What is Phthalimide Definition Preparation Reactions and Uses in Gabriel Synthesis
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.
FAQs on Phthalimide Structure Properties and Organic Reactions
1. What is phthalimide in chemistry?
Phthalimide is an organic compound with the formula C6H4(CO)2NH, consisting of a cyclic imide derived from phthalic acid. It contains a five-membered imide ring fused to a benzene ring and is classified as an aromatic imide. In structure, it has two carbonyl groups (C=O) attached to the same nitrogen atom. Phthalimide is widely used in organic chemistry, especially in the Gabriel synthesis for preparing primary amines.
2. What is the molecular formula of phthalimide?
The molecular formula of phthalimide is C8H5NO2. It can also be written structurally as C6H4(CO)2NH to highlight its imide functional group. The molecule contains:
- 8 carbon atoms
- 5 hydrogen atoms
- 1 nitrogen atom
- 2 oxygen atoms
3. How is phthalimide prepared?
Phthalimide is prepared by heating phthalic anhydride with ammonia to form a cyclic imide. The reaction occurs in two main steps:
- Phthalic anhydride reacts with NH3 to form phthalamic acid.
- On heating, phthalamic acid undergoes dehydration to give phthalimide.
C6H4(CO)2O + NH3 → C6H4(CO)2NH + H2O
This method is commonly used in laboratory preparation of phthalimide.
4. What is the structure of phthalimide?
The structure of phthalimide consists of a benzene ring fused to a five-membered imide ring containing two carbonyl (C=O) groups and one nitrogen atom. It is a cyclic imide where the nitrogen atom is bonded to two acyl groups. Key structural features include:
- An aromatic benzene ring (C6H4)
- Two adjacent carbonyl groups (–CO–)
- A single N–H group in the imide ring
5. Why is phthalimide acidic?
Phthalimide is weakly acidic because its N–H proton is stabilized by resonance with two adjacent carbonyl groups. When the proton is removed, the resulting phthalimide anion is resonance-stabilized over both C=O groups. This delocalization of negative charge increases stability and acidity. Although it is not as strong as mineral acids, it is more acidic than typical amines due to this resonance effect.
6. What is the Gabriel synthesis of amines using phthalimide?
The Gabriel synthesis is a method of preparing primary amines by reacting potassium phthalimide with an alkyl halide. The steps are:
- Phthalimide reacts with KOH to form potassium phthalimide.
- Potassium phthalimide reacts with an alkyl halide (R–X) via nucleophilic substitution to form N-alkylphthalimide.
- Hydrolysis or hydrazinolysis releases the primary amine (R–NH2).
7. What are the uses of phthalimide?
Phthalimide is mainly used as a reagent in organic synthesis and in industrial chemistry. Its important uses include:
- Preparation of primary amines via Gabriel synthesis
- Intermediate in the manufacture of dyes and pharmaceuticals
- Precursor in the synthesis of certain agrochemicals
8. What is the difference between phthalimide and phthalic anhydride?
The main difference between phthalimide and phthalic anhydride is that phthalimide contains a nitrogen atom, while phthalic anhydride does not.
- Phthalimide (C8H5NO2) is a cyclic imide with an –NH group.
- Phthalic anhydride (C6H4(CO)2O) is a cyclic anhydride formed from phthalic acid.
9. How does phthalimide react with potassium hydroxide?
Phthalimide reacts with potassium hydroxide to form potassium phthalimide by deprotonation of the N–H group. The reaction is:
C6H4(CO)2NH + KOH(aq) → C6H4(CO)2NK + H2O(l)
This occurs because the N–H proton is acidic. The resulting potassium salt acts as a strong nucleophile in the Gabriel synthesis.
10. Is phthalimide an amide or an imide?
Phthalimide is an imide, not a simple amide, because its nitrogen atom is bonded to two carbonyl (–CO–) groups. An amide has one carbonyl group attached to nitrogen (–CONH–), whereas an imide has two acyl groups attached to the same nitrogen. Since phthalimide contains two adjacent C=O groups bonded to one nitrogen in a ring, it is correctly classified as a cyclic imide.
