Gas–solid reactions between the different polymorphic modifications of barbituric acid and amines

Abstract

The two known crystalline polymorphic forms of barbituric acid (C 4 H 4 N 2 O 3 ) (form I and form II) and the dihydrate form [(C 4 H 4 N 2 O 3 )?2H 2 O] have been reacted with vapours of ammonia, methylamine, and dimethylamine and the crystalline products investigated by means of single crystal and powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and infrared spectroscopy. It has been shown that form I, II and the dihydrate form of barbituric acid react with ammonia leading to the same crystalline ammonium barbiturate salt NH 4 (C 4 H 3 N 2 O 3 ) 1a, while the gas-solid reactions of form II with methylamine, and dimethylamine yield the corresponding crystalline salts, CH 3 NH 3 (C 4 H 3 N 2 O 3 ) 1b and (CH 3 ) 2 NH 2 (C 4 H 3 N 2 O 3 ) 1c. Thermal desorption of the bases at ca. 200 uC leads to formation of a new crystal form of barbituric acid, form III, as confirmed by H 1 -NMR spectroscopy and by chemical behaviour. De-hydration of the dihydrate form has also been investigated showing that it releases water to yield exclusively crystals of form II.

Application of 1-Hydroxy-4,5-Dimethyl-Imidazole 3-Oxide as Coformer in Formation of Pharmaceutical Cocrystals

“…It is interesting to note that for pure anhydrous BA, existing in keto form, these bond lengths are 1.229 Å, 1.222 Å, 1.189 Å for C(2)=O(2), C(1)=O(1) and C(4)=O(3), respectively. Concluding this part, the presented X-ray results are consistent with a publication by Braga and coworkers, who, while studying the gas-solid reactions between the different polymorphic modifications of barbituric acid and amines, reported similar structural motifs with complex hydrogen bonding networks [47].…”

“…Concluding this part, the presented X-ray results are consistent with a publication by Braga and coworkers, who, while studying the gas-solid reactions between the different polymorphic modifications of barbituric acid and amines, reported similar structural motifs with complex hydrogen bonding networks [47].…”

“…Figure 16 shows the cellular viability after concentration-dependent treatment; the results indicate no significant toxicity in the case of incubation with the tested compounds in the 1-100 µM concentration range. The viability of cells was at a level of 80-100 Concluding this part, the presented X-ray results are consistent with a publication by Braga and coworkers, who, while studying the gas-solid reactions between the different polymorphic modifications of barbituric acid and amines, reported similar structural motifs with complex hydrogen bonding networks [47].…”

Thiobarbiturate and barbiturate salts of pefloxacin drug: Growth, structure, thermal stability and IR-spectra

“…Barbituric acid (H2ba) possesses specific, relatively weak acidic properties (pKa ca. 4.03 [9]) resulting from the presence of two methylene hydrogen atoms. Thiobarbituric acid (H2tba) is a stronger acid (pKa1 ca.…”

Die thermodynamisch stabile Form von fester Barbitursäure: das Enol‐Tautomer

“…In der Tat ist dies die stabilste Form in der Gasphase [2] und in Lçsung. [3] Auch im Festkçrper liegt Barbitursäure in der metastabilen Phase I, [4] der kommerziellen Phase II, [4b] der Hochtemperaturphase III [5] und in den Dihydraten [6] als Keto-Tautomer vor. Im Gegensatz dazu stellten wir nun fest, dass das kürzlich entdeckte tautomere Polymorph IV [7] aus Molekülen in der Enol-Form 2 besteht und dass dieses Polymorph unter Normalbedingungen die thermodynamisch stabile Phase ist.…”