Mechanism Of Nucleophilic Substitution Research Articles

A novel strategy to construct Janus metallamacrocycles with both a Ru-arene face and an imidazolium face.

The bottom-up construction of highly functional metallamacrocycles from simple building blocks is a challenge of much current interest. We have used solvothermal reactions of a bifunctional p-bitmb ligand with [Ru(arene)X2]2 in CH2Cl2 or CH2Br2 to generate the novel mononuclear metallamacrocyclic [RuX(arene)L2CH2]X3 complexes 1-3 (1, arene = p-cym, X = Cl; 2, arene = bip, X = Cl; 3, arene = p-cym, X = Br), which were characterized by various techniques. These complexes are "bowl-like" and have two faces: one coordinative Ru centre (arene)Ru(N,N)X bridged by L (L = 1,4-bis(imidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene, p-bitmb) to a dipositive bis-imidazolinium centre. Cl- or Br- anions can be trapped inside the cavity of the "bowl-like" structure, forming H-bonds with the backbone. Experimental (NMR and ESI-MS) and computational (DFT calculations) studies show that the source of the bridging -CH2- group is the dihalogenated solvent (CH2Cl2 or CH2Br2) that links the two arms of an initially formed non-cyclic complex (arene)RuX2L2 by a mechanism of nucleophilic substitution. Optimization of the reaction conditions afforded the macrocyclic complexes in almost quantitative yields. The applications of these complexes as anti-proliferative agents towards cancer cells and for selective anion sensing have been explored.

A computational study on the mechanism of ynamide-mediated amide bond formation from carboxylic acids and amines.

This paper reports a computational study elucidating the reaction mechanism for ynamide-mediated amide bond formation from carboxylic acids and amines. The mechanisms have been studied in detail for ynamide hydrocarboxylation and the subsequent aminolysis of the resulting adduct by an amine. Ynamide hydrocarboxylation is kinetically favorable and thermodynamically irreversible, resulting in the formation of a key low-lying intermediate CP1 featuring geminal vinylic acyloxy and sulfonamide groups. The aminolysis of CP1 by the amine is proposed to be catalyzed by the carboxylic acid itself that imparts favourable bifunctional effects. In the proposed key transition state TSaminolysis-acid-iso2, the amine undergoes direct nucleophilic substitution at the acyl of CP1 to replace the enolate group in a concerted way, which is promoted by secondary hydrogen bonding of carboxylic acid with both the amine and CP1. These secondary interactions are suggested to increase the nucleophilicity of the amine and to activate the Cacyl-O bond to be cleaved, thereby stabilizing the aminolysis transition state. The concerted aminolysis mechanism is competitive with the classic stepwise nucleophilic acyl substitution mechanism that features sequential amine addition to acyl/intramolecular proton transfer/C-O bond cleavage and a key tetrahedral intermediate. Based on the mechanistic model, the carboxylic acid substrate effect and studies of more acidic CF3SO3H as the catalyst are in good agreement with the experimental observations, lending further support for the mechanistic model. The bifunctional catalytic effect of the carboxylic acid substrate may widely play a role in related amide bond-forming reactions and peptide formation chemistry.

Mechanistic Insights from the Crystal Structure of Bacillus subtilis o-Succinylbenzoyl-CoA Synthetase Complexed with the Adenylate Intermediate.

o-Succinylbenzoyl-CoA (OSB-CoA) synthetase, or MenE, catalyzes an essential step in vitamin K biosynthesis and is a valuable drug target. Like many other adenylating enzymes, it changes its structure to accommodate substrate binding, catalysis, and product release along the path of a domain alternation catalytic mechanism. We have determined the crystal structure of its complex with the adenylation product, o-succinylbenzoyl-adenosine monophosphate (OSB-AMP), and captured a new postadenylation state. This structure presents unique features such as a strained conformation for the bound adenylate intermediate to indicate that it represents the enzyme state after completion of the adenylation reaction but before release of the C domain in its transition to the thioesterification conformation. By comparison to the ATP-bound preadenylation conformation, structural changes are identified in both the reactants and the active site to allow inference about how these changes accommodate and facilitate the adenylation reaction and to directly support an in-line backside attack nucleophilic substitution mechanism for the first half-reaction. Mutational analysis suggests that the conserved His196 plays an important role in desolvation of the active site rather than stabilizing the transition state of the adenylation reaction. In addition, comparison of the new structure with a previously determined OSB-AMP-bound structure of the same enzyme allows us to propose a release mechanism of the C domain in its alteration to form the thioesterification conformation. These findings allow us to better understand the domain alternation catalytic mechanism of MenE as well as many other adenylating enzymes.

Enzymatic hydrolysis by transition-metal-dependent nucleophilic aromatic substitution.

Nitroaromatic compounds are typically toxic and resistant to degradation. Bradyrhizobium species strain JS329 metabolizes 5-nitroanthranilic acid (5NAA), which is a molecule secreted by Streptomyces scabies, the plant pathogen responsible for potato scab. The first biodegradation enzyme is 5NAA-aminohydrolase (5NAA-A), a metalloprotease family member that converts 5NAA to 5-nitrosalicylic acid. We characterized 5NAA-A biochemically and obtained snapshots of its mechanism. 5NAA-A, an octamer that can use several divalent transition metals for catalysis in vitro, employs a nucleophilic aromatic substitution mechanism. Unexpectedly, the metal in 5NAA-A is labile but is readily loaded in the presence of substrate. 5NAA-A is specific for 5NAA and cannot hydrolyze other tested derivatives, which are likewise poor inhibitors. The 5NAA-A structure and mechanism expand our understanding of the chemical ecology of an agriculturally important plant and pathogen, and will inform bioremediation and biocatalytic approaches to mitigate the environmental and ecological impact of nitroanilines and other challenging substrates.

A Highly Reactive Imidazolium-Bridged Dinucleotide Intermediate in Nonenzymatic RNA Primer Extension.

Because of its importance for the origin of life, the nonenzymatic copying of RNA templates has been the subject of intense study for several decades. Previous characterizations of template-directed primer extension using 5′-phosphoryl-2-methylimidazole-activated nucleotides (2-MeImpNs) as substrates have assumed a classical in-line nucleophilic substitution mechanism, in which the 3′-hydroxyl of the primer attacks the phosphate of the incoming monomer, displacing the 2-methylimidazole leaving group. However, we have found that the initial rate of primer extension depends on the pH and concentration at which the activated monomer is maintained prior to the primer extension reaction. These and other results suggest an alternative mechanism, in which two monomers react with each other to form an imidazolium-bridged dinucleotide intermediate, which then binds to the template. Subsequent attack of the 3′-hydroxyl of the primer displaces an activated nucleotide as the leaving group and results in extension of the primer by one nucleotide. Analysis of monomer solutions by NMR indicates formation of the proposed imidazolium-bridged dinucleotide in the expected pH-dependent manner. We have used synthetic methods to prepare material that is enriched in this proposed intermediate and show that it is a highly reactive substrate for primer extension. The formation of an imidazolium-bridged dinucleotide intermediate provides a mechanistic interpretation of previously observed catalysis by an activated nucleotide located downstream from the site of primer extension.

Thermal reaction of the ionic liquid 1,2-dimethyl-(3-aminoethyl) imidazolium tetrafluoroborate: a kinetic and theoretical study.

Since the thermal stabilities of ionic liquids (ILs) are of significance for their application, an amine-functionalized IL 1,2-dimethyl-(3-aminoethyl) imidazolium tetrafluoroborate [aEMMIM][BF4] was chosen to study thermal decomposition mechanisms via the methods of FT-IR, (1)H NMR, TGA, TGA-MS and density functional theory (DFT) calculations. Theoretical and experimental results indicated that amine-functionalization reduces the thermal stability of [aEMMIM][BF4] compared to its non-functionalized counterpart. Moreover, we found that [aEMMIM][BF4] follows a unimolecular nucleophilic substitution (SN1) decomposition (98.8%), whereas the bimolecular nucleophilic substitution (SN2) decomposition (1.2%) is unfavorable. The SN1 and SN2 reactions were fully optimized at B3LYP/6-311++G(d,p) level, and the energies of reactant (R), intermediates (IM), transition state (TS) and product (P) were obtained and analyzed by reaction mechanism. The energy of the intermediate is higher than that of the reactants by 18.92kJmol(-1), and the energy of the TS is higher than that of the IM by 155.23kJmol(-1). This result indicates that the IM are also more stable than the P2 product, thus the reaction is endothermic. The chemical nature of the covalent and hydrogen bonds was analyzed by vibrational modes analysis (VMA), nature bond orbital (NBO) and the theory of atoms in molecules (AIM). Graphical Abstract Proposed thermal decomposition of [aEMMIM][BF4] via unimolecular ( SN1) and bimolecular( SN2) nucleophilic substitution mechanisms. The electrostatic potential surface (ESP) of the transition state illustrates that hydrogen bonds are generated when [BF4](-) is close to [aEMMIM](+), and SN1 decomposition is much favorable than SN2 decomposition.

High kinetic stability of ZnII coordinated by the tris(histidine) unit of carbonic anhydrase towards solvolytic dissociation studied by affinity capillary electrophoresis

Solvolytic dissociation rate constants (kd) of bovine carbonic anhydrase II (CA) and its metallovariants (M-CAs, M=CoII, NiII, CuII, ZnII, and CdII) were estimated by a ligand substitution reaction, which was monitored by affinity capillary electrophoresis to selectively detect the undissociated CAs in the reaction mixture. Using EDTA as the competing ligand for Zn-CA, the dissociation followed the unimolecular nucleophilic substitution (SN1) mechanism with kd=1.0×10−7s−1 (pH7.4, 25°C). The corresponding solvolysis half-life (t1/2) was 80days, showing the exceptionally high kinetic stability of t Zn-CA, in contrast to the highly labile [ZnII(H2O)6]2+, where the water exchange rate (kex) is high. This behavior is attributed to the tetrahedral coordination geometry supported by the tris(histidine) unit (His3) of CA. In the case of Co-CA, it showed a somewhat larger kd value (5.7×10−7s−1, pH7.4, 25°C) even though it shares the same tetrahedral coordination environment with Zn-CA, suggesting that the d7 electronic configuration of CoII in the transition state of the dissociation is stabilized by the ligand field. Among M-CAs, only Ni-CA showed a bimolecular nucleophilic substitution (SN2) reaction path in its reaction with EDTA, implying that the large coordination number (6) of NiII in Ni-CA allows EDTA to form an EDTA-Ni-CA intermediate. Overall, kd values roughly correlated with kex values among M-CAs, with the kd value of Zn-CA deviating strongly from the trend and highlighting the exceptionally high kinetic stabilization of Zn-CA by the His3 unit.

Ionic S(N)i-Si Nucleophilic Substitution in N-Methylaniline-Induced Si-Si Bond Cleavages of Si2Cl6.

N-Methylaniline-induced Si-Si bond cleavage of Si2Cl6 has been theoretically studied. All calculations were performed by using DFT at the MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) levels. An ionic SN i-Si nucleophilic substitution mechanism, which is a newly found nucleophilic substitution in silicon-containing compounds, is proposed in the N-methylaniline-induced Si-Si bond cleavage in Si2Cl6. Unlike general S(N)i-Si nucleophilic substitutions that go through a pentacoordinated silicon transition state, ionic nucleophilic substitution goes through a tetracoordinated silicon transition state, in which the Si-Si bond is broken and siliconium ions are formed. Special cleavage of the Si-Si bond is presumably due to the good bonding strength between Si and N atoms, which leads to polarization of the Si-Si bond and eventually to heterolytic cleavage. Calculation results show that, in excess N-methylaniline, the final products of the reaction, including (NMePh)(3-n) SiHCl(n) (n=0-2) and (NMePh)(4-n) SiCl(n) (n=2-3), are the Si-Si cleavage products of Si2Cl6 and the corresponding amination products of the former. The ionic S(N)i-Si nucleophilic substitution mechanism can also be employed to describe the amination of chlorosilane by N-methylaniline. The suggested mechanisms are consistent with experimental data.

Lanthanide-Catalyzed Oxyfunctionalization of 1,3-Diketones, Acetoacetic Esters, And Malonates by Oxidative C-O Coupling with Malonyl Peroxides.

The lanthanide-catalyzed oxidative C-O coupling of 1,3-dicarbonyl compounds with diacyl peroxides, specifically the cyclic malonyl peroxides, has been developed. An important feature of this new reaction concerns the advantageous role of the peroxide acting both as oxidant and reagent for C-O coupling. It is shown that lanthanide salts may be used in combination with peroxides for selective oxidative transformations. The vast range of lanthanide salts (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Y) catalyzes oxidative C-O coupling much more efficiently than other used Lewis and Bronsted acids. This oxidative cross-coupling protocol furnishes mono and double C-O coupling products chemo-selectively in high yields with a broad substrate scope. The double C-O coupling products may be hydrolyzed to vicinal tricarbonyl compounds, which are otherwise cumbersome to prepare. Based on the present experimental results, a nucleophilic substitution mechanism is proposed for the C-O coupling process in which the lanthanide metal ion serves as Lewis acid to activate the enol of the 1,3-dicarbonyl substrate. The side reactions-chlorination and hydroxylation of the 1,3-dicarbonyl partners-may be minimized under proper conditions.

Variable mechanism of nucleophilic substitution of P-stereogenic phosphoryl chloride with alkynyl metallic reagents.

The variable mechanism for substitution of P-stereogenic phosphoryl chloride with alkynyl metallic reagents, which depends on temperature, stoichiometry of starting materials, and the structure of the nucleophilic reagent, is assumed as either SN2-like or Berry pseudorotation of pentacoordinated phosphorus intermediates, affording inversion and retention products, respectively. The formation of the inversion product can be controlled to occur predominantly to afford (RP)-alkynylphosphinates.

A simple excited-state intramolecular proton transfer probe based on a new strategy of thiol-azide reaction for the selective sensing of cysteine and glutathione.

A simple azido-substituted fluorescent sensor showing a selective turn-on response to cysteine (Cys) and glutathione (GSH) over homocysteine (Hcy), sulfide and other amino acids has been constructed, which is based on the mechanism of selective nucleophilic substitution-rearrangement reactions.

Evaluation of four curing agents of epoxy resin and their effects above their thermal and dinamomechanical properties

ABSTRACTWere synthesized four new hybrid hardener agents type amino tertiary functionalized with allyl groups from : l, 6-Hexanediamine, Diethylenetriamine, Trietilentriamine and Tris (2-aminoethyl) amine, using the basic nucleophilic substitution mechanism, replacing bromide by amino tertiary group in the presence of tetrabutylammonium bromide as phase transfer agent, producing allyl amine corresponding: ALA-4, ALA-5, ALA-6 and TRIS respectively, which were evaluated as a hardening of epoxy resin DGEBA through photopolymerization process by UV ligth curing, adding a 10, 20 and 40% molar percentage of hybrid materials and the thiol corresponding to carry out the thiol-ene reaction (TMP TMP, PTKMP) with DMPA as initiator. The resinic materials obtained, were evaluated by the technique of dynamic mechanical analysis (DMA) at a heating rate of 5° C/min in a range from - 50° C to 150° C in nitrogen atmosphere. The formulations with hybrid hardening agent ALA 4- 20% -PTKMP and TRIS 10% -PTKMP were the materials with modulus 2289, 2971 Mpa and tgs of 102,103°C, respectively.

Reactivity measurement in estimation of benzoquinone and benzoquinone derivatives' allergenicity.

Benzoquinone (BQ) and benzoquinone derivatives (BQD) are used in the production of dyes and cosmetics. While BQ, an extreme skin sensitizer, is an electrophile known to covalently modify proteins via Michael Addition (MA) reaction whilst halogen substituted BQD undergo nucleophilic vinylic substitution (SNV) mechanism onto amine and thiol moieties on proteins, the allergenic effects of adding substituents on BQ have not been reported. The effects of inserting substituents on the BQ ring has not been studied in animal assays. However, mandated reduction/elimination of animals used in cosmetics testing in Europe has led to an increased need for alternatives for the prediction of skin sensitization potential. Electron withdrawing and electron donating substituents on BQ were assessed for effects on BQ reactivity toward nitrobenzene thiol (NBT). The NBT binding studies demonstrated that addition of EWG to BQ as exemplified by the chlorine substituted BQDs increased reactivity while addition of EDG as in the methyl substituted BQDs reduced reactivity. BQ and BQD skin allerginicity was evaluated in the murine local lymph node assay (LLNA). BQD with electron withdrawing groups had the highest chemical potency followed by unsubstituted BQ and the least potent were the BQD with electron donating groups. The BQD results demonstrate the impact of inductive effects on both BQ reactivity and allergenicity, and suggest the potential utility of chemical reactivity data for electrophilic allergen identification and potency ranking.

Cerium oxide for the destruction of chemical warfare agents: A comparison of synthetic routes

Four different synthetic routes were used to prepare active forms of cerium oxide that are capable of destroying toxic organophosphates: a sol–gel process (via a citrate precursor), homogeneous hydrolysis and a precipitation/calcination procedure (via carbonate and oxalate precursors). The samples prepared via homogeneous hydrolysis with urea and the samples prepared via precipitation with ammonium bicarbonate (with subsequent calcination at 500°C in both cases) exhibited the highest degradation efficiencies towards the extremely dangerous nerve agents soman (O-pinacolyl methylphosphonofluoridate) and VX (O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate) and the organophosphate pesticide parathion methyl. These samples were able to destroy more than 90% of the toxic compounds in less than 10min. The high degradation efficiency of cerium oxide is related to its complex surface chemistry (presence of surface OH groups and surface non-stoichiometry) and to its nanocrystalline nature, which promotes the formation of crystal defects on which the decomposition of organophosphates proceeds through a nucleophilic substitution mechanism that is not dissimilar to the mechanism of enzymatic hydrolysis of organic phosphates by phosphotriesterase.

Experimental and quantum-chemical study of nucleophilic substitution mechanism in berberine

Principal differences in the interaction mechanisms of alkaloid berberine with primary and secondary amines were investigated experimentally and by quantum-chemical calculations according to density functional theory (DFT/B3LYP) with 6-31G** basis set. The nucleophilic substitution of 9-metoxy group with primary amine was shown to proceed through a stage of σ-complex formation and led to 9-alkylamino derivatives of berberine. Analogous substitution with a secondary amine did not occur due to unfavorable thermodynamic parameters. The secondary amine participated in this reaction not as the attacking nucleophile, but rather as a bifunctional catalyst of berberine hydrolysis to berberrubine. The driving force for all these processes was the stabilization of products by hydrogen bonding. Based on the obtained results, we developed a new effective method for the preparation of berberrubine, one of the key intermediates in synthetic transformations of berberine. New 9-monoalkylamino derivatives of berberine containing indole moieties were synthesized.

Characterization and Modeling of the Collision Induced Dissociation Patterns of Deprotonated Glycosphingolipids: Cleavage of the Glycosidic Bond.

Glycosphingolipid fragmentation behavior was investigated by combining results from analysis of a series of negative ion tandem mass spectra and molecular modeling. Fragmentation patterns extracted from 75 tandem mass spectra of mainly acidic glycosphingolipid species (gangliosides) suggest prominent cleavage of the glycosidic bonds with retention of the glycosidic oxygen atom by the species formed from the reducing end (B and Y ion formation). Dominant product ions arise from dissociation of sialic acids glycosidic bonds whereas product ions resulting from cleavage of other glycosidic bonds are less abundant. Potential energy surfaces and unimolecular reaction rates of several low-energy fragmentation pathways leading to cleavage of glycosidic bonds were estimated in order to explain observed dissociation patterns. Glycosidic bond cleavage in both neutral (unsubstituted glycosyl group) and acidic glycosphingolipids was the outcome of the charge-directed intramolecular nucleophilic substitution (SN2) mechanism. According to the suggested mechanism, the nucleophile in a form of carboxylate or oxyanion attacks the carbon at position one of the sugar ring, simultaneously breaking the glycosidic bond and yielding an epoxide. For gangliosides, unimolecular reaction rates suggest that dominant product ions related to the cleavage of sialic acid glycosidic bonds are formed via direct dissociation channels. On the other hand, low abundant product ions related to the dissociation of other glycosidic bonds are more likely to be the result of sequential dissociation. Although results from this study mainly contribute to the understanding of glycosphingolipid fragmentation chemistry, some mechanistic findings regarding cleavage of the glycosidic bond may be applicable to other glycoconjugates.

Kinetics Modeling and Mechanism Study for Selective Esterification of Glycerol with Lauric Acid Using 12-Tungstophosphoric Acid Post-Impregnated SBA-15

Multiple kinetics models including simple power law model and mechanism-based models (nucleophilic substitution, Langmuir–Hinshelwood, and Eley–Rideal kinetics models) were investigated for selective esterification of glycerol with lauric acid using post-impregnated 12-tungstophosphoric acid SBA-15. Rate equations for all suggested models and mechanisms were derived, and appropriate experimental works were carried out. The model that best describes the studied reaction is found to be a combination of both a nucleophilic substitution mechanism and the Langmuir–Hinshelwood kinetics model with high accuracy and reliability of the model observed. The mechanism scheme describing the reaction from the bulk up to reactant molecular level and the interaction between reactant molecules on catalyst surface was outlined. Activation energy (Ea) of the studied reaction is found to be 35.62 kJ mol–1 with an Arrhenius constant, A, of 1141.2 L mol–1 g cat–1 h–1, which shows 40 wt %-HPW/IM to have a relatively low activat...

Study of the gas-phase fragmentation behaviour of sulfonated peptides

A series of singly and doubly protonated peptides bearing sulfonated residue have been studied, using both experiment and molecular modelling, to elucidate fragmentation chemistry of sulfonated peptides. Collision-induced dissociation mass spectra indicate that the sulfo group loss (neutral loss of 80Da) is the dominant dissociation channel. Modelling results suggest the proton transfer mechanism, where upon vibrational excitation, the acidic side chain proton is transferred from the sulfo group hydroxyl to the ester oxygen resulting in SO bond cleavage and formation of the unmodified hydroxyl containing residue and SO3. Conformations associated with potential energy profile of the reaction imply the charge remote nature of the proposed mechanism. The proposed proton transfer mechanism was compared with the intramolecular nucleophilic substitution (SN2) mechanism, the main pathway suggested for neutral loss of phosphoric acid from phosphopeptides. Both pathways (proton transfer and SN2) are available for sulfonated and phosphorylated peptides; however, each posttranslational modification favours different mechanism. The change of the bond dissociation enthalpies and the ability of stabilising the transition state structures are demonstrated as main factors responsible for each posttranslational modification activating a different pathway.

Reaction path analysis for 1-butanol dehydration in H-ZSM-5 zeolite: Ab initio and microkinetic modeling

Dispersion corrected periodic density functional theory (DFT) is used to construct a microkinetic model for 1-butanol dehydration in H-ZSM-5. The latter is applied to determine the effect of reaction conditions on dehydration rates, product selectivity and dominant reaction pathway. The consecutive reaction scheme of 1-butanol dehydration to ether followed by ether decomposition offers lower energy barriers as compared to the direct conversion of 1-butanol to 1-butene. The direct dehydration of 1-butanol to 1-butene occurs via an E2 (anti) elimination at low 1-butanol partial pressure and shifts to a 1-butanol assisted 1,2-syn-elimination with increasing 1-butanol partial pressure. The ether formation reaction proceeds via an SN2-type nucleophilic substitution mechanism, involving substitution of the –OH2 group of the protonated alcohol by 1-butanol, while ether decomposition predominantly occurs via a 1,2-syn-elimination mechanism. The effect of reaction conditions viz. reaction temperature, site time, 1-butanol and water partial pressure is studied. The reaction conditions govern the coverage of key surface species which in turn has a significant role in determining the dominant reaction mechanism and product selectivity. Under industrially relevant conditions, the presence of water has no significant effect on 1-butanol conversion and product selectivity. A higher reaction temperature, higher site time and lower 1-butanol partial pressure favor a higher 1-butene selectivity.

Fast and effective glycolysis of poly(ethylene terephthalate) catalyzed by polyoxometalate

Transition-metal-substituted polyoxometalates (POMs) K6SiW11MO39(H2O) (M = Zn2+, Mn2+, Co2+, Cu2+, Ni2+) show excellent catalytic activities in the glycolysis of poly(ethylene terephthalate) (PET) under mild conditions. The effects of temperature, catalyst amount and reaction time on PET degradation are investigated. The PET could be fast and completely degraded at low catalyst/PET molar ratio (0.13%) and high PET/EG weight ratio (1:4). The yield of bis(hydroxyethyl) terephthalate (BHET) exceeds 84% with the SiW11Zn as the catalyst under atmospheric pressure at 185 °C for 30 min. The catalyst and ethylene glycol (EG) can be easily separated from the products by filtration and can be reused together. After recycling eight times, the conversion of PET and the yield of BHET can still reach 100% and 83%, respectively. The possible nucleophilic substitution mechanism for PET glycolysis using the K6SiW11ZnO39(H2O) as the catalyst is proposed. The POM catalysts are hopeful to provide the possibility for other polymer degradation.