Organic synthesis
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I read a procedure regarding aspirin synthesis and noticed that they usually use phosphoric acid or sulphuric acid as catalyst. What will happen if hydrochloric acid is used? Will it have the same effect since HCl is also a strong acid?
Igloo writes
I cannot think of a good reason why concentrated hydrochloric acid cannot be used successfully as a catalyst during the synthesis of aspirin. After all it’s the introduction of extra hydrogen ions which matters. I expect that sulphuric acid and phosphoric acid were used in the past when the process was investigated for the first time, and these catalysts are now used as a matter of habit rather than for any other reason.
Incidentally, the other well-known strong acid – nitric acid – is rarely appropriate in acid catalysed reactions, since it is a powerful oxidising agent as well as an acid, and it would promote undesirable side-reactions.
Always carry out a risk assessment and check with your teacher before starting any practical work.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 17 December 2006
