کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
675388 | 1459597 | 2009 | 10 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Temperature- and moisture-dependent phase changes in crystal forms of barbituric acid
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کلمات کلیدی
Thermal analysis - آنالیز حرارتیBarbituric acid - اسید باربیتوریکthermochemistry - ترموشیمیMoisture sorption - جذب رطوبتDehydration - دهیدراسیون، کمآبی بدنSpectroscopy - طیفسنجیHydrate - هیدراتX-ray powder diffraction - پراش پودر اشعه ایکسCrystal polymorphism - پلی مورفیسم کریستالSolution calorimetry - کالری سنجی محلول
موضوعات مرتبط
مهندسی و علوم پایه
مهندسی شیمی
جریان سیال و فرایندهای انتقال
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
The dihydrate of barbituric acid (BAc) and its dehydration product, form II were investigated by means of moisture sorption analysis, hot-stage microscopy, differential scanning calorimetry, thermogravimetry, solution calorimetry, IR- and Raman-spectroscopy as well as powder X-ray diffraction. The dihydrate desolvates already at and below 50% relative humidity (RH) at 25 °C whereas form II is stable up to 80% RH, where it transforms back to the dihydrate. The thermal dehydration of barbituric acid dihydrate (BAc-H2) is a single step, nucleation controlled process. The peritectic reaction of the hydrate was measured at 77 °C and a transformation enthalpy of ÎtrsHH2-II = 17.3 kJ molâ1 was calculated for the interconversion between the hydrate and form II. An almost identical value of 17.0 kJ molâ1 was obtained from solution calorimetry in water as solvent (ÎsolHH2 = 41.5, ÎsolHII = 24.5 kJ molâ1). Additionally a high-temperature form (HT-form) of BAc, which is enantiotropically related to form II and unstable at ambient conditions has been characterized. Furthermore, we observed that grinding of BAc with potassium bromide (KBr) induces a tautomeric change. Therefore, IR-spectra recorded with KBr-discs usually display a mixture of tautomers, whereas the IR-spectra of the pure trioxo-form of BAc are obtained if alternative preparation techniques are used.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Thermochimica Acta - Volume 485, Issues 1â2, 10 March 2009, Pages 33-42
Journal: Thermochimica Acta - Volume 485, Issues 1â2, 10 March 2009, Pages 33-42
نویسندگان
Neslihan Zencirci, Elisabeth Gstrein, Christoph Langes, Ulrich J. Griesser,