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Reductions Involving Aldehydes or Ketones

a Write the c...

Question

(a) Write the chemical reaction involved in Wolff-Kishner reduction.
(b) Arrange the following in the increasing order of their reactivity towards nucleophilic addition reaction:
$C_{6} H_{5} C O C H_{3}, C H_{3} - C H O, C H_{3} C O C H_{3}$
(c) Why carboxylic acid does not give reactions of carbonyl group?
(d) Write the product in the following reaction
$C H_{3} C H_{2} C H = C H - C H_{2} C N 1. (i - B u)_{2} A l H - ------- \to 2. H_{2} O$
(e) A and B are two functional isomers of compound $C_{3} H_{6} O$ .On heating with NaOH and $I_{2}$ , isomer B forms yellow precipitate of iodoform whereas isomer A does not form any precipitate. Write the formulae of A and B.

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Solution

(a) In Wolff-Kishner reduction carbonyl group of aldehydes and ketones is converted into methylene group. Aldehydes or ketones are heated with hydrazine and KOH or ptoassium tert butoxide in ethylene glycol to forms alkanes.
$R - C (O) - R^{'} (i) H_{2} N - N H_{2}, H_{2} O - --------------- \to (i i) K O H / e t h y l e n e g l y c o l, Δ R - C H_{2} - R^{'} + N_{2}$

(b) $C_{6} H_{5} C O C H_{3} < C H_{3} C O C H_{3} < C H_{3} - C H O$
In general, aldehydes are more reactive than ketones.
The aromatic aldehydes and ketones are less reactive than aliphatic counterparts.
(c) The lone pair of electrons on O atom of -OH group of carboxylic acid is in resonance with carbonyl group. Hence, the carbonyl carbon of carboxylic acid is less electrophilic than the carbonyl carbon of aldehydes or ketones.
Hence, carboxylic acid does not give reactions of carbonyl group.
(d) DIBAL-H reduces nitriles to aldehydes.
$C H_{3} C H_{2} C H = C H - C H_{2} C N 1. (i - B u)_{2} A l H - ------- \to 2. H_{2} O C H_{3} C H_{2} C H = C H - C H_{2} C H O$
(e) B forms yellow precipitate of iodoform.
Hence, B is a methyl ketone as it undergoes haloform reaction.
Thus, B is acetone $C H_{3} C O C H_{3}$
The isomer A does not form any precipitate.
Hence, it is not a methyl ketone. Hence A is propanal $C H_{3} C H_{2} C H O$

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Q. (a) Write the chemical reaction involved in Etard reaction.

(b) Arrange the following in the increasing order of their reactivity towards nucleophilic addition reaction:

C H_{3} - C H O, C_{6} H_{5} C O C H_{3}, H C H O

p K_{a}

C l - C H_{2} - C O O H

lower than the that of

C H_{3} C O O H

?

(d) Write the product in the following reaction:

C H_{3} C H_{2} C H = C H - C H_{2} C N 1. (i - B u)_{2} A I H - -------- \to 2. H_{2} O

(e) A and B are two functional isomers of compound

C_{3} H_{6} O

. On heating with NaOH and

I_{2}

, isomer A forms yellow precipitate of iodoform whereas isomer B does not form any precipitate. Write the formulae of A and B.

Q. (a) Write the chemical reaction involved in Etard reaction.

(b) Arrange the following in the increasing order of their reactivity towards nucleophilic addition reaction:

C H_{3} - C H O, C_{6} H_{5} C O C H_{3}, H C H O

p K_{a}

C l - C H_{2} - C O O H

lower than the that of

C H_{3} C O O H

?

(d) Write the product in the following reaction:

C H_{3} C H_{2} C H = C H - C H_{2} C N 1. (i - B u)_{2} A I H - -------- \to 2. H_{2} O

(e) A and B are two functional isomers of compound

C_{3} H_{6} O

. On heating with NaOH and

I_{2}

, isomer A forms yellow precipitate of iodoform whereas isomer B does not form any precipitate. Write the formulae of A and B.

Q. (A),(B) and (C) are three non-cyclic functional isomers of a carbonyl compound with molecular formula

C_{4} H_{8} O .

Isomers (A) and (C) give positive Tollens' test whereas isomer (B) does not give Tollens' test but gives positive Iodoform test. Isomers (A) and (B) on reduction with Zn(Hg)/conc. HCI give the same product (D).

(a) Write the structures of (A),(B),(C) and (B).

(b) Out of (A), (B) and (C) isomers, which one is least reactive towards addition of HCN?

(A), (B)

(C)

are three non-cyclic functional isomers of a carbonyl compound with molecular formula

C_{4} H_{8} O

(A)

(C)

give positive Tollen's test whereas isomer

(B)

does not give Tollen's test but gives positive Iodoform test. Isomers

(A)

(B)

on reduction with

Z n (H g) / c o n c

H C l

give the same product

(D)

Write the structures of

(A), (B), (C)

(D)

.

Q. An aromatic compound 'A' (Molecular formula

C_{8} H_{8} O

) gives positive

2, 4

-DNP test. It gives a yellow precipitate of compound '

B

' on treatment with iodine and sodium hydroxide solution. Compound '

A

' does not give Tollen's or Fehling's test. On drastic oxidation with potassium permanganate it forms a carboxylic acid '

C

' (Molecular formula

C_{7} H_{6} O_{2}

), which is also formed along with the yellow compound in the above reaction. Identify

A

B

C

and write all the reactions involved.

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