Chemca Formula Sheet - Phenols

CHEMCA

EXAM MASTER FORMULA SHEET

Organic Chemistry: Phenols

Acidity, Electrophilic Substitution & Named Reactions

1. Structure & Acidic Nature

Phenols ($\ce{Ar-OH}$) are significantly more acidic than alcohols due to the resonance stabilization of the resulting phenoxide ion.

Acidity Mechanism

The phenoxide ion ($\ce{C6H5O-}$) is highly stabilized by resonance, dispersing the negative charge into the benzene ring.

\text{Acidity: } \ce{Phenol > H2O > Alcohol}

Substituent Effects

• EWG ($\ce{-NO2, -CN}$): Increase acidity (stabilize phenoxide). Effect is stronger at Ortho/Para positions.
• ERG ($\ce{-CH3, -OCH3}$): Decrease acidity (destabilize phenoxide).

Picric acid (2,4,6-trinitrophenol) is more acidic than most carboxylic acids!

2. Methods of Preparation

From Cumene (Industrial)

$\ce{Cumene (Isopropylbenzene) + O2 -> Cumene Hydroperoxide}$
$\ce{Cumene Hydroperoxide ->[H3O+] Phenol + Acetone}$

*Acetone is a highly valuable byproduct, making this method commercially viable.*

Other Lab Methods

• From BDC: $\ce{C6H5N2+Cl- ->[H2O][\Delta] C6H5OH + N2 + HCl}$
• Dow's Process: $\ce{C6H5Cl ->[NaOH][623 K, 300 atm] C6H5O-Na+ ->[H+] C6H5OH}$
• Alkali Fusion: $\ce{C6H5SO3H ->[NaOH][\Delta] C6H5O-Na+ ->[H+] C6H5OH}$

3. Electrophilic Aromatic Substitution

The $\ce{-OH}$ group is highly activating and strongly Ortho-Para directing.

Reaction	Reagents / Conditions	Major Product
Nitration (Dilute)	Dil. $\ce{HNO3}$, 298 K	o-Nitrophenol & p-Nitrophenol (o-isomer is steam volatile due to intra H-bond)
Nitration (Conc.)	Conc. $\ce{HNO3}$ + Conc. $\ce{H2SO4}$	Picric Acid (2,4,6-trinitrophenol)
Bromination (Polar)	$\ce{Br2 / H2O}$ (Bromine water)	2,4,6-Tribromophenol (White Ppt)
Bromination (Non-polar)	$\ce{Br2 / CS2}$ or $\ce{CHCl3}$, 273 K	p-Bromophenol (Monosubstitution)

4. Essential Named Reactions

Kolbe's Reaction

$\ce{C6H5O^-Na+ + CO2 ->[400 K, 4-7 atm] Sodium Salicylate ->[H+] Salicylic Acid}$

Salicylic acid is the precursor for Aspirin synthesis.

Reimer-Tiemann Reaction

$\ce{Phenol + CHCl3 + aq. NaOH ->[H+] Salicylaldehyde}$

Proceeds via Dichlorocarbene ($:CCl_2$) intermediate.

Reaction with Zinc Dust

Used to deoxygenate Phenol, converting it back to the parent hydrocarbon.

$\ce{C6H5OH + Zn ->[\Delta] C6H6(Benzene) + ZnO}$

5. Identification Tests for Phenols

Ferric Chloride Test

$\ce{Phenol + Neutral FeCl3 -> \text{Violet/Purple Complex}}$

*Aliphatic Alcohols DO NOT give this test.*

Liebermann's Nitroso Test

$\ce{Phenol + NaNO2 + H2SO4 -> \text{Red} ->[NaOH] \text{Deep Blue}}$

Specific test for phenols containing a free para position.

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Exam Master Review Sheet - Phenols