Choose your goal
Although they have many similarities, solvents are not all the same, they do not have a common origin and they do not serve an identical purpose. Depending on their properties and strengths, industry uses one type of solvent or another. In general, according to their chemical composition we distinguish the following types of substances:
Hydrocarbon solvents
They are composed exclusively of carbon and hydrogen atoms. Many of the solvents of this type used by industry are often derived from petroleum.
- Aliphatic hydrocarbons: these solvents are the raw material for many organic synthesis processes, as well as being widely used in industrial cleaning products. They are also essential in the production of fuel and, in fact, the efficiency or octane rating of the fuel will be higher or lower depending on the type of solvent used.
- Examples: Pentane, hexane, heptane, decane
- Alicyclic hydrocarbons: usually used for fuel production, they are also of interest for cleaning products and grease removal.
- Examples: Cyclohexane, methylcyclohexane
- Aromatic hydrocarbons: their high solubility makes them interesting for almost any industry. These solvents can be found in perfumes, pharmaceuticals, dyes…
- Examples: Benzene, toluene, xylene, ethylbenzene, styrene
- Halogenated hydrocarbons: their anaesthetic and antimicrobial properties make them very interesting substances for use in medicine.
- Examples: Methylene chloride, chloroform, trichloroethylene, carbon tetrachloride
Oxygenated solvents
They always contain oxygen atoms in their structure, which gives them a high capacity to dissolve a different variety of chemical compounds called “polar”.
- Alcohols: used in the cosmetics industry and in the manufacture of cleaning products.
- Examples: Methanol, ethanol, i-propanol, butanol
- Glycols: they are often used as antifreeze due to their high thermal stability.
- Examples: Ethylene glycol, diethylene glycol
- Ethers: one of the most common uses of these solvents is in the manufacture of inks and paints, as they are highly volatile.
- Examples: 2-methoxyethanol, ethoxyethanol, butoxyethanol, p-dioxane
- Esters: perhaps the most characteristic feature of these solvents is their scent, hence their typical use in perfumes.
- Examples: Methyl acetate, ethyl acetate, i-propyl acetate, n-butyl acetate
- Ketones: ketones are widely used in the manufacture of polymers, and another advantage is that they are soluble in water.
- Examples: Acetone, butanone-2, 4-Methyl-pentanone-2, hexanone-2, cyclohexanone
A huge importance for medicines
We may be able to live without make-up or perfume, but one thing is clear: medicines play a vital role in our society. Solvents, in turn, seem indispensable to the pharmaceutical industry due to their versatility. In fact, you will find them in almost every step of the production chain.
Toluene, for example, is used to make painkillers such as paracetamol and in medicines to treat bacterial infections such as penicillin. It can also dissolve and facilitate chemical reactions, an essential step in drug synthesis, and is very effective in extracting and isolating very pure active ingredients from natural sources such as plants. In addition, toluene is very useful in eliminating residues or impurities from the final mixture, making it attractive for drug design. From antihistamines to antivirals, its use extends to medicines of all kinds.
Another example of a solvent widely used in the pharmaceutical industry is dichloromethane, which is applied not only in more traditional medicines, but also in advanced therapies such as drug delivery systems based on nanoparticles. In general, dichloromethane is very effective in the manufacture of medicine coatings, which are necessary to ensure that the drug is not degraded or exposed to environmental deterioration. Like toluene, it can be used to isolate the active ingredients that form the basis of drugs and to remove impurities during the synthesis process.
Solvent virtues and vices
Like almost everything else, solvents have a dark side. Many are toxic to human health and pollute the environment. Many solvents are also volatile organic compounds (VOCs), which means they evaporate easily at room temperature and are released into the atmosphere. This has advantages for certain applications (such as paint and perfumes, for example), but also obvious negative consequences for the environment and air quality, including serious damage to the ozone layer.
As we cannot avoid breathing, we cannot avoid inhaling these compounds when they are in a gaseous state, which can eventually lead to respiratory problems. Also, some solvents are very persistent and do not degrade easily, giving them the ability to remain in the environment for long periods of time.
Moreover, prolonged human exposure to these solvents has been linked to damage to the immune system. In the most serious cases, certain solvents can cause brain damage or even cancer. A clear example is benzene, which is already subject to very strict legislation in the European Union. In other cases, direct contact with certain solvents can damage our skin, and if the skin absorbs these substances, they can eventually damage our internal organs.
A bet on doing things differently
The damage caused by these substances has been studied for decades: if we continue to use them, the problem will remain. But there are green alternatives that, while not as versatile or productive, at least eliminate the risks of traditional solvents.
Some are made from organic and vegetable waste, such as oils, and others are based on certain salts that are liquid at room temperature below 100 °C. Another area where a lot of effort is being made is that of supercritical fluids, which are compounds capable of remaining in an intermediate state between liquid and gas under certain conditions of temperature and pressure.
A clear example is carbon dioxide, which is abundant and harmless, and it has applications that are as curious as they are of everyday life: using high-pressure CO2, it is possible to produce decaffeinated coffee or infusions that are free of theine. And how is this achieved? It’s simple, but elegant: unroasted coffee beans are exposed to CO2, which binds to the caffeine molecules. These are then extracted along with the gas, ensuring that we can enjoy a good coffee without sacrificing a restful sleep at night.
Back to the campfire
At IMPACTIVE, we want to take it a step further. How are we doing this? By getting rid of solvents altogether. We want to replace these substances and employ a more sustainable approach for the pharmaceutical industry, thanks to a greener technique.
We are talking about mechanochemistry, a truly ancient science like alchemy, which allows us to go back to basics. It is about using the same concept that led the first human being to light a fire due to friction: by using mechanical energy, we can carry out transformations in substances, facilitating chemical reactions and even physical changes. And where does this mechanical energy come from? The list is endless: ball milling, extrusion, acoustic resonant mixing, pulverisation…
Through mechanochemistry we aim to produce active pharmaceutical ingredients (APIs) focused on three main diseases: hypertension, diabetes and cancer.
We still have a lot of work to do, but our goal is not just to get rid of solvents, but to try to make pharmaceuticals as ecological as possible at every step and to prove that we can change the rules of the game in drug formulation.