Both sodium borohydride $(NaBH_4)$ and lithium aluminum hydride $(LiAlH_4)$ reduce aldehydes and ketones to alcohols.
![reduction-carbonyls-hydrides reduccion-carbonilos-hidruros](/images/stories/organica-i/alcoholes/sintesis-reduccion-hidruros/reduccion-carbonilos-hidruros-01.png)
Ethanal is transformed by reduction with sodium borohydride to ethanol.
The mechanism occurs by attack of the hydride from the reductant on the carbonyl carbon. In a second stage the solvent protonates the oxygen of the alkoxide.
![reduction-carbonyls-hydrides reduccion-carbonilos-hidruros](/images/stories/organica-i/alcoholes/sintesis-reduccion-hidruros/reduccion-carbonilos-hidruros-02.png)
Lithium aluminum hydride works in an ether medium and transforms aldehydes and ketones into alcohols after an acid hydrolysis step.
![reduction-carbonyls-hydrides reduccion-carbonilos-hidruros](/images/stories/organica-i/alcoholes/sintesis-reduccion-hidruros/reduccion-carbonilos-hidruros-03.png)
The mechanism is analogous to that of sodium borohydride.
![reduction-carbonyls-hydrides reduccion-carbonilos-hidruros](/images/stories/organica-i/alcoholes/sintesis-reduccion-hidruros/reduccion-carbonilos-hidruros-04.png)
The lithium and aluminum reducer is more reactive than the boron one, it reacts with water and alcohols, releasing hydrogen. Therefore, it must be dissolved in aprotic media (ether).
![reduction-carbonyls-hydrides reduccion-carbonilos-hidruros](/images/stories/organica-i/alcoholes/sintesis-reduccion-hidruros/reduccion-carbonilos-hidruros-05.png)
The less reactive boron reducer decomposes slowly in protic media, allowing it to be used dissolved in ethanol or water.