Process for increasing the bleaching efficiency of persalts by using a partially acetylated sucrose as a bleach activator

Described is a process for increasing the bleaching efficiency of an inorganic persalt (peroxide) by adding to said persalt (peroxide) an activating agent comprising acetylated sucrose, the average acetylation degree of said acetylated sucrose being from 4.5 to 7.0.

The present invention relates to a process for increasing the bleaching 
efficiency of an inorganic persalt (peroxide) with respect to textiles or 
other products like paper, cellulose cork, hair etc. Although the 
following description refers to sodium perborate only, the present 
invention can equally be applied to other inorganic persalts (or 
peroxides) normally used in the field of bleaching and of detergency, for 
instance hydrogen peroxide and the alkalimetal percarbonates, 
persilicates, per-pyrophosphates etc. Preferred alkali metals are Na, K 
and Li, particularly Na. 
When an inorganic persalt (peroxide) is used alone, at a temperature equal 
to or higher than 80.degree. C., a very high activity may be observed. At 
a lower temperature, however, for instance 40.degree. C., in the absence 
of activating agents, the persalt (peroxide) efficiency falls to a very 
low level, thus jeopardizing the bleaching results (under the usual bath 
conditions). One class of traditional activating agents is represented by 
the completely acetylated sugars such as, e.g., penta-acetyl-glucose and 
octa-acetyl-sucrose. DE-A-1 246 658 teaches that also the partially 
acetylated sugars can be used, e.g., a disaccharide having three or more 
acetyl groups in the molecule.

In its broadest aspect the present invention relates to a process for 
increasing the bleaching efficiency of an inorganic persalt (or peroxide), 
in particular sodium perborate mono-or tetra-hydrate, by adding to said 
persalt (peroxide) an activating agent comprising acetylated sucrose, the 
average acetylation degree of said acetylated sucrose ranging from 4.5 to 
7.0, preferably from 5.5 to 6.5. 
The partially acetylated sucrose employed according to the present 
invention, hereinafter also referred to as "SUPA", may be prepared by 
deacetylation of octa-acetyl sucrose or of a sucrose having an average 
acetylation degree higher than 7; alternatively, one can directly 
acetylate sucrose or a sucrose having an average acetylation degree lower 
than 4.5. 
For the latter purpose (direct acetylation) one can use, as acetylating 
agent, acetic acid, acetic anhydride, acetyl chloride or ketene, 
preferably in the presence of an organic solvent, and/or a catalyst and/or 
an azeotropic agent (for instance benzene or isobutyl acetate); a 
stoichiometric excess and the temperature are the most important 
parameters for controlling the acetylation degree. 
The de-acetylation, on the other hand, can be carried out, e.g., by 
transesterification with a CH.sub.3 ONa/CH.sub.3 OH mixture, by catalytic 
deacetylation (hydrolysis) on alumina, by saponification (with caustic 
soda), by enzymatic methods or by a combination thereof. The 
de-acetylation (or acetylation) product actually is a mixture of compounds 
having different degrees of acetylation and even if the acetylation degree 
is the same, such compounds are, in turn, mixtures of isomers. Should a 
very narrow distribution be required, the reaction temperature and the 
ratios of the reactants must be controlled very carefully. A selective 
liquid-liquid extraction can provide a deep depuration of the product and 
an extremely narrow distribution around the prefixed (predetermined) 
acetylation degree. The average acetylation degree may be determined in 
several ways, for instance by .sup.1 H-NMR analysis or by titration after 
saponification; the results of the different methods usually show a 
deviation of 1 to 2 units in the first decimal. 
The SUPA employed according to the present invention shows, in contrast to 
other partially or completely acetylated sugars, a bleaching efficiency 
equal to or higher than that of the best activating agent ever known, 
namely TAED (tetraacetyl ethylene diamine), the preparation of said TAED 
being rather complicated. As compared to TAED, SUPA also shows the 
advantage of being recoverable from natural, hence renewable, sources and 
not from compounds directly or indirectly derived from oil. Aiming at a 
better protection of the environment, all this is likely to reduce the 
ecological problems. 
The higher the amount of SUPA (up to the stoichiometric ratio with respect 
to, e.g., perborate), the higher the bleaching efficiency of the 
activating agent added to the persalt (peroxide). Said feature, shared 
with TAED, makes the SUPA particularly suitable for satisfying the demand 
for continuously increasing amounts of activating agents present in the 
bleaching and/or detergent compositions, aiming at an always increasing 
bleaching effect. 
SUPA may be directly added as such to a composition containing the persalt 
(peroxide) or it can be previously mixed with the persalt (peroxide) 
intended for the bleaching process. In the case of granular compositions, 
SUPA may be added in granular form, showing suitable mechanical features 
and a suitable granulometric index. Obviously, the bleaching and/or 
detergent compositions containing SUPA and persalt (peroxide) may also 
contain other usual components, like anionic, non-ionic or amphoteric 
surfactants, neutral salts (for instance sodium sulfate), alkali metal 
salts (for instance sodium carbonate or tripolyphosphate), zeolites, 
carboxymethyl cellulose, perfumes, enzymes etc. The molar ratio of 
acetylated sucrose to persalt (peroxide) usually is from 10:90 to 50:50. 
When the persalt (peroxide) is exploited at a low temperature and for a 
short period of time, the amount of SUPA should preferably be increased. 
The following examples are provided for merely illustrative purpose and do 
not limit in any way the scope of the invention. The SUPA of example 1, 
hereinafter referred to as SUPAM6, having an average acetylation degree of 
6.0 (+/-0.2), was prepared as follows (by de-acetylation): 
1 kg of octaacetyl-sucrose, dissolved in 2.5 liters of toluene, was mixed, 
under stirring (at room temperature and for a few minutes), with a 
methanolic solution of sodium methoxide (concentration=1 g/liter). After 
neutralization on an ion exchange resin (AMBERLYST.RTM. I R 120 H.sup.+) 
the water-soluble acetylated sucroses were extracted by means of deionized 
water. The aqueous layer was concentrated under vacuum, resulting in a 
solid white foam. The organic layer, containing the compounds having the 
uppermost acetylation degree, was recycled, along with fresh octaacet, 
1-sucrose, to a new synthesis cycle. 
The solubility of the different kinds of SUPA in water was evaluated by 
dissolving 3.2 millimoles of SUPA in 250 ml of deionized water at 
60.degree. C., in the presence of 3.2 millimoles of sodium perborate 
tetrahydrate under magnetic stirring (250 rpm), and by measuring the time 
required for obtaining a clear solution. The dissolution times of the 
various products are recorded in the following tables. 
EXAMPLE 1 
An automatic washing machine (IGNIS) was made to run under the following 
conditions: 
washing program at 60.degree. C.; 
linen load: 3 kg of cotton swatch (white and clean) per washing cycle; 
6 g/washing cycle of SUPA-M6 were added, as given in Table 1, to the 
following detergent composition (which was also used in all the other 
examples): 
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sodium perborate tetrahydrate: 
30 g/washing 
detergent base (phosphorus-free, 
114 g/washing. 
free of bleaching agents): 
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Said detergent base contained: 
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(%) (w/w) 
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overall surfactants (linear sodium 
15.4 
dodecylbenzene sulphonate + soap + 
C.sub.13 -C.sub.15 alcohol, ethoxylated with EO) 
zeolite (4.ANG.) 28.6 
sodium silicate (SiO.sub.2 /Na.sub.2 O = 2) 
4.4 
sodium carbonate 16.5 
sodium sulfate 26.5 
carboxymethyl cellulose 
1.2 
antiincrustation copolymers 
4.8 
optical bleaching agents 
0.3 
water up to 100.0 
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For the determination of the bleaching efficiency (bleaching booster 
activity), the clean linen was washed together with 2 samples 
(swatches)/washing cycle, previously stained in a standard way, with red 
wine, by the European Institute of Sankt Gallen (EMPA 114). At the end of 
each washing cycle said 2 samples were dried and ironed; the whiteness 
degree was then measured by means of an Elrepho-Zeiss reflectometer. The 
resulting bleaching percentage (measure of the bleaching efficiency), 
given in Table 1, was determined by the formula: 
EQU bleaching (%)=(A-B)/(C-B).times.100 
where: 
A=whiteness degree of the swatch after the washing; 
B=whiteness degree of the swatch before the washing; 
C=whiteness degree of the swatch completely bleached. 
The whiteness degree of the swatches is expressed as percentage of the 
whiteness degree of MgO, as standard, when measured with a filter No.6 
(wave length=464 nm). The thus obtained percentage (69.5%) is given in 
Table 1, along with the results of the other examples. 
EXAMPLES 2 AND 3 
Example 1 was repeated by respectively increasing the amount of activator 
(SUPA-M6) to 12and 18 g/washing cycle, as given in Table 1 which also 
shows the obtained results. 
EXAMPLES 4 TO 6 (COMATIVE) 
Examples 1 to 3 were repeated, replacing SUPA-M6 by an equal amount of 
completely acetylated sucrose (M8); the results, given in Table 1, clearly 
show that a complete acetylation of sucrose, contrary to the common 
knowledge (until now), results in a sharp decrease of the bleaching 
efficiency. 
EXAMPLES 7 AND 8 (COMATIVE) 
Example 1 was repeated, replacing SUPA-M6 by an equal amount of activators 
consisting of sucrose at different acetylation levels, also obtained by 
de-acetylation of octa-acetyl-sucrose; the results are shown in Table 2. 
EXAMPLES 9 AND 10 
Example 1 was repeated, replacing SUPA-M6 by an equal amount (6 g/washing 
cycle) of two kinds of partially acetylated sucrose, having respectively 
an average acetylation degree of 5.5 and 6.2, obtained by direct 
acetylation (at 0.degree. C., for 6 hours and under stirring of a solution 
of sucrose (10 kg) in pyridine (150 liters))with acetic anhydride (16.5 
liters), followed by neutralization and solvent evaporation under vacuum. 
Data and results are given in Table 3 and FIG. 2. 
TABLE 1 
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ACTIVATOR AMOUNT 
(g/washing cycle) 6 12 18 
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BLEACHING (%) 
OBTAINED WITH THE FOLLOWING 
ACTIVATORS 
SUPA-M6 (Examples 1-3) 69.5 72.7 76.0 
(dissolution time: 5 min.) 
OCTAACETYL-SUCROSE 64.2 65.4 67.0 
(Examples 4-6)(*) 
(dissolution time: longer than 30 
minutes) 
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(*)comparative 
TABLE 2 
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Bleaching 
EX. ACTIVATOR (%) 
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1 SUPA-M6 69.5 
7(*) TETRAACETYL-SUCROSE (SUPA-M4) 
64.8 
(dissolution time: 2 min.)(**) 
8(*) NO ACTIVATOR ( blank; not 54.9 
activated perborate) 
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(*)comparative 
(**)Average acetylation degree = 4.0 (+/- 0.2) 
Results are graphically represented = in FIG. 1. 
TABLE 3 
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EX. ACTIVATOR Bleaching (%) 
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1 SUPA-M6 69.5 
9 SUPA-M5.5 68.5 
(dissolution time: 5 min.) 
10 SUPA-M6.2 69.3 
(dissolution time: 5 min.) 
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