ARTICLE pubs.acs.org/IECR
Cyclization of Pseudoionone to β-Ionone: Reaction Mechanism and Kinetics Madhvanand N. Kashid,*,† Igor Yuranov,‡ Pauline Raspail,† Petra Prechtl,‡ Jacques Membrez,‡ Albert Renken,† and Lioubov Kiwi-Minsker† †
Group of Catalytic Reaction Engineering (GGRC), Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland ‡ Process Development, Givaudan Suisse SA, 5, Chemin de la Parfumerie, CH-1214 Vernier, Switzerland
bS Supporting Information ABSTRACT: Cyclization of pseudoionone (PI) to β-ionone is an important reaction used in the synthesis of vitamin A and in perfumery. Though the reaction is used for commercial production, its mechanism and kinetics are not known, and the same holds for the optimal performance of the process. This paper deals with experimental investigations of reaction mechanism and kinetics. The inherent characteristics of the reaction such as heat of reaction, thermal stability, and reactants/products distribution in biphasic (sulfuric acid-toluene) system was investigated experimentally. To overcome the mass transfer limitations, the intrinsic kinetics was studied in a batch reactor using a solvent (1-nitropropane) miscible with the reactant and the homogeneous catalyst. It was revealed that the reaction consists of two steps with the first being rapid, while the second is relatively slower. Therefore, the kinetics of only the second step was investigated which was observed to be first order with an activation energy of 65 kJ/mol.
’ INTRODUCTION Cyclization of pseudoionone (PI) to β-ionone in the presence of an acidic agent (catalyst) is a commercially important reaction. The product is used in vitamin A synthesis and in perfumery. Conventionally, PI is slowly dosed to the reactor containing a biphasic mixture of concentrated sulfuric acid and an organic solvent because of the highly exothermic nature of the reaction. The heat management is of major concern to avoid thermal runaway and byproduct (mainly polymers) formation. The reaction takes place in dispersed acid phase and products transfer into the continuous organic phase upon dilution of acid with water. Moreover, the organic phase not only dissipates the heat produced during the reaction but also improves the quality of mixing in the reactor. Thus, choice of catalyst, mixing of different components, removal of heat, and extraction of ionones are the important issues in the achieving optimal performance. Cyclization of PI to R- or β-ionone has been reported in the literature about five decades ago.1 In this reaction, an acidic agent plays an important role as it decides the composition of the resulting ionone mixture. The reaction has been carried out using various acidic agents in different modes such as semibatch14 as well as continuous.5,6 During the past decade, significant research efforts were made on development of solid catalysts to overcome the problems associated with separation and reuse of concentrated acids.714 Though several studies have been published, the detailed reaction mechanism and intrinsic kinetics of cyclization is still not accessible. A detailed review of the literature on different investigations is given in the following section. The present work deals with the kinetics of cyclization of PI to β-ionone in the presence of sulfuric acid (H2SO4). The inherent characteristics of reaction such as heat of reaction, thermal stability, and reactants/products distribution in biphasic liquidliquid r 2011 American Chemical Society
system were investigated experimentally. To overcome the mass transfer limitations, the intrinsic kinetics was studied in a batch reactor using a solvent miscible with concentrated H2SO4 and ionones (homogeneous system). It was revealed that the reaction has two steps, cyclization of PI to ionones (mainly R-ionone) and isomerization of R-ionone to β-ionone, with the former being rapid while the latter being relatively slower.
’ LITERATURE REVIEW The reaction has been carried out using different types of catalysts (liquid, solid), modes of operation (batch, semibatch, and continuous), and fluid systems (single-phase (liquid), liquid liquid, and liquidsolid). The fluid systems result from the choice of solvent with some solvents forming single-phase (homogeneous) while others biphasic (heterogeneous) liquidliquid systems. Royals1 studied the effect of acidic agents on the product composition using a semibatch reactor in a biphasic liquidliquid system. The composition of ionone mixtures obtained was estimated from the refractive index, and an empirical correlation for % β-ionone in the mixture of ionones produced in the presence of concentrated acids as a function of acid strength was proposed %β-ionone ¼ 15 log K a þ 87:7
ð1Þ
where Ka is an acid dissociation constant. The analytical method used in this study was found to be inaccurate which was further corrected using the UV absorption technique.15 However, both Received: January 12, 2011 Accepted: May 13, 2011 Revised: May 13, 2011 Published: May 13, 2011 7920
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Figure 1. The proposed mechanism of PI cyclization and isomerization. Adapted from Semenovskii et al.3
studies have shown the influence of the acid strength on the cyclization kinetics. Further, different homogeneous catalysts were used for the cyclization in liquidliquid systems. Different types of acidic agents in combination with various organic solvents at elevated temperatures between 70 to 175 °C were used, and high ionones yield of about 97%2 were obtained. All studies showed H2SO4 as a favorable candidate for β-ionone production, which poses problems for technological processes such as equipment corrosion and handling when used in large quantities. Therefore, anhydrous hydrofluoric acid (HF) was used as an acidic agent instead of H2SO4.16 β-Ionone yields up to 91%, and R-ionone yields as low as 1.5% were observed. Finally, mixtures of trifluoroacetic acid and H2SO4 or trifluoroacetic and fluorosulfonic acids were employed as cyclization agents by Markovich et al.17 with aiming to reduce or eliminate the use of H2SO4 in β-ionone production. The amount of H2SO4 decreases to 1 1.25 mols per mole PI compared to the case of only H2SO4 where the molar ratio (H2SO4:PI) of about 56 is required. Trifluoroacetic acid can be reused upon the sulfuric acid neutralization with sodium carbonate and the separation of sodium sulfate. PI cyclization was studied in single-phase systems by Smit et al.4 and Semenovskii et al.3 Two solvents miscible with both PI and concentrated H2SO4 were used: nitropropane (NP) and nitromethane (NM). The reaction temperature was varied from 60 °C to þ60 °C, and a maximum ionone yield of ∼90% was obtained. It was supposed that the initial product of PI cyclization was R-ionone. The extent of its further transformation to β-ionone increased with an increase of reaction temperature, reaction time, and amount of concentrated H2SO4. The obtained cyclization results were in line with the results of R-ionone isomerization carried out under the same conditions. At 60 °C the main product of PI cyclization was found to be R-ionone (∼86%). On the basis of these results as well as the results obtained for cyclization of the cis- and trans-isomers of PI at 70 °C the authors3 claimed 1) the overall reaction is independent of the isomer configuration, 2) the main reaction of PI cyclization to R-ionone (∼90%) is always accompanied by a parallel direct cyclization of PI to β-ionone (∼10%), and 3) depending on the reaction conditions R-ionone can be transformed to the β-isomer. The proposed mechanism is shown in Figure 1.
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Cationic ion-exchange resins are commonly used as solid acid catalysts in organic synthesis. Lin and Zhao13 synthesized macroreticular polystyrene (PS) resin as catalyst for the cyclization of pseudoionone. A maximum yield of about 49.17% in 3 h was obtained. Similar ionone yields were obtained for other solid catalysts.10,12,14 The performance of solid catalysts was significantly lower than those reported for the homogeneously catalyzed reactions. A better performance was found in the recent studies,7,8 in which several solid acids were used. A high density of strong Brønsted acid sites showed an ionone yield of 79% which is comparable to the homogeneously catalyzed reaction. A mechanism of the solid catalyzed cyclization reaction was proposed, in which the PI molecule is initially activated on surface Brønsted acid sites and forms a common cyclic intermediate for the consecutive ionone isomer generation. This cyclic carbocation intermediate contains three different kinds of protons that upon direct detachment lead to R-, β-, or γ-ionones as primary products.9 From the chemical structure of the ionone molecules, the following stability order is proposed: β > R > γ-ionone. A continuous process for ionone production was first developed by Hertel et al.6 using two reactors: packed bed reactor and thin film evaporator. A maximum β-ionone yield of 90% was obtained. However, difficulties arose transferring the process to the industrial scale. Rheude et al.18 developed a continuous process where the reaction is quenched by cooling and subsequent hydrolysis of the reaction mixture with water. Mainly R-ionone was obtained for 2 to 3 mol of sulfuric acid per mole of PI, whereas β-ionone containing less than 2% of R-ionone was obtained for more than 5 mol of sulfuric acid per mole of PI. Different H2SO4 concentrations were used by Dobler et al.5 for a temperature 90%, while purity of toluene, nitropropane, and H2SO4 was g99.5%, g98%, and 96%, respectively. Initially ionone stability tests and calorimetric measurements were carried out using a differential scanning calorimeter and a 7921
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characterized using the following parameters Amount transferred Maximum transferrable CPI, 0 CPI Conversion : X ¼ CPI , 0 CR þ C β Yield : Y ¼ CPI , 0 CR þ Cβ Selectivity : S ¼ CPI , 0 CPI Cβ Proportion of β-ionone in product : x β ¼ CR þ Cβ
chemical/value
volume of reactor, V [mL]
250
stirring speed [rpm]
900
Extraction efficiency : E ¼
Semibatch operation solvents
toluene/1-nitropropane (NP)
temperature, TD and TS [°C]
5 5
amount of solvent [g]
51 102
amount of PI or R-ionone [g]
25
PI or R-ionone: H2SO4 [mole] PI dosing time [min]
1:4.8, 1:2.4, 1:1.2 45
additional stirring time after dosing [min]
e60
water dosing time [min]
45
Batch operation (kinetics) solvent
1-nitropropane (NP)
temperature, TD and TS [°C]
5 5
amount of solvent [g]
51 102
amount of PI or R-ionone [g] PI or R-ionone:H2SO4 [mole]
1 1:4.8 1:48
reaction time [min]
e60
reaction calorimeter (RC1e, Mettler Toledo, equipped with powerful stirrer and cryostat). The operating conditions used in the present work are listed in Table 1. Experiments were carried out in semibatch and batch modes. The former was used for PI conversion at concentrations corresponding to our reference protocol while the latter was carried out at lower concentrations to investigate the reaction kinetics. Besides, the reaction was investigated in two systems: bi- and single-phase. The biphasic reference system was a H2SO4-toluene system, while the single-phase system was prepared using 1-nitropropane (NP) as a solvent miscible with H2SO4 and PI. Following the reference procedure (biphasic, semibatch), the reactor was initially charged with concentrated H2SO4 and toluene which were then cooled to 10 °C under intense mixing. A known quantity of PI was dosed slowly to the reactor. The dosing rate was adjusted in a way that the temperature within the reactor did not exceed the target temperature (5 to þ5 °C). Once PI dosing was over, the mixture was stirred for 15 min, and then water was dosed slowly by maintaining temperature in the range of 5 to 0 °C to dilute H2SO4 and to extract ionone to organic phase. The final organic phase was washed with 10% NaHCO3 and dried with anhydrous Na2CO3. After appropriate dilution, the sample was injected to GC for analysis (injection temperature = 250 °C). A similar semibatch experimental procedure was used for the single-phase system. The idea was to overcome the mass transfer limitations existing in the biphasic system as NP is miscible with ionone and H2SO4. The kinetic experiments were carried out in a batch mode (single phase system) where a known amount of PI or R-ionone was injected to the mixture of H2SO4 and NP, and the samples were withdrawn in regular time intervals. Water was added to the samples forming a biphasic mixture of aqueous H2SO4 (60 wt %) and an organic phase. The organic phase was separated, washed with NaHCO3 solution to neutralize the traces of H2SO4, dried with anhydrous Na2CO3, and analyzed by GC. The results were
ð2Þ
th
where Ci is the concentration of i species and subscript 0 is its initial value. These concentrations were measured in organic phase, and the calculations were based on it.
’ RESULTS AND DISCUSSION Ionone Stability Test and Calorimetric Measurements. There are two highly exothermic steps within the process: the protonation of PI by H2SO4 and the dilution of H2SO4 by H2O. Since the reactants and products might be decomposed due to the heat released and consequent temperature increase, the operating conditions must be studied and optimized. First of all, the thermal stability of pure reactants and products were studied using differential scanning calorimetry. PI, R-ionone, and β-ionone were scanned for a wide temperature range, and it was observed that all ionones are stable up to 200 °C. The thermal effects of different steps in PI transformation were measured. It was difficult to measure the effect of some steps, and, therefore, a complementary theoretical method (group contribution19) was also used to calculate heat of formation for the investigation of heat of reaction. The reaction schemes are summarized in eq 3 and results obtained are listed in Table 2. The heat of the overall transformation of PI to β-ionone was measured after injection of PI to the mixture of H2SO4 and NP (reaction 1). It includes the heat of PI protonation, cyclization, and isomerization. We assume that the effects of R, β, and PI protonations are identical. Therefore, the heat of protonation was measured injecting β-ionone instead of PI and R-ionone (reaction 3). In order to determine the heat of isomerization of R- to β-ionone, calorimetric measurement after R-ionone injection into the H2SO4/NP mixture (reaction 2) was done. In addition, the heat of isomerization was calculated theoretically, and it was revealed that isomerization is a slightly endothermic reaction. Finally, the thermal effect of quenching (deprotonation of β-ionone and dilution of H2SO4) was measured after injection of H2O into the system when the reaction was completed (reaction 4).
Reaction 1: PI f β½Hþ Reaction 2: R f β = R½Hþ f β½Hþ Reaction 3: β f β½Hþ
Overall reaction Isomerization
=PI f PI½Hþ =R f R½Hþ Protonation
þH2 O
Reaction 4: β½Hþ s fβ
Acid dilution ð3Þ
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Table 2. Calorimetric Measurements for All Reactions in PI Cyclization heat of reaction (ΔHr) reaction
a
measurementa
estimation 113
cyclization of PI to β-ionone at 10 °C [kJ/mol of PI]
120
protonation of β-ionone with H2SO4 at 10 °C [kJ/mol of β-ionone]
71
isomerization of R-ionone to β-ionone at 10 °C [kJ/mol]
þ8
deprotonation of β-ionone and dilution of H2SO4 from 96% to 60% with water at 0 °C [kJ/mol of H2SO4]
30
Volume of RC1e = 800 mL, H2SO4 (96%) = 146.4 g, toluene = 244.1 g, PI = 60 g.
Figure 3. Yield and proportion of β-ionone for different operating conditions at complete conversion of PI (PI:H2SO4 molar ratio = 1:4.8, amount of toluene = 102 g).
Figure 2. Concentration of ionone in organic phase for different concentrations of H2SO4 (T = 0 °C). The yield corresponds to the organic phase only.
Combining all above reactions (eq 3), the overall reaction can be schematically represented as
The heat capacity of PI was also measured with the RC1e calorimeter and was found to be 1.93 kJ/kgK at 25 °C. Biphasic System: Semibatch Mode. The reaction of PI cyclization was performed in a laboratory stirred glass reactor in a semibatch mode using toluene as a solvent following the reference protocol. Since H2SO4 and toluene are immiscible, an emulsion is formed under stirring. The mixture was cooled to 10 °C and PI was dosed slowly. The color of the mixture changed from light yellow to dark brown. The reaction takes place in the H2SO4 phase. This was confirmed by stopping the process midway, allowing a phase separation, and analyzing the organic phase. The ionones were not detected in the organic phase. Due to protonation of the ionones, PI goes immediately to the acid phase. The products also stay in the same phase until water is added. Moreover, it was observed that together with
ionones 2030% of toluene is transferred to the acidic phase. These findings were confirmed separately by measurements of the partition coefficient of β-ionone in between toluene and H2SO4. After H2O addition, due to strong interaction between H2SO4 and H2O, the ionones are deprotonated and transferred to the organic phase. In order to investigate the amount of water required to extract ionones from reaction mixture, water was added slowly, organic samples were withdrawn in regular time intervals, and the amount of ionone in toluene was measured. The results are plotted in Figure 2. As can be seen, ionones stay in H2SO4 until the acid concentration reaches ∼80 wt % based on amount of H2SO4 and water only. With further water addition, β-ionone is transferred to organic phase. Therefore, in all further experiments H2SO4 was diluted up to 60 wt % in the last step. At 10 °C, the β-ionone yield was found to be ∼80%. At higher temperatures the yield diminished slightly to 74% at 0 °C and to 71% at 10 °C for the same extraction time. After 2 h under reaction conditions neither PI nor R-ionone was detected in the system. Therefore it can be concluded that the isomerization reaction in concentrated H2SO4 is irreversible. Experiments were carried out at different H2SO4 concentration, and it was observed that diluted H2SO4 led to the reduction of the overall yield and formation of unidentified byproducts (Figure 3). The experiments carried out without toluene using 96 wt % H2SO4 gives only 20% β-ionone yield due to poor mixing and heat dissipation of highly viscous reaction mixture. It indicates that concentrated H2SO4 and organic solvent is required for β-ionone production. The continuous phase (toluene) absorbs the reaction heat and reduces the overall viscosity resulting in better mixing and higher heat transfer 7923
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Figure 4. Experimental results from semibatch operation for biphasic system.
Figure 6. Typical concentrations versus time for PI, R-ionone, and β-ionone in homogeneous system in a batch reactor (solvent 102 g, H2SO4 6.1 g, PI 2.5 g, T = 20 °C).
Figure 5. Proposed transformation map of conversion of PI to β-ionone in biphasic system (R reaction, s undesired side reaction, BP byproduct).
performance. The viscosity of 96 wt % H2SO4 at 0 °C was found to be 0.025 Pas, and the average viscosity of H2SO4-toluene mixture (Toluene:H2SO4 = 1.6:1 (wt)) is approximately 10 times less. When the toluene-H2SO4 ratio is decreased, hot spots are formed making it difficult to control the reaction. Similar results were obtained under identical conditions using R-ionone as starting material (isomerization reaction) as shown in Figure 4. The results showed ∼20% unidentified loss of the product (independently of the reaction conditions), during the extraction. This was confirmed by dissolving β-ionone in toluene, extracting in concentrated sulfuric acid, and re-extracting in toluene by addition of water—∼80% of the initial amount of β-ionone was recovered. At higher temperatures the yield diminished to 74% at 0 °C and to 71% at 10 °C. To explain the obtained results, a PI-to-β-ionone transformation map is depicted in Figure 5. PI comes in contact with concentrated H2SO4 and transforms immediately to a protonated complex (PI[Hþ]) with an important heat release. As a consequence, the bulk concentration of PI in the organic phase becomes zero. PI[Hþ] is transformed very fast to R[Hþ] (R2) and in parallel to β[Hþ] (R4). Both transformations may involve different intermediate steps. It can be postulated that β-ionone is the thermodynamically favored product, while the initial conversion of PI to R-ionone rather than β-ionone is kinetically controlled. After quenching with water, the protonated complexes are decomposed (R5, R6) to form R- and β-ionones, which are transferred to the organic phase. During the quenching step and the transfer from H2SO4 to toluene, approximately 20% of the ionones are lost and nonidentified byproducts are formed (S1, S2). As the yield of ionones is not
influenced by the reaction temperature below 5 °C and by the residence time, byproduct formation in the H2SO4 phase (S3, S4) before dilution is negligible, if at all, the transfer of the byproducts from the inorganic to the organic phase is not proved. Single-Phase System. To overcome the mass transfer influences in the biphasic system, it was decided to replace toluene by a solvent miscible with concentrated H2SO4 and ionones. In this way, the reactions can be carried out in a single homogeneous phase. A further prerequisite was that the new solvent must be immiscible with diluted acid and water and chemically stable against concentrated H2SO4. Different solvents such as isobutyl acetate, isobutyl-methyl-ketone, ethylene carbonate, acetonitrile, propylene carbonate, phenyl acetonitrile, and NP were tested. With an exception of NP, the solvents were found to be either unstable under the reaction conditions (i.e., reacting with H2SO4) or soluble in water. Thus, NP was chosen for singlephase experiments.3 Single-Phase Semibatch Mode. PI was dosed to a homogeneous mixture of NP and concentrated H2SO4 for a period of 45 min (PI:H2SO4 = 1:4.8 (molar)), and a yield/selectivity of (Rþβ) ionones higher than 99% was observed. The product distribution was shifted to lower β/(Rþβ) i.e. xβ = 0.89. The (Rþβ) yield was slightly diminished to 95% when the reaction mixture was stirred for one hour more after the dosing, whereas the R-ionone was completely transformed to β-ionone i.e. xβ > 0.99. When the PI:H2SO4 molar ratio was changed to 1:2.4, R-ionone was not completely transformed to β-ionone showing xβ ∼ 0.6 at a (Rþβ) ionone yield >99%. With further increasing PI:H2SO4 molar ratio to 1:1.2 the (Rþβ) yield reduced to about 90% and xβ to 0.54. This composition remained unchanged with increasing residence time up to 1 h after the dosing. In the semibatch operation, the product yield was found to be temperature independent in the range of 5 to þ5 °C. When compared to the biphasic system, the product yield was considerably higher, while the R to β transformation rate was lower because of the dilution of H2SO4 by NP. For the PI:H2SO4 ratio equal or lower than 1:2.4, incomplete conversion to β-ionone was observed even two hours after the dosing. This fact suggests that H2SO4 does not only act as a catalyst but also as a 7924
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Figure 8. Arrhenius plot for isomerization reaction showing two different lines for R-ionone transformation and β-ionone formation. The kinetic parameters were investigated using the average values of intercepts and slopes as shown by dotted line. (Energy of activation = 65 kJ/mol and frequency factor = 5.4 1010 1/s).
The rate constant obtained for different temperatures from Figure 7 were plotted in the form of Arrhenius plot in Figure 8. Different rate constants were obtained for R-ionone transformation and β-ionone formation indicating a two step reaction. The average of two slopes of the plot (-Ea/R) gives an activation energy (Ea) of about 65 kJ/mol as shown by the dotted line in Figure 8.
Figure 7. Behavior of R- and β-ionone concentration at different temperatures (NP 102 g, H2SO4 61 g, PI 1 g).
complexation agent for the cyclization/isomerization reaction. At higher temperatures (>10 °C), the byproduct formation can no longer be neglected. Kinetics of Isomerization Reaction. In order to study the kinetics of the reaction, experiments were carried out in a batch mode where the mixture of H2SO4 and NP was cooled to a certain temperature and a known amount of PI was injected. The amount of PI was chosen based on the temperature rise after the injection. In the kinetics experiments, a temperature rise was limited to 2 °C. The samples were withdrawn in regular time intervals and analyzed by GC using the above-described procedure. The results are presented in Figure 6. The results confirm that the overall transformation takes place in two steps: cyclization of PI to R-ionone (step I) followed by isomerization of R-ionone to β-ionone (step II). It was revealed that step I is rapid, while step II is relatively slow. Therefore, the kinetics of only isomerization step (step II) was investigated. In Figure 7 the concentration of R-ionone and β-ionone is plotted as a function of time for different temperatures. It shows that R-ionone concentration decreases exponentially with an increased rate of decay at higher temperature. The integral method was used to investigate the order of the reaction, and it was found that the isomerization is a first order reaction.
’ CONCLUSION Experiments were carried out for different sets of operating conditions in biphasic and single-phase cyclization reaction. The PI-to-β transformation map was proposed, and the intrinsic kinetics of R-to-β isomerization was investigated. In the biphasic system, the reaction takes place in acidic phase where all ionones exist in protonated forms which are deprotonated upon the addition of water. The results showed ∼20% unidentified loss independent of the reaction conditions during the extraction. In order to overcome the mass transfer limitations of biphasic system, a miscible solvent (NP) was used and higher yield was obtained. It was observed that the overall transformation takes place in two steps: cyclization of PI to mainly R-ionone (step I) followed by isomerization of R-ionone to β-ionone (step II). Step I was found to be rapid, while step II was relatively slow. The kinetics of only step II was investigated which was found to be a first order reaction. In the future, efforts will be made to develop a new experimental technique to investigate the kinetics of step I. ’ ASSOCIATED CONTENT
bS
Supporting Information. Detailed information on different operating conditions and solvents used in the literature is presented in the form of a table. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail: madhvanand.kashid@epfl.ch. 7925
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’ ACKNOWLEDGMENT The authors acknowledge the financial support from the 7th European Framework Program PILLS Project (Grant agreement number: CP-FP 214599). Also thanks to Jeremy Double and Ian Houson from Britest limited (UK) for useful discussion and suggestions. ’ REFERENCES (1) Royals, E. E. Cyclization of Pseudoionone by Acidic Reagents. Ind. Eng. Chem. 1946, 38, 546. (2) Kharshan, M. A.; Kron, A. A.; Aulchenko, I. S. Method of producing ionine or homologs thereof. S.U. Patent 695,164, 1986. (3) Semenovskii, A. V.; Smith, V. A.; Kucherov, V. F. The Mechanism of Pseudoionone Cyclization. Dokl. Akad. Nauk. SSSRþ 1960, 132, 1107. (4) Smit, V. A.; Semenovskii, A. V.; Medvedeva, V. M.; Kucherov, V. F. On Pseudoionone Cyclization - a New Method of Alpha-Ionone Production for Pseudoionone Cyclization. Dokl. Akad. Nauk. SSSRþ 1959, 124, 1080. (5) Dobler, W.; Bahr, N.; Breuer, K.; Kindler, A. Continuous production of pseudoionones and ionones. U.S. Patent 2,006,014,984, 2004. (6) Hertel, O.; Kiefer, H.; Arnold, L. Preparation of ionones. U.S. Patent 4,565,894, 1986. (7) Diez, V. K.; Apesteguia, C. R.; Di Cosimo, J. I. Synthesis of Ionones by Cyclization of Pseudoionone on Solid Acid Catalysts. Catal. Lett. 2008, 123, 213. (8) Díez, V. K.; Marcos, B. J.; Apesteguía, C. R.; Di Cosimo, J. I. Ionone Synthesis by Cyclization of Pseudoionone on Silica-Supported Heteropolyacid Catalysts. Appl. Catal., A 2009, 358, 95. (9) Díez, V. K.; Apesteguía, C. R.; Di Cosimo, J. I. Synthesis of Ionones on Solid Brønsted Acid Catalysts: Effect of Acid Site Strength on Ionone Isomer Selectivity. Catal. Today 2010, 149, 267. (10) Guo, D. S.; Ma, Z. F.; Jiang, Q. Z.; Xu, H. H.; Ye, W. D. Sulfated and Persulfated TiO2/MCM-41 Prepared by Grafting Method and Their Acid-Catalytic Activities for Cyclization of Pseudoionone. Catal. Lett. 2006, 107, 155. (11) Guo, D. S.; Ma, Z. F.; Jiang, Q. Z.; Ye, W. D.; Li, C. B. FT-IR and Density Functional Theory Studies on Surface Acidity SO42-/SiO2. Chin. J. Catal. 2007, 28, 627. (12) Guo, D. S.; Ma, Z. F.; Yin, C. S.; Jiang, Q. Z. Preparation and Acid Catalytic Activity of TiO2 Grafted Silica MCM-41 with Sulfate Treatment. Chin. J. Catal. 2008, 21, 21. (13) Lin, Z. H.; Zhao, C. X. Macroreticular p-(omega-sulfonicperfluoroalkylated) Polystyrene Ion-Exchange Resins: a New Type of Selective Solid Acid Catalyst. Chem. Commun. 2005, 3556. (14) Lin, Z. H.; Ni, H. B.; Du, H. Y.; Zhao, C. X. A New type of Hybridized Macroreticular Catalyst: Polystyrene with both Perfluoroalkanesulfonic and Sulfonic Functional Groups. Catal. Commun. 2007, 8, 31. (15) Krishna, H. J. V.; Joshi, B. N. A Note on the Preparation of β-ionone. J. Org. Chem. 1957, 22, 224. (16) Panfilov, A. V.; Markovich Yu, D.; Zhirov, A. A.; Gorbach, L. A.; Kirsanov, A. T.; Ionin, V. N.; Davydovich, D. V. Method of beta-ionone synthesis. R.U. Patent 2,075,473, 1997. (17) Markovich, Y. D.; Panfilov, A. V.; Platunov, Y. N.; Zhirov, A. A.; Kosenko, S. L.; Kirsanov, A. T. New Cyclization Agents for the Synthesis of Beta-Ionone from Pseudoionone. Pharm. Chem. J-USSR 1998, 32, 603. (18) Rheude, U.; Horcher, U.; Weller, D.; Stroezel, M. Process for preparing ionones. U.S. Patent 6,288,282, 2000. (19) Joback, K. G.; Reid, R. C. Estimation of Pure-Component Properties from Group-Contributions. Chem. Eng. Commun. 1987, 57, 233.
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