Is Amine Flammable? (A comprehensive overview)

Is Amine Flammable?

Yes, amines are flammable. When burned amines readily catch on fire and produce toxic nitroxide gases (NOx). Nitroxide gases will usually be further oxidized to produce nitrogen gas (N2) and water.

Many synthetic amines are also highly toxic if inhaled, ingested or in contact with skin or eyes.

Amines can be defined as an ammonia molecule (NH3) with at least one of the hydrogen atoms replaced by a carbon atom. The amine with lowest molar weight is methyl amine (CH3NH2).

Chemically amine is a functional group in organic chemistry. There are literally millions of synthetic amines. They are vastly used in the industry of polymers, drugs, dyes, fertilizers, either in the final product or in the production phase.

There are also millions of different naturally occurring amines, including the polyfunctional amines (polyfunctional amines are amines that possess other functional groups in their molecules, such as alcohols and carboxylic acids). 

Naturally occurring amines will most often have other functional groups in the same molecules. Naturally occurring polyfunctional amines can be called alkaloids. Examples of polyfunctional amines in living beings include: morphine, dopamine, amino acids.

Overall Amines Flammability

If a compound contains an amine functional group or it is an amine it is very likely that it is flammable and potentially explosive, and many times toxic or even lethal to humans.

In terms of flammability, amines are somewhat comparable to hydrocarbons (automotive and aircraft fuels are all highly flammable hydrocarbons).

Since the number of known amines is way too high to evaluate each one of them individually, some representative amines were selected. These selected amines and their respective fire hazards will be discussed in the following sections.


Amine
Fire hazards (at standard temperature and/or pressure)
Physical stateFlash PointExplosive limitsAutoignition Temperature
MethylamineGas-10 ºC5% to 21%430 ºC
DimethylamineGas-6 ºC2% to 14%401 ºC
TrimethylamineGas-7 ºC2% to 11%190 ºC
AllylamineLiquid-28 ºC2% to 22%374 ºC
AnilineLiquid70 ºC1% to 11%630 ºC

Some Facts about the Fire Hazards Gaseous Amines

Methylamine is a colorless gas with an odor similar to ammonia that is highly flammable, poses a high explosive risk and is also very toxic. It is commercialized as a compressed gas or in ethanol or water solutions.

Dimethylamine and trimethylamine have similar fire hazards to methyl amine.

Allylamine is a liquid at standard temperature and pressure. Its flash point is lower than the previously mentioned amines, which means that it is more easily burned. Its explosive limits is at a wider range, making it more risky for explosions.

Some Facts About Aniline and Aniline Derivatives Fire Hazards

Aniline is characterized by a molecule consisting of a phenyl group (C6H5) in which the carbon missing and hydrogen atom is bound to a nitrogen atom, which in turn is bound to two other hydrogen atoms. The chemical formula of aniline is C6H5NH2 or C6H6N.

Aniline is a very versatile molecule in terms of its use as a starting material to more complex molecules. And so there is a vast number of anilines out there and also within human cells.

Aniline is flammable and explosive (data shown in the table above), although not as flammable as the lower weight amines such as methylamine. That is partially explained by the lower volatile of aniline in comparison with lower weight amines.

An worth mentioning example of aniline derivative is the pentanitroaniline ((NO2)5C6NH2) or C6H2N6O10). Pentanitroaniline is considerably more explosive than TNT (2,4,6-Trinitrotoluene, (NO2)3C6H2CH3 or C7H5N3O6), a widely used explosive.

One of the reasons that pentanitroaniline is so reactive is that each molecule of it will produce 3 molecules of nitrogen gas (N2) when subjected to a combustion reaction.

This means that a relatively large amount of energy is released because the formation of such a stable molecule, nitrogen gas, releases a lot of energy.

Amino Acids Flammability

Amino acids are natural molecules chemically characterized by having an amino group (NH2) bond to a saturated carbon atom, which itself is bound to a carboxylic acid group (COOH).

Amino acids have very distinct physical properties than hydrocarbons and than simple amines. They have low molar masses but they have very high polarity, turning them quite soluble in water and solids at room temperature.

This means that they hardly form vapors at regular temperatures and therefore their flash point is high overall (a high flash point, above 93 ºC, is often an indicator of low flammability).

Nonetheless, some factors must be considered. 

One factor is that amino acids can somewhat easily go through polymerization reactions under heat. Becoming more flammable and also producing volatile molecules that are also more propense to catch on fire.

Another factor is that an amino acid powder is very finely divided and forms a suspension in the air, an combustion reaction of the amino acid can occur at a faster speed if this suspension is subjected to a high source of heat (e.g. any type of flame). Which in turn produces heat at a fast rate, which can lead to explosions.

A study from 2019 reported data from ignition characteristics of a series of amino acids powders. For that the authors measured the minimum ignition energy and the minimum explosive concentration of seven widely used amino acids.

The authors of these studies concluded that branched chain amino acids such as leucine and isoleucine are more likely to catch on fire or cause explosions than linear amino acids.

Pyrolysis and pyrolizates investigations were performed, and the results showed that a number of flammable substances is produced when branched-chain amino acids are ignited.

Conclusion

As a conclusion, the term amine comprises an extensive volume of different substances which have some properties in common but also some very unique ones. 

In regards to the flammability of amines, it surely can be said that they are in the great majority flammable and pose a significant fire hazard.

Many amines can also pose a high risk of explosion given that a great number of them is kept pressurized. And many of them have a fairly high reactivity towards common materials.

Frequently Asked Questions (FAQs): Is Amine Flammable?

Is amine hazardous?

Most synthetic amines are at least somewhat hazardous. Examples of hazardous amines are propylamine (CH3CH2CH2NH2) and benzylamine (C6H5CH2NH2). Some strong poisons and venoms contain the amine functional group. On the other hand some amines are essential to life such as the nitrogen bases that are a fundamental part of DNA. Also a huge number of drugs contain the amine functional group. Drugs will most often contain other functional groups (e.g. alcohol group) making these amines polyfunctional amines.

Are amides combustible?

Yes, most known amides are combustible. The products of amides combustion include noxious and toxic NOx gases, carbon dioxide and water, as well as nitrogen gas in some cases.

Is Amine a base or acid?

Simple amines such as diethylamine and triethylamine are bases, and they are often used as such in the synthesis of many compounds of pharmaceutical, industrial and agricultural importance.

What is amine used for?

Amines are used in the synthesis of drugs, useful polymers, dyes, pesticides, water and gas purification.

Are amines corrosive?

Usually amines are not corrosive to the skin, or to everyday life materials. However amines are somewhat reactive in the presence of oxidizing agents. Under specific conditions, amines can generate corrosive substances.

If an amine is in contact with acidic materials such as silica, it can also lead to corrosion.

What are amides used for?

Amides can be used in the production of important polymers, including nylon and Kevlar. Many drugs have an amide group in their molecules.

Proteins, fundamental to life, are formed by the reaction of an amine group with an carboxylic acid group. The product of this chemical reaction is an amide. Proteins are molecules that contain hundreds of units of the amide functional group.

Does amine act as an acid?

That depends on what the amine in question is reacting with. If the other substance is a very strong base (such as lithium amide, LiNH2), an amine can act as an acid, that is it loses a H+ cation to the base, lithium amide in this example. That being said, in most cases amines that have no other functional group in their molecules will act as bases, that is they will have their nitrogen atom form a new bond with a H+ cation.

Do amines increase pH?

The amine functional group is relatively basic (tendency to abstract H+ cátions). If an amine with no other functional group is put in a water solution, the amine will act as a base and the molecules of water will act as an acid. As a consequence the concentration of H+ in the solution will decrease in comparison with pure water. The pH of pure water at standar temperature and pressure is around 7, when amine is put in pure water the pH will increase to a value higher than 7. If the amine in question has other functional groups the effect on the pH of a given aqueous solution will depend on the basicity or acidity of the amine as a whole.

Amino acids for instance have both a basic functional group (the amine group) and an acidic group (the carboxylic acid group). Most amino acids will decrease the pH of a neutral aquos solution.

What is rich and lean amine?

Those terms are used in processes of gas purification. Tubulations containing amines are capable of absorbing unwanted gases H2S and CO2. Once the amine becomes saturated with these unwanted gases, the amine can be called rich amine. An example of amine used in such systems is the N-methyl-N,N-diethanolamine ((HOCH2CH2)2CH3N).

References

A Comprehensive Guide to the Hazardous Properties of Chemical Substances Pradyot PatnaikJohn Wiley & Sons, 2007.

Database for some informations about chemicals: https://echa.europa.eu/substance-information

Amino acids flammability:

Wookyung Kim, Takuma Endo, Tomonori Kato, Hitoshi Tsuchiya, Kwangseok Choi, Ignition characteristics of amino acid powders, Journal of Loss Prevention in the Process Industries, Volume 62, 2019, 103976. https://doi.org/10.1016/j.jlp.2019.103976.

What was missing from this post which could have made it better?

Leave a Comment