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- Author or Editor: M. Paul x
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Abstract
Phosphorous pentasulfide is an important starting material for a number of commercial chemicals. Examples include lubricant additives (Spikes, Trib Lett 17:469–489, 2004), agricultural insecticides (Kirk-Othmer, Enycl Chem Technol 14:549–552, 1995), and mining ore flotation agents. Phosphorous pentasulfide is a mixture of several components, one of which is free elemental sulfur, present at levels of approximately 50 ppm to 20,000 ppm (2 %). The amount of free sulfur present in the phosphorous pentasulfide can impact manufacturing, such as zinc dithiosulfate processing. Therefore, an accurate and fast analytical method to measure elemental sulfur in phosphorous pentasulfide would be of value compared to what is available now.
Abstract
The usual determination of formaldehyde by gravimetry and spectroscopy extends down to 10−3 mg with only limited reproducibility. Radiochemical analysis using14C-labelled formaldehyde allows to determine amounts of 10−4 to 10−5 mg. This technique was, therefore, applied to detect reliably the amount of formaldehyde proportional to the activity in viscose rayon, spun in a formaldehyde containing spinning bath by using an ionisation chamber assay. The objects investigated were found to contain 2·10−5 mg to 1.4·10−4 mg formaldehyde, the relative error being lower than 4%. The scope of application of this method is discussed.
Herein, we illustrate how microreactor technology can be used as a tool for reaction screening and optimization, in addition to improving the reaction chemistry. We report the in-situ generation of azo compounds by reactive quenching of diazonium intermediates in microreactors. This involves an electrophilic aromatic substitution reaction, namely, an azo-coupling reaction performed in continuous-flow systems in the presence of a phase transfer catalyst with great emphasis on compounds that do not easily couple. Capitalizing on the benefits of a large surface area and the short molecular diffusion distances observed in microreactors, in-situ phase transfer catalyzed azo-coupling reaction of diphenylamine to p-nitroaniline was investigated. A rapid and easy optimization protocol was established which yielded a 99%, 22%, and 33% conversion of diphenylamine, carbazole, and triphenylamine, respectively, in approximately 2.4 min.
Abstract
The preparation of magnetic iron oxide nanoparticles within microreactors is reported. The proportion of γ-Fe2O3 and Fe3O4 in the sample was determined, an important parameter for reproducibility in applications.
In this perspective article, the use of continuous flow synthesis to prepare advanced pharmaceutical intermediates in developing economies is highlighted. Case studies are presented to suggest that cost effective local manufacture of life saving drugs, may potentially be implemented to facilitate better access to drugs to the underprivileged.
Abstract
Hydrazoic acid (HN3) was used in a safe and reliable way for the synthesis of 5-substitued-1H-tetrazoles and for the preparation of N-(2-azidoethyl)acylamides in a continuous flow format. Hydrazoic acid was generated in situ either from an aqueous feed of sodium azide upon mixing with acetic acid, or from neat trimethylsilyl azide upon mixing with methanol. For both processes, subsequent reaction of the in situ generated hydrazoic acid with either organic nitriles (tetrazole formation) or 2-oxazolines (ring opening to β-azido-carboxamides) was performed in a coil reactor in an elevated temperature/pressure regime. Despite the explosive properties of HN3, the reactions could be performed safely at very high temperatures to yield the desired products in short reaction times and in excellent product yields. The scalability of both protocols was demonstrated for selected examples. Employing a commercially available benchtop flow reactor, productivities of 18.9 g/h of 5-phenyltetrazole and 23.0 g/h of N-(1-azido-2-methylpropan- 2-yl)acetamide were achieved.
A highly scalable and efficient flow-system has been developed to perform the catalyzed acetylation of alcohols and phenols, such as salicylic acid, at room temperature in excellent yield. The volumetric throughput and the amount of product can be increased simply by increasing the diameter of a versatile catalytic 12-tungstosilicic acid-supported, silica monolith can be used to increase the quantity of product produced without having to changeing the optimal operatingreaction conditions.
Abstract
Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition above and below its melting temperature have been studied and compared with the primary (PKIE) and secondary kinetic isotope effects (SKIE) of13C and18O, respectively, in the decarboxylation of other heterocyclic acids. The temperature dependence of the secondary oxygen-18 isotope effects is negative in the total 221–255°C temperature interval investigated initially. The13C KIE measured above melting point of N.A. (temperature interval 235–270°C) are located in the range 1.007–1.009. Below melting point of nicotinic acid the13C KIE are larger and reveal the negative temperature dependence (13C KIE decreases with decreasing the reaction temperature from 1.013/at 230°C to 1.0114/at 221°C). A discussion of the above isotopic results is presented.
