Solid‐State Structure and Temperature/Evacuation‐Induced Dehydration of Sodium Saccharinate 1.875 Hydrate

Abstract

The anion of saccharin [1] is a polyfunctional ligand that binds to a plethora of metal ions. [2, 3] The solid hydrate of sodium saccharinate ("sodium saccharin" or "saccharinum soluble"; Scheme 1) is an edible chemical which constitutes more than half of the worlds artificial sweeteners, but which is suspected to be carcinogenic.[1] Although the compound has been extensively used for more than 150 years, its exact structure has not been unequivocally established. In most chemical catalogues it is listed as the dihydrate Na(sac)·2 H 2 O (sac = C 7 H 4 NO 3 S À ). An earlier effort to determine its crystal structure failed because of an unusually large monoclinic unit cell [4] and partial dehydration. Air-stable triclinic Na(sac)· 2 = 3 H 2 O is obtained upon recrystallization from ethanol. [5,6] Herein we report the first determination of the structure of the commercial artificial sweetener sodium saccharinate. The relative stability and the mechanisms of isobaric dehydration (heating at constant pressure) and isothermal dehydration (evacuation at constant temperature) of the two hydrates are also revealed.Recrystallization of sodium saccharinate from different solvents yielded two hydrates. Whereas the physicochemical analysis of the hydrate obtained from 95 % ethanol was consistent with the triclinic Na(sac)· 2 = 3 H 2 O described previously, [5,6] the monoclinic hydrate that was obtained from water was identical to the unpurified commercial product. Precise thermoanalytical measurements of the latter showed 1.87 ( 15 = 8 by diffraction, see below) water molecules per formula unit.The otherwise stable crystals of Na(sac)· 2 = 3 H 2 O are dehydrated [7] in two well-defined steps when heated under isobaric conditions. The intermediate Na ( The changes in the IR spectra [3, 8] and the final spectra obtained after evacuation and moderate heating of Na(sac)· 15 = 8 H 2 O are nearly identical (Figure 1). This observation indicates that the isobaric dehydration and the initial isothermal dehydration both proceed to give the same product, which was identified by thermal analysis to be Na(sac)· 9 = 8 H 2 O. Comparison of the infrared spectra obtained (Figure 2) confirms that the product is not the stable triclinic Na(sac)· 2 = 3 H 2 O. Figure 2 also shows that the isothermal dehydration commences more gradually than the isobaric one. The absence of additional spectral changes upon further evacuation indicates that prolonged isothermal evacuation does not affect Na(sac)· 9 = 8 H 2 O. The crystallographic data for the two hydrates and a detailed discussion of the monoclinic structure are given in Scheme 1. The atom-labeling scheme for the monoclinic hydrate of sodium saccharinate.

Structural Studies of the System Na(saccharinate)⋅n H2O: A Model for Crystallization

“…In summary, dihydrate 1 appears to be a good model for the structure of a nucleus in the crystallization reaction. [27] …”

On the puzzling case of sodium saccharinate 1.875-hydrate: structure description in (3+1)-dimensional superspace

“…Data indexing and integration (with respect to the supercell structure previously reported in P2 1 /n; Naumov et al, 2005;Banerjee et al, 2005) was performed up to the diffraction limit of 0.89 Å À1 with the CrysAlisPro 39.46 software (Rigaku Oxford Diffraction, 2018). Outlier rejection according to the Laue class 2/m was applied.…”

“…1. In spite of this artificial sweetener having been used in the food industry for over 100 years (Baran & Yilmaz, 2006), its crystal structure has been published only relatively recently (Naumov et al, 2005;Banerjee et al, 2005). The reason for that might be the unusual complexity of this Z 0 = 16 structure.…”

Nanoindentation im Kristall‐Engineering: Quantifizierung mechanischer Eigenschaften von Molekülkristallen

“…[84][85][86] So wandelt sich Berberinchloriddihydrat in einer Tablettenformulierung in das Tetrahydrat um und bewirkt damit erhebliche Veränderungen von Tabletteneigenschaften wie Härte, Zerfallszeit und Auflçsungsverhalten. [90][91][92][93] Die Verbindung kristallisiert mit einer großen Elementarzelle mit mehreren strukturell verschiedenen Einheiten. [90][91][92][93] Die Verbindung kristallisiert mit einer großen Elementarzelle mit mehreren strukturell verschiedenen Einheiten.…”

“…Handel erhältlichen Süßstoff identisch ist[94] und ein ausgezeichnetes Beispiel eines hydratisierten Systems darstellt, bei dem frisch gewachsene Kristalle eine große Menge an eingeschlossenem Strukturwasser enthalten [90][91][92][93]. Die Verbindung kristallisiert mit einer großen Elementarzelle mit mehreren strukturell verschiedenen Einheiten.…”