Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
FMC 1696 -
1078383
This invention relates to the formation of crystalline
[(mono-trichloro) tetra-(monopotassium dichloro)] penta-iso-
cyanurate by reacting an amino substituted triazine with
potassium hypochlorite in an aqueous medium.
Cyanuric acid is commonly represented as existing in
two tautomeric forms as follows:
1l IOH
/ \ N
\N/ HO-C~ ~ OH
H
The terms dichloroisocyanuric acid and dichloroisocyanurate
refer to the acid and salt respectively in either tautomeric
10 form. r
Cyanuric acid is the main product produced by heating
urea, biuret or mixtures thereof in a kiln at temperatures
of about 200- to 350-C. Unfortunately, the product produced
is only composed of about 80% cyanuric acid with the remainder
of the product comprisin~ amino substituted triazine impuri-
ties. The amino substituted impurities generally contain
about 25% ammelide and minor amounts of other impurities
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such as ammeline, melamine, ammeline:ammelide complex, and
cyanuric acid:melamine cGmplex. This cyanuric acid product
mixture is conventionally referred to as crude cyanuric acid.
Since it is quite difficult to separate the crude cyanuric
acid into its component parts to recover pure cyanuric acid,
various methods have been proposed to purify crude cyanuric
acid by converting the triazine impurities into cyanuric
acid by acid hydrolysis. This conversion is sometimes re-
ferred to as the acid digestion process.
The acid digestion process comprises mixing crude
cyanuric acid with a strong mineral acid to make a slurry
containing 10% to 15% undissolved solids. The mineral acids
disclosed as being operative are sulfuric, hydrochloric,
nitric and phosphoric acid, with sulfuric acid being pre-
ferred. The slurry is digested at reflux temperatures
(about 104 C) or at higher temperatures while under pres-
sure. These digestion processes result in hydrolysis of
most of the triazine impurities to cyanuric acid. Methods
employing this procedure are described in U.S. Patents
2,768,167, 2,943,088 and 3,107,244.
The use of mineral acid reactions, however, results in
partial hydrolysis of the cyanuric acid to ammonia and
carbon dioxide, thus decreasing cyanuric acid yields. The
formation of a purified cyanuric acid, however, is essential
for an efficient conversion of the cyanuric acid into chloro-
isocyanuric acids and their salts, preferably sodium, lithium
or potassium salts, by known processes employed in the prior
art.
Dichloroisocyanuric acid and trichloroisocyanuric acid
have been produced by mixing purified cyanuric acid with
sodium hydroxide and then chlorinating by the addition of
chlorine. Specifically, dichloroisocyanuric acid has been
produced by mixing cyanuric acid and sodium hydroxide in a
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mole ratio of 1:2 and then chlorinating the mixture by the
addition of chlorine, usually in two stages, until the pH
value is between 1.7 and 3.5. This process requires long
hold-up times for the chlorination reaction to approach
completion and therefore the reactors must be relatively
large to obtain sufficient hold-up times and yields.
U.S. Patent 3,035,056 discloses a process for producing
sodium dichloroisocyanurate by chlorinating 1 mole of tri-
sodium cyanurate with 2 moles of trichloroisocyanuric acid.
Such a reaction is not advantageous since it requires a
separate source of trichloroisocyanuric acid to obtain the
required reactant for the process.
U.S. Patent 3,712,891 discloses another process for
producing chloroisocyanuric acids by reacting purified
cyanuric acid and hypochlorous acid in an a~ueous medium
at a temperature of 0' to 50-C. The mole ratio of cyanuric
acid to hypochlorous acid is preselected to yield a product ;~
having the desired degree of chlorination, that is, a mole
ratio of cyanuric acid to hypochlorous acid of 1:2 produces
dichloroisocyanuric acid, whereas a molar ratio of cyanuric
acid to hypochlorous acid of 1:3 produces trichloroisocyanuric
acid.
In contrast, potassium-containing chloroisocyanurate
complexes such as [(mono-trichloro) tetra-(monopotassium
dichloro)] penta-isocyanurate and mixtures thereof, have
been produced by reacting potassium dichloroisocyanurate
and trichloroisocyanuric acid in an aqueous solvent system
at carefully controlled pH values and reactant ratios as
described in U.S. Patent 3,272,813. This reaction, however,
requires s-eparate sources of potassium dichloroisocyanurate
and trichloroisocyanuric acid as reactants and extensive
` purification procedures to remove the solvent system from
; the product complexes.
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` 1078383
In accordance with the present invention, [(mono-tri-
chloro) tetra-(monopotassium dichloro)] penta-isocyanurate
and mixtures thereof can be produced directly from unsub-
stituted or amino substituted triazines without the need
for an acid hydrolysis step to purify the crude cyanuric
acid, and without the need for separate sources of potassium
dichloroisocyanurate and trichloroisocyanuric acid, by re-
acting an unsubstituted or amino ~ubstituted triazine with
at least stoichiometric amounts of potassium hypochlorite
in an aqueous medium at a temperature of 35 to 70-C and at
a pH value of 3.2 to 5.7 for less than about five minutes
to completely N-chlorinate all of the available sites on
the triazine molecule that can be N-chlorinated and to
remove any N,N-dichloro exocyclic nitrogens; cooling the
reaction medium to precipitate [(mono-trichloro) tetra-
(monopotassium dichloro)] penta-isocyanurate; and recovering
crystalline [(mono-trichloro) tetra-(monopotassium dichloro)~
penta-isocvanurate.
The process of the invention permits the formation of
crystalline [(mono-trichloro~ tetra-(monopotassiùm dichloro)]
penta-isocyanurate and mixtures containing the same, such as
complex mixtures of ~(mono-trichloro) tetra-(monopotassium
dichloro)] penta-isocyanurate and (mono-trichloro) (mono-
potassium dichloro) di-isocyanurate, from unsubstituted
or amino substituted triazines in a commercially simple and
efficient manner without the concommitant metal corrosion
problems associated with the prior art acid digestion pro-
cesses, without the need for large expensive acid digestor
reactors, and without the long hold-up times required for
the prior art chlorination reactions to approach completion
to prepare potassium dichloroisocyanurate and trichloroiso-
cyanuric acid. It also permits recovery of a crystalline
product in exceptionally high yields and exceptionally high
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10783~3
purities in relatively short periods of time, that is below
about five minutes.
In the process of the invention, an amino substituted
triazine, such as melamine, ammeline, ammelide, ammeline:
ammelide complex and cyanuric acid-melamine complex or
mixtures thereof is mixed with a sufficient amount of po-
tassium hypochlorite to completely N-chlorinate all of the
available sites on the triazine molecule that can be N-
chlorinated and to remove any N,N-dichloro exocyclic nitro-
gens. Alternatively, purified cyanuric acid or crude cy-
anuric acid containing ammelide and other amino substituted
triazine impurities is mixed with potassium hypochlorite and
treated according to the process of the invention to like-
wise completely N-chlorinate all of the available sites on
the triazine molecule that can be N-chlorinated and to re-
move any N,N-dichloro exocyclic nitrogens. The phrase
"amino substituted triazines" as used herein, refers to the
specific amino substituted triazines enunciated above as
well as to crude cyanuric acid.
~he unsubstituted or amino substituted triazines are
employed in amounts sufficient to produce a triazine slurry
in the aqueous reaction medium. The unsubstituted or amino
substituted triazine slurry concentration is not critical.
From a commercial process standpoint, however, slurry con-
centrations from 3 to 20 weight % of the triazine based on
the weight of the reaction solution are desirable. Slurry
concentrations below about 3 weight % are not economical in
view of the small amounts of material being treated. Slurry
concentrations above about 20 weight % are difficult to
handle and accordingly are not advisable. Preferably, the
slurry concentration is between 6 and 14 weight % based upon
the weight of the reaction solution.
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1078383
The unsubstituted or amino substituted triazine slurry
is obtained by either mixing dry unsubstituted or amino
substituted triazine and potassium hypochlorite in water
or mixing aqueous solutions of one or both of these mate-
5 rials together.
To achieve complete conversion of the unsubstituted
or amino substituted triazine to [(mono-trichloro) tetra-
(monopotassium dichloro) penta-isocyanurate triazine, at
least stoichiometric amounts of potassium hypochlorite must
lO be employed to completely N-chlorinate all of the available
sites on the triazine molecule that can be N-chlorinated
and to remove any N,N-dichloro exocyclic nitrogens. These
amounts will vary with the particular triazine employed and
the desired potassium-containing chloroisocyanurate complex
15 product.
Under desirable temperature and pH conditions, [(mono- .
trichloro~ tetra-(monopotassium dichloro)] penta-isocyanurate,
commonly referred to as Compound I and mixtures containing
the same is produced when the mole ratio of potassium hypo-
20 chlorite to melamine is 11.2:1, the mole ratio of potassium
~ hypochlorite to ammeline is 8.2:1, the mole ratio of po-
s tassium hypochlorite to ammelide is 5.2:1, or the mole ratio
of potassium hypochlorite to cyanuric acid is 2.2:1. The
; mole ratio of potassium hypochlorite to either the amino
25 substituted triazine complexes or to crude cyanuric acid
is determined from the aforementioned stoichiometry based
upon the specific amino substituted triazines which are
; present.
Any stoichiometry substantially less than that stated
30 results in the undesirable production of mixtures containing
chlorinated amino substituted triazines and/or chlorinated
isocyanuric acids and/or their salts. Preferably, potassium
hypochlorite is employed in amounts of at least 10~ above
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78383
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the stoichiometric amount necessary to completely N-chlorinate
all of the available sites on the triazine molecule that can
be N-chlorinated and to remove any N,N-dichloro exocyclic
nitrogens, and most preferably in amounts of 15% to 30% above
the stoichiometric amount.
The stoichiometric reaction results in the formation of
1 mole of nitrogen trichloride for each exocyclic amino group
from each triazine molecule. The nitrogen trichloride formed
during the reaction may be removed by conventional procedures, ;;-
such as by sparqing the reaction medium with an inert gas and
removing the sparged nitrogen trichloride as a waste stream.
Other well known procedures for removing nitrogen trichloride
from a reaction medium may likewise be employed, which pro-
cedures do not constitute a part of this invention.
15Conversion of the unsubstituted or amino substituted tri-
azines into potassium-containing chloroisocyanurate complexes
is effected at pH values from 3.2 to 5.7 and at temperatures
from 35-C to 70-C. Higher or lower pH values should not be
employed since these result in the formation of potassium
dichloroisocyanurate and/or trichloroisocyanuric acid.
Higher or lower temperatures should not be employed since
these increase triazine ring rupture, thus decreasing product
yield.
Maximum conversion of the unsubstituted or amino substi-
tuted triazines into [(mono-trichloro) tetra-(monopotassium
dichloro)] penta-isocyanurate is achieved at pH values of 4.0
to 5.5 and at temperatures of 45 to 60 C, and preferably at
a pH value maintained between 4.7 and 5Ø Maximum conversion
of the unsubstituted or amino substituted triazines into mix-
tures of [(mono-trichloro) tetra-(monopotassium dichloro)]
penta-isocyanurate and (mono-trichloro) (monopotassium di-
chloro) di-isocyanurate is achieved at pH values maintained
from 3.5 to 4.0 and at temperatures of 45- to 60 C.
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The reaction pH must be maintained during the course of
the reaction within these pH values to obtain the noted
products. This is achieved by employing any organic or
mineral acid which is compatible with the system, that is an
acid that does not react with the starting compounds or re-
sulting complexe~. Preferred mineral acids include sulfuric
acid, hydrochloric acid, phosphoric acid, nitric acid, and
perchloric acid. Preferred organic acids include acetic
acid and propionic acid.
Reaction between the unsubstituted or amino substituted
triazines and potassium hypochlorite is extremely rapid under
operating conditions with complete conversions being achieved
in a matter of minutes. There is, however, a competing re-
action causing triazine ring breakdown, which reaction occurs
at a slightly slower rate. In order to maximize conversion
of the triazines into [(mono-trichloro) tetra-(monopotassium
dichloro)] penta-isocyanurate while minimizing triazine ring
rupture, the reaction is carried out in less than about 5
minutes and preferably in less than about 2 minutes. These
reaction times can be achieved by employing conventional
reactors. Reaction times of up to 90 seconds are feasible
with commercially available pipe reactors. A pipe reactor
is an elongated tubular reaction chamber wherein the feed
enters the reactor in one end and product exits out the
other end. ~he reaction takes place within the tube which
is heated by external sources. Use of the pipe reactors
greatly increases the production of the potassium con-
taining chloroisocyanurate complexes of this invention and
eliminates the need for larger type reactors.
Mixing of the unsubstituted or amino substituted tri-
azine and potassium hypochlorite to form the resulting
slurry as well as heating the aqueous medium are achieved
by conventional means and procedures. Mixing and heating
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1~78383
may be done separately or carried out in a single stage. Since
this is an exothermic reaction, temperature control of the
aqueous reaction medium is easily achieved by conventional
external cooling means. The reaction is then permitted to ;~
go to completion.
When the reaction is complete, the aqueous solution is
cooled by conventional means to precipitate the potassium-
containing chloroisocyanurate complexes. Preferably, the
reaction solution is rapidly cooled in less than about 10
minutes to below about 20-C and preferably to below about
10-C. Cooling is essential to prevent triazine losses due
by ring rupture and to lower the solubility of the com-
plexes in the reaction medium. The precipitated crystals
are recovered from the solution by any conventional liquid-
solid separatory means.
The recovered crystals may then be optionally driedand stored. Drying may be carried out in any conventional
manner to remove residual moisture and to produce a free-
flowing crystalline product. These procedures are well
known in the art and do not constitute a part of the in-
vention.
The invention will be better understood from a con-
sideration of the following examples. The examples are
given to illustrate the invention, and are not deemed to
be limiting thereof. All percentages given are based on
weight unless otherwise indicated.
EXample T
Production of [(mono-trichloro)
tetra-(monopotassium dichloro)]
penta-isocyanurate
A 7.65 gram (0.0593 mole) sample of crude cyanuric
acid prepared from urea assaying 80% cyanuric acid, 17%
ammelide and 3% ammeline was added to 102.4 grams of an
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aqueous solution containing 19 grams potassium hypochlorite.
This addition took place in less than two seconds. The
aqueous solution had a pH value of 10.5 and a temperature
of 35 C. The reaction temperature rose to 55 C and was
maintained at 55-C ~or two minutes. The pH value of the
reaction mixture was initially adjusted to and maintained
at 4.9 with acetic acid during the course of the reaction.
The reaction vessel was then quenched in an ice bath and
the reaction solution rapidly cooled to t5 C within two
minutes. A white solid precipitate was removed from the
slurry, washed and dried at 120-C under 20 mm Hg pressure.
The precipitate was pure [(mono-trichloro) tetra-(mono-
potassium dichloro)] penta-isocyanurate analyzing 66.3%
available chlorine. The total yield was 12.1 ~rams which
is equivalent to 87% recovery based on starting triazines.
Example II
Production of comPlex mixtures containing [(mono-trichloro)
tetra-(monopotassium dichloro)] pent~a-isocyanurate and
(mono-trichloro) (monopotassium dichloro) di-isocyanurate
A 7.65 gram (0.0593 mole) sample of crude cyanuric acid
prepared from urea assaying 78.9% cyanuric acid, 17.6% am-
melide, 3.4% ammeline and 0.1% melamine was added to 97.4
grams of an aqueous solution containing 13.6 grams potassium
hypochlorite. This addition took place in less than two
seconds. The aqueous solution had a pH value of 10.5 and
a temperature of 35-C. The reaction temperature rose to
55-C and was maintained between 55- and 60-C for two min-
utes. The pH value of the reaction mixture was initially
adjusted to and maintained at 3.7 with 9 grams glacial
acetic acid and 3 grams of 50% sulfuric acid during the
course of the reaction. The reaction vessel was then
quenched in an ice bath and the reaction solution rapidly
cooled to 15-C within two minutes. A white solid precipitate
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was removed from the slurry, washed and dried at 130 C under
20 mm Hg pressure. The precipitate was a mixture of crystal- r
line [(mono-trichloro) tetra-(monopotassium dichloro)] penta-
isocyanurate and (mono-trichloro) (monopotassium dichloro~
5 di-isocyanurate analyzing 70.1% available chlorine. The
total yield was 6.6 grams which is equivalent to 86% re-
covery based on starting triazines.
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