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An improved method for assessing relative nucleophilic substitution reactivities of polychlorinated benzenes
Stockholm University, Faculty of Science, Department of Environmental Chemistry. (Percistency)
Stockholm University, Faculty of Science, Department of Environmental Chemistry. (Percistency)
Stockholm University, Faculty of Science, Department of Environmental Chemistry.
2009 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 75, no 1, 78-82 p.Article in journal (Refereed) Published
Abstract [en]

An existing substitution reaction method was improved as part of a system to measure the persistency of selected chemicals in the environment by evaluating their chemical reactivity. Hexachlorobenzene (HCB), pentachlorobenzene, 1,2,4,5-tetrachlorobenzene and 1,2,4-trichlorobenzene were selected as model compounds. Sodium methoxide in methanol was used as a nucleophile and found to be stable for at least 35 days after preparation. The substitution reaction system was modified so that nitrogen protection was not necessary to avoid oxidation and hydrolysis effects, which led to improved results. The reactivity of polychlorinated benzenes (PCBz), which substituted chlorine for methoxide according to a second-order rate constant, increased as the number of chlorine atoms on the benzene ring increased. HCB was selected as a standard for the k2 calculations of the substitution reactions. A normalized k2 (kN) was calculated as kN = kPCBz/kHCB. GC–MS analysis confirmed that the reactions were pure nucleophilic aromatic substitutions without side reactions.

Place, publisher, year, edition, pages
2009. Vol. 75, no 1, 78-82 p.
Keyword [en]
Nucleophilic substitution, Polychlorinated benzenes, Nucleophile, Reactivity, Persistency, Chemical stability
National Category
Environmental Sciences
URN: urn:nbn:se:su:diva-26801DOI: 10.1016/j.chemosphere.2008.11.045ISI: 000265006300011PubMedID: 19152956OAI: diva2:211420
Available from: 2009-04-14 Created: 2009-04-14 Last updated: 2011-05-06Bibliographically approved
In thesis
1. Chemical reactivities as a mirror of environmental transformations - method development and assessment of some selected organohalogens
Open this publication in new window or tab >>Chemical reactivities as a mirror of environmental transformations - method development and assessment of some selected organohalogens
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The assement of chemical persistence is an important part of legislative protection of the environment and human health. Of the vast number of chemicals on the market today few have been properly assessed. The coordination between testing guidelines from different frameworks is limited and especially the methods for determination of biodegradation show poor reproducibility because of their highly complex nature.

In order to circumvent the multifactorial assessment methods that involve the use of e.g. soils and sediments an attempt to create a new approach to chemicals assessment was postulated by Green and Bergman in 2005. This approach puts the focus on testing the chemical reactivity of the compound in environmentally relevant transformation/degradation reactions, i.e. reduction, oxidation, hydrolysis-substitution-elimination (hse), radical reactions, and photolysis. These tests are to be performed in controlled abiotic laboratory experiments ensuring that the results reflect the transformation rate of the intended type of reaction for the investigated substance. To achieve an assessment of the presistence of the compound, the test results are then combined with data on physicochemical properties of the compound and a mathematic matrix describing the reactive power of the different types of reactions in each environmental compartment (air, water, soil, and sediment).

Thus far methods for testing of oxidation, photolysis, and hydrolysis-substitution-elimination reactions have been developed. Within this thesis a method for determining reduction was developed and further utilised to determine transformation products from reductive debromination of the three nonabrominated diphenyl ethers. The previously established method for hse was evaluated and further developed in a study of selected chlorobenzenes. Some novel brominated flame retardants were investigated using the previously developed photolysis method, and transformation products and quantum yields were determined. All of the papers presented within this thesis intend to build on the project of a new persistency assessment model. The results presented also contributes important information on the properties and transformation of some common organohalogen pollutants.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2011. 56 p.
National Category
Environmental Sciences
Research subject
Environmental Chemistry
urn:nbn:se:su:diva-56790 (URN)978-91-7447-299-8 (ISBN)
Public defence
2011-06-10, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (Swedish)
Formas, 216-2006-578
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 4: Manuscript. Available from: 2011-05-12 Created: 2011-04-27 Last updated: 2011-05-06Bibliographically approved

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