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Description  |
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The present invention relates to bleaching agents and processes for
bleaching.
According to the present invention there are provided bleaching agents
having the general formula:
##STR1##
wherein p.gtoreq.2 and p+c.gtoreq.3, or anions thereof, the benzene
nucleus being optionally substituted by a lower alkyl, chloro or nitro
group.
According to a second aspect of the present invention there is provided a
process for bleaching with an aqueous solution of a peroxyacid of general
formula:
##STR2##
where p.gtoreq.2 and p+c.gtoreq.3, or anions thereof, the benzene nucleus
being optionally substituted by a lower alkyl, chloro or nitro group.
Preferably, the compounds have the general formula:
##STR3##
wherein p.gtoreq.3 or anions thereof, the benzene nucleus being optionally
substituted by a lower alkyl, chloro, or nitro group. As the number of
peroxycarboxy groups substituted in the benzene ring increases, we have
found that the stability of the compound tends to decrease. In
consequence, the peroxyacids according to the present invention preferably
contain no more than 4 peroxyacid groups.
One use of the bleaching agents described herein is in removing stains from
textile fabrics. We have found that aromatic peroxyacids containing at
least two peroxycarboxy groups and one or more carboxy groups tend to be
less effective stain removers in alkaline solution than the corresponding
peroxyacids which do not contain carboxy groups in that a given
concentration of the carboxy-free compound tends to effect a higher %
stain removal than the corresponding carboxy containing compound. Although
we do not wish be bound by any theory, we believe that this phenomenon may
be caused by electrostatic repulsion between the bleaching species and the
negatively charged fabric surface. Carboxy groups have in general a much
lower pKa than the peroxycarboxy groups, and hence at any given pH a
higher proportion of carboxy groups will be ionised than is the case for
the corresponding peroxycarboxy groups. Thus, the tendency of the molecule
to be negatively charged increases as the proportion of carboxy groups
increases, and hence the degree of repulsion between bleaching species and
cloth increases. In consequence, preferably, the number of peroxycarboxy
groups at least equals the number of carboxy groups. In several highly
desirable embodiments the peroxyacid does not contain any carboxy groups.
Suitable peroxyacids include diperoxypyromellitic acid (1,4-and
1,3-isomers), diperoxyprehnitic acid (1,4-and 1,3-isomers),
triperoxytrimellitic acid, triperoxytrimesic acid, triperoxyhemimellitic
acid, tetraperoxypyromellitic acid and tetraperoxyprehnitic acid.
The peroxyacids described herein can be intimately contacted with a
desensitising amount of a desensitising diluent, i.e. an amount which
reduces the impact sensitivity sufficiently to render the composition
non-hazardous. In a standard drop weight test, 30 mg of material, which
has been sieved to finer than 710 microns, is placed on an anvil in the
apparatus. The anvil is centred and the sample tamped lightly by a force
of 5 Kg-cm. A weight is then dropped several times from a given height,
each time onto a fresh sample, and its effect observed. A positive result
can range from being merely a discoloured product, through emission of a
cloud of smoke, to, in an extreme case, an explosion. Tests are carried
out at a series of heights. A higher proportion of positive results occur
when a greater force is employed. The figure usually quoted is the median
point, i.e. the point at which 50% of the results at a given force are
positive. Compositions having a median point of at least 200 kg.cm are
considered to be non-hazardous, but to provide a greater margin of safety
compositions preferably have a median point of at least 300 kg.cm.
Generally the amount is within the range 0.5 to 10 parts by weight of
diluent per part of peroxyacid. Suitably the desensitising diluent can be
selected from hydrocarbons having melting points in excess of 30.degree.
C., e.g. microcrystalline waxes, aliphatic fatty acids e.g. lauric and
stearic acids, aromatic acids e.g. benzoic acid, alkyl e.g. t-butyl esters
of the aliphatic or aromatic acids, protein or starch materials boric acid
and especially alkali and alkaline earth metal salts or halogen-free acids
having a first dissociation constant of at least 1.times.10.sup.-3, e.g.
sodium sulphate, magnesium sulphate and sodium tripolyphosphate. The
intimate contact can be by way of admixing particles of the diluent with
the peroxyacid or by granulating or coating the peroxyacid with the
diluent. More than one diluent may be employed, conveniently first
contacting the peroxyacid with an unreactive diluent described
hereinbefore, and then coating the mixture with a second diluent. Such
second diluent can be selected from fatty acid alkanolamides, fatty
alcohol polyglycol ethers, polyglycol/polypropylene oxide polymers alkaryl
polyglycol ethers, polyethylene glycol and fatty acid esters and, amides
thereof, and esters and amides of glycerol and sorbitol, polyvinyl
alcohol, polymethyl methacrylate, dextrin, starch, gelatin carboxymethyl
methacrylate, solid hydrocarbons, aliphatic fatty acids, fatty alcohols,
sodium sulphate and magnesium sulphate. "Fatty," in the terms "fatty
alcohol" and "fatty acid," is used to denote at least 12, desirably from
12 to 26 carbon atoms in the longest chain. Normally the amount of coating
is within the range of 3% to 35% by weight based on the weight of the
coated product. Peroxyacids thus coated are less prone to decomposition
when stored in contact with alkaline surfactants, such as sodium salts of
alkyl benzene sulphonates, which are commonly employed in detergent and
bleaching compositions.
One convenient method of providing a desensitised composition suitable for
incorporation in a detergent composition and substantially isolated from
alkaline surfactants is to form a mixture of particulate peroxyacid with a
particulate inorganic diluent such as sodium sulphate or tripolyphosphate
or magnesium sulphate into tablets or extrudates. Such tablets or
extrudates by themselves effectively reduce the surface of diacyl peroxide
presented to the alkaline surfactants, and thus alleviate the problem of
loss of active oxygen during storage. The problem can be further
alleviated by providing an outer layer around the tablets or extrudates
comprising at least one of the compounds described in the immediately
preceding paragraph, generally in an amount of up to 20% by weight.
Alternatively any suitable organic compound described hereinbefore may be
formed into a sachet within which a desensitised composition can be
placed.
Detergent or bleaching compositions containing the peroxyacids also contain
a surfactant and a builder salt, often contain a processing additive and
detergent adjuncts such as organic sequestrants e.g. EDTA, peroxyacid
stabiliser e.g. dipicolinic acid, antiredeposition agents, perfumes,
optical brightening agents and inorganic active oxygen-containing
compounds, hereinfter called persalts, which generate perhydroxyl ions in
aqueous solution, such as sodium perborate tetrahydrate or sodium
percarbonate (the commercially available hydrogen peroxide addition
product).
Suitable builder salts can be either organic, for example,
aminopolycarboxylates, organic polyphosphates, sodium citrate or sodium
gluconate, or inorganic, for example, alkali metal carbonates, silicates,
phosphates, polyphosphates or aluminosilicates. Typically, builders are
present in proportions of from 1% to 90% by weight. Such compounds alter
the pH detergent/bleaching solutions. Preferably sufficient builder salt
is used to obtain a solution having a pH in the range of from pH 7 to 11,
more preferably from pH 8 to 11.
A typical processing aid is sodium or magnesium sulphate which is
conveniently incorporated in detergent or bleaching compositions in an
amount of from 1 to 40% by weight.
Where some builder salt or processing aid has been used to desensitise the
diacyl peroxide the amount so used is included in the total amount of
builder salt or processing aid present in the composition.
The surfactants may conventionally be water-soluble anionic, non-ionic,
ampholytic or zwitterionic surface active agents. Suitable surfactants are
often selected from acids and their alkali metal salts, alkyl sulphonates,
alkylated aryl sulphonates, especially linear alkyl benzene sulphonates,
sulphated aliphatic olefins, sulphated condensation products of aliphatic
amides and quaternary ammonium compounds. The surfactants are normally
present in the detergent composition in amounts of from 1% to 90% by
weight, often in a weight ratio to the builder salts of from 2:1 to 1:10.
The bleaching composition can include any compound or compounds which
enhance the bleaching or washing activity of organic peroxyacids, such as
ketones and aldehydes as described in U.S. Pat. No. 3,822,114 or certain
quaternary ammonium salts as described in British Pat. No. 1,378,671, both
to Proctor & Gamble.
Generally, bleaching solutions containing the peroxyacids contain at least
1 ppm available oxygen "av. ox" and for use in washing textile fabrics
e.g. cotton or polyesters often from 5 to 200 ppm. Solutions for cleaning
hard surfaces such as metal, plastic or wooden surfaces can contain from
200 ppm to 500 ppm "av.ox". Peroxyacid solutions described herein can be
used to bleach textile fabrics, wood and pulp and under the conditions,
and employing the equipment, used for bleaching with hydrogen peroxide or
inorganic peroxoacids.
Suitably, bleaching with the peroxyacids described herein can take place at
an ambient temperature or higher, conveniently from 20.degree. to
60.degree. C. or from 25.degree. C. to about 60.degree. C. In general, the
bleaching is effected at a controlled pH of about 8.5 to 11.5, Suitably
the solutions can be produced by dissolving appropriate amounts of the
detergent or bleaching compositions described hereinbefore.
Where the molecule contains an intramolecular acyl peroxide linkage, it is
preferable that the molecule should be used in conjunction with, and the
bleaching composition contain, at least one of the said persalts,
preferably in a ratio of from 1:2 to 2:1 molecules of persalt per acyl
peroxide linkage, and advantageously 1:1.
Peroxyacids described herein free of carboxy groups can be obtained by
oxidising the appropriate acid with hydrogen peroxide in non-aqueous polar
solvents e.g. methane sulphonic acid. In view of the inclusion of several
atoms of active oxygen per molecular it is advised that great care be
taken in the preparation. It is to be understood though, there where two
acid groups are ortho, there is a tendency for an internal acyl peroxide
to be formed instead of two peroxyacid groups, and that in consequence the
full peroxyacid is generated, in situ, by perhydrolysis of the acyl
peroxide. Thus oxidation of trimesic acid in methane sulphonic acid at
approximately 30.degree. C., with excess hydrogen peroxide produces
triperoxytrimesic acid, but under similar conditions oxidation of
pyromellitic acid produces a compound believed to contain two intra acyl
peroxide linkages.
Peroxyacids containing one or more carboxyl groups can be obtained by
protecting the carboxyl groups before oxidation, and employing slightly
gentler oxidative conditions. Alternatively where it is desired to obtain
a mixed carboxyperoxycarboxy compound where a peroxycarboxy group is
orthoto a carboxy group the preparation can be effected by reacting the
appropriate anhydride with hydrogen peroxide in aqueous conditions.
Specific embodiments of the present invention will now be described more
fully by way of example.
The effectiveness of bleaching agents according to the present invention is
compared with a conventional inorganic bleaching agent by washing stained
fabrics with 1 liter water containing 4 gms of a detergent composition
comprising linear alkyl benzene sulphonate 15%, sodium tripolyphosphate
37%, sodium silicate 6%, coconut monoethanolamide 3%, sodium
carboxymethylcellulose 1.5%, water 6% and balance sodium sulphate, the
percentages being by weight, and sufficient active oxygen containing
compounds to yield 10 ppm active oxygen in solution. The washing is
carried out at a temperature in the range of 30.degree., to 60.degree. C.
and at a pH of 9. The active oxygen containing compounds consist of (a)
sodium perborate tetrahydrate, (included for comparison) (b)
triperoxytrimesic acid. The fabrics comprise cotton or polyester cotton
mixture, and the stains are conventional household stains. The stain
removal is measured and broadly it is found that the order of stain
removal is (b)>(a) in the temperature range of 30.degree. to 60.degree. C.
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Description |
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