Halogen/lithium exchange in hydrocarbon media; basic and continuous reactor studies

The halogen/lithium (X/Li) exchange’s usefulness is challenged by the extreme conditions employed during the conversion of a bromo or an iodo substituent to an organolithium intermediate. Our preliminary disclosure reveals that simple X/Li exchanges can be accomplished at ambient temperature and in doped hydrocarbon media using n-BuLi. Use of a continuous reactor featuring brief reaction times (?1 s) and large product throughputs further facilitates the production of a product resulting from a sequential X/Li exchange and nucleophilic addition.     

Metalations utilizing aryllithiums; ortho-functionalization of p-bromoanisole (pBrA)

An ortho-metalation protocol has been developed, which permits the survival of a bromine substituent in p-bromoanisole. Eight derivatives of the generated ortho-lithiated intermediate have been prepared. A neglected metalation concept is being explored here; one which proposes that minimizing the pK_a difference between the aryl substrate and the conjugate acid of the metalating agent will lead to a regiospecific and selective metalation process.     

Metalation in hydrocarbon solvents: the mechanistic aspects of substrate-promoted ortho-metalations

The methoxy-substituted aromatic reagents 1,2- and 1,3-dimethoxybenzene (1,2-DMB and 1,3-DMB) and 1,2,4-trimethoxybenzene (1,2,4-TMB) each undergo directed ortho-metalation in high yield in n-BuLi/hydrocarbon media without the aid of a catalyst. These reactions, coined ‘substrate-promoted ortho-metalations’, proceed with the methoxy aromatic substrate functioning as both the directing metalation group (DMG) and as the deoligomerization agent. Evidence that the substrates themselves serve to deoligomerize n-BuLi comes from ¹³C NMR. The relative extent of metalated product formed as a function of time for each of the three aromatics directly correlates with the substrate's time-dependent ability to coordinate to n-BuLi as measured by ¹³C NMR. The interpretation of NMR results from experiments involving 1,2,4-TMB is consistent with the metalation proceeding via the activated complex [(1,2,4-TMB)₂·(n-BuLi)₂]. Finally, conclusions from solubility experiments are that for every substrate-promoted metalation investigated, a precipitate forms in the hydrocarbon solvent, and this precipitate mostly contains the ortho-lithiated aryl intermediate.     

Chain decomposition of 2,4,6-trinitrotoluene in hydrocarbon solvents

The rate constants for the thermal decomposition of 2,4,6-trinitrotoluene have been measured in toluene and other hydrocarbon solvents. The initial, observed rate constant (k _i) increases with dilution with toluene. The concentration dependence is described by the chain decomposition scheme with the transfer of the free valence to a solvent molecule. The activation energy and logk _i were found to linearly correlate with the dissociation energy of the C-H bond of the solvent.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1977–1980, August, 1996.     

Heat of solution of extractants in hydrocarbon solvents

Enthalpies of solution and dilution of tri-n-butylphosphate in n-dodecane, benzene and n-hexane and of tri-n-octyl- and tri-n-dodecylamine in benzene, and of the last also in chlorobenzene and n-octane have been determined by direct calorimetric measurements at 30°C. From known heats of vaporization of the extractants, the corresponding heats of solvation at infinite dilution have been derived.     

Adiabatic compressibility of solutions of ethylene–propylene copolymers in hydrocarbon solvents

Adiabatic compressibility measurements are reported on solutions in hydrocarbon solvents of a low M_w high ethylene content, and of both high and low M_w low ethylene content ethylene–propylene copolymers. In all solutions the observed adiabatic compressibility was lower than the solvent value by an increment which was a function of the solvent type. Comparison of the data for a high and low molecular weight sample of the same copolymer indicates no molecular weight effects. Changes in the composition of the copolymer, as indicated by NMR spectroscopy, have only a slight effect on the adiabatic compressibility. The dominant feature of these studies is the apparent correlation of the chain length of the alkane solvent with the decrement in the compressibility.     

The preparation of substituted bithiophenyl aldehydes via the ring opening of dithieno[2,3-b:3′,2′-d]thiophene in the presence of n-BuLi

In the presence of n-BuLi in THF at low temperature, the phenomena of ring opening of symmetric substituted dithieno[2,3-b:3′,2′-d]thiophenes were observed. After quenching the organolithium intermediates with dry DMF, a series of substituted novel bithiophenyl aldehydes were prepared in good to excellent yields. The mechanism shows the key step for the ring opening of dithieno[2,3-b:3′,2′-d]thiophene is the nucleophilic attack of butyl anion onto the sulfur atom of the central ring. Total ten samples of symmetric substituted dithieno[2,3-b:3′,2′-d]thiophenes and their ring-opened products, the substituted bithiophenyl aldehydes were characterized by ¹H NMR, ¹³C NMR, and HRMS. Two ring-opened products were confirmed by X-ray single crystal analysis.     

A study of the reaction of n-BuLi with Ti(Oi-Pr)4 as a method to generate titanacyclopropane and titanacyclopropene species

The use of the combination of reagents Ti(Oi-Pr)₄/n-BuLi, introduced by the group of J.J. Eisch in 2001, has only found a few applications so far, with sometimes conflicting observations. This article describes a study aimed at clarifying the nature, the stability and the reactivity of the active organometallic species involved. Reactions with CO₂ and other trapping reagents reveal that it is generated within a few minutes at 0 °C in THF, where it can be considered to be stable for 30 min. Most of our results are consistent with the expected titanacyclopropane nature of this reagent but some observations suggest that the chemistry at play may be more complicated.     

p-Iodinations in hydrocarbon media: continuous flow reactor application

Regiospecific iodination of aryl amines, that is, aryl compounds possessing strong electron donating groups (EDG’s) in the p-position, is described. This procedure features not only the unique use of hydrocarbon media for such substitutions but also the absence of any oxidants aside from iodine itself. Further potential of this hydrocarbon media based electrophilic aromatic substitution is demonstrated by the coupling of the iodination with an in situ halogen/lithium exchange and product forming nucleophilic addition in a batch process. The protocol was ultimately scaled to a continuous flow reactor using an isolated p-iodoarylamine. Constituted as described, these procedures possess enhanced atom-economical, green and safety aspects compared to existing literature protocols.     

Chemical and photechemical reactivity in micellar media and microemulsions IV: concentration effects on isophorone dimerization

A study of concentration effects in isophorone photodimerization shows the importance not only of interfacial processes but also of selective extraction of the reactants and products. From this work, another feature can be pointed out: microemulsification is a general phenomenon and microemulsions containing a polar component as the “oil” can be prepared.     

Preparation of organomagnesium reagents in hydrocarbon solvents without organic bases

A detailed investigation of the formation of n-R₂Mg compounds in hydrocarbon solvents in the absence of organic base is reported, including information on the nature of the solutions formed and by-products, the effect of the alkyl halide, the hydrocarbon solvent and temperature of formation. The colorless product solutions had relatively high R₂Mg/MgX₂ ratios ranging from about 4 for preparations from alkyl iodides to almost 30 for those from alkyl chlorides. sec-Butyl bromide reacted only in the presence of a stoichiometric amount of diethyl ether in hexane to form solutions of [s-BuMgBr-Et₂O]_x. The reactions of the n-R₂Mg compounds in hydrocarbon solutions were also examined. Possible implications are discussed regarding the nature of these compounds.     

3-Neopentylallyllithium II. Reactions in hydrocarbon media

Product distributions are reported for several reactions in hydrocarbon solvent of 3-neopentylallyllithium, the 1,4-addition product of tert-butyllithium and 1,3-butadiene. Protolysis with several agents yields predominately the “normal” products [(Ia) and (Ib)] with less than 6% of the terminal olefin observed. The ratio of the cis/trans isomers [(Ia) and (Ib)] parallels the ratio of the lithiated forms before protolysis. Reaction with chlorotrimethylsilane also shows no “rearranged” product. Carboxylation and ketone addition reactions, however, proceed with marked rearrangement unless the ketone is very hindered. Di-tert-butyl ketone and benzophenone give no rearranged product. Addition of a second mole of butadiene also results in predominant (60%) rearrangement of the neopentylallyl group. Bromination with molecular bromine and 1,2-dibromoethane yields a mixture of dibromo-derivatives in the former case and C₁₆-diolefin coupling products in the later case. Tentative mechanisms for protolysis and addition reactions are discussed.     

Solvent effects on infrared spectra of methyl 4-hydroxybenzoate in pure organic solvents and in ethanol/CCl4 binary solvents

Infrared spectroscopy studies of methyl 4-hydroxybenzoate (MHB) in 17 different organic solvents and in ethanol/CCl4 binary solvent were undertaken to investigate the solvent-solute interactions. The frequencies of carbonyl stretching vibration nu(C=O) of MHB in single solvents were correlated with the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The assignments of the two bands of nu(C=O) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of nu(C=O) of MHB in ethanol/CCl4 binary solvents showed that several kinds of solute-solvent hydrogen bonding interactions coexisted in the mixture solvents, with a change in the mole fraction of ethanol in the binary solvents.     

Dual influence of lithium chloride on the reactivity of polystyryllithium in ethereal solvents

Addition of LiCl to ethereal solutions of polystyryllithium retards propagation of the polymerization at low polymer concentration, but accelerates it at higher polymer concentrations. This phenomenon is accounted for by the dual action of LiCl. Its dissociation yielding free common Li⁺ ions which diminish the concentration of the reactive free polystyryl anions dominates at low electrolyte concentrations. However, at their higher concentrations the Li⁺ scavenging action of LiCl, resulting in the formation of LiClLi⁺ triple ions, becomes important, it reduces the concentration of the free Li⁺ ions and increases, therefore, the proportion of the reactive free polystyryl anions.     

Prediction of Henry''s constants by the UNIFAC-FV model for hydrocarbon gases and vapors in high-boiling hydrocarbon solvents

The design of absorption processes and gas liquid reactors requires the knowledge of gas solubility data. It is shown that a modified UNIFAC-FV model can be applied to predict Henry's constants for hydrocarbon gases and vapors in high-boiling hydrocarbon solvents. Very good agreement with experimental data has been achieved.     

Role of water in determining organic reactivity in aqueous binary solvents

Kinetic data for organic reactions in various binary water-organic solvent mixtures were collected and quantitatively analysed in terms of linear-free-energy relationships by using tert-butyl chloride (2-chloro-2-methylpropane) solvolysis as the reference system. Linear similarity plots for these kinetic data were determined for solvent systems ranging from pure water mixtures up to considerable amount of cosolvent, and 161 similarity coefficients were calculated from slopes of these plots. The existence of these linear plots demonstrated that the solvent effects are of some common nature in all analysed reaction mixtures independent of the reaction type and the cosolvent used. Therefore it was concluded that the observed effects could be connected to the specific solvating properties of water, which govern reactivity even in significant dilution of water by an organic cosolvent. This conclusion was supported by the linear interrelationship between the slopes of similarity plots of different reactions, and hydrophobicity parameters log P of the reacting compounds. The relative solvent effects observed in binary water-organic solvent mixtures were for the first time directly related to the structure of reacting compounds.      

Hydrophobie effects on photophysical and photochemical processes: VI. Character of aggregates formed by hydrocarbon with long chain in poor solvents

Dodecyl β-naphthoate and 3-octadecyl pyrene were used as fluorescence probes for estimation of microscopic polarity in aggregates formed by long chain hydrocarbon Cn (n-10, 12, 14, 16, 18) in dimethyl sulfoxide-water mixed solvent. The polarity in the aggregates is similar to that in cyclohexane. The average aggregation number (N?) was determined by using time resolved fluorescence technique. N? is dependent on substrate chain length and varies from 15 to 30. The microviscosity was also measured by fluorescence depolarization method. Above phase transition temperature, the microviscosity in aggregates is slightly larger than that in micelle, but below this temperature, the microviscosity in aggregates is as large as that in solid phase.     

Microwave assisted solid additive effects in simple dry chlorination reactions with n-chlorosuccinimide

Solid additives participate in the dry microwave assisted chlorination reaction of N-chlorosuccinimide with the xylenes affecting both yields and chemoselectivities. Total yields can be increased up to nine times for simple alkylaromatics and chemoselectivities can be altered according to the desired ring or α-side chlorination product by choosing the appropriate additive. We believe that in these reactions the solid additives play a very important role by increasing yields and affecting chemoselectivities, as well as behaving as microwave energy absorbers that consequently aid the transfer of heat to the active reagents.     

Excess enthalpies of some aromatic aldehydes in n-hexane, n-heptane and benzene

Calorimetric measurements of molar excess enthalpies, H^E, at 298.15 K, of mixtures containing aromatic aldehydes of general formula C₆H₅(CH₂)_mCHO (with m = 0, 1 and 2) + n-hexane, n-heptane or benzene are reported, together with the values of H^E at equimolar composition compared with the corresponding values of H^E for the aromatic ketones in the same solvents. The experimental results clearly indicate that the intermolecular interactions between the carbonyl groups (CHO) are influenced by the intramolecular interactions between the carbonyl and phenyl groups, particularly for the mixtures containing benzaldehyde.