Efficient Catalysis of Calcium Carbide for the Synthesis of Isophorone

Article pubs.acs.org/IECR

Efficient Catalysis of Calcium Carbide for the Synthesis of Isophorone from Acetone Yingjie Li,†,‡ Hong Meng,‡ Yingzhou Lu,‡ and Chunxi Li*,†,‡ †

State Key Laboratory of Chemical Resource Engineering and ‡College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, P. R. China S Supporting Information *

ABSTRACT: The liquid-phase aldol condensation of acetone for the synthesis of isophorone (IP) was studied under catalysis of CaC2 powder for the first time. The reaction products were analyzed by gas chromatography, gas chromatography−mass spectrometry, and X-ray diffraction. The catalytic behavior of CaC2 was studied at varying temperature, particle size, and dosage and compared with that of Ca(OH)2 and other basic catalysts. It was found that CaC2 shows excellent catalytic performance because of its strong Lewis basicity and dehydrating ability, and CaC2 is converted to Ca(OH)2 and acetylene simultaneously by the resulting water. Higher temperature, smaller catalyst size, and higher mass ratio of CaC2 are beneficial to the IP synthesis. The overall catalytic performance of CaC2 is superior to that of all basic catalysts reported heretofore. This process combines the hydrolysis of CaC2 and the aldol condensation of acetone into a one-pot reaction, which promotes the condensation of acetone greatly along with the quantitative reclamation of acetylene. Thus, this process can be thought of as a green, cost-effective, and efficient route for the synthesis of IP and provides a valuable use of CaC2.

1. INTRODUCTION Calcium carbide (CaC2) as a commodity chemical has been widely used in the production of vinyl chloride, vinyl acetate, carbon black, chlorinated solvents, and so forth by using acetylene as a raw material.1 In these processes, CaC2 is first hydrolyzed to acetylene accompanied by a great sacrifice of its reactivity, e.g., its dehydration, reduction, and nucleophilic substitution. Therefore, it is of great significance and practical value to develop its raw material uses in organic synthesis, and some possible reactions have been projected by West and Montonna.2 Toward this end, some pioneering works are worth mentioning, e.g., the preparation of vinyl ether,3,4 metal carbides,5 polyynes,6 nanostructured carbon materials,7,8 disubstituted alkynes,9−12 and 1-monosubstituted 1,2,3-triazoles.13 Similarly, we originally attempted to synthesize 2,5dimethyl-3-hexyne-2,5-diol by reacting CaC2 with acetone. To our surprise, the reaction occurred rapidly and completely with the formation of a huge amount of oily products, which were confirmed as a mixture of isophorone (IP) and condensation derivatives of acetone but not the target product. Meanwhile, we found that the catalytic activity of CaC2 is much better than the reported results heretofore, and thus we conducted an indepth study on this reaction. IP, as a key building block, is widely used in the manufacture of fine chemicals, e.g., polyurethanes,14−16 pharmaceuticals,17−19 fragrances,20 the solar energy industry,21 etc. Meanwhile, it is also an excellent solvent with moderate polarity and high boiling point. Therefore, its worldwide demand has increased significantly in recent years, and much © XXXX American Chemical Society

effort has been paid to the development of greener processes and efficient catalysts for the production of IP. Currently, IP is produced via liquid-phase aldol condensation of acetone using basic catalysts,22 such as Ca(OH)2, NaOH, and KOH. This process is useful but far from satisfactory because of its low yield, corrosiveness of the alkaline solution, and wastefulness of raw materials. To overcome these problems, many researches have been carried out toward finding a better catalyst or exploring an appropriate vapor-phase reaction process. Teissier and Kervennal23 reported a liquid-phase process with acetone conversion of 38% and an IP selectivity of 51%, where the reaction was run at 200 °C and 25 atm and catalyzed by a commercial magnesium aluminum double oxide (KW 2000). Jackson and Vaughn24 reported a vapor-phase process with an IP yield of 25.2% by using a Ca(OH)2 catalyst. Until now, many basic catalysts have been studied for this reaction, such as oxidized cesium/nanoporous carbon materials,25 Mo2N and Mo2C,26 vanadium phosphate,27 Nb2O5,28 and Mg−Zr mixed oxides,29,30 or further modification to enhance the catalysis of MgO,31−33 vanadium phosphate,34 and TiO235,36 by the addition of alkaline metals. The results show that a Mg−Al mixed oxide and its cation-doped one exhibit high selectivity of IP in a vapor-phase process,37 but the heterogeneous vaporphase reaction process suffers from many problems, e.g., low Received: February 4, 2016 Revised: April 11, 2016 Accepted: April 11, 2016

A

DOI: 10.1021/acs.iecr.6b00484 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research yield of IP, high energy cost, easy deactivation of the catalyst, and difficulty in catalyst preparation. In this work, we combine the hydrolysis of CaC2 and the aldol condensation of acetone into a one-pot reaction. The catalysis of CaC2 for the liquid-phase condensation of acetone under mild conditions was studied, and CaC2 was found to be an excellent catalyst because of its dual function of strong Lewis basicity and chemical dehydration. This process can be considered as a green, efficient, and energy-saving method for the synthesis of IP as well as a raw material use of CaC2.

2. EXPERIMENT 2.1. Materials. Acetone (analytical reagent, ≥99.5%) was purchased from Beijing Chemical Works (China). CaC 2 (industrial grade, 80%) was purchased from Alfa Aesar Chemical Company (China) and shattered into 100 meshes before use. The CaC2 used in all experiments was the freshly milled one, and its surface amount of Ca(OH)2 was negligible. Ca(OH)2 (analytical reagent, ≥95%) was purchased from Beijing Chemical Works (China). Ethanol absolute (analytical reagent, ≥99.7%) was purchased from Tianjin Damao Chemical Reagent Factory (China). 2.2. Catalytic Condensation of Acetone. To a magnetic agitated autoclave (45 mL) was added 10 g of acetone and 3.68 g of CaC2, and the autoclave was sealed with pressured nitrogen to 0.5 MPa. The autoclave was heated to a set temperature in a thermostatic oil bath, agitated magnetically under 200 rpm for a definite period of time, and then cooled to room temperature for sampling. Approximately 0.1 g of liquid sample was taken by a syringe with a microfiltration head and diluted with anhydrous ethanol. The resulting solution was analyzed by gas chromatography (Shimadzu GC-2010, Japan) equipped with a flame ionization detector and a 30-m-long FFAP capillary column. Nitrogen (99.999% in purity) was used as a carrier gas at a constant flow of 3.01 mL/min. The gas chromatography (GC) oven temperature was programmed from 50 °C (held for 3 min) to 230 °C (held for 2 min) at 18 °C/min, and 0.5 μL of sample was injected into the split mode when the injector temperature was set at 250 °C. The constituents of the liquid phase were identified by GC−mass spectrometry (MS) (Agilent 7890A5975C, American), and the mass spectra were searched for in the NIST 11 database. The head-space gas was sampled using a syringe and analyzed by GC using the same column as that mentioned above. The gas volume at standard conditions was determined by means of a draining method [see the Supporting Information (SI) for details]. The solid product was obtained via filtration, washed thoroughly with acetone and anhydrous ethanol, and dried by a rotary evaporator. X-ray diffraction (XRD) was conducted using a Bruker D8 ADVANCE instrument (Bruker, Karlsruhe, Germany) with Cu Kα radiation at a speed of 6°/min ranging from 2θ = 10 to 70°.

Figure 1. GC−MS spectra of the liquid product. Experimental conditions: 3.68 g of CaC2/10 g of acetone, 90 °C, 20 h.

(DAA), and phorone (P), a major product of IP, and higher polymers as a result of further condensation of IP (see the SI for details). This means that CaC2 has excellent catalysis for the aldol condensation, as justified by the much lower temperature required for the high conversion of acetone in comparison with other catalysts. The gases evolved during the reaction were collected by a draining method and analyzed by GC. About 885 mL of gas was collected, corresponding to 85.7% of the theoretical amount (see the SI for details), and the gas is virtually acetylene along with a trace amount of uncondensed acetone (see the SI for details). Besides, 3.45 g of solid was obtained, and its XRD pattern is presented in Figure 2. The

Figure 2. XRD patterns of solid samples before and after reaction. Experimental conditions: 3.68 g of CaC2/10 g of acetone, 90 °C, 20 h.

XRD pattern of the solid coincides well with Ca(OH)2, indicating that the catalyst CaC2 is completely converted to Ca(OH)2 by water, resulting from condensation of acetone. Therefore, the catalytic effect of CaC2 may be attributed to its strong Lewis basicity and the instant removal of water, which is helpful for driving the reaction forward. As proposed by several authors and shown in Scheme 1,32,33,35 the conversion of acetone to IP experiences a series of reactions, i.e., nucleophilic addition of carbonyl catalyzed by a basic catalyst, dehydration of the resulting oligomers, and Michael addition. It is seen that DAA is first formed via aldol condensation of two acetone molecules, which is further converted to MO by dehydration. Subsequent condensation and dehydration form a series of compounds, and only P can be

3. RESULTS AND DISCUSSION 3.1. Facile Catalytic Condensation of Acetone over CaC2. The condensation reaction of acetone under catalysis of CaC2 was carried out at 90 °C for 20 h, and the GC−MS result of the resultant liquid is presented in Figure 1. It is found that most of the acetone is converted to various products with different condensation degrees, viz., a small amount of light components including mesityl oxide (MO), diacetone alcohol B


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Industrial & Engineering Chemistry Research Scheme 1. Simplified Reaction Network for the Synthesis of IP from Acetone

It is worth pointing out that the catalytic behaviors of CaC2 and Ca(OH)2 are quite different. For condensation of acetone under catalysis of Ca(OH)2, the yield of C6 components increases gradually with time along with the decreasing concentration of acetone. In contrast, under the catalysis of CaC2, the reaction undergoes three stages, viz., initiation, ultrafast interfacial reaction, and excessive reaction. As shown in Figure 3, in the first stage, i.e., in the beginning 12 h, the conversion of acetone and the yield of C6 increase slowly with time, while the yield of IP is negligible. The lower reaction rate here may be ascribed to the limited usability of the catalytic sites exposed on the surface of tiny crystals of CaC2. As the reaction proceeds, the C6 intermediates accumulate steadily, and the crystalline CaC2 is gradually changed to a porous one because of its dynamic hydrolysis, leading to an increased exposure of the catalytic sites and instant removal of water, all of which are helpful to promote the follow-up reactions and initiate an ultrafast reaction hereafter. In the second stage, i.e., from 12 to 16 h here, the conversion of acetone and the yield of IP increase drastically with time, achieving 81.1% and 15.9%, respectively, within 4 h because of the favored conditions for a series reaction on the interface of the resulting porous catalyst. In the third stage, i.e., from 16 to 20 h, the conversion of acetone and the yield of IP increase only slightly, being 83.0% and 18.4%, respectively, at the end of the reaction. As inferred from the above discussion, the initiation period may be shortened reasonably if crystalline CaC2 can be smashed into ultrafine powders with much higher accessibility of the interfacial catalytic sites of the alkynyl anions. 3.3. Influence Factors of the Catalytic Condensation Reaction. For the heterogeneous catalytic reaction, both the temperature and accessibility of the active sites of the catalyst, i.e., the particle size and the dose of CaC2 here, are instrumental. The former influences the reaction kinetics and the reaction equilibrium if appropriate, while the latter changes the reaction rate via the mass-action law and mass transfer. For this, the effects of the temperature, catalytic particle size, and CaC2 dose were studied. The temperature effect on this reaction was studied using CaC2 as the catalyst, and the results are presented in Figure 4. When the temperature remains at 60 °C, the reaction has difficulty proceeding, leading to a negligible yield of IP in 20 h. This may be because less carbanion of acetone could be formed at such a lower temperature. As the temperature rises to 90 °C, the reaction proceeds rapidly after an initiation period with an acetone conversion of 81.1% and an IP yield of 15.9% within 16 h. As the temperature rises further to 120 and 150 °C, the conversion of acetone reaches a high level at the beginning 2 h, and the yield of IP reaches 14.3% and 21.3%, respectively. After

converted to the main product IP via Michael addition. It is worth pointing out that the strong Lewis basicity and chemical dehydration of CaC2 make the reactions much easier than those of other traditional catalysts, and thus the aldol condensation can proceed under very mild conditions. Besides, the coproduced acetylene can be reclaimed easily and used as usual without sacrificing its value, and the accompanying reaction heat from hydrolysis of CaC2 can be used as a supplementary heat source. Thus, the liquid-phase condensation of acetone with a CaC2 catalyst can be considered as a green, energy-saving, and cost-effective process and deserves further study. 3.2. Catalytic Behavior of CaC2 in the Condensation Reaction. To illustrate the unique catalysis of CaC2 for the aldol condensation reaction, two comparative experiments were conducted at 90 °C by using CaC2 and Ca(OH)2 as catalysts. Liquid samples were taken at different times, analyzed by GC, and compared in terms of acetone conversion, the C6 yield as an indication of dimerization, and the product yield of IP, as shown in Figure 3. It is found that Ca(OH)2 shows little

Figure 3. Catalytic performance of CaC2 (solid lines) and Ca(OH)2 (dotted lines). Experimental condition: 3.68 g of catalyst/10 g of acetone, 90 °C.

catalysis for the formation of IP, as indicated by the barely detectable IP component. In contrast, CaC2 shows excellent catalysis, as manifested by the high acetone conversion and IP yield, being 83.0% and 18.4%, respectively, within 20 h. Therefore, for the production of IP, the catalysis arises from CaC2 rather than its hydrated derivative Ca(OH)2, and the latter only has a weak catalytic effect on the dimerization of acetone. C


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Figure 4. Catalytic performance under different temperatures: solid lines for the acetone remaining and dotted lines for the IP yield.

Figure 6. Catalytic performance of CaC2 under different particle sizes. Experimental conditions: 3.68 g of CaC2/10 g of acetone, 90 °C, 8 h.

that, the IP yield increases slowly with time, reaches a maximum at 10 h, and then decreases. As shown in Figure 5,

Figure 7. Catalytic performance of CaC2 under different dosages. Experimental conditions: CaC2/10 g of acetone, 150 °C, 2 h.

Figure 5. Product constituents of the last 2 h for both 120 and 150 °C. Experimental conditions: 3.68 g of CaC2/10 g of acetone.

remarkably with an increase of the CaC2 dosage, but the yield of C6 decreases and the yields of higher polymers increase. These results indicate that the catalytic sites can be increased with increasing CaC2 dosage, resulting in an improved catalytic effect. Therefore, both smaller particle size and higher mass ratio of CaC2 are advantageous for the reaction kinetics of the aldol condensation because of the increased catalytic activity of CaC2. 3.4. Superiority of CaC2 over Traditional Catalysts. The reaction efficiency of the present system is compared with those reported previously with different catalysts and reaction conditions. As shown in Table 1, CaC2 shows better catalysis than all other liquid-phase catalysts and achieves a high catalytic efficiency reported heretofore. Besides, the present reaction can be performed facilely considering its lower reaction temperature, weaker corrosivity of the CaC2 catalyst, and negligible cost of the catalyst due to facile reclamation of the byproduced acetylene. In contrast, the traditional catalysts used in the vapor-phase reaction are expensive and easily deactivated because of carbon deposition at high temperature. Therefore, CaC2 may be deemed the best catalyst until now for the synthesis of IP through liquid-phase aldol condensation of acetone, considering its cheapness, high catalytic efficiency, low energy consumption, and environmental friendliness. 3.5. Proposed Catalytic Mechanism of CaC2. By referring to the catalytic mechanism of aldol condensation with strong base and the characteristics of CaC2, as well as the reaction behavior observed, the catalysis of CaC2 for the

the yield of higher polymers increases and the IP yield decreases in the last 2 h at 120 and 150 °C. These results indicate that the temperature has a profound influence on the reaction, and high temperature is propitious to the condensation reaction. However, further prolonging the time can induce excessive reaction and lead to a higher ratio of higher polymers. Besides, it is hard to find a suitable model to represent the reaction kinetics for this heterogeneous catalytic reaction because of the intrinsic complexity of the consecutive reaction as well as the changing catalytic surfaces of CaC2. Figure 6 compares the catalytic performance of CaC2 under different particle sizes at 90 °C. The conversion of acetone and the yield of C6 increase remarkably with a decrease of the CaC2 particle size, while the yield of IP rises to 6.4% until the CaC2 particle size decreased to 253 nm. With decreasing particle size of CaC2, more catalytic sites are exposed on the surface of the CaC2 crystal, which greatly promotes the condensation of acetone. Moreover, the higher surface area of the catalyst CaC2 is beneficial for mass and heat transfer of the heterogeneous reaction. However, accompanied with the generation of IP, a certain amount of higher polymers is produced. These results indicate that the initiation period has been shortened through an increase in the surface area of the CaC2, providing more interfacial catalytic sites. On the other hand, Figure 7 compares the catalytic performance of CaC2 under different dosages at 150 °C. The conversion of acetone and the yield of IP increase D


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Industrial & Engineering Chemistry Research Table 1. Comparison between the Present Catalysis and the Others Reported Previously entry

catalytic system

acetone conversion (%)

IP yield (%)

temp (°C)

time (h)

reaction phase

ref

1 2 3 4 5 6 7 8 9

CaC2 25% NaOH or 32% KOH 20% NaOH Mg1−xAlxO1+x Ca(OH)2 MgO−ZrO2 MgO Zr-doped Mg−Al mixed oxides Mg−Al mixed oxides

81.2 21.0/23.3 17.0 37.0

21.3 4.0/5.5 6.6 17.8 25.2 26.8 12.1 26.7 19.2

150 170 150 200 350 327 450 240 290

2 0.5 3 1

liquid liquid liquid liquid vapor vapor vapor vapor vapor

this work 22c 22d 23 24 30 31 37a 37c

54.3 37.0 36.8 31.3

2

Scheme 2. Proposed Catalytic Condensation Pathways of Acetone

present system is proposed and presented in Scheme 2. It is assumed that the reaction begins with the formation of carbanion via the removal of an acidic α-proton of the acetone molecule by the basic anion of CaC2, which attacks the carbonyl of another acetone to form DAA. This step may be rate-controlling38,39 because of the limited exposure of the catalytic active sites on the surface of the CaC2 crystal particles. As the reaction proceeds, the intermediate DAA is converted to MO with the help of the strong dehydrating agent CaC2. The carbanion of acetone further attacks the carbonyl of MO to form trimeric enol, which is transferred to P via dehydration. It is worth pointing out that CaC2 herein is not only a basic catalyst but also a dehydrating agent to instantly remove the resultant water, which is helpful for forwarding the aldol condensation and exposing more catalytic sites due to the gradual corrosion of the CaC2 crystals. Finally, the intermediate P is converted to cyclic IP via the Michael addition reaction. Meanwhile, side reactions of P may occur via subsequent aldol condensation, leading to the formation of higher polymers such as tetramers, pentamers, etc. As the reaction proceeds, the catalyst CaC2 is consumed gradually until it is completely gone, leading to termination of the catalytic condensation of acetone.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel. and Fax: +8610 64410308. Notes

The authors declare no competing financial interest.

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REFERENCES

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4. CONCLUSIONS CaC2 is used here for the first time for the synthesis of IP through the liquid-phase catalytic condensation of acetone, and CaC2 shows better catalysis than all other liquid-phase catalysts under mild conditions. Further, higher temperature, smaller catalyst size, and higher mass ratio of CaC2 are beneficial to the synthesis of IP. The excellent catalysis of CaC2 is ascribed to its strong Lewis basicity and strong dehydrating ability, which is helpful for forwarding the aldol condensation. The present process offers a green, cost-effective, and efficient route for the synthesis of IP, as well as a raw material use of CaC2.

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Draining experiment, constituents confirming the liquid products, and analyses of the gas-phase products (PDF)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b00484. E


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Efficient Catalysis of Calcium Carbide for the Synthesis of Isophorone

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