question_answer

  (a) How can the following conversions be carried out? (i) Ethanol to acetone                    (ii) Benzene to acetophenone   (iii) Benzoic acid to benzaldehyde (b) Describe the following giving a suitable example in each case. (i) Decarboxylation                                          (ii) Cannizzaro's reaction                                                             [3+2] Or (a) An organic compound 'A' contains 69.77% carbon, 11.63% hydrogen and rest is oxygen. The molecular mass of'A' is 86. It does not reduce Tollen's reagent but forms an addition compound with sodium hydrogen sulphite. 'A' gives a positive idoform test. On vigorous oxidation 'A' gives ethanoic and propanoic acids. Deduce the possible structure of 'A'. (b) State reasons for the following situations. (i) Monochloro ethanoic acid is a weaker acid than dichloro ethanoic acid. (ii) Benzoic acid is a stronger acid than ethanoic acid.                                                                                       [3 + 2]

Answer:

  (a) (i) Ethanol to acetone               [1] (ii) Benzene to acetophenone (iii) Benzoic acid to benzaldehyde (b) (i) Decarboxylation When sodium salt of a carboxylic  acid  is  heated  with  sodalime, hydrocarbon is formed by loss of carbon dioxide. It is called decarboxylation. Through it, carbon chain can be degraded             [1] (ii) Cannizzaro reaction Aldehydes without react with concentrated NaOH to give an acid salt by oxidation and an alcohol by reduction. Thus disproportionate of aldehyde takes place. This is called Cannizzaro reaction. Benzaldehyde, withoutalso show this reactions                                        [1] Or (a)

	%	Mol	Molar ratio
C H O	69.77 11.63 18.60	5.81 11.63 1.1625	5 10 0

[1] Empirical formula Empirical formula weight = 60 +10 +16 =86 Molar mass =86 Thus molecular formula It does not reduce Tollen's reagent: CHO absent It forms bisulphite complex : keto group Thus, A is                   [1] (b)   (i)  (/_) effect of the two Cl-atoms stabilises the to a greater extent as compared to (/_) (/_) effect of one CI-atom. Thus is weaker than .                                               [1] (ii) (A) is stabilised by resonance in only On the other hand ionises is stabilised in as well as in .