Impurities tetrabutylammonium salts

Hindered pyridines can act in three different ways [150,293-295]. The first is to trap protonic impurities and prevent adventitious initiation by water. This improves the control of molecular weights. The second role is similar to that of salts with common anions. The pyridinium salts formed in the system are accompanied by complex anions which may scavenge free ions in a similar manner as tetrabutylammonium salts. Hindered pyridines may also act as nucleophiles (or donors) and interact with some Lewis acids. These interactions will be directed toward the aromatic ring rather than the nitrogen atom which is protected by bulky tert-butyl groups in ortho position [293]. 

In this determination, 5 mL of a 0.1 g/L aqueous solution of the surfactant is passed through a cation exchange column (1x15 cm, containing 15 mL Dowex 50W-X8, acid form) to convert the salts to the corresponding acids. The acids are eluted with two 3-mL portions of water and four 6-mL portions of water, then titrated with tetrabutylammonium hydroxide, 0.1 M in 70 30 benzene/methanol. The first inflection corresponds to the total sulfonate, plus the first proton of sulfuric acid. The second inflection corresponds to neutralization of the second proton from sulfuric acid. A third inflection may be observed due to solvent impurities. If necessary because of poor water solubility of the surfactant, the initial sample dissolution and ion exchange is conducted at 55-C. 

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