PRPM112 LAB: EX 9

• PHENOLS


  organic aromatic compounds wherein the hydroxyl group is attached to a benzene ring
• PHENOLS


  considered as alcohols due to their OH group, however, differ in their chemical behavior
• PHENOLS


  difference with alcohols technically is due to the phenyl ring
• PHENOLS

  also known as hydroxybenzene or carbolic acid
• PHENOLS

  • toxic, colorless crystalline solid with sweet tarry odor
  • usually employed as an antiseptic and disinfectant
  • also used in cosmetic formulations and manufacture of some drugs (precursor)
• PROPERTIES OF PHENOLS

  BOILING POINT

  • generally have higher boiling points as compared to hydrocarbons having the same molecular masses
  • mainly due to the intermolecular H-bonding in between the OH groups
  • boiling point increase = number of C atoms increase
• PROPERTIES OF PHENOLS

  SOLUBILITY

  • governed by its ability to perform intermolecular H-bonding with polar solvents
  • H-bonds make it possible for the phenol to be slightly soluble to the water
  • however, an increase in the size of the aryl group attached to the hydroxyl group decreases it solubility in water
• PROPERTIES OF PHENOLS

  ACIDITY

  • acidic in nature due to its reactivity with active metals (e.g. sodium, potassium, etc.) to form corresponding phenoxides
• PROPERTIES OF PHENOLS

  ACIDITY

  • sp2 hybridized C of the benzene ring attached to the OH group functions as an electron-withdrawing group (decreases the electron density on the oxygen)
  • due to the delocalization of the electrons in the benzene ring, phenoxide ions are more stable (phenols are more acidic than alcohols)
  • in substituted phenols, its acidity decreases if an electron-donating group is attached to the ring and vice versa
• SYNTHESIS OF PHENOLS

  • diazotization of primary aromatic amines
  • primary aromatic amine with nitrous acid (NaNO2 + HCl) at ~5°C, benzene diazonium chloride is formed
  • diazonium salts are highly reactive and upon warming with water, will be hydrolyzed in to phenol
• SOLUBILITY TEST

  • phenol in 5% NaOH

  soluble; clear dark brown to black solution
• SOLUBILITY TEST


  function of test: identify solubility of phenols

  principle: phenols react with dilute aqueous sodium hydroxide to form sodium phenoxide (more soluble with water compared to phenol due to its phenyl ring)
• REACTION WITH FERRIC CHLORIDE

  • 1% phenol

  1. purple solution

  • 1% cathecol

  1. clear colorless solution

  • 1% thymol

  1. clear pale green solution

  • 1% α-naphthol

  1. dark red solution
• REACTION WITH FERRIC CHLORIDE


  • function of test: can detect the presence of phenolic compounds
  • reagent: ferric chloride
  • positive result: colored complexes
• formation of ferric phenoxide that absorbs visible light to give an excited state in which electrons are delocalized over both the iron atom and the conjugated organic system
• BROMINE WATER TEST


  1% phenol

  1. clear colorless solution with white precipitate

  salicylic acid

  1. clear colorless solution with white precipitate
• BROMINE WATER TEST


  function of test: can be used to identify phenolics (however, other compounds may also yield positive results)

  reagent: bromine water

  positive result: clear colorless solution with white precipitate
• bromination of phenol results to 2,4,6-tribromophenol product which appears as white precipitate while the side product of hydrobromic acid results to decolorization of the solution with an odor of an antiseptic
• FORMATION OF PHENOLPHTHALEIN

  5% HCl

  1. clear colorless solution

  5% NaOH

  1. pink solution
• FORMATION OF PHENOLPHTHALEIN

  phenol can also be used as precursor in the synthesis of several organic compounds

  one of which is an organic indicator phenolphthalein, used in acid-base titration
• phenol reacts with phthalic anhydride under an acid catalyst using an electrophilic aromatic substitution reaction
• the resulting solution can be further tested for its indicator property:

  1. colorless in acidic solutions
  2. pink to magenta in basic solutions
• MILLON’S TEST

  1% phenol

  1. clear golden brown solution

  5% albumin

  1. clear yellowish solution with red precipitate
• MILLON’S TEST


  function of test: determine the presence of phenolic compounds in amino acids

  reagent: Millon’s reagent (mercurous nitrate HgNO3 and mercuric nitrate Hg(NO3 )2 in nitric acid HNO3

  positive result: red precipitate (tyrosine is the only amino acid with phenol in its structure)
• amino acids and proteins with phenol radicals react with Millon’s reagent to form red colored complexes
• tyrosine 


  is the only amino acid with phenol in its structure