Benzidine Rearrangement Low-Temperature Selectivity
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Solution Overview
Problem
Conventional methods for producing 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl via benzidine rearrangement reactions result in low yields and require extended reaction times, especially when bulky substituents are present, due to decreased selectivity and heat generation issues.
Innovation Solution
A method involving a benzidine rearrangement reaction of 3,3′-bis(trifluoromethyl)hydrazobenzene at extremely low temperatures (−70° C. to −11° C.) in the presence of an organic solvent and an inorganic acid, with the option of using additives to prevent solidification and improve flowability, significantly reducing reaction time to less than an hour.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional benzidine rearrangement reaction is carried out at room temperature or higher, then reaction rate is fast, but selectivity decreases and yield is low (17-32%)
Solution Approach 1:
The patent applies parameter changes by conducting the benzidine rearrangement reaction at extremely low temperatures of -70°C to -11°C, which is a significant deviation from conventional reaction conditions. This temperature parameter change increases selectivity to 70% or more while maintaining acceptable reaction rates, directly resolving the contradiction between selectivity and productivity
2Reliability
If reaction time is extended to 2-10 hours to increase selectivity, then yield improves slightly, but productivity decreases
Solution Approach 1:
The patent changes the temperature parameter to -70°C to -11°C, which accelerates the reaction rate while maintaining high selectivity. This allows the reaction to reach high conversion in just 0.5-2 hours, significantly reducing the time loss compared to conventional 2-10 hour reactions while achieving 70% or more selectivity
3Device complexity
If bulky substituent group is present at meta position, then molecular complexity increases, but selectivity of rearrangement reaction decreases
Solution Approach 1:
The patent applies parameter changes by using extremely low temperatures of -70°C to -11°C, which compensates for the decreased selectivity caused by bulky substituent groups. This temperature parameter change stabilizes the transition state and directs the rearrangement to the desired product, achieving 70% or more selectivity even with bulky groups like trifluoromethyl at the meta position
4Reliability
If reaction is carried out at low temperature to increase selectivity, then selectivity improves to 70% or more, but reaction mixture may solidify
Solution Approach 1:
The patent uses an intermediary substance (additive) that prevents solidification of the reaction mixture at low temperatures. This additive acts as a mediator between the low temperature condition (required for selectivity) and the physical state of the mixture (required for operability), maintaining flowability while enabling the reaction to proceed at -70°C to -11°C with 70% or more selectivity
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 enhances the yield of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl to 35% or more, substantially shortening the reaction time and improving selectivity, making the process more efficient and productive.
Implementation Method 1
a benzidine rearrangement reaction of a hydrazobenzene having a bulky substituent group at the meta position
Data Source
AI summary
The object of the present invention is to provide a method which provides a diaminobiphenyl compound in a high yield and in a short period of time by a benzidine rearrangement reaction of a hydrazobenzene having a bulky substituent group at the meta position. Specifically, the present invention provides a method for preparing a diaminobiphenyl compound represented by the following formula (1):wherein, X1 and X2 are, independently of each other, a group selected from the group consisting of a trifluoromethyl group and, optionally fluorinated, isopropyl, isobutyl, sec-butyl, tert-butyl and neopentyl groups, comprising a step of subjecting a diphenylhydrazine compound represented by the following formula (2)wherein X1 and X2 are as defined above,to a benzidine rearrangement reaction in the presence of an organic solvent and an inorganic acid at a temperature of from −70° C. to −11° C.to obtain the diaminobiphenyl compound represented by the formula (1).