Chapter 8 - Amines

Abstract

This chapter deals with amines. MTBSTFA is the recommended reagent for silylating the amine functionality because it forms a more stable derivative than MSTFA, BSTFA, or BSA. Organic compounds with an odd number of nitrogen atoms will have an odd-mass molecular ion and prominent fragment ions at even masses. Underivatized diamines are difficult to identify by their mass spectra alone because of the low abundance of the molecular ion (<3%). If the carbon is alkyl substituted, then intense ions are observed at m/z 44, 58, or 72, and so on. If the unknown amine reacts with acetone or methyl-8, then it is a primary amine. With secondary amines, cleavage of the bond 13 to the nitrogen atom occurs preferentially at the shortest hydrocarbon chain. In the mass spectra of amino alcohols, the m/z 30 peak is intense while the m/z 31 peak is of relatively low abundance. A method to determine the number of amino groups present in the molecule requires the formation of a TMS derivative with MSTFA, which silylates both hydroxyl and amino groups. The molecular ions of the unsubstituted phenols are present, but are smaller than the underivatized aminophenols.