On the Mechanism of Nitration with Dilute Nitric Acid

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BULLETIN DE L'ACADEMIE
POLONAISE DES SCIENCES
S é r i e des s c i e n c e s c h i m i q u e s
Volume X X V I I I . No. 9-10,
1980
Publie en mars 1982
ORG INIC CHEMISTRY
O n the Mechanism of Nitration with Dilute Nitric Acid
by
Tadeusz URBAŃSKI
Presented on November 13. 1980
Summary. Dilute nitric acid (0.5-1.0% H N O , ) can nitrate 8-hydroxyquinoline and 8-hydroxy-5-nitroquinoline to yield 5,7-dinitro-8-hydroxyquinoline. It is now rationalized in terms of the
formation of nitronium ion in a readily oxidisable medium of a phenol: N O J - » N 0
+0 ~.
Similarly, nitrous acid (0.5-1.0",,) can yield a small quantity of 5,7-dinitro compound Ihrough
the formation of N 0 yielding dilute nitric acid.
+
2
2
2
4
It is well known that the nitronium ion ( N 0 ) is the nitrating agent,
there are however examples when the nitration can occur in media in which
the concentration of N 0 is too small to be detected spectroscopically [1].
This was pointed out by Bunton and Halevi [2] who succeeded to obtain
nitrate aromatic compounds with 40-60",, aqueous nitric acid. It was reported
[3] that the nitration of 1,5-dinitronaphthalene can occur with 70% nitric
acid to yield trinitronaphthalene. Bunton ei al. [4] rationalized their finding
in terms of reactions:
2
2
(1)
2HN0 ^H NO.t +NOJ,
3
(2)
2
H NO.t * N 0
2
+
2
+ H 0.
2
Thus, the hydrated nitronium ion (nitracidium ion) H N O t should be a source
of nitrating agent N 0 .
The problem of nitration with aqueous nitric acid was reviewed by Hanson
et al. [5]. They confirmed the idea of nitracidium ion being a nitrating
agent and pointed out that attention should be. paid to the presence of
nitrous acid in the system, as the nitration with dilute nitric acid can proceed
through the nitrosation by nitrous acid formed as a result of the oxidation-reduction reactions. This is a usual explanation of the nitration of phenols
with dilute nitric acid: the prior nitrosation of phenols is followed by oxidation
• [6, 7].
I can agree with this view up to a certain point, namely when mononit roderivatives of phenols are formed. However. 1 have found [8] that 82
2
[609]
T. Urbański
610
ь
-hydroxyquinoline can be converted to 5,7-dinitrocompound by boiling with 8%
nitric acid, and also [9] that the same result, on prolonged boiling, can be
achieved by highly dilute 0.5-1.0% nitric acid. The formation to dinitro
compound could not be explained in terms of nitrosation. It should involve
a simultaneous nitrosation in two places—an unknown reaction.
Another still stronger point is the experimental fact that 8-hydroxy-5-nitroquinoline can be nitrated by refluxing for 15 min with 0.5-1.0% nitric acid
to yield (ca. 50%) 5,7-dinitro-8-hydroxyquinoline [9]. It is well known that
nitrophenols cannot be nitrosated with nitrous acid and subsequently the
introduction to the nitro group in position 7 cannot occur through nitro­
sation. Nevertheless, the reaction with 0.5-1.0/ nitric acid proceeds in both
nitration of 8-hydroxyquinoline and its 5-nitro derivative with the evolution
of nitrous fumes indicating an oxidation-reduction process.
Also, a solution of 0.4-0.5% sodium nitrite in hydrochloric acid when
boiled with 8-hydroxyquinoline can produce a small yield (ca. 3%) of 5,7-dinitro-8-hydroxyquinoline. This is also accompanied by the evolution of
nitrous fumes. The N 0 evolved can yield in water H N 0 + H N 0 according
to the well-known reaction.
According to my opinion the described experimental facts can be ratio­
nalized in terms of the formation of the N O 2 ion in dilute nitric acid through
the reaction:
o
2
2
n o ;
->no
+
2
+
o
2
_
3
.
The reaction could take place particularly in the presence of readily
oxidisable substances, such as phenols. The N O 2 ion should also produce
an evolution of nitrous fumes.
Attention is drawn to the recent paper by Ross et al. [10] where they
expressed doubts as to the common scheme of nitration of phenol through
nitrosation.
INSTITUTE OF ORGANIC CHEMISTRY AND T E C H N O L O G Y . TECHNICAL UNIVERSITY, KOSZYKOWA 75.
00-662 WARSAW
(INSTYTUT CHEMII I TECHNOLOGII ORGANICZNEJ, POLITECHNIKA WARSZAWSKA)
REFERENCES
[1] T. U r b a ń s k i , Chemistry and technology of explosives, vol. I, Pergamon Press-PWN,
Oxford-Warsaw, 1964, pp. 25, 48,
[2] С A, B u n t o n , E. A. flalevi, J. Chem Soc., 1952, 4917
[3] E. R. W a r d , С D. J o h n s o n , L. A. D a y . ibid., 1959, 487.
[4] С A B u n t o n , E. A. H a l e v i , D R . L l e w e l l y n , ibid., 1952, 4913.
[5] С H a n s o n , M . W. T. P r a t t , M . S a h r a b i , in: Industrial and laboratory nitration,
ed. by L. F. Albright and C. Hanson, A C S Symposium Series 22, Washington D. C , 1976.
[and references therein],
[6] A V. K a r t a s h e v , Zh. Russ Fiz. Khim Obshch., 59, 819, 833 (1927)
[7] S. V e i b e l , Chem. Ber., 63, 1577, 1582 (1930),
[8] T, U r b a ń s k i , Roczniki Chem., 32, 415 (1958)
Mechanism of Nitration with Dilute Nitric Acid
611
[9] T. U r b a ń s k i , W. R u t k i e w i c z , Tetrahedron, 20, Suppl. 1, 97 (1964).
[10] D. S. Ross, G . P. H u m , W. G . B l u c h e r , J. Chem. S o c , Chem. Comm., 1980, 532.
Т. Урбаньски. О механизме нитрации разбавленной азотной кислотой
Разбавленная азотная кислота (0,5 1,0",, H N O ) может нитрировать 8-оксихинолйн
и 8-окси-5-нитрохинолпн, что ведёт к получению 5.7-динитро-8-оксихинолнна. Настоящая
работа объясняет это явление как реакцию образования нитрониевого иона в легкоокисляющейся среде фенола: N O > N O ? - ) - О - . Подобным образом, азотистая кислота
(0,5 1,0",,) может образовть небольшое количество 5,7-динитро соединения в реакции
образования N , 0 , , которая дает разбавленную азотную кислоту.
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-
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