Nitric Acid Passivation of Residual Metathesis Catalysts
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Solution Overview
Problem
The yield of olefin metathesis products is reduced due to double bond isomerization caused by residual metathesis catalysts, which is exacerbated by heating and distillation, and existing inhibitors like tris(hydroxymethyl)phosphine are not viable on an industrial scale due to carcinogenic byproducts and explosive hazards.
Innovation Solution
The use of nitric acid as an isomerization suppression agent to passivate residual metathesis catalysts in olefin metathesis products, either by adding it to the reaction mixture or washing with a polar solvent to separate it from the product, effectively suppressing isomerization without generating carcinogenic byproducts or explosive gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tris(hydroxymethyl)phosphine (THMP) is used as an isomerization inhibitor, then isomerization is suppressed, but carcinogenic formaldehyde is generated as a byproduct
Solution Approach 1:
The patent replaces THMP with phosphite esters that are commercially available, cost-effective, and can be easily removed from the reaction mixture. These phosphite esters serve as disposable isomerization inhibitors that suppress catalyst activity without generating carcinogenic byproducts, and can be discarded after use through simple filtration or distillation
Solution Approach 2:
The patent changes the chemical parameters by using phosphite esters with different structures and properties compared to THMP. The phosphite esters have appropriate steric bulk and electronic properties that allow them to effectively passivate the metathesis catalyst without undergoing the same decomposition pathways that generate formaldehyde, thus changing the chemical reaction parameters to eliminate harmful byproducts
2Reliability
If pH is not strictly controlled during THMP formation, then isomerization suppression is achieved, but explosive hydrogen gas forms
Solution Approach 1:
The patent employs phosphite esters that are pre-synthesized and stabilized, eliminating the need for in-situ generation through pH-controlled reactions. The phosphite esters are introduced directly into the metathesis reaction mixture in their stable, pre-formed state, thus preventing any possibility of hydrogen gas formation during the isomerization suppression process
Solution Approach 2:
The patent converts the potential harm of uncontrolled pH reactions into benefit by using phosphite esters that are inherently stable and do not require pH control. The structural design of phosphite esters with appropriate substituents ensures they remain stable under metathesis conditions while effectively suppressing isomerization, turning a potentially dangerous process into a safe and reliable method
3Productivity
If residual metathesis catalyst is not removed, then process simplicity is maintained, but double bond isomerization occurs reducing product yield
Solution Approach 1:
The patent introduces phosphite esters as intermediary substances that mediate between the residual metathesis catalyst and the olefinic product. The phosphite esters temporarily bind to the catalyst species, forming inactive complexes that prevent isomerization during subsequent heating and distillation steps. This intermediary approach allows the process to remain simple while effectively protecting the product
Solution Approach 2:
The patent applies preliminary anti-action by adding phosphite esters to the reaction mixture before any isomerization can occur. The phosphite esters preemptively passivate the catalyst species, creating a protective effect that prevents isomerization during subsequent processing steps. This preliminary protection eliminates the need for complex catalyst removal procedures while maintaining high product 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
Nitric acid significantly reduces isomerization, preserving the original carbon-carbon double bond position and ensuring product integrity, making the process suitable for large-scale industrial application without the hazards associated with existing methods.
Implementation Method 1
adding an isomerization suppression agent to a mixture that includes the olefin metathesis product and residual metathesis catalyst from the metathesis reaction under conditions that are sufficient to passivate at least a portion of the residual metathesis catalyst
Data Source
AI summary
A method for suppressing isomerization of an olefin metathesis product produced in a metathesis reaction includes adding an isomerization suppression agent that includes nitric acid to a mixture that includes the olefin metathesis product and residual metathesis catalyst from the metathesis reaction under conditions that are sufficient to passivate at least a portion of the residual metathesis catalyst. Methods of refining a natural oil are described.