CID 1146
(CH3)3N
Trimethylamine
- C 3
- H 9
- N 1
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- IUPAC name
- N,
N-dimethylmethanamine - Molar mass
- 59.1120(88) g/mol
- Atoms
- 13
- SMILES
- CN(C)C
- InChIKey
- GETQZCLCWQTVFV-UHFFFAOYSA-N
- PubChem CID
- 1146
Trimethylamine smells fishlike when faint and more like ammonia as the air grows richer in it. ChEBI (Chemical Entities of Biological Interest) classes it as a tertiary amine: ammonia with each of its three hydrogen atoms replaced by a methyl group, CH3. IUPAC, the international union that sets chemical naming rules, calls it N,N-dimethylmethanamine. The name reads the structure as methanamine with two extra methyl groups on its nitrogen, each marked by an N. The compound boils at 2.87 °C and travels as a liquefied compressed gas.
Water takes it up freely. Its solubility is 8.9 × 105 milligrams per litre at 30 °C in the Hazardous Substances Data Bank (HSDB), close to 900 grams in each litre. HSDB records it on sale as the liquefied gas or as a solution in water of 25, 30 or 40 per cent. The vapour that escapes from either is heavier than air and sinks.
Structure and bonding
The model holds 13 atoms and 12 single bonds: one nitrogen, three carbon and nine hydrogen atoms. The Labels button puts N on the central atom and every H on a C; no hydrogen is attached to the nitrogen.
In Ball-and-stick the three C–N bonds, each 1.462 Å (an ångström is a ten-billionth of a metre) in PubChem’s computed model, open 110.5° between any two. Turned edge-on to the carbons, the model shows the nitrogen 0.46 Å above their plane, a low pyramid with nitrogen at the apex. The Stick view makes that shallow rise easier to judge, and Space-filling buries the carbons under their hydrogens.
The drawn bonds match the real bonding: single bonds only, no charges, the neutral amine of the gas and the liquid. An acid adds a hydrogen ion to the nitrogen, giving the trimethylammonium ion, (CH3)3NH+, which the model does not show. HSDB puts the pKa of trimethylammonium, a logarithmic measure of acid strength, at 9.80.
Where it turns up
Fish is a major source of trimethylamine in the diet, according to HSDB, and the compound forms as nitrogen-rich plant and animal matter decays. MeSH (Medical Subject Headings) calls it a breakdown product of such matter, released as the free amine during putrefaction. It also taints foods other than fish. MeSH ties it to taints in eggs, the egg’s version of bad breath. Cows fed molassed sugar-beet pulp can give tainted milk, because the pulp is rich in betaines, from which trimethylamine forms.
Some plant foods raise it in people too: strawberries, kale juice and garlic all increase the amount in urine, on HSDB’s evidence. ChEBI records it as a metabolite of the bacterium Escherichia coli. International lists include it among flavouring agents and fragrance ingredients.
Why it matters
Gut bacteria make trimethylamine from the choline in food. Their enzymes destroy a significant fraction of eaten choline, leaving trimethylamine, dimethylamine and methylamine. An enzyme called flavin-containing monooxygenase 3 (FMO3) then adds an oxygen atom, turning it into trimethylamine N-oxide, a step HSDB describes as detoxifying and deodorising. In most people virtually all of it is converted. In a few, mutations in the FMO3 gene make the conversion inefficient, and the result is trimethylaminuria, or fishlike odour syndrome. The methylamines formed after eating choline could, HSDB notes, feed the formation of nitrosamines, compounds with marked cancer-causing activity.
In industry it is the starting point for choline salts. In 1972, HSDB records, 89 per cent of the trimethylamine used went into making choline chloride, an animal feed supplement. HSDB also lists it as a warning agent for natural gas, the role an odorant plays in propane. Reports to the US Environmental Protection Agency for 2023 put the country’s aggregated volume at 50 million to under 100 million pounds.
Properties
| Property | Value | Unit | Source |
|---|---|---|---|
| Molecular formula (Hill order) | C3H9N | ||
| Molar mass | 59.1120(88) g/mol | g/mol | IUPAC/CIAAW 2024 |
| Carbon atoms | 3 | ||
| Hydrogen atoms | 9 | ||
| Nitrogen atoms | 1 | ||
| Bonds | 12 | ||
| PubChem molecular weight | 59.11 g/mol | g/mol | PubChem |
Safety
Pure trimethylamine is an extremely flammable gas, harmful if inhaled, and its gas and water solutions are corrosive. The International Chemical Safety Card (ICSC) describes it as severely irritating to the eyes and airways. Breathing it in can cause lung oedema, fluid in the lungs, and the evaporating liquid can cause frostbite. Haz-Map also records a brief blue haze or halo in the vision of exposed people. The Pocket Guide of the US National Institute for Occupational Safety and Health lists workplace limits, and the PubChem Laboratory Chemical Safety Summary gathers its hazard classifications.
Questions
Why does trimethylamine smell like fish?
Amines as a group arise when bacteria break down proteins and other nitrogen-containing matter, and Chem1 notes their tendency to smell of rotten fish. Seafood is especially rich in nitrogen compounds that start to decompose very quickly, so the fishy smell of amines is no coincidence. Trimethylamine's own odour shifts with strength: fishlike when faint, nearer to ammonia when the air holds more of it.
What does the trimethylamine 3D model show?
It shows the molecule ChEBI describes: ammonia with each of its three hydrogen atoms replaced by a methyl group. All nine hydrogens sit on carbon, none on the nitrogen. The atom positions are PubChem's computed structure, not measured ones. The viewer draws atoms and bonds only: it shows the neutral molecule, not the trimethylammonium ion, (CH3)3NH+, that an acid forms by adding a hydrogen ion to the nitrogen.
Why does lemon juice help with fishy smells?
Acid turns an amine into an ion. On fish, lemon juice or another acid turns methylamine into the methylaminium ion, according to Chem1, and ions are not volatile, which leaves them without a smell. Trimethylamine also neutralises acids, releasing heat and forming salts, and its protonated form is the trimethylammonium ion, (CH3)3NH+, which carries a hydrogen ion on its nitrogen.
What is trimethylamine used for?
Much of it has gone into choline salts, chiefly choline chloride for animal feed. The Hazardous Substances Data Bank also lists quaternary ammonium compounds, disinfectants, plastics, a flotation agent and insect attractants, among them commercial fly baits that combine it with indole and egg solids. Pesticides, textile dyes and photochemicals are made from it as well. Industry produces it from methanol and ammonia over a catalyst, which gives mono-, di- and trimethylamine together.
Made of the same elements
Sources
- PubChem CID 1146, trimethylamine
- IUPAC/CIAAW, Abridged Standard Atomic Weights 2024
- PubChem Laboratory Chemical Safety Summary for trimethylamine (CID 1146)
- NIOSH Pocket Guide to Chemical Hazards, Trimethylamine
- Stephen Lower, Chem1 General Chemistry, §10.6 Types of Acids and Bases (LibreTexts, CC BY 3.0)