2CH3-CH-COOH=(浓H2SO4)=CH3-CH-COO +2H2O， OH OOC-CH-CH3 所以是CH3-CH-COO OOC-CH-CH3
乳酸在浓硫酸作用下，两分子相互反应，脱去两分子水，生成酯
H3C—CH—CO—O | | O—OC—HC—CH3
