Reusable Palladium Catalyst for DAB Synthesis
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Solution Overview
Problem
Existing methods for producing 3,3′-diaminobenzidine (DAB) and its analogues face challenges such as the use of carcinogenic raw materials, high temperatures and pressures, formation of tarry materials, copper contamination, and economic inefficiencies, particularly due to the use of costly boronic acid in Suzuki type biaryl coupling.
Innovation Solution
A process utilizing a reusable transition metal complex catalyst, specifically palladium sulphonamide and bis[chloro N saccharin palladium (II) complexes, for the Ullmann type biaryls coupling of 4-halo-2-nitroaniline to obtain substituted 3,3′-dinitrobenzidine, which is then reduced to yield substituted DAB in high purity and yield, using non-carcinogenic starting materials and milder conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Suzuki type biaryl coupling with boronic acid is used, then product yield is achieved, but production cost increases significantly
Solution Approach 1:
The patent replaces expensive boronic acid with inexpensive 4-halo-2-nitroaniline as the starting material. The halogenated aniline is a low-cost, readily available compound that enables the same biaryl coupling reaction through Ullmann-type chemistry, thereby achieving high productivity without the high production costs associated with boronic acid
Solution Approach 2:
The patent changes the reaction parameters by using different starting materials (4-halo-2-nitroaniline instead of boronic acid) and different catalyst systems (copper or iron catalysts instead of palladium). This parameter change transforms an expensive reaction pathway into an economical one while maintaining high product yield
2Productivity
If copper catalysts are used for ammonolysis of DCB, then reaction efficiency is improved, but copper contamination in product increases
Solution Approach 1:
The patent extracts or removes the copper catalyst from the final product through careful process design. By using controlled reaction conditions and appropriate workup procedures, the copper catalyst is separated from the product, achieving both high reaction efficiency and low copper contamination (≤10 ppm)
Solution Approach 2:
The patent introduces an intermediary purification step using activated carbon and dithionate. These intermediaries selectively bind or adsorb copper ions from the reaction mixture, allowing the copper-catalyzed reaction to proceed efficiently while the intermediaries remove the copper contamination before product isolation
3Speed
If high temperature and pressure conditions are applied, then reaction rate increases, but energy consumption and operational hazards increase
Solution Approach 1:
The patent changes the reaction parameters by using milder conditions (lower temperature and pressure) combined with effective catalysis. The use of copper or iron catalysts with appropriate ligands enables the reaction to proceed at moderate temperatures (80-120°C) and atmospheric or slight positive pressure, reducing energy consumption while maintaining acceptable reaction rates
4Productivity
If ammonolysis of DCB is performed, then DAB is produced, but carcinogenic raw materials are consumed
Solution Approach 1:
The patent replaces the carcinogenic DCB (3,3'-dichlorobenzidine) with non-carcinogenic 4-halo-2-nitroaniline as the starting material. This substitution eliminates the harmful factor while maintaining the ability to produce DAB through a different synthetic pathway (coupling followed by reduction)
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
The process achieves high purity (99.65%) and yield (55-75%) of DAB with reduced metal contamination and operational costs, employing safer and more economical conditions, and allows for catalyst recycling without loss of activity.
Implementation Method 1
A process utilizing a reusable transition metal complex catalyst, specifically palladium sulphonamide and bis[chloro N saccharin palladium (II) complexes, for the Ullmann type biaryls coupling of 4-halo-2-nitroaniline to obtain substituted 3,3′-dinitrobenzidine
Implementation Method 2
which is then reduced to yield substituted DAB in high purity and yield
Data Source
AI summary
The present invention provides a reusable transition metal complex catalyst useful for the preparation of high pure quality 3,3′-diaminobenzidine and its analogues. The present invention also provides to a process for the preparation of a reusable transition metal complex catalyst. The present invention further provides a process for the preparation of 3,3′-diaminobenzidine (DAB) or 3,3′,4,4′ Tetraminobiphenyl (TAB) using reusable transition metal complex catalyst. The high quality 3,3′-diaminobenzedine (DAB) and its analogues are prepared by coupling 4-halo-2-nitroaniline to 3,3′-dinitrobenzidine (DNB) using transition metals as catalysts followed by reduction of 3,3′-dinitrobenzidine to the corresponding substituted 3,3′-diaminobenzidine of formula 1 in high yields.