Bromine formation in inorganic bromide/nitrate mixtures and its application for oxidative aromatic bromination
Failid
Kuupäev
2020-07-15
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Üha enam pööratakse tähelepanu tehnoloogiate keskkonnasäästlikkusele ja jätkusuutlikkusele. Seetõttu lähtutakse ka keemias nn jätkusuutliku keemia põhimõtetest, mis ühendavad endas rohelise keemia printsiipe protsesside majanduslike ning sotsiaalsete aspektidega. Nende põhimõtete järgi tuleb keemilisi protsesse läbi viia, kasutades võimalikult ohutuid kemikaale maksimaalselt efektiivselt ja tekitades minimaalselt jäätmeid. Antud doktoritöös uuriti nende põhimõtete rakendamise võimalust aromaatsete ühendite broomimisel.
Broomitud aromaatsed ühendid on laialdaselt kasutusel nii orgaanilises sünteesis, ravimite, põllumajanduskemikaalide, tuletõkkevahendite kui ka värvainete tootmises. Traditsiooniliselt kasutatakse broomimiseks molekulaarset broomi. Br2 on toksiline kemikaal, mille kasutamisega kaasnevad mitmed tervise- ja keskkonnariskid. Neid riske võimaldab vähendada broomi genereerimine reaktsioonisegus vahetult enne broomimist. Ühe võimalusena võib broomi saada reaktsioonisegus bromiidioonide ja tugeva oksüdeerija vahelise redoksreaktsiooni käigus.
Käesolevas doktoritöös uuriti võimalust kasutada broomi tekkereaktsioonis oksüdeerijana kaaliumnitraati. Kaaliumnitraat on mõõdukalt tugev oksüdeerija, mistõttu on seda võrreldes mitme seni kasutatud oksüdeerijaga lihtsam käsitseda ja väheneb oluliselt kõrvalreaktsioonide toimumise võimalus. Uurimistöö jagunes kahte etappi, millest esimeses keskenduti broomi tekkereaktsiooni uurimisele ning teises tekkereaktsiooni kasutamisele erinevate aromaatsete ühendite broomimiseks.
Br2 tekkereaktsiooni uurimisel selgus, et tegu on autokatalüütilise reaktsiooniga, kus nitraatioonide redutseerumisel tekkivad nitritioonid katalüüsivad edaspidist broomi teket. Töös näidati, et Br2 tekkekiirust on võimalik antud reaktsioonisegus kergesti varieerida, muutes orgaanilist lahustit ja reagentide hulkasid.
Lisaks töötati välja kolm erinevat aromaatsete ühendite broomimismeetodit, mida oli võimalik kasutada nii aktiveeritud kui ka mitteaktiveeritud ühendite broomimiseks, varieerides bromiidioonide allikat (NaBr, HBr või AlBr3). Olulise aspektina tuleb mainida, et üks meetoditest toimub solvendivabades tingimustes, mis vähendab oluliselt protsessi käigus tekkivate jääkide hulka.
Societal interest towards environmental and sustainability aspects of production and industrial processes has 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 for generating bromine directly in the reaction mixture and avoiding free Br2 have been introduced. For this purpose, it is possible 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 a 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.
Societal interest towards environmental and sustainability aspects of production and industrial processes has 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 for generating bromine directly in the reaction mixture and avoiding free Br2 have been introduced. For this purpose, it is possible 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 a 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.
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Märksõnad
bromine, bromides, nitrates, aromatic compounds, bromination