Conversion of Ethyl Nitrite into Nitroethane.
The solution of the nitrite in paraffin oil was placed in a flask provided with an upright spiral condenser, which in turn was connected with a
combustion tube about 90 cm. long, filled with asbestos-wool (in order to expose a large surface to the gaseous nitrites), and heated in an asbestos
box provided with a thermometer. The gaseous nitrite was carried into the tube by means of a slow stream of dry carbon dioxide. The nitro-compound was
collected in a U-tube immersed in cold water, and the escaping nitrite in absolute alcohol or methyl alcohol cooled in ice-water. Fifteen or 20 c.c.
of the nitrite solution were used at a time. A 25 % solution is convenient, and a 50 per cent. solution loses nitrite very rapidly. As the gaseous
nitrite remains only momentarily in contact with the heated asbestos, the yield of the nitro-compound is small, the greater portion of the nitrite
escaping conversion. Within four or five hours the greater part of the dissolved nitrite passes through the heated tube. The oily nitro-compound was
easily recognised by the formation of the sodium compound on the addition of alcoholic sodium hydroxide solution. The nitro-compound was also reduced
to the corresponding amine, which was converted into the platinichloride.
The conversion commenced at 100°C, and was fairly rapid at 120-130°C, when oily drops began to collect in the empty U-tube. At the end of four to
five hours about 1 c.c. of the liquid collected, which responded very readily to the alcoholic sodium hydroxide test. If the temperature is raised to
about 135-150°C, acetaldehyde and acetic acid are produced along with the nitro-compound. At 150-180°C the acid is the main product of the
decomposition. The formation of the aldehyde and the acid is readily explained by the fact, fact that at a higher temperature the nitrite dissociates
into alcohol and nitrous acid, the latter decomposing into nitric acid, and the higher oxides of nitrogen which oxidise the alcohol to the aldehyde
and the acid. The best yield of the nitro-compound is obtained at 120-130°C.
Effect of Water and Alcohol on the Reaction
The presence of moisture, which is always present in the rapidly dried nitrites, facilitates the conversion of the nitrite into the nitro-compound. In
order to ascertain if the presence of larger quantities of moisture in the gaseous nitrites gives rise to a larger percentage of nitro-compounds, the
nitrites were passed through a wash-bottle containing water before entering the heated tube. It was found that when surcharged with moisture the
nitrite dissociated more rapidly, yielding larger quantities of alcohols, aldehydes and acids without any appreciable increase in the yield of the
nitro-compound. It appears that in the presence of traces of moisture, two reactions proceed simultaneously, the conversion of the nitrite into
nitro-compound and the dissociation of the nitrite; and with the increase in the proportion of water the latter reaction proceeds with greater
rapidity.
In order to determine if a better yield is obtained when an alcoholic solution of the nitrite is heated in a sealed tube, 10 cc of the solution were
sealed in a glass tube and heated over flame. During the act of sealing, the part of the tube containing the solution should be immersed in a freezing
mixture, otherwise explosions take place. The yield, however, was not very satisfactory. When heated at 100°C for five to six hours the solution,
after distilling off the unchanged nitrite, and alcohol, gave about 1 cc of liquid, which positively tested for a nitro-paraffin, and which boiled at
98-104°C. Because of the mixture with alcohol, the actual boiling point was lowered. If, however, the solution was heated to 150°C for twelve to
fifteen hours, the tube was found to, contain acetic arid, formed by the oxidation of the alcohol by nitric acid and higher oxides of nitrogen
produced from the decomposition of the nitrite, besides free nitrite. The proportion of the nitrocompound was very small.
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