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Vitamin E acetate ((+)-alpha-tocopherol acetate) is sold as semi-solid/liquid by Sigma and their safety data sheet gives the melting point as 25 °C. On the other hand, internet databases such as Chemspider show melting points of either -28 °C or 28 °C. Supplements labeled either Vitamin E or Vitamin E oil are packaged as solid, gel capsules or liquid.

What is the normal melting point, and what is the physical state at room temperature (20 °C)?

Update

There are at least three products on the market, the single (+) stereoisomer (derived from biological sources, CAS 58-95-7), the racemic mixture, and the "all-racemic mixture" (8 stereoisomers, with some pairs being diastereomers and other pairs enantiomers). The latter is produced synthetically with non-stereospecific steps (CAS 7695-91-2). All have the formula $\ce{C31H52O3}$. To clear up any confusion, the physical state of the single isomer, of the (+/-) racemic mixture and the "all-racemic mixture" would be of interest.

Vitamin E, depending on the source, has different numbers of methyl groups on the aromatic ring; these forms are referred to as alpha, beta and gamma. The alpha form is more common in Europe while the gamma form is more common in the US (due to different diets).

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    $\begingroup$ The +28°C value on ChemSpider (your link) must be a typo. The source given there is a spreadsheet titled "BradleyMeltingPointDataset" that contains two entries for "vitamin e acetate," with melting points of -27.5 and -28°C, which is in agreement with all the other values listed on ChemSpider. $\endgroup$ – Martin Oct 12 at 14:26
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    $\begingroup$ From alfa.com/en/prodspec/A14505 : "Appearance (Color): Clear, colourless to pale yellow; Form: viscous liquid; Assay (GC): > 96.0%." $\endgroup$ – Martin Oct 12 at 14:31
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    $\begingroup$ Take a sample, put it on DSC, and check out. Maybe someone already made a paper, though... In such molecules (long non-polar chain, aromatic ring...) it's quite possible that melting and freezing temp. are different and whole business is complicated. $\endgroup$ – Mithoron Oct 12 at 22:45
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+50
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Vitamin E acetate, or α-tocopheryl acetate, exists in two forms: D-form (solid/highly viscous at 20 °C) and a racemate (viscous liquid at 20 °C). Interestingly enough, the difference in physical properties is well denoted in German Wikipedia article, whereas English Wikipedia omits this. Also, I noticed many authoritative sources arbitrarily listing a melting point for one or another isomer without denoting the exact form, e.g. even CRC Handbook of Chemistry and Physics provides a single entry for vitamin E acetate with melting point −27.5 °C [1, p. 3-550], so no wonder online sources and sellers mix the things up a little.

More relevant details can be found in Handbook of Pharmaceutical Excipients [2, p. 32]:

d-Alpha tocopheryl acetate

Empirical formula $\ce{C31H52O3}$
Molecular weight 472.73
CAS number [58-95-7]
Synonyms (+)-(2R,4'R,8'R)-2,5,7,8-Tetramethyl-2-(4',8',12'-trimethyltridecyl)-6-chromanyl acetate; d-α-tocopheryl acetate; vitamin E.
Appearance A practically odorless, clear, yellow, or greenish-yellow colored viscous oil that may solidify in the cold.
Melting point 28 °C
Solubility Practically insoluble in water; soluble in ethanol (95%). Miscible with acetone, chloroform, ether, and vegetable oils.
Specific rotation $[α]_\mathrm{D}^{25} = +0.25^\circ$ (10% w/v solution in chloroform)
Comments Unstable to alkalis.

dl-Alpha tocopheryl acetate

Empirical formula $\ce{C31H52O3}$
Molecular weight 472.73
CAS number [7695-91-2]
Synonyms (±)-3,4-Dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H-1-benzopyran-6-ol acetate; (±)- (2RS,4'RS,8'RS)-2,5,7,8-tetramethyl-2-(4',8',12'-trimethyltridecyl)-6-chromanyl acetate; (±)-a-tocopherol acetate; α-tocopheroli acetas; all-rac-α-tocopheryl acetate; dl-α-tocopheryl acetate; vitamin E.
Appearance A practically odorless, clear, yellow, or greenish-yellow viscous oil.
Density $\pu{0.953 g/cm3}$
Melting point –27.5 °C
Refractive index $n_\mathrm{D}^{20} = \pu{1.4950 – 1.4972}$
Solubility Practically insoluble in water; freely soluble in acetone, chloroform, ethanol, ether, and vegetable oils; soluble in ethanol (95%).
Comments Unstable to alkali. However, unlike alpha tocopherol, the acetate is much less susceptible to the effects of air, light, or ultraviolet light. Alpha tocopherol acetate concentrate, a powdered form of alpha tocopherol acetate, is described in the PhEur 6.0. The concentrate may be prepared by either dispersing alpha tocopherol acetate in a suitable carrier such as acacia or gelatin, or by adsorbing alpha tocopherol acetate on silicic acid.

D-form may appear as a highly viscous oil, however it will become solid over time [3, p. 232] (emphasis mine):

D-α-Tocopheryl acetate. CAS: 58-95-7. Obtained by vacuum steam distillation and acetylation of edible vegetable oil products. Occurs colorless to yellow, nearly odorless, clear, viscous oil. May solidify on standing, and melts at about 25 °C. Unstable in presence of alkalies.

DL-α-Tocopheryl acetate. CAS:7695-91-2. Colorless to yellow or greenish yellow, nearly odorless, clear, viscous oil. Unstable in presence of alkalies.

D-α-Tocopheryl acetate concentrate. Obtained by vacuum steam distillation and acetylation of edible vegetable oil products. May be adjusted by suitable physical or chemical means. Occurs as light brown to light yellow, nearly odorless, clear, viscous oil.

References

  1. Haynes, W. M.; Lide, D. R.; Bruno, T. J. CRC Handbook of Chemistry and Physics: A Ready-Reference Book of Chemical and Physical Data, 97th ed.; CRC Press, 2016. ISBN 978-1-4987-5429-3.
  2. Handbook of Pharmaceutical Excipients, 6th Ed.; Rowe, R. C., Ed.; APhA, (PhP) Pharmaceutical Press: London, 2009. ISBN 978-0-85369-792-3.
  3. Food Additives, 2nd Ed., rev. expanded.; Branen, A. L., Ed.; Food science and technology; Marcel Dekker: New York, 2002. ISBN 978-0-8247-9343-2.
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