Phthalimide

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Introduction to Phthalimide - C₆H₄(CO₂)NH

It is an organic aromatic compound with the chemical formula C6H4(CO2)NH. It has a heteroatom Nitrogen present in it. It belongs to the nitrogen-containing compound. It is prepared from Phthalic anhydride. It is acidic in nature and its conjugate base is resonance stabilized. Resonance provides extra stability to the structure. It has one H atom attached to the nitrogen atom, which can be easily removed using any strong base. Then the resulting ion can be made to react with bromine, which will result in the formation of N-bromophthalimide. This process is known as Gabriel Phthalimide Synthesis, which is very important in the synthesis of aliphatic amines. In this article, we will discuss the phthalimide, preparation of phthalimide, the use of phthalimide, and reactions of phthalic anhydride.


Structure

The molecular formula of Phthalimide is C6H4(CO2)NH. It contains one benzene ring, two electrophilic carbonyl groups, a Nitrogen atom, and a Hydrogen atom. Another five-membered ring is also [present with a heteroatom N. The extra stability of this compound is due to the resonance structures. The structure of Phthalimide is shown below:

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Preparation of Phthalimide

Now, as we already know what is phthalimide, our next motive is to know about the preparation methods. It is derived from Phthalic anhydride. When Phthalic anhydride is heated in the presence of aqueous ammonia, Phthalimide is obtained as the product. The reaction is shown below:

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The second method involves the use of ammonium carbonate along with phthalic anhydride. Ammonium carbonate is slightly acidic in nature. When it is made to react with KOH, it results in the formation of Potassium phthalimide.

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Properties

Physical Properties

  • It is solid in nature and white in colour.

  • The molar mass of the compound is 147.33 g/mol.

  • Phthalimide melting point is 238℃ and the boiling point is 336℃.


Chemical Properties

  • It is acidic in nature with a pKa value of 8.3.

  • It is resonance stabilized.

  • It is an imide derivative and has a heteroatom present in it.

  • When it is reacted with base, it results in the formation of salts.

  • The reason for high acidity is the presence of two electrophilic carbonyl groups.


Reactions of Phthalic Anhydride

The main use of phthalimide is in the formation of aliphatic amines. The process is known as Gabriel Phthalimide synthesis. Phthalic anhydride is used here to synthesize phthalimide. Ammonium carbonate is made to react with phthalic anhydride in the presence of base KOH. It results in the formation of the potassium salt of phthalimide. Typically, this reaction uses the potassium salt of phthalimide.

When this salt is made to react with an alkyl halide, it gives N-alkylphthalimde as the product. When this product is reacted with hydrazine in the presence of the base, the desired product is obtained. 

The complete synthesis is shown below:

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Various alternatives to this reagent have been developed. In Gabriel synthesis, the Sodium salt of saccharin is also being used in place of salts of phthalimide. The alternate Gabriel Synthesis hydrolyzes and gives secondary amines easily.


Phthalimide Uses

  • It is widely used in the pharmaceutical industry for the synthesis of various chemical compounds containing nitrogen. It acts as a masked source of ammonia. So, it is more beneficial than free ammonia.

  • It is used in the synthesis of anthranilic acid which is extensively used in dye industries.

  • It is the chemical precursor in the chemical synthesis of peptides.

  • It is used in the synthesis of medicines because of its anti-inflammatory, analgesic, anticonvulsant properties.

  • The number of anti-inflammatory phthalimide derivatives has been synthesized as tumour necrosis inhibitors.

FAQ (Frequently Asked Questions)

1. What are the limitations of using Phthalimide in Gabriel Synthesis?

The main limitation is that it only forms aliphatic amines. Aromatic amines cannot be synthesized using this process. Another limitation is that it forms primary amines predominantly. Secondary and tertiary amines are not easily formed and they are less in yield. To overcome these limitations, a number of derivatives have been used. Salts of saccharin are used in presence of salts of phthalimide. It hydrolyzes easily and gives a better yield of secondary amines.

2. What is the use of phthalimide?

It is greatly used in the synthesis of medicines, chemical compounds due to its anti-inflammatory, analgesic, anticonvulsant properties. It is used extensively in the dye industry. It acts as a masked source of ammonia. So, it is useful in the synthesis of nitrogen-containing compounds.