Alkylation of salicylic acids.
The work described in this thesis has been directed at the development of a novel
synthetic route to alkylsalicylic acids. Associated reactions have also been studied. The
primary aim has been the synthesising of alkylsalicylic acids possessing an alkyl chain
containing more than eight carbon atoms. In addition, a limited study has also been carried
out into the sulfurisation of alkylphenols. Both the alkylsalicylic acids and the sulfurised
aJkylphenols are used as oil additives. They both act as detergents, keeping an engine clean
and neutralising any acids formed in the engine as a result of oxidation processes.
Chapter Icontains a general introduction to oil additives, principally the overbased
detergents, and an introduction to Friedel-Crafts chemistry, which is the basic reaction
employed in the alkylation of salicylic acid. Chapter 2 introduces the alkylation of salicylic
acid employing concentrated sulfuric acid as the catalyst, and using simple model
compounds to demonstrate the feasibility of the approach. The effect of varying the
alkylating substrate to produce an alkylsalicylic acid with an alkyl chain containing at least
eight carbon atoms is explored in Chapter 3.
Optimization of the alkylation reaction and the effect of altering a number of the
reaction parameters (e.g. temperature, catalyst and reaction duration) on the yield and
product distribution for a range of alkylating substrates is set out in Chapter 4. The work
contained in Chapter 5 concentrates on the synthesis and rearrangement of the esters of
salicylic acid and investigates the possibility that the esters are intermediates in the alkylation
reaction. Chapter 6 is concerned with the industrial implications of the alkylation of salicylic
acid. It concentrates in particular on the synthesis using industrially available alkenes and
the scale-up of the reaction.
An insight into the sulfurisation of alkylphenols, and the attempted identification of
products formed in the industrial process, can be found in Chapter 7. Finally, the
experimental details for Chapters 2 to 7 are contained in Chapter 8.