Substituted Amide Hydrolysis in Hot Compressed Water Using ZrO

Mar 23, 2015 - Department of Environment Systems, Graduate School of Frontier ... kinetic analysis of several N-substituted amides with the Taft equat...
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Kinetics of N‑Substituted Amide Hydrolysis in Hot Compressed Water Using ZrO2 Catalyst Makoto Akizuki* and Yoshito Oshima Department of Environment Systems, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8563, Japan ABSTRACT: Hydrolysis reactions of N-substituted amides in hot compressed water with ZrO2 were investigated. ZrO2 was used as a typical solid base catalyst. Through the kinetic analysis of several N-substituted amides with the Taft equation, the inductive, steric, and hydrogen bonding effects of N-substituent on the hydrolysis reaction rate were evaluated quantitatively. The N-substitution strongly affected the hydrolysis reaction rate with ZrO2. The inductive and steric effects of N-substituent on the reaction rate with ZrO2 were suggested to be almost the same as that with homogeneous base catalyst (NaOH). On the other hand, the reaction rate with ZrO2 was less suppressed by hydrogen bonding between the amide group’s H atom and water or the other amide compared to that with NaOH.

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INTRODUCTION Hot compressed water is a promising reaction medium for both organic synthesis reactions and degradation reactions.1−4 One of the important reactions in hot compressed water is hydrolysis of amides. Hydrolysis of amides has been investigated as a fundamental acid or base catalyzed reaction and as a model reaction for degradation of proteins.5−7 Hydrolysis of amides is also important for wastewater treatment. Recently, water pollution caused by the manufacturing and usage of pharmaceuticals has been reported,8−10 and their effects on human and aquatic organisms have become a concern. Among these pharmaceuticals, amide pharmaceuticals, which contain amide groups on their chemical structure, were not efficiently removed by a typical activated sludge treatment.8 In a previous study about wet oxidation of amides, it was reported that C−N bond scission occurred and biodegradability increased after the treatment.11 Hydrolysis of amides in hot compressed water is considered to be a promising method for decomposing and detoxifying amide pharmaceuticals. Hydrolysis of amides at low temperatures is generally conducted in the presence of homogeneous acid catalysts or base catalysts. In hot compressed water, hydrolysis proceeds even without catalyst, and research regarding several amides such as formamide,6 acetamide,5,6,12,13 N-methylformamide,7 N-methylacetamide,7 propionamide,14 acrylamide,14 benzamide,12,13 and 5-cyanovaleramide15 have been reported. Duan et al. mentioned that a water molecule could act as a general base or acid catalyst, or two water molecules could take part in the transition state to assist hydrolysis.7 Although hydrolysis of amides in hot compressed water proceeds without catalyst, high temperature or long reaction times were required. In addition, the research about hydrolysis of secondary amides and tertiary amides, which are generally seen in amide pharmaceuticals such as N,N-diethyl-m-methylbenzamide, is still limited. More knowledge about the reactions of N-substituted amides is required. To promote acid or base catalyzed reactions in hot compressed water, the use of solid acid or base catalysts has attracted much attention as an environmentally friendly © 2015 American Chemical Society

method. Various kinds of reactions, such as hydration of olefins16,17 and degradation of biomass derived materials,18−20 have been investigated. In solid acid or base reactions in hot compressed water, water properties strongly affect reaction rate and selectivity. In the previous study, we investigated the effects of water properties on the acidity of TiO2 and WO3/TiO2 in sub- and supercritical water and reported that water density strongly affected the reaction mechanism using TiO2 catalyst.21 To control the reactions, elucidating the characteristics of solid acid or base catalyzed reactions in hot compressed water through kinetic analysis is important. In the present study, hydrolysis reactions of N-substituted amides (Figure 1) in hot compressed water were investigated.

Figure 1. Amides investigated in this research. Received: Revised: Accepted: Published: 3611

February 6, 2015 March 18, 2015 March 23, 2015 March 23, 2015 DOI: 10.1021/acs.iecr.5b00528 Ind. Eng. Chem. Res. 2015, 54, 3611−3617

Article

Industrial & Engineering Chemistry Research

the predefined reaction time, the reactor was cooled to an ambient temperature by a water bath. The reactions with NaOH as a homogeneous base catalyst were also conducted in order to compare the reaction kinetics of the reaction with solid base catalyst (ZrO2). The reactions were performed using the same experimental setup for the heterogeneous catalyzed reactions with small modification. Amide solution and NaOH solution (0.10 mol/L at ambient temperature and pressure) were pumped separately, and the preheated amide solution was mixed with the sodium hydroxide solution at the entrance of the reaction tube (SUS316; internal diameter, 1.0 mm; length, 6 m). The flow ratio of amide solution/sodium hydroxide solution was 9/1. Analysis. A gas chromatograph-flame ionization detector (GC-2014; Shimadzu Corp.) with a capillary column (InertCap Wax; GL Sciences, Inc.) and a high-performance liquid chromatography-UV detector (LC-980; JASCO Corp.) with packed column (Finepak SIL C18S; JASCO Corp.) were used for analyzing the content of organics in the effluents. X-ray diffraction (XRD) (SmartLab; Rigaku Corp.) and N2 adsorption−desorption (NOVA 2200e; Quantachrome Corp.) were used for characterizing the catalysts. Character of Catalysts. In the XRD measurement of ZrO2 after conditioning in hot compressed water, only the peaks of monoclinic-ZrO2 were measured. The Brunauer−Emmett− Teller (BET) surface area was 30.1 m2/g, pore volume was 0.163 cm3/g, and mean pore diameter analyzed by the Berret− Joyner−Halenda method was 14.2 nm for the ZrO2. The XRD patterns of TiO2 had both the peaks of anataseTiO2 and rutile-TiO2. The weight fraction of anatase-TiO2 estimated by the reference intensity ratio method was 0.87. The BET surface area was 50.3 m2/g, pore volume was 0.375 cm3/g, and mean pore diameter was 34.5 nm for the TiO2.

ZrO2, which is a typical solid base catalyst in hot compressed water,22 was mainly used as a catalyst. The purpose of this study is to elucidate the effects of N-substitution on amide hydrolysis kinetics in hot compressed water and to clarify the characteristics of the reaction using ZrO2 catalyst.

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EXPERIMENTAL METHODS Reagents. N,N-Diethyl-m-methylbenzamide, N,N-dimethylbenzamide, N-phenylbenzamide, and benzamide were purchased from Tokyo Chemical Industries Co., Ltd. Nmethylbenzamide, NaOH, and TiO2 were purchased from Wako Pure Chemical Industries, Ltd. Zirconium hydroxide was purchased from Nacalai Tesque, Inc. Distilled water was prepared by distillation equipment (RFD240HA; Advantec Toyo Kaisha, Ltd.). The aqueous solution of amides and distilled water were degassed by bubbling N2 gas prior to their use. Preparation of Catalysts. ZrO 2 was prepared by calcination of zirconium hydroxide at 400 °C for 4 h. After calcination, ZrO2 was conditioned in hot compressed water at 300 °C for 12 h to prevent the change of crystal structure during the reaction. TiO2 was used after calcination at 300 °C for 3 h. Each catalyst in powder form was pressed into a pellet, and the pellet was crushed and sieved into the granular forms having diameters of 0.18−0.30 and 0.30−0.50 mm. Experimental Procedure. The reactions with heterogeneous catalysts were conducted using a fixed bed flow reactor (Figure 2). The aqueous solution of amide was pumped using a

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RESULTS AND DISCUSSION Reactions of Amide Using ZrO2 Catalyst. Figure 3a shows the N,N-diethyl-m-methylbenzamide conversion without catalyst at 300 °C and 8.6 MPa. The reaction proceeded without catalyst in hot compressed water. The main reaction products were m-methylbenzoic acid and diethylamine, which were the hydrolysis products of N,N-diethyl-m-methylbenzamide. Figure 3b shows the N,N-diethyl-m-methylbenzamide conversion with ZrO2 and TiO2 at 300 °C and 10 MPa. ZrO2 and TiO2 were used as typical solid base or acid catalysts which are generally used in hot compressed water.22 To compare the amount of degraded amide in a unit time using solid catalysts with that in the absence of catalyst, contact time, defined as the product of the volume of fixed-bed reactor and the void fraction of the bed divided by the volumetric flow rate in the reactor, was used as an indicator of the reaction time. Regardless of the catalysts, the main reaction products were also m-methylbenzoic acid and diethylamine. Compared to the reaction without catalyst, the reaction was considerably promoted by ZrO2 catalyst. The reaction rate with ZrO2 was also larger than that with TiO2. It was reported that ZrO2 showed stronger basicity and weaker acidity than TiO2 in supercritical water.22 Therefore, it was suggested that basicity of ZrO2 contributed to the large reaction rate of hydrolysis. Effects of temperature and pressure on the reaction rate with ZrO2 were examined. Figure 4 shows the temperature dependence of N,N-diethyl-m-methylbenzamide conversion with ZrO2. W/F, defined as the weight of loaded catalysts

Figure 2. Schematic diagram of experimental equipment.

high-pressure pump (PU-2080; JASCO Corp.), preheated, and fed into a fixed bed reactor set in a heating oven (GC 353B; GL Sciences, Inc.). The concentration of the amide solution was 2.1 × 10−3 mol/L (N,N-diethyl-m-methylbenzamide), 1.0 × 10−3 mol/L (N,N-dimethylbenzamide, N-methylbenzamide, benzamide), and 2.0 × 10−4 mol/L (N-phenylbenzamide) at ambient temperature and pressure. The amount of loaded catalyst was 8.1 × 10−2 to 1.0 × 101 g, and the height of the packed catalyst was 0.47−45 cm. The particle Reynolds numbers were 4.0−49 for the experiments of temperature and pressure dependence and 7.3−61 for the experiments of Nsubstitution effect. The stream emitted from the reactor was cooled immediately in a water-cooled heat exchanger and then depressurized using a back pressure regulator (SCF-Bpg; JASCO Corp.). The reactions without catalyst were conducted using a batch reactor. The reactor was made of SUS316, and its volume was 8 mL. A 4 ml sample of amide solution was loaded to the reactor in a glovebox filled with N2 gas, and then the reactor immersed to an isothermal fluidized sand bath to start the reaction. After 3612

DOI: 10.1021/acs.iecr.5b00528 Ind. Eng. Chem. Res. 2015, 54, 3611−3617

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Figure 5. Effect of pressure on N,N-diethyl-m-methylbenzamide conversion with ZrO2 at 360 °C. W/F = 3.7 × 104 kg s/m3. Particle size of ZrO2: 0.30−0.50 mm.

conducted with ZrO2 at 300 °C and 10 MPa. Reactions without catalyst and with NaOH as a homogeneous base catalyst were also examined to compare the reaction rate of these reaction systems with the reaction rate with ZrO2. Regardless of catalyst species and amide species, main products were hydrolysis products of corresponding amide species. In the reaction of each N-substituted amide without catalyst, benzamide was also produced as a minor product. However, the contribution to the reaction rate of N-substituted amides was estimated to be less than 8%, and this reaction did not affect the following discussion. Figure 6 shows the conversion of each amide. In the reaction with ZrO2, the effect of N-substitution on the reaction rate was large. Without the catalyst, the difference in the reaction rate of each amide was small. In the reaction with NaOH, Nsubstitution also affected the reaction rate, but the effect of each N-substituent was different from that with ZrO2. To discuss the difference in the reaction rate of each amide quantitatively, kinetic analysis was conducted. Figure 7 shows the pseudo-first-order plot of the reaction with ZrO2 at 300 °C and 10 MPa as an example. The straight relationships between W/F and −ln(1 − X) was observed. In the reaction without catalyst and with NaOH, plots of reaction time and −ln(1 − X) also gave straight lines. Therefore, we regarded the reactions as the first-order reaction of amide, and kinetic rate constants were evaluated from slopes of the pseudo-first-order plot. In solid catalyzed reactions, mass transfer might affect the reaction rate. Therefore, the influence of mass transfer on the reaction rate was estimated according to a published literature method.23 First, the effect of external mass transfer on the reaction rate was evaluated from the relationships between the amide concentration in bulk fluid (Cb) and that on the catalyst surface (Cs). For the evaluation, the literature values of water properties were used,24 and molecular diffusion coefficient of amides were estimated using the Wilke and Chang equation.25 The results are summarized in Table 1. The value of (Cb − Cs)/ Cb was at most several percent for all amides; this result indicates that the external mass transfer was negligible. Next, the effect of internal mass transfer on the reaction rate was assessed using the effectiveness factor (η), defined as the observed reaction rate divided by the reaction rate without mass transfer limitation. Effective diffusion coefficient of amides in catalyst pores was estimated using the random pore model.26 From N2 adsorption−desorption analysis, ZrO2 catalyst had only large pores between catalyst powders. Therefore, the

Figure 3. N,N-Diethyl-m-methylbenzamide conversion at 300 °C: (a) without catalyst and (b) with catalyst. ⧫, ZrO2; □, TiO2.

Figure 4. Effect of temperature on N,N-diethyl-m-methylbenzamide conversion with ZrO2. ●, 240 °C, 10 MPa; ◊, 260 °C, 10 MPa; ▲, 280 °C, 10 MPa; □, 300 °C, 10 MPa; ⧫, 330 °C, 22 MPa; ○, 360 °C, 22 MPa. Particle size of ZrO2: 0.30−0.50 mm.

divided by the volumetric flow rate in the reactor, was used as an indicator of the reaction time in subsequent sections. The reaction rate increased monotonically with increase of temperature. In addition, the conversion at 360 °C and W/F = 3.7 × 105 kg s/m3 was close to 1, suggesting that the reaction is considered irreversible under such low amide concentration under our experimental conditions. Figure 5 shows the pressure dependence of N,N-diethyl-mmethylbenzamide conversion with ZrO2 at 360 °C and W/F = 3.7 × 104 kg s/m3. The conversion was almost the same for all reaction pressures, and this result suggests that the reaction rate was not influenced by water density under such high water density conditions. In addition, this result also suggests that the basicity of ZrO2 was not changed with water density. Kinetic Analysis of N-Substituted Amides Hydrolysis. Reactions of several N-substituted amides and benzamide were 3613

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Figure 7. Pseudo-first-order plot of the reaction with ZrO2 at 300 °C and 10 MPa: (a) N,N-diethyl-m-methylbenzamide and (b) other amides. ●, N,N-diethyl-m-methylbenzamide; ◊, N,N-dimethylbenzamide; ▲, N-methylbenzamide; ⧫, N-phenylbenzamide; □, benzamide. Particle size of ZrO2: ●, ◊, and ▲, 0.30−0.50 mm; ⧫ and □, 0.18− 0.30 mm.

reaction, and substituent having large steric hindrance suppressed the reaction. In addition, existence of H atom bonded to N atom of amide group also suppressed the reaction because H atom could form hydrogen bond with water or other amide molecules. For evaluating inductive and steric effects of substituent on the reaction rate of aliphatic compounds quantitatively, the Taft equation was generally used.28 They modified the Taft equation, and evaluated effects of these three factors on the reaction rate of methacrylamides (CH2 C(CH3)CONR1R2) separately.27 The modified Taft equation was described as

Figure 6. Conversion of each amide at 300 °C: (a) with ZrO2, (b) without catalyst, and (c) with NaOH. ●, N,N-diethyl-m-methylbenzamide; ◊, N,N-dimethylbenzamide; ▲, N-methylbenzamide; ⧫, Nphenylbenzamide; □, benzamide. Particle size of ZrO2: ●, ◊, and ▲, 0.30−0.50 mm; ⧫ and □, 0.18−0.30 mm.

log k = log k 0 + ρ(σ1 + σ2) + δE N + hn

effective diffusion coefficients in these pores were estimated, and the values of our experiments were 3.5−4.8 × 10−9 m2/s. The results are shown in Table 1. In the reaction of some amides such as benzamide, mass transfer affected the reaction rate because of larger reaction rate. The estimated values of η were used to evaluate the reaction rate constants without mass transfer limitation. Table 2 summarizes the kinetic rate constants of each amide and each reaction system. Using these data, the difference in the reaction rate of each N-substituted amide is discussed in the following section. Quantitative Analysis of N-Substitution Effect Using Taft Equation. In the previous research about alkaline hydrolysis of N-substituted methacrylamides, it was reported that the reaction rate was determined by three main factors: by inductive and steric effects of N-substituent, and by the ability of the amides to form hydrogen bonds.27 In the case of alkaline hydrolysis, more electron-donating substituent suppressed the

(1)

where k is the rate constant and k0 is the reference rate constant. σ1 and σ2 are the inductive constants of R1 and R2. EN is the steric constant of NR1R2, and the value of CHR1R2 was taken as EN because NR1R2 and CHR1R2 are isosteric. n is the number of H atoms bonded to the N atom of amide group. ρ, δ, and h are coefficients which characterize the sensitivity to the corresponding factor. Using the modified Taft equation, the effects of Nsubstitution on hydrolysis kinetics in hot compressed water were analyzed quantitatively. Prior to analysis, effects of m-CH3 group bonded to the aromatic ring of N,N-diethyl-mmethylbenzamide was estimated. m-CH3 group is considered to show only inductive effect. Because m-methylbenzamide was difficult to obtain as a reagent, the reaction of pmethylbenzamide, which also shows only inductive effect and the effect of which is larger than that of m-methylbenzamide, was examined. The reaction rates of p-methylbenzamide 3614

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Industrial & Engineering Chemistry Research Table 1. Effects of Mass Transfer on Reaction with ZrO2 at 300°C and 10 MPa amide species

catalyst diameter (mm)

concentration in bulk fluid (Cb) (mol/dm3)

concentration difference in fluid film [(Cb − Cs)/ Cb] (%)

effectiveness factor (η)

0.30−0.50

1.5 × 10−3

7.1 × 10−2 − 8.7 × 10−2

0.99

0.30−0.50 0.30−0.50 0.18−0.30 0.18−0.30

7.2 7.2 1.4 7.2

0.38−0.48 0.30−0.55 0.83−1.2 1.5−2.5

0.94 0.92 0.89 0.77

N,N-diethyl-mmethylbenzamide N,N-dimethylbenzamide N-methylbenzamide N-phenylbenzamide benzamide

× × × ×

10−4 10−4 10−4 10−4

Table 2. Kinetic Rate Constants and Taft Equation Parameters of Each Amide Taft equation parameter amide species N,N-diethyl-mmethylbenzamide N,N-dimethylbenzamide N-methylbenzamide N-phenylbenzamide benzamide

Nsubstituent Et, Et Me, Me H, Me H, Ph H, H

kinetic rate constant

inductive effect (σ1 + σ2)28

steric effect (E)28

hydrogen atom (n)

ZrO2 (m3/kg s)

without catalyst (s−1)

NaOH (s−1)

−0.2

−1.98

0

2.2 × 10−3

5.0 × 10−5

1.2 × 10−3

−0.47 −0.07 −0.38 0

0 1 1 2

3.1 × 10−2 4.8 × 10−2 0.16 0.53

1.7 6.3 8.1 1.5

0 0.49 1.09 0.98

× × × ×

10−4 10−5 10−5 10−4

2.4 7.3 3.8 1.3

× × × ×

10−2 10−3 10−2 10−2

reaction with NaOH, and this indicated that the reaction with ZrO2 was also a base-catalyzed reaction. However, the hydrogen bond coefficient (h) of ZrO2 was larger than that of NaOH. One possible explanation is that hydrogen bond formation of amide molecule on ZrO2 surface with water or with the other amide was suppressed compared to amide molecule in bulk water, as shown in Figure 8. It was reported

without catalyst were almost the same as that of benzamide, and it indicated that the substituent did not affect the reaction rate. In the reaction with ZrO2, the kinetic rate constant of pmethylbenzamide was 10.5% smaller than that of benzamide. Because the inductive constant of p-CH3 group is 0.17 and that of m- CH3 group is 0.07,28 m-CH3 substituent was estimated to suppress the reaction rate about 4.5%. This value was small enough and did not affect the following discussion. The inductive constants (σ1 and σ2), steric constants (EN),28 and the number of H atom of amide group (n) of amides are also shown in Table 2. Using these values, the kinetic rate constants, and eq 1, the coefficients (ρ, δ, h) of each reaction system (with ZrO2, without catalyst, with NaOH) were evaluated. Because the modified Taft equation was originally applicable to N-monosubstituted amides (n = 1) and Ndisubstituted amides (n = 0), the coefficients were determined using the data other than benzamide (n = 2). The effect of two H atoms of benzamide on kinetic rate constants will be discussed later. The calculation was conducted using equation solving software (EQUATRAN-G; Omega Simulation Co., Ltd.). The coefficients and the regression coefficients of Taft plots are shown in Table 3.

Figure 8. Plausible explanation for the difference of hydrogen bonding effect in the reaction with NaOH and with ZrO2.

Table 3. Taft Equation Coefficients of Each Reaction System reaction system

log k0

ρ (inductive)

ZrO2 without catalyst NaOH alkaline hydrolysis at 70 °C27

−1.2 −3.6 −1.3 −4.1

1.2 0.35 1.5 1.0

δ (steric)

h (hydrogen bond)

regression coefficient (R)

0.60 0.31 0.66 0.78

−0.62 −0.72 −1.5 −1.4

1.0 1.0 1.0 0.97

that the rate-limiting step of the base-catalyzed amide hydrolysis was the degradation of the tetrahedral intermediate, which was produced by addition of one or two hydroxide ions to the amide molecule.29 If N atom of the amide molecule had an H atom, the reaction is considered to be suppressed because the intermediate was stabilized by hydrogen bond. On the other hand, the intermediate on base site of ZrO2 might be relatively difficult to make hydrogen bond because of steric hindrance; therefore, the suppression effect of hydrogen bonding on the reaction rate with ZrO2 was smaller than that with NaOH. In the reaction without catalyst, the inductive coefficient (ρ) was smaller than that of other reaction systems. A previous report suggested that two water molecules could take part in the transition state to assist amide hydrolysis in hot compressed water without catalyst.7 In the case of this reaction mechanism, the inductive coefficient should be smaller than that of basecatalyzed mechanism because the transition state is considered

All the coefficients of the reaction with NaOH were almost the same as the reported value of alkaline hydrolysis at 70 °C,27 and this result suggests that the reaction mechanism of the reaction with NaOH at 300 °C was the same as that of the base-catalyzed reaction at low temperature. The inductive and steric coefficients (ρ and δ, respectively) in the reaction with ZrO2 were almost the same as that in the 3615

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to have less electric charge. Therefore, smaller inductive coefficient in the reaction without catalyst was consistent with the previously proposed reaction mechanism in hot compressed water without catalyst. In addition, to discuss the hydrogen bonding effects of benzamide, the values of hn in eq 1 were calculated using evaluated ρ and δ (Table 3), Taft equation parameters of benzamide (Table 2), and the kinetic rate constant of benzamide. The values of hn for benzamide were −0.20 (ZrO2), −0.52 (without catalyst), and −2.1 (NaOH). The benzamide’s hn value of NaOH indicated that although the suppression effect of each H atom was small, total suppression effect of H atoms was larger compared to that of Nmonosubstituted amides (hn = −1.5). On the other hand, the benzamide’s hn value of ZrO2 suggested that the suppression effect of H atoms existed in benzamide was smaller than that existing in N-monosubstituted amides (hn = −0.62). Although more mechanistic consideration is needed regarding the effects of H atoms existing in benzamide, these results were consistent with the aforementioned findings that the suppression effect of hydrogen bonding on the reaction rate with ZrO2 was smaller than that with NaOH.

REFERENCES

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CONCLUSION Hydrolysis reactions of N-substituted amides with ZrO2 catalyst in hot compressed water were investigated. ZrO2 considerably promoted the hydrolysis of N,N-diethyl-m-methylbenzamide compared to the reaction without catalyst and with TiO2 catalyst probably because of the basicity of ZrO2. The hydrolysis reaction rate with ZrO2 increased monotonically with increase of temperature and did not change with increase of pressure. N-substitution of amides largely affected the hydrolysis reaction rate with ZrO2 catalyst. In addition, the N-substitution effects were different from that in the reaction without catalyst and with NaOH, which was used as an example of homogeneous base catalyst. Through kinetic analysis, it was suggested that the inductive effect and the steric effect of Nsubstituent in the reaction with ZrO2 were almost the same as that in the reaction with NaOH. On the other hand, the suppression effect on the reaction rate caused by hydrogen bonding between amide group’s H atom and water or the other amide was small in the reaction with ZrO2 compared to that with NaOH. Plausible explanation of these results is that hydrogen bond formation of amide molecule on ZrO2 surface with water or with the other amide was inhibited compared to amide molecule in bulk water; therefore, the suppression effect of hydrogen bonding on the reaction rate with ZrO2 was smaller than that with NaOH.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel./Fax: +81 4 7136 4694. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work has been supported by Kurita Water and Environment Foundation Grant (13A027). The XRD analyses were performed using facilities of the Institute for Solid State Physics, The University of Tokyo. All of this support is very much appreciated. 3616

DOI: 10.1021/acs.iecr.5b00528 Ind. Eng. Chem. Res. 2015, 54, 3611−3617

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DOI: 10.1021/acs.iecr.5b00528 Ind. Eng. Chem. Res. 2015, 54, 3611−3617