Phosphorus-based Acids Research Articles

Flame retardancy and thermal properties of rigid polyurethane foam conjugated with a phosphorus–nitrogen halogen-free intumescent flame retardant

In this work, a halogen-free intumescent combining phosphorus and nitrogen, flame-retardant 2-((2-hydroxyphenyl)(phenylamino)methyl5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide (HAPO) was successfully synthesized. It had been synthesized by reaction of 5,5-dimethyl-1,3, 2-dioxphosphinane 2-oxide with Schiff base. Its chemical structure was characterized in detail by Fourier transform infrared spectroscopy, 1H NMR, and 31P NMR spectrum. The flame-retardant polyurethanes were prepared with different loadings of HAPO. The thermal properties, flame retardancy and combustion behavior of the pure polyurethane foam thermosets were investigated by a series of measurements involving thermogravimetric analysis, limited oxygen index measurement, UL-94 vertical burning test, and cone calorimeter test. The results of the aforementioned tests indicated that HAPO can significantly improve the flame retardancy as well as smoke inhibition performance of polyurethane foam. Compared with the PU-Neat, the limited oxygen index of flame-retardant polyurethanes (15%) thermoset was increased from 19.5% to 23.8% and its UL-94 reached V-0 rating. In addition, the cone test results showed that the heat release rate, total heat release, rate of smoke release, and total smoke production of flame-retardant polyurethanes (10%) were decreased obvious sly. The apparent morphology of carbon residue was characterized by scanning electron microscopy, and results revealed that the modified polyurethane foam can form dense carbon layer after combustion. Thermogravimetric analysis results also indicated that the char amount of flame-retardant polyurethanes was obviously increased compared with PU-Neat. Based on the above analysis, we can draw the conclusions which in the condensed phase, phosphorus-based acids from the degradation of HAPO, this could promote the formation of continuous and dense phosphorus-rich carbon layer. In the gas phase, the flame-retardant mechanism was ascribed to the quenching effect of phosphorus-based radicals and diluting effect by non-flammable gases.

2-Hydroxy-N-phenylbenzamides and Their Esters Inhibit Acetylcholinesterase and Butyrylcholinesterase.

The development of novel inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) represents a viable approach to alleviate Alzheimer’s disease. Thirty-six halogenated 2-hydroxy-N-phenylbenzamides (salicylanilides) with various substitution patterns and their esters with phosphorus-based acids were synthesized in yields of 72% to 92% and characterized. They were evaluated for in vitro inhibition of AChE from electric eel and BuChE from equine serum using modified Ellman’s spectrophotometric method. The benzamides exhibited a moderate inhibition of AChE with IC50 values in a narrow concentration range from 33.1 to 85.8 µM. IC50 values for BuChE were higher (53.5–228.4 µM). The majority of derivatives inhibit AChE more efficiently than BuChE and are comparable or superior to rivastigmine—an established cholinesterases inhibitor used in the treatment of Alzheimer’s disease. Phosphorus-based esters especially improved the activity against BuChE with 5-chloro-2-{[4-(trifluoromethyl)phenyl]carbamoyl}phenyl diethyl phosphite 5c superiority (IC50 = 2.4 µM). This derivative was also the most selective inhibitor of BuChE. It caused a mixed inhibition of both cholinesterases and acted as a pseudo-irreversible inhibitor. Several structure-activity relationships were identified, e.g., favouring esters and benzamides obtained from 5-halogenosalicylic acids and polyhalogenated anilines. Both 2-hydroxy-N-phenylbenzamides and esters share convenient physicochemical properties for blood-brain-barrier penetration and thus central nervous system delivery.

Confined acids catalyze asymmetric single aldolizations of acetaldehyde enolates.

Reactions that form a product with the same reactive functionality as that of one of the starting compounds frequently end in oligomerization. As a salient example, selective aldol coupling of the smallest, though arguably most useful, enolizable aldehyde, acetaldehyde, with just one partner substrate has proven to be extremely challenging. Here, we report a highly enantioselective Mukaiyama aldol reaction with the simple triethylsilyl (TES) and tert-butyldimethylsilyl (TBS) enolates of acetaldehyde and various aliphatic and aromatic acceptor aldehydes. The reaction is catalyzed by recently developed, strongly acidic imidodiphosphorimidates (IDPi), which, like enzymes, display a confined active site but, like small-molecule catalysts, have a broad substrate scope. The process is scalable, fast, efficient (0.5 to 1.5 mole % catalyst loading), and greatly simplifies access to highly valuable silylated acetaldehyde aldols.

An acid inaccessible to aldol products

Organic Chemistry The aldol reaction is a venerable and widely applicable method for making carbon-carbon bonds. Ironically, it is most challenged by the simplest substrates. The trouble is that the product looks a lot like one of the reactants, and so it can latch onto the coupling partner instead. Schreyer et al. report that a bulky phosphorus-based acid catalyst alleviates this problem. The acidic site is buried in a pocket that is too small to activate the product for further reaction. The chiral geometry of the catalyst also induces high enantioselectivity. Science , this issue p. [216][1] [1]: /lookup/doi/10.1126/science.aau0817

ChemInform Abstract: Molecular Assemblies of Organooxotin Compounds

Several new structural forms of tin have been discovered recently. Most of these contain a distannoxane unit as the fundamental building block. In this account we review the reactions of mono-, di- and triorganotin precursors with carboxylic and phosphorus-based acids, and discuss the reaction pathways followed and the structures of the tin clusters

An Acidity Scale for Phosphorus-Containing Compounds Including Metal Hydrides and Dihydrogen Complexes in THF: Toward the Unification of Acidity Scales

More than 70 equilibrium constants K between acids and bases, mainly phosphine derivatives, have been measured in tetrahydrofuran (THF) at 20 °C by 1H and/or 31P NMR. The acids were chosen or newly synthesized in order to cover the wide pKαTHF range of 5−41 versus the anchor compound [HPCy3]BPh4 at 9.7. These pKαTHF values are approximations to absolute, free ion pKaTHF and are obtained by crudely correcting the observed K for 1:1 ion-pairing effects by use of the Fuoss equation. The acid/base compounds include 14 phosphonium/phosphine couples, 17 cationic hydride/neutral hydride couples, 9 neutral polyhydride/anionic hydride couples, 14 dihydrogen/hydride couples, and 4 other nitrogen- and phosphorus-based acids. The effects on pKα of the counterions BAr‘4- and BF4- vs BPh4- and [K(2,2,2-crypt)]+ versus [K(18-crown-6)]+ are found to be minor after correcting for differences in inter-ion distances in the ion-pairs involved. Correlations with ν(M−H) noted here for the first time suggest that destabilizatio...

ORGANOTIN CLUSTER CHEMISTRY

Abstract A rich cluster chemistry of organotin compounds has recently emerged based on Sn-O-Sn and Sn-S-Sn bonding formed in reactions of stannonic acids with carboxylic and phosphorus-based acids as participating ligands. In the development of the underlying chemistry, it was discovered that some members exhibit catalytic activity on transesterification and potentially in polymerization processes. Further, as new cluster compositions were uncovered, analogies became apparent with other cluster chemistries, particularly those involving aluminum-nitrogen and iron-sulfur systems. What follows is a description of the emerging cluster chemistry of these interesting new classes of organotin compounds, their interconversions, and possible applications.

The chemistry and applications of organotin(IV) complexes of phosphorus-based acids

Synthesis, reactivity, structural aspects and applications of organotin(IV) complexes with phosphorus-based acids are reviewed. Complexes are classified according to the number of organic groups on tin and the nature of the donor atoms (oxygen and/or sulphur) on phosphorus. In general, organotin complexes of these acids are synthesized either by the reaction of organotin oxide with a free ligand or by treating the organotin halide with the alkali metal salt of an add. Reactions of monoorganotin oxides with phosphorus-based adds proceed in a stepwise manner involving a variety of organotin clusters, some of which are now fully characterized. The structure of the organotin complexes of these ligands is influenced by the number of R groups on tin and the donor set of phosphorus (>PO 2, >POS, >PS 2). The >PO 2-type ligands usually prefer bidentate bridging or a chelating bonding mode, while >PS 2-type ligands bind an organotin moiety in a monodentate or chelating (asymmetric or symmetric) fashion. The application of these complexes as catalysts, corrosion inhibitors and biocides is discussed.

Organophosphorus compounds. Part 43. A molecular mechanics study: the structural effect of cyclic esters of phosphorus-based acids in hydrolytic reaction

Hydrolytic reactions of some cyclic esters of alkylphosphates and phosphonates have been studied using molecular mechanics calculations (Allinger 1977 force field, MM2 1985 program). Either the ratio of the ring opening and retention products, of hydrolysis of five-membered cyclic esters of alkylphosphates and alkylphosphonates or the structural effect of ring size and the endo-ring substituent on the hydrolytic rate constant (k) can be determined from the steric energy difference between the substrate and its pentaco-ordinated transition state (ΔE or ΔΔE). ΔE and ΔΔE can be evaluated by the method of molecular mechanics calculations MM2 1985.

ChemInform Abstract: Organotin Cluster Chemistry

Abstract A rich cluster chemistry of organotin compounds has recently emerged based on Sn-O-Sn and Sn-S-Sn bonding formed in reactions of stannonic acids with carboxylic and phosphorus-based acids as participating ligands. In the development of the underlying chemistry, it was discovered that some members exhibit catalytic activity on transesterification and potentially in polymerization processes. Further, as new cluster compositions were uncovered, analogies became apparent with other cluster chemistries, particularly those involving aluminum-nitrogen and iron-sulfur systems. What follows is a description of the emerging cluster chemistry of these interesting new classes of organotin compounds, their interconversions, and possible applications.