Terephthalic, isophthalic and phthalic acids are commodity chemicals valuable in the syntheses of a variety of different polymers. Current production of these benzenedicarboxylic acids relies on petroleum-derived xylenes as chemical feedstocks via Amoco-MidCentury oxidation, a process that releases sizeable amount of carbon dioxide and methane and poses other environmental challenge. Rather than generating greenhouse gases, this investigation focuses on using the single carbon (C1) greenhouse gases methane (CH4) and carbon dioxide (CO2) as synthetic starting materials. Proof-of-concept syntheses of terephthalic, isophthalic and phthalic acids are elaborated from acetylenemonocarboxylic acid, which is obtained by reaction of carbon dioxide with methane-derived acetylene.Acetylenemonocarboxylic acid was first employed as a dienophile in a cycloaddition reaction with isoprene to afford terephthalic and isophthalic acids. A more versatile synthetic approach employed metal-catalyzed or Bronsted acid-catalyzed hydration of acetylenemonocarboxylic acid to afford malonic acid semialdehyde and pyruvic acid. Proposed reaction of malonic acid semialdehyde with two equivalents of acetylenemonocarboxylic acid leads to terephthalic and isophthalic acids via intermediacy of coumalic acid. Proposed reaction of pyruvic acid with two equivalents of acetylenemonocarboxylic acid leads to phthalic and isophthalic acids via intermediacy of isocoumalic acid.
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