One-Pot Pyrazole Synthesis Yield and Temperature
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Solution Overview
Problem
The existing synthesis process for 5-ethyl-4-methyl-1H-pyrazole-3-carboxylic acid has low yield and requires high reaction temperatures, making it unsuitable for large-scale industrial production of the compound, which is a TAAR1 inhibitor used in treating various diseases.
Innovation Solution
A one-pot process involving the reaction of pentan-3-one with a dialkyl or diaryl oxalate in the presence of a base, followed by the addition of hydrazine hydrate or a hydrazine salt, an alkali metal hydroxide solution, and adjustment of pH to below 6, without isolating intermediates, to produce 5-ethyl-4-methyl-1H-pyrazole-3-carboxylic acid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the existing synthesis process (Skinner et al.) is used, then the reaction can be performed, but the yield is low (26%) and high reaction temperatures are required
Solution Approach 1:
The patent changes the reaction parameters by using a one-pot multi-step process with controlled temperature stages. The condensation step occurs at 60-80°C, followed by cyclization at room temperature or below, and hydrolysis at elevated temperature (60-100°C). This optimized parameter sequence achieves 75% yield compared to 26% in the prior art.
Solution Approach 2:
The synthesis is segmented into distinct sequential steps within a one-pot process: (a) condensation of pentan-3-one with dialkyl oxalate to form β-keto ester, (b) cyclization with hydrazine to form pyrazole ring, and (c) hydrolysis of ester to carboxylic acid. Each step has optimized conditions that collectively improve overall yield.
2Ease of manufacture
If the existing synthesis process is used, then the compound can be produced, but the process is not suitable for large-scale industrial production due to low yield and high temperatures
Solution Approach 1:
Multiple synthesis steps (condensation, cyclization, and hydrolysis) are merged into a single one-pot process without isolating intermediates. This integration eliminates multiple workup and purification steps, making the process more suitable for large-scale industrial production while achieving 75% overall yield.
Solution Approach 2:
The reaction proceeds continuously through multiple transformations in one pot without interruption or isolation of intermediates. The reaction mixture is simply treated with additional reagents and adjusted conditions to proceed from step to step, maintaining continuous useful action and improving manufacturing efficiency.
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 process achieves higher yields compared to existing methods, specifically a yield of 75% compared to 26% in the Skinner et al. process, while reducing reaction temperatures, making it more suitable for large-scale industrial production.
Implementation Method 1
reacting pentan-3-one (4) with a dialkyl or diaryl oxalate (5), wherein R is C1-C6-alkyl or C6-C14-aryl, in the presence of a base
Implementation Method 2
adding (i) hydrazine hydrate in the presence of an acid, such as acetic acid or hydrochloric acid or (ii) a hydrazine salt, such as hydrazine acetate or hydrazine hydrochloride, to the reaction mixture obtained from step a)
Implementation Method 3
adding an aqueous solution of an alkali metal hydroxide to the mixture obtained from step b)
Data Source
AI summary
The invention provides a process for manufacturing 5-ethyl-4-methyl-N-[4-[(2S) morpholin-2-yl]phenyl]-1H-pyrazole-3-carboxamide (Formula I), or a pharmaceutically acceptable salt thereof, on an industrial scale,comprising a one-pot process for manufacturing 5-ethyl-4-methyl-1H-pyrazole-3-carboxylic acid (1).