Phytol: Structure Determination and Synthesis
Phytol is a naturally occurring acyclic diterpene alcohol with the chemical formula C20H40O. Phytol is about one third of the chlorophyll (the green pigment found in plants) molecule and hence usually obtained by the alkaline hydrolysis of chlorophyll. Phytol is also a part of the molecule of vitamin E and vitamin K.
IUPAC name of phytol is (2E,7R,11R)-3,7,11,15-tetramethylhexadec-2-en-1-ol. Phytol is generally a colorless to yellow viscous liquid with a faint floral or grassy aroma, insoluble in water but soluble in organic solvents like ethanol and chloroform.
Natural Sources of phytol are Chlorophyll, Green Tea, Nuts, Marine Organisms, Insects, Essential Oils, and Cannabis etc.
Phytol is used as medicine in Anti-inflammatory, Pain Relief, Anti-anxiety (Anxiolytic),Sedative, Anticonvulsant, Antioxidant, Anti-tumor/Anti-cancer, Antischistosomal, and Immunomodulatory and Antimicrobial effects
Structure Determination of Phytol
1. Elemental analysis and molecular weight determine the molecular formula of phytol is C20H40O.
2. It takes up one mole of hydrogen on catalytic hydrogenation to form dihydrophytol, indicating the presence of one double bond in phytol.
C20H40O → C20H42O
3. Reaction with PCl5 and oxidation to acid having same number of carbon atoms confirms the oxygen atom present as primary alcohol i.e. -OH atteched at terminal carbon.
4. The general formula of acyclic compound is CnH2n+2, the fully saturated hydrocarbon of phytol will be C20H42. So, phytol must be acyclic.
5. Phytol on ozonolysis forms a saturated ketone (C18H36O) and glycoaldehyde (CHO.CH2OH). Formation of these two compounds confirms the position of dounle bond.
6. The ketone (C18H36O) undergoes haloform reaction which indicates that it must be a methyl ketone.
Thus phytol may be represented as
7. Since phytol (diterpene) is composed of four isoprene units, its number of hydrogen atoms suggests that the isoprene units must be present in reduced form and hence on the basis of the head to tail linkage of isoprene units, the ketone (C18H36O) may be assign as the following structure-
From the above discussion, the structure of phytol can be written as-
Synthesis of Phytol
F. Fischer Synthesis (1929)
Fischer et al. synthesized phytol from the ketone (6,10,14-trimethylpentadecan-2-one) in the following way. This synthesis primarily involves extending the carbon chain of the ketone and introducing the double bond and primary alcohol.
How to Calculate Number of Isoprene Units in Phytol
We know that an isoprene unit has five carbon atoms as its molecular formula is (C5H8) and phytol has twenty carbon atoms as its molecular formula is (C20H40O).
To find the number of isoprene units, simply divide the total number of carbon atoms in phytol by the number of carbon atoms in a single isoprene unit
Number of isoprene units = Total Carbon Atoms in Phytol/Carbon Atoms per Isoprene Unit
Number of isoprene units = 20/5 = 4
Therefore, phytol contains 4 isoprene units, which classifies it as a diterpene.
Source: Chemistry of Organic Natural Products vol.1 By O.P.Agarwal