Alkali fusion side reactions

Of the side reactions which frequent occur in alkali fusions, the following might be mentioned ... 

Replacement of the sulfo group by hydrogen instead of by hydroxyl, simultaneously forming sulfate instead of sulfite. This reaction is usually only an unimportant side reaction, but in certain cases it may become the main reaction. Thus, alkali fusion of 2,3-dihydroxynaphthalene-6-sulfonic acid does not give the expected 2,3,6-trihydroxynaphthalene, but instead, 2,3-dihydroxynaphthalene. 

Fusion with alkali in the presence of air (oxygen) often accomplishes oxidations impossible to obtain otherwise. For instance, the formalion of oxyacids from substituted phenols by direct oxidation of side chmns is difficult of accomplishment because of the much greater susceptibility of the hydroxyl group to attack and consequent tendency for the breakdown of the molecule. Alkali fusion accomplishes the desired reaction but with poor 3rields. Xylenols yield the corresponding mono- and dibasic acids by... 

The most important causes of deviation of the product from the desired composition are losses of metal by vaporization, oxidation or side reactions with the material of the fusion pot. In such cases the expected losses of a component are balanced by adding an extra quantity of that component to the starting mixture. A rough approximation of the extra quantity required is obtained from the fact that when the preparation is conducted properly and in closed crucibles (see below), not even the very reactive mixtures of alkali metals lose more than 5% of the starting weight. 

Figure 7.11. Diagram of the reaction and trapping unit used for alkali fusion reaction GC. The mounting rack and electrical control units are shown. A, storage area for unreacted samples B, storage area of reacted samples C, quartz reaction zone D, carrier gas inlet E, side with rubber septum F, variable temperature fiimace G, trap loop H, injector assembly into gas chromatograph I, combustion furnace surround transfer tubing J, metal cylinder behind platinum sample boat K, magnetic retriever.

Sulphonic Acids to Hydroxyl Compounds.—(4) Reactions with alkalies by fusion. In the aliphatic series the most important synthetic reaction for the formation of hydroxyl derivatives is the treatment of the alkyl halides with silver hydroxide, which reaction we have said does not occur in the benzene series when the substitution is in the ring and not in the side chain. The most important method for preparing ring-hydroxyl compounds is by the fusion of a sulphonic acid or its salt with alkalies, potassium or sodium hydroxide, a reaction which does not occur with the aliphatic sulphonic acids. 

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