6-Hydroxybiphenyl-2-carboxylic acid

Benzoic and hydroxybiphenyl carboxylic acids are widely used in the synthesis of drugs, biologically active compounds, and heat-resistant polymers. The known methods for preparation of aromatic hydroxy carboxylic acids include many stages, require not easily accessible starting compounds, and provide poor summary yields of the target products. 

The mesogenic units with methylenic spacers were prepared by reacting the sodium salt of either 4-methoxy-4 -hydroxybiphenyl or 4-phenylphenol with a bromoester in DMF at 82° C for at least 4 hours in the presence of tetrabutylammonium hydrogen sulfate (TBAH) as phase transfer catalyst. In this way, ethyl 4-(4-oxybi-phenyl)butyrate, ethyl 4-(4-methoxy-4 -oxybiphenyl)butyrate, ethyl 4-(4-oxybiphenyl)valerate, ethyl 4-(4-methoxy-4 -oxybiphenyl)-valerate, n-propyl 4-(4-oxybiphenyl)undecanoate and n-propyl 4-(4-methoxy-4 -oxybiphenyl)undecanoate were obtained. These esters were hydrolyzed with base and acidified to obtain the carboxylic acids. The corresponding potassium carboxylates were obtained by reaction with approximately stoichiometric amounts of potassium hydroxide. Experimental details of these syntheses were described elsewhere (27). 

The polyphilic surfactant F(CF2)6(CH2)uOC6H4C6H4COOH [121] is synthesized from the poly fluorinated alcohol prepared by 1-2 addition of perfluoro-hexyl iodide on tt>-undecenol, followed by reduction. The polyfluorinated alcohol is reacted with HBr/H2S04, and the resulting bromide is etherified with 4-cyano-4 -hydroxybiphenyl to give 4-(polyfluoroalkoxy)-4 -cyanobiphenyl. Hydrolysis yields the polyphilic carboxylic acid. 

---