Interesting German Nitroalkane patent
So we’ve all heard about the preparation of Nitroalkanes by destructive distillation of sodium alpha-haloalkanoates with sodium Nitrite.
An example for Nitromethane can be found here: http://www.orgsyn.org/demo.aspx?prep=CV1P0401
Below is an English translation of an old patent DE767509 from the German Reich that seems to improve substantially on the yields attainable with this reaction using magnesium 2-chloroacetate.
A process for the preparation of nitromethane
Patented in the German Reich at the 26 March 1939
Reich Patent office
Patent No. 767509
It is known that nitromethane can be prepared by reacting sodium chloroacetate with sodium nitrite. The yields in this process are poor, because side
reactions occur, which are primarily due to the alkaline nature of the reaction mixture. It has been proposed to neutralize the alkalinity occurring
during the reaction from formation of sodium carbonate by addition of suitable acids, a method which, however, was only able to increase the yield to
a small extent and in addition greatly increases the cost of the product.
It has also been attempted to circumvent the formation of the alkaline sodium carbonate by not reacting sodium chloroacetate but calcium chloroacetate
with sodium nitrite. By this measure the alkaline nature of the solution can be avoided during the reaction, because in place of the sodium carbonate,
calcium carbonate is formed. However this does not increase the yield, in spite of nitromethane being sufficiently resistant to calcium carbonate in
boiling aqueous solution.
It has now been found that substantially higher to almost quantitative yields of nitromethane are obtained if, instead of calcium chloroacetate, the
chloroacetates of barium and / or of magnesium are used under otherwise identical conditions with alkali nitrites, for example sodium nitrite in
aqueous solution.
Taking into account the known fact that during the reaction the most significant reduction in yield occurs by the hydrolysis of the introduced
chloroacetic acid, the yield increase by using other alkaline earth bases at the site of calcium is all the more surprising, because according to Am.
Chem. Journ. 15, p. 478, under otherwise identical conditions, the hydrolytic decomposition of salts of chloroacetic acid takes place independently of
the base on which the salts are based. In fact, even under otherwise identical circumstances, the potassium chloroacetate can be replaced by sodium
chloroacetate without affecting the yield.
Compared to the calcium chloroacetate the use of barium chloroacetate brings a substantially better yield, which further increases with the use of
equivalent amounts of magnesium chloroacetate under otherwise identical conditions, so that almost quantitative yields are obtained - a success that
was not foreseen from previous findings.
In particular, the yield increase was not foreseen. Rather, it was to be expected that magnesium chloroacetate would have the lowest yield because the
magnesium carbonate formed in the reaction would still have an (albeit small) alkalinity, which would be expected to reduce the yield.
It is appropriate to perform the procedure using an excess of chloroacetate. One uses between 1.3 to 1.5 moles of the chloroacetate in aqueous
solution and 1 mole of sodium nitrite, with good stirring and heating. An addition of sodium chloride may be advantageous.
The formed nitromethane distils immediately after its formation from the reaction vessel with water vapor. In the receiving vessel, nitromethane
separates out under the aqueous distillate with about 7 to 10% content. This oil is combined with the nitromethane obtained by distillation from the
aqueous layer and optionally dry distilled.
Although it is preferable to use bases that are as pure as possible for neutralization, there is no obstacle to the use of barium or magnesium oxides
and carbonates, as they can be obtained on a large scale. It is also possible to use mixtures of these bases as well as natural or artificial mixtures
with calcium.
Examples
I. 710 g of Chloroacetic acid are dissolved in 2L water and neutralized with barium carbonate. The solution of barium chloroacetate is then mixed
with a solution of 360g of sodium nitrite in 400cc of water. One allows a small part of this mixture to flow into a three-necked flask, in which, for
example, saline may be present, and heated until nitromethane development. Then, to the extent that the resulting water is distilled off with
nitromethane, new solution is added gradually. It is recommended to control the exceptionally strong foaming by gradual addition of a total of 0.5 g
of an antifoaming agent, for example Wax Acid Amide. The quantity of the previous and isolated from the aqueous solutions of distilled nitromethane is
87% of theory.
II. 710g of chloroacetic acid is dissovled in 2L of water, neutralized with raw caustic burned magnesite and the solution is mixed with 360g Sodium
Nitrite in 400cc of water. The mixture, worked up as in Example I, gives a nitromethane in yield of 93.5% of theory.
Operating under otherwise identical conditions except with chalk in place of barium carbonate or magnesite, a yield of 73% is obtained.
III. 710 g of chloroacetic acid is dissolved in 2L water and neutralized with a dolomite composed as follows: 37.0% MgO, 59.0% CaO, 1.2% SiO, 1.0%
Fe2 O3, 1.8% loss on ignition. It is mixed with a solution of 36 g of sodium nitrite in 400 g of water and worked up as in Example I. The yield is 8o%
of theory.
Questions:
Do we think this patent might be legitimate in terms of the yields claimed?
What kind of yield should we expect with magnesium alpha-chloropropionate as opposed to magnesium alpha-chloroacetate? Would expect that SN2 attack
more difficult on molecule with secondary halide as opposed to primary.
Would the yield likely be better using magnesium alpha-bromopropionate than magnesium alpha-chloropropionate?
Do we think that using magnesium 2-bromopropionate would improve on 50% yield in the old French reaction scheme using potassium 2-bromopropionate? (
V. Auger. Bull. Soc. Chim. FrancePost no. 3, 23, 333 (1900) )
Is it possible that the magnesium ions in this German patent are forming a chelate intermediate as in patent US4319059A or is this only possible in aprotic solvents?
What type of anti-foaming agent might be best to use these days?
Many thanks to anybody that takes the time to understand or answer. I know its a lot of questions, but hopefully you will like the patent translation.
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