I'm running an esterification of 2-methoxypropanol with an alkyl carboxylic acid using conc. H2SO4 as a the catalyst. The reaction started colorless, then faint yellow upon heating, and finally dark (black or brown) upon refluxing. I'll work up the reaction tomorrow but I can't stop thinking about the dark color. I have done many esterification but have not witnessed very dark colors especially with straight chain alkyl alcohols and carboxylic acids. What could be causing the dark color?