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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: mana on February 12, 2016, 12:32:15 PM

Title: aspirin or methyl salicylic?
Post by: mana on February 12, 2016, 12:32:15 PM: hi all
in aspirin synthesis if I use acetic acid, acylation reaction will occur on OH of salicylic acid and aspirin will produce, but if we use methanol, methyl salicylate will obtain. can any one tell me why acetic acid do not react with carboxylic functional group on salicylic acid?
thanks
Title: Re: aspirin or methyl salicylic?
Post by: AWK on February 12, 2016, 12:51:41 PM: Acetic anhydride is also used in this synthesis that esterifies salicylic acid at phenolic group. An excess of acetic anhydride forms mixed anhydride with acetylsalicylic acid which with alcohol (eg methanol) forms ester.
Title: Re: aspirin or methyl salicylic?
Post by: mana on February 12, 2016, 02:46:37 PM: Quote from: AWK on February 12, 2016, 12:51:41 PM
Acetic anhydride is also used in this synthesis that esterifies salicylic acid at phenolic group. An excess of acetic anhydride forms mixed anhydride with acetylsalicylic acid which with alcohol (eg methanol) forms ester.
thank you AWK, you are right, acetic anhydride is used with acetic acid to synthesis aspirin, but I can't understand why methanol react with acid carboxylic functional group and acetic anhydride react with phenolic group? I mean what is the reason of this regioselectivity?
Title: Re: aspirin or methyl salicylic?
Post by: AWK on February 12, 2016, 06:11:48 PM: For synthesis of aspirin any alcohol is not use. When you add methanol and much excess of acetic anhydride you can obtain wintergreen oil (methyl acetylsalicylate)
Title: Re: aspirin or methyl salicylic?
Post by: mana on February 15, 2016, 12:49:12 AM: Quote from: AWK on February 12, 2016, 06:11:48 PM
For synthesis of aspirin any alcohol is not use. When you add methanol and much excess of acetic anhydride you can obtain wintergreen oil (methyl acetylsalicylate)
if I use just salicylic acid and methanol, what will obtain?
Title: Re: aspirin or methyl salicylic?
Post by: AWK on February 15, 2016, 02:48:05 AM: Aspirin, methyl acetylsalicylate and methyl acetate. Ratio of these reagent will depend on temperatute and amount of acetic anhydride used.