Effect of binary aqueous‐organic solvents on the reaction of phenacyl bromide with nitrobenzoic acid(s) in the presence of triethylamine

Second‐order rate constants (k₂) of the reaction between phenacyl bromide and equimolar mixture of nitrobenzoic acid(s)–triethylamine have been determined in dimethylformamide (DMF)/acetonitrile (ACN)/acetone and aqueous mixtures of these solvents by conductometric method at 30°C. The rates of nitrobenzoic acids are found to be in the order: 4‐NO₂ > 3‐NO₂ > 3,5‐(NO₂)₂. Changes in the rate just by the addition of water (1% (v/v)) into organic component is rationalized. Decrease in the values of k₂ on increasing water content in organic solvent is explained on the basis of preferential solvation phenomenon. Single and dual regression analysis using the various solvent parameters of aqueous mixtures (E_T(30), Z, π*, β, α, and Y) resulted in π* and α as the best parameters to explain solvation of nitrobenzoates. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 401–409, 2004     

Reactions in the presence of organic phosphites,I: High temperature amidation in the absence of solvents

When reacted for periods of 5–10 min at temperatures of about 280–300°C in the presence of certain organic phosphites polymers that contain available carboxy and aliphatic amine groups undergo amidation. This reaction can increase the molecular weight of many aliphatic polyamides by their self-reaction in an extruder. Block or graft copolymers can be formed by reacting polymers that contain aliphatic amines with others that contain carboxyl. Studies of model compounds in the companion article (II) indicate that polymerization proceeds through an diaryloxy or dialkoxy amino phosphine intermediate to produce amide bonds and disubstituted phosphite reaction by-products. In the absence of primary amines in the reaction mixture an ester is slowly formed from the carboxyl end group of the polymer and the oxysubstituent of the phosphite. In no case was a phosphorus-containing mixed anhydride detected. The mechanistic identity of the low temperature reactions in article II and the high temperature reactions in this article has not been proved conclusively, however.     

Rate constants for reaction of 1,2‐dimethylimidazole with benzyl bromide in ionic liquids and organic solvents

The rate constant for the Menschutkin reaction of 1,2‐dimethylimidazole with benzyl bromide to produce 3‐benzyl‐1,2‐dimethylimidazolium bromide was determined in a number of ionic liquids and molecular organic solvents. The rate constants in 12 ionic liquids are in the range of (1.0–3.2) × 10^?3 L mol^?1 s^?1 and vary with the solvent anion in the order (CF₃SO₂)₂ N^? < PF₆^? < BF₄^?. Variations with the solvent cation (butylmethylimidazolium, octylmethylimidazolium, butyldimethylimidazolium, octyldimethylimidazolium, butylmethylpyrrolidinium, and hexyltributylammonium) are minimal. The rate constants in the ionic liquids are comparable to those in polar aprotic molecular solvents (acetonitrile, propylene carbonate) but much higher than those in weakly polar organic solvents and in alcohols. Correlation of the rate constants with the solvatochromic parameter E _T(30) is reasonable within each group of similar solvents but very poor when all the solvents are correlated together. Better correlation is obtained for the organic solvents by using a combination of two parameters, π* (dipolarity/polarizibility) and α (hydrogen bond acidity), while additional parameters such as δ (cohesive energy density) do not provide any further improvement. © 2004 Wiley Periodicals, Inc. *

1 This article is a US Government work and, as such, is in the public domain of the United States of America.

Int J Chem Kinet 36: 253–258, 2004     

Lipase catalyzed synthesis of macrocyclic lactones in organic solvents

A new method for the preparation of macrocyclic lactones from ω-hydroxyacid methyl esters is described. The approach utilizes intramolecular transesterification catalyzed by lipase in organic solvents. This procedure is also applicable to the synthesis of asymmetric lactones.     

Kinetic study of the crosslinking reaction of 1,2‐polybutadiene with dicumyl peroxide in the absence and presence of vinyl acetate

The crosslinking reaction of 1,2-polybutadiene (1,2-PB) with dicumyl peroxide (DCPO) in dioxane was kinetically studied by means of Fourier transform near-infrared spectroscopy (FTNIR). The crosslinking reaction was followed in situ by the monitoring of the disappearance of the pendant vinyl group of 1,2-PB with FTNIR. The initial disappearance rate (R₀) of the vinyl group was expressed by R₀ = k[DCPO]^0.8[vinyl group]^−0.2 (120 °C). The overall activation energy of the reaction was estimated to be 38.3 kcal/mol. The unusual rate equation was explained in terms of the polymerization of the pendant vinyl group as an allyl monomer involving degradative chain transfer to the monomer. The reaction mixture involved electron spin resonance (ESR)-observable polymer radicals, of which the concentration rapidly increased with time owing to a progress of crosslinking after an induction period of 200 min. The crosslinking reaction of 1,2-PB with DCPO was also examined in the presence of vinyl acetate (VAc), which was regarded as a copolymerization of the vinyl group with VAc. The vinyl group of 1,2-PB was found to show a reactivity much higher than 1-octene and 3-methyl-1-hexene as model compounds in the copolymerization with VAc. This unexpectedly high reactivity of the vinyl group suggested that an intramolecular polymerization process proceeds between the pendant vinyl groups located on the same polymer chain, possibly leading to the formation of block-like polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4437–4447, 2004     

The mechanism of the reaction of elementary astatine with organic solvents

The mechanism of the reaction of elementary astatine with benzene, toluene and monochlorobenzene were studied by means of radiogaschromatography. The reaction proceeds in two steps with benzene and toluene. In Step 1 the chemical bond of At₂ is cleaved by the disintegration of either astatine and the remained astatine reacts immediately with solvent. At Step 2 the compound produced at Step 1 is started to decompose by the decay of astatine. But this mechanism could not be applied to the astatine-monochlorobenzene system.     

Kinetics of the interaction of Cd(II)-histidine complex with ninhydrin in absence and presence of cationic and anionic micelles

Kinetics of the interaction of Cd(II)-histidine complex with ninhydrin has been carried out at pH 5.02 (acetic acid-sodium acetate buffer) under varying conditions of reactant concentrations, temperature, and surfactant concentrations. The order of the reaction with respect to Cd(II)-histidine complex was unity while it was fractional with respect to ninhydrin. On the basis of these studies a mechanism has been proposed. In the absence of the surfactants, the reaction followed rate equation: while, in presence of surfactants, the following rate equation was obeyed: Anionic micelles of sodium dodecyl sulphate catalyze the reaction with the rate reaching a maximum at ca. 0.10 mol dm⁻³ surfactant. The surfactant decreases activation enthalpy and makes it more negative. Cationic micelles of cetyltrimethylammonium bromide strongly inhibit the reaction and increase the activation enthalpy but make the activation entropy more positive than the SDS micelles. Added salts (KNO₃ and NaCl) inhibit the catalysis, and the effect is more with the latter. The rate constants, binding constants with surfactants, and the index of cooperativity have been evaluated. © 1997 John Wiley & Sons, Inc.     

CuI/PPh3‐catalyzed Sonogashira coupling reaction of aryl iodides with terminal alkynes in water in the absence of palladium

The Sonogashira cross‐coupling of aryl iodides with terminal alkynes catalyzed by a simple and inexpensive catalyst system of CuI/PPh₃ in water as the sole solvent has been reported. In the presence of CuI/PPh₃, with KOH used as a base, a number of aryl iodides were treated with alkynes to afford the corresponding products in moderate to excellent yields. Copyright © 2008 John Wiley & Sons, Ltd.     

Ferric chloride catalyzed photooxidation of alkanes by air in organic solvents

In the presence of catalytic amounts of FeCl₃, alkanes (cyclohexane, n-hexane), toluene and ethylbenzene are oxidized by air oxygen to CH₃CN, (CH₃)₂CO or CH₂Cl₂ under visible light irradiation to yield ketones and alcohols.

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FeCl₃ (, -), CH₃CN, (CH₃)₂CO CH₂Cl₂ .

     

Unexpected regioselectivity in the palladium‐catalyzed reaction of silacyclobutanes with aryl iodides

The reaction of aryl iodides with 1,1‐diphenyl‐silacyclobutane in the presence of a catalytic amount of Pd(PPh₃)₄ affords unexpected ring‐opening adducts, 1‐ and 2‐propenyl(triaryl)‐silanes, in good yields. On the other hand, the PdCl₂(PhCN)₂‐catalyzed reaction of 1,1‐diphenylsilacyclobutanes with aryl halides gives ­unexpected products, triarylsilanols, after ­hydrolysis in moderate yields. The catalysis involves the reaction of aryl–palladium intermediates with silacyclobutanes along with ­regioselective aryl–silicon bond formation. Copyright © 2001 John Wiley & Sons, Ltd.     

Copper‐catalyzed C‐N coupling reaction of tosylhydrazones

Tosylhydrazones are a kind of labile and highly reactive compounds, which are apt to be transformed into reactive diazo compounds and then into extremely reactive carbenes under the basic condition. In order to fulfil the valuable C‐N coupling reaction, diaryliodonium salts are evaluated and prove to be a class of efficient electrophiles. The reaction with ligand‐free copper salt as catalyst shows a wide range of substrate scope. A plausible mechanism is proposed.     

Pd‐catalyzed Desulfitative reaction of Aryltrifluoroborates with sodium Arenesulfinates in water

An efficient procedure for the synthesis of biaryls was catalyzed by Pd(CH₃CN)₄(BF₄)₂ is reported. This Pd‐catalyzed cross‐coupling reaction of aryltrifluoroborates with sodium arenesulfinates was developed under mild and environmentally benign conditions, in water without any ligand or additive. The reaction gave a range of structurally diverse unsymmetrical bi‐aryl molecules with excellent yields, in which the byproduct was sulfur dioxide. It is worth noting that this protocol is also applicable to many heterocyclic aromatics such as thiophene, furan, pyridine, quinoline, isoquinoline and indole.     

Acceleration of the diels-alder reaction by clays suspended in organic solvents

Rapid and stereoselective Diels-Alder reactions can be run in ethanol or methylene chloride in the presence of Fe^III- doped K10 montmorillonite.     

First palladium‐catalyzed denitrated coupling reaction of nitroarenes with phenols

The first palladium‐catalyzed protocol for the denitrated coupling reaction of nitroarenes with phenols has been developed, achieving unsymmetrical diaryl ethers in moderate to excellent yields. The cyclopalladated ferrocenylimine (catalyst Ic ) exhibited highly catalytic activity for this transformation with low catalyst loading (0.75 mol%) and short reaction time (2 h). The efficiency of this reaction was demonstrated by its compatibility with a range of groups. Moreover, the rigorous exclusion of air or moisture was not required in these transformations. Copyright © 2013 John Wiley & Sons, Ltd.     

Cyanide reaction with ninhydrin: elucidation of reaction and interference mechanisms.

A new sensitive spectrophotometric method has recently been developed for the trace determination of cyanide with ninhydrin. Cyanide ion was supposed to act as a specific base catalyst. Nevertheless, this paper demonstrates that the reported assay is based on a novel reaction of cyanide with 2,2-dihydroxy-1,3-indanedione, which affords purple or blue colored salts of 2-cyano-1,2,3-trihydroxy-2H indene. Hydrindantin is merely an intermediary of the reaction. The formation of a stable and isolable ninhydrin-cyanide compound has been confirmed by its preparation in crystalline form. Also, it is thoroughly characterized by elemental as well as MS, IR, UV/VIS and 1H NMR analyses. The Ruhemann's sequence of reactions of cyanide with ninhydrin has been reconsidered and an adequate mechanism of the reaction is proposed. As a consequence, the interference of oxidizers as well as copper, silver and mercury ions with the cyanide determination has been elucidated.     

Ambient‐temperature copper‐catalyzed atom transfer radical polymerization of methacrylates in ethylene glycol solvents

The use of ethylene glycol solvents in the room‐temperature atom transfer radical polymerization (ATRP) of various hydrophobic and hydrophilic methacrylates is demonstrated. Unlike many of the very polar solvents described in the literature for room‐temperature ATRP, these solvents have good solvency for a wide range of polymers and monomers and are cheap and relatively nontoxic. Ethylene glycols with one hydroxyl and one methoxy group, such as tri(ethylene glycol) monomethyl ether (TEGMME), provide optimal results. The polymerization of methyl methacrylate in TEGMME with CuBr/N,N,N′N′,N″‐pentamethyldiethylenetriamine as the catalyst requires the addition of CuCl₂ at the beginning of the reaction to produce well‐controlled polymerizations. This leads to polymers with predictable molecular weights and relatively narrow polydispersities. Polymerization in solvents that are fully methoxy‐capped terminate prematurely because of catalyst precipitation. The electrochemical behavior of copper complexes in selected solvents is examined to determine why these solvents provide good rates at room temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1588–1598, 2005     

Effects of mixed aqueous‐organic solvents on the rate of intramolecular carboxylic group‐catalyzed cleavage of N‐(4′‐methoxyphenyl)phthalamic acid

Kinetic study on the cleavage of N‐(4′‐methoxyphenyl)phthalamic acid (NMPPAH) in mixed H₂O‐CH₃CN and H₂O‐1,4‐dioxan solvents containing 0.05 M HCl reveals the formation of phthalic anhydride (PAn)/phthalic acid (PA) as the sole or major product. Pseudo first‐order rate constants (k₁) for the conversion of NMPPAH to PAn decrease nonlinearly from 60.4 × 10^?5 to 2.64 × 10^?5 s^?1 with the increase in the contents of 1,4‐dioxan from 10 to 80% v/v in mixed aqueous solvents. The rate of cleavage of NMPPAH in mixed H₂O‐CH₃CN solvents at ≥50% v/v CH₃CN follows an irreversible consecutive reaction path: NMPPAH PA. The values of k₁ are larger in H₂O‐CH₃CN than in H₂O‐1,4‐dioxan solvents. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 316–325, 2004