Detection of Alcohols

Cerric Ammonium Nitrate Test (Group Reagent for all alcohols):

Alcohols + (NH₄)₂[Ce(NO₃)₆] (cerric ammonium nitrate / CAN) → Red coloured complex

Lucas Test (distinguish 1°, 2°, 3°):

1° alcohol: 
\[ \mathrm{R}_2\mathrm{CH} - \mathrm{OH} \xrightarrow{\text{Conc. HCl} + \text{anhyd. ZnCl}_3} \] No reaction (no turbidity at room temperature)

2° alcohol:
\[ \mathrm{R}_2\mathrm{CH} - \mathrm{OH} \xrightarrow{\text{Conc. HCl} + \text{anhyd. ZnCl}_2} \mathrm{R}_2\mathrm{CH} - \mathrm{Cl} \]
Turbidity in ~5 minutes

3° alcohol: 
\[ \mathrm{R}_2\mathrm{CH} - \mathrm{OH} \xrightarrow{\text{Conc. Hcl} + \text{anhyd. ZnCl}_2} \mathrm{R}_3\mathrm{CCl} \]
Immediate turbidity

Benzyl and allyl alcohols react as rapidly as tertiary (exceptions)

Victor-Meyer's Test:

• 1° alcohol → Nitric acid derivative → red colour (with NaOH)
  \[ \begin{aligned} & \mathrm{RCH}_2-\mathrm{OH} \xrightarrow{\mathrm{P}+\mathrm{I}_2} \mathrm{RCH}_2-\mathrm{I} \xrightarrow{\mathrm{AgNO}_2} \mathrm{RCH}_2-\mathrm{NO}_2 \\[1ex] & \xrightarrow{\mathrm{HONO}} \underset{\text{Nitrolic acid}}{\mathrm{R} - \underset{\underset{\displaystyle \mathrm{NOH}}{||}}{\mathrm{C}} - \mathrm{NO}_2} \xrightarrow{\mathrm{NaOH}} \underset{\text{(Blood red colouration)}}{\mathrm{R} - \underset{\underset{\displaystyle \mathrm{NO}^- \mathrm{Na}^+}{||}}{\mathrm{C}} - \mathrm{NO}_2} \end{aligned} \]

• 2° alcohol → blue colour
  \[ \begin{aligned} & \mathrm{R}_2\mathrm{CHOH} \xrightarrow{\mathrm{P}+\mathrm{I}_2} \mathrm{R}_2\mathrm{CH} - \mathrm{I} \xrightarrow{\mathrm{AgNO}_2} \mathrm{R}_2\underset{\underset{\displaystyle \mathrm{N=O}}{|}}{\mathrm{CH}} - \mathrm{NO}_2 \\[1ex] & \xrightarrow{\mathrm{HONO}} \mathrm{R}_2\mathrm{C} - \mathrm{NO}_2 \xrightarrow{\mathrm{NaOH}} \text{Blue colouration} \end{aligned} \]

• 3° alcohol → no colour
  \[ \begin{aligned} & \mathrm{R}_3\mathrm{C} - \mathrm{OH} \xrightarrow{\mathrm{P} + \mathrm{I}_2} \mathrm{R}_3\mathrm{C} - \mathrm{I} \xrightarrow{\mathrm{AgNO}_2} \mathrm{R}_3\mathrm{H} - \mathrm{NO}_2 \\[1ex] & \xrightarrow{\mathrm{HONO}} \text{No reaction} \xrightarrow{\mathrm{NaOH}} \text{Colourless} \end{aligned} \]

Iodoform Test:

• Organic Compounds + 4I₂ + 6NaOH → yellow ppt. 
  The above reaction is known as the Iodoform test.
• Positive for: CH₃CHO (ethanal), CH₃COCH₃ (acetone), CH₃CHOH–R (2° alcohols with CH₃CHOH–), ethanol only among primary alcohols (CH₃CH₂OH)
• Diethyl ketone does NOT give iodoform test
• To give iodoform: must contain CH₃CO– or CH₃CHOH– group