Research On Hydrolysis Reaction Of Nitriles And Amides In Near-Critical Water

Near-critical water(near-critical water,NCW)refers to the compressed liquid water at the temperature between 170℃and 350℃.The outstanding performance of NCW comparing to the water at normal temperature and pressure is the large ionization constant.And thus,it possesses the property of acid/base catalytic function which will enable some of the acid-base catalytic reactions to occur without the addition of any acid/base catalysts.NCW also has a small enough dielectric constant,and can dissolve the organic and inorganic compounds.At the same time, near-critical water also has an excellent mass transfer and green,environmental protection properties,etc.And therefore it has the potential applications in green chemistry and chemical process,organic reactions areas.The literature review section of the thesis gave a brief introduction of the important applications in the green chemical process as well as the status of organic reactions research in NCW,and also summarized the applications in different kind of reactions such as hydrolysis,dehydration/hydration,alkylation,acylation, Diels-Alder reactions,rearrangements,condensations,hydrogen isotope exchange reaction,oxidation-reduction reaction,organometallic reactions.In present research, we have designed one type of reactor-batch reactor based on a full investigation of different types of reactions in NCW,which requires different type of reactors and reactor materials,also considering a combination of chemical thermodynamics and kinetics theory as well as the mass transfer,heat transfer and material balance in the reaction process,and as well as involving a consideration of the characteristics of our reactions.Nitrile is a kind of organic compounds containing cyano group,it is a starting material to synthesize a series of amine,acid and polymer.Hydrolysis reactions of nitriles have been widely applied in plentiful of organic synthesis such as amino acid, amide,carboxylic acid and its derivatives,which occupy an extremely important position in organic synthesis.Amides are also widely spread all over the nature,such as protein is the polymer linkaged with amide bond,it is also the hydrolysis intermediate of nitrile.The amide can be hydrolyized to acid as well the amide linkaged in protein hydrolyizing to amino acid.Research on amide hydrolysis can further understand clearly the deep hydrolysis reaction mechanism of nitrile as well as understanding the reactivity of protein amide linkage at a high temperature water.Up to now,researches on nitriles and amides hydrolysis especially dinitriles, diamides,N-alkyl substituted amides in near-critical water were relatively few and lack of systematical exploration and summary.In this dissertation, iminodiacetonitrile,adiponitrile,5-cyanovaleramide,adipamide and N-methylacetamide were selected as research models,and using self-developed high-temperature and high-pressure reactor to investigate their reaction kinetics and mechanisms in NCW,and finally the rule of these kind of nitriles and amides hydrolysis in NCW were also explored.1.Research on the hydrolysis of iminodiacetonitrile in near-critical waterFirst of all,this study utilizing the high-pressure reactor designed by ourselves attempt to employ NCW as solvent and reactant for iminoacetonitrile hydrolysis,and using rich of H⁺and OH^-dissociated by itself to realize the successful hydrolysis of iminoacetonitrile.Near-critical water is a promising reaction medium for conducting the hydrolysis of nitriles without the addition of any acid/base catalysts. Iminodiacetonitrile(IDAN)was chosen as a heteroatom-containing model compound for the hydrolytic kinetic and mechanism investigations of dinitriles because IDAN is an important raw material for the preparation of iminodiacetic acid (IDA)which is an indispensable intermediate in herbicide manufacturing. Hydrolysis of IDAN in near-critical water,without added catalysts,has been successfully conducted.Hydrolysis kinetics data of the reaction were measured at 10MPa with temperature and residence time ranges of 200-260℃and 10-60 min, respectively.The effects of temperature,pressure,and initial reactant/water ratio on conversion and yield have been investigated.Final reaction products primarily included iminodiacetic acid(IDA)and ammonia associated with other byproducts; gas formation was negligible.The maximum yield of IDA was 92.3mol%at 210℃, 10 MPa with a conversion almost of 100%.The apparent activation energy and lnA(min^-1)of IDAN hydrolysis were evaluated as 45.77±5.26 kJ/mol and 8.6±0.1 based on the assumption of pseudo-first-order reaction kinetics.Reaction mechanism and network are similar to that of base-catalyzed reactions of nitriles examined in less severe conditions.In this study,we first realized the green preparation of iminodiacetic acid,and provided basic experimental data for other dinitriles hydrolysis in NCW.2.Research on the hydrolysis of adiponitrile in subcritical waterHydrolysis of adiponitrile(ADN)was performed in subcritical water to research products distribution dependence on experimental conditions.An L₂₅(5⁶) orthogonal array design(OAD)with six factors at five levels using statistical analysis was employed to optimize the experimental conditions for each product in which the interactions between the variables were temporarily neglected.The six factors contained adiponitrile concentration(ADN con.,wt.%),temperature (Tem.,℃),time(T.,h),percentage of additives(reactant/additive,wt./wt.%), additives(A.),pressure(P.,MPa).Effects of these parameters were investigated using the direct analysis and analysis of variance(ANOVA)to determine the relationship between experimental conditions and yield levels of different products. The results showed that ADN con.and Tern,had significant influences on the yields of adipamide,adipamic acid,and adipic acid at P＜0.05,T.was the statistically significant factor for the yield of 5-cyanovalermic acid at P＜0.05,and ADN con.was the significant factor for the yield of 5-cyanovaleramide at P＜0.1.Finally,five supplementary experiments were conducted under optimized conditions predicted by the Taguchi method;the results showed that the obtained yield of each product was higher than that of the highest in the 25 experiments,also proving the reliability of orthogonal method.Carbon balance was calculated to demonstrate good experimental technique and reliable results.Based on experimental results,a possible reaction mechanism was proposed.Application of orthogonal test method, not only less cumbersome process of the experiment,but also provides a useful reference for the experimental conditions optimization study of other substances hydrolysis in NCW.3.Research on the hydrolysis of adipamide in near-critical water Hydrolysis of adipamide(ADAM)in high temperature water without added catalysts has been successfully demonstrated at temperatures ranging from 250 to 310℃under estimated pressures of up to 30 MPa for reaction times of 30 to 120 min. Final reaction products resulting from the hydrolysis of ADAM,primarily including adipamic acid and adipic acid,were detected by high performance liquid chromatography.Effects of temperature,time,pressure,reactant concentration,and pH on ADAM hydrolysis reaction kinetics have been investigated.The relations between ADAM concentration and residence time revealed that hydrolysis of ADAM inclines to pseudo-second-order reaction kinetics at the investigated temperature ranges.The higher content of adipamic acid in the reaction products at the initial hydrolysis reaction stage suggested that only one amide group was attacked at one time then followed by transformation to a carboxyl.The reaction rate constants, average apparent activation energy and pre-exponential factor were evaluated according to the Arrhenius equation.Based on the experimental results,hydrolysis reaction scheme and mechanism were proposed.The high reactivity of diamide in NCW provides an experimental basis for the other pollution-free degradation of polyamides,and promotes the applications of NCW as a green reaction medium in the other hydrolysis reaction.4.Research on the hydrolysis of 5-cyanovaleramide in near-critical waterHydrolysis of 5-cyanovaleramide(5-CVAM)in near-critical water,without the addition of any catalysts,was investigated.The experiments were conducted at temperatures of 250℃,270℃,290℃,310℃under the estimated pressure of 20 MPa for reaction times of 30 min,60 min,90 min,120 min.Final reaction products resulting from the hydrolysis of 5-CVAM,primarily including adipamide,adipamic acid,adipic acid,and trace of 5-cyanovalermic acid,were detected by high performance liquid chromatography;gas formation was negligible. 5-cyanovaleramide can be hydrolyzed to amide and acid in near-critical water without the addition of any catalysts.A nearly complete conversion was achieved at a reaction time of 120 min,at temperature of 310℃.The relations between the 5-CVAM concentration and residence time reveal that hydrolysis of 5-CVAM shows pseudo-second-order reaction kinetics at the investigated temperature ranges.Based on the results of the products quantitative analysis,a carbon balance was determined, and a possible hydrolysis reaction scheme of 5-CVAM was proposed.We confirmed for the first time the reactivity of two different functional groups in NCW,providing a literature reference for the selective hydrolysis of similar compounds.5.Research on the hydrolysis of N-methylacetamide in high temperature water N-methylacetamide(NMA)was selected as a model compound of N-substituted amide to investigate its hydrolysis kinetics and mechanism in high temperature water(HTW)with and without added acid or base catalysts at temperatures 200-400℃.The major products measured are acetic acid and methylamine.The reaction is reversible.Batch reactor studies revealed that there is no change of the reaction order no matter what the reaction condition is subcritical region or supercritical region.A global reaction order of one was tested for the NMA disappearance at temperatures of 200℃,300℃and 400℃,respectively. Examination the relations between water density and rate constant suggests a reaction order also of one in water.We also have examined the pH effect on the hydrolysis rate of NMA with added acid(HCl)and base(NaOH)in order to get its hydrolysis mechanism.The results suggest that apparent reactions order for H⁺and OH^-are basically one.These experiments also revealed three distinct regions of pH dependence.At low and high pH,the conversion increased rapidly with added acid and base.At near-neutral pH,however,the rate was essentially insensitive to changes in pH.We generated a detailed chemical kinetics model for the hydrolysis reaction in the literature.This three-parameter model fits the experimental data for NMA disappearance and formation of acetic acid and methylamine.We also found that the rate constant for hydrolysis increased with water density and with the addition of salts.This consistent with a polar hydrolysis reaction mechanism wherein the rate constant would be increased with increases the solvent polarity.An S_N2 mechanism with water as the nucleophile appears to be the most likely candidate.We reported for the first time the hydrolysis reaction mechanism of amide in high temperature water,and found a scientistic base for the hydrolysis possibility of amide linkages in peptide and protein in HTW.