Isopulegol

Structural formula
Structural formula without specifying the stereochemistry
General
Surname	Isopulegol
other names	5-methyl-2-prop-1-en-2-ylcyclohexan-1-ol ( IUPAC ) 2-isopropenyl-5-methyl-cyclohexanol
Molecular formula	C 10 H 18 O
Brief description	colorless liquid
External identifiers / databases
CAS number 89-79-2 (-) - isopulegol 104870-56-6 (+) - isopulegol 7786-67-6 (mixture of isomers) EC number 201-940-6 ECHA InfoCard 100.001.764 PubChem 170833 Wikidata Q2103922
properties
Molar mass	154.25 g mol −1
Physical state	liquid
density	0.912 g cm −3 (25 ° C)
boiling point	212 ° C
solubility	easily soluble in ethanol , slightly soluble in water
Refractive index	1.471 (20 ° C, (-) - shape) 1.469 (20 ° C, (+) - shape)
safety instructions
GHS hazard labeling (-) - isopulegol Caution H and P phrases H: 302-315-319-335 P: 261-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Isopulegol is a monoterpene and, like terpineols , is counted among the p -menthenols .

Isomers

Isopulegol exists in two mirror-image forms (-) - Isopulegol and (+) - Isopulegol. Since the compound has two asymmetric carbon atoms, include in addition to this pair of diastereomers and iso-isopulegol , neo-isopulegol and neoiso-isopulegol (each with their mirror-image construction isomers) to the group of isopulegols .

Isomers of isopulegol
Surname	(+) - isopulegol	(-) - isopulegol
other names	(1 S , 2 R , 5 S ) -2-Isopropenyl-5-methylcyclohexanol D -Isopulegol	(1 R , 2 S , 5 R ) -2-Isopropenyl-5-methylcyclohexanol L -Isopulegol
Structural formula
CAS number	104870-56-6	89-79-2
	7786-67-6 (mixture of isomers)
EC number	625-653-4	201-940-6
ECHA ID	100.154.129	100.001.764
PubChem	1268090	170833
	24585 (mixture of isomers)
Wikidata object	Q27285994	Q2103922
	Q54727900 (mixture of isomers)
boiling point	91 ° C at 16 hPa	212 ° C
GHS labeling	Caution	Caution
H-phrases	302-315-319-335	302-315-319-335
P-phrases	301 + 312 + 330-305 + 351 + 338	261-305 + 351 + 338

Occurrence

(-) - isopulegol

Lemongrass

(-) - Isopulegol - the natural substance is left-rotating ; hence the term “ L- Isopulegol” in English literature - is found in oils of lemongrass ( Cymbopogon citratus ), “East African Geranium” (presumably Pelargonium graveolens ), lemon eucalyptus ( Corymbia citriodora ) and round-leaved mint .

(-) - Isopulegol was also detected in cell culture for the first time in a fungus, the plant-damaging tubular fungus Ceratocystis coerulescens RWD 451 .

Natural extraction and synthesis

Eucaliptus ( Eucalyptus citriodora )

Natural extraction

Isopulegol can be obtained from a wide variety of plants, for example from the essential oils of Eucalyptus citriodora or lemongrass .

synthesis

It was first named in 1896 by Ferdinand Tiemann and R. Schmidt during the systematic investigation of the reactions of citronellal : "A cyclic alcohol, which we temporarily call isopulegol, is obtained from citronellal under the following conditions ..."

The substance can be obtained synthetically by catalytic cyclization (intramolecular Prins reaction of citronellal , also called intramolecular carbonyl-ene reaction). By choosing a suitable catalyst , the selectivity of the reaction for one or more stereoisomers of isopulegol can be increased. Typical catalysts are Lewis acids based on aluminum or silicon compounds , including zeolites such as clinoptilolite .

properties

Visually and chemically pure (≥ 99.7%) (-) - Isopulegol is odorless, but when added to citrus smells, it has a cooling effect similar to menthol . It works as a flavor / sensory enhancer .

Applications

Use in the synthesis of natural products

(-) - Isopulegol is also used for the production of other synthetic natural substances, for example flavorings, in particular optically active menthol stereoisomers by catalytic hydrogenation of the carbon-carbon double bond in isopulegol. Also Menthofurane (as in the peppermint plant occur) and the sweetener hernandulcin that especially in the plant Lippia dulcis occurs, can be made of isopulegol.

As early as 1982, Schmid and Hofheinz synthesized the sesquiterpene artemisinin , based on (-) - isopulegol, in eight synthesis steps , which is used to treat infections with multi-resistant strains of Plasmodium falciparum , the causative agent of tropical malaria .

Individual evidence

1. ↑ ^{a b c d e f g h i j k} data sheet (-) - Isopulegol, 99% from Sigma-Aldrich , accessed on June 5, 2016 ( PDF ).
2. ^ Richard J. Lewis: Food Additives Handbook . Springer Science & Business Media, 1989, ISBN 978-0-442-20508-9 , pp. 294 ( limited preview in Google Book search).
3. ↑ ^{a b c d e} data sheet (+) - Isopulegol, 99% from Sigma-Aldrich , accessed on June 5, 2016 ( PDF ).
4. ↑ ^{a b} entry on p-menthenols. In: Römpp Online . Georg Thieme Verlag, accessed on June 7, 2016.
5. ^ ^{A b c} Thomas E. Furia: Fenaroli's Handbook of Flavor Ingredients . Taylor & Francis, 1971, ISBN 978-0-87819-533-6 , p. 311.
6. ↑ Ernest Guenther: The essential oils . D. Van Nostrand Co., 1950, p. 729.
7. ↑ Entry on eucalyptus oils. In: Römpp Online . Georg Thieme Verlag, accessed on June 7, 2016.
8. ↑ Wolf-Gerald Koch and Volker Sinnwell: Isopulegol from Liquid Cultures of the Fungus Ceratocystis coerulescens (Ascomycotina) , Zeitschrift für Naturforschung C, Vol. 42, No. 1-2 (February 1987); doi : 10.1515 / znc-1987-1-227 .
9. ^ BR Rajeswara Rao, PN Kaul, KV Syamasundar, S. Ramesh, Flavor and Fragrance Journal (2003), 18 , pp. 133-135.
10. ↑ Raquel G. Jacob et al .: Green synthesis of (-) - isopulegol from (+) - citronellal: application to essential oil of citronella , Tetrahedron Letters Vol. 44 No. 18 (2003), pp. 3605-3608, doi : 10.1016 / S0040-4039 (03) 00714-7 .
11. ↑ The specified conditions were: heating citronellal with acetic anhydride and subsequent saponification of the acetic ester purified by distillation. The structure of Pulegol is given in the article as the structure for this "Isopulegol" .
12. ↑ Ferdinand Tiemann and R. Schmidt: About the connections of the citronellal series . In: Reports . tape 29 , no. 1 , January 1896, p. 903-926 , doi : 10.1002 / cber.189602901175 ( PDF ).
13. ↑ US Patent 2117463: Method of producing isopulegol of May 17, 1938 to Charles O. Terwilliger
14. ↑ Kelly A. da Silva et al .: Cyclization of (+) - citronellal to (-) - isopulegol catalyzed by H ₃ PW ₁₂ O ₄₀ / SiO ₂ , Catalysis Communications Vol. 5 No. 8 (2004), p. 425 -429; doi: 10.1016 / j.catcom.2004.05.001 .
15. ↑ Mercedes Fuentes et al .: Cyclization of Citronellal to Isopulegol by Zeolite Catalysis , Applied Catalysis, vol. 47 no. 2, pp. 367-374 (1989); doi: 10.1016 / S0166-9834 (00) 83242-X .
16. ↑ Wolfgang Legrum: Fragrances, between stink and fragrance , Vieweg + Teubner Verlag (2011) pp. 16-18, ISBN 978-3-8348-1245-2 .
17. ↑ United States Patent 5,773,410 (June 30, 1998): Method for purifying (-) - N-isopulegol and citrus perfume composition containing (-) - N-isopulegol obtained by the method ; Takeshi Yamamoto (Takasago International Corporation, Tokyo, Japan), accessed June 8, 2016.
18. ↑ Progress in the Chemistry of Organic Natural Products . Springer Science & Business Media, December 6, 2012, ISBN 978-3-7091-6527-0 , p. 129 f.