ISOTOPIC EXCHANGE OF HYDROGEN BOUND TO SILICON

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00809A000600370530-2
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 4
• Document Creation Date: December 22, 2016
• Document Release Date: September 27, 2011
• Sequence Number: 530
• Publication Date: January 24, 1951
• Content Type: REPORT

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CLASSIFICATION BECRET~"' '. SE~iE~
INFORMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS CD NO.
COUNTRY UssR
SUBJECT Scientific - Chemistry, nuclear physics
HOW
PUBLISHED Thrice-monthly periodical
WHERE
PUBLISHED Moscow/Leningrad
DATE
PUBLISHED 11 Sep 1950
LANGUAGE Russian
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NIYIT[0 [T LAM. R[~AOUYGiION Of TN YI [OAR I/ TAONI l1T[D.
DATE OF
INFORMATION 1950
DATE DIST.~7 Jan 1951
N0. OF PAGES 4
SUPPLE
REPORT
SOURCE Doklady Akademii Nauk SSSR, Novaya Seriya, Vol LXXIV, No 2, pp 299-3~?
~ r!
ISOTOPIC EXCHANGE OF HYDROGEN BOUND TO SILICON
A. I. Brodskiy and I. S. Khaskin
Inat Phya Chem imeni L. V. Pisarzhevskiy
Acad Sci Ukrainian SSR
Submitted 24 May 1950
This is a part of an extensive investigation in the course of
which results have been obtained which may be applied in procedures
aiming at the enrichment of heavy hydrogen isotopes. The compounds
listed in this paper do not, according to the text, exchange hydro-
gen under the conditions studied. Consequently, they would hold
Heavy hydrogen firmly, once it has been introduced by some means
other than exchange.
It ie known that isotopic exchange of hydrogen atoms at C-H links is
strongly retarded or does not take place at all, although it is observed, pro-
vided the link is weakened by the ,proper substitutions in the molecule. This
property has been explained (1) as follows: Carbon in compounds is surrounded
by an electron shell which contains no free electron pair to which deuterium,
from water or another source, can become attarhed before one of the C-H bonds
is broken. Thus the exchange requires a high activation energy and proceeds
slowly.
In agreement with these ideas, according to data in literature, the hydro-
gen exchange is also greatly hampered at H-H and B-H bonds, which also have no
free electron pairs.
The same peculiarities must be exhibited by the Si-H bond in organic sili-
con compounds, where the shell of the silicon atom also does not contain free
electron pairs. The. study of the isotope eachange in'these compounds can serve
as further proof of the relationships deduced above, and also is of interest in
itself, since it hae not yet been investigated.
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s~c~Er
Zn the present work, the exchange o? hydrogen at Si-H toads for deuterium
from heavy water and from heavy ethyl alcohol C~H UD was investigated on sil-
anes; HSi(C2H5)3 and HSi(C6H5)3, and also on trie~hoxy silane HSi(OC2H5)3 under
various experimental conditions. These compounds are sufficiently stable in
relation to the inaicated donors of deuterium.
The initial silicochloroform was obtained by the reaction of HC1 on silicon
at a temperature of 300?. Triethyl silane is obtained by the reaction of ailico-
chloroform with Grignard reagent and purification by fractionation (bp 107-108?,
d40 = 0.7301). Triphenyl silane is prepared in the same way. The product is
distilled off under reduced pressure and solidifies in a colorless crystalline
mass at a temperature of 36?. Triethoxy silane is obtained by the reaction of
silicochloroform with ethyl alcohol in a benzene solution (2) and is also puri-
fied by fractionation (bp 134?, d~ = 0.8753)?
The exchange took place in sealed glass ampoules, installed in a thermostat.
Water with triethyl silane or triphenyl silane forms a two-phase system, while
the former gives a homogenous solution with ethyl alcohol. In several experi-
ments the exchange with water took place in a homogenous pyridine or dioxane so-
lution. Triethoxy silane with ethyl alcohol forms a.?homogenous solution.
Since the silanes contain a large quantity of nonexchangeable hydrogen
atoms for each exchangeable one, the relative change of the density of water is
slight even at complete exchange. Therefore, in most of the experiments, the
deuterium content of the silane was determined after the exchange. For this
purpose, the material was burned and the deuterium content in the water obtained
was determined by the flotation method.
Similarly, the deuterium content in ethyl alcohol was determined. In sev-
eral experiments, the deuterium content in the water was determined after the
exchange. In these determinations, no change of density was found which ex-
ceeded the limits of experimental error.
The water was separated from the triethyl silane in a separatory funnel.
With ~-thy1 alcohol it gives an azeotropic mixture which boils at about 65?.
Therefore, after it has been established that there is no exchange with water,
the alcohol is washed out by the addition of water. The water is distilled off
from triphenyl silane and triethoxy silane with benzene by the procedure of Dean
and Stark. Before the isotope analysis, the silanes are cleaned by washing and
fractionation.
The results of some typical experiments are given in the appended table,
together with the temperature, the time of the exchange, and the catalysts
which were added.
From the data given, it can be seen that even under continuous heating
with acids or alkalies not one of the three silanes investigated displayed any
exchange with heavy water or heavy alcohol. In some cases, a negligible con-
tent of deuterium was found. It did not exceed a fev percent of that expected
in complete exchange. This may be attributed to the inclusion of traces of
water.
Analogous carbon compounds displayed similar behavior regarding exchange.
Triphenyl methane did not exchange hydrogen with heavy water at 110? for 144
hours in the presence of alkali, isobutane showed only slow exchange with 100
percent pure sulfuric acid containing tritium (3).
.~~C~RET
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1
SECRET
The exchange of hydrogen for deuterium at C-H bonds takes place through
ionization or electrophilic substitution (1). 'Phe data obtained are insuffi-
cient for a comparison of the exchange properties of hydrogen at bonds with -
carbon and silicon according to the ionization mechanism. The negative elec-
tric charge of carbott is greater than that of hydrogen, and this produces~a
partia]. polarization of the C--H*' bon3 which favors an electrophilic reac-
tion. Ott the other hand, the electronegativity of silicon is less than that
of the hydrogen, and therefore the bond is polarized in the reverse direction
Si+-H-. In this case, exchange according to the electrophilic mechanism ie
unlikely and nucleophilic substitution is typical. Accordingly, a nucleo-
philic reaction takes place between silanes and alkalis, metallic amines, al-
coholates, etc.
Until now, the existence of the exchange of hydrogen isotopes by nucleo-
philic mechanism has not been definitely proved, and the latter is also unlikely
because of the, low stability of the negative hydrogen ions. It is possible that
this explains the absence of exchange in the organic silicon compounds inve~-
tigated here under the conditions indicated.
1.
A. I. Brodakiy, Izv. AN SSSR, OKhN., No 1, 1949, PP 3,
2.
M. E. Havill, J. Jaffe, and H. W. Post, Joura. Org. Chem., Vol 13, p 280
(194&)
3.
T. D. Stewart and D. Harman, Journ. Am. Chem. Soc., Vol 68, p 1135 (1946);
M. S, I~arash, W. G. Brown, and J. G. McNab, Journi Org, Chem., Vol 2, p g6
(1937)
~ppended table followsa]
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SECCET
s
ECx~-r
50X1
Density of Water
Substance Donor
Catalyst
T
em~
-Time
Initial ~, From Combustion
of D20 of Gamma Unite
~
l-~/
(Fu
ch
co
ll ex-
ange
mputed}
(Found)
&Si(C2H5)3 D20
--
116
51
2.48
165
0
D2o
a2so4
116
49
2.48
163
0
D20
KO$
116
70 ~~
2.48
164
4
D204pyridine
--
118
50
20.44
1220
7
D20+dioxane
--
100
12
3.25
212
15
D20+dioxane
H2s04
100
15
3.25
211
6
c2x5oD
cH3coorta
116
117
6.49
346
0
c2x5on
t~so4
118
146
6.49
346
0
Hsi(c6H5)3 D2o
--
18
335
6.08
Sob
5
D2o
--
118
71
2.48
164
7
D2o
NaoH
103
18
6.04
340
13
D2o
H2SO4
118
?0
2.48
165
0
D2o+dioxane
H2s04
100
15
3.25
212
0
ssi(oc~$5)3 c2a5oD
--
20
49
6.50
350
2
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