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Notes and references
DOI: 10.1039/C9CC08907A
In C2H5ONa, the ionic Na-O layers are surrounded by non-polar
ethyl groups on both sides. Neighbouring layers are connected
by van der Waals contacts only (Fig. 3c). Thus, a non-polar
solvent, such as toluene, could penetrate between the layers,
and eventually exfoliate the layers, but cannot break the ionic
layers themselves. The large layers will remain intact, which
explains the observed low solubility of C2H5ONa in non-polar
solvents.
‡ CCDC-1943793 and 1943794 contain the crystallographic data
of 1 and 2.
In polar solvents, especially with solvent molecules containing
oxygen atoms, the layers are easily destroyed by the solvent.
The crystal structure of C2H5ONa · 2 C2H5OH resembles the first
step in the dissolution of C2H5ONa by ethanol: The Na-O layers
of C2H5ONa are reduced to Na-O chains, which are surrounded
by ethanol molecules. Further solvation leads to a molecular
complex in solution.
1
W. Dieckmann, Ber. d. Dt. Chem. Ges. 1900, 33, 2670-2684; L.F. Fieser,
M. Fieser and T.-L. Ho, Fieser&Fieser's Reagents for Organic Synthesis,
Wiley, 2006; K.S. Whitaker and D.T. Whitaker, e-EROS Encyclopedia of
Reagents for Organic Synthesis 2001, 1-4. For recent applications see,
e.g.: M. Kumar et al., J. Org. Chem. 2019, 84, 13624-13635; H.J.
Trubenstein et al., New J. Chem. 2019, 43, 14305-14312.
J. Liebig, Annalen der Pharmazie 1837, 23, 12-42, p.32.
A. Boultif and D. Louër, J. Appl. Cryst. 1991, 24, 987-993.
K. Shankland, E. Pidcock, J. van de Streek, W. I. F. David and W.D.S.
Motherwell, J. Appl. Cryst. 2006, 39, 910-915.
Apart from the phases 1 and 2, we observed two additional
phases, 3 and 4. They occured together with 1 and 2 in varying
amounts in several experiments upon the evaporation of an
ethanolic solution of C2H5ONa, depending on the applied
conditions (For details, see ESI). However, we could neither
isolate the phases 3 or 4, nor grow single crystals. Hitherto, all
our attempts to determine the crystal structures of 3 and 4
from X-ray powder data of the phase mixtures were to no
avail. Correspondingly, the chemical composition and the
crystal structures of 3 and 4 remain obscure.
2
3
4
5
B.O. Loopstra and H.M. Rietveld, Acta Cryst. 1969, B25, 787-791; H.M.
Rietveld, J. Appl. Cryst. 1969, 2, 65-71; R. A. Young (Ed.): The Rietveld
Method. IUCr Monographs on Crystallography 5, International Union of
Crystallography and Oxford Science Publications, 1995; B. van Laar and
H. Schenk, Acta Cryst. 2018, A74, 88-92.
The disolvate 2 is stable only in the presence of ethanol
vapours. The crystals decompose upon contact with dry air or
dry nitrogen. Under vacuum at 50 °C , 2 converts to the
solvent-free 1, too. In reverse, 1 reacts with moisture from the
air to a mixture which contains all four phases 1-4 in varying
amounts. This complex phase behavior, and the absence of
single crystals of C2H5ONa might be the reason why the crystal
structure of sodium ethoxide was not determined earlier.
6
7
A. A. Coelho, J. Appl. Cryst. 2018, 51, 210-218.
A.F. Wells, Structural Inorganic Chemistry, Oxford University Press,
Oxford, 1984, 119.
8
9
10
E. Weiss, Z. anorg. allg. Chem. 1964, 332, 197-203.
P.J. Wheatley, J. Chem. Soc. (London) 1961, 4270-4.
J.E. Davies, J. Kopf and E. Weiss, Acta Cryst. 1982, B38, 2251-2253; H.
Nekola, F. Olbrich and U. Behrens, Z. anorg. allg. Chem. 2002, 628,
2067-2070; E. Østreng, H.H. Sønsteby, S. Øien, O. Nielsen, H. Fjellvåg,
J. Chem. Soc. Dalton Trans. 2014, 43, 16666-72.
11
E. Keller, SCHAKAL99, Kristallographisches Institut der Universität
Freiburg, Deutschland, 1999.
In conclusion, this work reveals that the standard base sodium
ethoxide exhibits a layer structure of the "anti-PbO type" in
the solid state, which explains the limited solubility of
12
13
H. Lescoeur, Compt. Rend. Acad. Sci. 1895, 121, 691-692.
J.-M. Blanchard, J. Bousquet, P. Claudy, J.-M. Letoffe, J. Thermal Anal.
1976, 9, 191-203.
C2H5ONa in
non-polar
solvents.
The
disolvate
14
15
K. Chandran, R. Nithya, K. Sankaran, A. Gopalan, V. Ganesan, Bull.
Mater. Sci. 2006, 29, 173-179.
C2H5ONa · 2 C2H5OH, which apparently precipitates first on
synthesis, forms a chain structure, which resembles the first
step of the dissolution of C2H5ONa with ethanol. Thus, the
crystal structures of these simple compounds were finally
unravelled – a 180 years after their first synthesis.
Z.A. Starikova, E.P. Turevskaya, N.Ya. Turova, A.I. Yanovsky, J. Chem.
Soc., Dalton Trans. 2000, 3237-3238.
Acknowledgements: The authors thank Edith Alig for recording
numerous X-ray powder diagrams, and Lothar Fink (both
Goethe University, Frankfurt am Main) for the support in the
single-crystal structure determination of the disolvate.
Conflicts of Interests
There are no conflicts of interest to declare.
4 | J. Name., 2012, 00, 1-3
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