Material guide: helional — five names in the corpus, nitrogen in the bottle, and the control that showed no sex difference

The first time I counted this one in the corpus I found 26 formulas.

The real number is 61.

Name on the formula	Formulas	Median dose
helional	26	1.50%
tropional	20	3.00%
ocean propanal	7	1.00%
helional (IFF)	4	1.25%
helional™ (IFF)	4	2.10%

One CAS number, 1205-17-0. Merged, 61 formulas (6.4%), median dose 2.00%.

Tropional alone is a third of them, and that name contains none of the letters of helional. This is the third time this series has hit the same problem — omega-pentadecalactone has four names, eucalyptus oil and cineole are two names for different things, and this one has more than a dozen trade names I can count in the database.

The short version

• Five names, one molecule. Searching only for helional misses a third of its appearances.
• The storage field says store under nitrogen. Of the 1,232 materials carrying storage advice, that phrase appears in only 92 (7.5%). It is an aldehyde; what it fears is air.
• Seven GHS statements, including H317, may cause an allergic skin reaction and H411, toxic to aquatic life with long lasting effects. Only 369 records in the whole database carry any GHS data at all; 64 of those carry H317 and 42 carry H411.
• Not found in nature, while every one of its names is about the sea — ocean, marine, Floramelon, Heliofresh.
• The sperm-attractant story is not about this molecule. In a 500-subject study the sex difference belonged to bourgeonal (males 13 ppb, females 26 ppb); helional was tested in parallel and showed no difference.

The basics

Database name	ocean propanal
Main trade names	Helional (IFF), Tropional, Floramelon, Florial, Heliogan, Heliofresh, Neohelial
CAS	1205-17-0
Chemical name	2-methyl-3-(3,4-methylenedioxyphenyl)propanal
Formula	C₁₁H₁₂O₃
Molecular weight	192.21
Type	Natural/synthetic (in practice synthetic)
Odour	Watery, fresh, green, ozone, cyclamen, hay
Odour family	floral
Strength	Medium
Longevity	64 hours at 100% (a neat value)
Appearance	Pale yellow to yellow clear oily liquid
Boiling point	282–284 °C @ 760 mmHg
Flash point	> 93 °C
Vapour pressure	0.003 mmHg @ 25 °C (est)
logP	2.20 (est)
Water solubility	342.6 mg/L @ 25 °C (est)
Natural occurrence	Not found in nature
Storage	24 months or longer; cool, dry, sealed, away from heat and light, under nitrogen
Regulatory	JECFA, FEMA GRAS
Suppliers	50
Corpus position	61 formulas (6.4%), median dose 2.00%, range 0.14–20.45%

That "store under nitrogen"

Most materials' storage advice reads "cool, dry, sealed, away from heat and light". This one adds a clause.

So I counted: of the 1,232 materials in the database carrying storage advice, only 92 mention nitrogen — 7.5%.

It is an aldehyde. Air sensitivity is that class's shared problem, and what air does goes past "it smells different now".

Hagvall and colleagues, in Chemical Research in Toxicology in 2007, worked on geraniol rather than helional, but the logic of that paper applies to the whole problem. They investigated the mechanism of geraniol autoxidation at room temperature and used the mouse local lymph node assay to compare the sensitizing potency of pure geraniol, air-exposed geraniol, and its oxidation products.

Geraniol's autoxidation follows a different pattern from linalool's and limonene's, proceeding via allylic hydrogen abstraction near its two double bonds, primarily forming hydrogen peroxide together with the aldehydes geranial and neral, plus small amounts of a hydroperoxide.

The key sentence: autoxidation greatly influenced the sensitizing effect of geraniol. The oxidized samples had moderate sensitizing capacity, quite different from that of pure geraniol. The authors believe the hydroperoxide is the major contributor to allergenic activity, together with the two aldehydes, and they recommend that the possibility of autoxidation and subsequent formation of contact allergenic oxidation products be considered in risk assessments performed on fragrance terpenes.

That paper is not about helional, and the direction is even opposite — geraniol's oxidation produces aldehydes, while helional already is one. So I cannot carry the conclusion across.

What does carry across is the principle: what is in the bottle differs from what you bought, as a function of how often you have opened it. And on this material the supplier wrote nitrogen explicitly, which is their view of the matter.

In practice: decant into small bottles, open the large one rarely, work from stock solutions. Storage and oxidation has the full procedure.

Seven GHS statements

This field runs longer than most:

H303	May be harmful if swallowed
H313	May be harmful in contact with skin
H315	Causes skin irritation
H317	May cause an allergic skin reaction
H319	Causes serious eye irritation
H320	Causes eye irritation
H411	Toxic to aquatic life with long lasting effects

Acute toxicity: oral rat LD50 3,600 mg/kg, dermal rabbit LD50 above 2,000 mg/kg.

One thing cannot be skipped here: GHS coverage in the database is very low. Of 42,225 material records, only 369 carry GHS data. So "this one has seven statements and that one has none" usually means the other one has no data, not that it is safe. We were caught by this in the naturals article, and last article's cineole had an empty field too.

Among the 369 that do carry data: 64 include H317 and 42 include H411. Having both on one material is worth remembering.

What H317 means for a formula: it is the sensitization flag, and IFRA restrictions mostly exist for exactly this. Check current IFRA Standards for the limit.

What H411 means for a formula: a rinse-off product and a leave-on product are not the same case under this statement.

The sperm-attractant story is not about this one

A claim circulates online that a fragrance molecule activates an olfactory receptor on human sperm. There is real research behind it, but the lead is not helional — helional happens to be the control in that study.

Olsson and Laska, in Chemical Senses in 2010, set it up like this. Earlier work had shown that sperm chemotaxis critically involves the human olfactory receptor OR1D2, which is activated by the aromatic aldehyde bourgeonal. Their hypothesis: since both natural and sexual selection may act on receptor expression, human males should be more sensitive to bourgeonal than females.

Using a three-alternative forced-choice procedure, they determined olfactory detection thresholds in 500 subjects — 250 male, 250 female, aged 18 to 40.

The result:

Compound	Male mean threshold	Female mean threshold	Difference
Bourgeonal	13 ppb	26 ppb	significant
Helional	—	—	none
n-Pentyl acetate	—	—	none

Helional, a structural analog tested in parallel, showed no sex difference. Neither did n-pentyl acetate.

Three further findings are worth keeping: males and females did not differ in frequency of specific anosmia for any of the three odorants; threshold distributions were monomodal for all three in both sexes; and thresholds did not differ significantly between pre- and postovulatory females.

The authors note that to the best of their knowledge this is the first study ever to find a human male superiority in olfactory sensitivity, and suggest single nucleotide polymorphisms or copy number variations in olfactory receptor genes as the proximate cause, with a sex difference in bourgeonal's behavioural relevance as the ultimate cause.

So if someone tells you helional does something reproductive, that study was about a different molecule. And that study itself is about detection thresholds in the nose, not about what happens when something is applied to skin.

All the names say sea; the molecule is not from the sea

Odour field: watery, fresh, green, ozone, cyclamen, hay. Trade names: Ocean propanal, Floramelon, Heliofresh, marine, and so on.

And the natural occurrence field reads "not found in nature".

Another instance of the pattern from heliotropin and cyclamen aldehyde: the name describes what it reminds you of, not where it came from. The smell of the sea was constructed by this molecule; it was not carried in from the sea.

Incidentally the descriptor "cyclamen" attaches to both this and cyclamen aldehyde, and smelling the two side by side shows clearly how one odour note can be built from structurally unrelated molecules.

When you smell it

• Start at 2%. That is the corpus median; the range of 0.14% to 20.45% has marine and watery formulas built around it at the top end.
• It is more than watery. The hay descriptor is real, comes out at slightly higher concentrations, and is what most distinguishes it from a pure ozonic material.
• The strength field says medium with no dilution advice attached. That is not the common case in this series (cineole and omega-pentadecalactone both say "10% or below"), so it is relatively forgiving.
• Smell it beside cyclamen aldehyde. Both carry the cyclamen descriptor by different means.

The perfumery writer Arcadi Boix Camps wrote in 1978 that it has "a fresh melon fruity odor" and "is endowed with a great fixing power", and mentioned its role in Diorella and Dior Dior. That is commentary rather than measurement, and it is here as context rather than as data.

Buying and storage

Fifty suppliers. Buy on CAS 1205-17-0, because at least a dozen names circulate: Helional, Tropional, Floramelon, Florial, Heliogan, Heliofresh, Neohelial, Helionix, Heliolan, Heliobouquet, Heliolal, Helion.

Store as the database says: cool, dry, sealed, away from heat and light, under nitrogen. Most people cannot actually blanket with nitrogen, in which case the fallback is decanting into small bottles, so that each one has little headspace and gets opened rarely.

Flash point above 93 °C, shelf life 24 months or longer.

Regulatory and safety

Seven GHS statements as above, of which H317 is the sensitization flag.

Flavour listings are JECFA and FEMA GRAS — shorter than most materials in this series, with no CoE or FLAVIS.

Check current IFRA Standards for the limit — here is how. It carries H317, so this step is not optional.

→ Helional in the database: full physical data, 50 suppliers and suggested blends. → Search by odour: try "watery ozone green".

References

P. Olsson, M. Laska, Human male superiority in olfactory sensitivity to the sperm attractant odorant bourgeonal, Chemical Senses, 35(5), 427–432 (2010). PMID 20378596. doi:10.1093/chemse/bjq030

L. Hagvall et al., Fragrance compound geraniol forms contact allergens on air exposure, Chemical Research in Toxicology, 20(5), 807–814 (2007). PMID 17428070. doi:10.1021/tx700017v