Synthesis – Paracetamol, Tylenol, Actoaminophen

As you know, there are loads of organic reactions not covered in the syllabus. E.g. OH removal from benzene rings with zinc dust etc etc. I personally have heard at least two CIE chief examiners (one for paper 2 and one paper 4) say “the correct chemistry will always be credited”, from which it seems, in the final exams, if you know these reactions, you are able to use them if helpful when doing synthesis. However CIE are most likely to have questions on synthetic reaction pathways that use standard reactions that you have used in your course. You may me more likely to forget the ‘off-syllabus’ bits of knowledge but you should be OK with the standard reactions given that you’ve done them so many times already.

Because they want to test you primarily on the syllabus content, they will probably guide you through a synthesis in a step by step manner, rather than tell you to go from Step A to Step F with total freedom to do what every path you choose (but that is what we have done in class – as it’s very good practice). So you are very unlikely to be able to use any ‘special’ reactions.

Having said that, there are some alternatives ways of doing one step… While the advice for doing any particular step is: USE THE REACTION  SPECIFIED IN THE SYLLABUS, there are some alternatives.

E.g. Nitrobenzene to phenylamine. NaBH4 can be used in these conditions: NaBH4 in the presence of catalytic amounts of Ni(OAc)2.4H2O reduces varieties of nitro
compounds to their corresponding amines.
See the paper: Convenient Reduction of Nitro Compounds to their Corresponding Amines with Promotion of NaBH4/Ni(OAc)2.4H2O System in Wet CH3CN by Davood Setamdideh et al.

 

And so to my second main point:

The ethanoic anhydride (acetic anhydride as it’s sometimes called) can be used in water to selectively react with the NH2 group on the aromatic ring but leaves the phenolic (phenol like) OH group alone. Selective acylation occurs in these conditions.

This definitely isn’t in the syllabus, but paracetamol is an A-level examiners friend, often coming up across the exam boards as it employs many standard reactions in it’s creation.

See: http://www.rsc.org/learn-chemistry/resource/download/res00000058/cmp00000047/pdf or go to this page:  http://www.rsc.org/learn-chemistry/resource/res00000058/paracetamol-book?cmpid=CMP00000047

If your interested, you may like this “green Synthesis” document featuring another popular A-level synthetic target…. Ibuprofen… http://www.chem.uoa.gr/courses/organiki_1/greenchem/PDF_en/GREEN-CHEMISTRY-PDF-4-ORGASYNTHESIS-2012.pdf

 

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