Schmitt reaction

Knoevenagel reaction Knorr pyrrole synthesis. Kolbe>Schmitt reaction Leuckart reaction Mannich reaction... 

CARBOXYLATION OF PHENOLS ASPIRIN AND THE KOLBE-SCHMITT REACTION... 

The key compound m the synthesis of aspirin salicylic acid is prepared from phe nol by a process discovered m the nineteenth century by the German chemist Hermann Kolbe In the Kolbe synthesis also known as the Kolbe—Schmitt reaction, sodium phen oxide IS heated with carbon dioxide under pressure and the reaction mixture is subse quently acidified to yield salicylic acid... 

Carboxylation of Phenols Aspirin and the Kolbe-Schmitt Reaction... 

The Kolbe-Schmitt reaction is an equilibrium process governed by thermodynamic control The position of equilibrium favors formation of the weaker base (salicylate ion) at the expense of the stronger one (phenoxide ion) Thermodynamic control is also responsible for the pronounced bias toward ortho over para substitution Salicylate anion IS a weaker base than p hydroxybenzoate and predominates at equilibrium... 

The Kolbe-Schmitt reaction has been applied to the preparation of other o hydroxy benzoic acids Alkyl derivatives of phenol behave very much like phenol itself... 

Kolbe-Schmitt reaction (Section 24 10) The high pressure re action of the sodium salt of a phenol with carbon dioxide to give an o hydroxybenzoic acid The Kolbe-Schmitt reac tion IS used to prepare salicylic acid in the synthesis of as pinn... 

Carbon dioxide reacts with phenolates 1 to yield salicylate 2 with less reactive mono-phenolates, the application of high pressure may be necessary in order to obtain high yields. This reaction, which is of importance for the large scale synthesis of salicylic acid, is called the Kolbe-Schmitt reaction ... 

The Kolbe-Schmitt reaction is limited to phenol, substituted phenols and certain heteroaromatics. The classical procedure is carried out by application of high pressure using carbon dioxide without solvent yields are often only moderate. In contrast to the minor importance on laboratory scale, the large scale process for the synthesis of salicylic acid is of great importance in the pharmaceutical industry. 

The applicability of the Reimer-Tiemann reaction is limited to the formylation of phenols and certain reactive heterocycles like pyrroles and indoles. Yields are usually below 50%. In contrast to other formylation procedures, the Reimer-Tiemann reaction is ort/zo-selective it is therefore related to the Kolb e-Schmitt reaction. 

Sodium phenoxides can be carboxylated, mostly in the ortho position, by carbon dioxide (the Kolbe-Schmitt reaction). The mechanism is not clearly understood, but... 

Knoevenagel reaction Knorr p3rrrole synthesis. Kolbe-Schmitt reaction Leuckart reaction Mannich reaction Mccrwein-Ponndorf-Verley reduction Michael reaction Oppenauer oxidation... 

Salicylic acid. The preparation of salicylic acid by passing carbon dioxide into dry sodium phenoxide at 170-190° is the classical example of the Kolbe-Schmitt reaction. The latter is a method for introducing a carboxyl group directly into a phenol nucleus. 

The BASF route started from hydroquinone, which was converted to 2,5-dihydroterephthalic acid by a Kolbe-Schmitt reaction. One mole of this acid was treated with two moles of an arylamine, both components being in the form of a suspension in aqueous methanol. This was added to a small amount of a solution of vanadium(III) chloride and sodium chlorate. Gentle heating gave a 95% yield of 2,5-bis(arylamino)benzo-l,4-quinone-3,6-dicarboxylic acid. Ring closure to the trans-quinacridonequinone took place in the presence of concentrated sulphuric acid at 60-80 °C. This was then reduced to the required crude pigment by zinc or aluminium powder in caustic soda under pressure,in an aluminium chloride/urea melt or by the use of a sulphuric acid/polyphosphoric acid mixture. 

Example 2, the Marasse modification of the Kolbe-Schmitt reaction uses excess of anhydrous potassium carbonate in place of carbon dioxide ... 

---