Preparation of Phloroglucinol and its Mono-ethers

Instead of the dihydroxy benzene compounds or derivatives thereof mentioned above, monohydroxy benzene compounds also can be converted to phloroglucinol in like manner. The monohydroxy benzene compound however must carry two leaving groups at the right places so they can form two -yne bonds respectively between the C-atoms in the 3- and 5-positions, i.e. meta relative to the hydroxy group, and adjacent C-atoms of the benzene ring. 2,6-dichloro phenol is an example of a suitable monohydroxy compound. 

While as a practical matter phloroglucinol is formed from 2,6-dichloro phenol in one reaction step, it can be supposed that 4-chloro resorcinol arises as an intermediate and is converted into phloroglucinol under the reaction conditions. Thus 2,6-dichloro phenol might be considered as a precursor to 4-chloro resorcinol under these conditions. For practical reasons, however, we consider these compoimds to be equivalents and consider as precursors-all other compounds which upon reaction result in one of these two compounds. 

3- and 5-positions and carbon atoms adjacent thereto in the ring. Thus, in the latter case, one -yne bond can be formed between the carbon atoms at the 2- and 3- positions or the 3- and 4-positions and another -yne bond can be formed between the carbon atoms at the 4- and 5-positions or the 5- and 6-positions. Of course, the combination of two adjacent -yne bonds between the carbon atoms at the 3-, 4- and 5-positions does not occur, as this is chemically impossible. 

The proton abstracting agent must be sufficiently strong to promote the formation of the -yne bond so the hydroxides of the alkali metals lithium, sodium and potassium are of first choice. It reacts effectively at a molar ratio to the phenolic compound in the range between 12 1 and 30 1 a molar ratio of between 17 1 and 23 1 appears to be most advantageous. 

The heating or fusion is preferably carried out in the presence of a very small amount of water, which may be, for example, about 1-10 mL. of water, preferably about 2 1/2 to 5 mL. thereof, per 100 g of alkali calculated as KOH. 

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