Kinetics and mechanism of the reaction between phenyl isocyanate and alcohols in benzene medium

Removal of Flotation Collector O-Isopropyl-N-ethylthionocarbamate from Wastewater

Flotation collector O-isopropyl N-ethylthionocarbamate (IPETC) is widely used for separation of sulfide ores. Its removal from water by several oxidation processes was studied. Photocatalytic oxidation with air in the presence of iron salts, utilizing solar irradiation or artificial UV-A light is very efficient. Oxidation leads through the formation of O-isopropyl N-ethylcarbamate and several other reaction intermediates to total decomposition of organic compound in the final stage in 1 day. Similar results were obtained with a Fenton type oxidation with hydrogen peroxide and iron salts. Treatment with sodium hypochlorite yields mainly O-isopropyl N-ethylcarbamate. The formation of this compound in wastewaters can be of concern, since simple alkyl carbamates are cancer suspect agents.

Reaction Mechanisms and Rate Constants of Auto-Catalytic Urethane Formation and Cleavage Reactions

The chemistry of urethanes plays a key role in important industrial processes. Although catalysts are often used, the study of the reactions without added catalysts provides the basis for a deeper understanding. For the non-catalytic urethane formation and cleavage reactions, the dominating reaction mechanism has long been debated. To our knowledge, the reaction kinetics have not been predicted quantitatively so far. Therefore, we report a new computational study of urethane formation and cleavage reactions. To analyze various potential reaction mechanisms and to predict the reaction rate constants quantum chemistry and transition state theory were employed. For validation, experimental data from literature and from own experiments were used. Quantitative agreement of experiments and predictions could be demonstrated. The calculations confirm earlier assumptions that urethane formation reactions proceed via mechanisms where alcohol molecules act as auto-catalysts. Our results show that it is essential to consider several transition states corresponding to different reaction orders to enable agreement with experimental observations. Urethane cleavage seems to be catalyzed by an isourethane, leading to an observed 2nd-order dependence of the reaction rate on the urethane concentration. The results of our study support a deeper understanding of the reactions as well as a better description of reaction kinetics and will therefore help in catalyst development and process optimization.

Recent Progress in Vibropolaritonic Chemistry

Vibrational polaritonic chemistry is emerging as an exciting new sub-field of chemistry, one in which strong interactions with optical cavity vacuum fields are another degree of freedom alongside temperature, solvent, catalyst, and so on to modify thermochemical reactivity. The field stands at a fascinating juncture with experimental works on a variety of organic reactions continuing to blossom, just as many theoretical works appear which diverge significantly in their predictions compared to experiments. The outlook for the field is no doubt an exciting one as it seeks to unify the observed novel optical cavity-induced chemical phenomena with satisfying accompanying physical theory. In this minireview we highlight experimental works on vibrational polaritonic chemistry that have appeared most recently, focusing on the chemistry of the rate-limiting steps to provide mechanistic insight. We hope this review will encourage synthetic chemists to enter the field and we discuss the opportunities and challenges that lie ahead as polaritonic chemistry grows into the future.

Synthesis and antifungal activities of alkyl N-(1,2,3-thiadiazole-4-carbonyl) carbamates and S-alkyl N-(1,2,3-thiadiazole-4-carbonyl) carbamothioates

A series of alkyl N-(1,2,3-thiadiazole-4-carbonyl) carbamates and S-alkyl N-(1,2,3-thiadiazole-4-carbonyl) carbamothioates with unsubstituted or monobrominated straight chain alkyl groups were synthesized and evaluated as fungistatic agents against Gibberella zeae and Alternaria kikuchiana. These compounds showed variable antifungal activities at concentrations of 5 and 50 microg/mL. The results showed that antifungal activities depended on the length of the alkyl chain with the optimal chain length of 6-11 carbons. Carbamic acid, (1,2,3-thiadiazole-4-ylcarbonyl)-, hexyl ester (4) showed a strong fungistatic activity against A. kikuchiana at both concentrations, with 90.7 and 54% growth inhibition at 50 and 5 microg/mL, respectively. Carbamic acid, (1,2,3-thiadiazole-4-ylcarbonyl)-, heptyl ester (5); Carbamic acid, (1,2,3-thiadiazole-4-ylcarbonyl)-, octyl ester (6); and Carbamic acid, (1,2,3-thiadiazole-4-ylcarbonyl)-, undecyl ester (9) showed strong fungistatic activity against G. zeae at both concentrations. Their growth inhibitions against G. zeae at the concentration of 5 microg/mL were 78, 63, and 59%, respectively.

Synthesis of 11C-labelled N,N'-diphenylurea and ethyl phenylcarbamate by a rhodium-promoted carbonylation via [11C]isocyanatobenzene using phenyl azide and [11C]carbon monoxide

The reaction with phenyl azide and [11C]carbon monoxide to give N,N'-diphenyl[11C]urea and ethyl phenyl[11C]carbamate has been studied with the aim of development of a new methodology for carbonylation using [11C]carbon monoxide with high specific radioactivity. The synthesis of 11C-labelled N,N'-diphenylurea from phenyl azide and [11C]carbon monoxide, with 1,2-bis(diphenylphosphino)ethane-bound Rh(I) complex at 120 degrees C at a pressure of 35 MPa in the presence of aniline was accomplished in 82% trapping efficiency and 82% conversion yield. This approach was also useful for the synthesis of ethyl phenyl[11C]carbamate with lithium ethoxide as a nucleophilic reagent giving 90% trapping efficiency and 76% conversion yield. These reactions can be considered to proceed via a [11C]isocyanate or a [11C]isocyanate-coordinated Rh complex to give the corresponding 11C-products. This protocol provides the chemical basis for the synthesis of [11C]urea and [11C]carbamate derived from [11C]isocyanates.

The Alcoholysis Reaction of Isocyanates Giving Urethanes: Evidence for a Multimolecular Mechanism

A kinetic and mechanistic investigation of the catalyzed alcoholysis of isocyanates was undertaken. Both experimental and theoretical results showed that the alcoholysis should be understood by a multimolecular intervention of the alcohols. The alcoholysis of isocyanate was examined experimentally for 2-propanol and cyclohexanol in low and high concentrations. It is suggested that either two or three molecules of the alcohol are implicated from the kinetic study, while the reaction with trimers becomes dominant at high alcohol concentrations. In accordance with these results, theoretical study suggests an active participation of at least three alcohol molecules in a reacting supersystem, giving rise to a genuine effect. The detailed reaction mechanism for the alcoholysis reaction by methanol and methanol clusters (HN=C=O + n(CH(3)OH), n = 1-3) was modeled by ab initio methods, both in the gas phase and in solution. The nucleophilic addition occurs in a concerted way across the N=C bond of the isocyanate rather than across the C=O, similar to the isocyanate hydrolysis. The bulk solvent effect, which is treated by a polarizable continuum model (PCM), does not affect the preference of the alcohol to attack across the N=C bond as pointed out by the gas-phase values.