Write the mechanism of dehydration of ethyl alcohol with conc. H_2 SO_4 at 413 K.

$\displaystyle \mathrm{CH_3-CH_2-\overset{..}{\underset{..}{O}}-H \;+\; H^{+} \;\longrightarrow\; CH_3-CH_2-\overset{H}{\underset{..}{\overset{+}{O}}}-H}$

$\displaystyle \mathrm{CH_3CH_2-\overset{..}{\underset{|}{O}}{:}\;\underset{H}{}\;+\;CH_3-CH_2-\overset{+}{O}\!\!\big<^{H}_{H} \;\longrightarrow\; CH_3CH_2-\overset{+}{\underset{|}{O}}-CH_2CH_3 \;+\; H_2O}$

(with the lone pair on the first oxygen attacking the carbon bearing the $\displaystyle \mathrm{-\overset{+}{O}H_2}$ group; the O of the product carries an H below it)

$\displaystyle \mathrm{CH_3CH_2-\overset{+}{\underset{|}{O}}-CH_2CH_3 \;\longrightarrow\; CH_3CH_2-O-CH_2CH_3 \;+\; \overset{+}{H}}$

(the O of the reactant carries an H below it)