Oxime FormationThis reaction is one example of the many derivatives which can be formed from carbonyl containing molecules. Reaction of aldehydes and ketones with hydroxylamine gives oximes. The mechanism begins with a nucleophilic attack on the carbon of the carbonyl by the nitrogen of the hydroxylamine. The nucleophilicity of the nitrogen on the hydroxylamine is increased by the presence of the oxygen. This forms a tetrahedral intermediate which then undergoes a series of proton transfers. The sp2 carbon is reformed and water is eliminated. Oximes generally form a mixture of geometric isomers.

Synthesis of oximes is an important reaction in organic chemistry, because these versatile oximes are used for protection, purification, and characterization of carbonyl compounds. Nitriles, amides via Beckmann rearrangement, nitro compounds, nitrones, amines, and azaheterocycles can be synthesised from oximes. They also find applications for selective-activation. In inorganic chemistry, oximes act as a versatile ligand.Thehydrolysisof oximes proceeds easily by heating in the presence of variousinorganic acids, and the oximes decompose into the corresponding ketones or aldehydes, and hydroxylamines. The reduction of oximes bysodiummetal,sodium amalgam,hydrogenation, or reaction withhydridereagents produces amines. In general, oximes can be changed to the correspondingamidederivatives by treatment with various acids. This reaction is calledBeckmann rearrangement.Beckmann rearrangement is used for the industrial synthesis ofcaprolactam.Preparation of benzophenone oximePlace a mixture of 2.5 g benzophenone, 1.5 g hydroxylamine hydrochloride, 5 mL rectified spirit and 1 mL of water in a 50 mL round-bottomed flask. Add 2.8 g of sodium hydroxide pellets in portions with shaking; if the reaction becomes too vigorous, cool the flask with running tap water. When all the sodium hydroxide pellets has been added, attach a reflux condenser to the flask, heat to boiling and reflux for 5 minutes. Cool and pour the contents of the flask into a solution of 7.5 mL of concentrated hydrochloric acid in 50 mL of water contained in a 250 mL beaker. Filter the precipitate at the pump, wash thoroughly with cold water and dried. Recrystallise the precipitate from methanol and record the weight of the product, and its melting point. (Note: The oxime is gradually decomposed by oxygen and traces of moisture into benzophenone and nitric acid; it should be kept in a vacuum desiccator filled with pure dry carbon dioxide or nitrogen).Preparation of cyclohexanone oximeMeasure the 2.5 mL of 2.5 M aqueous hydroxylamine hydrochloride and the 2.5 mL of 2.5 M aqueous sodium hydroxide solution. Add these materials and one boiling stone to a 10mL Erlenmeyer flask. In the hood, add 0.48 g of cyclohexanone to the E. flask. Swirl the flask and gently place the flask on a water bath. Heat for 15 minutes and remove from water bath. Let cool slowly and undisturbed to room temperature. After flask has reached room temperature, immerse in a 100mL beaker approximately half full of ice water. Allow to cool for a minimum of 5 minutes. Collect crystals using vacuum filtration and a Hirsch funnel. Record mass collected. Obtain melting point.Reaction and Useful Data

Vanillin is obtained from vanilla and is widely used as deodorant, food flavour and one of the ingredients in pharmaceutical products