Jie Fu,Haoming Ren,Ju Zhu,Xiuyang Lu..,*

Catalysis,Kinetics and Reaction Engineering

Hydrolysis Kinetics of 2-Pyridinecarboxamide,3-Pyridinecarboxamide and 4-Pyridinecarboxamide in High-Temperature Water☆

Jie Fu1,Haoming Ren1,Ju Zhu2,Xiuyang Lu..1,*

1Key Laboratory of Biomass Chemical Engineering of Ministry of Education,Department of Chemical and Biological Engineering,Zhejiang University,Hangzhou 310027,China2School of Biological and Chemical Engineering,Zhejiang University of Science and Technology,Hangzhou 310023,China

A R T I C L EI N F O

Article history:

High-temperature water

Hydrolysis

Pyridinecarboxamide

Kinetics

Activation energy

A kinetic study is reported here on hydrolysis of three pyridinecarboxamides in high-temperature water in the temperature range of 190-250°C at 8 MPa.2-Pyridinecarboxamide,3-pyridinecarboxamide and 4-pyridinecarboxamide hydrolyze to corresponding picolinic acids.2-Picolinic acid is further decarboxylated to pyridine.Experiments at different temperatures show that the f i rst-order rate constants display an Arrhenius behavior with activation energies of(110.9±2.3),(70.4±2.1)and(61.4±1.8)kJ·mol?1for 2-pyridinecarboxamide,3-pyridinecarboxamide and 4-pyridinecarboxamide,respectively.These kinetic parameters for pyridinecarboxamide hydrolysis are more reliable and accurate than those from the consecutive hydrolysis of cyanopyridines.

?2014TheChemicalIndustry andEngineeringSocietyofChina,andChemicalIndustryPress.Allrightsreserved.

1.Introduction

High-temperaturewater(HTW),liquidwaterabove180°C,isagreen medium for chemical reactions.The properties of HTW are very different from those of ambient water.It has acid-or base-catalytic ability,good solubility for organic compounds,and wide tunability of physical properties[1-7].In recent years,the research on hydrolysis of nitriles in HTWattractsmuchattentionforpotentialapplicationsintreatmentofindustrialwastestreams[8]andproductionofcarboxylicacids[9-11],since HTW provides a green strategy without strong acid or base catalyst. Amide is the intermediate product of nitrile hydrolysis.A better understanding on the hydrolysis of amides in HTW would be important to useHTWforwastecleanupandcarboxylicacidproduction.Moreover,hydrolysis of amides in HTW may occur in the hydrothermal processing of proteincontainingbiomass[12].Therefore,thestudyonhydrolysisofamides could be useful for transformation of biomass to chemicals or fuels.

There is a considerable amount of literature on the hydrolysis of amide in HTW,but concentrating on aliphatic and aromatic amides[8, 12-23].ThehydrolysisofheterocyclicamidesinHTWisrarelyreported. In our previous work[24],the hydrolysis kinetics of 2-cyanopyridine, 3-cyanopyridine and 4-cyanopyridine in HTW were studied.The rate constants for the hydrolysis of 2-cyanopyridine,3-cyanopyridine, 4-cyanopyridine,2-pyridinecarboxamide,3-pyridinecarboxamide and 4-pyridinecarboxamide were obtained at each temperature by the equations of f i rst-order consecutive hydrolysis,and their activation energies were obtained by the Arrhenius equation.A model was established for the consecutive hydrolysis of the three cyanopyridines. However,thepredictionforhydrolysisofthethreepyridinecarboxamides with the model does not f i t the experimental data well,indicating that the kinetic parameters for hydrolysis of the three pyridinecarboxamides arenotsatisfactory.Thepyridinecarboxamidesareintermediateproducts in the consecutive reactions[24],and their measurement and data correlation may be diff i cult.More reliable kinetic work is needed for the hydrolysis of pyridinecarboxamides.

In this study,the hydrolysis kinetics of 2-pyridinecarboxamide, 3-pyridinecarboxamide,and 4-pyridinecarboxamide in HTW are investigated.Fig.1 shows the reaction pathways for hydrolysis of the three pyridinecarboxamides(2-picolinic acid can be decarboxylated subsequently).Withthekineticparameters,amodelisestablishedforthehydrolysis of these three pyridinecarboxamides.Moreover,the effects of substituent position and heterocyclic N on hydrolysis of heterocyclic amides in HTW are provided.

Fig.1.Reaction pathway for hydrolysis of pyridinecarboxamides.

2.Experimental

4-Pyridinecarboxamide(98%)was obtained from ACROS Organics,Belgium.3-Pyridinecarboxamide(99.5%)and 3-picolinic acid(99.5%)were obtained from Chengdu Kelong Chemical Co. Ltd.,China.2-Pyridinecarboxamide(99%)was obtained from TCI Chemical Co.Ltd.,China.4-Picolinic acid(99%)was obtained from Sinopharm Chemical Reagent Co.Ltd.,China.2-Picolinic acid(99%)was obtained from J&K Chemical Ltd.,China.They are all of analytical reagent gradeandwereusedasreceived.Deionizedwaterwaspreparedinhouse.

The reactor,experimental procedure,sampling,and analysis were described in our previous work[24].

Product yield was calculated as the moles of product divided by initial moles of pyridinecarboxamide loaded in the reactor.The mole balance was calculated as the total moles of products and pyridinecarboxamide in the reactor divided by the initial moles of pyridinecarboxamide.

3.Results and Discussion

3.1.Hydrolysis of 2-pyridinecarboxamide

Fig.2 shows the hydrolysis of 2-pyridinecarboxamide at 220°C, 8 MPa,and an initial 2-pyridinecarboxamide concentration of 0.5 g·L?1. 2-Pyridinecarboxamide decreased with time,while 2-picolinic acid and pyridine increased.The yield of 2-picolinic acid did not increase after 150minbuttheyieldofpyridineincreasedfurther,signalingthereaction pathway of 2-pyridinecarboxamide→2-picolinic acid→pyridine.The total moles in the reaction system were around 100%,indicating that 2-picolinic acid and pyridine are the only products.In the hydrolysis of 3-pyridinecarboxamide and 4-pyridinecarboxamide under the same conditions,pyridine was not found in the reaction systems.The total moles of these two reaction systems were also around 100%,which indicates that no by-product is yielded.

3.2.Effect of temperature on hydrolysis of 2-pyridinecarboxamide

Fig.3 shows the effect of temperature on hydrolysis of 2-pyridinecarboxamideataninitial2-pyridinecarboxamide concentration of 0.5 g·L?1and reaction pressure of 8 MPa.Pyridine is a product and its yield increases with time,so decarboxylation occurs in the system.The yield of 2-picolinic acid shows a characteristic of intermediate product,with the maximum value of 8%,6%and 4%at 230,240 and 250°C,respectively.Curves in Fig.3(a)correspond to the f i rst-order reaction model.

Fig.2.Hydrolysis of 2-pyridinecarboxamide at 220°C.

3.3.Effect of temperature on hydrolysis of 3-pyridinecarboxamide

Fig.4 shows the effect of temperature on hydrolysis of 3-pyridinecarboxamide at an initial 3-pyridinecarboxamide concentration of 0.5 g·L?1and reaction pressure of 8 MPa.3-Picolinic acid is the only product.Curves in Fig.4(a)correspond to the f i rst-order kinetic model.

3.4.Effect of temperature on hydrolysis of 4-pyridinecarboxamide

Fig.5 shows the effect of temperature on hydrolysis of 4-pyridinecarboxamide at an initial 4-pyridinecarboxamide concentration of 0.5 g·L?1and reaction pressure of 8 MPa.4-Picolinic acid is the only product.Curves in Fig.5(a)correspond to the f i rst-order kinetic model.

3.5.Kinetics of hydrolysis

It has been shown that hydrolysis of amides follows f i rst-order kinetics[8,12].Thus we f i t the data with ln(1?conversion)vs.time at each temperature using Trendline of Excel.The slope of the straight line represents the rate constant of hydrolysis at a certain temperature. Table 1 presents the results.The uncertainty is obtained by the LINEST function of Excel and expressed as standard deviations.The curves in Figs.3-5 show that the f i rst-order kinetics f i t the experimental data well.The variation of rate constants with temperature follows the Arrhenius equation.The Arrhenius parameters determined by linear regression of lnk vs.1/T are shown in Table 1.The kinetic data for hydrolysis of 2-pyridinecarboxamide,3-pyridinecarboxamide,and 4-pyridinecarboxamidefromtheconsecutivehydrolysisof2-cyanopyridine,3-cyanopyridine and 4-cyanopyridine[24]are also presented in Table 1,in which the rate constants of pyridinecarboxamides were obtained by f i tting the conversion of cyanopyridine,yield of pyridinecarboxamide,picolinic acid and even pyridine with the equations of f i rst-order consecutive reaction,and the errors in experiments and f i tting were accumulated.Although the kinetic parameters for hydrolysis of cyanopyridines and pyridinecarboxamides can be obtained simultaneously[24],the result is unsatisfactory.In this work, pyridinecarboxamides are used as reactants and the rate constants are obtained by directly f i tting the conversion of pyridinecarboxamides, so that experimental data and f i tting results for hydrolysis of pyridinecarboxamides are more reliable.

3.6.Effect of heterocyclic N and substituent position on hydrolysis

At 300°C and 8.7 MPa pressure,the rate constant of benzamide obtained is 0.0115 min?1[8].Based on our kinetic parameters,the rate constants at 300°C for 2-pyridinecarboxamide,3-pyridinecarboxamide, and 4-pyridinecarboxamide are 0.205,0.0162,and 0.0199 min?1, respectively.They are all greater than the rate constant of benzamide, and the rate constant of 2-pyridinecarboxamide is 18 times that of benzamide.It indicates that the heterocyclic N atom can lower the hydrothermal stability of benzamide,especially for ortho-pyridinecarboxamide. The activation energy for hydrolysis of 2-pyridinecarboxamide is much larger than those of 3-pyridinecarboxamide and 4-pyridinecarboxamide.The effect of substituent position on activation energy for pyridinecarboxamide hydrolysis is ortho＞meta＞para. Different from 3-pyridinecarboxamide and 4-pyridinecarboxamide, the hydrolysis of 2-pyridinecarboxamide yields a large amount of pyridine,which indicates that both ortho-pyridinecarboxamide and ortho-picolinic acid have lower hydrothermal stability.It is probably caused by the short distance between the substituents and heterocyclic Natom.Overall,ortho-pyridinecarboxamideandpicolinicacidaremore active than meta-and para-position pyridinecarboxamides and picolinic acids.

Fig.3.Conversion of 2-pyridinecarboxamide(a)yield of 2-picolinic acid(b)yield of pyridine(c)and mole balance(d)in hydrolysis of 2-pyridinecarboxamide at different temperatures.

Fig.4.Conversion of 3-pyridinecarboxamide(a)and mole balance(b)in hydrolysis of 3-pyridinecarboxamide at different temperatures.

Fig.5.Conversion of 4-pyridinecarboxamide(a)and mole balance(b)in hydrolysis of 4-pyridinecarboxamide at different temperatures.

Table 1Rate constants and activation energies for hydrolysis of pyridinecarboxamides(this work)and the consecutive hydrolysis of cyanopyridines[24]

4.Conclusions

2-Pyridinecarboxamide,3-pyridinecarboxamideand4-pyridinecarboxamide hydrolyze in hours in high-temperature water in the temperature range of 190-250°C at 8 MPa.For 3-pyridinecarboxamide and 4-pyridinecarboxamide,corresponding products are picolinic acids.2-Pyridinecarboxamide yields 2-picolinic acid and pyridine as products.The activation energies determined are(110.9±2.3),(70.4±2.1)and(61.4±1.80)kJ·mol?1for hydrolysis of 2-pyridinecarboxamide,3-pyridinecarboxamide and 4-pyridinecarboxamide,respectively.Compared to the rate constants and activation energies for pyridinecarboxamide hydrolysis obtained from the consecutive hydrolysis of cyanopyridines,those obtained directly from the hydrolysis of pyridinecarboxamides show smaller standard deviations and higher accuracies.

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30 November 2012

☆

Supported by the National Natural Science Foundation of China(21176218),and Zhejiang Key Innovation Team of Green Pharmaceutical Technology(2010R50043).

*Corresponding author.

E-mail address:luxiuyang@zju.edu.cn(X.Lu).

http://dx.doi.org/10.1016/j.cjche.2014.06.024

1004-9541/?2014 The Chemical Industry and Engineering Society of China,and Chemical Industry Press.All rights reserved.

Received in revised form 18 March 2013 Accepted 1 April 2013

Available online 30 June 2014