Why water should be avoided in steglich esterification reaction?
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Vitor Gilles,a
Mariana A. Vieira,a
Valdemar Lacerda Jr.,a
Eustáquio V. R. Castro,a
Reginaldo B. Santos,a
Ednilson Orestes,b
José W. M. Carneirob
and Sandro J. Greco*,a
a
Department of Chemistry, Center of Exact Sciences, Federal University of Espírito Santo,
29060-900 Vitória-ES, Brazil
b
Institute of Chemistry, Fluminense Federal University, 24210-150 Niterói-RJ, Brazil
A esterificação direta de naftoquinonas mostrou-se uma tarefa difícil. Metodologias mais
comuns envolvem a aplicação de cloretos de acila em piridina ou anidridos, entretanto, quando
ácidos de cadeia longa são utilizados tais metodologias se mostram ineficientes devido aos baixos
rendimentos obtidos. Apresentamos uma nova síntese de ésteres de cadeia longa de juglona baseado
na esterificação de Steglich utilizando um ácido de Lewis barato como cocatalisador. Rendimentos
obtidos são consideravelmente maiores do que os reportados previamente. Química computacional
foi utilizada para avaliar os efeitos do CeCl3 como cocatalisador. Os compostos preparados foram
testados como inibidores de deposição de parafinas em petróleo. Éster palmítico da juglona foi
capaz de reduzir 4 ºC na temperatura de início de aparecimento de cristais (WAT) do óleo estudado,
representando uma redução de 1,5% m/m de parafinas normais precipitadas.
Direct esterification on naphthoquinone presented itself as a hard task. Usual methodologies
apply acyl chloride in pyridine or anhydrides but with long-chain esters this procedure proved to
be ineffective because of the low yields obtained. We present a new synthesis of long-chain esters
of juglone based on Steglich esterification using a cheap Lewis acid as cocatalyst. Yields obtained
are considerably better than those found previously. Computational chemistry was used to evaluate
the effects of CeCl3 as cocatalyst. Prepared compounds were tested as wax deposition inhibitors
in crude oil. Palmitic ester of juglone was able to lower 4 ºC on the wax appearance temperature
(WAT) of the studied oil, representing a reduction of precipitated normal paraffin of 1.5% m/m.
Keywords: juglone, Steglich esterification, fatty acid, wax deposition inhibitor
Introduction
Esterification reaction is one of the oldest, most
widely used and most important chemical transformation
in organic synthesis, with wide application in chemical
industry, pharmaceuticals, food, perfume and cosmetics.1
This reaction is applied to natural products synthesis, in
protection or kinetics resolution of carboxylic acids and in
intramolecular reactions to prepare lactones.1
Since the first reaction presented by Fischer2
extensive
experimental research and many synthetic methodologies
have been developed. In older methods, carboxylic acid
was heated in the desired alcohols under acid catalysis,
usually employing concentrated sulfuric or hydrochloric
acid, phosphorous oxychloride (POCl3) and sulphonic
acids.3
Lewis acids are also catalysts largely applied to
esterification reactions, because they allow mild conditions
to be used, compared to Brønsted acids. Large amounts
of these acids are described in these reactions, such as
BF3.OEt2, AlCl3/ZnCl2, Zn(ClO4)2.6H2O, InCl3, SnCl2,
TiO(acac)2, Mn(OAc)3.2H2O, Fe2(SO4)3.H2O, FeCl3,
NiCl2.6H2O, CuCl2, Cu(NO3)2.3H2O, Cu(OTf)3, Sc(OTf)3,
ZrCl4.2THF, HfCl4.2THF, Zr(Oi
Pr)4/Fe(Oi
Pr)3, NbCl5/Al2O3
and I2, among others.4
Solid acids, like zeolites, oxides, aluminophosphates
and their modified forms, are also alternatives employed
to substitute traditional catalysis by Brønsted/Lewis acids.5
Mariana A. Vieira,a
Valdemar Lacerda Jr.,a
Eustáquio V. R. Castro,a
Reginaldo B. Santos,a
Ednilson Orestes,b
José W. M. Carneirob
and Sandro J. Greco*,a
a
Department of Chemistry, Center of Exact Sciences, Federal University of Espírito Santo,
29060-900 Vitória-ES, Brazil
b
Institute of Chemistry, Fluminense Federal University, 24210-150 Niterói-RJ, Brazil
A esterificação direta de naftoquinonas mostrou-se uma tarefa difícil. Metodologias mais
comuns envolvem a aplicação de cloretos de acila em piridina ou anidridos, entretanto, quando
ácidos de cadeia longa são utilizados tais metodologias se mostram ineficientes devido aos baixos
rendimentos obtidos. Apresentamos uma nova síntese de ésteres de cadeia longa de juglona baseado
na esterificação de Steglich utilizando um ácido de Lewis barato como cocatalisador. Rendimentos
obtidos são consideravelmente maiores do que os reportados previamente. Química computacional
foi utilizada para avaliar os efeitos do CeCl3 como cocatalisador. Os compostos preparados foram
testados como inibidores de deposição de parafinas em petróleo. Éster palmítico da juglona foi
capaz de reduzir 4 ºC na temperatura de início de aparecimento de cristais (WAT) do óleo estudado,
representando uma redução de 1,5% m/m de parafinas normais precipitadas.
Direct esterification on naphthoquinone presented itself as a hard task. Usual methodologies
apply acyl chloride in pyridine or anhydrides but with long-chain esters this procedure proved to
be ineffective because of the low yields obtained. We present a new synthesis of long-chain esters
of juglone based on Steglich esterification using a cheap Lewis acid as cocatalyst. Yields obtained
are considerably better than those found previously. Computational chemistry was used to evaluate
the effects of CeCl3 as cocatalyst. Prepared compounds were tested as wax deposition inhibitors
in crude oil. Palmitic ester of juglone was able to lower 4 ºC on the wax appearance temperature
(WAT) of the studied oil, representing a reduction of precipitated normal paraffin of 1.5% m/m.
Keywords: juglone, Steglich esterification, fatty acid, wax deposition inhibitor
Introduction
Esterification reaction is one of the oldest, most
widely used and most important chemical transformation
in organic synthesis, with wide application in chemical
industry, pharmaceuticals, food, perfume and cosmetics.1
This reaction is applied to natural products synthesis, in
protection or kinetics resolution of carboxylic acids and in
intramolecular reactions to prepare lactones.1
Since the first reaction presented by Fischer2
extensive
experimental research and many synthetic methodologies
have been developed. In older methods, carboxylic acid
was heated in the desired alcohols under acid catalysis,
usually employing concentrated sulfuric or hydrochloric
acid, phosphorous oxychloride (POCl3) and sulphonic
acids.3
Lewis acids are also catalysts largely applied to
esterification reactions, because they allow mild conditions
to be used, compared to Brønsted acids. Large amounts
of these acids are described in these reactions, such as
BF3.OEt2, AlCl3/ZnCl2, Zn(ClO4)2.6H2O, InCl3, SnCl2,
TiO(acac)2, Mn(OAc)3.2H2O, Fe2(SO4)3.H2O, FeCl3,
NiCl2.6H2O, CuCl2, Cu(NO3)2.3H2O, Cu(OTf)3, Sc(OTf)3,
ZrCl4.2THF, HfCl4.2THF, Zr(Oi
Pr)4/Fe(Oi
Pr)3, NbCl5/Al2O3
and I2, among others.4
Solid acids, like zeolites, oxides, aluminophosphates
and their modified forms, are also alternatives employed
to substitute traditional catalysis by Brønsted/Lewis acids.5
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