Question

In benzophenone reduction, how does H-bonding play a role in the determination of its physical state?

Answer 1

NaBH4 will convert aldehydes and ketones into alcohols, but it will not reduce carboxylic acids, esters, or amides. NaBH4 reacts only slowly with water and alcohols.

NaBH4 and LiAlH4 cannot reduce double or triple bonds by themselves. There are several methods of which the more common ones are hydrogenation and hydride transfer reagents. Hydride is the isolated atomic hydrogen anion, H-, or any compound containing hydrogen and another more electropositive element or group.

Hydride consists of a singly charged positive nucleus and two electrons of which one electron is weakly held and readily able to be donated. Hydrides are highly reactive, strongly basic and powerfully reducing in synthetic reactions. They are important reducing agents in industrial reactions though they are easily destroyed in the relatively acidic compound water . In most reactions with sodium borohydride, the aldehyde or ketone is dissolved in the reaction solvent and a solution of sodium borohydride is added, with external cooling if necessary, at a rate slow enough to keep the reaction temperature below 25°C.

Higher temperatures may decompose the hydride, and adding the carbonyl compound to the alkaline sodium borohydride solution may cause side reactions of base-sensitive substrates. The amount of solvent is not crucial, but enough should be used to completely dissolve the reactants Hydrogenation is a process that creates hydrogen bonds on carbon molecules, usually a pair of hydrogen atoms. This process is done by treating hydrogen as a reducing chemical in a chemical reaction between hydrogen and another compound. In this hydrogenation process, the chemicals are usually accompanied with a catalyst.

Catalysts are very much needed in this process to make it usable, without the presence of a catalyst this chemical reaction can only be possible at very high temperatures. Thus, in a laboratory setting, it is vital to have catalysts in this reaction. In short, hydrogenation has three components, unsaturated substrate, hydrogen (mostly in gaseous state), and a catalysts. The temperature of the reaction varies depending on the substrate and the activity of the catalyst. The substrate for hydrogenation is almost always alkenes that produce saturated alkanes as the end product.

This chemical process is very selective due to the steric hindrance that plays a role in determining where exactly would the hydrogen atoms be placed. There are few catalysts, namely, platinum, nickel, palladium, rhodium, and ruthenium. These are considered very active catalysts as they are able to operate at lower temperatures. Hydrogenation is a very exothermic reaction, which means a lot of heat is liberated from this chemical reaction. A more specific reduction method involves the hydride (H-) transfer reagents. This process only works for carbonyl groups.