Give chemical tests to distinguish between 

(i) Propanal and propanone, 

(ii) Benzaldehyde and acetophenone. 

(b) How would you obtain 

(i) But-2-enal from ethanal, 

(ii) Butanoic acid from butanol, 

(iii) Benzoic acid from ethylbenzene? 


(i) Propanal (CH3CH2CHO) can be distinguished from propanone (CH3COCH3) by iodoform test. 

Being a methyl ketone, propanone on treatment with I2/NaOHundergoes iodoform reaction to give a yellow ppt. of iodoform 

CH subscript 3 COCH subscript 3 space plus 3 NaOI space rightwards arrow stack CHl subscript 3 space with Iodoform below downwards arrow space plus CH subscript 3 COONa space plus 2 NaOH

Propanal space on space the space other space hand space doens space not space give space this space test.
CH subscript 3 CH subscript 2 CHO space rightwards arrow with space space NaOH space space space on top space No space yellow space ppt. space form

 
(ii) Benzaldehyde (C6H5CHO) and acetophenone (C6H5COCH3) can be distinguished by iodoform test. 

 stack straight C subscript 6 straight H subscript 5 COCH subscript 3 space with acetophenone below plus 3 NaOl space rightwards arrow straight C subscript 6 straight H subscript 5 COONa space plus CHI subscript 3 downwards arrow plus 2 NaOH

stack straight C subscript 6 straight H subscript 5 CHO with Benzaldehyde below space rightwards arrow with NaOI on top space No space Yellow space ppt space of space iodoform

Acetophenone, being a methyl ketone on treatment with I2 /NaOH undergoes iodoform reaction to give a yellow ppt. of iodoform. On the other hand, benzaldehyde does not give this test. 

 

 b)
i) 



ii) stack CH subscript 3 CH subscript 2 CH subscript 2 straight O with Butanol below straight H space rightwards arrow from space space space to straight K subscript 2 Cr subscript 2 straight O subscript 7 comma space divided by straight H subscript 2 SO subscript 4 of space space stack CH subscript 3 CH subscript 2 CH subscript 2 COOH with Butanoic space acid below


iii)

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How will you bring about the following conversions?

 (i) Propanone to propane

(ii) Benzoyl chloride to benzaldehyde

(iii) Ethanal to but-2-enal


 (i) Conversion of Propanone to Propane:


 (ii) Conversion of Benzoyl chloride to benzaldehyde:

(iii) On treatment with dilute alkali, ethanol produces 3-hydroxybutanal gives But-2-enal on hheating.

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2-chloro-2-methylpentane on reaction with sodium methoxide in methanol yields:

  • Both a and c

  • Only c

  • Both a and b

  • Both a and b


D.

Both a and b

Strong nucleophile left parenthesis straight O with minus on top Me right parenthesis polar solvent (MeOH) gives elimination products Products over substitution products but all products are possible in different yields.

Strong nucleophile left parenthesis straight O with minus on top Me right parenthesis polar solvent (MeOH) gives elimination products Products over substitution products but all products are possible in different yields.

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(a) Describe the following giving linked chemical equations: 

 (i) Cannizzaro reaction 

 (ii) Decarboxylation 

(b) Complete the following chemical equations: 

 


(i) Cannizaro reaction 

In this reaction, the aldehydes which do not have a -hydrogen atom, undergo self-oxidation and reduction (disproportionation) reaction on treatment with a concentrated alkali. 
Example: 

 

(ii) Decarboxylation 

The decarboxylation reaction can be carried out either by using soda lime or by electrolysis 

Using soda lime: Sodium salts of carboxylic acids when heated with soda lime (NaOH + CaO) in the ratio 3:1)  undergo decarboxylation reaction to yield alkanes. 

 RCOONa space rightwards arrow from heat to NaOH minus CaO of space straight R minus straight H space plus Na subscript 2 CO subscript 3

Electrolytic decarboxylation: Electrolysis of aqueous solutions of sodium or potassium salts of carboxylic acids give alkanes having twice the number of carbon atoms present in the alkyl group of acid. 

 This is known as Kolbe’s decarboxylation. 

 2RCOONa--> 2RCOO- + 2Na+

 H2O-->2OH- + 2H+

 
At Anode:-

2RCOO- - 2e---> CO2 + R - R

At Cathode:-

 2H+ + 2e----> H2


b) 

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 A compound 'A' of molecular formula C2H3OCl undergoes a series of reactions as shown below. Write the structures of A, B, C and D in the following reactions:

 

 

(b) Distinguish between the following:

(i) C6H5-COCH3 and C6H5 - CHO

(ii) Benzoic acid and methyl benzoate

(c) Write the structure of 2- methylbutanal.


(a) Using the given molecular formula, compound A is Ethanoyl Chloride CH3COCl, which undergoes reaction with poisoned palladium.
On carrying hydrogenation of A in the presence of poisoned palladium, we get an aldehyde. Hence, B can be Ethanal, CH3CHO.
An aldehyde, on treating with dilute alkali, undergoes aldol condensation reaction. Hence, C can be CH3CH (OH) CH2CHO.
On heating an aldol product, it loses water to produce a double bond and we get CH3CH=CHCHO.
Hence, we have

 

(b)
(i) Acetophenone has methyl group attached to carbonyl carbon while benzaldehyde does not. Therefore, we can use iodoform test to distinguish between the two. Acetophenone will undergo iodoform test and give a yellow precipitate.

C6H5-COCH3    C6H5COOH + CHI3

Acetophenone                           (yellow ppt.)

 

C6H5CHO    No reaction

Benzaldehyde

(ii) Benzoic acid can react with sodium bicarbonate to give brisk effervescence due to the release of CO2, while methyl benzoate does not.

C6H5COOH + NaHCO3----> C6H5COONa + H2O + CO2

Benzoic acid                                               (brisk effervescence)

 

C6H5COOCH3 + NaHCO3---> No reaction

Methyl benzoate

 

(c) The Structure of 2- methylbutanal is:

 

 

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