Hordenine hydrochloride (CAS 6027-23-2) is a small molecule with an outsized reputation: a phenethylamine alkaloid that occurs naturally in germinating barley, in several cactus species and in a handful of grasses, sold commercially as a 98% crystalline salt for nutraceutical formulation, brewing research and pharmacology. Its structure is almost aggressively simple – a para-hydroxylated phenethylamine carrying two N-methyl groups – and yet the substance is a persistent source of specification disputes, because almost every commercial number attached to it depends on which basis it is quoted against: free base or salt, wet or dry, HPLC area or titrimetric assay.
This article sets out the chemistry, the natural and synthetic routes to the molecule, the logic behind the specification, the analytical methods that actually distinguish hordenine from its near neighbours, and the compliance questions that decide whether a shipment can be sold at all. It is written for buyers and process chemists who already know what they want and need the numbers to line up. The material itself is catalogued on our Hordenine Hydrochloride 98% product page.
1. What hordenine is, and what it is not
Hordenine is N,N-dimethyltyramine: 4-[2-(dimethylamino)ethyl]phenol. The free base has CAS 539-15-1, formula C10H15NO and molecular weight 165.23; the hydrochloride has CAS 6027-23-2, formula C10H16ClNO and molecular weight 201.69. It is not an amino acid, not a betaine, and not a quaternary ammonium compound – the nitrogen is tertiary, which is the single most important structural fact about it. A tertiary amine is a base, not a permanent cation: it protonates and deprotonates with pH, it partitions into lipid phases in the uncharged form, and it cannot be titrated the way a quaternary ammonium salt can.
That distinction matters commercially because hordenine is routinely confused with, and substituted for, three related molecules that behave quite differently: tyramine (two N-H groups, a monoamine), N-methyltyramine (one N-methyl), and synephrine (N-methyl plus a benzylic hydroxyl). All four are phenethylamine alkaloids, all four appear in citrus or cactus material, and all four are sold as hydrochloride or tartrate salts to the same customer base. Later sections deal with how to separate them analytically; the point here is that the structural differences are quantitative, not cosmetic, and they change receptor affinity, metabolic stability and regulatory status.
2. Physical and chemical properties
| Property | Hordenine base | Hordenine hydrochloride |
|---|---|---|
| CAS | 539-15-1 | 6027-23-2 |
| Formula / MW | C10H15NO / 165.23 | C10H16ClNO / 201.69 |
| Appearance | Low-melting solid, discolours on storage | White to off-white crystalline powder |
| Water solubility | Sparingly soluble | Freely soluble |
| Base content | 100% | 81.92% |
| InChIKey | – | KIZRJFIRFPIRFS-UHFFFAOYSA-N |
| PubChem CID | – | 165396 |
Three properties drive every handling decision. First, the phenol: a para-hydroxy group on an electron-rich ring is an antioxidant in the good sense and an autoxidation substrate in the bad sense – exposed to air, light and traces of iron, solutions yellow and then brown. Second, the tertiary amine: it is volatile enough to be lost in aggressive drying and it adsorbs strongly to glass and to stainless steel, which is why dilute standard solutions lose concentration over time. Third, the salt’s hygroscopicity: the hydrochloride takes up atmospheric moisture, and a drum opened repeatedly in a humid warehouse will drift out of specification on loss on drying before the assay moves at all.
The phenolic pKa sits close to 10, so in the pH range where most formulations live (3 to 7) the phenol is fully protonated and uncharged, while the amine is fully protonated below pH 8 and largely uncharged above pH 9. That combination gives the molecule an isoelectric-like minimum in water solubility somewhere in the neutral range and makes extraction behaviour strongly pH-dependent: alkaline extraction pulls the free base into an organic phase, acidic back-extraction returns it to water as the salt.
3. Where it comes from in nature
Hordenine was first isolated from barley, and barley remains the best-known source: the alkaloid accumulates in the roots and in germinating grain, and it is one of the markers used in malting research to follow the progress of germination. It has since been found in a long list of cacti, including the mescaline-bearing species, in some Acacia species, and in a few marine organisms.
The biosynthetic route is a two-step methylation of tyramine. Tyrosine is decarboxylated to tyramine by a tyrosine decarboxylase; tyramine is then methylated on nitrogen, twice, by N-methyltransferases that use S-adenosylmethionine as the methyl donor, giving N-methyltyramine as the intermediate and hordenine as the product. The intermediate is not a trivial detail: many plant extracts sold as “hordenine” contain a substantial fraction of N-methyltyramine, and an HPLC method that resolves the two is therefore the difference between a specification you can defend and one you cannot.
Fermentations behave the same way. Because the route starts from tyrosine and relies on decarboxylase activity, hordenine appears in barley malt, in some fermented foods and in the presence of certain lactic acid bacteria. This is the origin of the recurring claim that hordenine is “naturally present in beer” – true in the microgram-to-milligram per litre sense, and irrelevant to the cost of producing a 98% crystalline material, which is always made synthetically.
4. How it is manufactured
Commercial hordenine is synthetic. Three route families appear in the literature and in patent filings; they differ in starting material, in the number of steps and in the impurity profile they leave behind.
4.1 Reductive methylation of tyramine
The shortest route: tyramine is treated with formaldehyde and formic acid under Eschweiler-Clarke conditions, or with formaldehyde and a hydrogenation catalyst under reductive amination conditions, to install both N-methyl groups in one pot. The reaction is cheap and high-yielding, and its characteristic impurities are exactly what the mechanism predicts – residual mono-methyl intermediate, plus dimers and formaldehyde-derived bridged by-products if the pH and temperature are not controlled. A supplier whose CoA shows a mono-methyl peak at 0.5% is telling you the methylation was stopped short.
4.2 Alkylation of a protected phenol with dimethylamine
The second family builds the phenethylamine chain rather than methylating an existing one: 4-(2-haloethyl)phenol, or its methyl ether, is reacted with dimethylamine, and the phenol is then liberated with acid or with boron tribromide if the methyl ether was used. This route avoids formaldehyde entirely and gives a cleaner profile with respect to bridged dimers, at the cost of an extra deprotection step and a halogenated waste stream.
4.3 Friedel-Crafts type alkylation of phenol
The third family attaches a pre-formed dimethylaminoethyl chain directly to phenol or to anisole. It is the most atom-economical on paper and the hardest to run selectively, because the same electrophile can attack at the ortho position and can react twice.
Whichever route is used, the final step is salt formation: the free base is dissolved in a suitable solvent and treated with hydrogen chloride, and the hydrochloride crystallises out. Salt formation is also the last purification gate, since most of the coloured and dimeric impurities stay in the mother liquor. This is why the difference between a 97% and a 99% product is usually not the chemistry but the number of recrystallisations – and therefore the yield, and therefore the price.
5. Reading the specification
The product we supply is specified at 98.0% minimum by HPLC, on the hydrochloride. That single line hides three decisions that a buyer should make explicit.
5.1 Basis: salt or free base
Because the salt is 81.92% hordenine by mass, a specification written as “hordenine 98%” is ambiguous by 18 percentage points. A 98% salt is an 80.3% base; a 98% base would be a 119.6% salt, which is impossible, so the two cannot be confused in practice – but a quotation can still be, and a formulation table copied from a paper that quotes base equivalents will be wrong by a fifth if the material is weighed as the salt.
5.2 Method: HPLC area versus titration
HPLC with UV detection at 280 nm, calibrated against an external hordenine hydrochloride standard, is the normal commercial method, and it is the right one: it resolves hordenine from N-methyltyramine, from tyramine and from the dimeric by-products, and it reports each of them. Area normalisation without a standard overstates purity when the impurities have different response factors, which phenolic impurities usually do. A titrimetric assay, by contrast, measures only the amine and will happily pass a sample that is 90% pure with a co-eluting non-basic impurity.
5.3 What the certificate should also carry
- Loss on drying. The salt is hygroscopic; a result above about 1% signals either a storage problem or incomplete drying, and both move the assay on an as-is basis.
- Chloride content, about 17.6% theoretical. The cheapest and most robust check that the material is the salt and not a blend. A result near 9% means the drum has been cut with free base or with an excipient.
- Related substances, individually named. N-methyltyramine, tyramine and any dimer should appear by name with limits, not as “single impurity”.
- Residual solvents. Methanol and ethanol are the usual crystallisation solvents; both are ICH Q3C class 2 or 3 and both should be reported.
- Heavy metals and elemental impurities. Iron is the one that matters functionally, because it catalyses the phenolic autoxidation that turns a white powder brown in the drum.
6. Analytical methods that actually distinguish it
Three techniques carry the weight, and they answer different questions.
6.1 HPLC-UV
Reversed-phase C18, water-acetonitrile with 0.1% formic acid, detection at 280 nm. The acidic mobile phase is not optional: at neutral pH the phenol partially ionises, peaks broaden and the retention time becomes sensitive to the sample matrix. Under acidic conditions hordenine, N-methyltyramine and tyramine separate cleanly in that elution order, and a run time of 25 to 30 minutes resolves the dimeric region.
6.2 LC-MS/MS
Positive electrospray, transition m/z 166.1 to 121.1 for hordenine – the protonated base losing dimethylamine to give the vinylphenol fragment – with a confirmatory transition to 58.1 corresponding to the dimethyliminium ion. This pair of transitions is close to diagnostic for the dimethyl compound, and its absence is how a mislabelled N-methyltyramine lot is caught.
6.3 NMR and chloride titration
1H NMR in D2O or DMSO-d6 shows the two N-methyl groups as a six-proton singlet, which distinguishes hordenine from every mono-methyl analogue at a glance; the aromatic pattern confirms para substitution, ruling out the ortho and meta isomers. Chloride by potentiometric titration or ion chromatography then confirms the salt stoichiometry. In combination these tests leave very little room for a substituted or diluted material to pass.
One negative test is worth stating plainly: optical rotation carries no information for hordenine, because the molecule has no stereocentre. A certificate that reports a specific rotation for this product is either a template error or a sign that the certificate was copied from a different product.
7. Applications
7.1 Nutraceutical and sports-nutrition formulation
Hordenine is used as an alkaloid ingredient in pre-workout, thermogenic and nootropic formulations, almost always in the 10 to 100 mg per serving range and almost always as the hydrochloride. Because the material is an active ingredient in a supplement, the dose basis must match the basis used in any supporting literature, and label declarations must be internally consistent. Three practical rules apply: declare the salt form on the label; convert base-equivalent doses into salt weights using the 0.8192 factor; and keep the hygroscopic powder in a sealed, desiccated environment during blending, since caking is a common cause of content-uniformity failures.
PolyBlueChem supplies this material as an industrial and research ingredient. We do not make health, performance or therapeutic claims for it, and formulators should verify the permitted status of the ingredient in the destination market before making any claim of their own.
7.2 Brewing and cereal science
In malting research hordenine is tracked as a germination marker and as a precursor in the formation of N-nitrosodimethylamine during kilning, since the dimethylamine released from the tertiary amine can be nitrosated. Analytical standard quantities – grams, not kilograms – are what this application needs, usually with a certificate that states the purity of the specific lot used to build the calibration curve.
7.3 Pharmacology research
Hordenine is a standard reference compound in work on trace amine-associated receptors, on noradrenaline release and on the pharmacokinetics of dietary amines, because it is one of the few phenethylamines that is both naturally occurring and readily available as a defined salt. Research quantities should be supplied with a CoA that reports the exact lot purity, given that dose-response work is only as reproducible as the standard.
7.4 Organic synthesis
As a protected-phenol-free N,N-dimethyltyramine, hordenine is a convenient starting material for quaternary ammonium derivatives, phenolic ethers and Mannich-type products, where the single free phenol gives one clean handle and the tertiary amine gives another.
8. Regulatory and compliance
Hordenine is not listed in the main international narcotics or psychotropic conventions, and it is not a scheduled precursor. That does not make it regulation-free, and three separate regimes can each stop a shipment:
- Novel food and supplement rules. Status as a food or supplement ingredient differs by jurisdiction and has changed in several markets in recent years. The buying decision should state the destination country and the intended use, and the compliance position should be confirmed for that combination, not for “hordenine” in general.
- Anti-doping. Hordenine has appeared on anti-doping monitoring programmes, which means it is monitored rather than prohibited. Monitoring lists are revised annually – check the current-year list rather than a cached page.
- Transport and hazard communication. The salt is not classified as dangerous goods for most transport modes, but the powder is a fine organic solid and should be handled with dust control, local exhaust ventilation and the usual PPE. An SDS in the destination language should accompany every shipment.
9. Purchasing guide
Six questions separate a usable quotation from a hopeful one:
- Is the assay on the salt or on the base, and by which method?
- Are N-methyltyramine and tyramine reported separately, with limits?
- What is the loss on drying, and what is the chloride content?
- Which solvent is used for the final recrystallisation, and what are the residual solvent results?
- What is the actual lot date, and how is the material packaged for long storage?
- What is the documented regulatory position for my destination and use?
Typical packaging is 25 kg net in fibre drums with a double polyethylene liner, with 1 kg and 5 kg development packs. Store below 25 degC, dry, protected from light, and expect a retest period rather than an indefinite shelf life: a phenolic amine in a hygroscopic salt matrix does not improve with age.
10. Frequently asked questions
Is hordenine HCl the same as hordenine?
Hordenine is the free base (CAS 539-15-1); hordenine hydrochloride (CAS 6027-23-2) is its salt. They are the same active moiety at different mass: 1 g of the salt contains 0.819 g of base, so 98% salt corresponds to 80.3% base.
Why is the hydrochloride preferred?
Stability and solubility. The free base is a low-melting solid that oxidises and discolours, and it is only sparingly soluble in water; the hydrochloride is a stable crystalline solid that dissolves freely – which is what a formulation, a fermentation medium or an analytical standard needs.
How can hordenine be distinguished from synephrine?
Two features. Hordenine is a para-hydroxy phenethylamine with two N-methyls and no benzylic hydroxyl; synephrine carries a benzylic hydroxyl and one N-methyl, which shows up as an extra methine signal in 1H NMR and shifts the LC-MS/MS fragmentation. The two are also sold as different salts in practice – hordenine as the hydrochloride, synephrine commonly as the tartrate.
Does hordenine occur in beer?
Yes, at trace levels, as a barley-derived alkaloid. That natural occurrence has no bearing on commercial supply, which is synthetic, and it does not make a 98% crystalline material a “natural extract”.
What documentation comes with a lot?
A certificate of analysis covering assay by HPLC, appearance, identification, loss on drying, chloride content, related substances and residual solvents, plus an SDS. Additional tests – elemental impurities, microbial limits, particle size – are available on request and are quoted separately.
References and scope note
Structural and identity data in this article are cross-checked against public chemical databases (PubChem CID 165396 for the hydrochloride) and against standard pharmacopoeial analytical practice; formula and molecular-weight arithmetic is reproducible from the atomic weights shown. No third-party analytical results are reproduced, and no clinical or health claims are made. Regulatory statements describe the categories that apply, not a legal opinion for any specific jurisdiction.
This article is provided for technical and commercial orientation. It is not medical, regulatory or legal advice, and it does not replace the destination-market assessment that any supplement or pharmaceutical ingredient requires.
For pricing, samples, a specification signed against your own monograph, or a discussion of the salt-versus-base arithmetic for your application, contact PolyBlueChem at polybluechem@163.com. Related reading: Phenethylamine Alkaloids Compared and Reading a Hordenine HCl Certificate of Analysis.