Investigations into the efficacy of methyhlphosphonic acid functionalised 1,4,7-triazacyclononane ligands in bleaching catalysis
2007
Shastri, Kirtida | Cheng, Eileen W. C. | Motevalli, Majid | Schofield, John | Wilkinson, Jennifer S. | Watkinson, Michael
In an attempt to reduce the dye and fabric damage caused by manganese complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane previously employed as low temperature bleaching catalysts in domestic laundry formulations, a novel series of analogues with chelating phosphonic acid pendant arms has been prepared. In order to identify possible bleaching catalysts more rapidly, and with reduced environmental impact, a bleaching screening test has been developed that seeks to identify metal–ligand combinations that may represent active low temperature bleaching catalysts. Of the four methylphosphonic acid containing ligands tested in combination with a range of transition metal salts, only two metal–ligand combinations with manganese salts displayed sufficient activity to take forward for further testing, with the efficacy of the ligands in the oxidative removal of stains decreasing as the number of pendant arms increased. Both of the active ligand systems produced greater dye damage than existing bleach activators, with the ligand with a single methylphosphonic acid pendant arm being particularly aggressive towards stained fabrics sensitive to oxidative damage. This indicates that the systematic addition of chelating pendant arms, whilst tempering the activity of the complexes as bleaching catalysts, unfortunately does not provide a solution to the problem of dye and fabric damage. In contrast to the activity observed in the bleaching screen, the activity of the manganese–ligand combinations in the epoxidation of some alkene substrates was found to bear no relation to the number of methylphosphonic acid pendant arms.
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