Undivided Electrolytic Cell for Gamma-Lactone Production
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Solution Overview
Problem
Existing methods for the electrochemical preparation of γ-lactones and γ-hydroxycarboxylic acid esters through reductive cross-coupling of α,β-unsaturated esters with carbonyl compounds face issues such as low current densities, unsatisfactory yields due to side reactions, and the use of divided electrochemical cells, which lead to membrane aging and increased costs.
Innovation Solution
The process involves reductive cross-coupling in an undivided electrolytic cell using a cathode made of lead, lead alloys, cadmium, mercury, steel, glassy carbon, or boron-doped diamonds, with a basic aqueous electrolyte containing bis-quaternary and multi-quaternary ammonium and phosphonium salts, maintaining an emulsion of starting materials and products to enhance selectivity and yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a divided electrochemical cell is used with a membrane, then the reductive cross-coupling reaction can be performed, but the membrane ages rapidly and service life is unsatisfactory
Solution Approach 1:
The patent removes the membrane component entirely by transitioning from a divided cell to an undivided cell configuration. This extraction of the membrane eliminates the aging and service life issues while maintaining the essential electrochemical reaction functionality through appropriate electrode and electrolyte design.
Solution Approach 2:
The patent merges the anode and cathode compartments into a single undivided reaction space, eliminating the need for a separating membrane. This consolidation simplifies the cell structure while achieving the same chemical transformation through careful control of electrode materials and electrolyte composition.
2Productivity
If low current density is used (0.4 A/dm²), then the reductive coupling reaction proceeds, but the current density is far removed from technically relevant values of >1 A/dm²
Solution Approach 1:
The patent changes the electrical parameter of current density from lab-scale values (0.4 A/dm²) to industrially relevant values (>1 A/dm²). This is achieved by optimizing the electrode configuration, electrolyte composition, and reaction conditions to enable high-current-density operation while maintaining product selectivity and yield.
3Loss of time
If binary mixtures of alcohols with water or dioxane are used as electrolytes, then the reaction can proceed, but the product has to be separated from the solvent after electrolysis which is time-consuming
Solution Approach 1:
The patent uses an aqueous electrolyte system that creates an environmentally benign reaction medium. The water-based electrolyte with conductive salts allows for easy product separation through standard aqueous-organic extraction techniques, eliminating the need for time-consuming separation from alcohol or dioxane solvents.
4Loss of substance
If alcohol-containing solvents are used, then the electrolyte can conduct, but the alcohol is oxidized during electrolysis and the true solvent is lost
Solution Approach 1:
The patent employs an aqueous electrolyte system where water serves as the stable, non-oxidizable solvent. This inert environmental base prevents the solvent oxidation problems encountered with alcohol-containing systems, as water is much more resistant to oxidation under the electrolysis conditions used.
Solution Approach 2:
The patent creates a composite electrolyte system combining water with conductive salts (such as tetraalkylammonium salts). This composite provides both the necessary electrical conductivity and the chemical stability of an aqueous system, avoiding the oxidation issues of organic alcohol solvents while maintaining reaction efficiency.
5Productivity
If graphite electrodes are used, then they can serve as an alternative to lead, mercury and cadmium electrodes, but the yields of lactone are unsatisfactory due to side reactions
Solution Approach 1:
The patent applies local quality by selecting specific electrode materials with particular properties suited to the reaction. Instead of using generic graphite electrodes that promote side reactions, the patent employs lead or cadmium electrodes at the cathode which provide the appropriate local chemical environment for selective reductive coupling, minimizing unwanted side reactions and maximizing lactone yield.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves high selectivity and yield for γ-lactones and γ-hydroxycarboxylic acid esters, avoiding side reactions and membrane issues, while allowing for easier product separation and reducing operational costs.
Implementation Method 1
electrochemical preparation of γ-hydroxycarboxylic acid esters and γ-lactones by reductive cross-coupling of α,β-unsaturated esters with carbonyl compounds
Implementation Method 2
a basic aqueous electrolyte with a conductive salt selected from bis-quaternary and multi-quaternary ammonium and phosphonium salts
Data Source
AI summary
The invention relates to a method for producing ?-hydroxycarboxylic esters and ?-lactones, which are suitable as aromatic substances, by electrochemical reductive cross-coupling of a,ß-unsaturated esters with carbonyl compounds in an undivided electrolytic cell, said cell having a cathode that consists of lead, lead alloys, cadmium, cadmium alloys, mercury, steel, glassy carbon or boron-doped diamonds, and using an alkaline aqueous electrolyte comprising a conducting salt which suppresses cathodic hydrogen formation.