Phenol L.O. To explore the effect of an OH group on the reactivity of the benzene ring. To be able to describe and explain the key reactions of phenol.

Phenol Structure: Phenol is an aromatic alcohol with formula C 6 H 5 OH - OH group is attached directly to the benzene ring - Almost colourless crystalline solid Properties: The OH group changes the reactivity of the benzene ring and the benzene ring changes the reactivity of the OH group. Hydrogen bonding from OH group = stronger intermolecular forces resulting in phenol being solid at room temperature. Acting as an ACID: OH group also hydrogen bonds with water. Therefore phenol dissolves in water and alkalis (forming soluble ionic salts). Weak acid so does not fully ionise in water and so does not react with carbonates to produce CO 2.

What are the products when phenol reacts with the following? Water NaOH Na

Phenol – reactions of the OH group Water -Phenol is a weak acid and dissolves only slightly in water forming a weakly acidic solution -Stronger acid than aliphatic alcohols -Ring helps weaken the O-H bond and stabilises the resulting anion C 6 H 5 OH(aq) C 6 H 5 O¯(aq) + H + (aq) NaOH -Phenol reacts with sodium hydroxide to form a salt - sodium phenoxide -Ionic and water soluble C 6 H 5 OH(aq) + NaOH(aq) C 6 H 5 O¯ Na + (aq) + H 2 O(l) Sodium -Phenol reacts with sodium to form an ionic salt - sodium phenoxide -Hydrogen is also produced (similar to sodium reacting with aliphatic alcohols such as ethanol) 2C 6 H 5 OH(s) + 2Na(s) 2C 6 H 5 O¯ Na + (s) + H 2 (g)

Phenol Preparation: An OH group cannot be directly added to a benzene ring by electrophilic substitution. - Instead, phenol is synthesised in a multi-stage process Step 1 - Nitration of benzene reagentsconc. nitric acid and conc. sulphuric acid (catalyst) conditionsreflux at 55°C equationC 6 H 6 + HNO 3 C 6 H 5 NO 2 + H 2 O mechanismelectrophilic substitution 1

Step 2 - Reduction of nitrobenzene reagentstin and conc. hydrochloric acid conditionsreflux equationC 6 H 5 NO [H] C 6 H 5 NH 2 + 2H 2 O mechanismreduction 2 Phenol 3 Step 3 - Diazotisation of phenylamine reagentsnitrous acid and hydrochloric acid (use sodium nitrite) conditionskeep below 10°C equationC 6 H 5 NH 2 + HNO 2 + HCl C 6 H 5 N 2 + Cl¯ + 2H 2 O reaction typediazotisation

Step 4 - Substitution of diazo group by OH reagentswater conditionswarm above 10°C equationC 6 H 5 N 2 + Cl¯ + H 2 O C 6 H 5 OH + N 2 + HCl reaction typehydrolysis / substitution 4 Phenol Naming derivatives of phenol

What does the OH group do to the reactivity of the benzene group? The OH groups ACTIVATES the benzene ring. Group ELECTRON DONATING Example(s) OH, CH 3 Electron density of ring Increases Ease of substitution Easier Position of substitution 2,4,and 6 ONE LONE PAIR of electrons on the oxygen of OH interacts with the delocalised electrons of the benzene ring, aiding E+ attack. This results in MILDER CONDITIONS for phenol reactions compared to the corresponding benzene reactions.

Electrophilic substitution Bromine - OH group is electron releasing - Increases the electron density of the delocalised system, so making substitution much easier compared to benzene - Electron density is greatest at the 2,4 and 6 positions, so substitution takes place at the 2,4 and 6 positions - Phenol reacts readily with bromine water WITHOUT A CATALYST - In fact so easy, multiple substitution takes place Nitric acid - Dilute HNO 3 reacts rapidly with phenol at room temperature. - Resulting product is a BROWN MIXTURE. - Main products are 2 and 4-nitrophenol. Compare this to the conditions required for nitration of a benzene ring when the ring is NOT activated. Phenol - reactions of the aromatic ring

Production of antiseptics and disinfectants Antiseptics – chemicals that kill microorganisms, but can be used safely on the skin. Disinfectants – chemicals that kill microorganisms. Very powerful reagent and as such is now not used on skin or living tissue as too dangerous. Phenol not used as an antiseptic as it burns the skin. Substituted phenols can however be used as an antiseptic – TCP, Dettol. Thermosetting plastics (resins) Thermoplastic polymers – soften on heating and can be moulded into different shapes. These shapes remain on cooling (e.g. polyethene, pvc) Thermosetting polymers – set hard on formation and CAN NOT be softened or moulded (BAKELITE) Uses of phenol

Polyethene and pvc Thermoplastic polymers

Bakelite Thermosetting polymer

NaOH (aq) CH 3 COCl 3Br 2 (aq) N.B: Phenol is only partially soluble and forms 2 layers with water at r.t. Ester formation = phenylethanoate Colourless solution White ppt formed (NO catalyst needed) + 3HBr (aq) + H HCl