gottingen (Germany),
December 17th, 19641
[VB 894/199 IE]
German version: Angew. Chem. 77, 431 (1965)
(a)
The water molecules then diffuse out of the lattice:
H2O
The Influence of Alpha-Radiation on
Metal Surfaces
(b)
The diffusion process according to (b) is dependent o n
direction owing to the anisotropy of the lattice 121. To form
a water molecule, two OH groups must react with one
another. The activation energy required for the proton
transfer is less for adjacent, than for non-adjacent OH groups.
At a given temperature, reaction (a) will therefore come to a
standstill when all adjacent O H groups have reacted. Due to
the statistical nature of the reaction, some O H groups will
remain unreacted; thus the isothermal dehydration of such
tt P H
The Synthesis of N-Glycolylneuraminic Acid and
the Biochemistry of Glycoproteins Containing
Neuraminic Acid
H . Faiilurd, Koln (Germany)
N-Giycolyl-D-glucosamine ( I ) was obtained by the reaction
of D-glucosamine hydrochloride with 1,3-dioxolane-2,4dione, prepared from glycollic acid and phosgene in dioxane
[I] (in collaboration with M.Blohrn).Inanalogy to the method
of Okujoma and Sinohara [2] the N-glycolyl-o-glucosamine
could be converted into the 4,6-benzylidene derivative (2)
by reaction with benzaldehyde and zinc chloride.
H OH
7 1
'1
H - 6 - N H j .H C l
HO-C-H
H-C-OH
I
H-C-0
$H,OH
-----+
a hydroxide cannot be complete. Similarly, a n oxide surface
densely covered with O H groups cannot be freed of the last
traces of water by merely evacuating at constant temperature,
but only by simultaneously raising the temperature.
Statistical calculations of the number of O H groups remaining
behind o n a surface showed degrees of dehydration of
around 90 %. Preliminary model calculations for threedimensional lattices (hydroxides with layer structure) gave
similar results.
[GDCh-Ortsverband Gottingen (Germany).,
December 17th, 19641
[VB 896/202 IE]
German version: Angew. Chem. 77, 4 3 1 (1965)
[ I ] M . C . Boli and H . F. Taylor, Mineralog. Mag. J. mineralog.
SOC.32, 754 (196i).
[ 2 ] F. Freund, Ber. dtsch. keram. Ges. 42 (1965), in the press.
Angew. Chem. intrrncrt. Edit. 1 Val. 4 (1965)
No. 5
H-C-OH
H-{-0
1
CH,OH
The 4,6-benzylidene-N-glycolylglucosamine (2) condenses
with potassium di-t-butyl enoloxaloacetate to yield the
corresponding t-butoxycarbonyl lactone [3]. Elimination of
COz and isobutylene from this compound and hydrogenolytic
removal of the benzylidene residue afford the y-lactone of
N-glycolylneuraminic acid, which opens in alkaline media to
give the free acid (3). Both the 4,6-benzylidene-N-glycolyl-
[*I Size about
50
A.
[ I ] G . W. Jourdian and S . Roseman, J. biol. Chemistry 237, 2442
(1962).
[2] T. H . Okujama and H . Sinoltora, Tohoku J. expt. Med. 68,
181 (1958).
[3] R . K h i and G . Baschang, Liebigs Ann. Chem. 659, 156
(1962).
445
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