Study On The Characteristics Of The Aldol Condensation Of Cycloalkanones With N-alkyl Aldehydes

The characteristics of the aldol condensation between cycloalkanones and n-alkyl aldehydes in non-catalytic,acid-catalytic,base-catalytic and acid-base mixed catalytic systems were studied using cyclopentanone and n-valeraldehyde,n-heptanal as the substrate. It was found that it had a good selectivity to the cross-condensation of cycloalkanones and n-alkyl aldehydes in the base-catalytic and acid-base mixed catalytic system,while acid-catalytic system could well promote the self-condensation of aldehydes and ketones.The reaction feature catalyzed by sodium hydroxide was evaluated in detail,in which the effects of the factors such as cyclopentanone/n-valeraldehyde molar ratio,temperature etc.on the reaction were evaluated.It was shown that the selectivity to 2-pentylidene-cyclopentanone was 80%and conversion of n-valeraldehyde was 83%,when cyclopentanone/n-valeraldehyde molar ratio was 1.1:1,the reaction temperature was 30℃,the concentration of sodium hydroxide solution was 1%.Reaction time is shortened from 6h to 3h after the addition ofβ-cyclodextrin phase transfer catalyst.When the reaction temperature was 40℃and the concentration of sodium hydroxide solution was 1.5%,n-heptanal conversion was 80%,while the selectivity to 2-heptylidene-cyclopentanone was 76%.The condensation reactions for two catalytic conditions were compared,which was catalyzed by dimethylamine and dimethylamine/acetic acid.The results showed that the selectivity to 2-pentylidene-cyclopentanone and conversion of n-valeraldehyde precursor with dimethylamine/acetic acid as catalyst were higher than those of dimethylamine catalyst. Conversion of n-valeraldehyde was 91%and the selectivity to 2-pentylidene-cyclopentanone was 89%when the dimethylamine/acetic acid molar ratio was 1.4:1.In the reaction between cyclopentanone and n-heptanal,n-heptanal conversion was 84%,while the selectivity to 2-heptylidene-cyclopentanone was 85%.The reactivity in the Mg,Al-mixed oxides catalyst system was discussed.The results indicated that the basic sites could be of the key catalysis activities,while the acid sites could assist to promote the reaction.Conversion of n-valeraldehyde was 93%with the selectivity to 2-pentylidene-cyclopentanone increased to 94%under the reaction conditions employed. Conversion of n-heptanal was 88%and the selectivity to 2-heptylidene-cyclopentanone increased to 91%.The catalyst could be reused five times without obvious decrease of the catalytic reactivity.