Rate Of Ring-opening Reaction Research Articles

Fully Automatized Optimization of Ring-Opening Reactions in Lactone Derivatives via Two-Step Machine Learning.

Cyclization and cycloreversion of organic compounds are fundamental kinetic processes in the design of functional molecules, molecular machines, nanoscale sensors, and switches in the field of molecular and nanoelectronics. We present a fully automatic computational platform for the design of a class of five- and six-membered ring lactones by optimizing the ring-opening reaction rate. Starting from a minimal initial parent set, our algorithm generates iteratively cascades of pools of candidate lactone derivatives where optimization and down-selection are performed without human supervision. We employ the density functional theory combined with the transition state theory to elucidate the exact mechanism leading to the lactone ring-opening reaction. On the basis of the analysis of the reaction pathway and the frontier molecular orbitals, we identify a simple descriptor that can easily correlate with the reaction rate. Consequently, we can omit computationally expensive transition state calculations and deduce the reaction rate from simple ground-state and ionic calculations. To accelerate the platform, we use a data set of the order of 800 molecules to train machine learning models for the prediction of targeted chemical properties, reducing the computational time by a 90% factor. We developed an evolutionary algorithm capable of generating data sets 3 orders of magnitude larger than the initial parent set. Thus, we can explore a large domain of chemical space using minimal computational effort. Our entire platform is modular, and our current implementation for lactone can be further generalized to more complex systems via substitution of the quantum chemical and fingerprinting modules.

A facile method to synthesis of a highly acrylated epoxidized soybean oil with low viscosity: Combined experimental and computational approach

This investigation deals with the introduction of an efficient technique to acrylate almost all of the epoxide groups on epoxidized soybean oil (ESO) and synthesize a highly acrylated ESO (AESO) by using viscosity control agents (VCAs). The effect of chemical structure, content, and addition step of VCAs (i.e. glycidyl neodecanoate, glycidyl hexanoate, and glycidyl acetate) on the reaction rate and viscosity was examined. Spectroscopy and analytical analyses as well as viscosity monitoring were employed to assess the acrylation reaction comprehensively. The intermolecular interactions were visualized by molecular dynamics simulation and quantified via the calculation of cohesion energy density to justify the viscosity changes during the reactions. Results demonstrated that the rate of ring-opening reaction is impaired by viscosity severely. Subsequently, the know-how for preparing the AESO with an acrylation degree of 3.5 via optimum reaction conditions was presented. Accordingly, this attempt indicated that the AESO diluted by acrylated glycidyl neodecanoate can be considered a promising oligomer along with other prominent diluents such as trimethylolpropane triacrylate and hexanediol diacrylate to prepare industrial light/UV-curable coatings with perfect performance (gel fraction: 97%, MEK double rub resistance: 75, Tg: 47 °C, hardness: 123, cross-cut adhesion: 4B, gloss: 97.5%, and water contact angle: 89°).

Soybean Oil Epoxidation: Kinetics of the Epoxide Ring Opening Reactions

The epoxide ring opening reaction (ROR) can be considered as the most important side reaction occurring in the epoxidation of soybean oil reaction network. This reaction consistently reduces the selectivity to epoxidized soybean oil (ESBO). The reaction is also important for producing polyols and lubricants. In this work, the reaction was studied in different operative conditions to evaluate the effect on ROR rate respectively: (i) The Bronsted acidity of the mineral acid (H2SO4 or H3PO4), used as catalyst for promoting the oxidation with hydrogen peroxide of formic to performic acid, that is, the reactant in the epoxide formation; (ii) the concentration of the nucleophilic agents, normally present during the ESBO synthesis like HCOOH, HCOOOH, H2O, H2O2; (iii) the stirring rate that changes the oil–water interface area and affects the mass transfer rate; (iv) the adopted temperature. Many different kinetic runs were made in different operative conditions, starting from an already epoxidized soybean oil. On the basis of these runs two different reaction mechanisms were hypothesized, one promoted by the Bronsted acidity mainly occurring at the oil–water interface and one promoted by the nucleophilic agents, in particular by formic acid. As it will be seen, the kinetic laws corresponding to the two mentioned mechanisms are quite different and this explain the divergent data reported in the literature on this subject. All the kinetic runs were correctly interpreted with a new developed biphasic kinetic model.

Radiation synthesis of crown ether functionalized microcrystalline cellulose as bifunctional adsorbent: A preliminary investigation on its application for removal of ReO4- as analogue for TcO4-

Supramolecular host immobilized cellulose-based adsorbent for TcO4- recognition from groundwater was developed. A novel bifunctional adsorbent composed of amine and crown ether group was newly synthesized by radiation grafting supramolecular host 2-aminomethyl-18-crown-6 (AM18C6) onto microcrystalline cellulose microsphere (MCC). The optimized condition for grafting reaction of glycidyl methacrylate (GMA) onto MCC was 30% GMA emulsion at dose of 20 kGy and the maximum conversion rate of ring opening reaction was 34.8%. 13C-NMR, XPS, FTIR and TGA were applied to characterize the bifunctional adsorbent and verified AM18C6 was successfully bonded to cellulose. Adsorption behaviors towards ReO4- as analogue for TcO4- were also investigated as function of contact time, solution pH, ReO4- concentration and competing anion. It was found that there were synergistic effects of amine and crown ether on ReO4- removal. Contributions of bifunctional adsorbent for ReO4- uptake were mainly dependent on amines under acidic condition while dependent on crown ether under neutral or weak alkaline conditions. The adsorption isotherm was well fitted by the Langmuir model with adsorption capacities of 114.2 mg/g at pH 2.36 and 8.199 mg/g at pH 7.00. This work provided a new way to immobilize crown ether onto microcrystalline cellulose and a new bifunctional adsorbent for separation of ReO4- and TcO4-.

Combined light naphtha isomerization and naphthenic ring opening reaction on modified platinum on chlorinated alumina catalyst

The effect of alumina phases on the catalytic performance of platinum (Pt) on chlorinated alumina catalysts studied in the combined light naphtha isomerization and naphthenic ring opening reaction. The results showed that the type of alumina had a great impact on the catalytic performance of the Pt on chlorinated alumina catalysts. The support prepared by a mixture of eta and gamma alumina with the ratio of 70:30 shows better surface area, acidity and catalytic performance. Extra pre-chlorination of catalysts had a positive effect on the catalytic performance in the butane isomerization reaction. Activities of prepared catalysts tested in a pilot plant with two consecutive fixed bed reactors under different operating conditions. Under the experimental conditions of this study, temperatures greater than 135 °C had a reverse effect on the octane number of the products. It was found that the high LHSV has a negative effect on the strong acidic sites and with returning the LHSV to the initial value, 22DMB/ΣC6 ratio and ring opening reaction rate could not be restored completely.

Adsorption and ring-opening of lactide on the chiral metal surface Pt(321)(S) studied by density functional theory.

We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321)(S). Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

ChemInform Abstract: Kinetics of Ring-Opening Radical Polymerization of Vinyloxiranes

Ring-opening radical polymerization has been followed by the flash photolysis method. As an initiator radical, the arylthiyl radical (ArS˙) was used; the addition reaction rate constants of ArS˙ to vinyl monomer containing epoxy-ring such as vinyloxiranes have been determined at first. The rate constant of ring opening reaction of the adduct radical changing to ArSCH2CH CROCH2˙ were determined in the form of the relative values, which were converted to the absolute values. The ring-opening reaction rate constants were ca. 106 s−1, which indicates that the ring-opening rates are faster than usual radical propagation rates. The rate constants for vinyl monomer with 5-member ring (1,4-epoxy-1,4-dihydronaphthalene) were similarly evaluated.

Preparation of two kinds of porphyrin‐functionalized polymeric materials based on poly(glyceryl methacrylate)

AbstractPoly(glyceryl methacrylate) (PGMA) was reacted with meso‐tetra(4‐hydroxylphenyl)porphyrin (THPP) in a homogeneous system via the ring opening reaction between epoxy and hydroxyl groups, which exist on the side chain of PGMA and the outside ring of THPP, respectively. Porphyrin‐functionalized PGMA with line‐type (denoted as HPP‐PGMA), on whose side chains hydroxylphenyl porphyrin (HPP) was bonded, was obtained. Grafting particles PGMA/SiO2 were also reacted with THPP, and the porphyrin‐immobilized particles (denoted as HPP‐PGMA/SiO2), on which HPP was supported, were produced. The above two target products were characterized using spectroscopy methods, such as infrared (IR), nuclear magnetic resonance (1H‐NMR), electronic absorption, and fluorescence emission. The effects of various factors on the bonding and immobilization reactions of HPP were studied in detail. The experimental results show that the soluble HPP‐PGMA has all the spectral characteristics of porphyrins and the absorption or emission intensity is increased with the increase in the bonding degree of HPP. In the preparation process of HPP‐PGMA, in order to avoid the occurrence of the crosslinking reaction and to obtain HPP‐PGMA with complete line‐type, the catalyst should be selected and the reaction time should be controlled. NaHCO3 is an appropriate catalyst. In the immobilization process of HPP on the grafting particle PGMA/SiO2, the greater the used amount of the catalyst triethylamine (TEA), the more rapid is the rate of ring opening reaction, resulting in higher immobilization amount of HPP. Besides, the immobilization amount of HPP is increased with the enhancement of the reaction temperature. Copyright © 2008 John Wiley & Sons, Ltd.

Additional Factors Affecting the Rate and Mechanism of Ring Opening Reaction

The reactions of thiosulphate ion with some bromoalkylamines of structure RR'N-(CH2)n-Br, where n = 2,3,4,5 or 6 and R - R1 - H, methyl, ethyl or isopropyl, were studied kinetically in an aqueous solution at different pH, The kinetic results for these reactions in basic medium gave explicit evidence in favour of the formation of cyclic intermediate during the reaction course. The rate of these reactions depends mainly on the reactivity of the cyclic intermediate. It has been found that thereactivity of large ring intermediate is mainly controlled by the energy of ring strain relief. As the ring size becomes small (smaller than five members) the rate of the reaction becomes very fast and can't be explained on the bases of ring strain relief only, In order to explain this observation other factors may affect the reactivity of the cyclic intermediate are taken into account, such as the electron density at the nitrogen atom, the sterochemical situation at the reaction centre and the probability of a successful reaction. Taking into account these factors gave a better explanation for the high reactivity of small ring are given, On the other hand, it has been observed that the reaction in acidic medium proceed with a different mechanism in which the reaction occurs by a direct attackment of the nucleophile on the methylene group attached to the bromo group. The dependence of the rate constants on temperature were studied in order to estimate the thermodynamic parameters which were utilized in the discussion of the factors affecting the rate of ring opening reaction.

Ring Opening Dynamics of a Photochromic Diarylethene Derivative in Solution

Photochromic ring opening reaction dynamics of 1,2-bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene in solution has been studied by femtosecond time-resolved fluorescence and transient absorption measurements. Time profiles of the transient absorption at several different probe wavelengths are identical, showing two time constants, 4 and 22 ps. The spontaneous fluorescence reveals time profiles identical to that in the transient absorption. A simple one step ring opening reaction mechanism is proposed, where the closed form in the excited state reaches the open form in the ground state through nonadiabatic curve crossing. The ring opening reaction rate is determined to be in the range (1.7−4) × 1010 s-1. A single 66 cm-1 wave packet motion in the excited state is observed, whose role on the ring opening reaction is speculated upon.

Segmented Poly(urethane-urea)s Synthesized Directly from Isocyanate-Terminated Prepolymers and Masked Diamines II. Kinetic and Mechanistic Study on Masking and Demasking Reaction

An attempt was made to clarify the mechanism of the reactions of acetone with propylenediamine (PDA) or ethylenediamine (EDA) for direct synthesis of poly(urethane-urea) (DSPUU reaction) by using the reaction products (masked diamines) and an isocyanate-terminated prepolymer. In the masking reaction of acetone with PDA at 40°C, 1-(N-isopropylidene)propanediamine (1), 2-(N-isopropylidene)propanediamine (1′), 2,2-dimethyl-4-methylimidazolidine (3) as main product, N,N′-diisopropylidenepropylenediamine (2) were formed in this order due to the dominant rate (k30=3.0 kg mol−1min−1) of the water-catalyzed reaction to form (3) in addition to the slow rate (k20=3.2×10−3 kg mol−1min−1) of (2). The concentration of (1′) remained lower than (1) because of the steric hindrance of the methyl group of the former. The formation reactions of (1) and (2) were more acid-catalyzed than the reverse reactions, leading to shorter equilibrated time and larger molar fractions of these compounds. The reaction profiles for acetone-EDA were analogous except for lower molar fraction of 2,2-dimethylimidazolidine (6) and larger N,N′-diisopropylideneethylenediamine. The rates of demasking reactions which are of importance in DSPUU reactions using masked EDAs were as follows; (i) the water- and acid-catalyzed ring opening reaction rate of (6), k−30 and k−3=1.43 and 0.26 kg mol−1min−1 and (ii) the acid-catalyzed hydrolysis reaction rates of the ketimine groups, k−1=5.09 and k−2=3.13 kg2mol−2min−1, respectively.

Model reaction of epoxy-containing siloxane

3-glycidyloxypropyltrimethoxysilane (GPTS), which contains hydrolizable silicon alkoxide bonds and a ring-openable epoxy group, was used as the model substance for studying the reaction conditions in producing transparent and non-shrinking sol-gel epoxy-SiO2 composites. When GPTS reacts with the mixture of H2O and n-butyric acid (nBA, used as a model curing agent) using triethylamine (TEA), pyridine or triphenylphosphine (TPP) as a catalyst at 50°C, the GPTS undergoes both hydrolysis and ring-opening reaction simultaneously and independently. The ring-opening reaction shows an induction period in the initial stage of the reaction when TEA was used as catalyst, while no induction period was observed when pyridine and TPP were used as catalyst. The rate of ring-opening reaction of epoxide group catalyzed by TPP and pyridine is faster that that catalyzed by TEA, but is still slower than the hydrolysis of SiOMe bonds. When 2-hydroxyalkylmercaptan was used as the curing agent (TEA as catalyst), the ring-opening reaction of GPTS was so reactive that the epoxide group not only reacted with mercaptan, but also reacted with H2O, and hence it is of no use to the synthesis of transparent and non-shrinking sol-gel epoxy-SiO2 composites. From the detailed study of the influence of the structure of siloxanes on the reactivity of hydrolysis, it is suggested that RSi(OR′)3 is the better type of precursor for the synthesis of transparent and non-shrinking sol-gel epoxy-SiO2 composites. The structures of R and R′ are also discussed in this paper.

An HPLC and spectrophotometric study of the hydrolysis of ICRF-187 (dexrazoxane, (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane) and its one-ring opened intermediates

The hydrolysis of the cardioprotective agent dexrazoxane ICRF-187 ((+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane) and its one-ring open intermediates has been examined over a wide pH range using both HPLC and spectrophotometric methods. The isolation of these one-ring open intermediates by HPLC allowed a study of their hydrolysis reactions to be carried out spectrophotometrically without interference from other competing hydrolysis reactions. In 40 mM NaOH (25°C) the half-life for the hydrolysis of ICRF-187 is 0.3 h, at pH 7.4 (37°C) 9.3 h and in 1.0 M HC1 (25°C) 560 h. However, at pH 7.4 (37°C) the half-time for the production of the fully ring-opened hydrolysis product, which is presumably the active metal ion binding form of the drug, is 28 h. A full kinetic analysis was carried out within a reaction scheme that included both parallel and consecutive reaction steps and allowed the determination of the individual ring-opening reaction rate constants.