Exp 6

• Sulphonic benzene acid is made by

  1. Reacting benzene with oleum

  2. Fusing with sodium hydroxide (molten state) at a high temperature, resulting in sodium phenoxide

  3. Acidifying sodium phenoxide to produce phenols

  
• Pyrolysis of sodium benzene sulfonate

  1. Reacting benzene sulfonic acid with aqueous sodium hydroxide

  2. Mixing the resulting salt with solid sodium hydroxide and fusing at a high temperature to produce sodium phenoxide

  3. Acidifying sodium phenoxide with aqueous acid to yield phenol

  
• Phenol coefficient


  The ratio of a dilution of a given test disinfectant to the dilution of phenol that is required to kill (to the same extent) a strain of Salmonella Typhi under carefully controlled time and temperature conditions
• If the dilution of a test disinfectant is 10-fold greater than the dilution of phenol, the phenol coefficient is 10. The phenol coefficient of phenol itself is 1.
• The phenol coefficient test has many drawbacks. Phenols and other germicides do not kill microorganisms uniformly, so variations in the phenol coefficient will occur. Moreover, the conditions used to conduct the test are difficult to reproduce exactly, so High variability between different measurements and laboratories is expected. Hence, the phenol coefficient may be unreliable.
• Several phenols are actually more bactericidal than phenol itself. Substitution with alkyl, aryl, and halogen (especially in the para position) groups increases bactericidal activity.
• Straight-chain alkyl groups enhance bactericidal activity more than branched groups. Alkylated phenols and Resorcinols are less toxic than the parent compounds while retaining bactericidal properties.

  
• Phenols


  Aromatic compounds containing a hydroxyl group (-OH) directly connected to the aromatic ring

  
• Phenol (carbolic acid)


  Colorless to pale-pink crystalline material with a characteristic "medicinal odor". Soluble to the extent of 1 part to 15 Part water, very soluble in alcohol and soluble in methanol and salol (phenyl salicylate).
• Phenol


  • Exhibits germicidal activity (general protoplasmic poison), is caustic to skin, exerts local anesthetic effects, and must be diluted to avoid tissue destruction and dermatitis
• Sir Joseph Lister introduced phenol as a surgical antiseptic


  1867
• Phenol is almost obsolete as an antiseptic and disinfectant
• Common Phenols


  • BHT (Butylated hydroxytoluene) - antioxidant/preservative in food
  • Uroshiol - active irritant in poison ivy and poison oak
  • o-cresol
  • m-cresol - useful disinfectants
  • p-cresol
  • Tetrahydrocannabinol - principal component of marijuana
  • Phenolphthalein - acid-base indicator
  • Adrenalin (epinephrine) - secreted by the adrenal gland in response to stress, fear, anger or heightened emotional states
• Properties of Phenols


  • Colorless, crystalline solid with a characteristic odor, and with a melting point of about 41oC
  • Slightly soluble in water, but very soluble in alcohol, ether, and other organic solvents
  • Highly poisonous
  • A weak acid - more acidic than alcohols and water, but less acidic than CH3COOH, and H2CO3
  • Reacts with NaOH to form a salt, of sodium phenoxide or sodium phenolate, but does not react with NaHCO3
  • Toxic to microorganisms, and widely used as antiseptics and disinfectants

  
• Joseph Lister first used phenol as disinfectant


  1867
• The antiseptic power of phenol is increased by substituting alkyl groups (up to six carbons) in the benzene ring. Example: 4-hexylresorcinol - used as an antiseptic in pharmaceuticals.
• Preparation of Phenols


  1. Hydrolysis of chlorobenzene with NaOH at high temperature and pressure in the presence of catalyst

  2. Production of synthetic phenol with benzene and propene, which react to form cumene. Cumene is then oxidized by air to cumene hydroperoxide, which is treated with dilute H2SO4 to obtain phenol and acetone

  
• Phenol is slightly soluble in water (dissolves with about 84.2 g in 1000 mL water (0.88 M)).
• Phenol does not react with sodium hydrogen carbonate.

  
• Reaction of phenol with sodium hydroxide

  C6H5OH + NaOH → C6H5ONa + H2O

  
• Phenol is easily neutralized by sodium hydroxide forming sodium phenoxide.

  
• Reaction of phenol with sodium

  Phenol is warmed in a dry tube until it is molten, and a small piece of sodium added. There is some fizzing as hydrogen gas is given off. The mixture left in the tube will contain sodium phenoxide.

  
• Reaction of phenol with bromine water

  Phenol + Br2(in water)

  
• There is an immediate formation of white precipitate when phenol reacts with bromine water.

  
• Reaction of phenol with neutral iron(III) chloride solution

  C6H5OH + FeCl3 ➔ [Fe(OC6H5)6]3- + 3H+ + 3HCl

  
• The reaction of phenol with Iron (III) ions forms a strong violet colored complex - ferric phenoxide.

  
• Alcohols


  Compounds in which one hydrogen of water is replaced by an alkyl group
• Phenols


  Compounds in which one hydrogen of water is replaced by an aryl group
• Differences between alcohols and phenols

  • Alcohols have the OH group attached to an alkyl group, phenols have the OH group attached to an aryl group
  • Alcohols are hydroxyl derivatives of alkanes, phenols are hydroxyl derivatives of benzene
  • Alcohols are colorless liquids with sweet smell and burning taste, phenols are colorless crystalline deliquescent solids with phenolic odor
  • Alcohols have pKa around 16-20, phenols have pKa around 10
  • Alcohols are readily soluble in water, phenols are sparingly soluble in water
  • Alcohols do not have resonance structures, phenolate ions have resonance structures

  
• Uses of Phenol


  • Medical uses - phenol sprays, antiseptic, disinfectant
  • Plastic manufacturing industry - used to prepare reagents
  • Paint industry - used to produce epoxy resins and polycarbonate plastics
  • Cosmetic industry - used in sunscreens, skin lightening creams, hair coloring solutions
  • Extraction industry - used in extraction of biomolecules and nucleic acids
• Reaction with NaOH, Reaction with Bromine water, Reaction with FeCl3 distinguish between ethanol and phenol.

  
• Reaction with NaOH and Reaction with FeCl3 indicate that phenol is a stronger acid than ethanol.
• Reaction with NaHCO3 and Reaction with Neutral Iron (III) Solution indicate that phenol is a weaker acid than dilute mineral acids like HCl, H2SO4 and HNO3.
• Phenol


  Stronger acid than ethanol
• Tests that indicate phenol is a stronger acid than ethanol


  • Reaction with NaOH
  • Reaction with FeCl3
• Phenol


  Belongs to the alcohol family, with aromatic rings. The -OH is attached to a sp2 hybridized carbon, unlike alcohols where it is attached to a sp3 hybridized carbon.

  
• Phenols are much stronger acids than alcohols
• Distinguishing phenols from alcohols

  Phenols dissolve in aqueous NaOH, whereas alcohols with six carbon atoms do not

  
• Tests that indicate phenol is a weaker acid than dilute mineral acids like HCl, H2SO4 and HNO3


  • Reaction with NaHCO3
  • Reaction with Neutral Iron (III) Solution
• Phenol and its derivatives have been used as antiseptics since 1800s