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Infrared Studies of the Mechanism of Adsorption of Urea-d₄, Methylurea-d₃, and 1,1-Dimethylurea-d₂ by Montmorillonite¹

ABSTRACT

Clay-organic complexes of urea-d₄, methylurea-d₃, and I,I-dimethylurea-d₂ with montmorillonite were examined by infrared spectroscopy in an effort to add to our understanding of the mechanism of adsorption of the substituted urea herbicides in soils. The complexes were examined in the infrared as dried thin self-supporting films. Deteration techniques were used to correlate infrared spectra with molecular structure. Urea-d₄ was found to be adsorbed in the interlayer space by montmorillonite through coordination of the carbonyl with the exchange cations. The degree of coordination with the exchangeable cation was least for Ca, intermediate for Ni (II), and largest for Al, representing alkaline earth cation-clay, transition metal cation-clay, and acid clay, respectively. Methylurea-d₃ and I,1-dimethylurea-d₂ reacted with montmorillonite through the carbonyl in a manner similar to urea. The reaction of dimethylurea with montmorillonite was limited by the presence of the methyl groups to the extent that its reaction was the same with Al or Ni as the exchange cation. The amino groups of urea, methylurea, and I,I-dimethylurea appear relatively inactive as bonding sites.

¹ Contribution from the Department of Agronomy, Purdue University Agr. Exp. Sta. (Journal Paper no. 3271), Lafayette, Ind.

² Former Graduate Assistant, now Assistant Chemist, Department of Soils and Plant Nutrition, University of California, Riverside, and Professor of Agronomy, Purdue University, Lafayette, Ind., respectively.

Received for publication March 28, 1968. Accepted for publication September 12, 1968.