Question

The main product of mustard oil reaction is __________.

Answer 1

Hoffman's Mustard oil test also known as mustard oil reaction is used to differentiate between primary , secondary and tertiary amines. In this test, the major product that is formed has a pungent smell.

Complete-step- by- step answer:
A. In mustard oil reaction, primary amines $(R-N{H}_{3})$ are warmed with alcoholic carbon disulphide $(C{S}_{2})$. It is followed by heating with excess of mercuric chloride $(Hg{Cl}_{2})$ to form alkyl isothiocyanates. These isothiocyanates have a pungent smell which is similar to the smell of mustard oil.
The reaction that takes place in this process is:

$R-N{ H }_{ 2 }\quad +\quad C{ S }_{ 2 }\quad \xrightarrow [ Hg{ Cl }_{ 2 } ]{ } \quad R-NCS\quad +\quad HgS\quad +\quad 2HCl$

Thus is in this reaction the main product formed is alkyl isothiocyanate.

B. Mustard oil reaction in secondary amines:
The secondary amines $(R-N{H}_{2}-R)$ are warmed with alcoholic carbon disulphide $(C{S}_{2})$ to form dithiocarbamic acid but it fails to react with mercuric chloride $(Hg{Cl}_{2})$.

C.Mustard oil reaction in tertiary amines:
The tertiary amines neither react with alcoholic carbon disulfide nor with mercuric chloride $(Hg{Cl}_{2})$.

Note: Alkyl isothiocyanate, when stabilized appears as a colorless to pale-yellow oily liquid. It has an irritating odor. The boiling point of alkyl isothiocyanate is 300°F. It is poisonous when ingested and skin absorbed. It emits toxic fumes when heated to high temperature. It is insoluble in water and is slightly denser than water. It is used to make other chemicals and as a fumigant.