A New, Convenient Reductive Procedure For The Deprotection Of 4-Methoxybenzyl (Mpm) Ethers To Alcohols

Selective introduction and removal of protecting groups is of great significance in organic synthesis.l The benzyl ether function is one of the most common protecting groups for alcohols. Selective oxidative removal of the 4-methoxybenzyl (MPM) ethers in the presence of benzyl ethers made the MPM moiety an alternative protecting group, and its utility in carbohydrate chemistry is well established. Several procedures have been developed for the cleavage of the 4-methoxybenzyl moiety, e.g. DDQ oxidation (eq 1),2e lectrochemical ~xidationh,~om ogeneous electron t r a n~f e rp,~ho toinduced single electron t r an~f e rb,o~ro n trichloride-dimethyl sulfide,6e tc. However, in all these methods isolation of the alcohol from the inevitable byproduct, 4-methoxybenzaldehyde [also dichlorodicyanohydroquinone (DDHQ) in the most commonly used method employing DDQI can be troublesome. Recently Wallace and Hedgetts7 discovered that acetic acid at 90 "C cleaves the aromatic MPM ethers into the corresponding phenols and 4-methoxybenzyl acetate (eq 21, whereas the aliphatic MPM ethers generated, instead of alcohols, the corresponding acetates (eq 3). Complimentary to this methodology, herein we report that sodium cyanoborohydride and boron trifluoride etherate reductively cleaves, cleanly and efficiently, the aliphatic MPM ethers to an easily separable mixture of the corresponding alcohols and 4-methylanisole

On-Chip Clock Network Skew Measurement using Sub-Sampling

We present a technique for an all-digital on-chip delay measurement system to measure the skews in a clock distribution network. It uses the principle of sub-sampling. Measurements from a prototype fabricated in a 65 nm industrial process, indicate the ability to measure delays with a resolution of 0.5ps and a DNL of 1.2 ps.

On an analytical-numerical procedure for the analysis of cylindrical shells with arbitrarily oriented cracks

An analytical-numerical procedure for obtaining stress intensity factor solutions for an arbitrarily oriented crack in a long, thin circular cylindrical shell is presented. The method of analysis involves obtaining a series solution to the governing shell equation in terms of Mathieu and modified Mathieu functions by the method of separation of variables and satisfying the crack surface boundary conditions numerically using collocation. The solution is then transformed from elliptic coordinates to polar coordinates with crack tip as the origin through a Taylor series expansion and membrane and bending stress intensity factors are computed. Numerical results are presented and discussed for the pressure loading case.

A new synthetic procedure for the preparation of pyridinium tetrafluoroborate and hexafluorosilicate

Pyridinium tetrafluoroborate (C5H5NHBF4) and pyridinium hexafluorosilicate [(C5H5NH)2SiF6] have been prepared in good yields and high purity by the reaction of pyridinium poly(hydrogen fluoride) with oxides and acids of boron and silicon respectively. The salts have been characterised by melting points, IR, 1H and 19F NMR spectroscopy and chemical analysis.

A rapid procedure for the isolation of spheroplasts from Mycobacterium smegmatis

Abstract is not available.

Optimal Parameter Trajectory Estimation in Parameterized SDEs: An Algorithmic Procedure

We consider the problem of estimating the optimal parameter trajectory over a finite time interval in a parameterized stochastic differential equation (SDE), and propose a simulation-based algorithm for this purpose. Towards this end, we consider a discretization of the SDE over finite time instants and reformulate the problem as one of finding an optimal parameter at each of these instants. A stochastic approximation algorithm based on the smoothed functional technique is adapted to this setting for finding the optimal parameter trajectory. A proof of convergence of the algorithm is presented and results of numerical experiments over two different settings are shown. The algorithm is seen to exhibit good performance. We also present extensions of our framework to the case of finding optimal parameterized feedback policies for controlled SDE and present numerical results in this scenario as well.

A gravimetric procedure for the determination of wet precipitated sulphur, dissolved sulphur, soluble sulphides and hydrogen sulphide

Elemental sulphur (in wet precipitated form or dissolved in organic solvents) and hydrogen sulphide have been determined gravimetrically at room temperature by conversion into copper sulphide by elemental copper in presence of an organic solvent such as benzene or acetonitrile. Any solvent in which sulphur is soluble can be used. The black copper sulphide formed can be weighed or determined iodometrically. Analysis indicates the black compound to be Cu1.8S. This room temperature method is a versatile one-step procedure sensitive to microgram or macro amounts of sulphur. It has been used for determining the solubility of sulphur in tetrahydrofuran and dioxan. The apparent heat of solution indicates that sulphur dissolves in these solvents without any marked solute—solvent interactions.

A simple procedure for purification of N-carbamoylputrescine: Application to assays of putrescine transcarbamoylase and agmatine iminohydrolase activities

The observation that N-carbamoylputrescine is quantitatively excluded on O-(carboxymethyl)-cellulose columns with simultaneous retention of putrescine and agmatine has been utilized to develop a sensitive radiometric assay for putrescine transcarbamoylase and a colorimetric assay for agmatine iminohydrolase. A simple procedure for obtaining bulk amounts of pure synthetic N-carbamoylputrescine by separation from putrescine and dicarbamoylputrescine on Dowex 50 (Na+) resin is described.

On an analytical-numerical procedure for the analysis of cylindrical-shells with arbitrarily oriented cracks

An analytical-numerical procedure for obtaining stress intensity factor solutions for an arbitrarily oriented crack in a long, thin circular cylindrical shell is presented. The method of analysis involves obtaining a series solution to the governing shell equation in terms of Mathieu and modified Mathieu functions by the method of separation of variables and satisfying the crack surface boundary conditions numerically using collocation. The solution is then transformed from elliptic coordinates to polar coordinates with crack tip as the origin through a Taylor series expansion and membrane and bending stress intensity factors are computed. Numerical results are presented and discussed for the pressure loading case.

A hybrid clustering procedure for concentric and chain-like clusters

K-means algorithm is a well known nonhierarchical method for clustering data. The most important limitations of this algorithm are that: (1) it gives final clusters on the basis of the cluster centroids or the seed points chosen initially, and (2) it is appropriate for data sets having fairly isotropic clusters. But this algorithm has the advantage of low computation and storage requirements. On the other hand, hierarchical agglomerative clustering algorithm, which can cluster nonisotropic (chain-like and concentric) clusters, requires high storage and computation requirements. This paper suggests a new method for selecting the initial seed points, so that theK-means algorithm gives the same results for any input data order. This paper also describes a hybrid clustering algorithm, based on the concepts of multilevel theory, which is nonhierarchical at the first level and hierarchical from second level onwards, to cluster data sets having (i) chain-like clusters and (ii) concentric clusters. It is observed that this hybrid clustering algorithm gives the same results as the hierarchical clustering algorithm, with less computation and storage requirements.

Sequence generator for periodic sampling of transient phenomena

A simple instrument that can provide a sequence of timed pulses for first initiating a transient process and then enabling sampling and recording periodically during the course of the transient event is described. The time delay between the first of these sampling pulses and the start of the transient event is adjustable. This sequence generator has additional features that make it ideal for use in acquiring the waveforms when a storage oscilloscope is used as the recording device. For avoiding the clutter caused by many waveforms being recorded at the same place on an oscilloscope screen such features as displacements of waveforms in the X and Y directions and trace blanking at places where the waveform is not required, have been incorporated. This sequence generator has been employed to acquire a sequence of Raman scattered radiation signals from an adiabatically expanding saturated vapour probed by a flashlamp-pumped dye laser.

Modified design procedure for a sparger reactor sequence

In an earlier communication[l] we have indicated a general graphical design procedure for a sequence of sparger reactors in which a second order liquid phase reaction proceeds in a stagewise fashion. The prediction of the reactant concentration in each stage and hence the conversion depended on a search procedure initiated along a straight line representing the mass balance equation at the given stage and drawn from the known feed stage located on the abscissa in a E-IU diagram for the given system.

An approximate mathematical procedure for the determination of characteristic parameters for a general case in three dimensional photoelasticity

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