Current Microwave Chemistry (v.2, #1)

Optical Characterization of Monodispersed Aqueous Cu2+-Doped CdS Nanoparticles Prepared Under Microwave Irradiation Conditions by Wei Zhu, Qihui Shen, Xinjian Bao, Xiao Bai, Tingting Li, Mingqiang Zou, Jinfeng Li, Yan Liu, Xiaoyang Liu (2-7).
Aqueous CdS:Cu nanocrystals (NCs) have been successfully prepared under microwave irradiation conditions. It appears that these nanocrystals contain abundant copper ions in their central interior, and they can diffuse through the interface of CuS nucleus and CdS coated layers via cation exchange processes. The crystal structure, shapes and optical properties of nanocrystals were determined by X-ray diffraction, high-resolution transmission electron microscopy, UVVis absorption and photoluminescence spectroscopy analyses. The crystal structure of CdS:Cu nanocrystals appears to be zinc blende. Compared with pure CdS nanocrystals, the aqueous CdS:Cu nanocrystals possess an enlarged optical window ranging from 538 to 640 nm. Plus, they are highly emissive and exhibit excellent chemical/photochemical stability, as demonstrated by the fact that samples can be stored for months without visualizing precipitation or other changes.

Microwave Induced Center-Doping of Transition Metals Ions in Aqueous CdS NCs with Special Optical Properties by Yan Liu, Wei Zhu, Xiao Bai, Tingting Li, Mingqiang Zou, Mingqiang Zou, Jinfeng Li, Jinfeng Li, Qihui Shen, Xiaoyang Liu (8-14).
Under microwave irradiation, we systematically studied the formation of transition metal ions (TM), Ag+, Mn2+, Cu2+, Fe2+, Co2+ and Ni2+, doped CdS semiconductor nanocrystals in a pure water solution. The center-doping strategy is essential for achieving efficient internal-doping to improve the optical properties and stability of doped nanocrystals. The resulting TM doped nanocrystals have a high photoluminescence quantum yield (~ 60%) and an amazingly large range of the visible spectrum (480 ~ 650 nm). For Mn2+ doped CdS nanocrystals, significant high photoluminescence quantum yield, between 20% and 50% even at more than 600 nm, was achieved and there is potential for them to be directly used as a consummate toner for multicolor sensing and encoding without ligand exchange. Highly emissive-doped nanocrystals synthesized under designed conditions have been found to have excellent stability; samples could be stored for months without precipitation. In practice, this approach has great potential to promote the metal doping of various semiconductor nanocrystals to realize the specific advantages of doped nanocrystals in water solution.

Facile One-Pot Synthesis of Oxo-Xanthenes under Microwave Irradiation by Amreeta Preetam, Davinder Prasad, Jatin K. Sharma, Mahendra Nath (15-23).
A convenient diversity oriented synthetic procedure for the construction of various oxo-xanthenes such as 12- aryl-8,9,10,12-tetrahydrobenzo[a]-xanthene-11-ones, 9-aryl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-diones and 9- substituted-2,3,4,9-tetrahydro-1H-xanthen-1-ones has been developed by using p-dodecylbenzenesulfonic acid as an efficient Brønsted acid catalyst under solvent-free microwave conditions. The present methodology is found to be operationally simple and demonstrates many advantages including shorter reaction times, easy purification steps and good to excellent yields of the target products.

Method for the Production of Natural Vanilla Extracts using a Conventional Microwave Oven by M.A. Olmedo-Suarez, M.P. Canizares-Macías (24-31).
A method to obtain vanilla extracts with 1 fold of concentration from cured vanilla pods using a conventional microwaves oven is proposed. With this method it was possible to obtain vanilla extracts containing 0.20% of vanillin, in only three days. This value is higher than that established as minimum value by international norms (0.11%) for extracts of vanilla. In this study, irradiation time, no-irradiation time, power and volume of extractant were evaluated. The temperature of the extractant (64% ethanol) at different irradiation times and powers with the aim of avoiding evaporation of the solvent was evaluated. The optimum conditions were: 450 W of power and three cycles of 10s of irradiation and 60 s of no-irradiation twice daily for 3 days. The extraction efficiency increased 90% and the extraction time decreased 66% with respect to the conventional manual method.

Microwave-Assisted Synthesis of Some New Benzimidazole Derivatives with their Antimicrobial Activity by Emre Mentese, Fatih Yil maz, Fatih Saban Beris, Olcay Bekircan, Bahittin Kahveci (32-39).
2-(2-Chlorobenzyl)-1H-benzimidazole (2) was prepared from the reaction of o-phenylenediamine and ethylimido- o-chlorophenylacetate hydrochloride (1) under microwave irradiation. The acetate and hydrazide derivatives of 2- (2-chlorobenzyl)-1H-benzimidazole (2) were synthesized respectively. Then, 2-[2-(2-chlorobenzyl)-1H-benzimidazol-1- yl]-N-(2,5-dioxopyrrolidin-1-yl)acetamide (5), 5-{[2-(2-chlorobenzyl)-1H-benzimidazol-1-yl]methyl}-1,3,4-oxadiazole- 2-thiol (6), acetohydrazide (7a-i) and N-phenylhydrazinecarbo thioamide derivatives (8a-c) were synthesized from hydrazide derivatives. Finally, the intramolecular cyclization of N-phenylhydrazinecarbo thioamide derivatives (8a-c) gave the corresponding 1,2,4-triazole-3-thione derivatives (9a-c). The newly synthesized compounds have been tested for their antimicrobial activity against three Gram-positive and three Gram-negative bacterias.

Design and Synthesis of Efficient ZnO Nanomaterials for Photocatalysis by Munusamy Thirumavalavan, Jiunn-Fwu Lee (40-43).
Metal oxide-based semiconductor photocatalysis has attracted much attention in recent years. In the cutting edge of efficient photocatalysis, various synthetic and modification strategies of oxides on the nanometer scale have evolved for surface tuning properties. Thus, it is interesting to study recent progresses in the development of surface tuned metal oxide-based nanomaterials as efficient photocatalysts. In this work, special importance, especially facile and feasible approaches is given to develop surface tuned, high thermal stability and hierarchically structured novel ZnO/Zn nanocrystallites. We also investigated the impact of both aggregation phenomenon and photoinduced charge separation in metal oxide nanoparticles. The photocatalytic ability of nano ZnO/Zn on the photodegradation of methylene blue under UV irradiation was investigated in aqueous solution. The result obtained in this work is a key to the rational design of mesoporous nanoparticle networks and helps to engineer composite nanomaterials for photocatalysis.

A reliable, green and energy-efficient synthesis of a series of 1-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)- yl)-2-(phenylamino)ethanone is reported. The reaction conditions were optimized using the conventional and microwave synthetic approaches. The un-precedented displacement of the chloro group of 2-chloro-1-(6,7-dimethoxy-3,4- dihydroisoquinolin-2(1H)-yl)ethanone with substituted anilines under microwave solvent free condition afforded titled glycinamides in moderate to good yield (66-84 %) in a short reaction time (3-4.5 min). All the synthesized compounds were evaluated for in vitro antibacterial activity against three bacterial strains Escherichia coli, Pseudomonas putida and Staphylococcus aureus. Among all the tested compounds, four compounds 5c, 5f, 5i and 5k exhibited moderate to significant activity against all the three tested strains of bacteria.

Microwave Assisted Reactions of Natural Oils: Transesterification and Hydroformylation/Isomerization as Tools for High Value Compounds by Liliana Damas, Goncalo N. Costa, Juvencio C. Ruas, Rui M. B. Carrilho, Artur R. Abreu, Gilberto Aquino, Mario J.F. Calvete, Marta Pineiro, Mariette M. Pereira (53-60).
A comparative study on the transesterification of natural oils obtained from Calophyllum inophyllum seeds was carried out using homogeneous (NaOH/MeOH) or heterogeneous catalysts, with conventional heating and under microwave irradiation. The results show that the microwave-assisted reaction using heterogeneous catalysts, obtained from renewable sources (rice husk and egg shell ashes), constitutes an energetically sustainable approach for transesterification. In order to obtain value-added products from natural oils, rhodium/monophosphite catalysts were applied to the hydroformylation of methyl oleate, also under conventional heating or microwave irradiation. Using conventional heating conditions (T = 80°C; Psyngas = 30 bar), high catalytic activity was observed with 98% chemoselectivity for aldehydes, while under microwave irradiation, using a CEM® Discover system equipped with syngas addition kit, high conversions were observed under mild reaction conditions (T = 60°C; Psyngas = 10 bar), mainly with formation of isomerization products.

An exceptionally efficient, environmentally safe and economic method has been developed for regioselective α-bromination of various aralkyl ketones in excellent yield with N-bromosuccinimide (NBS) under microwave irradiation (CEM discover) without use of either a solvent or a catalyst. After completion of the reaction, the NBS can be regenerated by using an environment friendly brominating agent NaBr/NaBrO3 in acetic acid. The present procedure offers various advantages such as a very short reaction time, simple work-up procedure, excellent yield of products and recovery of the reagents by green protocol.

Rapid Microwave-Assisted Synthesis of γ-Phosphonic Acid Quaternary Ammonium Antimicrobials for Biomedical Applications by Lukasz M. Porosa, Gideon Wolfaardt, Alan J. Lough, Daniel A. Foucher (69-82).
Novel water soluble γ-phosphonates and phosphonic acid quaternary ammonium compounds (QAC) with different alkyl chain lengths, a dansyl (DNS) fluorescent tag ([RN+Me2(CH2)3P(O)(OR1)2]Br-; R = CH3, C18H37, -DNS-NH- (CH2)3; R1 = Et, iPr, or H) or pyridinium ([C5H5N+(CH2)3P(O)(OR1)]Br-; R1 = iPr, or H) were synthesized in two or three steps (Arbuzov, Menshutkin and bis-dealkylation reactions) under MW conditions within minutes in good yields. These protocols were then compared to thermal heating (TH). Both H2O and MeCN were found to be effective solvents for the Menshutkin and the bis-dealkylation of phosphonate QAC. These reactions were carried out for the first time under MW heating sequentially or in a one-vessel procedure with mineral acids. New compounds were characterized by NMR spectroscopy, HRMS spectrometry and in two instances (17, 20) by X-ray crystallography. We provide X-ray crystallographic evidence for the isolation of the QAC phosphonic acids as the free acids containing the Br- counter ion instead of the previously suggested phosphobetaine internal salts. Self-assembled monolayers of the phosphonic acid QAC prepared in this study are expected to be suitable antimicrobial coatings for metal surfaces used for biomedical applications.

A Rapid Protocol to Synthesize γ-Butyrolactone Derivatives via the Microwave Technique by Marcos F. Pinatto-Botelho, Paulo Marcos Donate (83-87).
This work reports the synthesis of several 3-methoxycarbonyl-γ -butyrolactone derivatives (4-12) starting from dimethyl itaconate (1), an aryl bromide (2), and a carbonyl compound (3). The synthetic protocol used microwave irradiation, argon atmosphere, and acetonitrile as solvent. The synthesis furnished the target compounds in 80-96% yield; reactions lasted about 10-20 min.