US EPA

5930448 

Journal Article 

Mechanisms for the formation of ester compounds in the liquid-phase oxidation of cyclohexane 

Perkel, AL; Voronina, SG 

2019 

1 

Russian Chemical Bulletin
ISSN: 1066-5285
EISSN: 1573-9171 

68 

10 

1803-1820 

10.1007/s11172-019-2630-0 

WOS:000490004700001 

The channels of formation of ester compounds in the liquid-phase oxidation of cyclohexane are reviewed. At least 99.8% cyclohexyl esters of mono- and dicarboxylic acids are formed as a result of cyclohexanol acylation with mixed anhydrides including residues of all compounds with carboxyl groups present in the oxidized cyclohexane. The formation of mixed anhydrides is related to the fast reacylation of adipic anhydride with carboxylic acids. Alcoholysis of mixed anhydrides containing the formic acid residue with cyclohexanol leads mainly to cyclohexyl formate. The formation of epsilon-caprolactone during cyclohexane oxidation is the result of the Baeyer-Villiger oxidation of cyclohexanone with peroxy acids through alpha-hydroxy-alpha-hydroperoxy ester. A decrease in the yield of epsilon-caprolactone is reached under the conditions of decomposition or reduction of peroxy acids in the presence the compounds of variable valency metals or sulfur-containing reagents, respectively. The cobalt(II) and manganese(II) compounds stimulate the homolytic decomposition of alpha-hydroxy-alpha-hydroperoxy ester during which no lactone is formed. The cyclization of 5-hydroxypentanoic acid, which was formed by the oxidative transformations of cyclohexanone, leads to delta-valerolactone. The compounds of variable valency metals slightly affect the yield of delta-valerolactone. The mechanism of ester formation associated with the acylation of oxiranes formed by the radical chain oxidation of carbonyl compounds at the beta-CH bonds was proposed. 

cyclohexane; cyclohexanol; cyclohexanone; 2-hydroxycyclohexanone; adipic acid; adipic anhydride; epsilon-caprolactone; delta-valerolactone; cyclohexyl esters; liquid-phase oxidation; mechanism