Linear Alkylbenzene Sulfonic Acid, also known as LABSA or LAS has a chemical formula of CH3(CH2)11C6H4SO3H. LABSA exist as a brown liquid that is soluble in water and non-volatile. The properties of LABSA vary in physical and chemical properties depending on the length of the alkyl chain. It is also bio-degradable and hence easily distinguished from alkylbenzene sulfonate (ABS) by its linear, straight chain structure.
The commercial method of manufacturing LABSA is by sulfonating linear alkylbenzene (LAB) with either oleum (10-25% sulfur trioxide [SO3] in sulfuric acid) or an SO3-air mixture. The major product is para-alkylbenzene sulfonic acid. The reaction temperature has to be controlled during the addition of acid and the reaction goes into completion after 30 to 45 minutes. Too high temperature and reaction time and cause an undesirable dark-colored product.
Sulphuric acid (H2SO4) is preferred over use of sulphur trioxide due to cheaper SO3 and equipment cost. Reaction of pure SO3 it too aggressive an electrophilic reagent and forms a black char on contact due to the rapid exothermic reaction. As a result, cooling is required as high temperatures can promote formation of by-products.
Therefore, H2SO4 and oleum are more commonly used for sulfonation of alkyl benzene and sulphate fatty alcohols for heavy duty detergents. Water is formed in the reaction and hence dilutes the oleum and H2SO4. Sulfonation reaction stops when the concentration of H2SO4 drops by 90%.
Linear Alkyl Benzene Sulphonic Acid (LABSA) is the most commonly used synthetic surfactant due to its low cost and effectiveness. LABSA is an anionic surfactant widely used in a wide range of Domestic Detergents Powder and dish wash cleaner as an emulsifier, wetting agent due to its high solubility in water for foaming and low salt content. It lowers the surface tension of water, allowing stains to loosen and release from fabrics and surfaces.