Surfactants containing ethylene oxide: Relationship of structure to biodegradability

Anionic ethoxy sulfate and nonionic ethoxylate surfactants were prepared from the following straight‐chain hydrophobes: fatty or Ziegler primary alcohols, oxo alcohols derived from straight‐chain olefins, secondary straight‐chain alcohols and straight‐chain alkylphenols. These were studied to relate biodegrability to the following elements of structure: the nature of the connecting link, its position of attachment to the hydrophobe, the chain length of the hydrophobe, and the length of the ethylene oxide chain used. Previously described methods were used to estimate both rate and completeness of degradation in river water as well as activated sludge environments. Data are presented to support the following conclusions. All surfactants derived from straight‐chain primary and secondary alcohols are rapidly and completely degraded with loss of surfactant properties. The length of the ethylene oxide chain from zero up to ten units has no effect on the rate or the completeness of degradation. In such surfactants, the ethylene oxide chain is completely degraded. In contrast, surfactants from straight‐chain alkylphenols are not as rapidly or as completely degraded as those described above. The position of attachment of the phenol ring to the straight‐chain has a large effect on degradability; normal or primary attachment leads to a faster rate of disappearance than secondary attachment. Nonionic surfactants from straight‐chain alkylphenols containing ten to twelve moles of ethylene oxide are not completely degradable.