Synthesis of malonic acid

A possible novel method for obtaining malonic acid through electro-oxidation of 1,3-propanediol is suggested by the attached paper. In it they studied electro-oxidation of both 1,2- and 1,3-propanediol at various noble metal anodes in both acidic and alkaline conditions, and the conditions and reaction intermediates were studied using cyclic voltammetry and in situ infrared reflectance spectroscopy.

At the platinum anode, regardless of conditions, a mixture of C1, C2 and C3 products were always formed because of dissociative adsorption of 1,3-propanediol at the platinum electrode, leading to a mixture of formaldehyde, formic acid, malonic acid and CO₂.

But interestingly, at a gold anode, in alkaline conditions, malonic acid is the main product formed and no CO₂ evolution was measured.

To quote: "the 1,3-propanediol chemisorptions is not dissociative and all reaction oxidation products are C3 molecules" and "on the gold electrode in NaOH medium, no oxidation of malonic acid by voltammetry was observed, and the SPAIRS spectra recorded show only the bands of the water".

Considering this, I imagine that a simple divided cell with a gold (or gold-plated ) anode, an inert cathode, anolyte 1,3-PDO in aqueous NaOH and catholyte just aq. NaOH would be a very viable approach. The end result should be an alkaline solution of chiefly disodium malonate.

Since disodium malonate is insoluble in alcohol, isolation may be as simple as flooding the post-reaction anolyte with ethanol until it precipitates from solution.

Attachment: electrooxidation_study_PDO__ijcrcps12.pdf (837kB)
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