Stability is an important parameter to evaluate the quality, safety and efficacy of drug substances and pharmaceutical products. The stability studies aim to determine the ability of a formulation to maintain its specifications, in order to establish shelf life and recommended storage conditions. Despite the extensive relevance, until the 1980’s the stability assessment methods complied with technical and scientific principles without the intervention of regulatory acts by health authorities. The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) establishment in the 1990’s boosted the regulation on this issue, not only in the attended countries, but worldwide. In the Brazilian context, the first regulatory norm for stability studies was published in 2002 and it implied the requirement of the submission of a stability report for the sanitary registration of medicines. The development of the Brazilian legislation resulted, among other factors, from the progress of the analytical methods that have become increasingly efficient, sensitive and selective, which allows the achievements of results with greater accuracy and speed; and the use of modern techniques of solid form characterization, which provide important information about the stability of active ingredients and pharmaceutical products.

A thiourea derivative, N-[(phenylcarbonyl)carbamothioyl]benzamide, was synthesized and characterized by elemental analysis, thermal analysis, spectroscopic methods (Fourier transform infrared (FTIR), UV-Vis, Raman, matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF), tandem mass spectrometry (MS/MS) and nuclear magnetic resonance (NMR)) and quantum-chemical calculations. The synthetic route was simple and efficient, conducted just by one-step and no purification step was needed. The compound crystallizes in a non-centrosymmetric orthorhombic crystal system with a P21 21 21 space group, with a= 5.06220(10) Å, b= 11.8623(3) Å, c= 21.9682(8) Å. The molecular conformation of the solid is stabilized by the N-H···O intramolecular hydrogen bond, which was present in the X-ray structure and was also found in the optimized geometry. The theoretical analysis showed that this strong interaction remains even when molecules are solvated, i.e., the rotation barrier and the hydrogen bond strength are greater than the solvent stabilization energy. In addition to this hydrogen bond effect, the relative position of phenyl groups has a certain influence on the chemical behavior of this thiourea and probably for other phenylthioureas.