Trimethylamine: What is it? How is it formed? Chemical Properties, Uses and Related Syndromes

It is an organic compound that is the product of the decomposition of plants and animals.

It is the primary substance responsible for the foul smell since it is a nitrogen base and can be easily protonated to give the trimethylammonium cation.

Trimethylamine is a good nucleophile; it is used to synthesize choline, tetramethylammonium hydroxide, plant growth regulators, strongly basic anions, exchange resins, and dye leveling agents.

The reason trimethylamine smells so bad is that it is a common byproduct of plant and animal decay (and some infections), and it is believed that we have evolved to find these repulsive odors to prevent us from consuming rotten food.

The oxygenated precursor of trimethylamine is present in fish and breaks down to give that characteristic rotten fish smell.

Fish and other sea creatures are believed to contain this molecule to depress the freezing point of their body fluids and prevent urea, also present in the bodies of many sea creatures, from degrading proteins.

How is trimethylamine formed?

Considering that this compound gives off such an offensive odor, the molecular structure of trimethylamine is straightforward. It is a tertiary amine where the central nitrogen atom is attached to three methyl groups in a trigonal pyramidal geometry.


It is a gas at room temperature, but it is highly soluble in water, making it a powerful aqueous solution. Due to the lone pair of electrons and the electronegativity of nitrogen, trimethylamine is a good nucleophile, as mentioned before.

Neutral amines are such reactive nucleophiles that nature often employs a range of amine side groups that catalyze nucleophilic reactions by accepting protons.

On the other hand, the human body is known to contain enzymes called flavin monooxygenases (FMOs) that are believed to break down environmental toxins in the body. One of these, FMO3, removes nitrogen compounds obtained from the diet.

Mutated copies of FMO3 lose the ability to oxidize Me 3 N to Me 3 NO.

A source of trimethylamine in the choline compound (Me 3 N + CH 2 OH), which is found in eggs, liver, legumes, and some grains, is broken down by bacteria to form Me 3 N.

In turn, Me 3 N usually is oxidized in the liver to odorless TMAO, which is excreted from the body.

However, when the ability to oxidize trimethylamine deteriorates, large amounts of the unchanged amine are excreted, producing a very unpleasant fishy body odor which has led to the colloquial term ” fish odor syndrome. “

What is trimethylamine like?

Trimethylamine sucks. Opening a canister of this boiling gas outside the fume hood will keep your lab smelling for days. Even cracking the top will aggravate anyone within a ten-foot radius. It is not a smell that no one finds pleasant. It is the smell of dead and rotten fish.

Specifically, it is a colorless liquid with a boiling point of around 3.5 ° C, compared to the highest melting point of 224-226 ° C for the more polar Me 3 NO, which presumably has dipole-dipole intermolecular forces.

The trimethylamine compound is a known base, like ammonia, and also like this, it has a trigonal pyramidal structure.

The CNC bond angle is 110.9 °, compared to 107.2 ° in NH 3, presumably due to higher repulsions between the methyl groups. This angle reduces to 109.0 ° at Me 3 NO.

Chemical properties of the compound

Acidity 9.76

Appearance Colorless gas

Boiling point 2.87 °C

CAS number 75-50-3

Density 0.67 g / ml

EINECS number 200-875-0

InChI 1S/C3H9N/c1-4(2)3/h1-3H3


Melting point -117.08 °C

Molar mass 59.11 g / mol

molecular formula C 3 H 9 N

NFPA 704 H-2, F-4, R-0, C-NA

RTECS number N (C) (C) C

Solubility Miscible

Uses of trimethylamine

Although this compound may not smell good, it is a beneficial chemical. In the fishing industry, gas sensors designed to detect the trimethylamine emanating from its catch are used to determine the freshness of fish.

Besides being a common nucleophile, it is also used in herbicides, colorants, anion exchange resins, and plant growth regulators.

This disproves the old saying, “you can’t judge a book by its cover,” or in the case of trimethylamine, by its smell.

What is fish smell syndrome?

Trimethylamine is also released into the body fluids of people with “fish odor syndrome,” a genetic disorder with the clinical name of trimethylaminuria. This unfortunate condition causes body odor, breath, urine, or smell like rotten fish.

Those with trimethylaminuria cannot metabolize trimethylamine from food, and the molecule is thus released unchanged. It has been estimated that only 1% of the UK population carries the gene that causes trimethylaminuria.

There is no known cure for trimethylaminuria; however, you can find some relief by controlling your diet to avoid certain foods, such as fish, eggs, liver, broccoli, and other dark green vegetables.

Fish odor syndrome or trimethylaminuria can become quite distressing for individuals who suffer from it, especially those who go out to work and perform other social or recreational activities.

Trimethylaminuria usually shows more marked symptoms in women, mainly during their menstrual periods. On the other hand, this compound is found daily in foods rich in choline, such as eggs, wheat, and some meats.

The best way to avoid the syndrome is to eat less of the foods mentioned above and increase your consumption of those low in calories.