Phase-transfer reactions catalyzed by phosphonium salts bound to macroporous polystyrene supports

The rate of reaction of alkyl halides with aqueous sodium acetate or cyanide catalyzed by phosphonium salts supported on insoluble polystyrene resins, and rates of ion-exchange of the chloride ion in the catalysts against the acetate ion, were studied as a function of catalyst particle size, the percentage of ring substitution, the morphology of polymer support, and distance between active site and polymer backbone. Rates of 1-bromooctane or benzyl chloride with macroporous, 7–25% ring-substituted catalysts increased with increasing ring substitution. Rates with macroporous catalysts increased as a heptamethylene spacer was introduced between the active site and the polymer backbone. Rates of ion-exchange with macroporous catalysts were facilitated with increasing ring substitution or by the introduction of the spacer chain. A relation between the catalytic activity of macroporous or microporous catalysts and ion-exchange rates under triphase conditions was discussed.     

Hydrogen‐Bonding Catalysis of Alkyl‐Onium Salts

The synthetic utility of alkyl‐onium salt compounds is widely recognized in the field of organic chemistry. Among the wide variety of onium salts, quaternary ammonium, phosphonium, and tertiary sulfonium salts have been the most useful compounds in organic syntheses. These compounds have been very useful reagents in the construction of organic building blocks. In addition, onium salts are known as reliable catalysts, which are used to promote important organic transformations by serving as phase‐transfer and ion‐pair catalysts through the activation of nucleophiles. Although phase‐transfer catalysis is a major direction for onium salt catalysis, hydrogen‐bonding catalysis of alkyl‐onium salts, which is promoted via the activation of electrophiles, has recently become a relevant topic in the field of onium salt chemistry. This Minireview introduces new possibilities and future directions for alkyl‐onium salt chemistry based on its use in hydrogen‐bonding catalysis and on its overall utility.     

Preparation and synthetic application of cellulose-supported phase transfer catalysts

Esterification of potassium cellulosate with chloroacetyl chloride and acryloyl chloride under anhydrous conditions allowed the introduction of chloromethyl and vinyl groups respectively on to the cellulose backbone. Subsequent reactions with tributylphosphine, tributylamine and diethylamine generated a number of immobilized phosphonium and ammonium salts with degrees of functionalization in the range 0.2–0.7 mmol g^?1. These cellulose-supported species were used as phase transfer catalysts in displacement reactions of solid potassium acetate and phenoxide on alkyl halides, and also in the reduction of ketones by sodium borohydride. In favourable cases virtually quantitative conversions were achieved and even non-functionalized cellulose itself displayed some activity. None of the catalysts examined were active in the reduction of acetophenone although the o-hydroxy derivative was readily reduced. At the moment it is not clear whether or not some unfavourable thermodynamic distribution factors are involved; further work is in progress.     

季鏻盐型三相相转移催化剂的制备及其化学结构与相转移催化活性的关系

 使用两种 ω-氯代酰氯 (氯乙酰氯与氯丁酰氯) 对交联聚苯乙烯微球 (CPS) 进行 Friedel-Crafts 酰基化反应,使用 1,4-二氯甲氧基丁烷对 CPS 微球进行氯甲基化反应, 分别将可交换的氯引入 CPS 微球表面, 制备了化学改性的 CPS 微球. 然后使用三苯基膦对改性微球进行季鏻化反应, 制备了间隔臂 (spacer arm) 长度不同的三种季鏻 (QP) 盐型三相相转移催化剂 QP-CPS. 考察了主要反应条件对制备过程的影响, 并以氯化苄与乙酸钠合成乙酸苄酯的反应体系作为三相相转移催化的模型体系, 初步考察了 QP-CPS 的相转移催化活性,探索了催化剂结构与相转移催化活性的关系. 结果表明, 季鏻盐的化学稳定性较差,在制备过程中需控制反应时间与温度, 且宜选用极性较高的溶剂. 季鏻盐型三相相转移催化剂 QP-CPS 对乙酸苄酯的合成具有较高的催化活性, 在液-固-液之间可有效地实现反应物种乙酸根的转移. 与季铵盐 (QN) 型三相相转移催化剂 QN-CPS 相比, 季鏻盐型三相相转移催化剂 QP-CPS 具有更高的相转移催化活性. 间隔臂越长, QP-CPS 的相转移催化活性越高, QP-CPS 的亲水和亲油性能对相转移催化活性也有很大的影响.     

Radical-type reactions in protic and aprotic media: Comparisons in nickel-catalysed electrochemical reductive cyclisations

The electrochemical reductive cyclisation of unsaturated organic halides in the presence of Ni(II) complexes as catalysts was examined in aprotic solvents such as DMF and in protic solvents such as ethanol, butanol or ethanol–water mixtures. The presence of the alcohol media enhanced the rate of recycling of the catalytic species.     

A thermogravimetric study of phosphonium halides

The TG/DTG thermal curves for a series of phosphonium halides are presented. The stability of phosphonium salts increases in the order chloride < bromide ≈ iodide. While phosphonium salts with only nonpolar groups in the cation volatilize completely, increasing substitution by polar cyanoethyl groups results in residue formation. The kinetics of the thermal decomposition can be obtained using isothermal thermogravimetry.     

POLYMER—SUPPORTED SINGLE AND MIXED AMMONIUM AND PHOSPHONIUM SALTS AS CATALYSTS FOR PHASE—TRANSFER REACTIONS

In this study was to investigate,by phase-transfer catalysis,the activity of single and mixed ammonium and phosphonium salts grafted on a “gel-type“ stryene-7% divinylbenzene copolymer in the oxidation of benzyl alcohol with hydrogen peroxide.A wide variety of catalysts with different quaternary groups and different quaternary chain length substitutents were examined.The activity of single“onium“salts increases as a consequence of the association of ammonium and phosphonium salts grafted onn the same polymeric support.The activity of polymer-supported ammonium and phosphonium salts increases with the number of carbon atoms contained in the alkyl radicals of the -onium and of the functionalization degree with phosphonium groups.     

Dehydrochlorination of vinylidene chloride-vinyl chloride copolymer by aqueous sodium or potassium hydroxide solutions under two-phase conditions

The reaction of solid copolymer of vinylidene chloride and vinyl chloride with aqueous sodium or potassium hydroxide solutions in the presence of quaternary ammonium or phosphonium salts as phase transfer catalysts gave dehydrochlorinated products with chlorine-substituted polyene structure. Among the catalysts used tetrapropylammonium bromide was the best and potassium hydroxide was more active than sodium hydroxide. The activity of quaternary ammonium salts was discussed in terms of hydrophile–lipophile balance. The effects of temperature and the concentration of the bases and catalysts were investigated to obtain the optimum reaction condition. Treatment of the polymer films and solutions in tetrahydrofuran with aqueous bases under two-phase conditions also produced dehydrochlorinated films and powders.     

Structural characterization of mono- and bisphosphonium salts by fast atom bombardment mass spectrometry and tandem mass spectrometry

Positive-ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono- and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium salts typically contain abundant intact cations that can be used to establish the cationic relative molecular mass and diagnostic fragment ions that allow the characterization of structural subgroups. Depending on the functional group substitution on the alkyl group, additional fragment ions are observed which are formed by loss of small neutral molecules from the intact cation and that can be used for the differentiation of isomeric phosphonium salts. Molecular dication are typically observed in the FAB mass spectra of the bisphosphonium salts when they are analysed in 3-nitrobenzyl alcohol. In addition, production of singly charged ions by clustering with a counter ion, decomposition involving removal of one of the charge centres and one-electron reduction are generally observed. Structurally diagnostic fragments are also obtained. The fragmentation pathways of the ions derived from the phosphonium salts were elucidated by precursor ion and product ion tandem mass spectrometric experiments. For the phosphonium salts containing a long-chain hydrocarbon alkyl group, high-energy collision-induced decomposition of the intact cation is needed to obtain unambiguous structural information.     

Preparation of new polyether with oxetane pendant group

A new oxetane-containing polyether was synthesized by polycondensation of bisphenol-AF (BPAF) with 3,3-bis(chloromethyl)oxetane (BCMO) using the phase-transfer catalyzed method. The polycondensation proceeded very smoothly in aromatic solvents, catalyzed by quaternary ammonium or phosphonium salts, such as tetrabutylammonium bromide (TBAB) and tetrabutylphosphonium bromide (TBPB), to afford the polymer with high yield and molecular weight. Further, a polymer with relatively high molecular weight was obtained when the reactions were carried out in aromatic and lipophilic solvents such as benzene and nitrobenzene. The modification of this oxetane-containing polyether was easily achieved by carrying out ring-opening of the oxetane ring by using hydrogen chloride in methylene chloride, which produced a functional polymer containing hydroxyl and chloro groups. The oxetane-containing polyether was observed to be soluble in chlorinated aliphatic hydrocarbons such as methylene chloride and chloroform, as well as polar solvents such as DMSO, DMF, and DMAc, and also some common organic solvents such as benzene and toluene. However, it was insoluble in both aliphatic hydrocarbons as well as alcoholic solvents. The oxetane-containing polyether was observed to start losing weight at around 300°C under nitrogen atmosphere, and 10% weight loss was measured to be 411°C. The glass transition temperature of the oxetane-containing polyether was measured to be 134°C and the wide-angle X-ray diffraction pattern revealed this polymer to be semicrystalline. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 103–107, 1998     

Allylation of 5-Methylfurfural Catalyzed by Phase-Transfer Reagents in Aqueous Media

Allylation of 5-methylfurfural with allyl halide and zinc was performed by using quaternary ammonium and phosphonium salts as phase-transfer catalysts. The phosphonium salt showed higher activity than the ammonium salt. Excellent yields were obtained with both catalysts.     

Polymerization of 1,3-butadiene on cobalt and nickel halides

Butadiene polymerizes to cis-1,4 polymer on irregularly stacked, halogen-deficient crystals of cobalt(II) or nickel(II) halides. Halogen is removed from the halides by heating the salts under high vacuum or by photolyzing them in the presence of butadiene. Intrinsic viscosity and solubility of the polymer reach a steady state during polymerization. Cobalt chloride produces polymer of higher intrinsic viscosity than nickel chloride, but polymerization on nickel chloride is faster. Catalytic activity is attributed to the presence of ≤0.1% of nickel and cobalt monohalides in the catalyst.     

Catalytic phosphorylation of polyfluoroalkanols 13. Some ammonium and phosphonium salts as phosphorylation catalysts

It was shown that it is possible to use a series of ammonium and phosphonium salts as effective catalysts for the preparative synthesis of tris(polyfluoroalkyl) phosphates. The effect of the structure of substituted ammonium salts on their catalytic activity was studied in the phosphorylation of 1,1-dihydroperfluorobutanol by phosphorus oxychloride. It was determined that the reaction rate is affected not only by the solubility of the salt, but also by the nature of the ion pair and the steric access of the onium center for solvation by phosphoryl compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2789–2792, December, 1989.     

Hydrogenation of carbon monoxide in the presence of homogeneous ruthenium catalysts: effects of onium halides as promoters

The direct formation of ethylene glycol and ethanol from synthesis gas in the presence of a homogeneous ruthenium carbonyl catalyst is promoted by onium halides, such as ammonium, phosphonium and iminium halides. The catalytic activities for ethylene glycol and ethanol formation are dependent on the nature of the halides, and increase in the order I⁻ < Br⁻ < Cl⁻ and Cl⁻ < I⁻ ≤ Br⁻, respectively. The ruthenium catalyst in conjunction with (Ph₃P)₂NCl shows the highest activity for ethylene glycol formation. The catalytic activities are dependent on the electron-accepting abilities of the solvents. A moderate electron-accepting ability of the solvent is important for oxygenate formation.     

Efficient synthesis of β-halogeno protected l-alanines and their β-phosphonium derivatives

Ring opening of oxazolines, prepared from l-serinates, with trimethylsilyl halides (TMSX) led to β-halogeno-N-benzoyl-α-amino esters in good to excellent yields. Quaternization of triphenylphosphine by the β-bromo or -iodo amino esters gave the corresponding β-phosphonium salts in overall yields of up to 93% and with e.e. >96%. Hydrolysis of the ester function afforded the phosphonium salt bearing an N-benzoyl-α-amino acid substituent, with partial racemization. However, the reaction of the TMSX with the carboxylic salt, prepared by saponification of the starting oxazoline ester, furnished the corresponding β-halogeno-N-benzoyl-α-amino acids in 70–95% yields. Quaternization of triphenylphosphine by the bromo or iodo derivatives led to the phosphonium salts bearing a free acid function in 95% yield, without racemization. The efficiency of this synthesis was demonstrated by the preparation of these phosphonium salts in excellent overall yields, by a one-pot procedure starting from the oxazoline.     

Laser microprobe mass spectrometry of quaternary phosphonium salts: Direct versus matrix-assisted laser desorption

The use of laser microprobe mass spectrometry (LMMS) for the structural characterization of thermolabile quaternary phosphonium salts has been evaluated. A comparison has been made between LM mass spectra obtained by direct analysis of “neat” organic salts and the corresponding “matrix-assisted” LM mass spectra. Main limitations of LMMS for the direct analysis of neat organic salts (i.e., no matrix) result from (1) formation of artifact ions that originate from thermal degradation and surface recombination reactions and (2) poor shot-to-shot reproducibility of the spectra. Dilution of the organic salts in a suitable, UV-absorbing matrix (e.g., nicotinic acid) significantly enhances the quality of the LM mass spectra. Improvements are: (1) an increase of the ion yield of preformed cations, (2) reduction or elimination of thermal decomposition and other deleterious surface reactions, and (3) a much better shot-to-shot spectral reproducibility. An interesting analytical feature is that these LM mass spectra, which contain only a few matrix peaks, can be obtained for subnanogram amounts of sample. The results also show that triphenylphosphonium salts with polycyclic aromatic substituents can be used as “molecular thermometers” to probe both the temperatures experienced by the sample molecules during the laser-induced desorption ionization process and the internal energies of the desorbed ion species. In this way, quaternary phosphonium salts can be used for evaluating whether improvements have been achieved by applying different sample treatments. Comparison of four different matrices (i.e., nicotinic acid, ammonium chloride, glycerol, and 3-nitrobenzylalcohol) indicates that the effectiveness of a matrix to reduce thermal degradation and to decrease the internal energies of the ions depends on the UV-absorption characteristics and the volatilization/sublimation temperature of the matrix material.     

Formation of vinyl halides via a ruthenium-catalyzed three-component coupling

The ruthenium-catalyzed three-component coupling of an alkyne, an enone, and halide ion to form E- or Z-vinyl halides has been investigated. Through systematic optimization experiments, the conditions effecting the olefin selectivity were examined. In general, more polar solvents such as DMF favored the formation of the E-isomer, and less polar solvents such as acetone favored formation of the Z-isomer. The optimized conditions for the formation of E-vinyl chlorides were found to be the use of cyclopentadienyl ruthenium (II) cyclooctadiene chloride, stannic chloride pentahydrate as a cocatalyst, and for a chloride source, either ammonium chloride in DMF/water mixtures or tetramethylammonium chloride in DMF. A range of several other ruthenium (II) catalysts was also shown to be effective. A wide variety of vinyl chlorides could be formed under these conditions. Substrates with tethered alcohols or ketones either five or six carbons from the alkyne portion gave instead diketone or cyclohexenone products. For formation of vinyl bromides, a catalyst system involving the use of cyclopentadienylruthenium (II) tris(acetonitrile) hexafluorophosphate with stannic bromide as a cocatalyst was found to be most effective. The use of ammonium bromide in DMF/acetone mixtures was optimal for the synthesis of E-vinyl bromides, and the use of lithium bromide in acetone was optimal for formation of the corresponding Z-isomer. Under either set of conditions, a wide range of vinyl bromides could be formed. When alkynes with propargylic substituents are used, enhanced selectivity for formation of the Z-isomer is observed. When aryl acetylenes are used as the coupling partners, complete selectivity for the Z-isomer is obtained. A mechanism involving a cis or trans halometalation is invoked to explain formation of the observed products. The vinyl halides have been shown to be precursors to alpha-hydroxy ketones and cyclopentenones, and as coupling partners in Suzuki-type reactions.     

Phase-transfer reactions catalyzed by phosphonium salts attached to polystyrene resins by spacer chains

The rate of reaction of 1-halooctanes with aqueous sodium cyanide catalyzed by phosphonium salts attached to insoluble polystyrene resins by tetramethylene or heptamethylene spacers was studied as a function of catalyst particle size, degree of polymer crosslinking, percentage of ring substitution, and temperature. Rates of reaction of 1-bromooctane with 17–38% ring-substituted catalysts increased as spacer-chain length increased. Rates of reaction of 1-bromooctane decreased, whether the percentage of ring substitution increased or decreased from 17–19%. Rates of reaction of 1-chlorooctane increased with increasing spacer-chain length and decreasing percentage of ring substitution. Apparent activation energy for the reaction of 1-bromooctane with 9% ring-substituted, spacer-modified catalysts was 9–10 kcal/mol and 13 kcal/mol with 17–19% ring-substituted catalysts. The hydrophilicity of catalysts decreased with increasing spacer-chain length and decreasing percentage of ring substitution. The mechanisms of reaction were discussed in terms of intrinsic reactivity and intraparticle diffusion limitations on the reaction rates.     

有机磷试剂在肽合成中的应用

本文综述有机磷试剂在肽合成中的应用情况,介绍了各种用作氨基保护试剂的磷(膦)酰氯及硫代膦酰氯和四价鏻盐;并着重介绍了不同价态的有机磷试剂用于羧基活化的发展状况。 . t     

Nickel‐Catalyzed Cross‐Electrophile Coupling with Organic Reductants in Non‐Amide Solvents

Cross‐electrophile coupling of aryl halides with alkyl halides has thus far been primarily conducted with stoichiometric metallic reductants in amide solvents. This report demonstrates that the use of tetrakis(dimethylamino)ethylene (TDAE) as an organic reductant enables the use of non‐amide solvents, such as acetonitrile or propylene oxide, for the coupling of benzyl chlorides and alkyl iodides with aryl halides. Furthermore, these conditions work for several electron‐poor heterocycles that are easily reduced by manganese. Finally, we demonstrate that TDAE addition can be used as a control element to ‘hold’ a reaction without diminishing yield or catalyst activity.