Chlorothalonil

Dear Reader,

It has come to my attention that the EU will soon be banning a fungicide named chlorothalonil. This is a rather small molecule which has one benzene ring in it, two nitrile groups and four chlorine atoms. The molecular structure of this substance was reported by D. Britton (Cryst.Struct.Commun. , 1981, 10, 1501). Here is a picture of the molecule.

Some of the chemistry and biology of this pesticide is discussed in a paper from the EFSA. This is a paper with a lot of authors.

Maria Arena, Domenica Auteri, Stefania Barmaz, Giulia Bellisai, Alba Brancato, Daniela Brocca, Laszlo Bura, Harry Byers, Arianna Chiusolo, Daniele Court Marques, Federica Crivellente, Chloe De Lentdecker, Mark Egsmose, Zoltan Erdos, Gabriella Fait, Lucien Ferreira, Marina Goumenou, Luna Greco, Alessio Ippolito, Frederique Istace, Samira Jarrah, Dimitra Kardassi, Renata Leuschner, Christopher Lythgo, Jose Oriol Magrans, Paula Medina, Ileana Miron, Tunde Molnar, Alexandre Nougadere, Laura Padovani, Juan Manuel Parra Morte, Ragnor Pedersen, Hermine Reich, Angela Sacchi, Miguel Santos, Rositsa Serafimova, Rachel Sharp, Alois Stanek, Franz Streissl, Juergen Sturma, Csaba Szentes, Jose Tarazona, Andrea Terron, Anne Theobald, Benedicte Vagenende, Alessia Verani and Laura Villamar-Bouza, EFSA Journal, 2018, 16(1), 5126.

While the impurity hexachlorobenzene which is found in the commercial product was characterized by .N.Strel’tsova and  Yu.T.Struchkov (Zh.Strukt.Khim.(Russ.)(J.Struct.Chem.) , 1961, 2, 312). This should not be confused with lindane which is sometimes known as hexachlorobenzene. Lindane is an isomer of 1,2,3,4,5,6-hexachlorocyclohexane. Here is a picture of hexachlorobenzene.

Like the pesticide it is a simple flat molecule which is a hexagon of carbon atoms within a hexagon of chlorine atoms.

The commercial product also contains small amounts of deachlorobiphenyl, as it is a PCB it is something which automatically grabbs my attention. This was characterized by B.F.Pedersen (Acta Crystallogr.,Sect.B:Struct.Crystallogr.Cryst.Chem., 1975, 31, 2931). This is a bit different, due to steric effects the two benzene rings are not in the same plane. Here are two views of it. First we have the side view.

Now here is the end view which is almost along the axis formed by the C-C single bond which links the two benzene rings together.

In the European food safety authority report, two metabolites (biological breakdown products) code named R613636 (2,3,4,6-tetrachloro-5-cyanobenzamide) and R182281 (2,4,5-trichloro-6-hydroxybenzene-1,3-dicarbonitrile) were listed as being of concern. We hope that we can discuss this molecule and chemistry soon.