Esters (and other things) From Boiling Acid

We have been applying a combinatorial scheme to the Fischer esterification synthesis of under-characterized esters for the past few years. This year we combined either 4-methylbenzoic acid, 4-methoxybenzoic acid, or 2-methoxybenzoic acid with either 1-propanol or 2-propanol. The excess alcohol takes the role of both solvent and reagent. The water soluble alcohol is removed by liquid-liquid extraction after reflux. Many reaction solutions turn dark during reflux. These colorations, in my experience, are caused by very small amounts of likely polymeric material that is created in boiling sulfuric acid. These esters gave a thick liquid and/or soft solid when purified. Combining student fractions and continuing the purification with a chromatography separation is on my to-do list for the summer.


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