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Interfacial Catalysis at Oil/Water Interfaces
Published in Alexander G. Vdlkdv, Interfacial Catalysis, 2002
Heterogeneous chemical reactions between two reacting species located in immiscible phases are often inhibited due to the encounter problem. Conventional techniques to circumvent this mutual insolubility problem rely on the use of rapid agitation and the use of cosolvent, which exhibits both lipophilic and hydrophilic properties. If the reaction takes place at the phase boundary, it is expected that the rapid agitation may have an accelerating effect by increasing the interfacial contact. The addition of cosolvent may eliminate the phase separation and provide a homogeneous mixing state for the reaction to take place. The cosolvents commonly used are the protic solvents such as methanol and ethanol, and dipolar aprotic solvents such as acetonitrile, dimethyl formamide, and dimethyl sulfoxide. Although these cosolvents might resolve the mutual insolubility problem, they render certain disadvantages such as the problem of promoting competing hydrolysis pathways and the difficulties in their purification and removal. A plausible technique now widely known as “phase transfer catalysis” (PTC) developed for overcoming the encounter problem due to the mutual insolubility of solvents appeared in the late 1960s. In a PTC reaction, an added phase transfer catalyst is capable of transferring one of the reactants from its normal phase into a different phase where it can normally encounter and react under an activated state with the second reactant.
A facile one-pot, solvent-free synthesis of new pyrazolone-1,3-dithiolan hybrids through the reaction between 2-pyrazoline-5-ones, CS2, and α-chloroacetaldehyde
Published in Journal of Sulfur Chemistry, 2022
Leila Sabahi-Agabager, Saeideh Akhavan, Farough Nasiri
To optimize reaction conditions, the one-pot reaction between 1a, carbon disulfide and α-chloroacetaldehyde was selected as a model reaction to produce E and Z forms of pyrazolone-1,3-dithiolan hybrid 2a (Scheme 2). At first, the reaction as illustrated in Scheme 2 was carried out in DMSO in the presence of NEt3; the reaction yield was 55% whereas in a protic solvent such as methanol, the reaction did not occur (Table 1, entries 1, 2). To achieve an efficient and green procedure, the reaction was carried out under solvent-free conditions with an equimolar ratio of triethylamine. With these conditions, 2a formed in a yield of 82% (entry 3). The increase in the amount of triethylamine did not influence the yield of 2a. As presented in Table 1, other bases such as KOH, K2CO3, or 1,4-diazabicyclo[2.2.2]octane (DABCO) were ineffective in producing 2a (entries 3–5). The use of NBu3 as a base or tetra-n-butylammonium bromide (TBAB) as phase transfer catalyst, also did not improve the yield of reaction (entries 7, 8). Therefore, the use of triethylamine in solvent-free conditions was selected as the appropriate condition.
1,3,5-Trithianes and sulfur monochloride/sodium sulfide: an alternative route to 3,5-disubstituted 1,2,4-trithiolanes
Published in Journal of Sulfur Chemistry, 2020
Damiano Tanini, Francesca Trapani, Antonella Capperucci
Subsequently, 3a was reacted in DMF at ambient temperature with hydrate sodium sulfide (Scheme 4), which is used in the reaction with halides to form symmetrical disulfides [45], and indeed the trithiolane 5a was isolated, even if in moderate yield (22%), together with other sulfurated products, amongst which the 1,2,3,5-tetrathiane 6a was the major compound. Under these conditions the parent 1,1’-bis(mercapto)-dialkyl sulfide intermediate 4 was not isolated, being quickly oxidized to provide a direct access to 5a from 3a. In order to increase the yield of 5a the reaction was carried out in the presence of TBAB (tetrabutylammonium bromide) as phase transfer catalyst, but no considerable increase in yield was observed. On the contrary, when the reaction was performed at lower temperature (−10°C) the trithiolane 5a was achieved in higher yield (67%) as equimolar mixture of stereoisomers, and tetrathiane 6a was observed as minor compound (<5%) (Scheme 4). The reaction was also efficient with differently substituted trithianes, leading to variously 3,5-disubstituted 1,2,4-trithiolanes 5b–d under mild conditions (Scheme 4).
BNPs@Cur-Pd as a versatile and recyclable green nanocatalyst for Suzuki, Heck and Stille coupling reactions
Published in Journal of Experimental Nanoscience, 2020
Muhammed Ali Jani, Kiumars Bahrami
Afterward, the evaluation was conducted to change solvent effects for various solvents such as DMF, DMSO, and H2O instead of PEG (entries 6–8). The results revealed that using the other solvents did not lead to an improvement in reaction efficiency. Also, the aprotic solvents (DMF, DMSO) showed better results versus the protic solvents (H2O) which can be due to the nature of curcumin as a ligand in BNPs@Cur-Pd that is a hydrophobic molecule that can be solved freely in the aprotic solvents and this nature can enhance more interactions between solvent and catalyst. Also, the role of PEG solvent as a phase transfer catalyst can promote the basicity of Na2CO3 as well as the increased solubility of other precursors. Then, the optimization was performed on the effect of several bases (KOH, Et3N, and NaOEt) in the coupling reactions (entries 9–11). The obtained results revealed that sodium carbonate was still the best among the other bases to obtain a high yield of product. Finally, the temperature effect was evaluated at 25 °C, 60 and 80 °C and it was found that the Suzuki reaction proceeded effectively at 80 °C.