"Synthesis of Anthranilic Acid from Pthalamide"

 

Step II

"Synthesis of Anthranilic Acid  from Pthalamide"

Chemicals Required:

1. Phthalamide       
2. Bromine
3. Sodium hydroxide
4. Conc. HCI
5. Glacial acetic acid

Theory:

The most Common migration rearrangement reactions involve migration of atom or group of atoms from one atom or group of atoms i.e. 1-2 Shift.

A group may migrate to an e deficient carbon, nitrogen, oxygen, to e^- rich Carbon.

The Species which migrate may be an atom or a group a sigma bond.

Classification of Rearrangement:

Depending on electronic nature of migrating unit.

A rearrangement may be classified as follows,

(a) Nucleophillic or Aniontropic Rearrangment:

Aniontropic Rearrangment is where the migrating group migrate along with the electrons pair to electron deficient center.

 

(b) Electrophillic or cationtropic Rearrangement:

Cationtropic Rearrangement is where migrating group migrate without electron pairs to rich migarting center.

 

(C) Free Radical rearrangement:

Free Radical rearrangement is where the migrating groups changes its Position just with one electron.

 

(d) Sigma tropic Rearrangement:

Sigma tropic rearrangement is where the Cleavage or breakage of Sigma bonds occur simultaneously through cyclic transitions.

 

(a) Nucleophillic Rearrangement to an é^- deficient Nitrogen:

The electron deficient nitrogen is first generated by loss of alpha leaving group from nitrogen atom.

 

Hoffmann Re-arrangement:

There is a group related closely rearrangement, which converts N-Substituted amides to anthranilic acid. These migration involves migration of alkyl or aryl group from adjacent carbon to e-deficient Nitrogen.

Chemical reaction:

Mechanism:

Procedure:

I prepared sodium hypobromite by dissolving 7.5g of sodium hydroxide in about 40ml water in a conical flask. Then, I cooled the solution to 0^oC in ice bath and then I added 2.1 ml of bromine to it with stirring. Then I added 6g of phthalamide in cold solution with stirring and then poured the solution in 5.5g "NaOH" in 20ml water. Upon this addition flask becomes hot. Then, I warmed the reaction mixture in water bath at 80^oC for about 5 minutes. Then, I filtered it off. After that, I cooled the filterate in 500 ml flask containing crushed ice. Then, I added 15 ml HCL in filterate slowly with stirring untill the solution became neutral. Then, I added 5-6ml of glacial acetic acid acid. Finally, anthranilic acid was prepared.

Calculations:

Mass of pthalimide used = 6g

Molecular mass of pthalimide = 147g/mol

No. of moles of pthalimide = xm/M

                                                 6/147 = 0.04081 moles

Moles of pthalimide = 0.04081 moles

Amount of Br₂ used = V = 2.1ml

Density of Br₂ = 3.119 g/cm³

Density = mass/volume = m/v

d = m/v   =›   m = dV =› 2.1×3.11

                                   = 6.531g

Molecular mass of Br₂ = 70g/mol

No. of moles of Br₂ = m/M   = 6.531/70 = 0.0933 moles

Moles of Br₂ = 0.0933moles

Mass of NaOH used = 5.5g

Molecular mass of NaOH = 40g/mol

No. of moles of NaOH = m/M   =   5.5/50 = 0.1375 moles

Moles of NaOH = 0.1375 moles

1eq of pthalimide = 1eq of Br₂ = 1eq of NaOH = 1eq of anthranilic acid

0.04081moles of pthalimide=0.04081moles of Br₂=0.04081moles of NaOH= 0.04081 moles of anthranilic acid

So,

Moles of anthranilic acid = 0.04081moles

Molecular mass of antranilic acid = 137g/mol

Mass of anthranilic acid = n×M = 0.04081×137 = 5.59g

Theoretical yield of anthranilic acid = 5.59g

Actual yield of anthranilic acid = 3.2g

%age yield of anthranilic acid = 3.2/5.59×100 = 57.24%

Melting Point:

The melting point of anthranilic acid is 145^oC

Yield:

The Calculated amount of product is theoretical yield. The amount of product actually obtained is actual yield and when actual yield is divided by theoretical give obtained yield. It would give expected product yield.