A Facile, Mild, and Environmentally Benign Procedure for the Cleavage of Carbon–Nitrogen Double Bonds Using KMnO4 in the Presence of Montmorillonite K-10 Under Solvent-Free Conditions

Summary. An efficient and environmentally benign method for the conversion of oximes, semicarbazones, phenylhydrazones, and azines to their corresponding carbonyl compounds using KMnO₄/montmorillonite K-10 as a commercially available, non-toxic, stable, and inexpensive reagent is reported. Corresponding author. E-mail: Imbaltork@sci.ui.ac.ir Received August 23, 2002; accepted March 23, 2002     

Bismuth(III) nitrate pentahydrate: a convenient and selective reagent for conversion of thiocarbonyls to their carbonyl compounds

A variety of thioamides and thioureas are rapidly transformed to their oxo derivatives with Bi(NO₃)₃·5H₂O in excellent yields. However, thiono esters and thioketones are converted to their corresponding carbonyl compounds in only poor yields. Bi(NO₃)₃·5H₂O is relatively non-toxic, insensitive to air and inexpensive. These features coupled with the selective deprotection of thioamides and thioureas in the presence of thiono esters and thioketones make this method an attractive alternative to the existing routes for deprotection of thiocarbonyl compounds.     

An Efficient and Selective Solid State Oxidation of Thiols to Disulfides with Quinolinium Fluorochromate on Silica Gel

Various kinds of aliphatic (cyclic and acyclic), aromatic, and heterocyclic thiols are converted into the corresponding disulfides by quinolinium fluorochromate (QFC) on silica-gel in excellent yields. Selective oxidation of thiols in the presence of sulfides is also achieved under solid phase conditions.     

Efficient and Selective Conversion of Trimethylsilyl and Tetrahydropyranyl Ethers to their Corresponding Acetates and Benzoates Catalyzed by Bismuth(III) Salts

Summary.  A variety of TMS and THP ethers are efficiently converted to their corresponding acetates and benzoates with acetic and benzoic anhydrides in the presence of catalytic amounts of Bi(III) salts such as BiCl₃, Bi(TFA)₃, and Bi(OTf)₃. The present method is also effective for the selective acetylation and benzoylation of TMS and THP ethers of alcohols in the presence of phenolic ethers. Received May 21, 2001. Accepted June 25, 2001     

Chimney effect due to different vertical position of an isothermal horizontal cylinder confined between two adiabatic walls

The variation of natural convection heat transfer from an isothermal horizontal cylinder confined between two adiabatic walls of constant height is investigated by Mach-Zehnder interferometry technique. This paper focuses on the chimney effect due to the vertical position changes of cylinder (Y) located between two walls with a constant distance of W measuring 1.5 cylinder diameter. The cylinder’s local and average Nusselt numbers are determined for ratio of vertical position to its diameter ranging from Y/D = (0 to 10), and the Rayleigh number ranging from 3.5 × 10³ to 1.4 × 10⁴. There is an optimum distance between the walls in which the Nusselt number is maximum. Results are indicated with a single correlation which gives the average Nusselt number as a function of the ratio of vertical position to cylinder diameter and the Rayleigh number. The experimental data shows that there is an optimum vertical position for the cylinder at which the Nusselt number has a maximum value at each Rayleigh number. This optimal vertical position is derived from the correlation and is presented by an equation. The value of the optimum vertical position increases as the Rayleigh number increases.     

Rapid,highly efficient and chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by reusable electron‐deficient tin(IV)porphyrin

In this paper, rapid and highly efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) in the presence of catalytic amounts of high‐valent [Sn^IV(TPP)(OTf)₂] is reported. This catalytic system catalyzes trimethylsilylation of primary, secondary and tertiary alcohols as well as phenols, and the corresponding TMS‐ethers were obtained in high yields and short reaction times at room temperature. It is noteworthy that this method can be used for chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity. Copyright © 2009 John Wiley & Sons, Ltd.     

Highly efficient and chemoselective acetalization of carbonyl compounds catalyzed by new and reusable zirconyl triflate,ZrO(OTf)2

Various types of aromatic aldehydes were efficiently converted to their corresponding 1,3‐dioxanes and 1,3‐dioxolane with 1,3‐propanediol and ethylene glycol, respectively, in the presence of catalytic amount of ZrO(OTf)₂ in acetonitrile at room temperature. The catalyst can be reused several times without loss of its catalytic activity. Very short reaction times, selective acetalization of aromatic aldehydes in the presence of aliphatic aldehydes and ketones, very mild reaction conditions, reusability of the catalyst, and easy workup are noteworthy advantages of this method. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:131–135, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20523     

Cooling performance of a microchannel heat sink with nanofluids containing cylindrical nanoparticles (carbon nanotubes)

In this paper, we present the numerical method for explaining the cooling performance of a microchannel heat sink with carbon nanotubes (CNTs)-fluid suspensions. Here we will show that with increase of nanolayer thickness of multiwalled carbon nanotubes (MWCNTs) the microchannel heat sink temperature gradient will be decreased. By using a theoretical model for explaining the enhancement in the effective thermal conductivity of nanotubes (cylindrical shape particles) for use in nanotube-in-fluid suspension, we investigate the temperature contours and thermal resistance of a microchannel heat sink with MWCNTs (with ~25 nm diameter) dispersed in water.     

Virtual Path Design in Service-Specific ATM Networks

This paper addresses the problem of virtual path management in ATM networks, which is the problem of jointly selecting efficient virtual trunk routes and sizing them to meet end-to-end grade-of-service requirements. The problem is posed over capacitated networks and is formulated as a two-level multi-commodity network flow problem with linear side-constraints (physical layer capacity) and non-linear side constraints (end-to-end/link blocking). Through a variety of examples we show the method (i) generates solutions that agree with engineering judgement, (ii) can solve VP layout management for realistic size networks (of up to 200 nodes) in reasonable time and (iii) provides upper bounds on how far the solution strays from the mathematically optimal design.