Alcohols, Phenols and Ethers - Named Reactions

Purpose: Used for the preparation of alcohols from alkenes.
Reagents: - Step 1: $\text{BH}_3 / \text{THF}$ - Step 2: $\text{H}_2\text{O}_2 / \text{OH}^-$
Mechanism and Selectivity: - This reaction follows an Anti-Markovnikov addition pattern. - The $\text{-OH}$ group is added to the less substituted carbon of the double bond. - No carbocation rearrangement occurs during this process.
Reaction Pathway: - $\text{R-CH=CH}_2 \rightarrow \text{R-CH}_2\text{-CH}_2\text{-BH}_2 \rightarrow \text{R-CH}_2\text{-CH}_2\text{-OH}$
Pedagogical Trick: Remember this as the "Opposite of Markovnikov."

Purpose: Formation of alcohols; highly important for chemical conversions.
General Mechanism: involves the addition of a Grignard reagent ( $\text{RMgX}$ ) to a carbonyl group.
Structural Intermediate: $\text{R-C-OMgX}$
Alcohol Classification by Reactant: - Formaldehyde ( $\text{HCHO}$ ): Produces a primary ( $1^\circ$ ) alcohol. - Aldehyde (Other than Formaldehyde): Produces a secondary ( $2^\circ$ ) alcohol. - Ketone: Produces a tertiary ( $3^\circ$ ) alcohol.
Reaction Summary: - $\text{RMgX} + \text{HCHO} \rightarrow 1^\circ \text{ alcohol}$ - $\text{RMgX} + \text{Aldehyde} \rightarrow 2^\circ \text{ alcohol}$ - $\text{RMgX} + \text{Ketone} \rightarrow 3^\circ \text{ alcohol}$

Process: Conversion of Phenol into salicylic acid.
Reagents: - 1) $\text{NaOH}$ - 2) $\text{CO}_2$ - 3) $\text{H}^+$
Key Outcome: The $\text{-COOH}$ (carboxylic acid) group enters the ortho position relative to the hydroxyl group.
Major Product: Salicylic acid (also known as $\text{o-Hydroxybenzoic acid}$ ).
Structure of Product: Phenol ring with a $\text{-COOH}$ group at the ortho position.
Pedagogical Trick: " $\text{CO}_2$ enters ortho."

Process: Phenol is treated to introduce a formyl group.
Reagents: $\text{CHCl}_3$ (Chloroform) and $\text{NaOH}$ .
Key Outcome: The $\text{-CHO}$ (aldehyde) group is introduced at the ortho position of the Phenol.
Intermediate: The reaction proceeds via the formation of dichlorocarbene ( $\text{:CCl}_2$ ).
Major Product: Salicylaldehyde.
Pedagogical Trick: "Phenol + $\text{CHCl}_3 \rightarrow \text{CHO}$ group."

Purpose: A primary method for the synthesis of ethers.
Participants: Alkyl halide ( $\text{R-X}$ ) and Sodium alkoxide ( $\text{R'-O}^-\text{Na}^+$ ).
Mechanism: This is an $\text{S}_\text{N}2$ reaction.
Reaction Equation: - $\text{R-X} + \text{R'-O}^-\text{Na}^+ \rightarrow \text{R-O-R'} + \text{NaX}$
Constraints and Limitations: - The reaction works best with primary ( $1^\circ$ ) alkyl halides. - Using secondary ( $2^\circ$ ) or tertiary ( $3^\circ$ ) alkyl halides results in an elimination problem, leading to alkenes rather than ethers.

Importance: This is the major industrial method for the preparation of phenol.
Reactant: Cumene (Isopropylbenzene), defined as a benzene ring with a $\text{-CH(CH}_3\text{)}_2$ group.
Reaction Pathway: - Step 1: Oxidation with $\text{O}_2$ and light ( $\text{hv}$ ) to form Cumene hydroperoxide ( $\text{C}_6\text{H}_5\text{-C(CH}_3\text{)}_2\text{OOH}$ ). - Step 2: Hydrolysis with acid ( $\text{H}^+$ ) to yield the final products.
By-products: This process is efficient because it produces two valuable products simultaneously: Phenol and Acetone.
Pedagogical Trick: "Phenol + Acetone together."

Process: Formation of an ester from an alcohol or phenol and a carboxylic acid.
Reactants: $\text{R-OH}$ (Alcohol/Phenol) and $\text{R-COOH}$ (Carboxylic acid).
Reaction Equation: - $\text{R-OH} + \text{R-COOH} \rightleftharpoons \text{R-COOR} + \text{H}_2\text{O}$
Chemical Nature: The reaction is reversible.
Conditions: Requires heat and the use of concentrated $\text{H}_2\text{SO}_4$ as a catalyst.
Pedagogical Trick: "Alcohol + Acid = Ester."

Purpose: Used for the classification and identification of primary, secondary, and tertiary alcohols.
Reagent: Lucas reagent, which consists of $\text{HCl}$ and $\text{ZnCl}_2$ .
Chemical Equation: - $\text{R-OH} + \text{HCl} \xrightarrow{\text{ZnCl}_2} \text{R-Cl} + \text{H}_2\text{O}$
Observations at Room Temperature: - Tertiary ( $3^\circ$ ) Alcohol: Results in immediate turbidity. - Secondary ( $2^\circ$ ) Alcohol: Results in turbidity appearing in a few minutes. - Primary ( $1^\circ$ ) Alcohol: Shows no turbidity at room temperature.

General Trends: - Primary ( $1^\circ$ ) Alcohols: Oxidize to form Aldehydes. - Secondary ( $2^\circ$ ) Alcohols: Oxidize to form Ketones. - Tertiary ( $3^\circ$ ) Alcohols: Generally show no reaction under standard oxidation conditions.
Reagent Specifics: - PCC (Pyridinium chlorochromate): A mild oxidant that stops the oxidation of primary alcohols at the aldehyde stage. - $\text{KMnO}_4 / \text{K}_2\text{Cr}_2\text{O}_7$ : Strong oxidizing agents that drive the reaction further.

Purpose: To form alkenes from alcohols.
Reaction Conditions: Heat and concentrated $\text{H}_2\text{SO}_4$ .
Chemical Equation: - $\text{R-CH}_2\text{-CH}_2\text{-OH} \xrightarrow[\text{heat}]{\text{conc. H}_2\text{SO}_4} \text{R-CH=CH}_2 + \text{H}_2\text{O}$
Reactivity of Alcohols: The order of reactivity is 3^\circ > 2^\circ > 1^\circ.
Mechanism: Follows an $E_1$ mechanism.

Directing Effect: The $\text{-OH}$ group activates the benzene ring and is ortho and para directing.
Reaction Variants: - With Dilute $\text{HNO}_3$ : Produces two products, o-nitrophenol and p-nitrophenol. - With Concentrated $\text{HNO}_3$ : Produces 2,4,6-trinitrophenol, also known as Picric acid.

Reagent: Aqueous bromine ( $3 \text{ Br}_2 (aq)$ ).
Reaction Pathway: - $\text{Phenol} + 3 \text{ Br}_2 (aq) \rightarrow 2,4,6\text{-tribromophenol} + 3 \text{ HBr}$
Observations: Formation of a white precipitate.
Key Note: This reaction is highly reactive due to ring activation by the $\text{-OH}$ group, so no catalyst is required.