Titrations of weak acids in 1,1,3,3-tetramethylguanidine

The use of 1,1,3,3-tetramethylguamdine (TMG) as a medium for the titrations of weak acids has been investigated. The hydrogen electrode behaves reversibly in this solvent and can serve as an indicator electrode in titration reactions. The titrant was a o.1 M solution of tetrabutylammonium hydroxide in a 90-10% mixture of TMG and methanol. A hydrogen electrode dipping into a TMG solution saturated with benzoic acid served as reference electrode. Potentiometric titrations of a number of weak acids gave results accurate to at least ±0.5%. It was found that in most cases curcumin could be used as an end-point indicator with an accuracy comparable to that of the potentiometric titration.