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Double Silanolates of the Alkali Metals.

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Vacuum distillation of the crude adduct mixture afforded
t h e conventional adducts (/) an d (2). The two cyclodimerization prodlicts ( 3 ) a n d ( 4 ) were isolated as a crystalline
mixture f r o m the distillation residue. Separation of this
mixture by preparative gas chromatography yielded the purc
compounds ( 3 ) a n d ( 4 ) .
C o mp o u n d (3) was identified by comparison of its physical
a n d spectral properties with those of a n authentic sample [I].
1 M'p'[ncl
N M R [c.P.s.] [31
Potassium trimethylsilanolate is only sparingly soluble in organic solvents [ l , 21, b u t dissolves practically instantaneously
in solutions of th e lithium a n d sodium silanolates. Careful
evaporation of the clear solutions leads t o crystallization of
the double silanolates (2) an d ( 3 ) . C o m p o u n d ( I ) crystallizes
in the pure f o r m f r o m a solution of equimolar quantities o f
lithium a n d sodium trimethylsilanolates in car b on tetrachloride.
T h e structural identity of t h e two d o x y residues is shown by
the fact tha t the N M R spectra of ( I ) , ( 2 ) , a n d (3) in CC14
show only one sh ar p signal accompanied by weak 1H-13Ca n d IH-C-29Si satellites [2,4].
All the important bands in th e infrared spectra of the double
silanolates differ markedly from those of th e alkali metal
silanolates. T he spectroscopic results indicate th at the siloxy
oxygen a tom s in th e double silanolates are alternately coordinated t o the different alkali metal atoms. Since th e influence
of the lighter alkali metal predominates, the co m p o u n d s are
formulated as MI{ M2[OSi(CH3)3]2}.
Received, J u l y 28th, 1964
[ Z 803/631 I€]
German version: Angew. Chem. 76, 753 (1964)
Translated by Express Translation Service. London
[I] W . S.Tatlock and E. G. Rochow, J. org. Chemistry 17, 1555
[2] H . Schmidbaur, J. A. Perez-Garcia, and H. S. Arnold, Z . anorg. allg. Chem. 328, 105 (1964). Th e m.p. of NaOSi(CH3)3 is
265-267 "C, contrary to earlier data.
[31 Varian A 60, 60 Mc/sec, CC14 solution, 35 "C, tetramethylsilane a s internal standard.
[4] H. Schmidbaur, J. Amer. chem. SOC.85, 2336 (1963).
Electrophilically Induced Cyclodimerization
of Methylacetylene by Hydrogen Bromide 111
By Dr. K. Griesbaum
Central Basic Research Laboratory, Esso Research a n d
Engineering Company, Linden, New Jersey (U.S.A.)
Contrary t o a previous report [2] the reaction of hydrogen
bromide with methylacetylene affords n o t only th e classical
diadduct 2,2-dibromopropane (2), b u t a t least four additional components in th e indicated ratios [3].
H3C - C B r = CH
Ill, 2 4%
Angew. Chem. internat. Edit.
H,C - C B r 2 - C H 3
(21, 34%
Vol. 3 (1964) 1 No. 10
T h e structure proof of (4),m.p. 75-76"C, is based o n the
following d at a: elemental analysis pointed t o the empirical
formula (C3H5Br)n. T h e mass spectrum showed t h e characteristic 1-2-1 pattern (m/e = 240, 242, 244 respectively) of a
dibromo co mp o u n d [4] for t h e parent peak, thus establishing
t h e formula CsHIOBr2. Neither t h e infrared n o r t h e N M R
spectrum of ( 4 ) contained an y evidence for a double bond.
Th e N M R spectrum exhibited a singlet signal at T = 8.12 with
a relative intensity of 3 an d a four-line pattern centered at
T = 6.8 I [5] with a relative intensity of 2.
C o mp o u n d (5) could n o t b e isolated pure. Combined gasliquid chromatography a n d time-of-flight mass spectroscopy
[6] showed, however, t h at the compound is a dibromide
exhibiting t h e same molecular ion a n d fragment ions as (3)
a n d ( 4 ) . It is assumed, therefore, that (5) may represent one
of the isomeric 1,2-dibromo- I ,2-dimethylcyclobutanes.
H Br
Th e results reported here demonstrate t h at the electrophilic
addition of hydrogen bromide t o methylacetylene cannot be
exhaustively described by t h e classical theory of addition
reactions. It seems t h at t h e particular nature of t h e vinylcarbonium ion intermediate (6) [7] may be t h e key in understanding t h e cyclodimerization reactions of b o t h methylacetylene a n d allene [I].
Received, July 28th, 1964
[Z808/603 1El
German version: Angew. Chem. 76, 782 (1964)
[ I ] Cyclobutane Compounds, Part 11. - Part I: K. Griesbaum,
J. Amer. chem. SOC.86, 2301 (1964).
[2] M . S. Kharasch, J. G. McNab, and M . C. McNab, 3. Amer.
chem. SOC.57,2463 (1935).
131 Percent by weight based on capillary gas chromatography.
In some cases, substantial amounts of the isomeric I-bromopropenes were also formed, apparently by concurring radical
addition reactions. This complication could, however, b e effectively suppressed by the addition of inhibitor9 to the reaction
[4] J. H . Beynon: Mass Spectrometry and Its Application to
Organic Chemistry. Elsevier, Amsterdam 1960, p. 299.
[S] Th e midpoint of this quartet has the same position as the
methylene singlet signal of the trans-compound ( 3 ) . This is an
argument against the alternate possible structure of a 1,2dibromo-l,2-dimethylcyclobutanefor ( 4 ) . Since the methylene
groups in such a 1,2-dibromo compound would be vicinat to
only one bromine atom each, one would expect their signals at
higher fields.
[6] R . A. Brown and E. R . Quiram, Appl. Spectroscopy 17, 33
[7] P. E. Peterson and J. E. Duddey [J. Amer. chem. SOC. 85,
2865 (1963)l pointed out recently that the nature and the
chemistry of vinylcarbonium ions is rather ill-defined.
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metali, silanolates, alkali, double
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