Showing papers on "Lewis acids and bases published in 1970"

Chemistry of the bis[.pi.-(3)-1,2-dicarbollyl] metalates of nickel and palladium

Abstract: : The synthesis, reactions, and structures associated with the 'sandwich'-bonded bis(pi-(3)-1,2-dicarbollyl) complexes of nickel and palladium, (M(n+)(1,2-B9C2H11)2(n-4)(M=Ni,Pd), and their carbon-substituted derivatives are discussed. The nickel and palladium bis(dicarbollyl) systems each contain species with the metal atoms in the formal +2 (d8, two unpaired electrons for nickel, diamagnetic for palladium), +3 (d7, one unpaired electron), and +4 (d6, diamagnetic) oxidation states. X-ray diffraction studies coupled with magnetic, spectral, and electrochemical data were obtained for structural information. The uncharged (pi-(3)-1,2-B9C2H11)2M(IV) derivatives are Lewis acids which form addition compounds with a variety of 'soft' Lewis bases, e.g., halide ions, thiocyanate ion, naphthalene, etc. The C, C'-dimethyl-substituted nickel and palladium systems, M(1,2-B9H9C2(CH3)2)2, exhibit facile thermal ligand rearrangement reactions leading to three isomeric series of complexes. In these isomerization reactions, a ligand carbon atom in the icosahedral surface was found to migrate away from the metal atom while remaining adjacent to the carbon atom in the open pentagonal face of the ligand. Similar rearrangements occur in the unsubstituted Ni(1,2-B9C2H11)2 complex at 360-400C in the vapor phase. Cyclic voltammetry, optical resolution studies, kinetic and nmr data and their roles in the structure elucidation of these complexes are presented. (Author)

Evidence for a cyclic AA11 mechanism in the hydrolysis of benzylidene diacetates

Abstract: The acid-catalysed hydrolyses of a series of benzylidene diacetates have been studied. The rates of hydrolysis were found to depend on the Hammett acidity function H0, and plots of log kobs+Ho against log aw had negative slopes. The hydrolyses therefore occur by an A1 mechanism, and the correlation of the rates of reaction with σ+ establishes that the mechanism is AA11. The entropies of activation obtained are consistent with the formation of a cyclic transition state, in which a protonated acetoxy-group acts as a Lewis acid in assisting the loss of the second-acetoxy-group. p-Nitrobenzylidene diacetate appears to hydrolyse by the above mechanism at high acid concentrations, and by an AAc2 mechanism at lower acidities.Only p-methoxybenzylidene diacetate showed an appreciably uncatalysed reaction at 25°, and this reaction occurs by an SN1 type of process which also appears to involve a cyclic mechanism.

Preparation of a polyimide foam

Abstract: The reaction of phenyl isocyanate with phthalic anhydride to form N-phenylphthalimide is strongly solvent dependent and catalyzed by tertiary amines. Water and alcohol promote imide formation, but Lewis acids and organometallic compounds are ineffective. In DMSO solvent, benzophenone tetracarboxylic dianhydride (BTDA) and polymethylene polyphenol isocyanate (PAPI) polymerize with the evolution of carbon dioxide to yield a foamed polyimide. The solvent-freed open-celled foams exhibit exceptional fire resistance and thermal stability.

Preparation of carbamates

Abstract: N-SUBSTITUTED CARBAMATES ARE PREPARED BY REACTING AN ORGANIC CARBONATE WITH A PRIMARY OR SECONDARY AMINE IN THE PRESENCE OF A LEWIS ACID.

Polyarylsulfones, synthesis and properties,

Abstract: A new class of high molecular weight polyarylsulfones is described. Polymer synthesis and structure–property relationships are discussed. The polymers are prepared by Friedel-Crafts type polycondensation of aromatic sulfonyl chlorides with aromatic hydrocarbons. A number of Lewis acids in small quantities are useful as catalysts for the polymerization. The polymerization reaction is carried out at elevated temperatures in the melt or in solution. Inert, nonbasic solvents which are compatible with the Lewis acid catalysts such as nitrobenzene and dimethyl sulfone are useful for conducting the polymerization. Many of the polyarylsulfones are amorphous, rigid thermoplastics with unusually high softening points, having glass transition temperatures in the range of 200–350°C. Outstanding resistance to air oxidation at high temperatures is derived from incorporation of the deactivating sulfone groups in the aromatic polymer backbone. Melt stability and solubility in selected solvents are emphasized as basis for processibility by conventional solution casting and molding techniques. The combination of properties, which in addition to thermal stability includes a high level of mechanical and electrical properties, chemical inertness, and hydrolysis resistance makes these new arylsulfone polymers useful over a wide temperature range and in severe and corrosive environments.

Reactions of polyolefins with strong lewis acids

Abstract: 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.

Polymerization of coordinated monomers. IV. Copolymerization of methyl methacrylate– and methacrylonitrile–Lewis acid complexes with styrene

Abstract: Complexes of methyl methacrylate and methacrylonitrile with Lewis acids (SnCl4, AlCl3, and BF3) were copolymerized with styrene at −75°C under irradiation with a high-pressure mercury lamp in toluene solution. The resulting copolymers consisted of equimolar amount of methyl methacrylate or methacrylonitrile and styrene, regardless of the molar ratio of monomers in the feed. NMR spectroscopy showed the copolymers to have an alternate sequence. The tacticities of the copolymers varied with the complex to have an alternate sequence. The tacticities of the copolymers varied with the complex species: the copolymer from the SnCl4 complex system had a higher cosyndiotactieity, while those from the AlCl3 and the BF3 complex systems showed coisotacticity to predominate over cosyndiotacticity. NMR spectroscopic investigation of the copolymerization system indicated the presence of a charge-transfer complex between the styrene and the methyl methacrylate coordinated to SnCl4. The concentration of the charge-transfer complex was estimated to be about 30% of monomer pairs at −78°C at a 1:1 molar ratio of feed. The growing end radicals were identified as a methyl methacrylate radical for the AlCl3 complex–styrene system and a styrene radical for the SnCl4 complex–styrene system by the measurement of the ESR spectra of the copolymerization systems under or after irradation with a high-pressure mercury lamp. The tacticity of the resulting polymer appears to be controlled by the structure of the charge transfer complex. In the case of the SnCl4 complex a certain interaction of SnCl4 with the growing end radical seems to be a factor controlling the polymer structure. These copolymerizations can be explained by an alternating charge-transfer complex copolymerization scheme.

2-Substituted Imino-1,3-dithiolanes. Their Thermal Ring-isomerizations and Reactions with Epoxides

Abstract: Thermal ring-isomerization and reactions with epoxides of 2-substituted imino-1,3-dithiolanes (I) were studied. The methylimino (Ia) and ethylimino derivatives (Ib) were found to be ringisomerized to the corresponding 3-alkyl-1,3-thiazolidine-2-thione (V) at about 200°C, while the phenylimino compound (Ic) was not isomerized even under more drastic conditions. The influence of various additives including Lewis acids was also examined. In contrast to the oxygen analog of I, these imino compounds were not polymerized with Lewis acids, and catalysis of any additives on isomerization was not observed. The possibility that I thermally dissociated into methyl isothiocyanate and ethylene sulfide followed by their recombination to V would be excluded by the observation that the reaction of alkyl isothiocyanate with ethylene sulfide at 150°C afforded I in good yield. Reactions of I with epoxides were carried out regarding the isomerization mechanism. All these imino compounds reacted with epoxides to give the 2-ox...

Influence of Lewis acids on the Diels–Alder reaction. III. Rearrangement of dimethyl N-carbomethoxy-7-azabicyclo[2.2.1]2,5-heptadiene-2,3-dicarboxylate adducts to dimethyl N-carbomethoxy-3-aminophthalates

Abstract: Aluminum chloride accelerates the Diels–Alder reactions of 2- or 2,5-substituted N-carbomethoxypyrroles with dimethyl acetylenedicarboxylate, and also catalyzes rearrangement of the N-carbomethoxy-...

Complexes of Group III trimethyls with diamines

Abstract: Direct combination of the Lewis acids, Me3M (where M = B, Al, Ga, or In), and the diamines, Me2N(CH2)nNMe2 (where n = 1, 2, or 3) has given two series of complexes. A range of 1:1 complexes can be isolated with Me2NCH2NMe2 as ligand. With the other diamines, use of a 1:1 molar ratio of reactants yields crystalline 2:1 complexes with two moles of Me3M per mole of ligand. Excluding the reaction between Me3B and Me2NCH2NMe2, 2:1 complexes can be isolated by reacting the various Lewis acids with the appropriate molar quantity of the diamines. The complexes have been characterized by i.r. and proton n.m.r. spectroscopy and molecular weight measurements.A number of complexes of Me3Ga with methyl substituted ethylenediamines have been prepared and the effects of substitution on the nitrogen ligand atoms studied. Pyrolysis of these complexes has demonstrated the ready elimination of methane and has resulted in the formation of condensed Ga—N species.

Preparation of amides

Abstract: N-SUBSTITUTED AMIDES ARE PREPARED BY REACTING AN ESTER OF A CARBOXYLIC ACID WITH A PRIMARY OR SECONDARY AMINE IN THE PRESENCE OF A LEWIS ACID.

A Mössbauer study of adducts of triphenyltin chloride with oxygen-donor substances

Abstract: Mossbauer parameters for triphenyltin chloride and a number of its adducts with oxygen-donating Lewis bases are reported. The isomer shifts for all the compounds reported are constant within experi...

Phosphinic acids and esters of alkylated p-hydroxyphenylalkanes

Abstract: Phosphinic acids and their esters of alkylated phydroxyphenylalkanes are prepared from alkylated p-hydroxyphenylalkyl halides and phosphorus halides in the presence of a complexing metal halide Lewis acid followed by a dissociation of the reaction complex with water to form the corresponding phosphinic acid or with an alcohol followed by water to form the corresponding phosphinic ester. The phosphinic acids are useful as intermediates in preparing the phosphinates which in turn are useful as stabilizers of organic materials which are subject to oxidative deterioration.

Synergistic Effect in Solvent Extraction—Effect of Oxygen and Nitrogen Containing Organic Bases on the Stability of Zinc(II) and Cobalt(II) β-Diketonate Adducts—

Abstract: The effect of the organic Lewis bases acting as a synergist on the extraction of zinc(II) and cobalt(II) with benzoyltrifluoroacetone was studied. n-Hexyl alcohol, TBP TBPO and TOPO were used as oxygen-containing bases, and quinoline, isoquinoline, lepidine, acridine and quinaldine as nitrogen-containing bases. The stability constants between metal chelates and the adduct forming materials in the organic phase were obtained by curve fitting method. The results are summarized as follows: (1) Zinc(II) and cobalt(II) chelates formed adducts including one or two molecules of the bases per metal ion. Adduct formation was carried out successively. (2) The stability of adducts with oxygen-containing organic bases increased in the order, n-hexyl alcohol

The Influence of Aluminum-Containing Lewis Acids on Polyisobutylene, Isobutylene-lsoprene Copolymers (Butyl Rubber), and Chlorinated Isobutylene-lsoprene Copolymer (Chlorobutyl)

Abstract: The influence of aluminum-containing Lewis acids, eg, AlCl3, AlEtCl2, AlEt2Cl, AlEt3, and AliBu3, on polyisobutylene, isobutylene-isoprene copolymer (butyl rubber), and chlorinated butyl rubber has been investigated in nonpolar and polar solvents at various Lewis acid concentrations in the temperature range -10 to -78°C Polyisobutylene does not degrade even under the most aggressive conditions employed (AlEtCl2, -10°C) Butyl rubber degrades rapidly in the presence of AlEtCl2 in the range -10 to -50°C In contrast, no degradation occurs with the milder Lewis acid AlEt2Cl; however, in conjunction with small amounts of a suitable Bronsted acid (ie, HCl) immediate and extensive degradation takes place with AlEt2Cl as well Chlorobutyl rubber severely and very rapidly degrades in the presence of AlCl3 and AlEtCl2 With the less acidic AlEt2Cl and AlEt3, molecular weight breakdown can be prevented only when employing milder conditions, ie, at low Lewis acid concentrations in nonpolar solvents a

Cyclopolymerization of conjugated dienes

Abstract: The formation of essentially saturated polymers containing fused cyclohexane rings is a characteristic of the polymerization of conjugated dienes under the influence of all cationic or Lewis acid catalysts The amount of cyclic structures and non-terminal linear unsaturation is dependent upon the electron accepting ability of the catalyst, which may be greatly influenced by the nature of the solvent The cyclopolymerization generally proceeds to low conversion and then reaches a dormant state Addition of monomer to the dormant mixture reinitiates polymerization which again attains a limiting equilibrium conversion The molecular weight increases with conversion Polymerization in aromatic solvents results in the incorporation of phenyl groups in the polymer structure Polymers with low intrinsic viscosities have relatively high molecular weights as measured by light scattering The proposed polymerization mechanism leading to a perhydrophenanthrene structure involves initiation by a 1,2 or 1,4 monomer cation-radical and propagation through a 1,3 polymer cation-radical INTRODUCTION The polymerization of conjugated dienes with protonic or Lewis acids has been the subject of numerous investigations within the past 50 years In general, the polymers from butadiene and isoprene were reported to be low molecular weight products, varying in appearance from viscous liquids to brittle solids The microstructure consisted of predominantly trans-1,4 unsaturation, accompanied by 1,2 unsaturation, with little or no detectable cis-1,4 unsaturation However, chemical analysis indicated that the total unsaturation was considerably lower than indicated by a normalized infrared analysis wherein the unsaturation was presumed to total 100 per cent No identification of the structures responsible for the loss in unsaturation was made STRUCTURE OF CYCLOPOLYDIENES In the course of an investigation of the polymerization of butadiene and isoprene with Ziegler-type catalysts consisting of alkyl or arylmagnesium bromide or triethyl aluminum with titanium tetrachloride, it was noted that the conversion and the nature of the polymer are dependent upon the Mg/Ti and Al/Ti molar ratios1'2 The conversion curves contain two maxima (Figure 1), the first at an RMgX1TiC14 molar ratio of 05—1 or an AiR 3jTiCl4 molar ratio below 1 and the second at an Mg1Ti ratio of 3—5 or Al1Ti ratio of about 1

Stabilized mixture employing n-(beta-0,0-dialkyldithiophosphoryl) aryl sulfonamides

Abstract: WHEREIN R is selected from the group consisting of phenyl, ptolyl, p-chlorophenyl, 3,4-dichlorophenyl, 2,5-dimethylphenyl mnitrophenyl, and 2,5-dichlorophenyl and (2) a Lewis base and a process for preparing the mixture by dispersing the Lewis base into the sulfonamide. A mixture comprising (1) a N-(beta-0,0-dialkyldithiophosphoryl)aryl sulfonamides having the formula:

Dimerization and Co-dimerization of Olefinic Compounds by Co-ordination Catalysis

Abstract: Low molecular weight olefins and dienes, produced in large quantities and at low cost by petrol refining processes, such as steam cracking, may give rise by dimerization and co-dimerization to valuable intermediates. These olefinic and diolefinic dimers may find industrial applications in very important processes such as polymerization, oxo-synthesis, alkylation and so on.

Stereospecific Polymerizations of Methacrylic Esters Having Hetero Atoms in Their Pendant Alkyl Groups

Abstract: Various methacrylic esters with and without hetero atoms in their pendant ester groups were polymerized in toluene or in THF at −78°C using n-BuLi LiAlH4, or i-BuMgBr as an initiator. By comparing the isotacticities of the resultant polymers using the NMR spectral method, the influence of the hetero atom in the pendant ester group of the monomer on polymer stereoregularity was clarified. The experiments showed that the isotacticities of those polymers containing nitrogen or oxygen atoms in their side chains were lower than the isotacticites of those not containing such atoms. On the basis of these results the assumption was made that such depressing effects in isotactic propagation were caused by Lewis basicity of the nitrogen or oxygen atoms in the pendant ester groups. Furthermore, the effect of THF added to the polymerization reaction mixture, the effects of monomer concentration, the number of carbon atoms between the hetero atom and ester oxygen, and of the counter cation, all substantiated this assumption. The effect of hetero atoms on the syndiotacticities of the resultant polymers was also briefly studied.

Polyfluoroheterocyclic compounds. Part XVII. Preparation and nucleophilic substitution of tetrafluoropyrazine and the orientational effect of substituents in polysubstitution

Abstract: Chlorination of various pyrazine derivatives, preferably pyrazine-2,3-dicarboxylic acid, provides tetrachloropyrazine, which gives tetrafluoropyrazine when heated with potassium fluoride. A series of trifluoropyrazines has been obtained by reaction between tetrafluoropyrazine and nucleophiles in which the attacking atom is carbon, nitrogen, or oxygen. Trifluorohydroxypyrazine does not tautomerise appreciably to a pyrazinone. The structures of the difluoropyrazines resulting from a second nucleophilic substitution have been deduced by 19F n.m.r. spectroscopy, and substituent shielding parameters obtained from trifluoropyrazines give notably consistent values when applied to difluoropyrazines. Alkyl and chlorine substituents in a trifluoropyrazine direct nucleophilic attack to the para-, and alkoxy-substituents to the ortho-position. Tetrafluoropyrazine is also substituted in the presence of protic or Lewis acids; tetrabromopyrazine and a dibromodifluoropyrazine are obtained by use of aluminium bromide and hydrogen bromide. Various other halogeno-fluoropyrazines are obtained by incomplete fluorination of tetrachloropyrazine or from reaction of trifluorohydrazinopyrazine with metal halides.