Tonalid

• 📂 CAS N° 21145-77-7

• ⚖️ MW 258,4 g/mol

• 📝 Odor Type: musk 

• 📈 Odour Strength: medium, 400hrs + tenacity in 10% DPG sol. 

• 👃🏼 Odor Profile: Musky sweet, a bit mineral or crystal. Salty, humid, dry woody ambery earthy and dusty. It's one of my favorites. 

• 👅 Flavor Profile: NOT FOR FLAVOR USE 

• ⚗️ Uses: Only used in masculine fragrance and or fougere. The average amount is much lower than the previous musks.

Careful: restricted or forbidden

What is Tonalide?

Fixolid or Musk tetralin It is named chemically 1-(3,5,5,6,8,8-hexamethyl-5,6,7,8-tetrahydro-2-naphthalenyl) ethanone. It appears as white crystalline powder or chunks. Sweet woody-musky odor of considerable tenacity. The degree of muskiness seems to vary with the concentration of the material in solution. At concentrations below 5 or 6, there is a marked improvement in the pleasant-musky notes and very Iittle, hard-woody, or unnatural chemical-musty notes. 

The latter may appear in higher concentrations, but odor descriptions vary significantly from one observer to another, and also with the age of the material.  This “Tetralin’’-type musk was developed shortly after the first and temporarily successful “Phantolid” musk (see Acetyl hexamethylindan) and the title material has been able to hold the market for quite some time in spite of violent competition from a wealth of new “Non-Nitro” musks, appearing on the perfume chemical market during the past decade. The material has the advantage of good volubility in alcohol, no color, or the tendency of discoloration in functional products, but it does tend to produce “sour” notes in finished goods if the pH is slightly on the acid side (lower than 7).  The tenacity is distinctly inferior to that of Cyclopentadecanolide, also inferior to the Oxahexadecanolides.  But material remains a remarkable milestone in the perfume chemistry and its use at present is mainly reduced but its relatively high cost in comparison to certain musks. Many of the indan-types \ tetralin-type musks suffer from the fact that they appear as mixtures of several isomers and homologs as a result of a reaction by which they are manufactured.

Perfume and flavor chemicals (1969), S Arctander.

1954 - Tonalide Story

Besides being competitive and tedious, the elucidations of Phantolid and Moskene structures also had adventitious benefits, especially in the field of structure-odor relationships. Hence, acetylation of Moskene hydrocarbon, devoid of a methyl group at the 2-position of the indan, delivered a nor-Phantolid that still possesses a musk odor, but of weaker power. All other derivatives with missing methyl substituents compared to Phantolid verified the trend, the lesser the number of methyl groups, the weaker the musk. Taking that forward obviously led the chemists to think that an extra methyl could be favorable for the musk impression. Preparation of the fully methylated analog of Phantolid was therefore undertaken, which required the preparation of heptamethylindan.

First attempts from PFW to produce the heptamethyl indan from para-cymene were unsuccessful. But PFW chemists developed an alternative procedure of indane synthesis by a reaction of styrenes with alkenes in acidic media; accordingly a patent to prepare heptamethylindan from dimethylstyrene and tetramethyl ethylene was deposed the 5 of October 1954.

With the belief of having in hand the proper heptamethylindan, PFW chemists prepared the acetylated compound thought to be methyl-Phantolid. The product indeed exhibited a strong musk odor, and this new ketone named Tonalid was protected by patent the 11 October 1954 but things were a little less straightforward than they appeared. This patent document is very interesting to examine, after the classical claims describing procedures and properties, a curious addendum was inserted. “It appears in light of more refined methods of observation that some of the musk odorants set out in Table 1 and the Examples should be re-described as follows.” Then a table is found with the previously prepared indane compounds re-attributed with tetraline structures. Specifically for the methyl-Phantolid “actual description - 1,1,2,2,3,3,5-heptamethyl-indane methyl ketone” is replaced by the “correct description – 1,1,3,4,4,6-hexamethyl-tetraline-7-methyl ketone.”

This last minute correction was probably done by the PFW chemists after realizing that the envisioned indan structure was not present in the synthesized compound, an unexpected reaction path having led to a tetralin core instead. This unusual course of styrene reaction with a crowded alkene was discussed in the 1963 JOC paper by Carpenter[21] together with Versalide. As shown on Scheme 10, the reaction starts by the formation of a cymyl carbocation after styrene protonation. Then, tetramethylethylene present in the medium is probably too encumbered to react with the tertiary cation, so in lieu, the attack is assured by traces of unencumbered dimethyl-1-butene that might form by isomerisation under acid catalysis from the former. The resulting cation is prevented from proceeding via Friedel- Crafts cyclization to an indan again because of steric hindrance, it thus evolves through a 1,2 hydride-shift to a novel carbocation, farther along the chain, which then has no hindrance to ring- close into a tetralin. It is noteworthy, that the initially envisioned permethylated indane was prepared for the first time only in 1987 by Mayr and al. under particular conditions to prevent proton catalysis to do so, cumyl chloride is made to react with an excess of tetramethyl ethylene in a twofold Friedel-Crafts reaction triggered by titanium tetrachloride. The excess of alkene serves as a ‘proton sponge’ preventing acid-catalyzed isomerizations, the fully methylated indan can therefore be isolated in 72% yield. It seems that the synthesis of methyl-Phantolid was never attempted later on; whilst the preparation of methyl-Tonalid would prove fruitful for Firmenich, as we will see in the last chapter with Vulcanolide.

Tonalid is the second member of the tetralin musks and went on to experience great commercial success, being the most employed PCM after Galaxolide. Despite the high secrecy surrounding the world of fine perfumery, we can find reliable sources indicating the presence of Tonalid in luxury perfumes together with musks from the other families. We can cite Paris (Yves Saint Laurent, 1983) by Sophia Grojsman where “Galaxolide (5%) was introduced as part of the musk complex in conjunction with musk ketone, cyclopentadecanolide, and Tonalid. It is also present in Obsession (Calvin Klein 1985) in which Jean Guichard used “Galaxolide (5%), Tonalid, ethylene brassylate, and musk ketone and Fahrenheit (Dior, 1988) where J.-L. Sieuzac used 11% of Tonalid. It is more generally said that Tonalid “was largely employed in masculine toiletries as it blends particularly well with coumarin in Fougère perfumes.”

The crucial role of chirality observed in odorant compounds prompted the chemists at the Sumitomo Chemical Company to engage in the selective syntheses of both enantiomers of tonalid. The preparation relied on precursors from the chiral pool, hence enantiopure chrysanthemic acid was converted into pyrocine, which served as a double electrophile in consecutive Friedel-Crafts reactions with toluene. The resulting bicyclic carboxylic acid was submitted to Kochi’s decarboxylation reaction to give a chloromethyl derivative, which upon reductive dehalogenation and acetylation provided (-)-(3S)-Tonalid. This isomer possesses a “strongly musky odor.” The same sequence applied to the chrysanthemic antipode, gives access to (+)-(3R)-Tonalid, having a “light and sweet aromatic odor.”

The revolution brought by the release of Phantolid on the market of aromachemicals fostered intensive research programs within the main actors of the domain. As we just have seen, PFW and Givaudan were the first to fish out musky pearls among the plethora of compounds sieved. But other racers joined the chase and had a rational approach to ferret out other jewels and thread them onto the necklace of musks. This will bring us to examine how the work of Muus Gerrit Jan Beets from Polak & Schwarz’s (to become IFF) within musk odorants, which culminated in the discoveries of Celestolide and Galaxolide.

** PFW (Polak’s frutal works)

— A Chemical History of Polycyclic Musks (Chem. Eur. J. 10.1002/chem.202000577), Dr. Olivier R.P. David

Sources and information:

• National Center for Biotechnology Information (2020). PubChem Compound Summary for CID 89440, Tonalid. Retrieved November 24, 2020 from https://pubchem.ncbi.nlm.nih.gov/compound/Tonalid.