Chemoselective Thioether Oxidation for Benzoic Acid Synthesis
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Solution Overview
Problem
Existing methods for producing 2-alkyl-4-trifluoromethyl-3-alkylsulfonylbenzoic acids are inefficient due to the use of complex and expensive reagents, low yields, and the need for toxic cyanides and transition metal catalysts, which pose environmental and health risks.
Innovation Solution
A process involving the reaction of 1,3-dichloro-2-alkyl-4-trifluoromethylbenzenes with thiols, followed by selective oxidation, replacement of the sulfoxide group with a metal, and carboxylation using carbon dioxide, avoids the use of cyanides and transition metal catalysts, utilizing cheaper reagents like peracetic acid and hydrogen peroxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If transition metal-catalyzed cyanation of chloroaromatics is used to prepare substituted benzoic acids, then the carboxylic acid group can be formed, but highly toxic cyanides and expensive chemically sensitive catalysts are used requiring complex waste stream processing
Solution Approach 1:
The invention extracts and eliminates the toxic cyanide group from the synthetic pathway. Instead of using cyanation followed by saponification, the patent employs thiolation followed by oxidation to sulfoxide and subsequent carboxylation, completely removing cyanide from the process and eliminating associated toxicity and waste treatment requirements
Solution Approach 2:
The invention replaces expensive transition metal catalysts with simple organometallic reagents (lithium alkyl or lithium aryl) that are cheaper and easier to handle. The catalyst system is replaced with straightforward organometallic chemistry that does not require complex catalyst recovery or special handling procedures
2Manufacturing precision
If metalation of 3-fluoro-4-trifluoromethylbenzoic acid with butyllithium followed by reaction with methyl iodide is used to introduce methyl group, then the substitution can be achieved, but the yield is low (50.7% of theory) and the process is expensive and uneconomical
Solution Approach 1:
The invention performs preliminary thiolation of the chloroaromatic compound before introducing the alkyl group. By first converting the chlorine to a thioether group, then selectively oxidizing to sulfoxide, and finally using the sulfoxide as a leaving group for metalation and carboxylation, the process achieves higher overall yields through a multi-step sequence that avoids the low-yield direct metalation-alkylation route
Solution Approach 2:
The invention introduces a thioether intermediate that is subsequently oxidized to sulfoxide. This sulfoxide intermediate serves as a mediator that facilitates the introduction of the carboxylic acid group through metalation, providing a more efficient pathway than direct metalation of the aromatic ring
3Ease of manufacture
If sulfoxide groups are exchanged for metal with organometallic compounds followed by reaction with carbon dioxide, then the carboxylic acid can be formed, but depending on the nature of substituents, undesirable reactions occur
Solution Approach 1:
The invention achieves selective oxidation of one thioether group to sulfoxide in the presence of another thioether group. This local differentiation allows the sulfoxide to be selectively exchanged for metal and converted to carboxylic acid, while the other thioether group remains intact and does not participate in unwanted side reactions
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 and reduces environmental impact by eliminating the need for toxic substances, while using more economical and easily handled reagents, improving the efficiency of 2-alkyl-4-trifluoromethyl-3-alkylsulfonylbenzoic acid production.
Implementation Method 1
in a second step the aryl bisthioether (III) is selectively reacted with an oxidizing agent to form an aryl monosulfoxide monothioether (V)
Implementation Method 2
in a third step the sulfoxide group is exchanged for a metal and the organometallic compound thus obtained is converted to benzoic acid (VII)
Implementation Method 3
the organometallic compound thus obtained is converted to benzoic acid (VII)
Implementation Method 4
in a fourth step, the remaining thio group is oxidized with an oxidizing agent, optionally in the presence of an oxidation catalyst
Data Source
AI summary
Disclosed is a method for producing 2-alkyl-4-trifluoromethyl-3-alkyl sulfonyl benzoic acids of formula (I). In said formula, the substituents represent groups such as alkyl and substituted phenyl.