The summer of 1994 saw an amazing media war between Unilever and Proctor & Gamble (P&G), the two leading detergent manufacturers. Unilever announced their new Persil PowerTM, with a new manganese accelerator to improve bleaching at lower temperatures. The launch was backed by a massive advertising campaign costing more than the development costs. P&G responded to the threat to their market share by publishing 'knocking copy', which claimed that the new washing powders produced holes in one's boxer shorts. Unilever cried foul and denied the allegations, but soon changed their formulation anyway. The battle dragged on through the summer and autumn and eventually Unilever conceded defeat: the 'miracle' manganese compound did indeed attack certain dyes under extreme conditions, putting holes in boxer shirts and blouses alike, and Unilever had to withdraw it from the market. They lost market share, the investment in R&D ,in manufacture and in marketing the product was lost and it had a substantial effect on Unilever's 1994 balance sheet. And, interestingly, there was an Irish connection which will be revealed later. The catalyst only damaged a few dark colours on thin cotton fabrics, and was the best in the market for some stains, but the negative publicity and the tattered boxer shorts were devastating and Persil Power, after an initial surge, gradually lost ground as consumers switched to safer brands.
The famous shorts
Most washing powders in Europe contain peroxide-based bleaches, either sodium peroxoborate or sodium carbonate peroxohydrate. These liberate hydrogen peroxide in water which starts to bleach around 60oC. For this reason washing in Europe has traditionally been done at a much higher temperature than in the US where chlorine-based bleaches were used, which operate at a lower temperature. 15 years ago detergent manufacturers started adding tetraacetyl ethylenediamine (TAED) which forms peracetic acid with hydrogen peroxide, and this bleaches at lower temperatures. Low temperature bleaching saves energy and the detergent manufacturers have been looking for something which bleaches at lower temperatures and is cheap and environmentally friendly. Unilever claimed to have found this with their new manganese catalyst which activates the hydrogen peroxide.
Bleaching involves using an oxidising agent to selectively destroy stains by oxidising and destroying the coloured molecules producing the stain. These are usually organic molecules and strong oxidants cleave covalent bonds and destroy the colour along with the molecular structure. Textiles are also made from organic molecules, which can also be attacked by bleaches and their structure weakened. If the bleach is too strong, therefore, the fabric will be destroyed along with the stain. The aim, of course, is to get the balance right.
Hydrogen peroxide requires a fairly high temperature before it starts bleaching and the process is catalysed by transition metal ions. Thus it can bleach rapidly even at low temperatures. TAED is not a catalyst: it produces a more reactive compound by a stoichiometric reaction, thus a large amount is needed, and it is used up during bleaching. A catalyst needs smaller amounts of material. Transition metal ions such as Fe2+ produce hydroxyl radicals, OH., with hydrogen peroxide, which is a powerful oxidant at room temperature. This chemistry is used in Fenton's Reagent, used in analysis (it oxidises organic compounds) and to destroy organic pollutants in effluent. Rust particles on cloth can result in holes as the iron reacts with bleach to produce a powerful local oxidant.
Manganese and iron are the best possibilities for a peroxide catalyst, but the compound used must be not only be a good, stable catalyst, it must also be non-toxic, environmentally-friendly and fairly cheap. Such catalysts were investigated over a decade ago and rejected, according to Proctor & Gamble, as causing unacceptable damage to clothes. Unilever chemists now claim to have found a system which works (patented in 1991) using manganese complexed heterocyclic nitrogens in ligands such as I and II (below). The chemistry behind the new product was revealed in Nature (23/6/94).
Structure of the new ligands
The new manganese complexes are claimed to be efficient, selective oxidation catalysts at room temperature i.e. in cold water and at pH's greater than 9 where most detergents are buffered. The manganese probably ends up trapped in the zeolite builders used in modern detergents to trap calcium and magnesium ions. Free manganese ions cannot be used as the manganese would precipitate out as brown MnO2 and cause stains. The manganese is in a similar environment in the complexes to that found in some Mn metalloenzymes, where the complexed manganese can change oxidation state reversibly without being lost from the complex. The model bleaching experiments use standardised tea-stained tea cloths! It is thought that the manganese forms a mixed-valency complex and that the actual catalyst involved depends on pH.
The diagrams below show a typical ligand and manganese complex of the sort used in the catalyst. Note that the manganese is in the +4 state and presumably cycles between +3 and +4 which are very close in energy.
Typical ligand: triazacyclononane (TACN)
Typical manganese complexes which catalyses peroxide bleaching:
The manganese complex is soluble and thus this is an example of homogeneous catalysis and the catalyst, comprising less than 0.1% of the detergent, in regenerated during the wash.
The new Unilever detergent not only contains new bleaching chemistry, it also has a new zeolite builder, and a new surfactant based on alcohol sulphates. The new formulation is 30% less in volume and 15% less in weight than other compact detergents for the same performance. The process for making the detergent (a blending process) has also been changed to save energy: spray-drying has been replaced by a mixing processes which generates its own heat of mixing for drying and uses 20% less energy. Three new plants have been built to produce the new detergents: at Manchester (UK), Mannheim (Germany) and Milan (Italy). The development costs were around £100 million and launching and marketing the product cost over twice as much! Newspaper reports (June 1994) claim that Unilever will eventually have spent œ500 million in developing, manufacturing and launching the new product. There is intense rivalry between Unilever and Proctor & Gamble in Europe (Unilever's base) and in N. America (P&G's base). P&G until now have led in the innovation stakes and in the marketing stakes: P&G introduced biological powders first (containing enzymes as catalysts), and were first with both liquid and concentrated detergents. P&G's European market share has climbed to 33%, while Unilever has stuck on 23%. (Henkel has 25% of the European market and others make up 18.4%). The market is worth £6 billion a year, so it is worth fighting for. Unilever claim to have increased their share substantially since the launch and despite P&G's attacks. In July 1994 and in February 1995 the Consumer's Association reported on Persil Power. In the latest article it called on Unilever to put warnings of the packets telling customers not to use it on colours, publicising the compensation scheme and offering to swop packers of Persil Power for New Generation Persil (its replacement) in dissatisfied..
However, because of the Persil Power flop P&G increased their UK market share from 50.6% to 52.8%, while Unilever dropped from 32.6% to 31.0%. Unilever admitted in February 1995 that the Persil Power disaster cost them £57 million. Tons of the original-formula powder were destroyed and it was relaunched in the summer with only 20% of the original manganese content. This loss was on top of the £200 million it cost to develop the new product.
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Most recent revision Sunday, November 17, 1996