Palladium-catalyzed reactions of vinylidenecyclopropanes with acetic acid

Pd(PPh₃)₄-catalyzed reactions of vinylidenecyclopropanes 1 with acetic acid proceeded smoothly at 80 °C in toluene to give the corresponding acetylated dienes 2 in moderate to good yields in the presence of DPEphos ligand. The plausible mechanism is proposed on the basis of the control and deuterium labeling experiments.     

The role of solvent in some oxygen-transfer reactions of peroxy compounds

Solvent–solute interactions in the peroxyacid oxidations are believed to be specific rather than electrostatic in nature. The kinetic solvent effects reported for the oxidations of organic sulfides, olefins, acetylenes, nitrosobenzenes, thioketones, and aryl sulfines reveal that in each case the rates are fast in nonbasic solvents (e.g., benzene, nitrobenzene, and halogenated hydrocarbons) relative to those in basic solvents such as DMF, dioxane, and alcohols. The rates in CF₃CH₂OH and aqueous or partially aqueous media are again higher than those in the basic solvents. This remakably similar pattern of sensitivity of rates to changes in the solvent nature appears to be characteristic of these oxidations as demonstrated by the existence of linear free-energy relationship. The behavior is best understood in terms of cyclic transition states for these oxidations in which charge separation is avoided by intra- or intermolecular hydrogen bonding depending on the nature of the solvent. Solvent effects on sulfoxide oxidation and on oxidations by hydrogen peroxide and t-butylhydroperoxide are also briefly discussed.     

The role of noninnocent solvent molecules in organocatalyzed asymmetric Michael addition reactions

A proline-catalyzed asymmetric Michael addition between ketones and trans-beta-nitrostyrene was studied by using the density-functional theory with mPW1PW91 and B3LYP functionals. Improved insight into the enantio- and diastereoselective formation of gamma-nitroketones/-aldehydes is obtained through transition-state analysis. Consideration of the activation parameters obtained from gas-phase calculations and continuum solvation models failed to reproduce the reported experimental stereoselectivities for the reaction between cyclohexanone and 3-pentanone with trans-beta-nitrostyrene. The correct diastereo- and enantioselectivites were obtained only upon explicit inclusion of solvent molecules in the diastereomeric transition states that pertain to the C--C bond formation. Among the several transition-state models that were examined, the one that exhibits cooperative hydrogen-bonding interactions with two molecules of methanol could explain the correct stereochemical outcome of the Michael reaction. The change in differential stabilization that arises as a result of electrostatic and hydrogen-bonding interactions in the key transition states is identified as the contributing factor toward obtaining the correct diastereomer. This study establishes the importance of including explicit solvent molecules in situations in which the gas-phase and continuum models are inadequate in obtaining meaningful insight regarding experimental stereoselectivities.     

Recovery of milligrams of products in acetic acid at millimolar concentration via solvent extraction

The system acetic acid-water-carbon disulphide divides into two immiscible layers when the water and acetic acid concentrations are about equal. One layer is almost pure carbon disulphide. Reaction products can be isolated from acetic acid via dilution with water and extraction with carbon disulphide.     

Kinetics and mechanism of the cleavage of phthalic anhydride in glacial acetic acid solvent containing aniline

Apparent second-order rate constants (k(n)(app)) for the nucleophilic reaction of aniline (Ani) with phthalic anhydride (PAn) vary from 6.30 to 7.56 M(-1) s(-1) with the increase of temperature from 30 to 50 degrees C in pure glacial acetic acid (AcOH). However, the values of pseudo-first-order rate constants (k(s)) for the acetolysis of PAn in pure AcOH increase from 16.5 x 10(-4) to 10.7 x 10(-3) s(-1) with the increase of temperature from 30 to 50 degrees C. The values of k(n)(app) and k(s) vary from 5.84 to 7.56 M(-1) s(-1) and from 35.1 x 10(-4) to 12.4 x 10(-4) s(-1), respectively, with the increase of CH(3)CN content from 1% to 80% v/v in mixed AcOH solvents at 35 degrees C. The plot of k(s) versus CH(3)CN content shows a minimum (with 10(4) k(s) = 4.40 s(-1)) at 50% v/v CH(3)CN. Similarly, the variations of k(n)(app) and k(s) with the increasing content of tetrahydrofuran (THF) in mixed AcOH solvent reveal respective a maximum (with k(n)(app) = 17.5-15.6 M(-1) s(-1)) at 40-60% v/v THF and a minimum (with k(s) = approximately 0-1.2 x 10(-4) s (-1)) at 60-70% v/v THF. The respective values of DeltaH* and DeltaS* are 15.3 +/- 1.2 kcal mol(-1) and -20.1 +/- 3.8 cal K(-1) mol(-1) for k(s) and 1.1 +/- 0.5 kcal mol(-1) and -51.2 +/- 1.7 cal K(-1) mol(-1) for k(n)(app), while the values of k(n) (= k(n)(app)/f(b) with f(b) representing the fraction of free aniline base) are almost independent of temperature within the range 30-50 degrees C. A spectrophotometric approach has been described to determine f(b) in AcOH as well as mixed AcOH-CH(3)CN and AcOH-THF solvents. Thus, the observed data, obtained under different reaction conditions, have been explained quantitatively. An optimum reaction condition, within the domain of present reaction conditions, has been suggested for the maximum yield of the desired product, N-phenylphthalamic acid.     

Removal of 2,4-Dichloro phenoxy acetic acid pesticide by solvent sublation: Experimental and theoretical studies

The removal of the pesticide 2, 4 D from water using solvent sublation process was investigated in this paper. A lab scale unit was set up and various experimental runs were carried out to study the efficiency of the removal process. The experimental findings show that the method is very effective (>90% removal) in removing traces (ppb level) of the pesticide which is not easily removable by simple air stripping. In addition a mathematical model was developed to describe the experimental findings. Some parameters of the model were measured or calculated while others such as the aqueous mass transfer coefficient and the solute partition coefficient were adjusted to fit the experimental data. The calibration of the model was carried out using the experimental results of change in gas flow rate (the easiest parameter to vary). A numerical sensitivity analysis was carried out using the calibrated model to study the effect of various parameters such as the bubble radius, aqueous phase drag-up by air, column radius and ratio of organic to aqueous volume phases.     

Room temperature sonochemical initiation of thiol-ene reactions

Thiol-ene 'click' reactions have been initiated for a range of primary alkenes using ultrasound in both toluene and water. The method is particularly effective in aqueous solutions in the presence of air.     

Influential role of ethereal solvent on organolithium compounds: the case of carboranyllithium

The influence of ethereal solvents (diethyl ether (Et(2)O), tetrahydrofuran (THF) or dimethoxyethane (DME)) on the formation of organolithiated compounds has been studied on the 1,2-C(2)B(10)H(12) platform. This platform is very attractive because it contains two C(c)-H adjacent units ready to be lithiated. On would expect that the closeness of both C(c)-H units would induce a higher resistance of the second C(c)-H unit being lithiated following the first lithiation. However, this is not the case, which makes 1,2-C(2)B(10)H(12) attractive to get a better understanding of the ethereal solvent influence on the lithiation process. The formation of carboranyl disubstituted species has been attributed to the existence of an equilibrium in which the carboranyl monolithiated species disproportionates into dilithium carborane and pristine carborane. The way Li(+) binds to C(c) in the carboranyl fragment and how the solvent stabilizes such a binding is paramount to drive the reaction to the generation of mono- and disubstituted carboranes. In fact, the proportion of mono- and disubstituted species is a consequence of the formation of contact ion pairs and, to a lesser extent, of separated ion pairs in ethereal solvents. All ethereal solvents generate contact ion pairs in which a large degree of covalent C(c)-Li(solvent) bonding can be assumed, according to experimental and theoretical data. Furthermore, Et(2)O tends to produce carboranyllitium ion pairs with a higher degree of contact ion pairs than THF or DME. It has been determined that for a high-yield preparation of monosubstituted 1-R-1,2-C(2)B(10)H(11), in C(c)-R (R=C, S or P) coupling reactions, the reagent type defines which is the most appropriate ethereal solvent. In reactions in which a halide is generated, as with ClPPh(2) or BrCH(2) CH=CH(2), Et(2)O appears to produce the highest degree of monosubstitution. In other situations, such as with S(8), or when no halide is generated, THF or DME facilitate the largest degree of monosubstitution. It has been shown that upon the self reaction of Li[1,2-C(2)B(10)H(11)] to produce [LiC(4)B(20)H(22)](-) the nucleophilicity of the carboranyllithium can even be further enhanced, beyond the ethereal solvent, by synergism with halide salts. The mediation of Li(+) in producing isomerizations on allyl substituents has also been demonstrated, as Et(2)O does not tend to induce isomerization, whereas THF or DME produces the propenyl isomer. The results presented here most probably can be extended to other molecular types to interpret the Li(+) mediation in C-C or other C-X coupling reactions.     

The deoxydative substitution reactions of nicotinamide and nicotinic acid N-oxides by 1-adamantanethiol in acetic anhydride

The reaction of nicotinamide N-oxide with 1-adamantanethiol in acetic anhydride yielded a mixture of 2-and 6-(1-adamantylthio)nicotinamides (49%, in the ratio of 24:1) and 2-, 5-, and 6-(1-adamantylthio)nicotino-nitriles (18%, in the ratio of 79:1:20). From a reaction of nicotinic acid N-oxide with 1-adamantanethiol, there was isolated 2-(1-adamantylthio)nicotinic acid as the only sulfide in 23% yield. Carbon? sulfur bond cleavage took place when 2-(1-adamantylthio)nicotinic acid, or the corresponding amide or nitrile, were boiled with concentrated hydrochloric acid to furnish 2-mercaptonicotinic acid and 1-chloroadamantane, quantitatively. The reaction of nicotinamide N-oxide alone in acetic anhydride at 135° formed N-acetyl-2-hydroxynicotinamide (61%), 2-hydroxynicotinonitrile (0.5%) and N,N-diacetyl-2-acetoxynicotinamide (0.8%).     

The mechanism of the sonochemical degradation of benzoic acid in aqueous solutions

The sonolytic degradation of benzoic acid in aqueous solution was investigated at an ultrasonic frequency of 355 kHz. The degradation rate was found to be dependent upon the solution pH and the surface activity of the solute. The degradation rate was favoured at a solution pH lower than the pK _a of benzoic acid. At pH < pK _a, HPLC, GC and ESMS analysis showed that benzoic acid could be degraded both inside the bubble by pyrolysis and at the bubble/solution interface by the reaction with OH radicals. At higher pH (> pK _a) benzoic acid could only react with OH radicals in the bulk solution. During the sonolytic degradation of benzoic acid, mono-hydroxy substituted intermediates were observed as initial products. Further OH radical attack on the mono-hydroxy intermediates led to the formation of di-hydroxy derivatives. Continuous hydroxylation of the intermediates led to ring opening followed by complete mineralization. Mineralization of benzoic acid occurred at a rate of < 40μM/h.     

The solvent effects in the reactions of carboxylic acids with oxiranes. 1. Kinetics of the reaction of acetic acid with epichlorohydrin in butan‐1‐ol

Kinetics of the reaction of acetic acid with epichlorohydrin in the presence of chromium(III) acetate in butan‐1‐ol solution have been studied. The partial reaction orders with respect to reagents were found. The reactions were of first‐order with respect to both epichlorohydrin and catalyst and zeroth order with respect to acetic acid. A kinetic model for the overall process has been proposed. The reaction constants have been calculated along with the activation parameters. The effect of dilution on the rate of addition is discussed. In the equimolar mixture of acetic acid and epichlorohydrin the apparent rate constant of the addition k₁ initially decreases to increase again at the concentration of butan‐1‐ol exceeding 3 M. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 378–387, 2000     

醋酸溶液中Pd-CuPc/Y催化甲烷选择氧化制甲醇

以氯化铜、钼酸铵、苯酐、氯化铵、尿素和NaY分子筛为原料,采用苯酐-尿素法制备了酞菁铜/分子筛复合物CuPc/Y.采用等体积浸渍法将金属钯担载在CuPc/Y上制备了Pd-CuPc/Y催化剂,并在醋酸水溶液中考察了其催化甲烷选择氧化合成甲醇反应的性能,结果表明,催化性能与反应温度、溶剂中CH₃COOH与H₂O的混合比例、对苯醌用量、反应时间等因素有关,在0.5%Pd-0.5%CuPc/Y添加量0.5 g、CH₃COOH与H₂O体积比4∶1、对苯醌用量1 000 μmol、反应时间3 h、反应温度150 ℃的条件下,甲醇的最佳生成量为1 840 μmol.Pd-CuPc/Y催化剂可以多次循环使用,但由于催化剂流失和催化剂表面的钯粒子聚集的原因,循环使用后的催化剂催化活性有所下降.Pd-CuPc/Y在醋酸溶液中催化甲烷选择氧化合成甲醇是亲电取代反应和活性氧物种氧化共同作用的结果.     

无溶剂条件下N-磺酸琥珀酰亚胺催化乙酰化反应(英文)

A small amount of succinimide-N-sulfonic acid efficiently catalyzed the acetylation of a variety alcohols, phenols, thiols, amines and aldehydes with acetic anhydride at room temperature under solvent free conditions. This catalyst has the advantages of excellent yields and short reaction times and the reaction can be carried out on a large scale, which makes it potentially useful for industrial applications.     

Acoustic emission from cavitating solutions: implications for the mechanisms of sonochemical reactions

The acoustic emission from collapsing cavitation bubbles generated using ultrasound of 20 kHz and 515 kHz frequencies in water has been measured and correlated with sonoluminescence and hydroxyl radical production to yield further information on the frequency dependence of sonochemical reactions. A reasonable correlation was found, and the results suggest differences in the predominant types of cavitation observed under laboratory conditions.     

Bromothiophene reactions. II. A novel rearrangement in the zinc and acetic acid reduction

The elimination of the α-bromine atoms of the bromothienylethanolamine derivatives 2a,b,c,d with zinc and acetic acid unexpectedly involved a migration of the ethanolamine side chain from the 3 to the 2 position in the thiophene ring. Experiments carried out with simpler analogous compounds 3, 4 and 6 seem to indicate that this rearrangement takes place only in those cases in which the carbon atom of the side chain next to the ring supports an oxygen atom capable of being protonated in the reaction medium. A tentative mechanism is proposed to explain the experimental results.     

Experimental and theoretical studies of the kinetics of the reactions of OH radicals with acetic acid, acetic acid-d3 and acetic acid-d4 at low pressure

The kinetics of the reactions of OH with acetic acid, acetic acid-d3 and acetic acid-d4 were studied from 2 to 5 Torr and 263-373 K using a discharge flow system with resonance fluorescence detection of the OH radical. The measured rate constants at 300 K for the reaction of OH with acetic acid and acetic acid-d4 (CD3C(O)OD) were (7.42+/-0.12)x10(-13) and (1.09+/-0.18)x10(-13) cm3 molecule-1 s-1 respectively, and the rate constant for the reaction of OH with acetic acid-d3 (CD3C(O)OH) was (7.79+/-0.16)x10(-13) cm3 molecule-1 s-1. These results suggest that the primary mechanism for this reaction involves abstraction of the acidic hydrogen. Theoretical calculations of the kinetic isotope effect as a function of temperature are in good agreement with the experimental measurements using a mechanism involving the abstraction of the acidic hydrogen through a hydrogen-bonded complex. The rate constants for the OH+acetic acid and OH+acetic acid-d4 reactions display a negative temperature dependence described by the Arrhenius equations kH(T)=(2.52+/-1.22)x10(-14) exp((1010+/-150)/T) and kD(T)=(4.62+/-1.33)x10(-16) exp((1640+/-160)/T) cm3 molecule-1 s-1 for acetic acid and acetic acid-d4, respectively, consistent with recent measurements that suggest that the lifetime of acetic acid at the low temperatures of the upper troposphere is shorter than previously believed.     

Generation and consumption rates of OH radicals in sonochemical reactions

In this study, a KI aqueous solution or Methyl Orange (MO) aqueous solution was irradiated by an ultrasonic wave under the same experimental condition. The rates of oxidation of KI and MO by OH radicals differed by an order of magnitude. When the consumption of OH radicals by chemical reactions with species other than KI or MO is taken into account, numerical analysis of chemical kinetics model yields the same generation rate of OH radicals by the action of an ultrasonic wave for the experiments of KI and MO solutions.     

Ammonium chloride promoted Ugi four-component, five-center reaction of alpha-substituted alpha-isocyano acetic acid: a strong solvent effect

[reaction: see text] Conditions have been developed for the multicomponent synthesis of di- and tetrapeptide (7) based on the unique reactivity of alpha-isocyano acetic acid (4 and its alpha-substituted derivatives) by an Ugi four-component, five-center reaction. Simply mixing 4, a carbonyl compound (aldehyde or ketone, 8), and a secondary amine (9) (ratio: 1:1:2) in toluene in the presence of 1.5 equiv of ammonium chloride afforded the desired product in good to excellent yield as a mixture of two diastereomers.