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Advanced Level Organic Chemistry: Aromatic compounds in nature & pharmaceuticals

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Part 7.13 The chemistry of AROMATIC COMPOUNDS

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK KS5 A/AS GCE IB advanced level organic chemistry students US K12 grade 11 grade 12 organic chemistry

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All my advanced level aromatic chemistry notes

All my advanced A level organic chemistry notes

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Part 7.13 Examples of aromatic compounds from the pharmaceutical industry and examples of aromatic compounds found in natural products


Examples of synthetic aromatic compounds from the pharmaceutical industry

molecular structure of Paracetamol Ibuprofen Aspirin structural formula doc brown's advanced A level organic chemistry notes 

Examples of analgesics - pain-killers - anti-inflammatory drugs

Acetylsalicylic acid is one chemical name for the brand Aspirin.

N-(4-hydroxyphenyl)ethanamide is the IUPAC name for the brand Paracetamol.

2-(4-(2-methylpropyl)phenyl)propanoic acid is the IUPAC name for the brand Ibuprofen.

diagram of manufacture synthesis of the drug paracetamol benzene phenol 4-nitrophenol 4-amibophenol N-(4-hydroxyphenyl)ethanamide

Phenol is manufactured from benzene by several different processes.

 (The details not required, but you should know the last three reactions in the synthesis route.)

C6H6  == [O] ==>  C6H5OH

Phenol is nitrated with nitric acid to give mainly 4-nitrophenol (desired product) and some 2-nitrophenol.

C6H5OH  +  HNO3 ===> O2NC6H4OH  +  H2O

The 2-nitrophenol is removed by steam distillation to leave mainly 4-nitrophenol.

Note the desired orientation of the intermediates so that the final product's orientation is correct.

The 4-nitrophenol is reduced with hydrogen (Ni catalyst ?) to 4-aminophenol.

O2NC6H4OH  +  6[H]  ===> H2NC6H4OH  +  2H2O

4-aminophenol is ethanoylated with ethanoic anhydride to yield N-(4-hydroxyphenyl)ethanamide aka 'Paracetamol'

H2NC6H4OH  +  (CH3CO)2O  ===> CH3CONHC6H4OH  +  CH3COOH


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Examples of naturally occurring aromatic compounds - the natural occurrence of the benzene ring!

 Use of the term 'aromatic' derives from the smell of oil from natural products - usually 'aromatic' plants.

Today the term refers to compounds containing a benzene ring, fused benzene rings or other ringed compounds that chemically behave as an aromatic compound.

Aromatic compounds from the natural world often have a strong pleasing smell and are naturally found in wine, spices, perfumes, fragrance oils, and essential oils extracted from plants.

(c) doc bThe simplest aromatic aldehyde, benzaldehyde (right) smell's of almonds and is a naturally occurring compound found in bitter almond oil. It is synthesised by the chemical industry for use in food flavourings and fragrances in the perfume industry.

Salicin (below) is a naturally found in the bark of willow and poplar trees. For thousands of years it was known to have a pain-killing action when ingested, it is an anti-inflammatory agent. The Salicin molecule consists of a phenol attached by an ether linkage to hexose sugar molecule.

molecular chemical history of Aspirin Salicin acetylsalicylic acid acetyl-2-hydroxybenzoic acid soluble aspirin analgesic pain-killer anti-inflammatory drug medicine

 The search for molecules having a similar effect. Salicylic acid (2-hydroxybenzoic acid) is derived from the metabolism of Salicin and is used in medical treatment. However, synthetic acetylsalicylic acid (Aspirin) was found to be a more effective painkiller. Soluble Aspirin is absorbed more quickly minimising irritating the stomach.

An 'aspirin' related aromatic acid derived molecule is C8H8O3, (c) doc b or , methyl 2-hydroxybenzoate.

Commonly known as methyl salicylate or 'oil of wintergreen', a molecule that has mild pain killing properties. This methyl ester of salicylic acid is a colourless, viscous liquid with a sweet, fruity minty odour and used in mint candies. It  is produced by many species of plants, particularly wintergreens, from which it can be obtained by distillation. These days it is mostly manufactured synthetically, by esterifying 2-hydroxybenzoic acid with methanol, and used as a fragrance and flavouring agent.

Many plants produce methyl salicylate in small quantities, often in response to biotic stress e.g. infection by pathogens, where it plays a role in the induction of resistance. Methyl 2-hydroxybenzoate is also released in some plants when they are damaged by herbivorous insects, where they may function as a cue aiding in the recruitment of predators. Some plants produce methyl salicylate in larger quantities to aid direct defence against predators or pathogens

intermolecular and intramolecular hydrogen bonding in methyl 2-hydroxybenzoate methyl salicylate diagram image oil of wintergreen doc brown's advanced organic chemistry

Incidentally, methyl 2-hydroxybenzoate can exhibit both intermolecular and intramolecular hydrogen bonding.
 

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