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7/28/2019 Picramic Acid
1/5
Picramic Acid
Reaction:
10 Gms. picric acid and 10 gms. of 35 % soda lye are dissolved in 600 c.cs. water contained in a
glass or iron vessel holding at leas' 1 1/2 litres. After heating up to 550 the liquid is stirred vigorously
and a solution of 40 gms. crystallized sodium sulphide and 100 c.cs water is run in, in a thin stream,
during 10 minutes. After the addition, 127.5 gms. of powdered picric acid are scattered in, about a
teaspoonful at a time, a solution of 220 gms. sodium sulphide in 400 c.cs. water being allowed to runin simultaneously during 10 minutes. The addition of the picric acid should end just at the same time
as that of the sodium sulphide. If the temperature should exceed 65 a little ice must be added. After
all has been added, stirring is continued for a further 10 minutes, after which 400 gms. of ice are
added quickly, whereupon the sodium salt of the picramic acid is completely precipitated at once.
After standing 10 hours it is filtered off and washed with 10 % brine. The free picramic acid is obtained
by stirring up the sodium salt with 500 c.cs. of water, warming to 8o, and acidifying with dilute
sulphuric acid until just acid to Congo. After cooling and standing for 10 hours the product is filtered
off, the yield being about 100 gms. of 100 % product.
10 gms. Picric acid. 10 gms.
36% NaOH. 40 gms. Na2S +9H2O.
Modification. - The partialreductionof picric acid can, of course, be carried out in various ways. Thus,
instead of making the addition gradually and so neutralizing, as it were, the resultant alkali with this
acid, the sodium salt may be reduced, the requisite quantity of hydrochloric acid being run in
simultaneously.
For instance, 6-10 gm.-molecule (=137.5) picric acid are dissolved in 1200 c.cs. water at 500 with the
aid of 36 gms. soda; complete solution, however, is not effected. When the carbon dioxide has been
driven off, 1 gm.-molecule (=240 gms.) crystallized sodium sulphide dissolved in 450 c.cs. water is run
in during half an hour with good stirring. At the same time a mixture of 108 gms., 30 % Hc1, and 300
c.cs. water is run in so that the acid takes about a minute longer than the sodium sulphide. After all
has been added, stirring is continued for half an hour without heating, the mixture allowed to stand for12 hours and filtered. The precipitate is washed with 100 c.cs. saturated brine. The crude sodium
picramate is dissolved in 2 litres water, and the filtered solution poured into a dilute hydrochloric acid
made up of 70 c.cs. of 30 % hydrochloric acid and 400 c.cs. water at 900. The pure picramic acid is
completely precipitated within 24 hours; it is then filtered off and washed with a little water, after which
it is pressed and dried at 8o, the yield being about 100 gms. = 83 % of theory.
On the works scale the former of the two methods given is the more satisfactory, as the gradual
addition of the substances can be better regulated.
In recent years picramic acid has become very important as an azo component. It gives very fast wool
colours which are distinguished by the fact that they can be dyed with the aid of
127.5 gms. Picric acid.
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220 gms.
Na2S
+9H2O.
400 gms. Ice.
137.5 gms. Picric acid.
36 gms. Soda.
240 gms.
Na2S
+9H2O.
108 gms. Hc1 (30 %). 300 c.cs. H2O.
Water. 70 Ccs.
30%
Hc1 + 400 C.CS.
H20.
chromic acid. Examples of these are the Metachrome colours of the BerlinAnilineCo., e.g.Metachrome Brown:
For the most part thesedyesare difficultly soluble in water and in the dry state are often explosive, forwhich reason they must either be ground up with a large quantity of Glauber salt, or placed on the
market as aqueous pastes.
The diazo compound of picramic acid was the first example of this class of substances to be
discovered, and led to the important researches of Peter Griess.
a-Nitronaphthalene and a-Naphthylamine.1
Reaction:
http://chestofbooks.com/science/chemistry/Processes-Dye-Chemistry/Mixture-Of-Aminoazo-Toluene-And-Aniline.htmlhttp://chestofbooks.com/science/chemistry/Processes-Dye-Chemistry/II-Dyes-6-Azo-Dyes.htmlhttp://chestofbooks.com/science/chemistry/Processes-Dye-Chemistry/II-Dyes-6-Azo-Dyes.htmlhttp://chestofbooks.com/science/chemistry/Processes-Dye-Chemistry/Mixture-Of-Aminoazo-Toluene-And-Aniline.html7/28/2019 Picramic Acid
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The nitration of naphthalene takes place very vigorously so that poly-nitro products are readily
obtained. The naphthalene used should be extremely pure as otherwise the yields are unfavourably
influenced. If no satisfactory naphthalene is obtainable, it is advisable to purify some by distillation
and, if necessary, by subsequent heating with 5 % of its weight of concentrated sulphuric acid. As the
nitration must be performed at a temperature below the melting-point of the naphthalene, the
substance must be finely powdered (to pass through a sieve with 400 meshes per sq. cm.), as larger
particles would escape the action of the nitric acid.
128 Gms. naphthalene are added to a mixture of 103 gms. nitric acid of 60 % (400 Be.), and 300 gms.
of 80 % sulphuric acid. Stirring is continued without interruption for 6 hours at 500, the temperature
being finally increased to 6o during 1 hour, after which it is cooled down. The nitronaphthalene floatsupon the surface of the acid in porous cakes, and consists of about 95 % a-nitro compound, together
with some unchanged naphthalene and a very little dinitro derivative. -Nitronaphthalene is either
absent or present only in traces.
128 gms. Naphthalene. 103 gms. Hno3, 400 Be. 300 gms. H,So4 80 %.
1 See also O. N. Witt, Chem. Ind. (1887), 215; S. Paul, Z.f. a. Ch. (1897), 145.
The crude product is melted up several times with boiling water by which means the acid is
completely removed and the naphthalene carried off by the steam. The melted product is then poured
into cold water, which is kept well agitated, the nitronaphthaleneseparating out in the form of small
spheres.
To obtain the compound completely pure, it is dried by melting it at 120 in an air oven. It is then
treated with 10 % of its weight of ligroin (b.p. about 1500), or crude xylene or cymene may be used
instead. It is then filtered hot through a smooth filter and allowed to stand in a closed vessel for some
time. A crystalline cake is formed which is well pressed out in a cotton cloth. This purification should
be repeated until the nitronaphthalene shows a melting-point of 61 . It is thus obtained in the form of
yellow, glistening crystals. A considerable portion of the nitronaphthalene always remains behind in
the mother-liquors and may be recovered by distilling off the solvent.
Crude nitronaphthalene is reduced by Bechamp's method by means of iron and a little hydrochloric
acid; the mixture must not, however, be heated too high or else too much naphthalene will be formed;
but it is not possible to prevent this reaction altogether, as, for instance, in the preparation of aniline,although in the latter case its effect is but slight.
200 Gms. iron turnings, 100 gms. water, and 10 c.cs. of 30 % hydrochloric acid are placed in an iron
reducing pot, fitted with an "anchor" stirrer. As soon as the evolution of hydrogen has ceased at 500
the nitronaphthalene is added in small portions, taking care, by means of external cooling, that the
temperature rises no higher. One gm.-molecule (=173 gms.) nitronaphthalene (calculated as air-dried
substance) is reduced within 4 hours, with continuous stirring. It is inadvisable to proceed more
quickly or undesired azo compounds may be formed. The mixture is now treated with enough soda to
give a distinctly alkaline reaction, after which the contents of the reduction vessel are transferred to a
basin. The separation of the a-naphthylamine formed is best effected even in the laboratory by
distilling with super-heated steam, for which purpose the whole reduction product together with water,
iron, and iron oxide are placed in the oil-heated pot shown in Fig. 36,PlateXIV. The water is distilledoff completely with continuous stirring by heating the oil-bath to 2000, after which super-heated steam
at 2500 is blown in (Fig. 17).1
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200 gms. Fe. 100 gms. H2O.
10 c.cs.
30 %.
Hc1.
173 gms. Nitronaphthalene.
1 The illustration is diagrammatic and does not show the stirrer. In order to ensure the easy
separation of the iron oxide and naphthylamine, it is advisable for the mixture to be kept stirred.
Fig. 17. - Apparatus for distilling in a current of superheated steam.
If the distillation is carried out properly, it is possible to distil over half to one part naphthylamine for
each part water. A small amount of finely divided iron powder, graphite from the cast-iron, and iron
oxide, are always carried over with the base. As soon as the point is reached at which the steam at
2600 carries over only discoloured products or none at all, the distillation is complete; it should ccupy
from 1-1 1/2 hours according to the method of heating. There remans in the kettle a black very finely
divided mass, which is pyrophorous, and therefore must not simply be thrown away. After cooling, the
naphthylamine is separated from the mother-liquor, melted, and dried at no in the air oven, after
which it is vacuum-distilled. The base is obtained as a completely colourless crystalline product. The
yield from 1 gm.-molecule of naphthalene is about no gms. pure a-naphthylamine. M.p. 50o.
Notes on Works Practice. - (a) Nitronaphthalene. A portion of the waste nitrating acid is always made
use of again by simply making up to 80 % by the addition of stronger sulphuric acid. The residue is
used for acidifying alkali melts, etc. With correct grinding (disintegration at 6o) it is possible to obtain
practically quantitative yields in the nitration. The nitronaphthalene is also used for the preparation of
1:5-nitronaphthalene and 1:5 naphthylamine sulphonic acids. Further, the nitronaphthalene has been
applied (first by the B.A.S.F.) to the preparation of the diazo compound of aminonaphthol sulphonic
acid 1:2:4; on heating with sodium sulphite it yields naphthylamine disulphonic acid 1:2:4, together
with somenaphthionic acid; the former can be diazotized and converted into the diazo compound of
the above mentioned sulphonic acid on treatment with sodium bicarbonate and sodium hypochlorite.
The following scheme illustrates the course of this curious reaction (see D. R. P. 160536):
http://chestofbooks.com/science/chemistry/Processes-Dye-Chemistry/Sulphanilic-Acid-Metanilic-Acid-Naphthionic-Acid-Nitraniline-Sulphonic-Acids.htmlhttp://chestofbooks.com/science/chemistry/Processes-Dye-Chemistry/Sulphanilic-Acid-Metanilic-Acid-Naphthionic-Acid-Nitraniline-Sulphonic-Acids.htmlhttp://chestofbooks.com/science/chemistry/Processes-Dye-Chemistry/Sulphanilic-Acid-Metanilic-Acid-Naphthionic-Acid-Nitraniline-Sulphonic-Acids.htmlhttp://chestofbooks.com/science/chemistry/Processes-Dye-Chemistry/Sulphanilic-Acid-Metanilic-Acid-Naphthionic-Acid-Nitraniline-Sulphonic-Acids.html7/28/2019 Picramic Acid
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Although this process is quite satisfactory it has been replaced by the still cheaper Sandmeyer
method.
(b) a-Naphthylamine. The reduction is carried out in a similar apparatus to that which has already
been described on several occasions. But owing to the stiff, porridgy consistency of the reduction
liquid, it is not possible to use a plough- or propeller-stirrer, but the "anchor" type must be utilized,such as that given in Plate II. The steam distillation is effected in an apparatus similar to that indicated
in Fig. 19. The incoming steam is almost invariably pre-heated in a special superheater. Satisfactory
apparatus of this type is supplied by various makers.
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