Thermal behavior of pinan-2-ol and linalool.

Linalool is an important intermediate for syntheses of isoprenoid fragrance compounds and vitamins A and E. One process option for its production is the thermal gas-phase isomerization of cis- and trans-pinan-2-ol. Investigations of this reaction were performed in a flow-type apparatus in a temperature range from 350-600 °C and a residence time range of 0.6-0.8 s. Rearrangement of the bicyclic alcohol led to linalool, plinols arising from consecutive reactions of linalool and other side products. Effects of residence time, temperature, surface-to-volume-ratio, carrier gas, and the presence of additives on yield and selectivity were studied. Furthermore, the effects of such parameters on ene-cyclization of linalool affording plinols were investigated. Results indicate that manipulation of the reaction in order to affect selectivity is difficult due to the large free path length to other molecules in the gas phase. However, conditions have been identified allowing one to increase the selectivity and the yield of linalool throughout pyrolysis of pinan-2-ol.

Ball milling in organic synthesis: solutions and challenges.

During the last decade numerous protocols have been published using the method of ball milling for synthesis all over the field of organic chemistry. However, compared to other methods leaving their marks on the road to sustainable synthesis (e.g. microwave, ultrasound, ionic liquids) chemistry in ball mills is rather underrepresented in the knowledge of organic chemists. Especially, in the last three years the interest in this technique raised continuously, culminating in several high-quality synthetic procedures covering the whole range of organic synthesis. Thus, the present tutorial review will be focused on the highlights using this method of energy transfer and energy dissipation. The central aim is to motivate researchers to take notice of ball mills as chemical reactors, implementing this technique in everyday laboratory use and thus, pave the ground for future activities in this interdisciplinary field of research.

Fast, ligand- and solvent-free synthesis of 1,4-substituted buta-1,3-diynes by Cu-catalyzed homocoupling of terminal alkynes in a ball mill.

A method for the Glaser coupling reaction of alkynes by using a vibration ball mill has been developed. The procedure avoids the use of ligands and solvents during the reaction. Aryl- and alkyl-substituted terminal alkynes undergo homocoupling if coground with KF-Al(2)O(3) and CuI as a milling auxiliary and catalyst. Furthermore, an alternative protocol has been developed incorporating 1,4-diazabicyclo[2.2.2]octane (DABCO) as an additional base allowing the use of KF-Al(2)O(3) with a lower KF loading. Besides Cu salts, the homocoupling of phenylacetylene is also catalyzed by Ni or Co salts, as well as by PdCl(2). TMS-protected phenylacetylene could be directly converted into the homocoupling product after in situ deprotection of the alkyne by fluoride-initiated removal of the trimethylsilyl group.

Switchable selectivity during oxidation of anilines in a ball mill.

A solvent-free method for the direct oxidation of anilines to the corresponding azo and azoxy homocoupling products by using a planetary ball mill was developed. Various oxidants and grinding auxiliaries were tested and a variety of substituted anilines were investigated. It was possible to form chemoselectively either azo, azoxy, or the nitro compounds from reaction of aromatic anilines. The selectivity of the solvent-free reaction is switchable by applying a combination of oxidant and grinding auxiliary. Furthermore, a comparison with other methods of energy input (microwave, classical heating, and ultrasound) highlighted the advantages of the ball mill approach and its high energy efficiency.

Fate of monoterpenes in near-critical water and supercritical alcohols assisted by microwave irradiation.

The rearrangement of alpha- and beta-pinene was studied under microwave irradiation in near-critical water and supercritical lower aliphatic alcohols, with the aim of identifying the pathway of alpha- and beta-pinene isomerization. Generally, two pathways occur, pyrolysis on the one and acidolysis on the other hand, whereby acidolysis is predominant in the case of near-critical water and the second pathway is favored for experiments employing supercritical alcohols. The different behavior of these two structurally related solvents is attributed to the increased availability of protons if water is heated to 270 degrees C and 80 bar, thus enhancing the autoprotolysis of water. The application of alcohols instead furnished rearrangement products clearly attributed to thermal pyrolysis route by the formation of radical reaction intermediates.

Quantum chemical investigation of the thermal rearrangement of cis- and trans-pinane.

The thermal rearrangement reactions of cis-pinane, 1, and trans-pinane, 2, into beta-citronellene, 3, and isocitronellene, 4, have been investigated using ab initio multiconfigurational CASSCF and CASSCF MP2 calculations. Concerted as well as stepwise retro-[2+2]-cycloaddition conversion mechanisms are discussed and the corresponding stationary points along the relevant reaction paths from the bicyclic starting compounds into their acyclic isomers have been optimized. Our calculations show that the stepwise retro-[2+2]-cycloaddition via biradicals is energetically favoured with respect to the concerted mechanism. In the biradical pathways to 3 and 4, it was found that a gauche ring opening of the cyclobutane ring in 1 and 2, respectively, shows significantly lower activation barriers than the competing anti ring opening. With the predicted reaction paths, the calculated activation energies are in very good agreement with experimental values. The reaction mechanisms can explain the differences in the reactivity of 1 and 2, as well as the selectivity differences with respect to the formation of 3 and 4, reported in previous kinetic studies.

Solvent-free and time-efficient Suzuki-Miyaura reaction in a ball mill: the solid reagent system KF-Al(2)O(3) under inspection.

Although a plethora of synthetic procedures mediated by KF-loaded aluminas is available in the literature, there is almost no data concerning the influence of parameters such as alumina modification or KF-loading on experimental results. Hence, the Pd-catalyzed, solvent-free Suzuki-Miyaura reaction was chosen as model reaction to investigate the effect of the above mentioned parameters on the results of coupling reactions. The results from ball milling experiments led to the conclusion that self-prepared and commercially available KF-Al2O 3differ in water content. The higher the residual water content, the higher are the product yields.

Mechanistic and kinetic insights into the thermally induced rearrangement of alpha-pinene.

The thermal rearrangement of alpha-pinene (1) is interesting from mechanistic as well as kinetic point of view. Carrier gas pyrolyses with 1 and its acyclic isomers ocimene (2) and alloocimene (3) were performed to investigate the thermal network of these hydrocarbons. Kinetic analysis of the major reaction steps allows for a deeper insight in the reaction mechanism. Thus it was possible to explain the racemization of 1, the formation of racemic limonene (4), and the absence of the primary pyrolysis product 2 in the reaction mixture resulting from thermal rearrangement of 1. Results supported the conclusion that the reactions starting with 1 involve biradical transition states.

Kinetic model for the thermal rearrangement of cis- and trans-pinane.

On the basis of pyrolysis experiments with cis-pinane ( 1a), trans-pinane ( 1b), beta-citronellene ( 2), and isocitronellene ( 3), rate constants and activation parameters for the thermal rearrangement of the title compounds were calculated. Combining these with experimental parameters (residence time) allows for the kinetic modeling of the thermal rearrangement of 1a, 1b, 2, and 3. The chosen model of competitive first-order reactions describes the thermal behavior of the title compounds in a very good manner over a wide temperature range.

UV-spectroscopic quantitative determination of non-aromatic amines in ionic liquids.

In the last decade, ionic liquids have shown great promise in a plethora of applications. Nevertheless, little attention has been paid to the characterization of the purity of these fluids, which ultimately lead to non-reproducible data in the literature. Derivatization with carbon disulfide is used to quantitatively determine primary and secondary non-aromatic amines (detection limit: 0.2 wt%), such as 1-butylamine, morpholine or pyrrolidine, in ionic liquids. The corresponding dithiocarbamates formed are analyzed by ultraviolet spectroscopy at wavelengths between 277 and 285 nm.

Decontamination of soil containing POPs by the combined action of solid Fenton-like reagents and microwaves.

The effect on halogenated aromatics of solid, non-toxic oxidants such as sodium percarbonate and the urea/hydrogen peroxide complex (Fenton-like reagents) was investigated. A microwaves-assisted, solvent-free method for soil decontamination is presented. It marks a considerable advance in the search of more efficient, environment-friendly procedures for the degradative oxidation of persistent organic pollutants. Residual pollutants in treated soil samples were determined by GC/MS analysis after solvent extraction or direct thermal desorption. Results showed that 4-chloronaphthol, 2,4-dichlorophenoxyacetic acid and p-nonylphenol had been degraded completely, 2,4-dibromophenol to a large extent.

Aquasonolysis of thiophene and its derivatives.

The rate constants and products of the aquasonolysis of thiophene, tetrahydrothiophene, 2-methylthiophene, 2,5-dimethylthiophene, and 2-ethylthiophene have been investigated. The sonolysis of the selected compounds in aqueous solution follows pseudo-first-order kinetics. The aquasonolytical rate constants correlate very well with the water solubility and Henry's Law constants of thiophenes. Surprisingly, vapour pressures and heats of formation of thiophenes have little effect on their aquasonolytical rates. The pseudo-first-order rate constant for the decay of thiophene decreases as its initial concentration increases. These results indicate that the transfer process of organic solutes between cavitation bubbles and the bulk liquid can strongly affect the aquasonolysis. Furthermore, carbon disulfide, diacetylene, and dimers can be detected as common products during ultrasonic irradiations. Hence, the predominant pathway of the aquasonolysis of thiophenes is the pyrolysis during the collapse of cavities.

Aquasonolysis of thioethers.

The aquasonolytical rate constants and products of diethyl sulfide, diallyl sulfide, dipropyl sulfide, dibutyl sulfide, diethyl disulfide, and dipropyl disulfide have been investigated. The sonolysis for model compounds in aqueous solutions follows the pseudo-first-order kinetics. Disulfides are more rapidly sonicated than sulfides. Neither vapour pressure nor thermostability of thioethers can obviously affect their aquasonolytical rates. Higher Henry's Law constant and hydrophobicity of substrate result in a higher aquasonolytical rate constant. Furthermore, the aquasonolytical rate constant decreases as the initial concentration of dipropyl sulfide increases. CS2, COS, thiols, thiirane, lower sulfides, butenyne, and butadiene are detected as principal very volatile products during ultrasonic irradiations. Thiophene, benzene, 1,5-hexadiene, and cyclopentadiene are additionally obtained during the aquasonolysis of diallyl sulfide. Furthermore, trisulfides, trithiolane, and other cyclic thiolanes as volatile products are observed. These results demonstrate that thioethers undergo thermal decomposition during their aquasonolyses. The transfer process of volatile thioethers between cavitation bubbles and bulk liquid remarkably affect the aquasonolysis, and the hydrophobicity of substrate dominates the transfer process.

Sonochemical reaction of selected cyclic C6Hx hydrocarbons in organic solvents.

The rates and products of the sonochemical reactions of benzene, 1,4-cyclohexadiene, 1,3-cyclohexadiene, cyclohexene, and cyclohexane in selected organic solvents have been investigated. The sonochemical reactions of these educts in the investigated organic solvents follow first-order kinetics. Generally, they are sonicated more rapidly in polar than in non-polar solvent; higher volatility of the solute results in faster sonolysis in the organic solvents. However, the sonication of cyclohexane in n-decane and the sonication of benzene in n-propanol are exceptional cases. Since cyclohexane exhibits a much higher lipophilicity and benzene a much higher hydrophilicity than other educts, it might be more difficult to transfer either educt from the bulk liquid into the cavitation bubbles. In tetrachloroethylene, the reactivity of the tested educts with in situ generated chlorine as well as chlorine-containing radical intermediates can accelerate the rate of sonochemical reactions under the employed conditions. In n-propanol and n-decane, the pyrolysis during the collapse of the cavitation bubbles is the only reaction pathway of sonolysis. In tetrachloroethylene, the pyrolysis during the collapse of the cavitation bubbles and the free radical reaction in the bulk liquid may occur simultaneously. Except for the products generated from sonolysis, products formed from chlorine transformations (substitution or addition reactions) are detected. Benzene is hardly decomposed in tetrachloroethylene. However, when FeCl3 is added into the reaction system, benzene is sonoconverted rapidly, and the product chlorobenzene was detected. In organic solvents, the sonoreaction rates and the sonoproducts are dependent on the physicochemical properties of the solvents used, as well as the volatility, the polarity and the reactivity of educts.

Benzene formation during aquasonolysis of selected cyclic C6Hx hydrocarbons.

Yield and selectivity of benzene produced from aquasonolysis of the selected cyclic C6Hx hydrocarbons, i.e., 1,4-cyclohexadiene, 1,3-cyclohexadiene, cyclohexene, cyclohexane, and methylcyclopentane, have been investigated in this work. Benzene cannot be detected during the aquasonolysis of cyclohexane and methylcyclopentane. The order of yield and selectivity of benzene was as follows: 1,4-cyclohexadiene>>1,3-cyclohexadiene>>cyclohexene. The initial concentrations of substrates can affect the yield of benzene. During the aquasonolysis of 1,3-cyclohexadiene and cyclohexene, other C6 species except benzene were also found. It was suggested that benzene could directly be generated by formal dehydrogenation of cyclic C6Hx hydrocarbons.

Critical factors in sonochemical degradation of fumaric acid.

The effects of critical factors such as Henry's Law constant, atmospheric OH rate constant, initial concentration, H2O2, FeSO4 and tert-butanol on the sonochemical degradation of fumaric acid have been investigated. The pseudo first-order rate constant for the sonochemical degradation of 1mM fumaric acid is much lower than those for chloroform and phenol degradation, and is related to solute concentration at the bubble/water interface and reactivity towards hydroxyl radicals. Furthermore, fumaric acid is preferentially oxidized at the lower initial concentration. It is unreactive to H2O2 under agitation at room temperature. However, the degradation rate of fumaric acid increases with the addition of H2O2 under sonication. 0.1 mM of fumaric acid suppresses H2O2 formation thanks to water sonolysis, while degradation behavior is also dramatically affected by the addition of an oxidative catalyst (FeSO4) or radical scavenger (tert-butanol), indicating that the degradation of fumaric acid is caused by hydroxyl radicals generated during the collapse of high-energy cavities.

Aquasonolysis of selected cyclic C(6)H(x) hydrocarbons.

Aquasonolysis rates and products of selected cyclic C(6)H(x) hydrocarbons, benzene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, cyclohexene, cyclohexane, and methylcyclopentane have been investigated. The sonolysis of selected compounds in aqueous solution follows first-order kinetics, and the aquasonolysis rate correlated well with the water solubility. The degradation rate decreased with the increase of initial concentration. The effect of initial concentration on the degradation of cyclohexene was more significant than that of benzene. The transfer process of organic solutes between cavitation bubbles and the bulk liquid affects the rates and products of their aquasonolysis.

Sonoelectrochemical degradation of triclosan in water.

The sonoelectrochemical degradation of triclosan in aqueous solutions with high-frequency ultrasound (850kHz) and various electrodes was investigated. Diamond coated niobium electrode showed the best results and was used as standard electrode, leading to effective degradation and positive synergistic effect. The influence of different parameters on the degradation degree and energy efficiency were evaluated and favorable reaction conditions were found. It could be shown that 92% of triclosan (1mgL(-1) aqueous solution) was degraded within 15min, following pseudo-first order kinetics.

Sonoelectrochemical degradation of phenol in aqueous solutions.

The sonoelectrochemical degradation of phenol in aqueous solutions with stainless steel electrodes and high-frequency ultrasound (850kHz) was investigated. A 60% synergetic effect was obtained in the combined reaction system. High concentration of electrolyte (sodium sulfate) and a high electrical voltage are favorable conditions for the degradation of phenol. A nearly complete degradation of phenol was achieved with 4.26g/L Na(2)SO(4) and 30V electrical voltages at 25°C in 1h. The degradation of phenol follows pseudo-first order kinetics. Considering costs and application, the energy efficiency of the reaction system with different reaction conditions was evaluated.