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Soil Science Society of America Journal Abstract -

Effect of Acidity on Reactions of Organic Acids and Amines with Montmorillonitic Clay Surfaces1


This article in SSSAJ

  1. Vol. 33 No. 6, p. 859-863
    Received: July 22, 1968
    Accepted: July 15, 1969

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  1. Robert D. Harter and
  2. James L. Ahlrichs2



The effect of pH on the nature of 2,4-D, Amiben, aniline, and urea adsorbed by montmorillonite has been characterized. In all cases the infrared spectra of air dry systems indicated a change of the compound to the acid or protonated form when the corresponding suspension pH was two to three pH units higher than the pKa of the molecule. This is consistent with previous studies which indicated that the clay surface in air dry systems is more acid than shown by electrometric pH readings of the suspension. At pH levels below the pKa the acids show evidence of adsorption by the clay. The amines acquire a positive charge and are capable of interacting with the clay exchange complex. Spectra of the aniline and urea adsorbed to acid clay were nearly identical to those of their hydrochlorides in the same environment, indicating reactions with the acid clay surfaces by protonated molecules.

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