Synthesis of Para Red 14Nitrophenylazo2naphthol

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Synthesis of Para Red1-(4-Nitrophenylazo)-2-napht
hol

• Ted Williams
• Tom Cronin
• Portland Community College
• CH 243 Spring 2005

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Why Para Red

• Substituted benzene reaction
• Qualitatively identified product
• Whee!
• I memorized the 17 step reaction for a diazonium
  salt for the final in CH 242

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Para Red Synthesis

• Starting Materials
• 2-Acetanilide, a mono-substituted benzene
• 2-Naphtol, mono-substituted fused ring aromatic
  alcohol
• Synthesis in four steps
• Nitration of mono-substituted benzene
• Reduction of original substituent
• Synthesis of Diazonium Salt
• Azo linkage between Diasonium Salt and Naphtol

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IUPAC Naming of Para Red

• 1-(4-nitrophenylazo)-2-naphthol

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Interesting Details

• Extremely concentrated acids (H2SO418M, HNO316M)
• Couldnt use normal filtration
• I learned this after loosing half our product in
  a filter paper mush
• Used a centered glass filter for all other
  filtrations

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More Interesting Details

• Very little purification required
• Just filtering
• Highly selective reaction
• More to come on that
• Most reactions conducted below 10 C
• Maintain selectivity by preventing less
  energetically favorable reactions from occurring

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Nitration of Substituted Benezene

• Para Substitution
• But why not ortho substitution?

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Say the Magic Word
Steric Hindrance
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Why the para substitution is favored over the
ortho

• Steric hindrance favors the para substitution
• Free rotation about the N-benzene bond
• Keeping the reaction mixture cold (lt10 C ) also
  improves yield by favoring the most stable form

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Nitration to p-nitroacetanilide

• H2SO4HNO3 -gt NO2
• NO2 added drop wise at 7 C
• Allow reaction to reach room temperature
• Pour back into 7 C water, forming precipitate

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Reduction to p-nitroaniline

• Reaction conducted under reflux conditions
• Proton supplied by concentrated sulfuric acid
• Precipitates when added to water

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Diazonium Salt Synthesis4-Nitrobenzenediazonium
hydrogen sulfate

• H2SO4 NaNO2 -gtNO
• Basically a transfer of H from N to O
• Much milder acidic conditions (1M)
• Conducted at 7 C

HSO4-
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Azo Linkage to 2-Naphtol

• Azo linkage between two aromatic rings via NN
• Mildly basic conditions, made slightly acidic at
  the end of the reaction
• Conducted at 7 C
• Final Product 1-(4-Nitrophenylazo)-2-naphthol

Para Red
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Discussion of Results

• Huge yield losses trying to use paper filter
• approximately 5 net yield
• pH detection was difficult in the last step due
  to the dye, we may not have had it acidic enough
• IR spectra indicated good purity for each
  intermediate, no unexpected or missing peaks
• Melting point of para red suggested a mixed
  product of para red and p-nitroaniline

• I really enjoyed this experiment
• I really like chemistry
• Our experiment worked
• I like cake
• I am a fish

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You pick who is who