Common pain relievers like acetaminophen (Tylenol) and ibuprofen (Advil) have a dirty little secret: Producing them involves chemicals derived from crude oil. Now, a team of chemists from the University of Bath in the UK has shown how to manufacture these medicine cabinet staples using a waste product from the forestry and paper industries. The researchers detailed the process in a freely available paper published in June to the journal ChemSusChem.
One ring to rule them all
The remarkably versatile petrochemicals (compounds derived from oil and natural gas) currently utilized to make essential pain relievers are called benzenoids, organic hydrocarbon compounds that contain a benzene ring (which is composed of six carbon atoms in the shape of a ring with alternating single and double bonds). Benzenoids are incredibly useful, as they can be broken down to manufacture polymers, drugs, pesticides, flavors, stabilizers, and lubricants.
The University of Bath chemists wondered if there was a suitable replacement for benzenoids that is renewable, inexpensive, and widely available. After some searching, they found that turpentines could fit the bill. These substances are primarily extracted from pine trees and consist of resins dissolved in a volatile oil. Around 360,000 metric tons of turpentines are available each year at a price of roughly 25 cents per liter.
One type of turpentine, called β-pinene, is most suitable for the creation of pain relievers. Structurally, the molecule is rather complicated, with two fused rings (a bicyclic compound) that form a bridgehead. The first step was to convert this into a monocyclic compound (with one ring), so chemists converted it into 4-isopropenyl-cyclohexanone (4-IPEC). From there, it was a three-step process to turn 4-IPEC into acetaminophen and a five-step process to transform it into ibuprofen — both of which contain that signature benzene ring.
As a bonus, the researchers also produced a compound called 4-HAP from turpentine, which is a precursor for pharmaceutical drugs like beta-blockers (used to manage abnormal heart rhythms and high blood pressure) and salbutamol (found in asthma inhalers).
A matter of cost and scale
Crucially, the chemical recipes are readily scalable, the researchers say. They can make use of continuous flow reactors, in which raw materials for a chemical reaction are continuously fed into a machine and emerge as a final product, rather than being “cooked up” in batches one by one. Four years ago, researchers at the University of Wisconsin-Madison announced that they had found a way to synthesize acetaminophen from a compound found in poplar trees, but the process wasn’t as scalable nor was the base compound as widely available.
While the present research appears to have addressed both of those issues, the scientists behind it admit that their renewable method of making common pain relievers cannot presently compete on cost with the current fossil fuel-based method. It is, however, ready to be utilized should oil prices rise further and remain elevated or if it becomes necessary to further limit fossil fuel extraction to protect ecosystems and stave off catastrophic climate change.