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Synthesis of Carboxylic Acids

Synthesis of Carboxylic Acids

There are many possible synthetic pathways that yield carboxylic acids. Some of these are further discussed below.

Alcohols and aldehydes may be oxidized into carboxylic acids. Alkenes may be converted into carboxylic acid through oxidative cleavage of the double bond with neutral or acid permanganate, for instance. However, the alkene must contain at least one hydrogen located at the double bond, otherwise only ketones are formed. The intermediate stage of an alkene's oxidative cleavage with permanganate is a 1,2-diol. If the alkene is not water-soluble, potassium permanganate can be made soluble in an organic solvent by the application of the crown ether (a cyclic polyether) 18-crown-6. 18-crown-6 complexes the potassium ion in its center, while its periphery is non-polar. As a result, potassium ions can be dissolved in an organic solvent, such as benzene, and the negatively charged permangnate ion is, thus, forced to dissolve, as well. The reactivity of permanganate ions that are dissolved in such a way is much higher than that of permangante ions in aqueous solution, as they are not solvated.

Fig.1
Oxidation of alcohols and aldehydes yields carboxylic acids.
Fig.2
Vicinal diols are intermediates of alkenes' oxidative cleavage with permanganate.
Tab.1
Starting productProduct
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Fig.3
Mouse
Fig.4
Fig.5
Oxidative cleavage of 1,2-diphenylethene with permangante and 18-crown-6.
Tab.2
Starting productProduct
Mouse
Fig.6
Mouse
Fig.7

Many alkenes may be converted into carboxylic acids through ozonization and subsequent oxidative workup.

Fig.8
Oxidative cleavage of cyclic alkenes yields dicarboxylic acids.
Tab.3
Starting productProduct
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Fig.9
Mouse
Fig.10
Fig.11
Methyl groups bound to an aromatic ring can be oxidized to carboxyl groups.
Tab.4
Starting productProduct
Mouse
Fig.12
Mouse
Fig.13

In a haloform reaction with iodine, bromine, or chlorine, methyl ketones are converted into the corresponding carboxylic acid and haloform.

Fig.14
Haloform reaction.
Tab.5
Starting productProduct 1Product 2
Mouse
Fig.15
Mouse
Fig.16
Mouse
Fig.17

A Gringard reaction with carbon dioxide yields a carboxylate whose carbon chain contains exactly one carbon more than the alkyl halide applied. Hydrolysis of the carboxylate leads to the formation of the carboxylic acid. The reaction is diversely applicable and proves to be an easy source of many carboxylic acids.

Fig.18
Grignard reaction with carbon dioxide yields carboxylic acids.
Fig.19
Example of a Grignard reaction with carbon dioxide.
Tab.6
Starting productGrignard compoundProduct
Mouse
Fig.20
Mouse
Fig.21
Mouse
Fig.22

Exercises

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