Atherton-Todd Reaction Research Articles

Cyano group‐containing DOPO derivative for improving the flame retardancy, smoke suppression, and mechanical properties of epoxy resins

AbstractIn order to obtain an efficient flame retardant and smoke suppressor without sacrificing mechanical properties of epoxy resin (EP). A cyano group‐containing 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) derivative (CP‐DOPO) was proposed and synthesized through one‐step Atherton–Todd reaction between DOPO and 4‐cyanophenol. The comprehensive performance analysis of CP‐DOPO‐based EP composite was conducted by measuring the flame retardancy, smoke suppression, and mechanical properties. The flame‐retardant test findings shows that the EP/4CP‐DOPO sample achieves UL‐94 V‐0 rating with 4 wt% low addition of CP‐DOPO. Moreover, EP/6CP‐DOPO sample presents a LOI of 36.5%, a 28.1% reduction in the peak heat release rate, and a 42.1% substantial decrease in total smoke production, demonstrating its desirable flame retardancy and smoke suppression properties. Significantly, different from the traditionally additive flame retardants, the mechanical properties of EP matrix will not be affected by the incorporation of CP‐DOPO but a 17.7% increasement of flexural properties compared to EP. This research not only provides an ingenious strategy for designing and preparing high‐effective flame retardant but also enhances the comprehensive performance of EP resins in practical applications.

Preparation of High-Transparency Phosphenanthrene-Based Flame Retardants and Studies of Their Flame-Retardant Properties.

Transparency is an important property for polymer flame retardants, especially epoxy resin (EP) flame retardants, and flame-retardant epoxy resins that maintain a high transparency and low chromatic aberration play important roles in the optical, lighting, and energy industries. Herein, a DOPO-based flame retardant 6,6'-((sulfonylbis(4,1-phenylene))bis(oxy))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) with a high transparency and low chromatic aberration was prepared via the classical Atherton-Todd reaction and named SBPDOPO. Its chemical structure was characterized with Fourier IR spectroscopy and NMR spectroscopy. An EP loaded with 7 wt% SBPDOPO passed the UL-94 V-0 rating with an LOI value of 32.1%, and the peak heat release rate, total heat release, and total smoke production were reduced by 34.1%, 31.6%, and 27.7%, respectively, compared with those of pure EP. In addition, the addition of SBPDOPO improved the thermal stability, residual mass, and glass transition temperature of the EP. On this basis, the EP containing 7 wt% SBPDOPO maintained a high transparency and low color aberration, with a transmittance of 94% relative to that of pure EP and a color aberration ΔE of 1.63. Finally, the flame-retardant mechanism of SBPDOPO was analyzed, which demonstrated that it exerted both gas-phase and condensed-phase flame-retardant effects, and that SBPDOPO/EP had high potential for application scenarios in which both flame retardancy and transparency are needed. SBPDOPO/EP has great potential for applications requiring both flame retardancy and transparency.

Chemodivergent Staudinger Reactions of Secondary Phosphine Oxides and Application to the Total Synthesis of LL-D05139β Potassium Salt.

Unprecedented Staudinger reaction modes of secondary phosphine oxides (SPO) and organic azides are herein disclosed. By the application of various additives, selective nitrogen atom exclusion from the azide group has been achieved. Chlorotrimethylsilane mediates a stereoretentive Staudinger reaction with a 2-N exclusion which provides a valuable method for the synthesis of phosphinic amides and can be considered complementary to the stereoinvertive Atherton-Todd reaction. Alternatively, a 1-N exclusion pathway is promoted by acetic acid to provide the corresponding diazo compound. The effectiveness of this protocol has been further demonstrated by the total synthesis of the diazo-containing natural product LL-D05139β, which was prepared as a potassium salt for the first time in 6 steps and 26.5 % overall yield.

Chemodivergent Staudinger Reactions of Secondary Phosphine Oxides and Application to the Total Synthesis of LL–D05139β Potassium Salt

AbstractUnprecedented Staudinger reaction modes of secondary phosphine oxides (SPO) and organic azides are herein disclosed. By the application of various additives, selective nitrogen atom exclusion from the azide group has been achieved. Chlorotrimethylsilane mediates a stereoretentive Staudinger reaction with a 2‐N exclusion which provides a valuable method for the synthesis of phosphinic amides and can be considered complementary to the stereoinvertive Atherton–Todd reaction. Alternatively, a 1‐N exclusion pathway is promoted by acetic acid to provide the corresponding diazo compound. The effectiveness of this protocol has been further demonstrated by the total synthesis of the diazo‐containing natural product LL‐D05139β, which was prepared as a potassium salt for the first time in 6 steps and 26.5 % overall yield.

Synthesis of new symmetrical diamidophosphates based on <i>meta</i>-phenylenediamine under microwave irradiation

A new series of diphosphorylated amidophosphates was obtained as a result of the reaction of meta -phenylenediamine with dialkylphosphites in the presence of CCl4 and triethylamine (Atherton-Todd reaction) under microwave irradiation. Structure of all the obtained amidophosphates was established on the basis of 31P, 1H, 13C NMR, IR spectroscopy and mass spectrometry methods, as well as single crystal X-ray diffraction and elemental analysis data.

Triple Silicon, Phosphorous, and Nitrogen-Grafted Lignin-Based Flame Retardant and Its Vulcanization Promotion for Styrene Butadiene Rubber.

In this study, we present an innovative environmental silicon-, phosphorus-, and nitrogen-triple lignin-based flame retardant (Lig-K-DOPO). Lig-K-DOPO was successfully prepared by condensation of lignin with flame retardant intermediate DOPO-KH550 synthesized via Atherton-Todd reaction between 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and γ-aminopropyl triethoxysilane (KH550A). The presence of silicon, phosphate, and nitrogen groups was characterized by FTIR, XPS, and 31P NMR spectroscopy. Lig-K-DOPO exhibited advanced thermal stability compared with pristine lignin supported by TGA analysis. The curing characteristic measurement showed that addition of Lig-K-DOPO promoted the curing rate and crosslink density to styrene butadiene rubber (SBR). Moreover, the cone calorimetry results indicated Lig-K-DOPO conferred impressive flame retardancy and smoke suppression. The addition of 20 phr Lig-K-DOPO reduced SBR blends 19.1% peak heat release rate (PHRR), 13.2% total heat release (THR), 53.2% smoke production rate (SPR), and 45.7% peak smoke production rate (PSPR). This strategy provides insights into multifunctional additives and greatly extends the comprehensive utilization of industrial lignin.

Et4NCl-Promoted Electrochemical Atherton-Todd Type Reaction to Construct P(O)–F Bonds

An electrochemical synthetic strategy to construct P(O)-F bonds was developed via the Atherton-Todd reaction. Promoted by Et4NCl, a series of biologically active phosphoric fluorides were synthesized by use of commercially available P(O)-H feedstocks and Et3N·3HF as the F-source. With this protocol, some potentially functional P(O)-OR and P(O)-SR motifs could also be smoothly forged. This sustainable fluorination approach features step-economy, is chemical-oxidant- and metal-catalyst-free, and offers low cost and mild conditions. Additionally, cyclic voltammetry and control experiments were conducted to propose a reasonable mechanism.

Synthesis of Amidophosphates Based on 1-Ethynyl-1-Aminocyclohexane Upon Microwave Activation and their Biological Activity

The researches for developing the methods for synthesizing new functionally substituted derivatives of alicyclic dialkylamidophosphates, establishing their structure, and searching for promising biologically active compounds in their series, are modern and relevant. The given study aimed to develop the synthesis of amidophosphates based on the example of phosphorylation of 1-ethynyl-1- aminocyclohexane with dialkyl phosphites in the presence of triethylamine in carbon tetrachloride in the Atherton-Todd reaction conditions using microwave irradiation of the reaction mixture. The reaction of 1-ethynyl-1-aminocyclohexane with dialkyl phosphites was carried out in a CCl4 excess at an equimolar ratio of reagents, triethylamine was used as an HCl acceptor. The highest yields of dialkyl- N-(1-ethynylcyclohexan-1-yl)amidophosphates were achieved by adding equimolar amounts of dialkyl phosphites to the mixture of 1-ethynyl-1-aminocyclohexane, triethylamine, and CCl4 followed by the subsequent activation of the mixture in a microwave reactor (MAS-II Plus MW) (MW 102 W, 115 °C, microwave irradiation time was 3‒5 min). The composition and structure of the obtained compounds were proved by elemental analysis, IR, 1H, 13C, 31P NMR spectroscopy, and X-ray diffraction analysis (XRD). The biological tests carried out in laboratory and field conditions allowed identifying diethyl-N-(1-ethynylcyclohexan-1-yl) amidophosphate among the synthesized compounds, which produces a high growth-regulating effect on the growth, development, and yield of agricultural crops.

A DOPO-Based Compound Containing Aminophenyl Silicone Oil for Reducing Fire Hazards of Polycarbonate

A novel P/N/Si-containing flame retardant (marked as DASO) was synthesized through an Atherton-Todd reaction between 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide and aminophenyl silicone oil, and further used for reducing fire hazards of polycarbonate (PC). The chemical structure of DASO was verified via FTIR, 1H, and 31P NMR. Upon the incorporation of 2 wt% DASO, the FRPC composite achieved a high limiting oxygen index (LOI) of 32.2% and a desired UL-94 V-0 rating. In this case, the peak heat release rate (PHRR) and total smoke production (TSP) were reduced by 26% and 44% as compared with the pure PC, respectively. The improved fire safety contributed to the flame retardant roles of DASO in both the condensed phase and gas phase. The presence of DASO promoted the formation of dense and highly graphited char layer in the condensed phase, and released non-combustible gases and phosphorus-containing radicals in the gas phase. Furthermore, the FRPC composites displayed comparable elongation at break but a slightly reduced tensile and impact strength.

Recent Advances of the Atherton-Todd Reaction

Recent Advances of the Atherton-Todd Reaction

Synthesis of ortho-Phosphated (Hetero)Arylamines through Cascade Atherton-Todd Reaction/[3,3]-Rearrangement from Arylhydroxylamines and Dialkyl Phosphites.

A practical and facile strategy for the synthesis of ortho-phosphated (hetero)arylamines from readily available arylhydroxylamines and dialkyl phosphites via cascade Atherton-Todd reaction/[3,3]-rearrangement was developed. This method is amenable to various arylhydroxylamines such as phenylhydroxylamines, naphthylhydroxylamines, and pyridylhydroxylamines, has mild reaction conditions, is oxidant-free, and has good functional-group compatibility and excellent regioselectivity.

Environmentally-benign rigid polyurethane foam produced from a reactive and phosphorus-functionalized biopolyol: Assessment of physicomechanical and flame-retardant properties

In the present study, after the epoxidation reaction of sunflower oil (SF) was optimized using a response surface methodology (RSM) of central composite design (CCD), the oxirane ring-opening reaction of epoxidized SF was carried out with 1,4-butanediol, and consequently, the SF-based biopolyol (14BD-pol) was obtained. A novel and reactive phosphorylated biopolyol (DPP-14BD-pol) was synthesized using the Atherton-Todd reaction of diphenyl phosphite (DPP) with the 14BD-pol. The DPP-14BD-pol was characterized in detail and a series of environmentally-benign RPUFs were fabricated using one-shot and free-rising methods with the partial substitution of DPP-14BD-pol (10, 25, 50 php). The obtained bio-RPUFs were assessed through the effect of the increasing amount of DPP-14BD-pol on the morphology, physicomechanical, thermal, and flame retardant properties. With the increase in DPP-14BD-pol addition, the apparent density and compressive strength values of bio-based RPUFs increased from 43.1 to 46.7 kg/m3 and from 239 to 260 kPa, respectively. The thermal conductivity values of bio-based RPUFs varied between 27.49 and 28.14 mW/m.K. The cellular structures were in polyhedral form, and the cell size distributions were quite homogeneous. The LOI values slightly improved from 19.3% to 20.5% up to the amount of 50 php DPP-14BD-pol. These results show that DPP-14BD-pol can partly replace the petroleum-based polyol to synthesize water-blown bio-based RPUFs with the properties that meet the demands of the polyurethane industry.

Thermal and mechanical properties of thiol-ene photocured thermosets containing DOPO-based liquid reactive flame retardant synthesized by metal-free azide-alkyne click reaction

The use of metal-free click reactions for the design and synthesis of novel flame retardant reactive monomers for thiol-ene photopolymerization is an intriguing area of research. In this study, we have prepared a new, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based, P- and N-containing reactive flame retardant via the metal-free azide-alkyne click reaction. For this purpose, first, azide-functionalized DOPO (DOPO-N3) has been synthesized via Atherton–Todd reaction, and then this compound has been reacted with acetylene dicarboxylic acid diallyl ester (ACDAE) to give the flame retardant monomer, namely DOPO-triazole diallyl ester (DTDAE). As prepared flame retardant monomer was characterized by nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) spectroscopies. Thermoset materials prepared by using DTDAE displayed over 90% gel content values. Polar triazole and phosphorous units rendered the surface of the thermosets hydrophilic. The thermal stability of the networks was enhanced, char yields increased and the glass transition temperatures (Tgs) were increased. The limiting oxygen index (LOI) values of the crosslinked materials increased up to 27.8% as the DTDAE content was increased in the formulations. The synthetic method described in this study provides a practical approach for the synthesis of a P- and N-containing flame retardant through a metal-free azide-alkyne click reaction Also, the fact that DTDAE is in a liquid state makes this study valuable as it indicates that it can be easily dispersed. It is also believed this promising compound can be used in different polymer structures and formulations to develop new flame retardants in future studies to be applied in industrial applications.

Facile synthesis of a reactive P/N/S-containing compound toward highly effective flame retardancy of epoxy resin with high transparency and improved mechanical strength

It is still a great challenge to develop flame-retardant epoxy resins (EP) with high transparency. Herein, a reactive P/N/S-containing compound (DOPT) was designed and synthesized by the Atherton-Todd reaction between p-toluenesulfonamide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. The addition of DOPT simultaneously improved the flame retardancy, fire safety and mechanical strength meanwhile kept the better transparency of the EP At 5 wt% DOPT loading, the modified EP (FREP-5) achieved a LOI value of 37.5% and UL-94 V-0 rating, with maintaining almost the same transmittance of the pure EP. Meanwhile, the FREP-5 also gave the lowest values of the peak heat release rate, total heat release, total smoke production and fire growth rate, revealing the enhanced fire safety of the flame-retardant EP. The significant improvement of flame retardancy of FREP thermosets was ascribed to the physical barrier effect of phosphorus-rich char in condensed phase, and the quenching and diluting effects of abundant phosphorus-containing free radicals and nitrogen/sulfur-containing inert gases in gaseous phase. Furthermore, the results of dynamical mechanical analysis and mechanical performance test revealed that the incorporation of DOPT improved the tensile and flexural strength of epoxy thermoset. In summary, DOPT is a novel highly efficient flame retardant for EP, which enables EP to maintain its potential application in the optical fields.

Frontispiece: Enantiodivergent Kinetic Resolution of 1,1′‐Biaryl‐2,2′‐Diols and Amino Alcohols by Dipeptide‐Phosphonium Salt Catalysis Inspired by the Atherton–Todd Reaction

Asymmetric Catalysis The enantiodivergent kinetic resolution of 1,1′-biaryl-2,2′-diols and amino alcohols by dipeptide-phosphonium salt catalysis is reported by Tianli Wang et al. in their Research Article on page 14921

Frontispiz: Enantiodivergent Kinetic Resolution of 1,1′‐Biaryl‐2,2′‐Diols and Amino Alcohols by Dipeptide‐Phosphonium Salt Catalysis Inspired by the Atherton–Todd Reaction

Asymmetrische Katalyse Die enantiodivergente kinetische Racematspaltung von 1,1′-Biaryl-2,2′-diolen und Aminoalkoholen durch Dipeptid-Phosphoniumsalz-Katalyse wird von Tianli Wang et al. im Forschungsartikel auf S. 15048 berichtet.

Enantiodivergent Kinetic Resolution of 1,1'-Biaryl-2,2'-Diols and Amino Alcohols by Dipeptide-Phosphonium Salt Catalysis Inspired by the Atherton-Todd Reaction.

A highly enantiodivergent organocatalytic method is disclosed for the synthesis of atropisomeric biaryls via kinetic resolution inspired by a dipeptide-phosphonium salt-catalyzed Atherton-Todd (A-T) reaction. This flexible approach led to both R- and S-enantiomers by fine-tuning of bifunctional phosphonium with excellent selectivity factors (s) of up to 1057 and 525, respectively. The potential of newly synthesized O-phosphorylated biaryl diols was illustrated by the synthesis of axially chiral organophosphorus compounds. Mechanistic investigations suggest that the bifunctional phosphonium halide catalyst differentiates between the in-situ-generated P-species in the A-T process, mainly involving phosphoryl chloride and phosphoric anhydride, thus leading to highly enantiodivergent O-phosphorylation reactions. Furthermore hydrogen bonding interactions between the catalysts and phosphorus molecules were crucial in asymmetric induction.

Enantiodivergent Kinetic Resolution of 1,1′‐Biaryl‐2,2′‐Diols and Amino Alcohols by Dipeptide‐Phosphonium Salt Catalysis Inspired by the Atherton–Todd Reaction

AbstractA highly enantiodivergent organocatalytic method is disclosed for the synthesis of atropisomeric biaryls via kinetic resolution inspired by a dipeptide‐phosphonium salt‐catalyzed Atherton–Todd (A‐T) reaction. This flexible approach led to both R‐ and S‐enantiomers by fine‐tuning of bifunctional phosphonium with excellent selectivity factors (s) of up to 1057 and 525, respectively. The potential of newly synthesized O‐phosphorylated biaryl diols was illustrated by the synthesis of axially chiral organophosphorus compounds. Mechanistic investigations suggest that the bifunctional phosphonium halide catalyst differentiates between the in‐situ‐generated P‐species in the A‐T process, mainly involving phosphoryl chloride and phosphoric anhydride, thus leading to highly enantiodivergent O‐phosphorylation reactions. Furthermore hydrogen bonding interactions between the catalysts and phosphorus molecules were crucial in asymmetric induction.

Carbon dioxide adducts from DOPO‐grafted polyethylenimines as both blowing agents and flame retardants for polyurethanes

AbstractThe high risk of flammability of polyurethane foams (PUFs) and the high global warming potentials of polyurethane (PU) blowing agents rank key problems to be solved in PUF industry. Herein, 9,10‐dihydro‐9‐oxa‐10‐phosphenanthrene‐10‐oxide (DOPO)‐grafted polyethylenimines (PEIs) are synthesized via Atherton–Todd reaction, with grafting rate ranging from 13.3% to 28.3%. The grafted PEIs further react with CO2 to obtain corresponding CO2 adducts (DOPO‐PEI‐CO2s). On the one hand, these CO2 adducts can disperse into PU foaming mixture to release CO2 as a climate‐friendly blowing agent. The resultant PUFs possess a density about 56 kg m−3 and a compressive strength over 200 kPa, suitable for some industrial applications. On the other hand, the DOPO grafting endows the PUFs with moderate flame retardancy, increasing the PUFs' limiting oxygen index value from 19.7 to 25 vol%, and decreasing the horizontal burning speed from about 360 mm min−1 down to 130 mm min−1. This study for the first time provides a type of polyurethane (PU) raw material that can serve as both blowing agents and flame retardants.

A zwitterionic serine modified chitosan derivative for improving protein stability and activity

A zwitterionic phosphoryldiserine (PDS)- chitosan conjugate was synthesized via Atherton-Todd reaction, and its degree of substitution of PDS and structure were characterized by 1H and 31P NMR spectra, ICP, FTIR and XRD. Thermal analysis confirmed that there existed the freezing bound water surrounding PDS-chitosan due to the introduction of zwitterionic PDS groups onto chitosan backbone. In vitro cytotoxicity and hemolysis assay demonstrated that PDS-chitosan had excellent cell compatibility. UV adsorption and fluorescence spectra revealed that the model protein, bovine serum albumin (BSA) tended to keep its native conformation and showed better thermal stability in aqueous media in the presence of PDS-chitosan. We also found that the esterase-like activity of BSA could be enhanced by low concentration of PDS-chitosan (CBSA = 0.33 mg/mL, CPDS-chitosan = 0.0625 and 0.125 mg/mL, pH = 7.4, T = 25 °C). The results indicated that zwitterionic PDS-chitosan showed great potential for maintaining protein function in biomedical applications.