Dibal h

The mechanism of the reaction of sodium borohydride with aldehydes and ketones proceeds in two steps. In the first step, H(-) detaches from the BH4(-) and adds to the carbonyl carbon (an example of [1,2]-addition). This forms the C-H bond, and breaks the C-O bond,  resulting in a new lone pair on the oxygen, which makes the oxygen negatively charged (FYI: we call these negatively charged oxygens alkoxides , as they are deprotonated alcohols).  In the second step, a proton from water (or an acid such as NH4Cl) is added to the alkoxide to make the alcohol. This is performed at the end of the reaction, a step referred to as the workup .

LiAlH 4 contains wt% hydrogen, thereby making LAH a potential hydrogen storage medium for future fuel cell -powered vehicles . The high hydrogen content, as well as the discovery of reversible hydrogen storage in Ti-doped NaAlH 4 , [36] have sparked renewed research into LiAlH 4 during the last decade. A substantial research effort has been devoted to accelerating the decomposition kinetics by catalytic doping and by ball milling . [37] In order to take advantage of the total hydrogen capacity, the intermediate compound LiH must be dehydrogenated as well. Due to its high thermodynamic stability this requires temperatures in excess of 400 °C, which is not considered feasible for transportation purposes. Accepting LiH + Al as the final product, the hydrogen storage capacity is reduced to wt%. Another problem related to hydrogen storage is the recycling back to LiAlH 4 which, owing to its relatively low stability, requires an extremely high hydrogen pressure in excess of 10000 bar. [37] Cycling only reaction R2 — that is, using Li 3 AlH 6 as starting material — would store wt% hydrogen in a single step (vs. two steps for NaAlH 4 which stores about the same amount of hydrogen). However, attempts at this process have not been successful so far. [ citation needed ]

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Dibal h

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