The reactivity of organothallium compounds. Kinetics and mechanism of iodination of diarylthallium salts by molecular iodine in dioxane

The kinetics and mechanism of the reactions of diarylthallium, trifluoroacetates with molecular iodine in dioxane solutions have been studied. The reaction has the overall second order with the first order with respect to each reagent. The effect of substituents in the aromatic ring on the rate constant of iodination is described by the equation logk ₂ρσ⁺(ρ=-1.60, r=0.97). The reaction is catalyzed by the iodide ion. The activation enthalpies and entropies of iodination of diarylthallium trifluoroacetates in dioxane and di(p-anisyl)thallium trifluoroacetate in various solvents have been calculated. The effect of solvents on the rate constant of iodination of di(p-anisyl)thallium trifluoroacetate has been studied. The reaction mechanism is considered as an electrophilicS _EC process. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 451–455, March, 1999.     

Exchange of organometallic compounds with mercury metal : VII. Interaction of di-p-anisylthallium chloride with mercury in pyridine,ethylenediamine and dimethyl sulfoxide; prevailing role of homogeneous reaction

Kinetic study of the interaction of di-p-anisylthallium chloride with mercury metal, in pyridine, ethylenediamine, or dimethyl sulfoxide solutions, show that in the former two solvents with the following experimental conditions: solution volume 10 ml, mercury surface area 10 cm², 60°C, and without stirring of mercury, the Hg/Tl exchange occurs via the homogeneous reaction (80–90 percent) with dissolved mercury. In DMSO, under the same experimental conditions, the contribution of the homogeneous reaction is nearly the same as that of the heterogeneous one. This was determined by the study of the experimental exchange rate dependence on organic phase volume, and mercury or di-p-anisylthallium chloride solubilities in the solvents, as well as from analysis of kinetic curves for the exchange in saturated and unsaturated solutions of mercury metal in the solvents studied.In the same reactor (polarographic cell) the Hg/Hg exchange of organomercurials with Hg metal may be thought to occur via a heterogeneous reaction as the prevalent process. The difference in behaviour between organothallium and organomercury compounds may be explained by the far lower adsorbance of organothallium compounds when compared with the respective organomercury compounds. The possible mechanism of the Hg/Tl exchange involving organobimetallic intermediates is proposed.     

Kinetics of reaction of copper with substituted benzyl chlorides in dipolar aprotic solvents

The reaction of copper with benzyl chlorides in dipolar aprotic solvents has been investigated. The kinetic and thermodynamic parameters of the reaction of copper with benzyl chloride in dimethyl sulfoxide, dimethylacetamide, and hexamethylphosphoramide have been obtained. Hammett plots of log (k/k°) versus the substituent constant σ gave good correlation. The structure of the organic group has little effect on the rate of reaction of benzyl chloride with copper. The kinetic and thermodynamic parameters were correlated with donor number of solvent (DN). The ratio k_RBr/k_RCl and Hammett ρ values provide evidence in favor of the halogen atom transfer mechanism. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 547–555, 2007     

Reactions of 2-thiophenesulphonyl chloride with anion and neutral nucleophiles: Solvent effects on nucleophilic reactivity correlations

The reaction kinetics of 2-thiophenesulphonyl chloride with anion and neutral nucleophiles was studied in H₂O, D₂O and in protic solvents-H₂O (10% $\text{v}\text{v}$) and aprotic solvents-H₂O (10% $\text{v}\text{v}$) mixtures at 25°. Analysing the rate constants measured in water by Bronsted, Ritchie and Edwards equations the conclusion drawn that, for the nucleophilic order against the sulphonyl sulphur, basicity is of prime importance, although there may well be some dependence on polarizability and solvation. Solvent isotope effects show that the reactions occur by nucleophilic catalysis rather than by a general base mechanism. Water is the solvent in which there is the greater reactivity than in either protic solvents or aprotic-protic mixtures. By solubility measurements and applying Parker's equation the contributions of solvation energies of both reactants and transition states to the free energy of activation are calculated. Solvent effects on nucleophilic reactivities are discussed in terms of S parameters (similar to Ritchie N₊ parameters), and by the approach of multiparameter empirical correlations. The data point out that solvation plays a large role on nucleophilic order. A complete comprehension of the problem would require an equation that takes into some account solvent effects. The homogeneous comparison of 2-thiophenesulphonyl chloride data with those of α-disulphone, p-anisyl p-methoxybenzenesulphinyl sulphone and benzenesulphonyl chloride shows that the same factors are involved in driving the nucleophilic reactivity for these compounds.     

Linear polybenzyls. II. Lack of structure control in benzyl chloride polymerization

Polybenzyls were prepared from benzyl chloride with different catalysts and solvents and at different temperatures. A model compound reaction for the polymerization was studied by reacting benzyl chloride with an excess amount of diphenylmethane to determine the effect of reaction conditions on substitution distribution. The degree of branching of polybenzyl samples was characterized from the infrared absorption spectra by using peaks assigned to para and ortho disubstitution products and monosubstitution units. The degree of branching so obtained correlated well with the results from the model compound reactions and with the thermal stabilities of the polymers. Anthracene unit formation was also related to the isomer content, and addition of complexing agents such as SO₂ or tetranitromethane caused a reduction in branching during polymerization. An unusual glass transition behavior was observed in these polymers.     

Novel cis–trans enantiomeric conglomerates: triage and absolute configurations via anomalous X-ray scattering. A photochemical second order asymmetric transformation

Three tricyclic imides were prepared by a Diels–Alder reaction of 6-arylfulvenes and maleic anhydride, followed by treatment with NH₃. The exo isomers were found to exist as conglomerates when the aryl group was either p-tolyl or p-anisyl (although not phenyl). Triage of the p-tolyl racemate, followed by reaction with p-toluenesulfonyl chloride in CH₂Cl₂/Et₃N, led to the crystalline enantiopure N-tosylimides (these were also conglomerates). X-ray diffraction analysis of the N-tosylimides via the anomalous dispersion technique led to assignment of the absolute configurations (as either E or Z). The original p-tolyl imide enantiomers were found to racemize under UV irradiation in CHCl₃. Based on this, a possible second order asymmetric transformation under photochemical conditions was attempted, and indeed led to the isolation of crystalline imide with a small ee (∼15%).     

“One pot” synthesis of tertiary amines: Ru(II) catalyzed direct reductive N-benzylation of imines with benzyl bromide derivatives

The direct reductive N-benzylation of imines by reaction with benzyl bromide derivatives, in the presence of [RuCl₂(p-cymene)]₂ catalyst and PhSiH₃, is performed under mild conditions without additional base. This reaction proceeds by a tandem imine hydrosilylation/nucleophilic substitution with benzyl bromide derivatives to result the tertiary amines.     

Reaction of singlet oxygen with some benzylic sulfides

Product distribution, total quenching rate (k_T), and rate of chemical reaction (k_r) with singlet oxygen have been determined for some alkyl, benzyl, α-methylbenzyl, and cumyl sulfides. Their contributions depend on the steric hindering around the sulfur atom. In protic solvents, the sulfoxide is the main product via a hydrogen-bonded persulfoxide. In apolar solvents, intramolecular α-H abstraction leads to oxidative C-S bond cleavage, with varying efficiency. The behavior of sulfides is compared to that of alkenes and amines.     

Solvent effects on kinetics of an heteroatomic nucleophilic substitution reaction in ionic liquid and molecular solvents mixtures

Rate constants, k _A, for the aromatic nucleophilic substitution reaction of 2-chloro-3,5-dinitropyridine with aniline were determined in different compositions of 2-propanol mixed with hexane, benzene, and 2-methylpropan-2-ol and 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO₄]) with dimethyl sulfoxide at 25°C. The obtained rate constants of the reaction in pure solvents are in the following order: 2-methylpropan-2-ol > dimethyl sulfoxide > 2-propanol > hexane > benzene > [Emim][EtSO₄]. Molecularmicroscopic solvent parameters corresponding to the selected binary mixtures were utilized to study the kinetics of a nucleophilic substitution reaction in order to investigate and compare the effects of the solvents on a chemical process. The influence of solvent parameters including normalized polarity (E _T ^N ), dipolarity/polarizability (π*), hydrogen bond donor acidity (α), and hydrogen bond acceptor basicity (β) on the second-order rate constants were investigated and multiple linear regressions gave much better results with regard to single parameter regressions. The dipolarity/polarizability of media has a positive effect in all mixtures regarding zwitterionic character of the reaction intermediate and the hydrogen bond acceptor basicity of the solvent by stabilizing of activated complex increases the reaction rate.     

Prediction of solvents extraction-the organochlorine pesticides in soil using solubility parameter

Prediction of the optimal extraction solvent based on the solubility parameter to extract the typical organochlorine pesticides from Jiangxi red soil was reported in this paper. Hildebrand solubility parameters, including dispersion coefficient (δ_d), polarity (δ_p) and hydrogen bonding (δ_h), of extraction solvents (including hexane, dichloromethane, hexane/methanol (4:1, v/v), hexane/acetone (1:1, v/v), hexane/dichloromethane (1:1, v/v) and organochlorine pesticides were calculated using group contribution method. The solvents, such as hexane/methanol (4:1, v/v) and hexane/acetone (1:1, v/v) were selected as ideal extraction solvents to extract o,p′-DDT o,p′-DDE and o,p′-DDD with high recoveries (>82%), furthermore, these solvents can be used to extract α-endosulfan, Endrin and HCB with the reliable recoveries (>75%). The estimated finding by solubility parameters was supported by the results of soxhlet extraction.     

The rearrangement and solvolysis of furfuryl arenesulfinates

Furfuryl benzenesulfinate, furfuryl p-toluenesulfinate and 5-nitrofurfuryl benzenesulfinate were synthesized, and their behaviour under various conditions was investigated. The first two esters were found to undergo readily rearrangement to sulfone. In nonhydroxylic solvents, a mixture of furfuryl aryl sulfone and 2-methyl-3-furyl aryl sulfone is obtained. The ratio between the two sulfones changes with the polarity of the solvent. In hydroxylic solvents, only rearrangement to the furfuryl aryl sulfone takes place, and this is accompanied by solvolysis of the ester. A kinetic study of the reaction in ethanol and aqueous ethanol solvents indicated an ionization mechanism. It is suggested that under these conditions the sulfone is formed by recombination of ion pairs. A kinetic study of the rearrangement under nonsolvolytic conditions was also performed in order to obtain the effect of the solvent and the effect of added salts on the rate of rearrangement. This study has shown that the rate of rearrangement is sensitive to the ionizing power of the solvent. The addition of perchlorate was found to have a stronger effect on the formation of the furfuryl sulfone than on the 2-methyl-3-furyl sulfone. In this case an ionic mechanism is also suggested, and the two sulfones may arise by recombination from two different species of ion pairs.     

Diarylphosphinic azides: Photochemical reactions including rearrangement in methanol

On photolysis in methanol the diarylphosphinic azides AR₂P(O)N₃ (Ar = phenyl,p-tolyl,p-anisyl,p-chlorophenyl) rearragement with loss of nitrogen to form (monemeric) metaphosphonimidates which are trapped by the solvent to give methyl NP-diarylphosphonamidates (7) (41–53%). Diarylphosphinic amides (18–42%) are also usually formed, presumably from (triplet) nitrenes. The limited evidence available suggests that the rearrangements take place directly from the photo-excited azides rather than via (singlet) nitrene intermediates. One of the products of rearrangement, methyl NP-di(p-chlorophenyl)phosphonamidate, suffers extensive photochemical dechlorination giving methyl N-phenyl-P-p-chlorophenylphosphonamidate.     

DMSO-catalyzed chlorination of alcohols using N-phenylbenzimidoyl chloride

N-phenylbenzimidoyl chloride has been demonstrated as an efficient chlorination reagent catalyzed by dimethyl sulfoxide (DMSO) in conversion of alcohols to corresponding chlorides. The reaction conditions were mild, and most of the substrates gave satisfactory yields. The configuration inversion of the chlorination was proved using optically active phenyl alcohols. The amount of DMSO can be as low as 0.001 eq without reducing the efficiency of the chlorination. A plausible mechanism for the reaction was proposed and proved by experiments. The reaction is stereoselective and potentially chemoselective among primary benzyl alcohols, secondary benzyl alcohols, and unactivated aliphatic alcohols.     

From p-Xylene to Ibuprofen in Flow: Three-Step Synthesis by a Unified Sequence of Chemoselective C−H Metalations

Ibuprofen was prepared from an inactive and inexpensive p-xylene by three-step flow functionalizations through chemoselective metalations of benzyl positions in sequence using an in situ generated LICKOR-type superbase. The flow approach in the microreactor facilitated the comprehensive exploration of over 100 conditions in the first-step reaction by varying concentrations, temperatures, solvents, and equivalents of reagents, enabling optimal conditions to be found with 95 % yield by significantly suppressing the formation of byproducts, followed by the second C−H metalation step in 95 % yield. Moreover, gram-scale synthesis of ibuprofen in the final step was achieved by biphasic flow reaction of solution-phase intermediate with CO₂, isolating 2.3 g for 10 min of operation time.     

Elaboration of the ether cleaving ability and selectivity of the classical Pearlman's catalyst [Pd(OH)2/C]: concise synthesis of a precursor for a myo-inositol pyrophosphate

The cleavage of propargyl, allyl, benzyl, and PMB ethers by Pd(OH)₂/C can be tuned in that order, by varying the reaction conditions. Other moieties such as C-C double bonds, esters, trityl ether, p-bromo and p-nitrobenzyl ethers are stable to these reaction conditions. Cleavage of allyl ethers can be made catalytic by using 1:1 mixture of Pd(OH)₂/C and Pd/C. The synthetic potential of the selective ether cleaving ability of Pd(OH)₂/C, essentially under neutral conditions, has been demonstrated by an efficient synthesis of a precursor for the preparation of an inositol pyrophosphate derivative.     

LIGAND COUPLING AND PSEUDOROTATION IN THE REACTION OF ALKYL 2-PYRIDYL SULFOXIDE WITH GRIGNARD REAGENTS

Abstract

In the reaction of benzyl 2-pyridyl sulfoxide (1) with C₆H₅CH₂MgCl, the incoming Grignard reagent tends to couple preferentially with 2-pyridyl group at lower temperatures, whereas, at higher temperatures, coupling between benzyl and 2-pyridyl groups with 1 tends to increase due presumably to the relatively more facile pseudorotation² at higher temperatures.     

Polycondensation of benzyl chloride and its derivatives: A study of the reaction at different temperatures

The polycondensation reactions of benzyl chloride, α-chloroethylbenzene, and benzhydryl chloride in the presence of SnCl₄ or AlCl₃ as catalysts have been investigated in the temperature range between +80° and ?135°C. Polycondensations of benzyl chloride and α-chloroethylbenzene are quite similar in the reaction kinetics and are thought to occur by the same displacement mechanism. Polycondensation of benzhydryl chloride, however, seems to involve the formation of benzhydryl carbonium ions. At low temperatures linear polymers tend to be formed, in contrast with branched polymers produced at room temperature. Steric effects are found to play a major role in protecting polymers from branching at lower temperatures. Polybenzyl polymers are found to be less linear than poly(-α-methylbenzyl), even when prepared at ?135°C.     

Starch Formates: Synthesis and Modification

Starch can be efficiently converted into the corresponding formates homogeneously using N-formyl imidazole obtained by the reaction of 1,1′-carbonyldiimidazole and formic acid in dimethyl sulfoxide as a solvent. Starch formates are soluble in polar aprotic solvents, not susceptible against hydrolysis, and not meltable. Thermoplastics could be generated by conversion of starch formates with long-chain fatty acids exemplified by the conversion with lauroyl chloride in N,N-dimethylacetamide, leading to mixed starch laurate formates. The mixed esters show melting temperatures mainly dependent on the amount of laurate ester moieties.     

Di-p-nitrobenzyl azodicarboxylate (DNAD): an alternative azo-reagent for the Mitsunobu reaction

Di-p-nitrobenzyl azodicarboxylate is prepared in 83.6% yield in two steps as a bright yellow solid, which can be used as an azo-reagent in the Mitsunobu reaction. When a chiral secondary alcohol was used, sufficient configurational inversion of alcohol occurred under Mitsunobu conditions. That the hydrazine produced from DNAD is semisoluble in some solvents such as THF and CH₂Cl₂ makes it separated easily from the reaction mixture just via filtration. Then the recovered hydrazine compound can be re-exposed to oxidant to produce DNAD. Because DNAD is more stable than DIAD at ambient temperatures and allows easy separation, it is a good alternative azo-reagent for the Mitsunobu reaction.     

Cold NaOH/urea aqueous dissolved cellulose for benzylation: Synthesis and characterization

Cold NaOH/urea aqueous dissolved cellulose was studied for the synthesis of benzyl cellulose by etherification with benzyl chloride. By varying the molar ratios of benzyl chloride to OH groups in cellulose (1.5–4.0) and reaction temperatures (65–70 °C), benzyl cellulose with a degree of substitutions (DS) in the range of 0.29–0.54 was successfully prepared under such mild conditions. The incorporation of benzyl groups into cellulose was evidenced by multiple spectroscopies, including FT IR, ¹H NMR, ¹³C NMR, CP/MAS ¹³C NMR and XRD. In addition, the thermal stability and surface morphology of the benzyl cellulose was also investigated with regard to the degree of substitution. The results indicated that the benzyl cellulose product with a low DS (0.51) in the present study reached the same solubility in many organic solvents as compared to those prepared in heterogeneous media. After benzylation, the sample decomposed at a lower temperature with a wider temperature range, which indicated that the thermal stability of benzyl cellulose was lower than that of the native cellulose. In addition, benzylation resulted in a pronounced reduction in crystallinity as well as a fundamental alteration of morphology of the native cellulose.