Preparation of esters using acyl chloride
- Ethanoyl chloride is an example of an acyl chloride that will react instantly with cold ethanol to give ethyl ethanoate which is an ester. It’s a nucleophilic addition-elimination reaction.
- In this reaction, the nucleophile first attacks the positive carbon atom from one of the lone pairs on the oxygen of an ethanol molecule. It is the addition stage of the reaction.
- In the elimination stage, the carbon-oxygen double bond reforms and a chloride ion is pushed off.
- The elimination stage is followed by the removal of a hydrogen ion by the chloride ion to give ethyl ethanoate and hydrogen chloride.
- However, it can be concluded as a nucleophilic substitution reaction, as it involves nucleophilic substitution of -Cl by -OR.

Preparation of phenol
- By pyrolysis of sodium salt of benzene sulfonic acid:
  - Phenols can be produced in large amounts by the pyrolysis of sodium salt of benzene sulfonic acid.
  - In this method, benzene sulfonic acid reacts with aqueous sodium hydroxide to give sodium salt of benzene sulfonic acid.
  - The resulting salt is mixed with solid sodium hydroxide and heated at a high temperature i.e., about 350 °C to give sodium phenoxide, which is then acidified with aqueous acid to make phenol.
- Using phenylamine
  - Phenylamine is treated with HNO₂or a mixture of NaNO₂ and a dilute acid below 10 °C to produce diazonium salt. Upon further warming of the diazonium salt with H₂O, phenol is produced.
  - In this reaction, the reaction between HCl and the nitrite ions produces nitrous acid (HNO₂).
  - Nitrous acid is always made in situ and is kept in an ice bath since it decomposes very readily.
  - While forming diazonium salt, the phenylamine is first dissolved in hydrochloric acid in an ice bath, forming phenylammonium chloride solution.
  - A solution of sodium nitrite, NaNO₂ is added very slowly to the phenylammonium chloride solution, keeping the temperature below 10 °C. The product thus formed is benzenediazonium chloride.
  - When the mixture is warmed, a black oily product is formed which contains phenol, and nitrogen gas is given off.

Acidity of phenol:
- Phenol is a weak acid.
- A hydrogen in phenol can break away from the -OH group in the form of hydrogen ion and transfer to a base. After losing hydrogen ion by phenol, a phenoxide ion is formed.
- As phenol is a very weak acid, the position of equilibrium lies well to the left.
- Stability of phenoxide ion:
  - The phenoxide formed is stabilised to some extent by resonance, because the negative charge on the oxygen atom is delocalised around the ring.
  - One of the lone pairs on the oxygen atom overlaps with the delocalised electrons on the benzene ring.
  - This leads to delocalisation which extends from the ring over the oxygen atom. As a result, the negative charge is no longer entirely localised on the oxygen, but is spread out around the whole ion.
  - Spreading the charge around makes the ion more stable than it would be if all the charge remained on the oxygen.
  - However, oxygen is the most electronegative element in the ion and the delocalised electrons are drawn towards it.
  - There will still be a lot of charge around the oxygen, which will tend to attract the hydrogen ion back again. So, the phenoxide ion is estabilised by resonance, even though phenol is a very weak acid.

Relative acidities of acid:
- The strength of any acid is determined by the stability of the conjugate base.
- Any factor which makes the conjugate base more stable will increase the acidity of the acid due to the stabilising the negative charge on conjugate base stablisise the conjugate base.
- For example the phenoxide ion of phenol.
- Negative charge stabilised in two ways.
  - First is by bringing the negative charge closer to the positively charged nucleus makes it more stable.
  - Second, the negative charge can also be stabilised by spreading charge over a larger volume. Diffused charge is more stable than concentrated charge.
    An example is how resonance serves to stabilise charges. In such a case, the charge is being spread across multiple atoms, therefore, it reduces the individual charge density.
- Relative acidity of phenol and ethanol:
- The phenoxide ion obtained after the removal of a proton is stabilised by resonance.
- But, the ethoxide ion obtained after the removal of a proton is destabilised by the +I effect of C₂H₅ group.
- So, phenol is a stronger acid than ethanol.

Relative acidity of ethanol and water:
- Ethanol is a weaker acid than water, because the electron releasing C₂H₅ group in ethanol increases the electron density of oxygen.
- This decreases the polarity of the O−H bond in ethanol, resulting in a decrease in acidic strength.
The order of acidity of water, ethanol and phenol are as follows:

32.01 - Alcohol and Phenol

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