Bleach activators are compounds that react with hydrogen peroxide in aqueous solution to form peroxy acids. Peroxy acids are more active bleaches than hydrogen peroxide at lower temperatures (<60 °C). Bleach activators are a component of most laundry detergents. The most common bleach activators used commercially are tetraacetylethylenediamine (TAED) and sodium nonanoyloxybenzenesulfonate (NOBS). NOBS is the main activator used in the U.S.A. and Japan. TAED is the main activator used in Europe.
Bleach activators are typically made up of two parts: the peroxy acid precursor and the leaving group; and are modified by altering these parts. The peroxy acid precursor affects the bleaching properties of the peroxy acid: determining the activity, selectivity, hydrophobic/hydrophilic balance and oxidation potential. The leaving group influences the solubility, perhydrolysis rate and storage stability of the activator.
Mechanism of Bleach Activation
Bleach activation is also known as perhydrolysis. Persalts are inorganic salts that are used as hydrogen peroxide carriers (examples include sodium percarbonate and sodium perborate). Persalts and bleach activators are included together in powder laundry detergents that contain bleach. In the wash, both compounds dissolve in the water. When dissolved in water, the persalt releases hydrogen peroxide (e.g. from sodium percarbonate): 2Na2CO3∙3H2O2 → 2Na2CO3 + 3H2O2
In a basic wash solution, hydrogen peroxide loses a proton and is converted to the perhydroxyl anion: H2O2 ↔ H+ + HO2−
The perhydroxyl anion then attacks the activator, forming a peroxy acid: HO2− + RC(O)X → X− + RC(O)O2H
Only the perhydroxyl anion, and not the hydrogen peroxide molecule, reacts with the bleach activator. In aqueous solutions, the hydroxide ion is also present, but owing to the greater nucleophilicity of the perhydroxyl anion, it will react preferentially. Once formed, the peroxy acid can act as a bleach.