4 Oxidative Esterification of Alcohols and Aldehydes
Direct production of ester from alcohols or aldehydes is also important as well as
direct oxidation of alcohols to carboxylic acid, because esters are produced from
aldehydes by two steps: the oxidation of aldehyde to carboxylic acid followed by
acid-catalyzed esterification. Oxidative esterification to produce methyl esters has
been achieved by Au/TiO 2 [105–110], Au/Fe 2 O 3 [111, 112], Au/Al 2 O 3 [113, 114],
Au/SiO 2 [115–117], Au/polymers [118, 119], Au/graphene oxide (GO) [120, 121],
and Au/MOF [55, 122] in the presence of bases such as NaOMe, K 2 CO 3 , and
Na 2 CO 3 .
Base-free oxidative esterification has been attempted by using basic supports;
Au/MgO [123, 124], Au/La 2 O 3 [125], Au/CeO 2 [126–129], and AuNiO x /SiO 2 -
Al 2 O 3 -MgO [130] catalyzed the oxidative esterification of aldehydes in methanol
to give the corresponding methyl esters in the absence of base. In particular,
AuNiO x /SiO 2 -Al 2 O 3 -MgO produced methyl methacrylate selectively from
methacrolein, which has been operated in the industrial process since 2008 by
Asahi Kasei Corporation (Scheme 5). The oxidative esterification of biomassderived compounds, such as furfural and 5-hydroxymethyl furfural (HMF), was
performed over Au/ZrO 2 in the absence of base to obtain dimethyl furan-2,5dicarboxylate and methyl 2-furoate, respectively (Scheme 6) [129, 131–
137]. Au/β-Ga 2 O 3 also exhibited high catalytic activity for the oxidative esterification of various alcohols in methanol to produce the corresponding methyl esters
including benzyl alcohol [138]. Although the basic sites contribute to the activation
of alcohols, the acidic sites activate the carbonyl group, facilitating the reaction.
Compared to the oxidative esterification for the synthesis of methyl esters, the
production of ethyl esters is more challenging because of lower nucleophilicity of
ethanol than that of methanol and easy oxidation of ethanol, which make difficult the
selective oxidation of aldehydes or the substrate alcohols while ethanol is intact.
Au/NiO x /SiO 2 -Al 2 O 3 -MgO catalyzed the oxidative esterification of methacrolein in
Scheme 5 Oxidative esterification of methacrolein with methanol to methyl methacrylate over
Au/NiO x /SiO 2 -Al 2 O 3 -MgO [130]
Scheme 6 Oxidative esterification of furfural and HMF with methanol to give the corresponding
methyl esters
Gold Nanoparticles for Oxidation Reactions: Critical Role of Supports and Au. . .
23
Direct production of ester from alcohols or aldehydes is also important as well as
direct oxidation of alcohols to carboxylic acid, because esters are produced from
aldehydes by two steps: the oxidation of aldehyde to carboxylic acid followed by
acid-catalyzed esterification. Oxidative esterification to produce methyl esters has
been achieved by Au/TiO 2 [105–110], Au/Fe 2 O 3 [111, 112], Au/Al 2 O 3 [113, 114],
Au/SiO 2 [115–117], Au/polymers [118, 119], Au/graphene oxide (GO) [120, 121],
and Au/MOF [55, 122] in the presence of bases such as NaOMe, K 2 CO 3 , and
Na 2 CO 3 .
Base-free oxidative esterification has been attempted by using basic supports;
Au/MgO [123, 124], Au/La 2 O 3 [125], Au/CeO 2 [126–129], and AuNiO x /SiO 2 -
Al 2 O 3 -MgO [130] catalyzed the oxidative esterification of aldehydes in methanol
to give the corresponding methyl esters in the absence of base. In particular,
AuNiO x /SiO 2 -Al 2 O 3 -MgO produced methyl methacrylate selectively from
methacrolein, which has been operated in the industrial process since 2008 by
Asahi Kasei Corporation (Scheme 5). The oxidative esterification of biomassderived compounds, such as furfural and 5-hydroxymethyl furfural (HMF), was
performed over Au/ZrO 2 in the absence of base to obtain dimethyl furan-2,5dicarboxylate and methyl 2-furoate, respectively (Scheme 6) [129, 131–
137]. Au/β-Ga 2 O 3 also exhibited high catalytic activity for the oxidative esterification of various alcohols in methanol to produce the corresponding methyl esters
including benzyl alcohol [138]. Although the basic sites contribute to the activation
of alcohols, the acidic sites activate the carbonyl group, facilitating the reaction.
Compared to the oxidative esterification for the synthesis of methyl esters, the
production of ethyl esters is more challenging because of lower nucleophilicity of
ethanol than that of methanol and easy oxidation of ethanol, which make difficult the
selective oxidation of aldehydes or the substrate alcohols while ethanol is intact.
Au/NiO x /SiO 2 -Al 2 O 3 -MgO catalyzed the oxidative esterification of methacrolein in
Scheme 5 Oxidative esterification of methacrolein with methanol to methyl methacrylate over
Au/NiO x /SiO 2 -Al 2 O 3 -MgO [130]
Scheme 6 Oxidative esterification of furfural and HMF with methanol to give the corresponding
methyl esters
Gold Nanoparticles for Oxidation Reactions: Critical Role of Supports and Au. . .
23