Ok, I figured I could just pop this thread back to life rather than start a new one or continue in the short question thread...
methylene iodide can be a pretty usefull reagent, and is much more ffective than DCM under atmospheric conditions. Beside the iodide swap mentionned
above, it seems CH2I2 is generally made from CHI3 by using sodium aresenite, not a nice thing to play with. I've looked briefly into tow other method
of preparation from CH3I.
From iodoform and sodium ethoxide (KOH could possibly be used also): I've translated the revelant parts of an old Ann. article where iodoform
is reacted with 3 eqs of EtONa to form CH2I. No yields mentionned though:
Partial Translation of Ann. Chim. Phys., , 53 (3), 313 (1858)
[Quote]
Memoire on methylene iodide
by M. Alexandre BOUTLEROW
Professor of Chemistry at the University of Kasan
Considering that sodium ethoxide has a similar constitutuion to sodium hydroxide, I thought it would be interesting to compare the action of iodine on
these two compounds, so I studied the action of this simple compound on the ethoxide.
When powdered iodine is added in portions to cristallized sodium ethoxide, a vigorous reaction immediatly occurs, followed by heat evolution: the mass
liquifies and turns brown; but after a while, as soon as all the iodien has reacted, this coloration disappears. By continuing the addition of iodine,
we fianlly obtain a thick and yellow magma.
For the complete decomposition of the ethoxide to occur, and the brown color indicating excess I2 to persists, more than one equivalent of iodine for
each equivalent of ethoxide are required. When the mixture is distilled on a water bath, some alcohol is collected, containing a heavy oily compound
which can be seperated by addition of water. When diluted with water, the distillation residu dissolves nearly entirely, leaving some iodoform. The
aqueuse solution contains some sodium iodide and sodium formate, but no iodate. By evaporating this solution and distilling the inorganic residu with
tartaric acid, some formic acid can be detected in the distillate, using a silver salt. At the same time the alcohol seems to be regenerated in this
recation, that we can surely express by the following equation:
8 C4H5O2Na + 16 I = C2HNaO4 + 6C4H5O2H + 3 C2HI3 + 7NaI (?? apparently they hadn't worked out the structures completely yet!)
By using one equivalent of iodine for each equivalent of ethoxide, and by gradually distilling to near-dryness, a quite large amount of oil is
obtained in the distillate, compared to the amount of iodoform that stays in the residu; on the other hand, the latter is found in exces if the yellow
magma is directly diluted with water without been submitted to distillation. These observations seem to indicate that the oily compound is only a
by-product from the action of sodium ethoxide on iodoform. I had to study this action.
On solid iodoform container in a large container, is added a mildly-concentrated solution of sodium ethoxide obtained by dissolution of sodium metal
in a rather large volume of absolute ethanol. Brief warming in a hot water bath is needed to get the reaction started. The mixture quickly heats up to
a vigorous reflux, with no gas evolution. Once the reaction is finished and the liquor is no longer alkaline, a new portion of ethoxide is added and
the mixture is heated; these operations are repeated until 3 equivalents of ethoxide (based on the amount of sodium dissolved) are added. At this
moment, the liquid is slightly basic, but remains so. It is heated for another few minutes, then diluted with water. A yellowish, milky solution is
obtained, and after a moment a brown oily substance crashes out of solution. When the reaction is well performed, the oil contains little impurities;
but is heating is excessive, or that a too alrge excess of ethoxide has been employed, the oily substance is contaminated with a brown decomposition
product, pulveresent and insoluble in alcohol.
On the opposit, unreacetd iodoform remains if heating was insufficient or that too little ethoxide was added.
Exces alcali seems to prevent deposition of the product; the addition of a few drops of acid easily induces deposition. After 24h, all the oil has
crashed out, and the aqueous solution become colorless. The oil is decanetd, washed and readily steam-distilled.
The compound thus obtained is identical to the oil obtained by the action of iodine on sodium ethoxide, as confirmed by elemental analysis. When
distilled, it boils around 181°C, but is partially decomposed, loosing iodine. The distilled product is always colored, and during the distillation
the head temperature increases as the residu darkens more and more.
Afetr having been distilled in steam and dried over fused calcium chloride, the compound thus obtained presents the following caracteristics: it is a
yellowish oil, very refractive, possesing the surprising property of hardly wettening glass; it's smell is analogous to that of chloroform, and
reminds taht of ethyl iodide, it taste is very sweet (!!). It the denser of all organic substances, it's density at 5°C equals 3.342; at the
temperatur eof +2°C, it solidifies in large shiny shards, that only melt at +5°C. the solidification, once started, continues even at 3°C. During
cristillazation, there is a very significant reduction of volume. It's dilatation coefficent is very high [...]. This compound is not atatcked by
concentrated KOH or by hot mildly-concentrated nitric acid.
The analysis leads to te following structure:
C2H2I2,
which represents the methylene iodide [...].
[...]
A few months ago, M Brüning published in the Annalen der Chemie und Pharmacie, the results his work in M Strecker's laboratory, where he describs a
product obtained by the action of ethanolic potash on iodoform. This product posses all the properties of methylene iodide: same density (3.345), same
boiling point (181-182°C), same % of carbon and hydrogen obtained by titration. But the quantity of iodine found by M. Brüning is too small, which
lead him to suggest the structure
C2H2I2O,
very unlikely for a condensation corresponding to 4 volumes of steam (?). Not having enough material at my disposition, I could not measure the vapor
density which is very simialr for both structures. [...]
Wanting to investigate the variosu products formed at the same time as methylene iodide, I evaporated the aqueous solution decanted from the oil.
After having checked it contained, apart from sodium iodide, salts of volatil organic acids, I distilled the residu with excess tartaric acid. The
distille dsolution was strongly acidic, and droplets of oil where noticed on the surface. Neutralized with Ba(OH)2, it gave afetr evaporation a
inorganic residu that I failed to cristallize. The carbon, hydrogena nd barium contents seem to indicate presence of volatils fattya cids of teh
series CnHnO4.[...]
These results indicate beyond doubt the presence of fatty acids of considerable molecular weight, being at least valerianic acid. On the other side,
we witnessed the presence of formic acid in the distillates. This synthetic formation of molecules having up to 10 or even 12 carbons by the reaction
of two compounds which contain 2 and 4 carbons, where the temperature does not exceed 100°C, seemed to me as being worth mentionning.
|
Come to mind, I have an aluminum vessel used
for diethylether. If this can meets EU regulations, it might withstand a lot of pressure...
As you say, you need only
1/10 the amount of NaBH4 on a weight basis, so KI would be the most expensive compound in this prep! I really don't know why iodides are so expensive,
maybe it's because they have a somewhat limited use in industry.