Caffeine

Formula: C₈H₁₀N₄O₂
Molecular weight: 194.1906
IUPAC Standard InChI: InChI=1S/C8H10N4O2/c1-10-4-9-6-5(10)7(13)12(3)8(14)11(6)2/h4H,1-3H3
IUPAC Standard InChIKey: RYYVLZVUVIJVGH-UHFFFAOYSA-N
CAS Registry Number: 58-08-2
Chemical structure:
This structure is also available as a 2d Mol file or as a computed 3d SD file
The 3d structure may be viewed using Java or Javascript.
Other names: 1H-Purine-2,6-dione, 3,7-dihydro-1,3,7-trimethyl-; Alert-Pep; Cafeina; Caffein; Caffine; Cafipel; Coffeine; Guaranine; Koffein; Mateina; Methyltheobromine; No-Doz; Refresh'n; Stim; Thein; Theine; 1,3,7-Trimethyl-2,6-dioxopurine; 1,3,7-Trimethylxanthine; Cafamil; Cafecon; Caffeine, synthetic; Eldiatric C; Nix Nap; Nodaca; NCI-C02733; Theobromine, 1-methyl-; Theophylline, 7-methyl; Xanthine, 1,3,7-trimethyl; 3,7-Dihydro-1,3,7-trimethyl-1H-purine-2,6-dione; Coffein; Kofein; Organex; Monomethyl derivative of Theophylline; Theobromine Me; Theophylline Me; Caffedrine; Hycomine; NSC 5036; Tri-Aqua; Wigraine; 7-Methylxanthine, N,N'-dimethyl-; 1,3,7-Trimethyl-3,7-dihydro-1H-purine-2,6-dione; A.S.A. and Codeine Compound; Anacin; Anacin Maximum Strength; Bayer Select Headache Pain; Cafergot; DHCplus; Dasin; Fiorinal; Hycomine Compound; Midol Maximum Strength; Norgesic; P-A-C Analgesic Tablets; Phensal; Propoxyphene Compound 65; SK-65 Compound; Synalgos; Synalgos-DC; Vanquish; component of A.S.A. Compound; component of Ansemco 2; component of Dilone; component of Midol; component of P-A-C Compound; component of Percodan; 71701-02-5; 95789-13-2; A.S.A. and Codeine Compound (Salt/Mix); Anacin (Salt/Mix); Anacin Maximum Strength (Salt/Mix); Bayer Select Headache Pain (Salt/Mix); Cafergot (Salt/Mix); DHCplus (Salt/Mix); Dasin (Salt/Mix); Fiorinal (Salt/Mix); Hycomine Compound (Salt/Mix); Midol Maximum Strength (Salt/Mix); Norgesic (Salt/Mix); P-A-C Analgesic Tablets (Salt/Mix); Phensal (Salt/Mix); Propoxyphene Compound 65 (Salt/Mix); SK-65 Compound (Salt/Mix); Synalgos (Salt/Mix); Synalgos-DC (Salt/Mix); Vanquish (Salt/Mix); component of A.S.A. Compound (Salt/Mix); component of Ansemco 2 (Salt/Mix); component of Dilone (Salt/Mix); component of Midol (Salt/Mix); component of P-A-C Compound (Salt/Mix); component of Percodan (Salt/Mix)
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Phase change data

Go To: Top, Gas phase ion energetics data, References, Notes

Data compiled as indicated in comments:
TRC - Thermodynamics Research Center, NIST Boulder Laboratories, Chris Muzny director
AC - William E. Acree, Jr., James S. Chickos
DH - Eugene S. Domalski and Elizabeth D. Hearing

Quantity	Value	Units	Method	Reference	Comment
T_fus	509.3	K	N/A	Bruns, Reichelt, et al., 1984	Crystal phase 1 phase; Uncertainty assigned by TRC = 0.1 K; TRC
T_fus	508.	K	N/A	Grady, Hays, et al., 1973	Uncertainty assigned by TRC = 1. K; TRC
Quantity	Value	Units	Method	Reference	Comment
T_triple	508.3	K	N/A	Weinstein, Leffler, et al., 1984	Crystal phase 1 phase; Uncertainty assigned by TRC = 1.5 K; DSC; TRC

Enthalpy of vaporization

Δ_vapH (kcal/mol)	Temperature (K)	Method	Reference	Comment
15.5 ± 0.57	634. to 743.	DSC	Boller and Wiedemann, 1998	AC

Enthalpy of sublimation

Δ_subH (kcal/mol)	Temperature (K)	Method	Reference	Comment
24.76	423.	UV	Ebeling and Franck, 2010	Based on data from 373. to 473. K.; AC
26.91 ± 0.57	315. to 364.	ME	Boller and Wiedemann, 1998	AC

Enthalpy of fusion

Δ_fusH (kcal/mol)	Temperature (K)	Method	Reference	Comment
5.93	507.7	DSC	Guo, Sadiq, et al., 2010	AC
4.747	509.5	DSC	Dong, Li, et al., 2007	AC
5.23	510.2	DSC	Pinto and Diogo, 2006	AC
4.632	510.2	DSC	Klous, Bronner, et al., 2005	AC
4.37	510.	N/A	Domalski and Hearing, 1990	See also Ohm and Lippold, 1985.; AC
5.007	508.3	DSC	Weinstein, Leffler, et al., 1984, 2	AC

Enthalpy of phase transition

ΔH_trs (kcal/mol)	Temperature (K)	Initial Phase	Final Phase	Reference	Comment
0.225	426.	crystaline, II	crystaline, I	Cesaro and Starec, 1980	to form.; DH
1.338	512.	crystaline, I	liquid	Cesaro and Starec, 1980	to liquid.; DH
0.2302	414.	crystaline, II	crystaline, I	Bothe and Cammenga, 1979	Low temperature to a high temperature transition.; DH
1.233	509.3	crystaline, I	liquid	Bothe and Cammenga, 1979	DH

Entropy of phase transition

ΔS_trs (cal/mol*K)	Temperature (K)	Initial Phase	Final Phase	Reference	Comment
0.53	426.	crystaline, II	crystaline, I	Cesaro and Starec, 1980	to; DH
2.61	512.	crystaline, I	liquid	Cesaro and Starec, 1980	DH
1.63	414.	crystaline, II	crystaline, I	Bothe and Cammenga, 1979	Low; DH
2.41	509.3	crystaline, I	liquid	Bothe and Cammenga, 1979	DH

In addition to the Thermodynamics Research Center (TRC) data available from this site, much more physical and chemical property data is available from the following TRC products:

Gas phase ion energetics data

Go To: Top, Phase change data, References, Notes

Data compiled as indicated in comments:
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron

Ionization energy determinations

IE (eV)	Method	Reference	Comment
7.95	PE	Dougherty, Younathan, et al., 1978	LLK
8.50	CTS	Slifkin and Allison, 1967	RDSH

References

Go To: Top, Phase change data, Gas phase ion energetics data, Notes

Bruns, Reichelt, et al., 1984
Bruns, S.; Reichelt, J.; Cammenga, H.K., Thermochemical investigation of theophylline, theophylline hydrate and their aqueous solutions, Thermochim. Acta, 1984, 72, 31. [all data]

Grady, Hays, et al., 1973
Grady, L.T.; Hays, S.E.; King, R.H.; Klein, H.R.; Mader, W.J.; Wyatt, D.K.; Zimmere, R.O., Drug purity profiles, J. Pharm. Sci., 1973, 62, 459. [all data]

Weinstein, Leffler, et al., 1984
Weinstein, D.I.; Leffler, A.J.; Currie, J.A., Phase Transitions in Bicyclic Compounds, Mol. Cryst. Liq. Cryst., 1984, 104, 95. [all data]

Boller and Wiedemann, 1998
Boller, A.; Wiedemann, H.G., Journal of Thermal Analysis and Calorimetry, 1998, 53, 2, 431-439, https://doi.org/10.1023/A:1010133106907 . [all data]

Ebeling and Franck, 2010
Ebeling, H.; Franck, E.U., Spectroscopic Determination of Caffeine Solubility in Supercritical Carbon Dioxide, Berichte der Bunsengesellschaft für physikalische Chemie, 2010, 88, 9, 862-865, https://doi.org/10.1002/bbpc.19840880918 . [all data]

Guo, Sadiq, et al., 2010
Guo, Kun; Sadiq, Ghazala; Seaton, Colin; Davey, Roger; Yin, Qiuxiang, Co-Crystallization in the Caffeine/Maleic Acid System: Lessons from Phase Equilibria, Crystal Growth & Design, 2010, 10, 1, 268-273, https://doi.org/10.1021/cg900885n . [all data]

Dong, Li, et al., 2007
Dong, Jia-Xin; Li, Qiang; Tan, Zhi-Cheng; Zhang, Zhi-Heng; Liu, Yi, The standard molar enthalpy of formation, molar heat capacities, and thermal stability of anhydrous caffeine, The Journal of Chemical Thermodynamics, 2007, 39, 1, 108-114, https://doi.org/10.1016/j.jct.2006.05.009 . [all data]

Pinto and Diogo, 2006
Pinto, Susana S.; Diogo, Hermínio P., Thermochemical study of two anhydrous polymorphs of caffeine, The Journal of Chemical Thermodynamics, 2006, 38, 12, 1515-1522, https://doi.org/10.1016/j.jct.2006.04.008 . [all data]

Klous, Bronner, et al., 2005
Klous, Marjolein G.; Bronner, Gaby M.; Nuijen, Bastiaan; Ree, Jan M. van; Beijnen, Jos H., Pharmaceutical heroin for inhalation: Thermal analysis and recovery experiments after volatilisation, Journal of Pharmaceutical and Biomedical Analysis, 2005, 39, 5, 944-950, https://doi.org/10.1016/j.jpba.2005.06.011 . [all data]

Domalski and Hearing, 1990
Domalski, Eugene S.; Hearing, Elizabeth D., Heat Capacities and Entropies of Organic Compounds in the Condensed Phase Volume II, J. Phys. Chem. Ref. Data, 1990, 19, 4, 881, https://doi.org/10.1063/1.555876 . [all data]

Ohm and Lippold, 1985
Ohm, A.; Lippold, B.C., Surface tension of solid drugs and its correlation with solubility, Int. J. Pharm. Tech. Prod. Mfg., 1985, 6, 4, 1. [all data]

Weinstein, Leffler, et al., 1984, 2
Weinstein, D.I.; Leffler, A.J.; Currie, J.A., Phase Transitions In Bicyclic Compounds, Molecular Crystals and Liquid Crystals, 1984, 104, 1-2, 95-109, https://doi.org/10.1080/00268948408070401 . [all data]

Cesaro and Starec, 1980
Cesaro, A.; Starec, G., Thermodynamic properties of caffeine crystal forms, J. Phys. Chem., 1980, 84, 1345-1346. [all data]

Bothe and Cammenga, 1979
Bothe, H.; Cammenga, H.K., Phase transitions and thermodynamic properties of anhydrous caffeine, J. Therm. Anal., 1979, 16, 267-275. [all data]

Dougherty, Younathan, et al., 1978
Dougherty, D.; Younathan, E.S.; Voll, R.; Abdulnur, S.; McGlynn, S.P., Photoelectron spectroscopy of some biological molecules, J. Electron Spectrosc. Relat. Phenom., 1978, 13, 379. [all data]

Slifkin and Allison, 1967
Slifkin, M.A.; Allison, A.C., Measurement of ionization potentials from contact charge transfer spectra, Nature, 1967, 215, 949. [all data]

Notes

Go To: Top, Phase change data, Gas phase ion energetics data, References

Symbols used in this document:

T_fus	Fusion (melting) point
T_triple	Triple point temperature
ΔH_trs	Enthalpy of phase transition
ΔS_trs	Entropy of phase transition
Δ_fusH	Enthalpy of fusion
Δ_subH	Enthalpy of sublimation
Δ_vapH	Enthalpy of vaporization

Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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