PHASE-TRANSITIONS AND THERMODYNAMIC PROPERTIES OF ANHYDROUS CAFFEINE

被引:70
作者
BOTHE, H
CAMMENGA, HK
机构
[1] Institut für Physikalische Chemie, Technische Universität Braunschweig, Braunschweig
来源
JOURNAL OF THERMAL ANALYSIS | 1979年 / 16卷 / 02期
关键词
D O I
10.1007/BF01910688
中图分类号
O414.1 [热力学];
学科分类号
摘要
Caffeine has been found to display a low-temperature β- and a high-temperature α-modification. By quantitative DTA the following data were determined: transformation temperature 141±2°; enthalpy of transition 4.03±0.1 kJ·mole-1; enthalpy of fusion 21.6±0.5 kJ·mole-1; molar heat capacity {Mathematical expression} in good accord with drop-calorimetric data. For the constants of the equation log (p/Pa)=-A/T+B, static vapour pressure measurements on liquid and solid α-caffeine, and effusion measurements on solid β-caffeine yielded: {Mathematical expression}. The evaporation coefficient of β-caffeine is 0.17±0.03. © 1979 Wiley Heyden Ltd., Chichester and Akadémiai Kiadó, Budapest.
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页码:267 / 275
页数:9
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