I have it on my hard drive, but I didn't think it was useful to upload it there before I had collected a few methods on making 2-bromopropionic acid to go with it... I'm too much of a perfectionist.
SUMMARY OF THE INVENTION
An .alpha.-bromoalkanoic acid, e.g., .alpha.-bromopropionic acid, is reacted with an alkali metal nitrite, e.g., NaNO2 in the presence of Mg2+ ion provided by adding a magnesium salt, e.g., MgSO4, to the mixture, all in a solution of an aprotic solvent, e.g., dimethyl sulfoxide. This mixture is allowed to react with stirring at room temperature and then neutralized with a mineral acid, e.g., HCl. The product is a nitroalkane, which in the case of starting with .alpha.-bromopropionic acid is nitroethane.
DETAILED DESCRIPTION OF THE INVENTION
Without attempting to describe the mechanism, the following equation shows the reaction: ##STR1## wherein M is an alkali metal R is H or an alkyl group of 1-4 carbon atoms and the solvent is aprotic. After reacting the mixture it is neutralized with a mineral acid.
Thus, an .alpha.-bromoalkanoic acid reacted with an alkali metal nitrite in the presence of Mg.sup.++ ion in an aprotic solvent will yield a nitroalkane having one less carbon atom than the starting bromo-alkanoic acid. The alkali metal is converted to the salt of the mineral acid used to neutralize the mixture.
The .alpha.-bromo acids useful in the process are, for, example bromoalkanoic acids having from 2 to 6 carbon atoms. Thus, .alpha.-bromoacetic, .alpha.-bromopropionic, .alpha.-bromobutanoic, .alpha.bromopentanoic and the like acids maybe employed.
Alkali metal nitrites useful in the process are sodium and potassium nitrites. It is believed that the function of the magnesium ion is to form a chelate intermediate which can then be decomposed by the addition of a mineral acid, decarboxylating the alkanoic acid moiety. Ionizable magnesium compounds useful in the process are magnesium alkoxides, such as magnesium methoxide, magnesium sulfate, magnesium chloride or bromide.
Both the magnesium compound and the nitrite are employed in a molar equivalent amount based on the moles of bromo acid used. In order to insure complete reaction of the halo acid a slight excess of each of these is employed. The reaction to form the chelate is considered complete upon the substantial disappearance of the nitrite, i.e., the amount equivalent to the bromoacid.
Aprotic solvents employed are selected from amides and sulfoxides, e.g., dimethyl formamide and dimethyl sulfoxide.
EXAMPLE 1
To a mixture of magnesium methoxide (0.11 mole) and dimethyl sulfoxide (50 ml) .alpha.-bromopropionic acid (0.11 mole) ws added at 20°C. with stirring. To this mixture a solution of sodium nitrite (0.145 mole) in dimethyl sulfoxide (65 ml) was added at room temperature. Then, the reaction mixture was stirred at room temperature for 6 hours and was neutralized upon addition of diluted hydrochloric acid. Analysis of the reaction mixture indicated more than 99% conversion of .alpha.-bromopropionic acid and 94.5% yield of nitroethane.
EXAMPLE 2
In the manner of Example 1 sodium nitrite, .alpha.-bromopropionic acid and magnesium methoxide were reacted in dimethyl sulfoxide as the aprotic solvent. The reaction time was 2 hours for one run and 22 hours for another. Reaction was conducted at room temperature. The run at 2 hours converted only 94.5% of the acid and yielded 72.7% nitroethane. The second run at 22 hours gave a conversion of >99% and a yield of 100%.
At room temperature the reaction apparently takes about 4-5 hours to go to completion. At higher temperatures of 40°C. up to about 75°C. the reaction time is shorter. Thus, one or two hours or even less time at 75°C. will completely convert the bromoacid to the intermediate which can then be decomposed to the nitroalkane.
When using dimethyl sulfoxide as solvent temperatures approaching 100.degree. C. should be avoided since the solvent will volatilize and decompose at about 100.degree. C. Other aprotic solvents may not have this disadvantage.