The Mechanism of Aromatic Sulphonation

Horning, William Clarke (1953) The Mechanism of Aromatic Sulphonation. PhD thesis, University of Glasgow.

Abstract

It has recently been shown that in aromatic nitration and halogenation in strongly acid media the substituting agent is a positively charged ion. Although a similar attacking entity has been postulated for sulphonation, little experimental work has been done on that line. The present research is a study of the kinetics of aromatic sulphonation in fuming sulphuric acid coupled with a study of the nature of the medium and the effect of changing acid concentration on the rate of nitration. In Part I, the ionization constants of a series of aromatic nitro-compounds are given. These were measured by a spectropho tome trie method and used to determine the value of Hammett's acidity function, H0, for the range of acid concentrations from 99% H2SO4 to 36% SO3 (108.2% H2SO4). It is shown that the change in pKa between nitrobenzene and various meta- and para-substituted nitrobenzenes agrees very well with the theoretical values predicted from an electrostatic model. It is also demonstrated that the acidity function H+ , defined for the addition of a proton to a positively-charged base, is a few tenths of a logarithmic unit higher than the H0 scale in anhydrous sulphuric acid and that the difference decreases in media of higher ionic strength. Finally, a comparison is made of these results and available cryoscopic measurements. In Part II, measurements on the kinetics of sulphonation of nitrobenzene, p-nitrotoluene and p-halogensubstituted phenyltrimethylammonium ions are given for the concentration range 4 to 40% SO3. The reactions were followed spectrometrically and were for the most part carried out at 25

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Organic chemistry
• Date of Award: 1953
• Depositing User: Enlighten Team
• Unique ID: glathesis:1953-79125
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 31 Mar 2020 09:09
• Last Modified: 31 Mar 2020 09:09
• URI: https://theses.gla.ac.uk/id/eprint/79125