Lewis acid-base titrations employing megacycle-frequency oscillators : Titration involving stannic chloride in acetonitrile and benzene solution

By using a megacycle-frequency oscillator to follow the reaction, the Lewis acid, stannic chloride, can be titrated with nitrogen bases in acetonitrile as solvent and with oxygen bases in benzene as solvent with an error of 0.5–4%; reverse-order titrations were equally successful. The characteristic maxima and minima in the titration curves indicate that in acetonitrile stannic chloride probably forms AB, A3B4 and A4B3 adducts with piperidine, and AB and A4B3 adducts with pyridine; no adduct was indicated for diphenylamine. In benzene solution, stannic chloride forms (a) AB2 adducts with MeOH, EtOH, n-PrOH, iso-PrOH, n-BuOH, sec.-BuOH and iso-BuOH, (b) AB and AB2 adducts with acetone and tetrahydrofuran, and (c) an AB adduct with dioxane; the stoichiometry for a group of ethers is less decisive. The presence of the 1:1 tetrahydrofuran-stannic chloride adduct in benzene supports the belief that pentacoordinate tin exists in certain adducts with oxygen bases. The megacycle-frequency oscillator was also applied to the estimation of the relative base strength of Lewis bases toward a given Lewis acid by assuming that the instrument response increase, as an ether or alcohol was added to stannic chloride in benzene, is due to the formation of the new coordinate bond. Agreement of the data obtained with the limited existing data on relative base strengths of ethers is good in those cases where comparable steric factors are involved.     

The molecular structure of benzene sulphonyl chloride

An electron diffraction structure analysis was carried out on benzene sulphonyl chloride, C₆H₅SO₂Cl, utilizing data from concurrent vibrational spectroscopie calculations. The following bond lengths (r_a parameters): C-H 1.14 ± 0.03 Å, C-C 1.403 ± 0.010 Å, S-O 1.417 ± 0.012 Å, C-S 1.764 ± 0.009 Å and S-Cl 2.047 ± 0.008 Å and bond angles (r parameters): C-S-C1 100.9 ± 2.0°, C-S-O 110.0 ± 2.5°, O-S-O 122.5 ± 3.6° and O-S-Cl 105.5 ± 1.8° were determined for an asymmetric model in which the benzene ring is rotated by 75.3 ± 5.0° relative to the plane containing the sulphur-chlorine bond and bisecting the O-S-O angle. The experimental data could equally well be approximated by a symmetric model with the benzene ring perpendicular to the reference plane described previously, if a particularly large amplitude of vibration was associated with the shortest rotation-dependent carbon-chlorine distance. The bond configuration around the sulphur atom in benzene sulphonyl chloride is consistent with the structural variations observed for a series of sulphone molecules.     

The preparation and some reactions of 2, 3, 5, 6-tetrachlorophenylmagnesium chloride

The reaction of pentachlorobenzene with metallic magnesium in THF at 10–15°C gives after hydrolysis 1, 2, 4, 5-tetrachlorobenzene (76%) and pentachlorobenzene (8%); after trimethylsilylation, 1, 2, 4, 5-tetrachloro-3-(trimethylsilyl)benzene (74%), pentachloro(trimethylsilyl)benzene (8%) and 1, 2, 4, 5-tetrachlorobenzene (6%); after iodination, 1, 2, 4, 5-tetrachloroiodobenzene (44%), pentachloroiodobenzene (12%) and 1, 2, 4, 5-tetrachlorobenzene (9%); and finally after carbonation, 2, 3, 5, 6-tetrachlorobenzoic acid (58%). These products indicate that in the Grignard reaction a mixture of largely 2, 3, 5, 6-tetrachlorophenylmagnesium chloride and some pentachlorophenylmagnesium chloride is formed. The formation pentachlorophenylmagnesium chloride is explained on the basis of metal—hydrogen exchange reaction between 2, 3, 5, 6-tetrachlorophenylmagnesium chloride and the unreacted pentachlorobenzene.     

Merrifield-like resin beads by acid catalyzed incorporation of benzyl chloride into dehydrochlorinated PVC

A method is presented for preparing Merrifield-like resin beads starting from poly (vinyl chloride) (PVC) in spherical bead form. In this method, first, PVC is partially dehydrochlorinated in boiling methanolic KOH (20%) solution to create minute amounts of allylic carbon centers. Those centers trigger the un-zipping process and make further dehydrochlorination possible at relatively low temperatures (180-200 °C), while retaining the bead shapes. Acid catalyzed reaction of the dehydrochlorinated PVC particles with benzyl chloride at 180 °C yields crosslinked spherical bead polymers possessing chloromethyl benzene functions as high as 3.4 mmol g⁻¹. Experiments showed that, high yields of benzyl chloride insertions can be attained by using PVC samples with 40-50% of unsaturations. In the study transformation yields in each step were followed by conventional analytical methods and IR spectrometry. It was also demonstrated that modification of the chloromethyl groups either with KCN or sodium acetate proceeds with nearly quantitative yields, as in the case for chloromethylated styrene-divinyl benzene resins.     

Friedel-crafts polymerisations with α,α′-dimethoxy-p-xylene—I The initiation step with stannic chloride as catalyst

A white insoluble 1:1 complex is formed between stannic chloride and α,α′-dimethoxy-p-xylene (DMPX) when the Friedel-Crafts copolymerisation of DMPX and benzene is carried out in a series of solvents using stannic chloride as catalyst. As the reaction proceeds, the precipitate dissolves, being converted to a 1:1 and later a 1:2 complex of stannic chloride and methanol, the latter being a product of the reaction. The 1:1 stannic chloride:methanol complex is an active catalyst for the polymerisation while the 1:2 complex is relatively inactive. The rate of the reaction is also strongly dependent upon the dielectric constant of the medium.For these reasons, a precise quantitative investigation of the kinetics of the polymerisation will be almost impossible but experimental conditions are specified whereby a partial investigation may be made for comparison with the SnCl₄/benzene/di(chloromethyl) benzene system previously studied.     

Photo-oxidation of poly(vinyl chloride)

The photo-oxidation of PVC has been studied over the temperature range 30–150°C. Initiation with ultraviolet (2537A) radiation has been correlated with the presence of minute amounts of ozone. The contribution of atomic oxygen and singlet oxygen (¹Δ_g) molecules to the initiation mechanism is discussed. The β-chloroketones probably formed in the photo-oxidation of PVC, decomposed according to a Norrish type I reaction without loss of chlorine atoms. The gaseous products of the photo-oxidation of PVC at 30°C were carbon dioxide, carbon monoxide, hydrogen, and methane. Hydrogen chloride was obtained only when PVC was heated at high temperatures. When PVC was photo-oxidized and then heated at high temperature, benzene was obtained in addition to hydrogen chloride. The gaseous products from the photo-oxidations of model compounds, such as 4-chloro-2-butanone and 2,4-dichloropentane, were also compared with those from PVC. Hydrogen chloride was detected only after photo-oxidation at temperatures of 25°C or higher. Therefore, it was concluded that hydrogen chloride is mainly a product of thermal decomposition. Since unsaturation was not observed in photo-oxidized PVC films, the cause of discoloration is unclear. When PVC was modified by stabilizers or additives, the oxidative degradation was further complicated by side reactions with the additives.     

Squaric acid-based peptidic inhibitors of matrix metalloprotease-1

[structure: see text] A series of squaric acid-peptide conjugates were synthesized and evaluated as inhibitors of MMP-1. The cyclobut-3-enedione core was substituted at the 3-position with several functional groups, such as -N(alkyl)OH, -NHOH, and -OH, that are designed to bind to the zinc atom in the active site of the metalloprotease. The 4-position of the cyclobut-3-enedione was derivatized with mono- or dipeptides that are designed to bind in the S1' and S2' subsites of the enzyme, and position the metal chelating group appropriately in the active site for binding to zinc. Positional scanning revealed that -N(Me)OH provided the highest level of inhibition among the chelating groups that were tested, and Leu-Tle-NHMe was the preferred amino acid sequence. A combination of these groups yielded an inhibitor with an IC50 value of 95 microM. For one inhibitor, conversion of one of the carbonyl groups on the cyclobut-3-enedione core to a thiocarbonyl group resulted in a 18-fold increase in potency, and yielded a compound with an IC50 value of 15 microM.     

Extraction of pertechnetate by triphenyltin chloride and trioctyltin chloride

The extraction of pertechnetate in form of ionogene associates with triphenyltin and trioctyltin cations into chloroform, benzene, toluene and nitrobenzene was studied. As aqucous phases solutions of^99mTcO ₄ ^? in deionized water and in diluted solutions of NaCl, HCl, NaNO₃, HNO₃ NaClO₄, HClO₄ and NaOH were used. Concerning the organic phases, at the use of triphenyltin chloride the extractibility of pertechnetate increases in the sequence: toluene «chloroform, benzene nitrobenzene and approximately in the sequence: NaOH<NaCl, HCl<NaNO₃<H₂O<NaClO₄ concerning aqueous phases. For trioctyltin chloride in chloroform the extractibility of TcO ₄ ^? increases approximately in the sequence of aqueous phases: NaOH<HCl, NaNO₃, NaClO₄, NaCl«H₂O and in nitobenzene in the sequence NaOH<NaClO₄<HCl<NaNO₃, NaCl«H₂O. The extractibility for trioctyltin chloride is in general slightly lower as compared with triphenyltin chloride. The results of the extraction are presented in the form of graphical plots of technetium distribution ratio (D _Te′ logD _Tc) or extraction yield (E _Tc, %) against concentration of the investigated component in aqueous or organic phase. In some of the systems of the systems studied practically quantitative extraction of pertechnetate into organic phase has been achieved.     

Iodine(III)-mediated ethoxychlorination of enamides with iron(III) chloride

The combination of (diacetoxyiodo)benzene and iron(III) chloride in ethanol allows the efficient regioselective ethoxychlorination of a broad range of enamides. Mechanistic studies tend to rule out the involvement of free radical species and point towards the implication of a mixed [chloro(ethoxy)iodo]benzene intermediate.     

Quantitative amine functionalization of polymeric organolithium compounds with 3‐dimethylaminopropyl chloride in the presence of lithium chloride

The addition of lithium chloride promoted the coupling reaction of hydrocarbon solutions of poly(styryl)lithium (PSLi) and poly(isoprenyl)lithium (PILi) with 3‐dimethylaminopropyl chloride to form the corresponding ω‐dimethylamino‐functionalized polymers. Quantitative amine functionalization was achieved for PSLi and PILi in the presence of 1 and 10 equivalents, respectively, of LiCl in benzene; the functionalization efficiency was only 67% for PSLi and 85% for PILi in the absence of LiCl. The polymer products were characterized by size exclusion chromatography, thin‐layer chromatography, and amine end‐group titration. The pure amine‐functionalized polymers were isolated by silica gel column chromatography. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 145–151, 2000     

Pyrolysis of poly(vinyl chloride)

A pyrolysis–gas chromatography–mass spectrometric technique has been developed to study the thermal degradation of poly(vinyl chlorides) polymerized at different temperatures. Hydrogen chloride and benzene evolution during successive stages of pyrolysis have been quantitatively determined and correlated to the tacticity and molecular weight of the polymer. It was found that lowering the temperature of polymerization and molecular weight depresses benzene evolution and increases char weight but does not affect the HCl yield. It is suggested that the syndiotactic trans microstructure favored at low temperature of polymerization yields polyenes which cannot cyclize to form benzene. As the molecular weight decreases, the increase in number of vinyl chain ends facilitates pyrolytic crosslinking and char formation.     

Branching generation during the free radical copolymerization of p-vinyl benzene sulfonyl chloride with styrene

The branching generation during the free radical copolymerization of chain transfer monomer p-vinyl benzene sulfonyl chloride (VBSC) with styrene was investigated by a simple mathematic model. Chain transfer constant of VBSC was determined to be around 0.3 by fitting the ¹H-NMR monitored experimental results with a mathematic model. According to the theoretical analysis, the obtained poly(VBSC) and its copolymers were substantiated to have a grafting-like main chain with residual pendent sulfonyl chloride groups after consuming most of the vinyl groups. The copolymerization results of VBSC with styrene at varied feed ratios demonstrated that conversion of sulfonyl chloride groups was lower than that of the monomer, which was in agreement with the theoretical results. The glass transition temperature, number average molecular weight and distribution of those obtained polymers were primarily investigated. Comparing with other chain transfer monomers, VBSC has a chain transfer constant much closer to unity therefore a more branched polymer is expected. Additionally, the branched polystyrene with residual sulfonyl chloride groups is hopefully to be further used as ATRP macroinitiators or reactive intermediates to synthesize functional polymers with complex structure.     

A possible mechanism for benzene formation during the pyrolysis of poly(vinyl chloride)

We studied the evolution of hydrogen chloride and benzene from two PVC samples differing only in molecular weight, during a slow pyrolysis experiment. It appears that the evolution rates and total amount of benzene decrease rapidly when molecular weight increases. Twenty to 30 benzene molecules are formed per initial chain-end. The proposed radical mechanism involves a cyclohexadienyl radical as intermediate and initiation from terminal 1-chloro-vinyl units.     

Convenient Preparation of 1,4-Dibenzylbenzene using Zinc Chloride in the Presence of Polar Solvents

1,4-Dibenzylbenzene was successfully synthesized by the Friedel-Crafts benzylation of benzene with 1,4-bis(chloromethyl)benzene using zinc chloride in the presence of polar solvents. In particular, zinc chloride dissolved in primary alcohols or ketones with a molar ratio of 1 was a highly effective catalytic system in the reaction.     

Conformational studies by nuclear magnetic resonance in nematic phases: Benzyl chloride

Spectra of benzyl chloride were analysed in two nematic phases (PCH and ZLI). The existence of the molecule as conformer with the C? Cl bond perpendicular or parallel to the benzene plane can be safely excluded. The data are consistent with a conformer with the C? Cl bond forming an angle of 60° with the benzene plane. A full discussion of the conformational problem was not possible owing to the small number of independent D_ij couplings related to the internal motion. In addition, when dealing with low potential barriers, the LCNMR technique does not give rigorous answers.     

1,2-Bis(2-pyridylethynyl)benzene, a novel trans-chelating bipyridyl ligand. structural characterization of the complexes with silver(I) triflate and palladium(II) chloride

The design, synthesis, and complexation characteristics of the bipyridyl ligand 1,2-bis-(2-pyridylethynyl)benzene are described. The X-ray crystallographic characterization of the 1:1 complexes of 1,2-bis(2-pyridylethynyl)benzene with silver(I) triflate and palladium(II) chloride are described. In the X-ray crystal structure of the silver(I) triflate complex the ligand is essentially planar with negligible distortion compatible with a good fit of the cation in the "cavity" between the pyridine N atoms. Indeed the silver center is almost linear with the N(1)-Ag(1)-N(2) angle of 177.02(10) degrees. The ligand is also essentially planar in the palladium(II) chloride complex with square planar coordination about the palladium with the N(1)-Pd(1)-N(2), Cl(2)-Pd(1)-Cl(2), and N(1)-Pd(1)-Cl(2) angles at 179.53(7), 177.17(2), and 90.52(5) degrees, respectively.     

Copolymerization of 2,2-diallyl-1,1,3,3-tetraethylguanidinium chloride and alkyl methacrylates

Radical copolymerization of 2,2-diallyl-1,1,3,3-tetraethylguanidinium chloride with methyl methacrylate and allyl methacrylate in the bulk and methanol solution in the presence of azobis-isobutyric acid dinitryle at 70–90°C has been studied. Copolymerization of 2,2-diallyl-1,1,3,3-tetraethylguanidinium chloride with methyl methacrylate or allyl methacrylate in the bulk proceeds with formation of random copolymers enriched in methacrylate units; in the copolymerization of 2,2-diallyl-1,1,3,3-tetraethylguanidiny chloride with methyl methacrylate in methanol, the copolymerization constants of the monomers become close. The kinetic parameters of the reaction have been studied, the relative activities of the monomers have been determined. It has been found that 2,2-diallyl-1,1,3,3-tetraethylguanidinium chloride is copolymerized with allyl methacrylate or methylmethacrylate to form pyrrolidinium structures in the cyclolinear polymer chain. At high degrees of conversion of the copolymerization of 2,2-diallyl-1,1,3,3-tetraethylguanidinium chloride with allyl methacrylate, the viscosity increases and the side polymer chains are crosslinked by “allyl bonds” to form insoluble copolymers, swelling in benzene and DMSO.     

Study of the benzylation of benzene and other aromatics by benzyl chloride over transition metal chloride supported mesoporous SBA-15 catalysts

The benzylation of benzene by benzyl chloride to diphenylmethane over FeCl₃, InCl₃, GaCl₃, ZnCl₂, CuCl₂ and NiCl₂ supported on mesoporous SBA-15 at 353 K has been investigated. The redox property due to the impregnation of the SBA-15 by transition metal chloride seems to play a very important role in the benzene benzylation process. Among the catalysts, the FeCl₃/SBA-15 showed both high conversation and high selectivity for the benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > anisole. More interesting is the observation that this catalyst is always active and selective for large molecules like naphthenic compounds such as methoxynaphthalene and he can also be reused in the benzylation of benzene for several times. Kinetics of the benzene benzylation over these catalysts have also been investigated.     

Polymerization of aromatic nuclei. XVI. Mechanism of chain propagation in the polymerization of benzene by aluminum chloride–cupric chloride

A study was made of the mechanism of benzene polymerization by aluminum chloride-cupric chloride. Our main effort was devoted to propagation with the aim of resolving a literature conflict as to whether a cationic or radical pathway is involved. When equimolar mixtures of benzene and haloarene are polymerized, the resulting copolymers are composed almost exclusively of benzene monomer. This approach is based on the known relative reactivities of the monomers toward electrophilic and radical species. The amount of haloaromatic present in the copolymer was determined by elemental analyses and confirmed by infrared spectroscopy. These results are strongly indicative of propagation by an electrophilic moiety. The presence of oxygen in the reaction mixture was found to have no significant effect on the rate or yield of the polymerization, in contrast to a previous published report. The progress of the reaction was followed by titration of the evolved hydrogen chloride. Phenyl radicals, obtained by the thermal decomposition of benzoyl peroxide in benzene, were found to be incapable of initiating the polymerization in the presence of cupric chloride. Increased yields of biphenyl and the presence of chlorobenzene point to oxidation of intermediate radicals by cupric chloride. None of the experimental evidence is satisfactorily interpreted by radical propagation. The data are nicely rationalized on the basis of cationic chain extension, apparently via a radical cation initiator.     

Regiochemistry of the reactions of phenylenedioxytrichlorophosphorane with phenylacetylene and propargyl chloride in the presence of benzyltrimethylammonium chloride

NMR studies revealed that the reactions of phenylenedioxytrichlorophosphorane with phenylacetylene and propargyl chloride in the presence of benzyltrimethylammonium chloride predominantly yield derivatives of 2,7-dichloro-2-oxobenzo[e]-1,2-oxaphosphorinine, i.e., the benzene ring is selectively chlorinated in the meta-position to the endocyclic O atom of the phosphorinine heterocycle.