The kinetics of the thermal decomposition reaction of cis-6-phenyl-5,6-(2- phenyl-propilydene)-3,3-tetramethylene-1,2,4-trioxacyclohexane (I) was investigated in the temperature range of 100-130°C in selected solvents of different physicochemical properties to evaluate a solvent effect on the reaction.Facultad de Ciencias Exacta

Cafferata, Lázaro F. R.

Cañizo, Adriana Inés

Eyler, G. N.

Mateo, Carmen Margarita

Rimada, Rubén S.

Molecules

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Molecules 2000, 5 362IHOOOThermal Decomposition Reaction of cis-6-Phenyl-5,6-(2-phenyl-propilydene)-3,3-tetramethylene-1,2,4-trioxacyclohexane inDifferent SolventsL. F. R. Cafferata1, G. N. Eyler2, A. I. Cañizo2, C. M. Mateo2 and R. S. Rimada11Laboratorio LADECOR, Facultad de Ciencias Exactas, UNLP, La Plata, Argentina2Laboratorio de Química, Facultad de Ingeniería, UNCPBA, Olavarría, ArgentinaE-mail: acanizo@fio.unicen.edu.arAbstract: The kinetics of the thermal decomposition reaction of cis-6-phenyl-5,6-(2-phenyl-propilydene)-3,3-tetramethylene-1,2,4-trioxacyclohexane (I) was investigated in thetemperature range of 100-130°C in selected solvents of different physicochemical propertiesto evaluate a solvent effect on the reaction.IntroductionIt is interesting to mention that the antimalarial activity of the plant extract Qinghaosu is associatedwith the presence of the 1,2,4-trioxane ring in molecules of compounds (Artemisinin) found in itscomposition [1].IHere, available kinetic data on the thermal decomposition reaction of I in solvents with differentphysicochemical properties are presented to learn about the solvent effect on its thermolysis.ExperimentalMaterialsThe trioxane I was prepared by methods described elsewhere [2]. The organic solvents were com-Molecules 2000, 5 363mercial analytical reagents purified by standard techniques.Kinetic methodsGlass ampoules half filled with the appropriate I solution were thoroughly degassed under vaccumand immersed in a thermostatic bath at selected temperatures. The remaining concentration of I in thereaction solution was quantitatively determined by RP-HPLC (UV detection). In benzene solvent, ki-netic data were obtained by GC analysis (FID detection). The reaction products were identified by GC-MS and RP-HPLC.The first order rate constant values were obtained by least mean squares treatment of the data plot-ting the values of the [I] vs. time. The activation parameters were calculated according to the Eyringequation [3].Results and DiscussionRate measurements on the thermal decomposition of I, up to at least c.a. 60% of I conversion ineach solvent, show an evident effect of the solvent in the temperature and initial concentration rangesof 100-130°C and 0.36-1,70 x 10-3 M, respectively, (Table 1). The rate constant values increase as thesolvent polarity increases.Table 1. First-order rate constant values at 120°C in solution.SOLVENT 103 x [I], mol/L 106 x kexp, s-1n-hexanebenzeneacetonitrilemetanol0.600.500.650.364.0093.3173390The temperature effect was evaluated by the Arrhenius  equation and the corresponding activationparameters for the O-O bond unimolecular homolysis of I were calculated. The first step of the reac-tion mechanism is the formation of a biradical which later decomposes.A stepwise mechanism was confirmed by analysis of the reaction products.Acknowledgements: This research project was financially supported by CONICET, PROGRAMALADECOM, Facultad de Ingeniería-SECyT de la UNCPBA y CIC de la Provincia de Buenos Aires.References and Notes1. (a) Jefford, C. W.; Rossier, J. C., Boukouvalas, J. J. Chem. Soc., Chem. Commun. 1987, 713; (b)Molecules 2000, 5 364Jefford, C. W.; Rossier, J. C., Boukouvalas, J. J. Chem. Soc., Chem. Commun 1987, 1593 and ref-erences cited therein.2. Jefford, C. W.; Cafferata, L. F. R.; Mateo, C. M. Unpublished.3. Huyberechts, S.; Halleux, A.; Kruys, P. Bull. Soc. Chim. Belg. 1955, 64, 203.

Thermal decomposition reaction of cis-6-phenyl-5,6-(2-phenyl-propilydene)- 3,3-tetramethylene-1,2,4-trioxacyclohexane in different solvents

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Molecules 2000, 5 362
I
H
O
O
O
Thermal Decomposition Reaction of cis-6-Phenyl-5,6-(2-phenyl-
propilydene)-3,3-tetramethylene-1,2,4-trioxacyclohexane in
Different Solvents
L. F. R. Cafferata1, G. N. Eyler2, A. I. Cañizo2, C. M. Mateo2 and R. S. Rimada1
1Laboratorio LADECOR, Facultad de Ciencias Exactas, UNLP, La Plata, Argentina
2Laboratorio de Química, Facultad de Ingeniería, UNCPBA, Olavarría, Argentina
E-mail: acanizo@fio.unicen.edu.ar
Abstract: The kinetics of the thermal decomposition reaction of cis-6-phenyl-5,6-(2-
phenyl-propilydene)-3,3-tetramethylene-1,2,4-trioxacyclohexane (I) was investigated in the
temperature range of 100-130°C in selected solvents of different physicochemical properties
to evaluate a solvent effect on the reaction.
Introduction
It is interesting to mention that the antimalarial activity of the plant extract Qinghaosu is associated
with the presence of the 1,2,4-trioxane ring in molecules of compounds (Artemisinin) found in its
composition [1].
I
Here, available kinetic data on the thermal decomposition reaction of I in solvents with different
physicochemical properties are presented to learn about the solvent effect on its thermolysis.
Experimental
Materials
The trioxane I was prepared by methods described elsewhere [2]. The organic solvents were com-
Molecules 2000, 5 363
mercial analytical reagents purified by standard techniques.
Kinetic methods
Glass ampoules half filled with the appropriate I solution were thoroughly degassed under vaccum
and immersed in a thermostatic bath at selected temperatures. The remaining concentration of I in the
reaction solution was quantitatively determined by RP-HPLC (UV detection). In benzene solvent, ki-
netic data were obtained by GC analysis (FID detection). The reaction products were identified by GC-
MS and RP-HPLC.
The first order rate constant values were obtained by least mean squares treatment of the data plot-
ting the values of the [I] vs. time. The activation parameters were calculated according to the Eyring
equation [3].
Results and Discussion
Rate measurements on the thermal decomposition of I, up to at least c.a. 60% of I conversion in
each solvent, show an evident effect of the solvent in the temperature and initial concentration ranges
of 100-130°C and 0.36-1,70 x 10-3 M, respectively, (Table 1). The rate constant values increase as the
solvent polarity increases.
Table 1. First-order rate constant values at 120°C in solution.
SOLVENT 103 x [I], mol/L 106 x kexp, s-1
n-hexane
benzene
acetonitrile
metanol
0.60
0.50
0.65
0.36
4.00
93.3
173
390
The temperature effect was evaluated by the Arrhenius  equation and the corresponding activation
parameters for the O-O bond unimolecular homolysis of I were calculated. The first step of the reac-
tion mechanism is the formation of a biradical which later decomposes.
A stepwise mechanism was confirmed by analysis of the reaction products.
Acknowledgements: This research project was financially supported by CONICET, PROGRAMA
LADECOM, Facultad de Ingeniería-SECyT de la UNCPBA y CIC de la Provincia de Buenos Aires.
References and Notes
1. (a) Jefford, C. W.; Rossier, J. C., Boukouvalas, J. J. Chem. Soc., Chem. Commun. 1987, 713; (b)
Molecules 2000, 5 364
Jefford, C. W.; Rossier, J. C., Boukouvalas, J. J. Chem. Soc., Chem. Commun 1987, 1593 and ref-
erences cited therein.
2. Jefford, C. W.; Cafferata, L. F. R.; Mateo, C. M. Unpublished.
3. Huyberechts, S.; Halleux, A.; Kruys, P. Bull. Soc. Chim. Belg. 1955, 64, 203.


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Thermal decomposition reaction of cis-6-phenyl-5,6-(2-phenyl-propilydene)- 3,3-tetramethylene-1,2,4-trioxacyclohexane in different solvents

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