H3C-CH2-CH(OH)-CH3 (i) NaI, H3PO4; (ii) Mg, dry ether; (iii) D2O Product [X] Product [X] formed in the above reaction…

Step 1: Butan-2-ol + NaI/H3PO4 → 2-iodobutane

$\ce{H3C-CH2-CH(OH)-CH3 + NaI ->[ H3PO4 ] H3C-CH2-CHI-CH3 + H2O}$

The -OH is converted to -I (nucleophilic substitution, SN2 with inversion at C2). Product: 2-iodobutane ($\ce{H3C-CH2-CHI-CH3}$)

Step 2: 2-Iodobutane + Mg/dry ether → Grignard reagent

$\ce{H3C-CH2-CHI-CH3 + Mg ->[ dry ether ] H3C-CH2-CH(MgI)-CH3}$

The C-I bond is converted to C-MgI (carbanion equivalent). Grignard: sec-butylmagnesium iodide

Step 3: Grignard + D2O → deuterium incorporation

Grignard reagents react with $\ce{D2O}$ (deuterium oxide) in the same way as with water — the C-Mg bond is protonated/deuterated:

$\ce{H3C-CH2-CH(MgI)-CH3 + D2O -> H3C-CH2-CHD-CH3 + Mg(OD)I}$

The carbanion equivalent (C-Mg) gets a deuterium from $\ce{D2O}$.

Product [X] = $\ce{H3C-CH2-CHD-CH3}$ (2-deuterobutane) ✓

Key Points to Remember:

• Grignard + $\ce{D2O}$ → R-D (deuterium incorporation at the carbanion carbon).
• This is used as a synthetic tool to introduce deuterium at specific positions.
• NaI/H3PO4 converts alcohols to iodides (alternative to HI).
• The sequence: alcohol → iodide → Grignard → deuterated compound.