Preparation and physical characterization of pure beta-carotene.
Pure all-trans beta-carotene has been prepared on the 10's of grams scale by isothermal Fractional Dissolution (FD) of commercial laboratory samples in tetrahydrofuran (THF). beta-Carotene purified in this way is black, with a faint brownish tinge. The electronic spectra of black samples extend into the near infrared, with end-absorption past 750 nm. Black samples react directly with dioxygen under mild conditions to yield the familiar orange or red powders. Pure beta-carotene rigorously obeys Beer's Law in octane over the entire UV-Vis spectral range, while commercial laboratory samples and recrystallized samples do not. NMR self-diffusion coefficient data demonstrate that beta-carotene exists as simple molecular solutions in octane and toluene. The anomalously high crystallinity of beta-carotene can be attributed (from analysis using molecular mechanics) to the facts that: (1) the number of theoretically possible conformers of beta-carotene is extremely small, and (2) only a small fraction of these (ca. 12%, or 127) may actually exist in fluid phases.
Laughlin
Robert G
RG
Miami Valley Laboratories, The Procter & Gamble Company, Cincinnati, OH 45239, USA. rglaughl@zoomtown.com
Bunke
Gregory M
GM
Eads
Charles D
CD
Laidig
William D
WD
Shelley
John C
JC
D003116:Color; D004058:Diffusion; D009682:Magnetic Resonance Spectroscopy; D009795:Octanes / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D012995:Solubility; D013056:Spectrophotometry, Ultraviolet; D019207:beta Carotene / Q000138:chemical synthesis* / Q000737:chemistry / Q000302:isolation & purification
D009795:Octanes; D019207:beta Carotene; D010100:Oxygen; C026728:octane