Worawan Bhanthumnavin

Organocatalyzed Asymmetric α-Oxidation, α-Aminoxylation and α-Amination of Carbonyl Compounds

Organocatalytic asymmetric α-oxidation and amination reactions of carbonyl compounds are highly useful synthetic methodologies, especially in generating chiral building blocks that previously have not been easily accessible by traditional methods. The concept is relatively new and therefore the list of new catalysts, oxidizing and aminating reagents, as well as new substrates, are expanding at an amazing rate. The scope of this review includes new reactions and catalysts, mechanistic aspects and synthetic applications of α-oxidation, hydroxylation, aminoxylation, amination, hydrazination, hydroxyamination and related α-heteroatom functionalization of aldehydes, ketones and related active methylene compounds published during 2005–2009.

N-Salicyl-β-aminoalcohols as a new class of ligand for catalytic asymmetric Strecker reactions

An enantioselective Strecker synthesis employing novel chiral titanium complex catalysts derived from structurally simple chiral N-salicyl-β-amino alcohols is described. Reactions of N-benzylidenebenzylamine with trimethylsilyl cyanide in the presence of the catalyst (10 mol%) gave the corresponding α-aminonitrile in good to excellent yields, along with relatively high enantioselectivity (up to 86% ee). Similar reactions with various imines derived from aromatic aldehydes resulted in moderate to good enantioselectivity (44–81% ee).

A convenient synthesis of N-boc-protected α-aminonitriles from α-amidosulfones

Abstract Synthesis of N‐Boc‐protected α‐aminonitriles starting from N‐Boc‐protected α‐aminosulfones is described. Treatment of the sulfone with two equivalents of potassium cyanide in 2‐propanol or dichloromethane‐H2O under phase transfer condition affords crystalline N‐Boc‐protected α‐aminonitriles in good yield. Hydrolysis of the aminonitriles provides a convenient access to racemic α‐amino acids.

Volatile organic compound sensor arrays based on zinc phthalocyanine and zinc porphyrin thin films

In this paper, organic thin films based on two types of metal-macromolecules, i.e., zinc-2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (ZnTTBPc) and zinc-5,10,15,20-tetra-phenyl-21H,23H-porphyrin (ZnTPP), were demonstrated to discriminate among diverse volatile organic compounds (VOCs) even if they have very similar functional group. The ZnTTBPc and the ZnTPP thin films have been prepared by spin coating technique and then were tested for their optical response to VOCs, which share a similar carbonyl (C = O) group, namely acetone, formaldehyde (in a mixture form with methanol) and acetic acid, based on UV-Vis absorption. The transduction employs the optical response of selected spectral ranges arranged in an array configuration, which is then subjected to the principal component analysis (PCA). The PCA results have shown successful discrimination of these VOCs. Density functional theory (DFT) calculation was employed to study the interactions between these VOCs and the sensing materials. The calculation yields different degrees of interactions for each VOC, in compliment with the experimental results. This work supports the prospects of this organic sensor for beverage industry where VOCs are abundant in their products.

Electrical Characterization of Diamond-Like Carbon Films Synthesized by Plasma Enhanced CVD Technique

Diamond-like carbon (DLC) films have been deposited on silicon substrates using microwave plasma enhanced chemical vapor deposition (PE-CVD) process of CH4 in H2 gas mixture. The well-faceted good quality DLC film with distinct diamond Raman spectroscopic characteristics are found at low CH4 concentration. Schottky barrier diode (SBD) structures are fabricated onto the grown DLC films using Ti/Au and Al as ohmic and rectifying contacts, respectively. The responses of DLC-SBD to DC and time varying signals have been studied. The frequency dependent response results are compared to models, which includes as input parameters the depletion and bulk regions resistances and capacitances trap effects, and SBD parameters of which extracted from the DC I-V characteristics. It is found that the frequency dependent properties of DLC-SBD can be associated with deep trap states inside the DLC material rather than with only the SBD geometrical structure.

Grafting of Phosphonate Monomer onto Natural Rubber Latexes via Emulsion Polymerization

The synthesis of phosphorus-containing monomer, methacryloyloxyethyl phenyl benzenephosphonate (MPBP), was carried out. The monomer was successfully prepared as evidenced by 1H NMR, 13C NMR, FT-IR and MS analyses. Subsequently, MPBP was grafted onto natural rubber particles via emulsion polymerization. It was found that as the reaction temperature increased from 40 to 70 oC, percent grafting efficiency increased from 72% to 85%. Transmission electron microscopy (TEM) of the grafted NR showed a semi core-shell morphology. Thermogravimetric analysis (TGA) of grafted NR indicated a two step degradation. Moreover, the grafted polyMPBP promoted the char residue of up to 3.5%. Flame tests revealed that the grafted NR exhibited an increased LOI value (20.5 %) over that of pure NR (17.0 %).

Synthesis of Conducting Polymer Films by Plasma Polymerization Process

A microwave (MW) plasma reactor for the synthesis of polythiophene (PTh) thin films as well as in situ doping during polymerization process has been designed and assembled. Plasma polymerization parameters were studied. A good MW power was found to be in the range of 150-250W. PTh films were characterized by various spectrophotometric methods. IR analyses showed absorption frequencies of important functional groups. PTh films exhibited UV-Vis spectra indicative of increased conjugative systems as the MW power increased although at 300 and 380W partial fragmentation was evident. Surface analysis by SEM revealed a uniformly deposited film morphology. EDS results were also suggestive of partial fragmentation of the films at high MW powers. Preliminary conductive measurements revealed that the undoped films exhibit higher conductivity (3 to 9×10-5 s.cm-1) than PTh typically prepared from electrochemical methods.

Microwave Plasma Source for Fabrication of Micro- and Nano-Crystalline Diamond Thin Films for Electronic Devices

The design and utilization of an affordable compact-size high-density plasma reactor for micro- and nano-crystalline diamond (MCD/NCD) thin film deposition is presented. The system is based on a 2.45 GHz domestic microwave oven magnetron. A switching power supply module, which yields a low-voltage high-current AC filament feeding and a high-voltage low-current DC cathode bias, is constructed to serve as the magnetron power source. With a high stability of the power module combined with the usage of water cooling gaskets, over 100 h of plasma processing time was achieved without overheating or causing any damage to the magnetron. Depositions of well-faceted MCD/NCD thin films, with distinct diamond Raman characteristics, were obtained using H2–CH4 discharge with 1–5% CH4. Metal–semiconductor diode structures were fabricated using gold and aluminum as ohmic and rectifying contacts, respectively, and their responses to DC signals revealed a high rectification ratio of up to 106 in the intrinsic MCD/NCD devices.

Effects of Photoirradiation on Electrical Characteristics of Chemical Vapor Deposited Diamond Schottkey Barrier Diode

Diamond Schottky barrier diodes (SBDs) are fabricated on thin polycrystalline diamond films deposited by the microwave plasma-enhanced chemical vapor deposition (CVD) process. The diodes are photoirradiated with white light of different intensities while the changes in their electrical response to DC and time-varying signals were recorded. For time-varying signals, large signal sinusoidal waveforms, which drive the diodes between reverse bias and forward bias, have been utilized. The experimental results of the large switching signal test are compared with those of computer simulations. The results indicate that deep-lying and/or interface states of the CVD diamond SBDs, rather than the minority carrier storage effect in the CVD films, are responsible for the photoirradiation-dependent properties of diamond SBDs.

Environmentally Benign Microwave-Assisted Sonogashira Preparation of Aromatic Compounds

An efficient Sonogashira-type coupling reaction of terminal alkynes and aryl bromides by microwave activation with short reaction time under mild conditions are presented. It is illustrated herein that the traditional Sonogashira coupling reaction can be achieved with a much more efficient yet environmentally friendly condition. In contrary to the usually required 10 mol% Pd loading and the use of conventional heating at 60 °C for 24 h in order for a reaction to proceed satisfactorily, with a 100 W microwave activation, the reaction of terminal alkynes with substituted aryl bromides can be achieved with only a 2.5 mol% Pd in 10 min. The yield was improved with microwave irradiation.