Analysis of primary amines as Schiff bases

The number of reagents that has been used for the identification of primary amines is possibly larger than for any other class of compounds [5], But most of these classical derivatives lie beyond the scope of this chapter. They are covered in other parts of the book acylation in Chapter 3, silylation in Chapter 4 and alkylation in Chapter 5. The different nitrophenyl derivatives are discussed in Chapter 8, and Chapter 9 presents the options for preparing fluorescent derivatives. The only derivatization fitting into the framework of this chapter is the condensation with carbonyls resulting in the formation of Schiff bases or, in the case of aromatic amines, anils. 

In the past, Schiff base condensations of primary amines have been carried out mainly with benzaldehyde and p-nitrobenzaldehyde, less often with 2,4-dinitro-benzaldehyde. Derivative formation occurs rapidly on warming for 10-30 min without or with a solvent (usually alcohol or acetic acid) [5]. Benzylimines from aliphatic amines are stable oils which can be distilled 

These Schiff bases are obtainable in good yields. They are e isy to purify by recrystallization and possess sharp melting points. However, with the development of gas chromatographic techniques, reasons for derivative formation other than characterization, by melting point have predominated. At present the main objectives are  

we would like to illustrate these points with a few examples. We will see that, quite unlike the situation existing for the analysis of carbonyl compounds, the classical reagents have been largely replaced. 

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