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Home >> Chemistry Homework Help >> Organic Chemistry Help >> Aldehydes Ketones from Alcohols
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Since aldehydes and ketones are first oxidation products of alcohols, hence, they can be prepared from alcohols by oxidation or dehydrogenation methods. (a) By direct oxidation: Aldehydes are prepared by oxidation of primary alcohols. Acidified potassium permanganate or potassium dichromate in generally used as oxidising agents. Aldehydes are very susceptible to further oxidation to carboxylic acids. The reaction is controlled by distilling out aldehydes as soon as it is formed. (i) Chromic acid (CrO3 in acetic acid) or H2CrO4 in aqueous acetone (Jone’s reagent) can oxidize 1˚ alcohols to aldehydes stage only. (ii) Chromic acid in acetone oxidizes allylic alcohols to vinyl ketones. Ketones can be prepared by using similar oxidising agents from secondary alcohols. Secondary alcohols can also be conveniently oxidized to ketones by opppenauer oxidation. The reaction involves refluxing a secondary alcohol with aluminium tert-butoxide in excess of acetone or cyclohexanone when 2˚ alcohol oxidizes to ketone and acetone reduces to isopropyl alcohol. In this method also the ketone cannot get oxidized further to an acid. Similarly, cyclohexanol can be converted to cyclohexanone by an identical method. (b) By Catalytic Dehydrogenation: when vapours of primary or secondary alcohols are passed over copper gauze at 573 K, they get dehydrogenated to form aldehydes or ketones respectively. The dehydrogenation reaction is a better method of preparation because there is no risk further oxidation of aldehydes. Services: - Aldehydes Ketones from Alcohols Homework | Aldehydes Ketones from Alcohols Homework Help | Aldehydes Ketones from Alcohols Homework Help Services | Live Aldehydes Ketones from Alcohols Homework Help | Aldehydes Ketones from Alcohols Homework Tutors | Online Aldehydes Ketones from Alcohols Homework Help | Aldehydes Ketones from Alcohols Tutors | Online Aldehydes Ketones from Alcohols Tutors | Aldehydes Ketones from Alcohols Homework Services | Aldehydes Ketones from Alcohols
Since aldehydes and ketones are first oxidation products of alcohols, hence, they can be prepared from alcohols by oxidation or dehydrogenation methods. (a) By direct oxidation: Aldehydes are prepared by oxidation of primary alcohols. Acidified potassium permanganate or potassium dichromate in generally used as oxidising agents. Aldehydes are very susceptible to further oxidation to carboxylic acids. The reaction is controlled by distilling out aldehydes as soon as it is formed. (i) Chromic acid (CrO3 in acetic acid) or H2CrO4 in aqueous acetone (Jone’s reagent) can oxidize 1˚ alcohols to aldehydes stage only. (ii) Chromic acid in acetone oxidizes allylic alcohols to vinyl ketones. Ketones can be prepared by using similar oxidising agents from secondary alcohols. Secondary alcohols can also be conveniently oxidized to ketones by opppenauer oxidation. The reaction involves refluxing a secondary alcohol with aluminium tert-butoxide in excess of acetone or cyclohexanone when 2˚ alcohol oxidizes to ketone and acetone reduces to isopropyl alcohol. In this method also the ketone cannot get oxidized further to an acid. Similarly, cyclohexanol can be converted to cyclohexanone by an identical method. (b) By Catalytic Dehydrogenation: when vapours of primary or secondary alcohols are passed over copper gauze at 573 K, they get dehydrogenated to form aldehydes or ketones respectively. The dehydrogenation reaction is a better method of preparation because there is no risk further oxidation of aldehydes.
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