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Synthesis of Substituted Salicyaldehydes

IP.com Disclosure Number: IPCOM000125544D
Publication Date: 2005-Jun-07
Document File: 3 page(s) / 30K

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Abstract

Abstract: A process for the production and purification of salicylaldehydes is described which involves formation of a Schiff base or its acid salt from the salicylaldehyde and an amine, followed by separation of the Schiff base or its acid salt and then hydrolysis to provide the salicylaldehyde.

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Synthesis of Substituted Salicyaldehydes

Abstract: A process for the production and purification of salicylaldehydes is described which involves formation of a Schiff base or its acid salt from the salicylaldehyde and an amine, followed by separation of the Schiff base or its acid salt and then hydrolysis to provide the salicylaldehyde.

In the synthesis of optionally substituted salicylaldehydes (i.e. Formula II) from the corresponding phenols (i.e. Formula I), paraformaldehyde is normally used as the formylation agent along with a catalyst such as anhydrous tin(II) chloride, anhydrous tin(IV) chloride, anhydrous magnesium dichloride, a Grignard reagent, or montmorillonite KSF, and in some cases along with a tertiary amine such as tributylamine or triethylamine. Yields vary from as low as 20% to near 80% depending on the nature of the substituents Xn and the reaction conditions.  Isolation and purification to afford salicylaldehyde products of high purity is challenging due to contamination with unreacted starting phenols or non-aldehyde by-products.

To facilitate purification we have developed a process wherein a Schiff base is formed by contacting the crude, optionally substituted salicylaldehyde-containing product with an alkylamine.  The Schiff base or its acid salt is separated from unreacted starting phenols and non-aldehyde impurities in the crude product, and then the Schiff base or its acid salt is hydrolyzed to liberate the optionally substituted salicylaldehyde, which is isolated by distillation or crystallization.  This process provides a superior means to efficiently isolate in high purity the optionally salicylaldehyde from the crude product.

wherein n is an integer from 0 to 5; X is H, C1–C5 alkyl, halogen, NO2 or OR1; R1 is C1–C4 alkyl; R is C1–C6 alkyl; and alkyl is straight-chain or branched.

Optionally substituted salicylaldehydes of Formula II can be prepared by...