Application of infrared spectroscopy to the analysis of primary fatty amide mixtures

The composition of fatty amide mixtures, containing mostly simple primary amides, has been studied by means of an infrared method utilizing the Amide I carbonyl absorption band. In dilute chloroform solution the amides, CH3(CH2)nCONH2, absorb consistently at about 5.95 ॖ and do not display apparent association or enolization. The concentration of unsubstituted amides has been quantitatively related to the intensity of the Amide I band throughout the range from 1 to 100%. With the scale expansion the sensitivity of the method may be extended to 0.03% without difficulty. The influence of certain impurities on the intensity of the Amide I band is discussed. Carbonyl absorption from fatty acids, ketones, and esters constitutes an interference.N‐monosubstituted amides also contribute to the absorption observed at 5.95 ॖ, but their presence is indicated by additional absorption at about 6.60 ॖ. The determination of small amounts of amides in amines may be accomplished by measuring the total Amide I absorption of a sample dissolved in tetrachloroethylene and relating this absorption to that of known mixtures run under identical conditions.