Question

Iodoform on heating with KOH gives
A.\[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{CHO}}\]
B.\[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOK}}\]
C. \[{\rm{HCOOK}}\]
D. HCHO

Answer 1

Hint: Iodoform is also named chemically as triiodomethane. It is a crystalline solid of yellow colour which belongs to the organic halogen family. It is useful in the antiseptic form in medicines for skin diseases.

Complete Step by Step Solution:
Let’s discuss the reaction of iodoform with KOH. The chemical formula of iodoform is \[{\rm{CH}}{{\rm{I}}_{\rm{3}}}\] . When an iodoform reacts with potassium hydroxide , potassium formate is formed. The reaction is as follows:

\[{\rm{CH}}{{\rm{I}}_{\rm{3}}} + 4{\rm{KOH(aq)}} \to {\rm{HCOOK}} + 3{\rm{KCl}} + 2{{\rm{H}}_{\rm{2}}}{\rm{O}}\]

So, the above reaction gives the product Potassium formate (HCOOK), Potassium chloride and water.

Hence, option C is right.

Additional Information: The formation of iodoform takes place when iodine and sodium hydroxide is warmed with ketones and aldehydes possessing –COCH3 group.
\[{\rm{R}} - {\rm{CO}} - {\rm{C}}{{\rm{H}}_{\rm{3}}} + {{\rm{X}}_{\rm{2}}} + {\rm{Base}} \to {\rm{RCO}}{{\rm{O}}^ - } + {\rm{CH}}{{\rm{X}}_{\rm{3}}}\]; swhere X is halogen. X is Cl, Br, I and Fluorine.

Let’s understand the iodoform test in detail. Iodoform test detects the presence of carbonyl compounds having structure \[{\rm{R}} - {\rm{CO}} - {\rm{C}}{{\rm{H}}_{\rm{3}}}\] and alcohols of the formula \[{\rm{R}} - {\rm{CH}}\left( {{\rm{OH}}} \right) - {\rm{C}}{{\rm{H}}_{\rm{3}}}\] of a given unknown substance.

When iodine and methyl ketone undergoes reaction in the basic medium, a yellow coloured precipitate of antiseptic smell is produced. Also, some secondary alcohols possessing atleast one methyl group also produced yellow coloured ppt. when reacts with iodine (basic medium). This is the iodoform test. For example,

\[{\rm{R}} - {\rm{CO}} - {\rm{C}}{{\rm{H}}_{\rm{3}}} + {{\rm{I}}_{\rm{2}}} + {\rm{NaOH}} \to {\rm{RCO}}{{\rm{O}}^ - }{\rm{N}}{{\rm{a}}^ + } + {\rm{CH}}{{\rm{I}}_{\rm{3}}}({\rm{yellow}}\,{\rm{ppt}}{\rm{.}})\]

Note: The iodoform test also helps to distinguish between methanol and ethanol. Ethanol whose chemical formula is \[{\rm{C}}{{\rm{H}}_{\rm{3}}} - {\rm{C}}{{\rm{H}}_{\rm{2}}} - {\rm{OH}}\] possesses alpha hydrogens. And it gives the positive iodoform test. But, due to the absence of alpha hydrogen atoms in methanol( whose chemical formula is HCHO), it gives a negative iodoform test.