On 4 September at 14:15 Ida Rahu will defend his thesis „Bromine formation in inorganic bromide/nitrate mixtures and its application for oxidative aromatic bromination” for obtaining the degree of Doctor of Philosophy (Chemistry).
Prof. Jaak Järv (PhD), UT Institute of Chemistry
Alex R. Khomutov (PhD), Russian Academy of Sciences, Institute of Engelhart, Russia.
Societal interest towards environmental and sustainability aspects of production and industrial processes have been growing more than ever during recent decades. Nowadays, chemistry is based on so-called “sustainable chemistry” principles which combine green chemistry concepts with economic and social aspects. Therefore, chemical processes must be designed and carried out in such ways that their efficiency is high, all the used chemicals are as safe as possible, and the waste production is kept to a minimum. In this dissertation, possibilities to apply these principles to aromatic bromination were studied.
Brominated aromatic compounds are widely used in organic synthesis and production of medicines, agricultural chemicals, fire retardants and dyes. Traditionally, molecular bromine is used for their production, but this chemical is very toxic and difficult to handle. Its use causes several health and environmental hazards. Therefore, methods to generate bromine directly in the reaction mixture and avoid free Br2 have been introduced. A possibility is to use the redox reaction between bromide ions and a strong oxidiser.
In the present work, potassium nitrate was studied as a possible oxidising agent. It is moderately strong oxidiser which significantly reduces the occurrence of side reactions and simplifies its handling compared to other oxidisers used in these methods. The research was divided into two parts. The first part is focused on the bromine formation reaction and the second part on its application for aromatic bromination.
The study of the Br2 formation reaction revealed that it is an autocatalytic reaction in which the nitrite ions formed by the reduction of nitrate ions catalyse the further formation of bromine. It has been shown that the rate of bromine formation in this reaction mixture can be easily changed by using different organic solvents and amounts of reagents.
In the research, three different bromination methods have been developed, which allow to brominate both activated and non-activated aromatic compounds by choosing the suitable source of bromide ions (NaBr, HBr or AlBr3). In addition, the developed solvent-free bromination method significantly reduces waste production during the process.