Highly efficient method for oximation of aldehydes in the presence of bis-thiourea complexes of cobalt, nickel, copper and zinc chlorides

Behzad Zeynizadeh,Serve Sorkhabi

doi:10.5267/j.ccl.2019.12.001

Abstract

Highly efficient method for oximation of aldehydes in the presence of bis-thiourea complexes of cobalt, nickel, copper and zinc chlorides

Highlights

Aldoximes and ketoximes are valuable chemical intermediates that are widely utilized in the chemical industry.[1,2] They are usually prepared by the reaction of carbonyl compounds and hydroxylamine hydrochloride in the presence of acids or bases including sulfuric acid[3], formic acid[4], pyridine[5], sodium acetate and sodium hydroxide.[6,7] Because of some limitations such as low yield of the products, long reaction times and the presence of acid or base sensitive functionalities in aldehyde or ketonic compounds, the classical methods usually are not suitable
In a case for using NaZn5W19, the oximation reaction was led to low yields of the corresponding aromatic aldoximes due formation of byproducts and carboxylic acids while aliphatic aldehydes were used as substrates
This method suffers from two major drawbacks: relatively high cost of hydroxylamine and the derived serious problems via disposing large amounts of inorganic salts which are co-produced in oximation reactions

Summary

Introduction

Aldoximes and ketoximes are valuable chemical intermediates that are widely utilized in the chemical industry.[1,2] They are usually prepared by the reaction of carbonyl compounds and hydroxylamine hydrochloride in the presence of acids or bases including sulfuric acid[3], formic acid[4], pyridine[5], sodium acetate and sodium hydroxide.[6,7] Because of some limitations such as low yield of the products, long reaction times and the presence of acid or base sensitive functionalities in aldehyde or ketonic compounds, the classical methods usually are not suitable. Aldoximes and ketoximes are valuable chemical intermediates that are widely utilized in the chemical industry.[1,2] They are usually prepared by the reaction of carbonyl compounds and hydroxylamine hydrochloride in the presence of acids or bases including sulfuric acid[3], formic acid[4], pyridine[5], sodium acetate and sodium hydroxide.[6,7]. Because of some limitations such as low yield of the products, long reaction times and the presence of acid or base sensitive functionalities in aldehyde or ketonic compounds, the classical methods usually are not suitable. Among the documented catalyst systems for the formation of oximes, most studies are focused on the ammoximation of cyclohexanone and a very limited range of substrates have been investigated In this context, Sloboda-Rozner reported a sandwich-type polyoxometalate (POM) cluster, Na12[WZn3(H2O)2(ZnW9O34)2], which catalyzes the reaction of NH3 and H2O2 to afford the in situ preparation of hydroxyl amine.[34]. In line with the outlined strategies and continuation of our research program directed to the application of bis-thiourea metal complexes of cobalt, nickel, copper and zinc chlorides, MII(tu)2Cl2, as catalysts for reduction of nitro compounds[41] and silylation of alcohols[42], we wish to introduce a new and highly efficient method for the selective oximation of structurally diverse aromatic and aliphatic aldehydes versus ketones using the combination system of MII(tu)2Cl2/ NH2OH·HCl in a mixture of CH3CN-H2O (1:1) at room temperature (Scheme 1)

Results and Discussion

Conclusions

General

Preparation of bis-thiourea metal chloride complexes

Typical procedure for oximation of 4-chlorobenzaldehyde with Co(tu)2Cl2/NH2OH·HCl system