Unit 4.3 Alcohols and Phenols

Oxidation is gain of oxygen or loss of hydrogen

Reduction is loss of oxygen and gain of hydrogen

A hydrocarbon with an OH group

A benzene ring with an OH group attached

-Reduction of an aldehyde
-Reduction of a carboxylic acid
-Nucleophilic substitution of terminal halogenalkane

No, as the reaction will always run to completion

Lithium tetrahydrido aluminate (LiAlH₄), as a strong reducing agent is required

ethoxyethane

It is a strong enough reducing agent to reduce water, so any reactions involving it must be done completely dry. Ethoxyethane is also highly flammable

The reduction of a carbonyl using an aqueous solution of sodium tetrahydridoborate (NaBH₄)

Carbonyls are more readily reduced than carboxylic acids, so a weaker reducing agent may be used

Using square brackets: [H]

A halogenoalkane may have its halogen substituted for an OH- group by reacting it with aqueous sodium hydroxide

The polar OH- group allows the formation of hydrogen bonds

Shorter alcohols are water soluble as the number of hydrogen bonds broken and formed during dissolving is comparable, and so are the energies

-Hydrogen chloride (HCl + ZnCl)
-Phosphorous V chloride (PCl₅)
-Thionyl chloride (SOCl₂)

Using hydrobromic acid (NaBr + H₂SO₄ → HBr)

Using phosphorous III iodide ($PI_3$)

Boiled under reflux as HCl gas is bubbled through the solution

No specific conditions, the reactions occurs readily under standard conditions

No specific conditions, the reactions occurs readily under standard conditions

Using thionyl chloride ($SOCl_2$), as all secondary products are gaseous, reducing the number of purification steps required

The 2 reagents form HBr in situ, which is easier than using premade hydrobromic acid.

Heated under reflux

One where elimination and addition occur simultaneously

The alcohol

[ alcohol ] yl [ carboxylic acid ]
noate (start with alcohol, finish with acid)

A carboxylic acid with the hydroxide group replaced by a chlorine (ROCl)

They are very reactive as the chlorine is a very strong leaving group

The alcohol and acid chloride esterify, producing the ester and HCl

Standard conditions in the presence of $H_2SO_{4[conc]}$

Carboxylic acids > Phenol > Water > Alcohol

Phenol + water ⇌ Phenoate ion + Hydroxonium ion

One of the lone pairs on the oxygen overlaps with the pi-electron cloud, spreading the charge across the whole molecule

Oxygen is still electronegative enough to draw the delocalised electrons towards itself, forming a region of negative charge, which will tend to attract the H+ back

An acid-base reaction occurs, forming Sodium phenoxide and water

The addition of sodium carbonate (Na₂CO₃) solution. Phenol is too weak of an acid to react, whereas carboxylic acids will react, producing CO₂ gas

-It is fairly insoluble in water.
-It reacts with sodium hydroxide solution to give a colourless solution (and therefore must be acidic).
-It doesn't produce carbon dioxide with sodium carbonate or hydrogencarbonate solutions (and so must be only very weakly acidic).

Phenol is more reactive than benzene due to the disruption of the pi-electron cloud by the hydroxide group

The -OH group has a 2,4 directing effect

The addition of bromine water. A positive test will result in the solution changing from yellowish-brown to colourless, and a white precipitate forming (2,4,6-tribromophenol).

2,4,6-tribromophenol and HBr

Benzene requires concentrated sulphuric acid, nitric acid, and heat to be nitrated, whereas phenol only requires dilute nitric acid and no heating

2-nitrophenol and 4-nitrophenol

2,4,6-trinitrophenol (picric acid)

The increased electron density from the overlapping of the oxygen's lone pair with the delocalised cloud results in a higher susceptibility to electrophilic attack

Addition of aqueous ferric chlorde (FeCl₃). A positive test will result in the formation of an intense violet-purple complex in solution