Note: Descriptions are shown in the official language in which they were submitted.
094/2~00 ~1~ 6 ~ 7 0 PCT~4100~5
BLEACHING AGENTS
Field of the invention.
This invention is concerned with organic peroxyacids
and their manufacture. The invention is particularly con-
cerned with the stability of said organic peroxyacids.
Backqround of the invention.
It is well known that organic peroxyacids are able to
function as bleaching agents in a detergent composition.
Organic peroxyacids which have been proposed for such use
include peroxybenzoic acid, peroxyphthalic acid, isomers and
substituted derivatives thereof, peroxyalkanoic acids and
15 diperoxyalkanedioic acids such as diperoxyazelaic acid and
diperoxydodecanedioic acid. Discussion of such acids can be
found in US Patents 4,100,095, 4,170,453 and 4,325,828 as
well as numerous other documents. Another series of acids
which have been proposed are phthalimido substituted
20 peroxyalkanoic acids disclosed in EP-A-325288.
Amidoperoxyacids which contain a polar amide linkage part
way along a hydrocarbon chain have been disclosed in US
Patents 4,634,551 and 4,686,063.
25 An obstacle to the commercial utilization of organic
peroxyacids is various problems of stability. US Patent
4,170,453 recognises and discusses separate categories of
instability problem. One is instability of the peroxyacid
when subjected to heat (or to friction or shock which give
30 rise to local heating), another is storage stability of the
peroxyacid prior to use and a third problem concerns
stability of a peroxyacid-containing wash liquor. It is
well known that peroxyacids are inherently unstable and
capable of undergoing an exothermic decomposition if heated
35 or, in many instances, if handled in such a way that heat is
generated by application of force, e.g. as a result of
friction or impact. This form of instability is more
W094/2~00 ~ PCT~4/~5
pronounced for compounds with higher proportions of
available oxygen.
W0 90/07501 (Interox) describes the variation in stability
of peroxyacids according to features of their structure.
This document teaches that phthalimido peroxyacetic acid is
somewhat explosive whereas longer chain homologues are
relatively more stable.
Storage stability has been presented in the prior art as a
somewhat different problem. ~f course, a material which
undergoes abrupt exothermic decomposition is not displaying
stability in storage but even without such decomposition a
peroxyacid may undergo progressive decomposition during
storage as a result of reaction with impurities or other
materials with which it has been mixed.
It has been recognised that transition metal ions can
catalyse unwanted decomposition of peroxyacid compounds and
it has, therefore, been proposed to mix peroxyacid com-
pounds with chelating agents to enhance storage stabilityof organic peroxyacid-containing compositions and/or
stabilise the wash liquor against unwanted decomposition of
the peroxyacid. Inter-alia such use of chelating agents is
disclosed in US Patents 4,170,453 and 4,100,095. This
disclosure is also reviewed in EP-349220.
In contrast with such problems of storage stability, the
prior art has treated the exothermic decomposition of
peroxyacids initiated by heat as unavoidable. Thus US
Patent 4,100,095 explains that there is a temperature
called the self-accelerating decomposition temperature, at
which the exothermic decomposition of organic peroxyacid
can become a runaway reaction leading to the generation of
sufficient heat to cause ignition. It is pointed out that
such decomposition can be initiated by point sources of
heat such as friction.
215~1 7~
094/206~ PCT~4/00~5
3 -
In order to control this hazard it is taught that theperoxyacid should be mixed with a so-called exotherm
control agent which undergoes an endothermic decomposition
when heated. Consequently in the event of some local
heating of the composition, the heat liberated by decom-
position of the peroxyacid is taken up by endothermic
decomposition of the exotherm control agent and runaway
decomposition is prevented.
Consistent with these understandings, the prior art has
disclosed that organic peroxyacids may be incorporated into
compositions which contain only a minority proportion of
peroxyacid and which also contain a chelating agent for
sequestering transition metal ions, this chelating agent
being incorporated for the purpose of promoting storage
stability of the peroxyacid and/or stability of the
peroxyacid in a wash liquor during use. Examples of such
compositions are disclosed in US Patents 4,091,544 and
4,170,453.
European published application 349220 is concerned with
amidoperoxyacids which contain an amide link in a hydrocar-
bon chain. This Patent teaches that the storage stability
of these peracids can be improved considerably by washing
the peracids with phosphate buffer and leaving some
phosphate in contact with the peracid after washing. It is
pointed out that the amidoperoxyacids are acid sensitive
and this beneficial effect of phosphate buffer is prin-
cipally attributed to neutralisation of residual strong
acid left from the reaction in which the amido peroxyacid
is prepared. The phosphates which are used may be or-
thophosphates or pyrophosphates or a mixture of the two.
Such phosphates have the ability to sequester transition
metal ions. However, in this prior document they are
relied upon for buffering ability and it is suggested that
additional chelating agents may be incorporated to further
promote storage stability.
to ~ 3% by weight of the binding agent, as calculated on
W094~ PCT~4/00~5 ~ j
~1S~17~ 4
Thus the teaching of the prior art is that storage
stability of organic peroxyacids and compositions con-
taining them can be promoted by measures which include the
incorporation of chelating agents. However, no measures
are proposed to counteract the exothermic instability
initiated by heat or pressure apart from the incorporation
of a so-called exotherm control agent to prevent local
thermal decomposition from becoming a runaway reaction.
Definition of the invention
In radical contrast with this established view, we have
found that the thermal instability of peroxyacids made by
conventional methods can be beneficially modified.
Broadly, we have found that by contacting a peroxyacid with
a binding agent for transition metal ions it is possible to
raise the temperature at which thermal decomposition oc-
curs.
Accordingly in a first aspect the present invention
provides the use of a binding agent for transition metal
ions to enhance stability of a substantially water-in-
soluble organic peroxyacid against exothermic decomposition
initiated by heat.
In a second aspect this invention provides a composition
comprising from 80 to 99.9% by weight of a substantially
water-insoluble organic peroxyacid mixed with from 0.1 to
20% by weight of a binding agent for transition metal ions,
which binding agent and peroxyacid are stable in the
presence of each other, with the proviso that the
peroxyacid does not includes an amide linkage.
The improvement in stability when an organic peroxyacid is
in contact with a binding agent for transition metal ions
can be observed by differential scanning calorimetry (DSC)
which shows the temperature or temperature range over which
exothermic decomposition occurs. In general, bringing an
organic peroxyacid into contact with a binding agent in
3S~2 (~)
t ~ t ~ ~ 5 '
s ` ~ 7 C
accordance with this invention leads to a composition in
which the temperature of thermal decomposition has
increased. The decomposition may also occur over a
temperature range of different width. Thus, differential
scanning calorimetry may show an increase in the
temperature at which maximum decomposition occurs and/or an
increase in the temperature at which decomposition be~ins.
The outcome of a DSC measurement will show these results as
a shift in the position of a peak, or as a shift in the
base of the peak at its lower temperature side, respec-
tively.
Bringing an organic peroxyacid into contact with a binding .
agent for transition metal ions can be done in various
ways.
One possibility is simply dry-mixing the two materials in
solid form to obtain a mixture containing from 80 to 99.9%
by weight of the peroxyacid.
Another possibility is to wash a substantially water-in-
soluble peroxyacid with a solution or suspension of thebinding agent and leave from 0.3 to 3% by weight,
prefera~ly from 1 to 2% by weight, more preferably from 1
to 1.5% by weight, of the binding agent, as calculated on
the total weight of peroxyacid and binding agent, in con-
tact with the peroxyacid. The final pH of the thus obtainedmaterial is in the range of from 3.5-6.0, more prefera~ly
of from 4-5.
Thus a third aspect of this invention provides a process
for enhancing the thermal stability of a substantially
water-insoluble organic peroxyacid which does not include
any amide linkage, comprising washing the peroxyacid with
an aqueous solution or suspension of a binding agent for
transition metal ions under conditions such that from 0.3
to ~ 3% ~y weight of the binding agent, as calculated on
the total weight o~ ~inding agent and peroxyacid, remains
in contact with the peroxyacid and a final pH of from 3.5-
AM~NI~ED S~ET
W094/20600 PCT~4/0~5 ~
2~ ~ li 7~ -
6.0 is obtained.
A preferred possibility is to precipitate the organic
peroxyacid in the presence of the binding agent, such that
0.3-3% by weight, preferably 1-2% by weight, more
preferably 1-1.5% by weight of the binding agent, as cal-
culated on the total weight of peroxyacid and binding
agent, remains in contact with the peroxy acid. The final
pH of the thus-obtained material is in the range of from
3.5-6, preferably from 4-5. This leads to a beneficial
enhancement of stability, and moreover it is then possible
to wash the peroxyacid further without losing the enhanced
stability. Thus, a composition obtained in this way is
more robust than compositions obtained in other ways.
Therefore, a fourth aspect of this invention provides a
process for enhancing the stability of a substantially
water-insoluble organic peroxyacid which comprises
precipitating the peroxyacid in the presence of a binding
agent for transition metal ions such that 0.3 - 3.0% by
weight of the binding agent, as calculated on the total
weight of binding agent and peroxyacid, remains in contact
with the peroxyacid and a final ph of from 3.5 - 6.0 is
obtained.
This preferred process can be carried out as a step in the
conventional procedure by which a peroxyacid is made. This
procedure consists of oxidising the appropriate carboxylic
acid with hydrogen peroxide in a strong acid medium, and
then quenching the reaction. Conventionally this quenching
has been done by running the reaction mixture into ice and
water. In order to implement the preferred process of the
invention the reaction mixture is run into an aqueous
solution containing a precursor for the binding agent.
Another, possible way to implement this invention is to
dissolve the peroxyacid in an organic solvent,
(dichloromethane for instance) and wash the solution with
21~6~7~
0g4/206~ ~ , , ! PCT~4/00
an aqueous solution of the binding agent before separating
the peroxyacid from the organic solvent. A suitable a-
queous solution of binding agent would be phosphate buffer
at about pH 4.
Yet another way to use a binding agent to enhance the
stability of an organic peroxyacid is to bring the binding
agent into contact with an organic acid and then use the
resulting acid as the starting material for making the
corresponding peroxyacid.
Thus a process for enhancing the stability of an organic
peroxyacid may comprise either
(i) washing the corresponding acid with an aqueous solution
of a binding agent for transition metal ions under con-
ditions that 0.3-3% by weight of the binding agent remains
in contact with the acid, or
(ii) precipitating the corresponding acid in the presence
of a said binding agent for transition metal ions, and then
(iii) oxidising the acid from step (i) or step (ii) to the
peroxyacid.
As a result of the above-indicated processes of the inven-
tion, a particulate composition is effectively obtained,
said composition comprising particles of the organic
peroxyacid with the binding agent trapped in said par-
ticles.
The bindinq aqent
Suitable binding agents should not react to any substantial
extent with the peroxyacid, under conditions to which they
are exposed. Thus for example, ethylene diamine
tetraacetic acid is oxidised by peroxyacids in solution and
so would not be suitable, except for use by mixing with dry
solid peroxyacid.
The binding agent may possibly form an insoluble salt with
at least one transition metal or may function by forming a
W094/20600 2 1 5 61.7~ 8 PCT~4/00~5 ~
co-ordination complex with at least one transition metal
ion. Thirdly the binding agent may bind to transition
metal sites in impurity particles present in colloidal
suspension.
It is generally desirable that a binding agent should have
good affinity for one or more transition metal ions, e.g.
for ferric ion which is a likely trace contaminant.
The affinity of a complexing agent L for a metal ion M can
be expressed by the equilibrium constant for the complex
forming reaction
nL + M MLn
The equilibrium constant R is given by
K = [MLn]
[L] n tM]
where [MLn] ~L] and tM~ are the concentrations of the co-
ordination complex, the free complexing agent and the free
metal ion in aqueous solution under specified conditions of
t~mr~rature and ionic strength, e.g. 25C and zero ionic
strength.
Such an equilibrium constant is also referred to as the
stability constant for the complex. It may be the overall
equilibrium constant for the formation of a complex through
several steps in sequence, or the equilibrium constant for
a single step reaction.
For this invention, a binding agent which forms a co-or-
dination complex should preferably form a complex with at
least one transition metal ion with a stability constant K
of at least 1o6 in aqueous solution at 25C and at zero
ionic strength.
Numerous stability constants are recorded in the scientific
~o g4/2~ 9 ~ 1 7D PCT~4/00~5
literature. Two compilations of such data are:
Stability Constants of Metal Ion Complex, IUPAC Chemical
Data Series No. 21, and
Critical Stability Constants by Arthur E Martell and Robert
M Smith.
Preferably a complexing agent forms such a co-ordination
complex with at least one transition metal ion, significant
examples of which are the ions of iron, manganese, cobalt,
nickel, zinc and copper. More preferably the complexing
agent forms such a complex with at least Fe3+.
Binding agents for transition metals which are suitable for
the present invention include dihydrogen orthophosphate,
pyrophosphate, polyacrylate, titanium chloride, stannic
salts, and stannous salts. The effectiveness and hence the
suitability of a binding agent can be assessed by differen-
tial sc~nning calorimetry as mentioned further below.
The preferred binding agent is dihydrogen orthophosphate.
The peroxyacid
The present invention is applicable to substantially water-
insoluble organic peroxyacids, having a solubility between
O.1 and 5 mmol in water at ambient temperatures and a pH of
from 3.5-6. As indicated above, a wide variety of such
acids are known.
Peroxyacids which are particularly envisaged include
phthalimido-substituted peroxyalkanoic acids of formula
o
Il
~ N - R - CO3H
Il
O
where R is an arylene or alkylene group of up to lO carbon
~ 7~ 10 PCT~4/00~5
atoms, notably alkylene of 2 to 7 carbon atoms.
Other categories of peroxyacids are the diperoxy alkane
dioic acids of formula
HO3C-R-CO3H
and peroxyalkanoic acids of formula
CH3-R-C03H
wherein, in either case, R denotes an alkylene group of 2
to 18 carbon atoms especially 2 to 12 carbon atoms, op-
tionally incorporating a heteroatom in the carbon chain,
such as the nitrogen atom of an amide linkage.
Another category is the corresponding aromatic acids in
which R denotes an arylene group, e.g. perbenzoic acid,
substituted perbenzoic acid and diperoxyisophthalic acid.
The production of peroxyacids may be carried out by
known methods. Preferred is the oxidation of the cor-
responding organic acid using hydrogen peroxide in an acidmedium, notably an organic sulphonic acid such as
methanesulphonic acid or a mineral acid such as sulphuric
acid.
When the reaction medium comprises a mineral acid,
such as sulphuric acid, all or part of it can be premixed
with the hydrogen peroxide to form an equilibrium mixture
containing for example permonosulphuric acid that can
itself perform the peroxidation reaction. Such pr~ ;ng
separates the exothermic dilution/reaction between hydrogen
peroxide and sulphuric acid from the peroxidation reaction.
The stability of a sample of a peroxycarboxylic acid
can be assessed by differential scanning calorimetry (DSC).
In this technique a sample is heated steadily and the heat
input rate is monitored. An endothermic transition, such
as melting, appears as a peak in the heat input rate at the
7 ~
~ 094/20600 PCT~4/00465
11 , . .
melting temperature. Exothermic decomposition appears as a
drop in heat input. The results are normally shown by
means of a recording pen which draws a graph of neat input
against temperature.
WOg4/2~ 1 ~ 12~'
EXAMPLES
The invention will be explained and demonstrated
further by the following Examples which refer to the
drawings. All of the drawing figures reproduce the print-
out from a differential scanning calorimeter and are thus agraph of heat input rate against temperature for a sample
of material.
ExamPle 1
A phosphate buffer solution was prepared by dissolving 14
grams analytical grade sodium dihydrogen orthophosphate in
1 litre of deionised water. The acidity of the buffer
solution was measured and found to be pH 4.5.
A commercial sample of diperoxydodecanedioic acid,
determined by analysis to be substantially pure, was inves-
tigated by DSC. The resulting print-out is reproduced as
Fig. 1. As can be seen the material showed a strong
exothermic decomposition at approximately 83C.
1 gram of this peroxyacid was mixed with 20 ml of the
phosphate buffer solution and stirred at 60OC for 1 hour.
After this the water-insoluble acid was filtered off and
dried in air at 20C. It was then again investigated by
DSC and the resulting print-out is reproduced as Fig. 2.
As can be seen from this figure there was a remarkable
change. The sample displayed an endothermic transition
between 90 and 100C, attributed to melting and the
exothermic decomposition took place at temperatures in
excess of 100C.
ExamPles 2.1-2.4
The thermal stability of several other types of peroxyacids
was investigated using the same testmethod as used in
Example 1. By applying DSC measurements, exothermic decom-
position temperatures could be found for these peroxyacidsbefore and after washing them with the phosphate buffer
solution. The results are shown in Table 1
W094/2~00 ~ ¦~gl 7 ~ PCT~4/00
13
TABLE 1
Example Type of peroxyacid Exotherm.decomposition
no. temperatures (C)
before wash after wash
2.1 Pernonanoic acid 55 125
2.2 Perbenzoic acid 102 114
10 2.3 p-sulphonated
perbenzoic acid 199 220
2.4 m-chloro-perbenzoic acid 91 110
It can be seen that in all above cases a significant
increase of the decomposition temperature occurred after
washing with the phosphate buffer solution.
Example 3
Phthalimido-6-peroxyhexanoic acid was prepared by a
method similar to Example 1 in WO 90/07501 but with the
procedure for working up the reaction modified to embody
the present invention, as follows:
Phthalimido-6-hexanoic acid (2g) was added to stirred
methanesulphonic acid (lSmls = 22.29) in a beaker, forming
a solution therein. The mixture was cooled to below 5C in
a water/ice bath. 85% by weight aqueous hydrogen peroxide
(approx 80% w/w) was added with continuous stirring into
the reaction mixture progressively during a period of about
S to 10 minutes while keeping the temperature below 5C,
until a total amount of 3.5 moles per mole of carboxylic
acid has been introduced, i.e. a 2.5 molar excess compared
with the stoichiometric amount. The reaction mixture was
then stirred for a further 50 minutes.
At the end of this time the reaction mixture was poured
W094/20600 ~ 7~ PCT~
into a stirred, ice cold solution consisting of 30 grams
disodium hydrogen orthophosphate dissolved in 750 grams
demineralised water. Before addition this solution was at
approximately pH 8.0 and at the end of the addition the pH
had dropped to between pH 4.0 and pH 4.5.
The desired peroxyacid precipitated from the solution and
was washed with an aqueous solution containing 13g/l
NaH2PO4, pH 4.5, and collected by filtration. The filter
cake was allowed to dry in air and ~x~;ned by DSC. The
resulting print-out is reproduced as Fig. 3. This showed
endothermic melting at about 90C followed by exothermic
decomposition reaching a peak at approximately 165C.
Some of the peroxyacid prepared in this way was washed with
demineralised water before drying and DSC. The print-out
from that DSC is reproduced as Fig. 4. This showed very
little change from the acid which had not been washed with
water. This indicates that when the peroxyacid is
precipitated in the presence of a binding agent for tran-
sition metals, the stabilisation effect is not dependent on
binding agent which is merely adsorbed at the surface of
the particles of the acid.
Example 4
A commercial sample of phthalimido-6-peroxyhexanoic acid
was investigated by DSC. The resulting print-out is
reproduced as Fig. 5. This sample contained about 5% of
the corresponding phthalimido hexanoic acid. It can be
seen that this sample showed endothermic melting between
about 80 and 90C followed by exothermic decomposition
reaching a maximum at about 125C.
A sample of this peroxyacid was purified to ap-
proximately 98% purity by dissolving 5g of the peroxyacid
in 150ml dichloromethane, then washing the solution with
two 50ml quantities of aqueous Na2HP04 buffer solution at
~1~6170
094/2~ PCT~4/00~5
pH 8.5, then washing with water and drying over sodium sul-
phate. After this the peroxyacid was recovered by
evaporating the organic solvent. Thus purified acid was
again investigated by DSC. The print-out is reproduced as
Fig. 6 which shows rapid decomposition sharply following
the onset of melting at about 9OC. Recrystallization from
acetonitrile produced a purer peroxyacid which was even
less stable.
A 1 gram sample of the commercial peroxyacid was
washed with 20ml phosphate buffer at pH 4.5 in the same
manner as in Example 1. After drying the phosphate-washed
acid it was investigated by DSC.
The resulting print-out resembled Fig. 3. It again
showed endothermic melting at about 9OC followed by
exothermic decomposition. This reached a peak at ap-
proximately 155C, which was slightly lower than
in Fig. 3.
When a sample of the peroxyacid was washed with
phosphate buffer as just described and then washed again
with demineralised water and dried the resulting acid was
much less stable, decomposing exothermically at ap-
proximately 9OC. This indicates that the stabilisation isbrought about by orthophosphate which has remained mixed
with the peroxyacid, presumably adsorbed on the surface of
peroxyacid particles.
Example 5
Phthalimido-6-peroxyhexanoic acid purified as in
Example 3 was mixed, dry, with sodium dihydrogen phosphate
in an acid:phosphate weight ratio of 8:2. The resulting
mixture was then examined by DSC and the trace is
reproduced as Fig. 7. Comparison with Fig. 6 shows that
the sharp exothermic decomposition peak shown in Fig. 6 has
been transformed into a broader peak extending from ap-
W094/20600 ^ ~1 $61 7~ 16 PCT~W4/00465
proximately 100 to 160C with a maximum at about 140C.
ExamPle 6
The previous Example was repeated using polyacrylic
acid in place of sodium dihydrogen phosphate. The resul-
ting DSC trace is reproduced as Fig. 8. Once again the
exothermic decomposition has been transformed from the
sharp peak below 100 seen in Fig, 6 into a broad band
extending over a temperature range.
