Form 5 Chemistry – ORGANIC CHEMISTRY 3

        IODOFORM TEST

Ø  This is the chemical test for presence of terminal methyl group which is directly bonded to carbon with OH^– group or (to carbonyl group in the case of carbonyl compounds) by giving yellow ppt of trichloromethane ( Iodoform) CHI₃.

Ø  When compounds with terminal methyl group bonded to carbon with OH  group is heated with 1₂ in presence of  NaOH they give yellow ppt of Iodoform.

Example

CHEMICAL TEST TO DISTINGUISH BETWEEN PRIMARY, SECONDARY AND TERTIARY ALCOHOLS.

 – Three classes of alcohol can be distinguished by using Lucas reagent.

– Lucas reagent is the mixture of concentrated HCl and ZnCl mixed at equal proportion.

– With Lucas reagent at room temperature, primary alcohol do not form cloudness or turbidity ( insoluble substance) at all.

– Secondary alcohol tends to form turbidity ( insoluble substance which is chloroalkane within 5 minutes).

– Tertiary alcohol, tend to form turbidity immediately.

Example

Qn. Gave chemical test to distinguish between

 i. Ethanol and propanol ( I test)

            ii.  Butan – 1-ol and butan – 2- ol (2 test)

iii.  Butan -2- ol and 2- methyl propan – 2-ol ( 2 test apart from using Lucas reagent)

ANS

i.  Ethanol gives positive Iodoform test while propanol give negative Iodoform test.

ii.   1^st TEST
With Lucas reagent at room temperature butan -2-ol give turbidity ( cloudness) within 5 minutes while butan -1-ol  do not give turbidity at all.

         2^nd TEST ( Iodoform Test)
           Butan -2- ol  give positive iodoform test while but-1-ol give negative iodoform test.

    iii.1^st TEST
When butan -2- ol  is mixed with solution the orange colour of   is changed to green while 2- methylpropan- 2 – ol do not show any change.

2^nd TEST
      Butan decolourise  KMnO₄  with black ppt appearing at the bottom of the beaker which is deep purple while 2-methylpropan do not.

NECTA 2006 PP₂ QN. 8(a)
Organic compound C₄H₁₀O   reacts with  PCl₅ to form an organic compound “Q”  In organic compound “N” and gas ‘R’ which produce denser white fumes with a aqueous ammonia “P” also react with a mixture of Iodine and  NaOH  forming a sodium salt “W” and triodomethane.

 i.   Identify and write the structural formula Q, R and W.

ii.   Write an equation of each of the above reaction.

ANS:
The molecular formula   confirm general molecular formula of  C_nH_2n+2O

– Thus P is either alcohol or ether.
– A gas which produce dense white fumes with aquous ammonia is  HCl
– So since the reaction “P” and PCl₅  produce HCl then there is OH group in P.
– Hence compound “P” reacts with mixture of iodine and NaOH to give triodemethane then compound “P” give positive Iodoform.
– Hence in “P” there is terminal methyl groups bonded to carbon with group. This “P” is butan -2-ol.

Its structure is

  –   Q is 2 – chlorobutane
  –    Its structure is
–    N is  PoCl₃
–    R is HCl
–    W – is sodium propanoate
–     Its structure is

 CHEMICAL REACTIONS OF PHENOL

Generally chemical reactions of phenol can be divided into two types;
 i.   Electrophilic substitution reactions inside  OH^– group.
 ii.  Electrophilic substitution reactions in benzene ring.

1. ELECTROPHILIC SUBSTITUTION REACTION INSIDE  OH^–  GROUP

a) REACTION WITH ALKALINE SOLUTION
    Unlike Alcohol, phenol react with alkaline soluble NaOH
        i.e.  Alcohol + Alkaline solution. e.g, No reaction

The reactions give one of the differences between alcohol and phenol

b)  REACTION WITH ALKALING METALS
Phenol reacts, with alkaline metals like    etc to form phenoxide and hydrogen gas is involved.

The reaction show one of the similarities between alcohol and phenol.
i.e
Alcohol + alkaline metal Allcoxide + Hydrogen gas.

c)  FORMATION OF ETHER

Phenol react with haloalkane in presence of acqueous sodium hydroxide to form ether.

Generally

The reaction show another similarity between alcohol and phenol although in alcohol there is no need of .

i.e

Example

d) FORMATION OF ESTER
Phenol reacts with acyl compounds in presence of NaO to form ester.

and phenol  i.e  alcohol also reacts with acyl compounds  to form ester although in alcohol there is no need of  NaOH_(aq).

e) REACTION WITH SODIUM CARBONATE.
Phenol reacts with sodium carbonate to form phenoxide and the gas which turn lime water milky i.e. CO₂ gas is evolved.

–  The reaction show another difference between alcohol and phenol  i.e. Alcohol reacts with  .

II.  ELECTROPHILIC SUBSTITUTION REACTION IN BENZENE RING
– Under this heading phenol reacts like benzene the only difference is that OH^–  group in phenol directs incoming electrophile at ortho and Para position.

      TESTS OF PHENOL
Phenol turns blue litmus paper into red

–  With ion (III) Chloride phenol tends to form purple violet color of ion(III) phenoxide.

– With bromine water phenols tend to form white ppt of  2-tribomophenol.

SOME DIFFERENCES BETWEEN ALCOHOL AND PHENOL

Do not undergo oxidation easily

2

Do not react with bromine water

Form white ppt of 2, 4, 6 – tribomophenol with bromine water.

3

Do not react with FeCl₃

 

Form purple colouration with ion(III) chloride.

4

Form ester ( has fruity smell)

 

Do not react with carboxylic acid

5

Do not react with sodium hydroxide solution

 

Form white ppt of sodium phenoxide with NaOH_(aq).

6

Do not react with sodium carbonate

 

Form white ppt of sodium phenoxide and gas which turns lime water milky (i.e CO₂  is evolved).

 

SIMILARITIES BETWEEN ALCOHOL AND PHENOL

– Evolve hydrogen  gas with alkaline metals.
– They form ether with haloalkane.
– They form ester with acyl compound.
– They reacts with hydrogen halide.