Matches – with their power to give anybody an almost instant flame – are often taken for granted. I will be taking you through my extraction process of red phosphorus, the beautiful red allotrope of the element phosphorus that can be found commonly in the striker pads of match boxes. Although we may not recover much of the chemical, it is always fun to explore the science and appreciate common household products a little more.
Ever wondered how safety matches work? Well never fear as you will be educated today. The secret to the match comes down to potassium chlorate and red phosphorus. Potassium chlorate (KClO3), a very strong oxidising agent, is the most important ingredient of the match head, often composing around 50% by weight of the match head mixture. Red phosphorus on the other hand, an extremely combustible fuel, is the most important ingredient of the match box red striker pads, also often composing around 50% by weight of the striker pads.
When the match head is run along the striker pad with force, the resulting flame is caused by the formation of a very small amount of the explosive mixture commonly known as Armstrong’s mixture. It is formed due to a small amount of red phosphorus being removed from the striker pad and mixing with the potassium chlorate. The friction produces enough heat to cause the very heat sensitive Armstrong’s mixture to ignite, leading to a small flame.
As you can tell, matches have some potential for extracting some useful chemicals, but I must crush your expectations. There is such a small amount of each chemical that you can go through multiple match boxes and hardly even get a few grams of crude product. Also you shouldn’t be interested in the potassium chlorate as it is dangerously oxidising, landing it on the UK regulated substances list as an explosive precursor, requiring an EPP license to have the chemical in your possession.
Instead we will be just attempting to extract the red phosphorus, with a few uses such as producing phosphoric acid. The possession of red phosphorus is illegal in some countries due to being unfortunately connected with the synthesis of certain illegal drugs; check your country’s laws before attempting this extraction, in the UK it is legal.
The other 50% that composes striker pads is mostly glass, to improve friction when striking a match, and adhesives, to hold the striker pad to the box. We will use acetone to remove the adhesives but we will leave the glass as shouldn’t affect any reactions we use the red phosphorus in although when weighing out accurate masses of the red phosphorus the glass will need to be taken into account. Typically 25% of the red phosphorus mixture will be glass.
|Red phosphorus||Highly flammable
It is highly flammable and explosive when mixed with oxidising substances.
There is a serious risk of the liquid catching fire. Its vapour may catch fire above -20°C.
It can cause severe eye damage and will degrease the skin.
For a 15-minute exposure, the concentration in the atmosphere should not exceed 3620mg m-3. The smell can be detected by most people at about 47mg m-3, well below the level which could cause harm.
Can dissolve some types of plastics.
- Gloves and goggles should always be worn when handling chemicals to protect your sensitive eyes and skin.
- As mentioned, red phosphorus is extremely flammable so it is important to avoid any open flames in your work space. Acetone is also highly flammable, so this applies for working with acetone as well.
- Acetone can be quite dehydrating to your skin which can be irritating, so again gloves are recommended and to avoid skin contact where possible. Acetone also readily evaporates at room temperature so it is suggested that you work in a well ventilated area due to the harmful vapour.
Using a pair of scissors, I cut the match boxes to acquire just the cardboard that has a striker pad surface. I scratched the striker pads with a metal spatula to see if the red composition was loose enough to be removed without a solvent but this was very difficult. I dampened a cotton ball with water and wiped it along the striker pads in the hope to soften them although the metal spatula was still unable to scrape off the red composition effectively this way.
I had to switch the water out for a different solvent as I thought might happen and another cotton ball was dampened with acetone in the hope of removing any adhesives. This seemed to work but the thin layer of acetone applied evaporated too quickly to be useful. I decided to add a small volume of acetone to a 100ml glass beaker and soak half a striker pad face-down in the acetone until the cardboard was visibly soaked. I found the red composition of the striker pad to be easily removed in this way.
I then soaked all of the striker pads in this way and then held at a slant towards a receiving container, in my case a 100ml glass beaker, and I scraped the red composition into the receiving container using a metal spatula. The method worked well although cardboard from below the surface was occasionally scraped off as well, contaminating the red composition; this was a more frequent event if the striker pads were allowed to dry so working fast was relatively important. Also I did not use a large enough receiving container and I ended up with a small loss of the red composition as it missed the container so I upgraded and transferred everything to a 250ml beaker.
Once all of the red composition was transferred to the 250ml beaker, I added a small volume of acetone to cover the red composition and provide a further wash to remove any adhesives. I agitated the red composition with the metal spatula a few times and then the excess acetone was decanted off. I repeated this process a couple of times and then I transferred the damp red composition to a few sheets of printing paper and left it to dry.
The dry red composition should now be pure enough to be called red phosphorus in my opinion, although it will still contain various impurities such as cardboard scraped off from the match box. The red phosphorus was transferred to a piece of paper to weigh, giving a yield of a respectful 0.506g.
This averaged out as a recovery of just over 0.1g per match box as we had used five match boxes although I suspect one of the two brands I used had significantly more red phosphorus due to larger striker pads. I can see this as a reliable method to extract small amounts of red phosphorus. Other brands of match boxes though may react differently to this method of extraction with acetone and so it may not be viable as some people recommend water to loosen the striker pads instead.
Further reading or watching:
YouTube channel NileRed – Red Phosphorus from Matchboxes