*3.1. General*

Methimazole **1** 99%, Ph Eur quality, was purchased from CU Chemie Ueticon, Lahr, Germany (water content 0.4%), 1,2-dichloroethane (Fisher, Hampton, NH, USA) (water content, 0.02%), dichloromethane (Merck KGaA, Darmstadt, Germany) acetone (Sigma, St. Louis, MO, USA) (water content, 0.2%), methanol dried (Merck KGaA, Darmstadt, Germany), water was purified in a house system (Thornton

2000CRS, Mettler Toledo, Colombus, OH, USA) and was of HPLC grade. Dichloromethane was dried under anhydrous sodium sulphate and distilled prior to use. All other used chemicals were of analytical grade. pH measurements were performed using Mettler Toledo (Columbus, OH, USA) Seven Multi pH meter, and prior to measurement, it was calibrated in six points. Ionic chromatography measurements were performed on Thermo (Waltham, MA, USA) ionic chromatography using LC chlorine standard. HPLC analysis was performed on an Agilent Technologies (Santa Clara, CA, USA) HPLC instrument under gradient elution at a flow rate of 0.6 mL/min using mobile phase A (ammonium acetate, Merck KGaA, Darmstadt, Germany buffer) and mobile phase B (acetonitrile, Merck KGaA, Darmstadt, Germany) at the Zorbax C18 column. The effluent was monitored using the Agilent DAD/UV detector. <sup>1</sup>H NMR and <sup>13</sup>C NMR spectra were recorded on a Bruker (Billerica, MA, USA) Advance 600 and 150, respectively, with DMSO-*d6* or D2O as a solvent. Mass spectra were recorded on an Agilent 6550 iFunnel quadrupole time-of-flight mass spectrometer equipped with dual AJS ESI source (Agilent Technologies Santa Clara, CA, USA). Hot stage microscopy was carried out using an Olympus (Shinjuku City, Tokyo, Japan) BX51 microscope combined with a Linkam THMS 600 hot stage (Linkam Scientific Instruments, Waterfield, UK) and a digital camera (QImaging, Surrey, Canada) for image capture. A small amount of the sample was placed onto a glass slide and viewed with 100x magnification and partially polarised light. It was simultaneously being heated from ambient temperature at a rate of 10 ◦C/min. Thermal analysis was performed using a Mettler DSC 1 instrument (Mettler Toledo, Greifensee, Swizerland) in aluminium pans with a pierced lid at a heating rate of 10 ◦C/min under the inert nitrogen atmosphere with a flow rate of 55 mL/min. Temperature calibration was performed using the indium metal standard. TGA data were collected on a Mettler Toledo (Greifensee, Switzerland)) TGA/SDTA 851e system. The sample was loaded onto a pre-tared alumina crucible and was heated at a heating rate 10 ◦C/min over the temperature range 25–300 ◦C. A nitrogen purge at 50 mL/min was maintained over the sample. The instrument was temperature calibrated using certified NiMn3Al and nickel. All weighing operations were carried using Mettler Toledo (Greifensee, Switzerland)) balance, daily calibrated according to the internal program.
