April 04, 2012

Hydroxy Derivatives Three Marks

1. Alcohols cannot be used as a solvent for Grignard reagents. Why?
         Grignard reagents are decomposed by alcohol to alkane.
     Or Alcohols react with Grignard reagents.     Or Alcohols are sufficiently acidic to react with strong bases R : and H  :
                       R– OH + CH3MgX RO – MgX + CH4
2. Give a brief account on coupling reaction of phenol with benzene diazonium chloride. Or Write the dye test for phenol. Or How Phenol is identified by dye test? Give equation. Or Write a note on coupling reaction.
       Phenol couples with benzene diazonium chloride in alkaline medium to form p-hydroxy azobenzene.
3. Give chemical test to distinguish between ethanol and methanol.
Haloform Reaction:
           When alcohols containing CH3CHOH- group is treated with halogen and alkali, undergo haloform reaction.
                  Since methanol does not contain CH3CHOH- group, it does not undergo haloform reaction.
                     I2/KOH                     I2                          KOH
C2H5OH CH3CHO CI3CHO CHI3 + HCOOK
4. How can Terylene be prepared? Or How is Terylene prepared from glycol / ethylene glycol? Or How is Dacron prepared? Give any one of its uses.
             With Terephthalic acid, ethylene glycol forms the condensation polymer ‘Terylene’ (also known as dacron or terene).
Extensively used as a synthetic fibre.
5. How can the consumption of alcohol by a person be detected?
             The breath analysis test for the detection of ethanol involves the oxidation of alcohol in the breath of a person who has consumed alcohol, by acidic potassium dichromate and observing the change in the colour of the chromium ion CrVI from yellow orange to CrIII which is blue green colour.
8H+  +  Cr2O72-   +  3C2H5OH  ----------->  2Cr3+   +    3C2H4O  +   7H2O
6. How is benzyl alcohol prepared by Grignard's synthesis?
           Benzyl alcohol is prepared by the action of phenyl magnesium bromide on formaldehyde.
7.  How is phenol identified? Or  Give tests to identify phenol.
1. Neutral ferric chloride Test: Phenol gives violet colour with neutral ferric chloride.
2. Halogenation: When phenol is treated with bromine water the colour of bromine disappears with the formation of white precipitate. The white precipitate consists of 2, 4, 6-tribromo phenol.
3. Dye test: Phenol couples with benzene diazonium chloride in alkaline medium to form p-hydroxy azobenzene, a red orange dye.
4. Phthalein fusion: Phenols are heated with phthalic anhydride and con. H2SO4  to give Phenolphthalein. This can be tested by the formation of pink colour when it is treated with sodium hydroxide.
8. How is phenol prepared by Dow's process? Or Explain Dow's process.
              Phenol is prepared by heating Chloro benzene with caustic soda at high temperature and pressure.                             
                                        623K
C6H5Cl + NaOH   C6H5OH + NaCl
                                       300 atm.
         This reaction is an example of aromatic nucleophilic substitution.
         The replacement of nuclear halogen is difficult because of the stronger C–Cl bond compared to that in alkyl halides. Yet, this reaction is used for the large scale preparation and is known as Dow’s process.
9. How will you convert C2H5OH to C2H5 O C2H5                   
        C2H5OH undergo intermolecular dehydration by treating with con. H2SO4 to give C2H5OC2H5.
                                                               H2SO4
              2C2H5OH C2H5 O C2H5 + H2O
                                          410K
10. Phenols are soluble in alcohols. Why?
Phenols are soluble in alcohols (and ether) due to intermolecular hydrogen bonding.
11. Phenol is insoluble in NaHCO3 solution but acetic acid is soluble. Give reason.
Phenols are weakly acidic. Hence phenols dissolve only in a strong base like NaOH to form salt.
                     C6H5OH + NaOH C6H5ONa + H2O
          Acetic acid is a stronger acid than phenol. Hence acetic acid dissolves even in a weak base like NaHCO3 to form salt..
12. What happens when ethylene reacts with cold dilute alkaline KMnO4?
          By the action of cold dilute alkaline KMnO4 (known as Baeyer’s reagent) on ethylene, ethylene glycol is formed.                               Alkaline KMnO4
            CH2 = CH2 + H2O + (O)           CH2OH - CH2OH
13. Why is glycol more viscous than ethanol?
               Because of the presence of two hydroxyl groups the intermolecular hydrogen bonding is made much stronger. Hydrogen bond can be formed between both OH groups resulting in a polymeric structure.
This leads to high viscosity.
14. Write a note on Kolbe's reaction.
              When sodium phenoxide is heated with carbon dioxide at 400K under pressure, sodium salicylate is formed. This is decomposed by dilute HCl, when salicylic acid is formed. CO2 is the electrophile in this reaction.
15. Explain the synthesis of glycerol from propylene. Or How is glycerol synthesized from propylene?
Starting from propylene (obtained in the cracking of petroleum) glycerol is synthesised as given below:
16. Give any three uses of benzyl alcohol.
1.  as a local anaesthetic in intravenus subcutaneous injections.
2.  as an antiseptic in ointments.
3.  as esters in perfumery. (Benzyl acetate has fragrance of Jasmine)
4.  as benzyl benzoate in the treatment of asthma and whooping cough.
5.  in the manufacture of synthetic resins.
17. How is allyl alcohol obtained from glycerol? Or What is the action of oxalic acid on glycerol at 533 K?
              When glycerol is heated with oxalic acid at 533 K, glyceryl dioxalate is formed which eliminates two molecules of carbon dioxide forming allyl alcohol.
The elimination of two molecules of carbon dioxide takes place by the cyclic re-organisation of bonds in the di-ester.
18. How is ethylene glycol converted into 1, 4-dioxan?
             Conc. H2SO4 being more powerful acid and dehydrating agent removes two molecules of water from glycol forming 1, 4-dioxan.
19. How is nitroglycerine prepared from glycerol?
               Glycerol when treated with a well cooled mixture of conc. H2SO4 and fuming nitric acid, nitroglycerine is formed.
20. How is phenolphthalein prepared? Or How will you convert phenol to phenolphthalein?
                Phenol is heated with phthalic anhydride and con. H2SO4 to give Phenolphthalein. This can be tested by the formation of pink colour when it is treated with sodium hydroxide.
21. How is tertiary butyl alcohol converted to isobutylene? Or How will you convert 2-methyl-2-propanol into 2-methyl propene? Or What happens when the vapour tert - butyl alcohol is passed over heated copper at 573 K?
Catalytic dehydrogenation:
             Dehydrogenation of tertiary butyl alcohol / 2-methyl-2-propanol by passing the vapours over heated copper at 573 K gives isobutylene / 2-methyl propene.
Absence of α-hydrogen in tertiary alcohol under the above condition leads to only dehydration to olefin.
22. Starting from phenol how would you obtain picric acid?
           Reaction of phenol with nitrating mixture - conc. H2SO4 and conc. HNO3 mixture - gives picric acid.
23. What happens when glycerol reacts with KHSO4? Or How does glycerol react with KHSO4? Or How is acrolein formed? Or Convert Glycerol to Acrolin
              When glycerol is heated with potassium bisulphate, KHSO4 (or conc. H2SO4 or P2O5) dehydration takes place. Two β-elimination reaction takes place to give acrolein or acrylic aldehyde.
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24. Give the Victor Meyer's test for tertiary alcohol.
Absence of α - H in tertiary alcohol makes it inactive to nitrous acid.
25. Give short notes on Riemer - Tiemann reaction
When phenol is refluxed with Chloroform and Sodium hydroxide, a formyl group – CHO is
introduced at the ortho or para position to – OH group, ortho or para Hydroxy benzaldehyde is formed

Similarly with CCl4 and NaOH, ortho or para Hydroxy benzoic acid is formed
26. Write the equation for action of heat on ethylene glycol with conc. Phosphoric acid.
When heated with conc. phosphoric acid, ethylene glycol eliminates a molecule of water forming diethylene glycol. (Intermolecular dehydration)

27. Give the oxidation reaction of phenol.
28. Write the Victor Meyer's test for secondary alcohol.
29. How are 1-propanol and 2-propanol distinguished by oxidation method?
1 - propanol with acidified potassium dichromate is first oxidised to propanaldehyde and then to propanoic acid.
2 - propanol with acidified potassium dichromate is first oxidised to propanone and then to ethaanoic acid with lesser number of carbon atoms.

Acidified Potassium permanganate oxidises the Alcohols directly to the Carboxylic acid.
 30. How is formic acid prepared from glycerol?
When glycerol is heated with Oxalic acid at 373 K – 383 K Glycerol mono formate is formed. This on hydrolysis gives Formic acid
31. What is glycerose? How is it prepared from glycerol?

Glycerose - A mixture of Glyceraldehyde and Dihydroxy acetone.
Milder oxidising agents like Bromine water or Fenton’s reagent [FeSO4 + H2O2] or sodium hypobromite (NaBrO) - oxidises glycerol to ‘glycerose

32. Explain Schotten - Baumann reaction
The reaction of phenols with benzoyl chloride in presence of sodium hydroxide to form benzoates is known as Schotten - Baumann reaction
                                         NaOH
C6H5OH + C6H5COCl            C6H5OCOC6H5 + HCl
33. How will you prepare benzyl alcohol from toluene?
Benzyl alcohol is prepared by the Chlorination of Toluene followed by Hydrolysis with aqueous NaOH.
                        Cl2                               NaOH
C6H5CH3              C6H5CH2Cl        →        C6H5CH2OH + NaCl
                     – HCl     Benzyl chloride
Or Benzyl alcohol is prepared by the Oxidation of Toluene by Chromium trioxide and Acetic anhydride Or Chromyl chloride Or Air in presence of V2O5 at 773 K followed by Reduction with Sodium amalgam and Water Or Zinc and Hydrochloric acid Or NaBH4 Or LiAlH4.
.                       (O)                                       2 [H]
C6H5CH3                  C6H5CHO                              C6H5CH2OH
                 Air / V2O5                       LiAlH4 Or NaBH4
                773 K / – H2O
Or Benzyl alcohol is prepared by the Oxidation of Toluene by acidified KMnO4 Or acid K2Cr2O7 Or alkaline KMnO4 followed by Reduction with LiAlH4
                  H+ / KMnO4 or K2Cr2O7                       LiAlH4                        LiAlH4
C6H5CH3                                      C6H5COOH             [C6H5CHO]            C6H5CH2OH
                             OH  / KMnO4

7 comments:

  1. why methyl alcohol cant be synthesised by grignard reagent and aldehyde

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    Replies
    1. Methyl alcohol cannot be synthesised by Grignard reagent and Aldehyde since the Alcohol contains only one Carbon atom

      Similarly, Formic acid cannot be prepared by Grignard reagent and Carbon dioxide since the Acid contains only one Carbon atom

      Note: Alcohol & Carboxylic acid contains one extra C atom compared to the original halide from which the Grignard reagent was prepared

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    2. And also alcohol is used as a decomposing agent for grignard reagent. Thus it is not synthesized.

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  2. Its a valuable content shared,would like to know more about it.

    Ethylhexyl Glycerin

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