Os resultados apresentados contribuem para o desenvolvimento da pesquisa sobre antioxidantes derivados de matéria prima natural e renovável revelando, que o desempenho desses materiais é comparável ao de antioxidantes comerciais e, além disso, apresenta meio eficiente e viável de agregar valor a um substrato que apresenta potencial comercial, mas que ainda é pouco explorado.
De acordo com os dados experimentais, a separação e a caracterização dos componentes majoritários do LCC, assim como a síntese de derivados alquilados, nitrados, fosforados e tiofosforados obtidos a partir desses constituintes, foi realizada de forma eficiente e com bons rendimentos.
Os estudos eletroquímicos, mais especificamente a determinação do valor de Epa e
de Ip, observados durante as análises dos compostos majoritários do LCC e dos derivados
alquilados e nitrados obtidos a partir do cardanol, permitiram classificar cardol e cardanol
terc-butilado como os compostos fenólicos com maior capacidade de inibição do processo oxidativo, definir o mecanismo de ação desses compostos, o qual se baseia essencialmente na formação de uma radical fenóxido que é estabilizado pela presença de grupos doadores de elétrons que contribuem para o melhor desempenho desses aditivos; determinar a melhor eficiência dos compostos insaturados frente a seus análogos saturados, bem como avaliar o efeito do pH no desempenho desses compostos em suas formas saturadas e insaturadas.
Os testes de oxidação acelerada, por sua vez, permitiram avaliar o desempenho dos compostos fenólicos diretamente adicionados ao substrato oxidável (biodiesel de buriti), assim como determinar a relação entre a concentração e a eficácia desses compostos em amostras de biodiesel, apontando cardol como o melhor antioxidante. Os experimentos de oxidação acelerada permitiram também comprovar o melhor desempenho dos compostos insaturados e compreender mais claramente o mecanismo de ação desses aditivos, confirmando os resultados apresentados no estudo eletroquímico e permitindo concluir que a metodologia desenvolvida nesse trabalho pode ser aplicada eficientemente para a avaliação do desempenho de compostos dessa natureza.
Os resultados obtidos a partir das análises termogravimétricas de amostras de biodiesel dopadas com os compostos fosforados confirmaram a ação antioxidante dessa classe de compostos, mostrando que a inserção de grupamentos fosforados aos compostos derivados do LCC permite a obtenção de aditivos com ação antioxidante melhorada, que podem ser aplicados eficientemente na inibição do processo oxidativo de biocombustíveis.
Dada à versatilidade apresentada pelos componentes majoritários do LCC, muito ainda pode ser feito com relação ao desenvolvimento de compostos com ação antioxidante melhorada. Os resultados aqui apresentados indicam que a funcionalização do cardanol e do cardol deve ser direcionada para o desenvolvimento de compostos que possam ser obtidos de forma rápida com a adição de substituintes doadores de elétrons que promovam a estabilização do radical fenóxido e melhorem a ação antioxidante desses compostos.
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ElectrochimicaActa
j o ur na l h o me p ag e :w w w . e l s e v i e r . c o m / l o c a t e / e l e c t a c t a
Electrochemicalandcomputationalstudiesofphenolicantioxidantsfromcashew
nutshellliquid
FranciscoJ.N.Maiaa,∗,ClaudenilsondaS.Clementea,ThiagoM.B.F.Oliveirab,DiegoLomonacoa, TúlioI.S.Oliveiraa,MayaraO.Almeidaa,PedrodeLima-Netob,AdrianaN.Correiab,SelmaE.Mazzetoa
aDepartamentodeQuímicaOrgânicaeInorgânica,UniversidadeFederaldoCeará,Bloco940CampusdoPici,60455-970Fortaleza,CE,Brazil bDepartamentodeQuímicaAnalíticaeFísico-Química,UniversidadeFederaldoCeará,Bloco939CampusdoPici,60455-970Fortaleza,CE,Brazil
a r t i c l e i n f o
Articlehistory: Received5March2012
Receivedinrevisedform5June2012 Accepted17June2012
Available online 1 July 2012
Keywords:
Cashewnutshellliquid Antioxidants BHT
Electrochemistry Computationalstudies
a b s t r a c t
ThisworkstudiedtheantioxidantactionoftechnicalCNSLconstituents,cardol(CD)andcardanol(CDN),
anditssyntheticderivativeterc-butylatedcardanol(terc-CDN)byelectrochemicalandcomputational
methods.Theelectrochemicalanalyseswereperformedbysquarewavevoltammetryandcyclicvoltam-
metryindifferentpHs.Theresultsshowedthatallcompoundspresentedloweroxidationpotentialswhen
comparedtothecommercialproductBHT(Epa=0.989V).Cardolpresentedthebestvalues(Epa=0.665V),
followedbyterc-CDN(Epa=0.682V)andCDN(Epa=0.989V).TheenergyoftheHOMOandLUMOorbitals,
theMillikenchargeandtheanalysisofmolecularconvergenceobtainedbycomputationalmethodscon-
firmedtheresultsobtainedinelectrochemicalanalysisprovingthatbothtechniquescanbeefficiently
appliedtothistypeofstudy.
© 2012 Elsevier Ltd. All rights reserved.
1. Introduction
The cashew nut shell liquid (CNSL) is a by-product of the cashewnutproductionandis anaturalsourceofsaturatedand unsaturatedlong-chainphenols.Itscompositionconsistofamix- tureofmeta-alkylphenols,whichhasbeenappliedinpaintand varnishproducts,foundrycoreoils,automotivebrakeliningindus- try,laminatingandrubbercompoundingresins,surfacecoatings, epoxyresins,woodcompositeadhesivesandinthemanufactureof anionicandnon-ionicsurfaceactiveagents[1,2].
Recentstudieshavedocumentedtheuseoftheconstituentsof CNSLasantioxidantsorasbasisfortheproductionofnewcom- poundswithantioxidantaction [3].Accordingwiththeauthors thesecompoundsinhibittheoxidationoforganicmaterialsasbio fuels,lubricantsandpolymer,throughofthedecompositionofradi- calspeciesformedduringtheoxidationoforganicmaterialtowhich wereadded[4].
Onthebasisofthemodeofextraction,theCNSLcanbeclassi- fiedintotwotypes:naturalandtechnical(t-CNSL).Inthefirstcase, majorcompoundsareanacardicacid(60–65%),cardol(15–20%), cardanol(10%), andtracesof2-methylcardol.Dependingonthe conditionsoftheroastingprocess,thecompositionofthet-CNSL canchangeand reachhighercardanolcontent(60–65%),dueto
∗Correspondingauthor.Tel.:+558533669019. E-mailaddress:[email protected](F.J.N.Maia).
thethermolabilityofthecarboxylicgroupofanacardicacid,which becomescardanol.[3].
Aswellasothernaturalphenoliccompounds(e.g.flavonoids and tocopherols) and synthetic antioxidants, such as butylated hydroxytoluene(BHT)andbutylatedhydroxyanisole(BHA),both cardanol and cardol can act as primary antioxidants, donating hydrogenatoms,whichreactwithfreeradicalsformedduringthe initiationstepoftheoxidativeprocess.Inthissense,manyworks havestudiedtheantioxidantactionoftheCNSLconstituentsand derivativesindifferentsubstrates,applyingdifferentmethodsto evaluatetheperformanceofthesecompounds[5].
Manytechniquesanddifferentmethodshavebeenemployed toevaluatetheperformanceofantioxidants,forexample:differ- entialscanningcalorimetry[6],thermogravimetric(TG)[7]and acceleratedoxidationprocess[8](whichrequireextendedanalysis periods),Fouriertransforminfraredspectroscopy(FTIR)[9],visible andultravioletspectroscopy(UV–vis)[10],whichrequireaninitial processofthesampleoxidation.
On the other hand, the electrochemical analysis is a rapid methodthatrequiressmallamountsofsample,presentshighsensi- tivityandthatareefficientlyemployedonevaluationofantioxidant actionofphenoliccompounds[11].Measurementsofthereducing capacityandelectrochemicalbehaviormayprovideusefulinfor- mationaboutthefreeradicalscavengingactivityofphenols[12]. Themechanismofelectrochemicaloxidationofnaturalphenolic compoundswasrecentlystudiedforAbdel-Hamidetal.[11]and Simi ´cetal.[12].TheauthorsshowedthatfactorssuchaspHandthe
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Thermal studies of new biodiesel antioxidants synthesized from a natural
occurring phenolic lipid
Diego Lomonaco⇑, Francisco Jonas N. Maia, Claudenilson S. Clemente, João Paulo F. Mota,
Antonio E. Costa Junior, Selma E. Mazzetto
Laboratório de Produtos e Tecnologia em Processos, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, Campus do Pici, Bloco 940, Cx. Postal 6021, CEP 60455-760, Fortaleza, Ceará, Brazil
a r t i c l e i n f o
Article history:
Received 26 September 2011
Received in revised form 19 January 2012 Accepted 28 January 2012
Available online 19 February 2012
Keywords: Biodiesel Antioxidant Cardanol Thermogravimetry IPDT a b s t r a c t
This article reported the synthesis of phosphorylated compounds derived from cardanol, a phenolic by- product of the cashew (Anacardium occidentale L.) industry, and its application as antioxidants for biodie- sel. These compounds were added in biodiesel samples in three different concentrations (500, 1000 and 2000 ppm) and their antioxidants activities were tested by thermogravimetric analysis (TG), analyzing
the onset (Te) and endset (To) temperatures values as reference parameters, as also by evaluating their