Low-toxicity boron-containing fire-retardant additives for polymeric coatings

The possibility of using borates as fire retardants was examined. For polymeric materials prepared at high temperatures, a new zinc borate, trizinc decaborate monohydrate, was suggested.     

Complementary anion binding by bidentate boron-containing Lewis acids

Anion binding by the pyroborates (catB)₂O (1, cat = O₂C₆H₄-1,2) and (S,S-Ph₂C₂H₂O₂B)₂O (2) has been investigated by spectroscopic, structural and titration methods. 1 has been shown to act as a bifunctional Lewis acid, exemplified by the complementary (1:1) binding of bidentate bases such as acetate and dihydrogen phosphate. The former complex has been characterized in the solid state by X-ray diffraction and a binding constant of 1500 ± 550 M⁻¹ determined in chloroform solution. The reaction of 2 with acetate, by contrast, leads to breakdown of the Lewis acid chelate and to the formation of the homochiral borate anion [(S,S-Ph₂C₂H₂O₂)₂B]⁻ in good yield (84% based on the chiral component).     

Reactions of polyolefins with strong lewis acids

Treatment of a cyclohexane solution of low density polyethylene and polystyrene with anhydrous aluminum chloride causes chemical reaction between the two polymers which results in the formation of a graft copolymer. The initial copolymer-forming reaction is very rapid, and prolonged contact of the polymers with aluminum chloride causes subsequent degradation in molecular weight. Treatment of separate solutions of polyethylene, isotactic polypropylene, and ethylene–propylene copolymers with aluminum chloride was studied as a function of time. The intrinsic viscosities of the polymers dropped from initial values of 2.4–6.5 to 0.55–0.85 in 5 min, followed by a slower decline over the next 2 hr. In the case of polypropylene, the low molecular weight fragments largely retained the isotactic structure, which demonstrates that stereochemical isomerization is not a major reaction.     

Palladium-catalyzed carbonylation of chlorobenzene in the presence of lewis acids

Carbonylation of chlorobenzene to 4-chlorobenzophenone and/or benzoyl chloride may be catalyzed by PdCl₂ in the presence of Lewis acids MCl₃ (M=Al, Ga). Such a C−Cl bond carbonylation with a phosphine-free catalyst was previosly unknown.     

Bromination of pyridine in the presence of some lewis acids

The bromination of pyridine in the form of complexes with some Lewis acids and in the presence of catalytic amounts of the latter was studied. It is shown that bromination takes place readily at 100 °C in the presence of catalysts such as AlCl₃, ZnCl₂, CuCl₂, SbCl₃, InCl₃, TeCl₄, and HgCl₂. The principal bromination products are 3-bromopyridine and 3,5-dibromopyridine. The problem of the possibility of so-called back-bonding in the case of elements of the higher periods (particularly In, Te, and Sb) is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1236–1239, September, 1981.     

Bromination of quinoline in the presence of some lewis acids

Data on the bromination of quinoline in acetic anhydride and in the presence of salts of p and d elements are presented. High catalytic activity of the investigated salts, particularly the salts of p elements, was demonstrated. An unexpected orientation of the bromination of quinoline in 94% sulfuric acid in the presence of copper sulfate was discovered.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 548–550, April, 1985.     

Esterification of polymeric carboxylic acids

Polymers containing pendant carboxyl groups have been essentially completely esterified with little apparent change in molecular weight by the use of one of the following reagents: (1) trialkyl orthoesters, (2) dimethylformamide dialkyl acetals, (3) tertiary amines followed by alkyl halides, (4) quaternary ammonium hydroxide followed by alkyl halides. The use of some of these methods permits preparation of certain polymers that were previously not readily accessible.     

Neutral organic lewis acids of π type

The interaction of some neutral acids of π type, bearing appropriate unsymmetrical substitutions at the C?C group with some selected bases (H₂O, NH₃, OH^?), is compared with that of the parent compound of a new set of neutral π acids, bearing symmetrical substitutions at the C?C group with the same bases. The analyses of the interaction energy, performed according to two decomposition schemes, with and without the counterpoise corrections, make clear the similarity of symmetrically and unsymmetrically substituted neutral organic acids.     

Reaction of alkyl 2-chloro-1,1,2-irifluoroethyl ethers with lewis acids

Ethyl 2-chloro-1,1,2-trifluoroethyl ether heated with boron trifluoride etherate gave ethyl fluoride and chlorofluoroacetyl fluoride. When heated with aluminum chloride, it afforded a mixture of ethyl fluoride, ethyl chloride, chlorofluoroacetyl fluoride, and chlorofluoroacetyl chloride. Treatment of the acyl halides with ethanol yielded ethyl chloro- fluoroacetate. Butyl and octyl 2-chloro-1,1,2-trifluoroethyl ethers gave directly butyl and octyl chlorofluoroacetates, respectively, under similar conditions.     

Activation of oxaziridines by lewis acids: application in enantioselective sulfoxidation

The preparation of new and easily accessible chiral N-alkyloxaziridines for asymmetric sulfides oxidation was investigated. Most significantly, we report here that inert N-alkyloxaziridines can be activated by Lewis acids to achieve a fast, selective, and efficient oxygen atom transfer to sulfides. Asymmetric sulfoxidation by three new chiral oxaziridines (two of them were structurally characterized by X-ray analysis) afforded enantioselectivities ranging from 22% to 63% ee with the simplest aryl alkyl sulfides.     

Photochemical generation of cationic lewis acids via deligation of metal-sandwich complexes

Photoinduced loss of one or both ligands from bis(arene) metal complexes provides an attractive route to cationic Lewis acids that can function as initiators for polymerization and crosslinking reactions. In this article, we examine the spectroscopy, photochemistry and photoinitiation activity of two such complexes: Fe(mes)₂²⁺ (mes is mesitylene) and Cr(tol)₂⁺ (tol is toluene). Acetonitrile solutions of Fe(mes)₂²⁺ undergo photochemical loss of both mesitylene rings to yield solvated Fe²⁺. The quantum efficiency of deligation ranges from 0.6 to 1.0 depending upon excitation wavelength, but is independent of complex concentration, solvent, oxygen concentration and excess counter-ion. Reaction appears to occur from both ligand field and ligand-to-metal charge transfer excited states. Low thermal stability, however, limits the use of Fe(mes)₂²⁺ as a practical photoinitiator. Deligation of both arene rings also occurs upon 366 nm irradiation of Cr(tol)₂⁺ in acetonitrile. The quantum efficiency for this process is 0.04 and is independent of oxygen concentration. Photoinitiated crosslinking and insolubilization occur in a thin film of COP (copolymer of glycidyl methacrylate and ethyl acrylate) containing Cr(tol)₂⁺.     

Photoinitiation by radical-cationic mechanism in the polymerization of isobutylene with lewis acids

ESR spectra of Lewis acids (VCl₄, TiCl₄, TiBr₄, SnCl₄, and AlBr₃) and their mixtures with isobutylene were investigated in a n-heptane solution in the dark and under irradiation at 400–480 nm at ?80 to ?150°C. A signal was observed only upon irradiating mixtures of VCl₄, TiCl₄, or TiBr₄ and isobutylene. The signal was identified as an isobutylene radical-cation by comparison with a simulated spectrum. A signal indicating the presence of peroxy radicals were recorded in measurements carried out in the presence of oxygen; these radicals originated from reaction of the isobutylene radical-cation with oxygen. Radical-cation initiation by visible light is indicated by the polymerization of isobutylene by VCl₄, TiCl₄, and TiBr₄ and by ESR spectra. The inhibiting effect of oxygen in photochemically initiated polymerization of isobutylene was also elucidated.     

Mechanism of novel consecutive rearrangements of cyclobutene-fused diphenylhomobenzoquinones catalyzed by lewis acids

Lewis acid catalyzed rearrangements of highly strained [2 + 2] photoadducts 1a-d of diphenylhomobenzoquinone with various acetylenes were investigated under the influence of AlCl(3), SnCl(4), BF(3), and TiCl(4). With the relief of steric strain, these tricyclo[5.2.0.0(3,5)]non-8-ene-2,6-diones underwent the three steps of consecutive skeletal transformations. The first step was the two-way cyclobutene ring-cleavage reaction with a Wagner-Meerwein vinyl migration to either Lewis acid activated carbonyl function. This process virtually occurred under the anchimeric assistance of the endo-phenyl ring to give, after proton transfer, the phenylene-bridged tetracyclic keto alcohols 2 and 3, respectively. The next step was the acid-induced cyclopropane ring cleavage of only 3 to lead to bicyclic diones 4 via a following stereoselective proton transfer. The last one involved a Michael-type intramolecular cyclization of 4 accompanied by a proton transfer to afford thermodynamically less stable tricyclic diones 5alpha which epimerized to 5beta only by TiCl(4). The factors that control the selectivity and the reactivity of these tandem reactions were addressed on the basis of the X-ray crystal analyses as well as the PM3 calculations. It was found the present Lewis acid-catalyzed rearrangements were very dependent on the substituents of 1a-d and the nature of the Lewis acids.     

Titanium-based lewis acids for living cationic polymerizations of vinyl ethers and styrene: Control of lewis acidity in design of initiating systems

This brief account discusses the development of HCl/TiCl_4-n(OR)_n (n = 1–4), the titanium-based new initiating systems for living cationic polymerizations of vinyl ethers and styrene. The focus of this development is controlling the Lewis acidity of the metal halide components [TiCl_4-n(OR)_n] or “activators” in relation to the structure of the monomers. Thus, for vinyl ethers, relatively mild Lewis acids such as TiCl(OiPr)₃ and TiCl₂(OiPr)₂ are effective, whereas for styrene, a stronger Lewis acid such as TiCl₃(OiPr) is employed along with an added salt (nBu₄N⁺Cl⁻). In both cases, living polymers of controlled molecular weights can be obtained in methylene chloride solvent at −15°C.     

Preparation and study of properties of boron-containing polymer based on lactic and boric acids

Russian Chemical Bulletin - The method for the synthesis of a composition based on polylactic acid (PLA) and containing boric acid (BA) was proposed. The results of gravimetric analysis of granules...