Physicochemical studies on the application of insecticides to sheep fleece. V.—The influence of carbon‐chain length and halide ion of cationic wetting agents on their reaction with natural fleece

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Abstract
The influence of variation in chain length on the reactions between fleece and cationic wetting agents has been studied, with particular reference to octadecyl‐, cetyl‐, tetradecyl‐and dodecyl‐pyridinium chlorides. Reactions with cetyltrimethylammonium chloride closely resemble those with cetylpyridinium chloride. The inactivation of the wetting agents, and change in weight of the fleece samples, have been determined over ranges of concentration, and the two properties correspond closely in all instances. With octadecyl and cetyl compounds considerable inactivation occurs, but with the tetradecyl and dodecyl compounds the interfacial activity of the wetting agent is enhanced; this is attributed to the increase in the solubility of the long‐chain cation‐suint anion complex with decrease in cation chain‐length. At C14 and below, the flocculation of suspended matter, which is typical of the longer chains, does not occur. All the curves may be interpreted on the basis of the α, β and γ mechanisms discussed in earlier Parts. The effect of addition of sodium chloride on reactions with cetylpyridinium chloride is considered. Dodecyl‐ and tetradecyl‐pyridinium compounds have been used to compare the properties of the various halides. The change in properties produced by one step in the series Cl‐→ Br‐→ I‐ is approximately equivalent to an increase of two carbon atoms in the cation chain‐length.