Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for producing
naphthoquinone.
Naphthoquinone is a widely used organic material
in the chemical process industry. It is used particularly
for the production of dyestuffs and higher quinones in~
cluding tetrahydroanthraquinone and anthraquinone.
In Kir~ Othmer's Encyclopedia of Chemical Techno-
logy, second edition, volume 16, page 910, it is indicated
that l,4-naphthoquinone can be prepared in high yield by the
action of potassium dichromate and sulphuric acid on 4-
amino-naphthol hydrochloride but that the direct oxidation--
of naphthalene to naphthoquinone appears to be of little
value. Further, Weyker et al in U.S. Patent 2,938,913
issued May 31st, 1960 describe and claim a method for the
direct oxidation of naphthalene to naphthoquinone and
phthalic anhydride using a vanadium pentroxide catalyst at
high temperatures and in a pressurized system. Although
this process of Weyker et al, or modifications of it, are
used on a commercial basis, it has the disadvantage of
producing a considerable amount of phthalic acid as well as
the desired 1,4-naphthoquinone.
Gorbachev and Vabel in Zhur. viz. Khim, 28, 1782 -
(8) (1954) describe the oxidation of naphthalene by ceric
sulphate at 40 to 70C in a one phase system containing
naphthalene, acetic acid, sulphuric acid and ceric sulphate.
They showed that the rate of oxidation of naphthalene
appro~imately doubled with each 10C rise in operating
temperature. Also, the rate of naphthalene oxidation was
approximately first order with a respect to the dissolved
ceric ion concentration. Therefore, higher dissolved ceric
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ion concentrations and higher operating temperatures resulted
in more rapid conversion of naphthalene to naphthoquinone.
However, they did not develop a commercially viable naphtho-
quinone production method. The naphthoquinone generated in
the one phase system they describe is exposed to ceric ion
and is thus further oxidized, resulting in low naphtho-
quinone yields. Further, their naphthalene and naphtho-
quinone concentrations were extremely low. In addition
Gorbachev and Vabel did not discuss methods of separating
the naphthoquinone from the cerium oxidant.
British Patent 1,192,037 to-Imperial Chemical
Industries describes a method for the oxidation of naphtha-
lene to naphthoquinone in a two phase system. Naphthalene
is dissolved in a variety of solvents at naphthalene con-
centrations between 0.05 molar and 0.26 molar to produce ahomogenous organic phase. Ceric sulphate in 4N sulphuric
acid or ceric ammonium nitrate in 4N acid is used as a
catalyst. Suitable cerium solutions may be prepared having
concentrations of 0.01 to 0.15 molar in 4N sulphuric acid.
A more rapid reaction is obtained using the more soluble
ceric ammonium nitrate in 4N nitric acid. The use of
concentrated ceric ammonium nitrate in nitric acid, although
having the advantage of giving a more rapid reaction - as
would be expected from the results of Gorbachev and Vabel
above - produces a substantial amount of unwanted l-nitro-
naphthoquinone byproduct. This failing is also illustrated
in ICI's Canadian patent 899,856 and British patent 1,203,434.
The above approach to naphthoquinone production
with a cerium oxidant by ICI is not commercially viable as
it suffers from a number of drawbacks, including:
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1. By using an organic solvent to dissolve
the naphthalene, the upper operating
temperature is restricted to the
boiling point of the solvent.
2. By using an organic solvent to dissolve
the naphthalene a large and complicated
solvent recovery system must be in-
cluded in any naphthoquinone production
plant. This is prohibitively expensive
since a large amount of solvent would
have to be removed from a small amount
of naphthoquinone product and unconverted
naphthalene.
3. By using an organic solvent the initial
naphthalene concentration in the organic
phase is limited by the solubility of
naphthalene in that solvent at the given
operating temperature.
4. By using an electrochemical cell contain-
ing diaphragms, the maximum ceric ion
content of the electrolyte is limited
to the maximum solubility of the cerous
sulphate salt.
5. Naphthoquinone is produced in extremely
dilute concentration, for example 0.2
molar maximum even if 100% yield at
100% conversion were achieved starting
with 0.2 molar naphthalene. The cost
of recovering extremely dilute naphtho-
uinone from a naphthalene solvent mix-
996
ture is prohibitive on a commercial
scale.
6. The operating temperature is restricted
in the above patents to the range ~0 to
80C in order to restrict the formation
of byproducts, for example l-nitronaph-
thalene.
7. The reaction rates are slow, for example
1 to 2 hours, because reagents are very
dilute and operating temperatures are
relatively low. --
8. By having a very dilute naphthalene
reagent mixing costs for ensuring
that the aqueous ceric ion oxidant and
naphthalene reagent are well dispersed
are high.
9. The oxidation of naphthalene by ceric
sulphate is mass transfer controlled in
addition to being kinetically controlled.
The speed at which naphthalene can be
converted to naphthoquinone is strongly
dependent on the rate at which naphthalene
molecules can make contact with ceric ion.
By using a solvent to dissolve naphthalene
the ceric ion - naphthalene contact rate
is restricted by the speed with which
naphthalene molecules within the solvent
can diffuse (mass transfer) to the solvent-
ceric ion interface where they can react.
By eliminating the solvent entirely a
9~ '
much greater concentration of naphtha-
lene molecules is always in direct
contact with the ceric ion oxidant.
The speed of the naphthalene oxidation
reaction is therefore substantially
limited by the use of a solvent. In
addition it is important to expose ceric
ion to an excess of naphthalene molecules
to prevent byproduct formation due to
ceric ion reacting with other organic
species e.g. naphthoquinone in the absence
of naphthalene molecules. Byproduct for-
mation and ceric ion wastage is substan-
tially reduced by oxidizing naphthalene in
the absence of a solvent even at high
naphthoquinone concentrations (see Table
1) ~
The present invention seeks to overcome the -`
disadvantages in the prior art that have prevented the
production of naphthoquinone by the oxidation of naphthalene
using cerium oxidants. The present invention shows that
naphthalene can be readily converted to naphthoquinone in
very high yields and in high concentrations, higher than
demonstrated by ICI or Gorbachev and Vabel, by operating at
very high temperatures, for example greater than 81C,
without the need for an organic solvent dur~ng the nap-
hthalene oxidation and at ceric sulphate concentrations much
larger than those disclosed anywhere in the prior art.
Accordingly, in one aspect the present invention
is a process for producing naphthoquinone that compri~es
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oxidizing naphthalene with ceric sulphate at a temperature
above the melting point of naphthalene with vigorous agi-
tation of the reaction mixture in the presence of sulphuric
acid but in the absence of any organic solvent. The mixture
resulting from the oxidation may be contacted with an or-
ganic solvent to extract the naphthoquinone. Alternatively,
fractional sublimation may be used to separate the naph-
thoquinone from the reaction mixture.
The sulphuric acid used is preferably in the range
0.5 molar to 2.0 molar.
It should also be noted that the ceric sulphate
can be regenerated from the cerous sulphate produced by the
oxidation of naphthalene with ceric sulphate, by reoxidizing
the cerous sulphate back to the ceric sulphate state.
Techniques for this recovery are known in the art. A
particularly preferred process is described in our co-
pending Canadian application Serial Number 351,645 filed May
9th, 1980. However, additional electrolytic processes may
be used to regenerate the ceric ion. Ozonolysis may also be
used.
The melting point of naphthalene is 80C. A
preferred temperature for carrying out the process is thus
at or above about 81C, for example 81 to 85C but higher
temperatures can be used. The concentration of the naphtha-
lene in the reaction mixture is about 6.3 molar because theconcentration of liquid naphthalene at about 81C is 6.3
molar. The ceric sulphate concentration should be at least
0.05 molar at the start of the naphthalene oxidation,
however starting ceric sulphate concentrations in excess of
0.4 molar, particularly 0.5 molar, are preferred.
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The following experiments illustrate the inven-
tion. The results and reaction conditions are set out in
Table 1.
Examples
In the following examples the oxidation of naphth-
alene was carried out by adding solid naphthalene to a ceric
sulphate - sulphuric acid oxidant at or above 81~C. The
reaction was carried out in a closed glass container and the
contents were stirred vigorously with a magnetic stirrer bar
for 15 minutes. The organic mixture resulting was dissolved
in an organic solvent and analyzed using high pressure
liquid chromatography to determine naphthalene conversion
and naphthoquinone yield.
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The oxidations were carried out in 20 minutes or
less, in contrast with the one to two hours required by the
prior art. This brief reaction time is due to the defined
reaction conditions. By eliminating the use of a solvent
the need for a solvent recovery system is eliminated and
very concentrated naphthoquinone can be generated, for
example about 2 molar, even at moderate naphthalene con-
versions, for example 40% or less.
The present invention therefore discloses a
commercially viable process for the production of naphtho
quinone by the oxidation of naphthalene.
