Alkylation On Graphite: Introduction to Green Technologies

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Alkylation On Graphite Introduction to Green
Technologies
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Friedel Crafts Alkylation

• Synthesis of alkyl benzenes from alkyl halides
  and a Lewis acid, usually AlCl3.

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Friedel Crafts Alkylation

• Reactions of alkyl halide with Lewis acid
  produces a carbocation.
• The carbocation will act as an electrophile.

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Friedel Crafts Alkylation
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Limitations of Friedel Crafts Alkylation

• Only alkyl halides can be used (F, Cl, I, Br).
• Aryl halides and vinylic halides do not react
  (their carbocations are too hard to form).

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Limitations of Friedel Crafts Alkylation

• If you have electron withdrawing group, then
  there wont be any alkylation.

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Limitations of Friedel Crafts Alkylation

• Multiple alkylations occur because first one
  activate the ring.

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Limitations of Friedel Crafts Alkylation
Rearrangement of Carbocations are Possible!!!
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Todays Task

• Alkylation of p Xylene with 2 bromobutane
  using graphite.
• Learn about Green Technologies.
• Characterization by 1H and COSY NMR.

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Allotropes of Carbon

• Diamond is very strong due to tetrahedral
  arrangement.

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Allotropes of Carbon

• Graphite is a soft material due to hexagonal
  arrangement.

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Allotropes of Carbon

• Fullerene and Carbon Nanotubes have similar
  structure to Graphite.

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Allotropes of Carbon

• Amorphous Carbon does not have any crystalline
  structure like Diamond or Graphite.

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Why we choose Graphite???

• It is Cheaper.
• Graphite acted as catalyst for
• 1. Friedel Crafts Benzoylation of Aromatic
  Compounds
• 2. Cleavage of Ethers by Acyl Halides.
• Graphite Doped Metal Halides acted as catalyst
  for electrophilic alkylation of aromatic
  compounds.

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Procedure

• Take 100 mL RB flask and add
• 1. 5 mL of p Xylene.
• 2. 0.44 mL of 2 bromobutane.
• 3. 0.5 gram of graphite.
• Set up a refluxion apparatus and do the refluxion
  for 1 ½ hour.
• Circulate Cold water during refluxion.

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Procedure

• Cool the reaction mixture to room temperature.
• Filter the graphite using Frit funnel.
• Wash the Graphite with 15 mL of hexane.
• Dry the Graphite in the air for 10 more minutes
  and return to me.

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Procedure

• Transfer the filtrate into a fresh and dry RB
  flask.
• Evaporate all the solvents using rotary
  evaporator.
• Once you removed all the solvents weigh the
  product (its a liquid).

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Procedure

• Do the evaporation one more time and weigh the
  product.
• If you get the consistent weight then you
  calculate the percent of yield.
• If you dont get the consistent value, do the
  evaporation till you get consistent weight.

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Chemical Reaction
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Mechanism

• Partial Charge on alkyl halide may be produced
  by
• 1. Metal Impurities in the Graphite
• 2. ? electrons in the Graphite
• Formation of the Transition State is still
  Enigmatic.
• Dr. Seradas research group is trying to find the
  exact mechanism and they found reactivity of
  halide in the following order.
• Tertiary Halide gt Secondary Halide.
• No Reaction occurred with Primary Halide

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Green Chemistry

• By definition
• Green Chemistry is the design, development, and
  implementation of chemical products and processes
  to reduce or eliminate the use and generation of
  substances hazardous to human health and the
  environment.
• Advantages
• 1. Reduce Pollution
• 2. Low Cost
• 3. Simplicity in Process and Handling

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Green Chemistry Example
Carcinogenic
Dangerous to Handle
Flammable
Synthesis of 1, 8 Dimethoxy 9, 10 -
anthraquinone
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Green Chemistry

• Why Todays reaction is Environmental Free???
• 1. No need of using strong Lewis Acid catalysts.
• 2. Catalysts can be Reusable.
• 3. Produces Minimum Waste.
• 4. Simple Procedure.
• 5. Low cost.
• 6. No Toxic Reagents.
• 7. High Yield and less by products.

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Characterization

• 1H NMR and COSY Spectrum.
• COSY (CORRLATED SPECTROSCOPY) is 2D NMR.
• One dimensional NMR involves with only one Radio
  Frequency pulse.
• Where as 2D consists of a sequence of Radio
  Frequency (RF) pulses with delay period of time.

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Characterization

• Involves a series of one dimensional (1D)
  experiments.
• 1. COSY use to have two 1D 1H NMR spectrum

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Characterization

• Intensities of the peaks in the spectrum can be
  represented using 3D.
• 1. Contours
• 2. Different Color
• The diagonal peaks are intensities for particular
  signal.

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Characterization

• Two kinds of peaks are in 2D NMR.
• 1. Diagonal Peak The peaks on the diagonal
  called Diagonal Peaks.
• 2. Cross Peak The peaks off the diagonal
  called Cross Peaks.
• The peaks on the diagonal when matched with
  cross-peaks are coupled each other (means those
  two protons are from adjacent carbon).

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Cross Peak
Diagonal Peak
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Characterization

• ID proton NMR can tell about
• 1. Chemical Shift value
• 2. Number of Protons
• 3. Multiplicity
• You cannot easily differentiate between two
  singlet and a doublet using 1D 1H NMR.
• It is not very easy to interpret a complex 1D 1H
  NMR (NMR of Natural Products).
• But COSY helps very well to solve the above
  difficulties.

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Characterization
Singlet
Doublet

• We have Nine different protons, so we will get
  Nine signals in 1H NMR.
• We are using COSY to differentiate these two
  singlet and doublet

Singlet
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Notes

• Work Four People together.
• Do not throw the used Graphite.
• Do not contaminate any chemicals.