Ketone

Ketones are chemical compounds which act as functional group is a non-terminal carbonyl group ( > C = O) included. A ketone group [C- C (O )-C ] contains three carbon atoms. Ketones all contain at least three carbon atoms. In contrast to the carbonyl carbon of aldehydes here is connected in both directions with the binding carbon atoms. Ketones may be considered as products of oxidation of secondary alcohols. The derived from the alkanes ketones is also called alkanones. Correspondingly, one denotes the Relating to alkenes and alkynes ketones as alkenones (see enones ) or alkynones. The simplest ketone is acetone. A simple aromatic ketone benzophenone ( diphenyl ketone ). A mixed ketone is acetophenone ( methyl phenyl ketone ).

Nomenclature

According to the IUPAC nomenclature obtain ketones the suffix -on, if the carbonyl group is the group contained in the molecule with the highest priority. Accordingly, the derived from propane ketone propanone ( acetone CH3 -CO- CH3, common name ) is called. When ketones having more than three carbon atoms, the carbonyl group is in the main chain and obtains the smallest possible number, this can be essential either to the name or, for more complex molecules, directly before the ending -on. For example, states: CH3 -CH2-CH2 -CO- CH3 accordingly 2 -pentanone or pentane - 2-one. If the carbonyl group does not have the highest priority, the prefix is used oxo. For example, say CH3 -CO- CH2 -CHO 3- Oxobutanal.

Very often, however, the ketones are named, which followed from the name of the alkyl groups of the ending- ketone exist ( Radikofunktionelle nomenclature ). As is also known as methyl ethyl ketone, butanone (MEK). If the substituent is a phenyl group, the ending- phenone is common, for example, acetophenone.

Properties

Low molecular weight ketones are colorless, mobile liquids and soluble in water due to the polarity of the carbonyl group. Low molecular weight ketones are characterized by a mostly pleasant, fruity odor. Higher molecular weight ketones are solid substances.

Ketones have due to the I effect of the alkyl substituents on the carbonyl carbon atom, a lower reactivity than aldehydes and not prone to polymerization. In contrast to the aldehydes, there is no reaction with ketones in the Fehling test, because the ketone group to obtain the carbon skeleton can not be further oxidized.

Production

  • Ketones can be prepared by the oxidation of secondary alcohols.
  • A further preparation method is ozonolysis of alkenes.
  • The main method of production of aromatic ketones is the Friedel-Crafts acylation.
  • After the ketone synthesis of Gilman and Van Ess is obtained from a carboxylic acid ( R1 1 ) and an alkyllithium compound ( R2) by hydrolysis of the analogous ketone
  • Another production method is the reaction of Weinreb amides with alkyl lithium compounds and subsequent aqueous acidic workup.
  • A now historical synthesis, the so-called Kalksalzdestillation is heated in the dry calcium salts of carboxylic acids and the gas released ketone is re-condensed ( for example for the preparation of acetone from calcium acetate ).
  • Acetone precipitated as a co-product in the industrial synthesis of phenol by the cumene process ( Hock process ) to.
  • Addition of water to alkynes.

Reactions

Ketones undergo similar one such as aldehydes, addition and condensation reactions.

Ketones (R1, R2, R3 = organyl rest ) are standing with their tautomeric form, the enols in equilibrium ( keto -enol tautomerism ) when a hydrogen atom is bonded to the α - carbon atom:

To protect against undesirable reactions ketones with diols to form acetals (see protecting group ) implemented:

In implementing the Vollacetals with water under acid catalysis occurs again, the ketone, that is, the protecting group is removed.

Ketones can be oxidatively attack only under drastic reaction conditions, in contrast to the aldehydes. It is a bond between the carbonyl carbon and an adjacent carbon will split. The resulting molecular fragments are carboxylic acids.

Important representatives of the ketones

  • Acetone, cyclohexanone,
  • Raspberry Ketone, mycosporine

Use

  • Acetone: solvents, detergents
  • Cyclohexanone Preparation of Perlon
  • Raspberry Ketone: smell of raspberries

Spectroscopy of Ketones

In IR spectra of ketones and aldehydes to find the characteristic band of the C = O stretching vibration in the range of 1690-1750 cm -1.

2-Pentanone Weinreb ketone synthesis Addition reaction Integrated Authority File
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