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skeletal formula of the phthalimide molecule
ball-and-stick model of the phthalimide molecule
IUPAC name
Other names
Phthalimidoyl (deprotonated)
3D model (JSmol)
ECHA InfoCard 100.001.458
Molar mass 147.13 g·mol−1
Appearance White solid
Melting point 238 °C (460 °F; 511 K)
Boiling point 336 °C (637 °F; 609 K) sublimes
<0.1 g/100 ml (19.5 °C)
Acidity (pKa) 8.3
Basicity (pKb) 5.7
−78.4×10−6 cm3/mol
Related compounds
Related Amides
Related compounds
Phthalic anhydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Phthalimide is the organic compound with the formula C6H4(CO)2NH. It is the imide derivative of phthalic anhydride. It is a sublimable white solid that is slightly soluble in water but more so upon addition of base. It is used as a precursor to other organic compounds as a masked source of ammonia.[2]


Phthalimide can be prepared by heating phthalic anhydride with aqueous ammonia giving 95–97% yield. Alternatively, it may be prepared by treating the anhydride with ammonium carbonate or urea. It can also be produced by ammoxidation of o-xylene.[2]


Phthalimide is used as a precursor to anthranilic acid, a precursor to azo dyes and saccharin.[2]

Alkyl phthalimides are useful precursors to amines in chemical synthesis, especially in peptide synthesis where they are used "to block both hydrogens and avoid racemization of the substrates".[3] Alkyl halides can be converted to the N-alkylphthalimide:

C6H4(CO)2NH + RX + NaOH → C6H4(CO)2NR + NaX + H2O

The amine is commonly liberated using hydrazine:

C6H4(CO)2NR + N2H4 → C6H4(CO)2N2H2 + RNH2

Dimethylamine can also be used.[4]

Some examples of phthalimide drugs include thalidomide, amphotalide, taltrimide and talmetoprim. With a trichloromethylthio substituent, a phthalimide-derived fungicide is Folpet.


It forms salts upon treatment with bases such as sodium hydroxide. The high acidity of the imido N-H is the result of the pair of flanking electrophilic carbonyl groups. Potassium phthalimide, made by reacting phthalimide with potassium carbonate in water at 100 °C or with potassium hydroxide in absolute ethanol,[5] is used in the Gabriel synthesis of primary amines, such as glycine.

Natural occurrence[edit]

Kladnoite is a natural mineral analog of phthalimide.[6] It is very rarely found among a few burning coal fire sites.


Phthalimide has low acute toxicity with LD50 (rat, oral) of greater than 5,000 mg/kg.[2]


  1. ^ "Phthalimide". Chemicalland21. Retrieved 15 November 2011.
  2. ^ a b c d Lorz, Peter M.; Towae, Friedrich K.; Enke, Walter; Jäckh, Rudolf; Bhargava, Naresh; Hillesheim, Wolfgang, "Phthalic Acid and Derivatives", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a20_181.pub2
  3. ^ "Phthalimides". Retrieved 2013-02-07.
  4. ^ "Deprotection – removal of amine protecting groups (phthalimide and dimethylaminosulphonyl)". Archived from the original on 2014-12-03. Retrieved 2013-02-07.
  5. ^ Salzberg, P. L.; Supniewski, J. V. "β-Bromoethylphthalimide". Organic Syntheses. 7: 8. doi:10.15227/orgsyn.007.0008.; Collective Volume, 1, p. 119
  6. ^ "Kladnoite". Retrieved 15 November 2011.

General reading[edit]

  • Vollhardt, K. Peter C.; Schore, Neil Eric (2002). Organic Chemistry: Structure and Function (4th ed.). New York: W. H. Freeman. ISBN 978-0-7167-4374-3.
  • Finar, Ivor Lionel (1973). Organic Chemistry. 1 (6th ed.). London: Longman. ISBN 0-582-44221-4.