Reactions with heterocyclic amidines. VI. Synthesis and chemistry of pyrazol-5-yl,and 1,2,4-triazol-5-ylhydrazonyl chlorides

The 4-bromo-3-phenylpyrazol-5-ylhydrazonyl chlorides (Ia,b) and 1,2,4-triazol-5-ylhydrazonyl chlorides (IIa,b) were prepared via coupling of diazotized 4-bromo-3-phenyl-5-aminopyrazole (III) and 5-amino-1,2,4-triazole (IV) with α-chloro derivatives of acetylacetone and of ethyl aceto-acetate. Compounds Ia and IIa,b were utilised for the synthesis of several new heterocyclic derivatives.     

Commutativity theorems for s-unital rings with constraints on commutators

Let R be an associative s-unital ring with the polynomial identity \( y^{s}[x^{n},y]=\pm [x,y^{m}]x^t\) or \( y^{s}[x^{n},y]=\pm x^{t}[x,y^{m}]\) , where m, n, s and t are given non-negative integers such that m > 0 or n > 0 and m ≠ n if s = m ? 1 and t = n ? 1. Using similar methods as in our recent papers [1] and [2], we prove here the commutativity of R for various values of m, n, s and t, under appropriate constraints on torsion of commutators.     

Effect of cold work on the dissolution kinetics in the precipitating Al-2 wt% Mg alloy

The fracture stress _f was taken to assess the mechanism of dissolution of the -phase in the Al-2 wt% Mg alloy. The role of pre-cold working the polycrystalline samples was investigated. The dissolution of the -phase was carried out at different temperatures. The relation between the fracture stress and the time of dissolution showed peaky curves. The rise of _f towards a maximum was attributed to the progressive dissolution of the precipitates. The position of the peak was found to shift towards lower times of dissolution with the increase of the dissolution temperature or the increase of the pre-cold work. Considering the peak position indicative of a certain degree of dissolution, equivalent times and temperatures of the dissolution mechanism were thus found and the activation energy was calculated. Pre-cold working the samples before the dissolution act decreased the activation energy responsible for the process from 1·95×10^–19 J to about 0·48× 10^–19 J. The initial drop in _f observed for heavily cold worked samples pointed towards the possible effect of excess vacancies created by cold work.The authors are really grateful for the enlightening discussions with Prof. R. Kamel.     

KINETICS AND MECHANISM OF THE REACTION BETWEEN OLIGOSILOXANES AND P-TRICHLORO-N-DICHLOROPHOSPHORYL MONOPHOSPHAZENE (Cl3P[dbnd]N-POCl2)

Abstract

³¹P NMR investigation has been made of the action of Cl₃P[dbnd]N-POCl₂(I) first on hexamethyldisiloxane (Me₃Si)₂O and then on oligosiloxanes Me₃Si-(OSiMe₂)_n-OSiMe₃ n = 2 and n=3. The reactions were carried out in bulk or in solution with molar ratios siloxane/(I) varying from I to 5. It was demonstrated that only the monosubstitution of a chlorine atom by the -(OSiMe₂)_n,-OSiMe₃ species n = 0, 2, 3 with elimination of trimethylchlorosilane occurred leading to the derivatives Cl₂OP-N[dbnd]PCl₂O(SiMe₂-O)_nSiMe₃ (II). For n=2, 3 the siloxane redistribution reactions were observed by ²⁹Si NMR analysis. A two steps mechanism is proposed. consisting in a nucleophilic substitution, involving a tricoordinate phosphazenium intermediate, followed by the formation of an active ionic centre probably an oxonium ion, arising from the solvatation by the siloxane of this phosphazeniurn ion and /or of (II) leading to the redistribution reactions. The influences of the solvent, of trimethylchlorosilane, of the temperature, and of the addition of a protonated species (MDH) were investigated.     

Best constants for metric space inversion inequalities

For every metric space (X, d) and origin o ∈ X, we show the inequality I _o (x, y) ≤ 2d _o (x, y), where I _o (x, y) = d(x, y)/d(x, o)d(y, o) is the metric space inversion semimetric, d _o is a metric subordinate to I _o , and x, y ∈ X \ {o} The constant 2 is best possible.     

Studies on the Uptake of Rare Earth Elements on Polyacrylamidoxime Resins from Natural Concentrate Leachate Solutions

Synthesis of poly(acrylamidoxime) resin from polyacrylonitrile performed with different crosslinking ratios 2, 5, and 10 wt% of divinylbenzene as crosslinking agent, using methylbenzoate and dioctylphthalate as pore producing solvent, the reaction mixture occurred under nitrogen. Studies carried out on diluted solution from rare earth elements (REEs) concentrate contains impurities as Cu²⁺, Ni²⁺, Zn²⁺, Fe³⁺, Al³⁺, Si⁴⁺, Th⁴⁺, U⁶⁺, Ca²⁺, and K⁺. Changing some parameters as pH of the solution, time of feeding and type of acid as HCl, HNO₃, H₂SO₄. The adsorption efficiency of resin is in the order pH 6 > pH 5 > pH 4 > pH 2 with excluding pH 6 due to the precipitation of some of REEs with the impurities and complete precipitation of Dy ion during pH adjustment, the adsorption in HNO₃ > HCl > H₂SO₄ media.     

Studies towards the total synthesis of hygrocins A and B

The western segment of hygrocins A–B has been synthesized through the coupling of a chiral C5–C13 synthon with the sterically demanding hexasubstituted naphthalenic core. The C5–C13 chiral fragment has been assembled via a stereoselective Johnson orthoester rearrangement of an optically pure allylic alcohol derived from d-glucose. Our studies lay the platform for the determination of the absolute configuration of the unassigned C8-stereocenter of the title compounds in addition to the completion of the total synthesis of the unique ansamacrolides hygrocins A and B.     

Experimental comparison of performance and emission characteristics of 4-stroke CI engine operated with Roselle and Jatropha biodiesel blends

The environmental degradation, combined with the continuous depletion of the world's fossil fuel reserves, has forced the search for alternative fuels. This study was performed to investigate the performance of novel biodiesels in the CI engine. The experiments were performed at three different compressions ratios (16:1, 17:1, 18:1) and four loading conditions (25%, 50%, 75%, 100%). Different types of fuels such as jatropha biodiesel (JB), roselle biodiesel (RB), and ternary biodiesel (TB) were prepared and analyzed. The thermal performance of different fuels was analyzed in terms of brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), and exhaust gas temperature (EGT). The emission characteristics such as CO₂ emission, NO_x emission, and smoke emission were analyzed for all types of fuels. The results of these fuels in the engine were compared with mineral diesel (MD). The BTE was increased with increasing compression ratios and loads for all types of fuels. The BSFC was increased with increasing compression ratios but decreased with increasing loads. The increase in emission of NO_x was observed at higher compression ratios and loads. However, the CO₂ emission was decreased at higher loads and lower compression ratio. The performance curves achieved with a 20% jatropha biodiesel blend showed results that were approximate to those obtained with pure MD. The comparative analysis between different fuels showed that JB exhibit higher thermal performance as compared to other biodiesels. Therefore, JB can be a better alternative to conventional fuel.     

An unsteady thermal investigation of a wetted longitudinal porous fin of different profiles

Journal of Thermal Analysis and Calorimetry - The unsteady thermal behavior of a porous longitudinal fin in a fully wet circumstance in the existence of convection as well as radiation effect is...