Xiang-Guang Meng

Adsorption of phenol, p-chlorophenol and p-nitrophenol onto functional chitosan

Functional chitosan, chemically modified by salicylaldehyde (CS-SA), beta-cyclodextrin (CS-CD), and a cross-linked beta-cyclodextrin polymer (EPI-CD) were prepared as adsorbents to remove phenol, p-nitrophenol and p-chlorophenol from aqueous solution. Langmuir and Freundlich models were applied to describe the adsorption isotherm of phenols, and adsorption parameters were evaluated. Functional chitosan displayed outstanding adsorption ability for phenols. To our surprise, CS-CD exhibited specific adsorption ability for p-chlorophenol. The possible adsorption interaction was discussed. Effects of pH and KCl on the adsorption suggested that the adsorption of phenols was predominated by hydrogen bonding, hydrophobic interaction and pi-pi interaction not electrostatic interaction. Effect of temperature indicated that the low temperature was favorable for the adsorption of phenols. Separation of phenols and adsorbent regeneration were carried out by simple washing with ethanol and filtrating.

Comparative kinetics of carboxylic esters hydrolysis catalyzed by the zinc(II) complex of a macrocyclic Schiff base ligand

The comparative kinetic investigation of the hydrolysis of p-nitrophenyl picolinate (PNPP) and p-nitrophenyl acetate (PNPA) catalyzed by the tetracoordinate macrocyclic Schiff base complex of zinc(II) (1) at 30 °C is reported. The results indicate that the (1) catalyzed hydrolyses of PNPP and PNPA are acid-base catalytic processes and that the active species is the metal bound hydroxide ion, namely, ZnL—OH−. (1) promoted hydrolysis of PNPP proceeds much faster than that of PNPA. At pH 7.51, the apparent second-order rate constants kc for hydrolysis of PNPP and PNPA are 0.254 and 7.28 × 10−3 mol−1 dm3 s−1, respectively. The difference in hydrolytic rates may be attributed to the difference of hydrolytic mechanisms by which the PNPP and PNPA operate. The reasons are discussed in detail.

Direct oxidation of secondary alcohol to ester by performic acid

The reaction pathways and kinetics of the oxidation reactions of 1-phenylethyl alcohol (PEA), 1-(3,4-dimethoxyphenyl)ethanol (MVA), 1-(4-hydroxy-3-methoxyphenyl)ethanol (HMOPE), 1-(3-aminophenyl)ethanol (APE), 1-(4-methylphenyl)ethanol (MPE) and cyclohexanol with performic acid (PFA) were investigated in formic acid solvent. An unexpected new reaction pathway, from which the secondary alcohols can be directly oxidized to corresponding esters, was found. The reaction products (esters and ketones) of oxidation of PEA, MVA, HMOPE, APE, MPE and cyclohexanol were detected at different reaction times. The reaction rate constants, k1, k2, k3 and power orders α, β, γ of PFA concentration for three oxidation reactions pathways: alcohol to ester, alcohol to ketone and ketone to ester were obtained, respectively. These findings might provide a new insight into the technology of lignin degradation.

Hydrolysis of BNPP Catalyzed by the Crowned Schiff Base Co(II) Complexes in Micellar Solution

Two symmetrical double aza‐crowned Schiff base cobalt(II) complexes were synthesized and characterized, and the metallomicelle made up of the cobalt(II) complexes and surfactant, as mimic hydrolytic metalloenzyme, was used in catalytic hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP). The analysis of specific absorption spectrums of the hydrolytic reaction systems indicated that key intermediates made up of BNPP and Co(II) complexes are formed in reaction processes of the BNPP catalytic hydrolysis. In this article, the mechanism of BNPP catalytic hydrolysis has been proposed based on the analytic result of specific absorption spectrum. A kinetic mathematical model, for the calculation of the kinetic parameter of BNPP catalytic hydrolysis has been established based on the mechanism proposed. The acid effect of reaction system, the structural effect of the complexes, the effect of surfactant micelles and the effect of temperature on the rate of BNPP hydrolysis catalyzed by the complexes have been discussed.

Metallomicellar Catalytic Hydrolysis of Bis(4‐nitrophenyl) Phosphate by CuIINiII Heterodinuclear Complexes in Brij35 Micellar Solution

The hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) catalyzed by metallomicelles formed from three asymmetry oxamido‐bridged Cu(II)Ni(II) heterodinuclear complexes containing different diamine groups and Brij35 micelle has been investigated kinetically in the pH range of 6.0–10.0 at 25°C. The results indicate that these complexes show relative high reactivity in Brij35 micellar solutions. Complex III exhibited a more effective catalytic function than complex I and complex II for the hydrolysis of BNPP, which was attributed to the different structure of the diamine group in the complex. The apparent rate constants (k obsd ) of BNPP hydrolysis increased with the increasing pH values of reaction media and then reached saturation near pH 9.0. The kinetic and thermodynamic parameters (K and k) were obtained, and the studies show that the hydrolysis of BNPP involves a bifunctional mechanism and is an intramolecular nucleophilic reaction. In the reaction systems, the kinetically active species has been determined to be the aquo‐hydroxo form of the complex CuNi(H2O)OH in Brij35 micellar solution.

Hydrolysis of PNPP Catalyzed by Cu (II), Ni (II) Schiff Base Complexes in CTAB Micellar Solution

The kinetics of hydrolysis of p‐nitrophenyl picolinate(PNPP) catalyzed by metallomicelles formed from Cu (II), Ni (II) Schiff base complexes (CuL, NiL) and CTAB micelle were investigated in the pH range of 6.0–9.0 at 30°C. For the Cu (II) Schiff base complex CuL, the apparent rate constants (k obsd) of PNPP hydrolysis initially increased with the increasing pH of reaction media, then fell off. For the Ni (II) Schiff base complex NiL, the k obsd always increased with the increasing pH. The kinetic and thermodynamic parameters were calculated. The hydrolysis rate of PNPP catalyzed by Cu (II) complex was much larger than that by Ni (II) complex in CTAB micellar solution. The catalytic mechanism of the PNPP hydrolysis was discussed in detail, and the possibly active specie for the catalytic hydrolysis of PNPP was the monohydroxo metal complex.

Hydrolysis of BNPP Catalyzed by the Crowned Schiff Base Co(II) Complex Containing Benzoaza‐15‐Crown‐5 in Micellar Solution

It has been reported that three aza crowned Schiff base cobalt (II) complexes were synthesized and characterized, and the metallomicelle made up of the cobalt (II) complexes and surfactants(Brij35, CTAB, LSS), as mimic hydrolytic metalloenzyme, was used in catalytic hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP). The analysis of specific absorption spectrums of the hydrolytic reaction systems indicated that key intermediates made up of BNPP and Co (II) complexes are formed in the reaction process of BNPP catalytic hydrolysis. The mechanism of BNPP catalytic hydrolysis proposed is based on the analytic result of specific absorption spectra. Based on the mechanism proposed, a kinetic mathematical model for the calculation of the kinetic parameter of BNPP catalytic hydrolysis has been established. The acid effect of reaction system, structure effect of the complexes, effect of temperature and effect of micelles on the rate of BNPP hydrolysis catalyzed by the complexes have been discussed.

Selective Oxidation of Aromatic Olefins Catalyzed by Copper(II) Complex in Micellar Media

The selective oxidation of aromatic olefins 1,2-dimethoxy-4-vinylbenzene (DEVB) and 2-methoxy-4-vinylphenol (MOVP) by H2O2 into 1-(3,4-dime-thoxyphenyl)ethanol (MVA) and 1-(4-hydroxy-3-methoxyphenyl)ethanol (HMOPE) catalyzed by copper(II) complex CuL (L = 6,8,15,17-tetramethyl-7,16-dihydrodibenzo-1,4,8,11-tetraazacyclotetradecine) were achieved in cationic surfactant cetyl trimethylammonium bromide (CTAB), anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and nonionic surfactant Triton X-100 (TX-100) micellar media, respectively. Micelle showed great influence on both reaction rate and selectivity of product. Aromatic olefins could be oxidized into corresponding aromatic ketones in aqueous solution, but into secondary alcohols in micellar media. The combination of TEMPO and CuL/H2O2 resulted in relatively fast reaction rate and S > 96% selectivity of aromatic ketones. The reaction rate constants, k1, k2 and k3 for three oxidation reactions pathways: olefin to ketone, olefin to alcohol and alcohol to ketone were obtained, respectively. The kinetic study indicated that the CuL catalyzed oxidation of olefins by H2O2 to alcohols was a relatively rapid and major reaction and ketone was generated by the direct oxidation of olefins, not by further oxidation of alcohol in micellar media.Graphical Abstract

Metallomicellar Catalysis: Hydrolysis of PNPP Catalyzed by Copper(II), Zinc(II), Cerium(IV) Complexes with Long Alkyl Pyridine Ligands in CTAB Micellar Solution

A kind of new functional surfactant with substituted long alkyl pyridine was synthesized and its Ce(IV), Zn(II), and Cu(II) complexes were used as hydrolytic metalloenzyme models. The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by the metallomicelles in CTAB micellar solution was investigated at different pH and 30°C. Kinetic parameters of catalytic hydrolysis were obtained by employing the ternary complex kinetic model for metallomicellar catalysis. Effects of the structure of ligands and microenvironment of reaction on the hydrolytic reaction of PNPP have been discussed in detail. From the apparent rate constants (k obsd ) of the catalytic hydrolysis of PNPP, it can be seen that the catalytic effect of complexes of ligand L2 with long hydrocarbon chain was stronger than that of ligand L1, and complex CuL2 showed higher catalytic efficacy on the hydrolytic reaction than those of ZnL2 and CeL2. However, experiment results in this article showed that ZnL2 and CeL2 are more susceptible to environment than CuL2. The catalytic mechanism was proposed, and the possibly active species for the catalytic hydrolysis of PNPP was determined to be the hydroxylated metal complex.

Efficient Hydrolytic Breakage of β-1,4-Glycosidic Bond Catalyzed by a Difunctional Magnetic Nanocatalyst

A novel difunctional magnetic nanocatalyst (DMNC) was prepared and used to catalyse the hydrolytic breakage of β-1,4-glycosidic bonds. The functional nanoparticle displayed excellent catalytic activity for hydrolysis of cellobiose to glucose under moderate conditions. The conversion of cellobiose and yield of glucose could reach 95.3 and 91.1 %, respectively, for a reaction time of 6 h at pH 4.0 and 130°C. DMNC was also an efficient catalyst for the hydrolysis of cellulose: 53.9 % microcrystalline cellulose was hydrolyzed, and 45.7 % reducing sugar was obtained at pH 4.0 and 130°C after 10 h. The magnetic catalyst could be recycled and reused five times without significant loss of catalytic activity.