Question

Reaction Of Toulene?

`C_6H_5CH_3`(Toulene) reacts with 2 equivalents of
`Cl_2` and then the product of that reaction reacts with `NaOH`(aqueous) gives aldehyde.

What does the 2 equivalents of `Cl_2` in the above reaction mean and what is its purpose in the reaction?

Answer 1

Here's what I get.

Explanation:

An equivalent of chlorine is the mass of `"Cl"_2` that will react with 1 mol of `"H"` atoms.

For example, consider the reaction:

`"C"_6"H"_5"CH"_2"-"color(red)("H") + color(red)("Cl")"-Cl" → "C"_6"H"_5"CH"_2"-Cl" + color(red)("HCl")`

One mole of chlorine reacts with one mole of `"H"` atoms, so one equivalent of chlorine is the same as one mole of chlorine.

The "2 equivalents of chlorine" tells you that there is enough chlorine to replace two moles of `"H"` atoms.

`underbrace("C"_6"H"_5"CH"_3)_color(red)("bottom") + "2Cl"_2 → underbrace("C"_6"H"_5"CHCl"_2)_color(red)("(dichloromethyl)benzene") + "2HCl"`

The base-catalyzed hydrolysis of a gem-dihalide gives an aldehyde or a ketone.

The first part of the reaction consists of an ordinary nucleophilic substitution to produce a gem-chlorohydrin.

The gem-chlorohydrin is unstable and quickly loses a molecule of `"HCl"`.

`"C"_6"H"_5"CHCl"_2 stackrelcolor(blue)("OH"^"-" color(white)(mm))(→) [underbrace("C"_6"H"_5"CH(OH)Cl")_color(red)("unstable intermediate")] → underbrace("C"_6"H"_5"CH(=O)")_color(red)("benzaldehyde")`