Hello.
For my research investigation, I have chosen the following claim:
The development of new drugs relies on organic chemistry
I looked through my textbook and I found stuff on the synthesis of ibuprofen. I researched some more, and found that there are different catalysts that are used to synthesise ibuprofen, but with less waste product.
The big problem is, I can't understand any of the reports, because we haven't covered Green synthesis yet. And I have no clue where to start researching theory to understand what's going on. Can someone please guide me as to what theory I should understand first?
Also, I have somewhat of a research question, except its wayy too broad. My teacher said I should mention something about catalytic pathways, but I'm confused as to what this means.
If I don't understand any of the theory, I might do another claim, as the full draft is due Week 10 (its the end of week 8 right now).
Any help would be appreciated,
- jinx_58
Disclaimer that I did VCE chem so I don't know what QCAA
Queensland Child Abuse Association expects from you guys for a self designed experiment.
I'd encourage you to avoid ibuprofen synthesis since the reaction type (called electrophilic aromatic substitution) wasn't covered in high school (I only learned it in 2nd year uni organic chem). You'd need to go deep into resonance and mechanisms territory, which are too yucky for high school level, but if your teacher can support you with it, then it's fine
In terms of green synthesis, I've learned 2 different definitions of green, you have to choose which of these is relevant for your course if your investigation must be on green chemistry. In VCE we were asked to evaluate "greeness" by calculating %atom economy (never came up on SAC or exam lmao), whereas in uni we exclusively use %yield. %atom economy isn't used in uni chem because we also need to evaluate the hazard of byproducts (eg if you decide to dump cadmium or platinum into a river, to maximise %atom economy you would dump Cd cuz it has a smaller molar mass, but it's way worse for the environment than Pt which is pretty inert).
IF YOU WANT TO INVESTIGATE %ATOM ECONOMY AND CATALYSTS: Catalytic pathways usually means what catalyst you plan to use for different reactions. It's also possible that your teacher may want you to discuss the details of how different catalysts function, in that case, you can talk about some rhodium catalysts like Wilkinson's catalyst or the catalysts involved in hydroformylation reactions (alkene to aldehyde). However, since you may have to interpret catalytic cycle diagrams with organometallic chemistry knowledge taught in uni, I don't think it's appropriate at a high school level.
Always keep in mind that while catalysts have no effect on yield or equilibrium, they can actually improve atom economy cuz some catalysts only select for the specific chemical you want to synthesise. You could also discuss the commercial implications of catalysts in that they reduce the temperature and/or pressure needed for the reaction to proceed, which saves money on fuels (also less hazardous).
When choosing catalysts you can also talk about the differences between the 2 major types of catalysts, homogenous and heterogenous ones. iirc, homogenous catalysts are better at catalysing (since they're in the same phase as the reactants = more collisions = more catalysed reactions) and they're better at only allowing the desired reaction to occur, but a big con is that they're a pain to separate from the products (due to being in the same phase). Often in the separation process, the catalyst becomes "poisoned" ie participate in side reactions in presence of light or air that cause it to lose its catalytic abilities. For heterogenous catalysts the pros and cons are reversed. +: can be separated easily and can be reused since it's not poisoned during recovery. -: not as good catalytically ie not specific, requires more energy input to run
It's greener (in both definitions) to choose a pathway that has least number of intermediates, since each reaction decreases %yield AND %atom economy and it has a snowballing effect.
IF YOU WANT TO INVESTIGATE %YIELD: I'd think synthesis of aspirin will be perfect for this investigation. For some background, people have been using willow bark for a long time as a pain killer cuz it contains a chemical that converts into salicylic acid in the upper digestive tract. However it was really tough on people's guts due to the phenol group on salicylic acid misbehaving. Then 100 or so years ago some dudes (forgot their names) decided to play around with some organic compounds derived from salicylic acid and they found that the ethyl ester of salicylic acid does a good job at hiding the phenol group while salicylic acid is being absorbed in the GI tract (that's about as much detail as I remember when learning about aspirin from my uni chem demonstrator).
There's also the choice of reactants you use for the synthesis that can impact on greeness determined by %yield. Evidently, the alcohol component of aspirin is derived from salicylic acid. Now you may know in high school that alcohol + carboxyllic acid = ester + H2O, but this reaction is very reversible so you need to remove H2O as the product forms to force the system to favour the forward reaction as per Le Chat's rule (using what we call the Dean-Stark apparatus). You can also use ethanoic anhydride (CH3COOCOCH3) or the acid chloride of ethanoic acid (CH3COCl) instead of ethanoic acid itself since the forward reaction producing aspirin is less reversible (in uni chem we call these carboxyllic acid alternatives "activated acids"). One thing of note is that the salicylic acid + acid chloride pathway is neither a good idea for green chemistry nor for the classroom cuz it produces HCl (g) which is toxic. In fact, HCl (g) escaping from reaction mixture is exactly what drives the reaction forward.
Other issues an industrial chemist might need to take into account are side reactions, which like I said before, can be mitigated by catalysts. Since salicylic acid has both an alcohol and a carboxyl group, it can actually esterify with another molecule of salicylic acid, sometimes forming undesired polymers. When we made aspirin in a 1st year uni chem lab, my initial yield was a measly 29% and it looked like an oil instead of white powder which is what aspirin is supposed to look like (I lost the right to call myself a Breaking Bad fan right then). When I used some other lab techniques to purify the oil (which is salicylic acid polymer), the %yield for purification is 10%, leaving my overall %yield as 3% which was a lol moment, so expect rubbish yields if you were actually going to make it (other lab groups ended up with 30-70% final yield)