It is known that
β-cyclodextrin and substrate can form a host-guest complex in water [
15,
16]. This complexation depends on the size, shape and hydrophobicity of the guest molecule. Such interaction can enhance the solubility of the substrate in water [
17]. In comparison with the oxidation of benzyl amine or cyclohexylmethanamine in
β-cyclodextrin aqueous media (entries 1 and 9), the reaction rate was lower in ethanol aqueous media (entries 2 and 10), as did the yield of the corresponding nitriles, indicating that
β-cyclodextrin worked not only as a solubilizing agent but also as a catalyst in these reactions [
18,
19]. In the present system,
β-cyclodextrin could activate the substrates by forming hydrogen bonds and break the N—H bond of these, which could accelerate the oxidation and improve the selectivity of the corresponding nitriles. However, when the benzyl amine was modified by introducing Cl groups into the aromatic ring, the obtained (2,4-dichlorophenyl)methanamine presented less promotion in
β-cyclodextrin aqueous media compared with in ethanol aqueous media owing to the effect of space configuration (entries 3-4). Similarly, due to the large naphthalen-1-ylmethanamine molecule, the corresponding cyclodextrin-naphthalenylmethanamine complex might be a little difficult to form [
11] and the reaction rate also decreased (entries 5, 6). It should be noticed that 2-phenylethanamine could form the stable inclusion complex with
β-cyclodextrin, whereas the yield of the product 2-phenylacetonitrile was not improved in
β-cyclodextrin aqueous media.
β-Cyclodextrin might activate less the b-position of the 2-phenylethanamine because of the space configuration (entries 7, 8). Similar to the deprotection of 2-heptyl-1,3-dioxolane[
12] or oxidation of 2-octanol and 1-octanol [
11] in water, where the interaction between hydroxyl groups on
β-cyclodextrin and the groups to be reacted in the substrates could be hardly performed, the oxidation of octan-1-amine proceeded faster in the ethanol aqueous media than in the
β-cyclodextrin aqueous media due to better solubility (entries 11, 12).