VioletAbsolute.com

Sweet violet, one accepted name

Kew's International Plant Names Index records Viola odorata L., published by Linnaeus in Species Plantarum in 1753, in the family Violaceae.1 The GBIF backbone taxonomy carries the same name as accepted, under the common name sweet violet.2 It is the species perfumers mean: the leaf absolutes analysed by chemists in Nice and Grasse carry Viola odorata in their titles, and one of their papers calls it “a plant largely used in the perfume industry”.34 Violet absolute, in other words, is named for one species, not a family of look-alikes.

Leaf absolute, flower oil

Two parts of the plant reach perfumery, on very different terms. Absolutes isolated from the leaves are “valuable materials for the flavor and fragrance industry”,3 and absolutes in general are “obtained by organic solvent extraction of raw plant materials”.4 The safety literature files the leaf absolute as a raw material in its own right, with monographs titled simply “Violet leaf absolute” in 1976 and 1979.56 The flower belonged to another economy: violet flower oil was once one of the most valuable perfumery materials,7 and one review, writing of the years before the 1890s, puts 33,000 kg of flowers behind a kilogram of violet oil.8 Ruzicka and Schinz were still studying the essential oil of violet flowers in 1942.9

The aldehyde that smells of cucumber

The leaf's signature molecule was named early. In 1934 Ruzicka and Schinz published the constitution of violet-leaf aldehyde, nona-2,6-dienal, from violet-leaf oil, and in the next paper a synthesis of it or of one of its stereoisomers.1011 In 1952 Franz Sondheimer reported a synthesis of the violet leaf perfume 2(trans),6(cis)-nonadienal, the isomer now written (2E,6Z).12 The same molecule sits in the salad bowl: aroma-extract dilution analysis ranked (E/Z)-2,6-nonadienal first among the odorants of cucumber, followed by (Z)- and (E)-2-nonenal.13 That shared aldehyde is why a violet leaf and a cucumber can smell like relatives.

France and Egypt, told apart by the nose

Violets for absolute are “mainly cultivated in France and Egypt and extracted locally”, and the two origins smell different “both in top and heart notes”.3 A 2014 study pairing headspace GC/MS with GC-olfactometry identified 70 compounds in leaf absolutes, 61 of them not reported before for the species. Ethyl hexanoate and (2E,6Z)-nona-2,6-dienol, the alcohol of the leaf aldehyde, were specific to the French sample; (E,E)-hepta-2,4-dienal, hexanoic acid, limonene, tridecane and eugenol to the Egyptian ones, where cis- and trans-rose oxide also stood out as odorant markers.3 A 2016 metabolomics study found leaf-absolute fingerprints differing “according to geographical locations, and/or adulterations”.4

Tourrettes-sur-Loup, the violet village

Tourrettes-sur-Loup, inland from the Côte d’Azur, owes its renown to the violet, its principal crop from the 1880s; the nineteenth-century growth of the perfume industry at Grasse gave its growers their opening.14 They first grew the Parma violet, also produced at Toulouse, before the variety ‘Victoria’ became the village's main flower. It grows from October to March on small terraced plots, worked by hand, and a festival has honoured it every year since 1952.14 On 6 March 2010 the commune opened the Bastide aux Violettes, a living museum of the flower and its growers,14 with greenhouse visits in the picking season.15

Flowers in winter, leaves in summer

The two harvests split the year. Flowers go into bouquets sold between Christmas and Valentine's Day, and into confectionery: one Tourrettes family business crystallises violets by coating them in sugar and drying them in a heated cabinet.14 The leaves are gathered outside the flowering season, for perfumery: between early May and late July they are mown and delivered the same day to Grasse, where they are processed to go into perfumes.14 The Pays de Grasse skills around perfume — growing perfume plants, processing natural raw materials, composing — were inscribed by UNESCO in 2018.16 That listing recognises a practice, not a product. VioletAbsolute.com has no affiliation with UNESCO, any grower or any perfume house.

Tiemann, Krüger and the ionones

The flower's scent belongs to the ionones, whose name joins “iona”, Greek for violet, to ketone.8 In 1893 Ferdinand Tiemann and Paul Krüger published “Ueber Veilchenaroma”, on the aroma of violets, in the Berichte of the German Chemical Society.17 Working from orris root oil, cheaper and similar in odour, they made ionone in two steps: citral condensed with acetone in alkali to pseudoionone, then cyclised with acid, the choice of acid setting the ratio of α- to β-ionone.8 An in-depth analysis of violet flower oil in 1972 confirmed a mixture of α- and β-ionone as responsible for the odour of violets.7 Global use of the two is put at approximately 100 to 1,000 tonnes a year.8

Irones, the orris branch

The detour ran through the iris. Iris pallida is grown in parts of Italy, France and Morocco, and its sun-dried rootstocks take on “a pleasant violet-like scent which increases with time”. From orris oil Tiemann and Krüger isolated and named irone, synthesising α-ionone along the way for comparison; irone's correct constitution came 54 years later and its stereochemistry only in 1971.7 A 1947 paper by Ruzicka and colleagues, in their long series on violet odorants, is titled “Die Konstitution des Irons”.18 Violet flower oil kept puzzles of its own: a 1972 paper called parmone a “Phantomverbindung”, a phantom compound, in violet flower oil.19 Searching orris for the violet, the chemists had, as one account puts it, “actually discovered what they were initially looking for”.7

Who builds on a name like VioletAbsolute.com

• Fine fragrance houses. “Violet leaves” is a note houses still patent new molecules for.20
• Natural-extract producers. France and Egypt, extracted locally.3
• Analytical and authentication labs. Origin and adulteration both show in the fingerprint.4
• Growers and the Grasse trade. Leaves mown in summer, delivered the same day.1416
• Confectioners. Sugar-crystallised violets belong to the craft.14
• Aroma-chemical makers. Ionones from citral, by the hundreds of tonnes.817

1. Viola odorata L. (1753).IPNI, Kew
2. Viola odorata L., sweet violet.GBIF Backbone Taxonomy
3. Saint-Lary L et al. Volatile compounds of Viola odorata absolutes.Chem Biodivers, 2014
4. Saint-Lary L et al. Metabolomics of violet leaf absolutes.Chem Biodivers, 2016
5. Violet leaf absolute (monograph).Food Cosmet Toxicol, 1976
6. Violet leaf absolute.Monographs on Fragrance Raw Materials, Elsevier, 1979
7. Galano J-M. Molecule of the Month: cis-γ-irone.University of Bristol, School of Chemistry
8. Aloum L et al. Ionone is more than a violet’s fragrance.Molecules, 2020
9. Ruzicka L, Schinz H. Über das ätherische Öl der Veilchenblüten.Helv Chim Acta, 1942
10. Ruzicka L, Schinz H. Veilchenriechstoffe IV: Veilchenblätteröl.Helv Chim Acta, 1934
11. Ruzicka L, Schinz H. Veilchenriechstoffe V: Synthese des Veilchenblätteraldehyds.Helv Chim Acta, 1934
12. Sondheimer F. Synthesis of the violet leaf perfume, 2(trans),6(cis)-nonadienal.J Am Chem Soc, 1952
13. Schieberle P et al. Potent odorants in cucumbers and muskmelons.J Food Sci, 1990
14. Les violettes emblématiques de Tourrettes.Côte d’Azur France, official regional tourism site
15. Bastide aux Violettes, Tourrettes-sur-Loup.Provence-Alpes-Côte d’Azur Tourism
16. The skills related to perfume in Pays de Grasse.UNESCO, 2018
17. Tiemann F, Krüger P. Ueber Veilchenaroma.Ber Dtsch Chem Ges, 1893
18. Ruzicka L et al. Die Konstitution des Irons.Helv Chim Acta, 1947
19. Uhde G, Ohloff G. Parmon, eine Phantomverbindung im Veilchenblütenöl.Helv Chim Acta, 1972
20. Chapuis C (Firmenich SA). Violet leaves odorants. US 9,115,329 B2.US patent, 2015