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Chapter 2
2.5 Unit processes and connected operations
2.5.1 N-acylation
[6, Ullmann, 2001, 9, Christ, 1999, 16, Winnacker and Kuechler, 1982] *010A,B,D,I,X*
See also Section 4.3.2.1 for environmental issues and treatment of waste streams from
N-acetylations.
N-acylation is a widely spread reaction for the protection of anilinic amino groups before
chlorinations, nitrations or sulphonations are carried out. Arylides (amides of acetoacetic acid)
are important intermediates, e.g. for organic pigments.
Chemical reaction
The most important N-acylation agents are:
• acetic acid
• acetic anhydride, other carboxylic anhydrides
• diketene
• acetoacetic ester
• acetic chloride, other acyl halides
• N-carboxy anhydrides.
They work according to the substitution:
R’ – NH2 + X – CO – R � R’ – NH – CO – R + HX
where HX is released. HX may be, e.g. H2O, CH3COOH, C2H5OH, HCl.
(the reaction with diketene is an addition).
Operations
Figure 2.11 shows a typical sequence of operations for N-acylations and the typical waste
streams. Amine and an equimolar amount of an acylation agent are typically dissolved in H2O
or diluted acetic acid (for acetoacetic ester, xylene is often used) and heated. Reaction water or
acetic acid or ethanol and solvent are distilled off and the product is obtained directly or
following crystallisation (occasionally by salting out) and filtration.
40 Dezember 2005 OFC_BREF