Synthesis of paminobenzoic acid: Step 2

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Synthesis of p-aminobenzoic acid Step 2
2
Goal

• We have to oxidize the methyl group in p
  -acetotoluidide.
• Characterization of the product by Melting Point,
  IR, and 1H NMR.

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Terms

• Carboxylic Acid.
• Oxidation.
• Coupling constant.

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Introduction

• Carboxylic acid is a important family in organic
  chemistry.
• The name is the contraction of the parts the
  carbonyl and hydroxyl groups.
• You can write general formula for an organic acid
  in three ways.

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Sources

• Carboxylic acid is naturally present in variety
  of eatables and living beings.
• Stinging Ants, source of formic acid, HCOOH.

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Sources

• The root of Garden Heliotrope is a source of
  valeric acid, CH3(CH2)3COOH.

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Sources

• The bark of White Willow tree (Salix alba) is a
  source of salicylic acid, HO-C6H4-COOH, from
  which aspirin made.

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Sources

• Vinegar Acetic acid
• Milk Propionic acid
• Butter Butyric acid

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Sources

• The smell from the dirty gym socks and running
  shoes is due Caproic acid, CH3-CH2-CH2-CH2-CH2-COO
  H.

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Preparation

• Organic acids can be prepared by many ways
• 1. Oxidation of primary alcohol or aldehydes.
• 2. Oxidation of alkyl chain on aromatic rings.
• 3. Reaction of Grignard reagents with CO2.
• 4. Hydrolysis of alkyl cyanides.

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Preparation

• The most common reagents used for oxidizing
  alcohol to acids are
• 1. KMnO4
• 2. CrO3
• 3. HNO3
• 4. Ag2O

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Preparation

• KMnO4You can easily remove the waste i.e. MnO2.
• CrO3 It is very difficult to separate chromium
  waste from the solution.
• HNO3 Some times it may decompose your compound.
• Ag2O Mild oxidant and it is useful for the
  oxidation of aldehydes to acids.

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Preparation

• Grignard reagents add to the carbon dioxide.
• Hydrolysis of the intermediate (Mg-complex) gives
  the acid.

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Preparation

• Reaction with Grignard Reagent
• You need a ultra dry condition.
• You should maintain the inert atmosphere.

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Preparation

• The cyanide functional group can be hydrolyzed to
  acid.
• This reaction requires acid or bases.
• The nitrogen in the cyanide is converted into
  ammonium ion.

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Preparation

• Aromatic acids can be easily prepared by
  oxidizing an alkyl side chain on aromatic ring.
• Carbon on the ring does not oxidize.
• The reaction involves attack of oxidant at a C-H
  bond adjacent to the benzene ring.

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Preparation

• Longer side chains are also oxidized to a
  carboxyl group.

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Preparation

• If no C-H bond in the benzylic position (adjacent
  to the benzene ring), however, the aromatic ring
  is oxidized although only under severe reaction
  condition.

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Preparation

• Reagents other than KMnO4 for the oxidation of
  alkyl groups are
• K2Cr2O7 / H2SO4
• O2 / CH3COOH / Co (III)

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Procedure

• Take 3.75 g of p - acetotoluidide in a 500 mL
  Erlenmeyer flask.
• Add 10 g of magnesium sulfate and 250 mL of
  distilled water.
• Place it on a steam bath and maintain 85? C.

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Procedure

• Make a solution of 10.25 g of KMnO4 in 35 mL of
  hot water (boiling temperature).
• Add the KMnO4 solution to the p - acetoluidide
  solution in small portions over 30 minutes with
  constant stirring or swirling the flask.

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Procedure

• Filter the hot solution using filter paper and
  large funnel.
• Wash the brown solid with little hot water (may
  be 20 mL)
• Throw the brown solid to the trash. Why???
• Brown solid is the MnO2 and it is waste product.
  Our compound is in the solution.

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Procedure

• If the filtrate (solution) is not colorless, add
  ethanol in drop wise until the color is
  discharged.
• Filter the solution again using fresh filter
  paper.

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Procedure

• Cool the colorless solution and acidify it using
  20 sulfuric acid till the solution become
  acidic (use Blue litmus or Congo red)
• You will see a nice white color solid.
• Filter it using Buchner funnel.
• Dry them using water suction.

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Characterization

• Do the following studies of dry compound.
• 1. Melting Point.
• 2. IR spectrum.
• 3. 1H NMR spectrum.

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1H NMR
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1H NMR

• 1H NMR is the most powerful tool available for
  structural determination of small organic
  compounds.
• The number of signals shows how many different
  kinds of protons are present.
• CH3-CH3 1 signal
• CH3-CH2-Cl 2 signal
• Benzene 1 signal

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1H NMR

• Electron withdrawing group or electronegative
  elements generally cause a downfield chemical
  shift.
• C-CH3 0.9 ppm
• CH3-CO 2.0 ppm
• C-CH2-Cl 3.7 ppm
• C-CH-Cl2 5.8 ppm
• CH-Cl3 7.3 ppm

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1H NMR

• Hydrogen atom attached to a carbon that is part
  of a multiple bond or aromatic ring usually
  appear downfield.
• C-CH2-CH2 1.20 1.35 ppm
• CH2C 4.60 5.00 ppm
• Benzene 6.60 8.00 ppm

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1H NMR

• We can integrate the area under each peak.
• Peak area is directly proportional to number of
  proton responsible for the particular peak.

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1H NMR

• 13C nuclei gives single peak and does not split
  by neighboring 13C nuclei.
• 1H nuclei signal split by neighboring protons.
• The splitting pattern gives us information about
  the number of nearest 1H neighbors that a
  particular kind of 1H nucleus may have.

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1H NMR

• Chemically equivalent protons do NOT split each
  other.
• Non equivalent protons on adjacent carbons always
  interact each other.
• CH3 CH3 Do not split
• CH3 CH2 - Cl Split each other

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1H NMR

• If you DO NOT have protons on neighboring carbon
  atom then the signal will not split.
• CH3 CO CH2 Cl Do not split

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1H NMR

• If a 1H nucleus or a set of equivalent 1H nuclei
  has n 1H neighbors, its NMR signal will be
  split into n1 peaks.
• CH3CH2O-CH2-CH3
• CH3-CH2 will be appearing as a triplet.
• CH3-CH2 will be appearing as a quartet.

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1H NMR

• Difference between the peaks of multiplet
  measured in Hz called coupling constant.
• Not dependent on strength of the external field

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1H NMR

• If the chemical shift values are in ppm, then the
  coupling constant is
• Difference between two peaks x Strength of the
  Magnet
• The strength of our magnet is 200 MHz.

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1H NMR

• -OH, -NH2 protons always appear as a broad
  signal.
• CH3-OH
• NH2-CH2-CH2-NH2

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1H NMR

• Aldehydes (-CHO) and Carboxylic Acid (-COOH)
  protons are always appear at above 12.0 ppm.

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1H NMR

• The handouts have 1H NMR of p-toluidine.
• Find the coupling constant for the aromatic
  protons.
• Assign the signals with appropriate protons from
  the chemical shift.

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1H NMR

• Record 1H NMR for p - acetoluidide.
• Find the coupling constant of aromatic 1H.
• Compare the chemical shift values.
• Assign the signals.

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Notes

• KMnO4 makes stain.
• Work in pairs (means 2 students).
• Do not spill the chemicals around the balance.
• Use spatula to take the chemicals out from the
  container.
• Do not leave any glass wares around the sink.