CHARACTERIZATION OF BASIC SITES OF ALKALINE CARBONS BY KNOEVENAGEL CONDENSATION

The characterization of the carbon surface basicity by condensation of benzaldehyde with ethyl cyanoacetate, ethyl acetoacetate, diethyl malonate, and ethyl bromoacetate as test reactions were studied with a series of lithium, sodium, potassium, and cesium exchanged activated carbon (Norit RX 1 Extra). The importance of active sites and the measurement of the surface area in determining the reactivity of the carbons is emphasized. The activity of the carbons increases when the ionic radius of the alkali cation increases; the activity increases in the order Li < Na < K < Cs. Under reaction conditions, it was found that most of the basic sites in alkaline carbons have 10.7 less-than-or-equal-to pK(a) less-than-or-equal-to 13.3, and there are a few sites in the range of 13.3 less-than-or-equal-to pK(a) less-than-or-equal-to 16.5. The treated activated carbon that had not been subjected to exchange by alkali metal cations exhibited mostly basic sites able to abstract protons with 9 less-than-or-equal-to pK(a) less-than-or-equal-to 10.7.