Ketone

A ketone is a Composé organics, belonging to the family of the carbonyl compounds, of which one of carbons carries a grouping carbonyl. The Aldéhyde S have a primary education carbon and the ketones a secondary carbon (related to exactly 2 atoms of close carbons) which carries the grouping carbonyl. A ketone thus contains the sequence:

où R1 and R2 is carbonaceous chains, and not simple atoms of hydrogène

One can for example quote the Acétone (propan-2-one) CH3-CO-CH3.

Nomenclature

  • principal Group:

The name of ketone is obtained by adding the suffix - one in the name of hydrocarbon corresponding, by specifying the place of the connection carbonyl in the carbonaceous chain

  • secondary Group:

One adds the prefix oxo- , by specifying his place in the carbonaceous chain

Principal ketones

Properties, reactivity

They are general with aldehydes and ketones. See the general article carbonyl compound.

Formation

One obtains ketones with a oxidation spared of a secondary alcohol. That requires a strong oxidising agent. However, here, there is no " risque" : a ketone after being formed cannot be oxidized any more, contrary to the aldehyde, which still can the being in Carboxylic acid.

Industrial oxidation

  • oxidation by O2 of the air

One can use as Fe2O3 catalyst or MnO3 with 400°C, or a catalyst containing money towards 600°C.

  • catalytic Dehydrogenation of primary education alcohols

Alcohol is gas. One uses as cataysor CuO towards 400-500°C, Ag, Cu towards 300°C, ZnO or ZrO towards 300-400°C.

  • Proceeded of Wacker-Hoechst

Chemical oxidation

One often uses the potassium dichromate, or the Cr (VI) (via PCC for example), but the reagent most usually used is the reactive of Jones : CrO3 in the presence of sulphuric acid in acetone. Sometimes, if the presence of an acid is awkward, one uses the reactive of Sarett : CrO3 in pyridine.

Hydrolize alkyne compounds

By adding water to a Alkyne compound in acid medium, a grouping Carbonyle will be formed on carbon carrying triple connection having less hydrogen (Règle of Markovnikov), with the proviso of having mercury oxidized +2 like Catalyseur (Hg2+). Other carbon carrying triple connection will be tiny room by gaining two atoms of Hydrogène.

By ozonolyse of olefinic hydrocarbons

The Ozonolyse consists in treating a reagent with the Ozone and the Eau. Here, the Alcène undergoes a ozonolyse to form a grouping Carbonyle, with the proviso of having like Catalyseur ethanoic acid (or acetic acid) and Zinc oxidized +2 (Zn2+). This forms a very unstable cyclic intermediary: the ozonide, which is transformed then into ketone or Aldéhyde. In order to obtain a ketone starting from an olefinic hydrocarbon, at least a carbon carrying the double connection must be exclusively related to other carbons, or else, an aldehyde will be formed. The reaction also releases from the Hydrogen peroxide.

For example, by treating 2-methylbut-2-ene with ozone and water (with catalysts necessary), one obtains the Propanone (a ketone), the éthanal or acetaldehyde (an aldehyde) and it hydrogen peroxide.

Use of ketones

Acétalisation

The Acétal isation is a reversible reaction making it possible to transform a carbonyl compound and two alcohols (or a diol) into acetal . This reaction allows in fact to protect the carbonyl group, or alcohol.

Reaction

Conditions

  • acid Heating

  • Catalysis (in general APTS or anhydrous HCl)

Characteristics and remarks

  • When an aldehyde is used, one names the product obtained " acétal". When a ketone is used, one names the product obtained " cétal". However, more and more one uses the acetal term as generic term to indicate the 2 products. One on the other hand always calls the reaction (as well for aldehydes and ketones) " acétalisation "

  • This reaction is in general in discredit of the cétal (contrary to acetals). If one wants to support it in the direction of the formation of this one, one uses an alcohol excess (which is used consequently occasion as solvent). It is also necessary to distill water (heteroazeotropic distillation) using the apparatus of Dean and Stark. To support the reaction reverses, it is the opposite: one puts a water excess to hydrolize the cétal.

  • When one wants to protect the function carbonyl, one generally uses a diol, like the ethane-1,2-diol:

  • This reaction can very be also well used to protect a function alcohol, as local private individuals the diols.

  • In certain cases, the reaction can stop with hemi-acetal (case of cyclic hemi-acetals).

Action of a organomagnésien

A mixed Organomagnésien reacts on a ketone to form a tertiary alcoholate. Carbon carrying the organomagnésien is added on carbon carrying the grouping carbonyl. In aqueous medium, alcoholate, bases strong, gains a proton to form an alcohol.

Reaction of Wittig

The Réaction of Wittig transforms a ketone into ethylene derivative. It transforms in fact connection C=O in liason C=C.

Reaction of Shapiro

Reduction of ketones

Out of alcohols

Industrially

One uses the Dihydrogène H2 in an inert solvent, in the presence of a catalyst (heterogeneous Catalyze). They are very often metals, like the Platine (Pt), the palladium (Pd), the Nickel (Ni) or the Rhodium (Rh). If ever the ketone has also a connection C=C, this one also is hydrogenated (the reaction is easier on C=C than on C=O). To avoid that, it is necessary to carry out a nucleophilic addition of hydrides. The reaction is Exothermique.

By the hydrides

See addition nucleophilic of hydrides (low).

Out of alkane

nucleophilic Additions

of Hydride S (LiAlH4, NaBH4)

The addition of hydrides allows the reduction of the Oxygène grouping Carbonyle without however deteriorating a double connection (the part Alcène) of a molecule, compared to the simple addition of hydrogen.

A ketone also carrying an olefinic hydrocarbon, when treated with a hydride, produces an alcoholate which carries an olefinic hydrocarbon. This alcoholate, treated with a weak acid (as water) is then transformed into alcohol which carries an olefinic hydrocarbon.

of Organometallic

Organomagnésien S mixed, or Organolithien S.

Cétolisation (concentration of 2 ketones)

Oxidation of Baeyer-Villiger

transformation into Ester

One can also obtain a carbonyl derivative (ketone or aldehyde) by hydrolysis of function imine, of general formula RR' C=N, in acid or basic catalysis. This hydrolysis makes it possible for example to obtain a ketone like finished product of the addition of a Hard grindstone reagent (organomagnésien mixed) on a nitrile.

Tests of recognition

  • Additions of composed of type Z-NH2 (amines): formation of a precipitate.

  • Reaction haloforme: characterize alpha-methylated ketones. In the presence of a halogen in basic medium, it is formed a haloforme. For example, with iodine and propanone, there would be an iodoform (precipitated yellow).

But these methods using of the chemical reactions with ketone, destroy it. One uses now more readily the methods of spectrometry (NMR and infra-red) allow to detect this function without destruction of the sample.

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