High-temperature water unlocks urea as nitrogen-source towards imidazoles

Area of Science:

• Organic Synthesis
• Green Chemistry
• Heterocyclic Chemistry

Background:

• Urea is an abundant, non-toxic chemical with high nitrogen content, making it a potential green reagent for organic synthesis.
• Traditional uses of urea in synthesis include acting as a building block, solvent component, catalyst, or pH adjuster.
• The use of urea as an ammonia (NH3) source for constructing small organic compounds is underexplored.

Purpose of the Study:

• To develop a novel, environmentally friendly method for synthesizing imidazoles using urea as the nitrogen source.
• To investigate the aquathermolysis of urea in high-temperature water (HTW) to generate ammonia for the Debus-Radziszewski multicomponent reaction (MCR).
• To evaluate the efficiency and greenness of this new synthetic approach compared to existing methods.

Main Methods:

• Aquathermolysis of urea in high-temperature water (HTW) at 190 °C to generate ammonia (NH3).
• Debus-Radziszewski multicomponent reaction (MCR) using the in-situ generated ammonia, various 1,2-diketones, and aldehydes.
• Assessment of green metrics, including E-factor and Process Mass Intensity (PMI), and comparison with literature data.

Main Results:

• Successfully synthesized 23 lophine analogues (imidazoles) within 1-3 hours using urea as the sole nitrogen source.
• The reaction proceeds efficiently without the need for additional catalysts, reaction auxiliaries, or volatile organic compounds (VOCs).
• The method demonstrates comparable or superior performance to classical syntheses, especially for acid-sensitive substrates.
• Green metrics indicate the synthesis is environmentally friendly, with E-factor and PMI values comparable to established methods.

Conclusions:

• High-temperature water (HTW) facilitates the efficient generation of ammonia from urea for imidazole synthesis via MCR.
• This catalytic and solvent-free approach offers a greener alternative for constructing imidazole derivatives, including lophine analogues.
• The method is robust, versatile, and suitable for synthesizing compounds with acid-sensitive functional groups.