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Category name:
Alkyl aryl sulfonate category

Justifications and discussions

Category definition:
The chemicals in this group consist of a benzene (aryl) ring with a sulfonic acid substituent group and an alkyl chain that can vary in length and extent of branching.

Category description:
The substances are grouped on the basis of a common functional group, alkaryl earth metal, and a common precursors and/or the likelihood of common breakdown products via physical and biological processes, which result in structurally similar chemicals
Category rationale:
The chemicals in this group are salts of structurally related linear alkylbenzene sulfonates (LAS) that are anionic surfactants with molecules characterised by a hydrophobic (non-polar) tail and a hydrophilic (polar) head (NICNAS, 2016). This alkaryl aryl sulfonate categorization was used by the American Council Petroleum Additives (Panel) Health, Environmental, and Regulatory Task Group (HERTG) under the Environmental Protection Agency’s High Production Volume (HPV) Chemical Challenge Program (HERTG, 2001; HERTG, 2005).
These substances are prepared by sulfonation of either synthetic alkylbenzene substrates or naturally occurring alkyl-aromatic-rich fractions of heavy lubricating oil base stocks derived from petroleum streams. The alkyl substituent group may vary in number (e.g., mono- or dialkyl), position (e.g., predominantly meta or para to the sulfonic acid position), chain length (e.g., C14 to C30) or in the degree of branching. They are manufactured by reacting the parent alkylbenzenes with sulfuric acid or sulfur trioxide to give the corresponding sulfonic acid, which is neutralised with a calcium, sodium, barium or magnesium base to form the desired salt. The salts can also be complexed (overbased) with an excess of metal carbonate. The overbased products exist in the lubricating oil diluent as a reverse micelle. The more overbased a chemical, the more diluted it is. Thus, the overbased chemicals are considered to be diluted analogues compared with members that are not overbased (NICNAS, 2016).
Most of the chemicals in the alkyl aryl sulfonate category group have similar end uses, typically in lubricating oils and cleaning products. The salts are expected to dissociate almost completely below the critical micelle concentration.

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