             Conversion of Aliphatic Nitrites into Nitro-compounds
                 By Panchanan Neogi and Tarinicharan Chowdhuri
                              ?? p 701-707 (1916)

One of us has already shown (Neogi, T., 1914, 105, 2371) that the idea of
tautomerism cannot properly be applied to the case of nitrites and
nitro-compounds, and has advanced the theory that formation of aliphatic:
nitrites and nitro-compounds may ho attributed to two causes, namely, (1)
isomeric conversion of nitrites into nitro-compounds, and (2) formation of
unstable intermediate additive compounds. The present investigation was
undertaken with the object of finding experimental evidence of the conversion of
aliphatic nitrites into nitro-compounds. Experiments show that aliphatic
nitrites are partly converted into the corresponding nitro compounds by the
action of heat.

Conversion of Ethyl Nitrite into Nitroethane.

The apparatus employed in the case of methyl and ethyl nitrites was the same.
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 per cent. 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.[1] 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.

In order to ascertain if a better yield is obtained when art alcoholic solution
of the nitrite is heated in a sealed tube, 10 c.c. of the solution were sealed
in a glass tube and heated in a furnace. During  the act of sealing, the part of
the tube containing the solution should be immersed in a freezing mixture, as
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 c.c. of liquid, which responded
to the test for a nitro-paraffin and boiled at 98-104°C. Owing to the admixture
of 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.[2]


Influence of Moisture on the Conversion

In order to study the influence of moisture, the gaseous nitrite was dried by
passage through one or two calcium chloride tubes and then passed into the
heated tube, when it was found that very little liquid collected in the
receiving U-tube and most of the nitrite was passing out unchanged. This
phenomenon was observed in the case of all the nitrites. It appears that 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, namely,
the conversion of the nitrite into nitro-compound and the dissociation of the
nitrite; and with the increase in the proportion of water thelatter reaction
proceeds with greater rapidity.

Reduction of Aliphatic Nitrites to Amines

Gaudion (Ann,. Chim, Phys., 1912, [viii], 25, 1.25) observed that by passing a
mixture of hydrogen and aliphatic nitrites over heated finely-divided nickel or
copper, amines are obtained, but he was unable to explain definitely how amines
could be produced by the reduction of nitrites. We have also obtained amines by
passing a mixture of the nitrites and hydrogen through a heated tube containing
reduced nickel, The formation of small quantities of amines by the reduction of
aliphatic nitrites can now readily be explained in view of the above
experiments. It is the nitro-compounds that are actually formed which undergo
redaction to amines, and not the nitrites themselves. Sabatier and Senderens
(Compt. rend., 1902, 135, 225) have, as a matter of fact, shown that aliphatic
nitro-compounds are thus reduced to amines by hydrogen in presence of heated
nickel.

Theories of the Formation of Aliphatic Nitro-compounds

The partial conversion of aliphatic nitrites into nitro-compounds has a
theoretical bearing on the formation  of nitro-compounds. Neogi, (T., 1914, 105,
231) has already shown that the theory of tautomerism cannot be applied to the
aliphatic nitrites and nitro-compounds, as heavy atoms of silver and mercury as
well as heavy alkyl radicals cannot be supposed to oscillate between an oxygen 
and all nitrogen atom, the true tautomerides being nitro-compounds and nitrolic
acids. He therefore advanced two other hypotheses to account for the formation
of nitro-compounds, namely, (1) isomeric conversion, and (2) formation of
unstable additive compounds. The results of the present investigation show that
the conversion of aliphatic nitrites into nitro-compounds takes place at a
higher temperature, but, as the yield is very small, it alone is incapable of
explaining the formation of the large quantities of nitro-compounds obtained by
the interaction of silver or mercurous nitrite and alkyl iodides. The
interaction of silver or mercurous nitrite and alkyl iodides is completed at
100°C, whilst the conversion of aliphatic nitrites into nitro- compounds,
although commencing at 100°C, does not proceed to an appreciable extent below 
120-130°. Moreover, ethyl and methyl nitrites, being gaseous, escape at the
moment of formation, and have little chance of conversion into the
nitro-compounds during digestion. In the case of the higher nitrites, however,
especially when the interaction of alkyl sulphates and alkali nitrites takes
place at a higher temperature, isomeric conversion would be partly responsible
for the formation of the nitro-compounds.

The theory of isomeric conversion not being adequate to explain the formation of
the entire quantity of the nitro-compound actually produced, the formation of
unstable intermediate compounds becomes the only alternative explanation of the
formation of the aliphatic nitro-compounds. This additive hypothesis is
summarised thus: Nitrous acid, which forms aliphatic nitrites, and not
nitro-compounds with alcohols, evidently possesses the oxylic constitution
HO-N=O, and the inorganic nitrites, including silver and mercurous nitrites,
being obtained simply by the neutralisation of nitrous acid with inorganic
oxides, would also possess the same constitution. When the alkyl iodides react
with silver or mercurous nitrite, or when the alkyl sulphates react with alkali 
nitrites, two reactions take place, namely, (1) the aliphatic nitrites are
obtained by direct interchange, and (2) unstable intermediate compounds are
formed, which decompose with the formation of nitro-compounds thus:

              AgO-N=O + C2H5I => AgO-N(C2H5)-OI => C2H5-NO2 + AgI
           KO-N=O + C2H5KSO4 => KO-N(C2H5)-OKSO4 => C2H5-NO2 + K2SO4

The relative proportions in which the nitro-compounds would be produced would
depend on the extent to which the intermediate compounds are formed. As the
nitrites and nitro-compounds arc formed in many cases in almost equal
quantities, the two reactions proceed in those cases to all almost equal extent.
To the reactions thus indicated is to be added the effect of the partial
conversion of the nitrites into nitro-compounds where the digestion takes place
at a higher temperature. In the case of nitrous acid the intermediate compounds
not being formed, no nitro-compounds are obtained.

[1] Blank experiments were made with nitrites, nitrate, alcohols, aldehydes, and
    acids containing methyl, ethyl, propyl, isopropyl, butyl, and amyl groups
    which were found not to give the alcoholic sodium hydroxide test.

[2] In the experiments with the different nitrites the liquid obtained is five
    or six experiments was collected and fractionated, and from alcohol,
    aldehyde, acid and nitro-compounds were identified.
