Search results for "Anhydrous"
showing 10 items of 48 documents
Electrocarboxylation of benzyl chlorides at silver cathode at the preparative scale level
2008
Abstract The electrocarboxylation of benzyl chlorides to the corresponding carboxylic acids performed at silver cathodes was investigated both theoretically and experimentally in order to find the influence of the operative parameters on the selectivity and on the Faradic efficiency of the process. Theoretical considerations were confirmed by the electrocarboxylation of 1-phenyl-1-chloroethane performed in undivided cells equipped with sacrificial anodes both in a bench-scale electrochemical batch reactor and in a continuous batch recirculation reaction system equipped with a parallel plate electrochemical cell. Selectivity and Faradic yields higher than 80% and 70%, respectively, were obta…
Determination of the composition of isomeric mixtures of allylstannanes by means of 119Sn and 13C NMR measurements
1993
Abstract Allylstannanes of the type Bun3Sn(C3H3) ((C3H3 = allenyl and propargyl) Me3Sn(C4H7), Bun3Sn(C4H7), Ph3Sn(C4H7), Me3Sn(C4H7)2 and Bun3Sn(C4H7)2 [C4H7 = (E)-but-2-enyl, (Z-but-2-enyl, and but-1-en-3-yl] were prepared via Grignard reactions as isomeric mixtures whose compositions can be directly determined by 119Sn and 13C NMR spectrometry. The 119Sn and 13C δ-values of all possible isomers together with the isomeric compositions of freshly prepared compounds and after isomerization in dry methanol under reflux are reported. The course of isomerization of some compounds in anhydrous methanol at room temperature or in the presence of Bu3SnCl was followed by 119Sn NMR spectrometry.
Crystal and molecular structure of anhydrous betaine, (CH3)3NCH2CO2
1999
Abstract 1–Carboxy–N,N,N–trimethylmethanamanium inner salt or anhydrous betaine, (CH3)3NCH2CO2, FW=117.15 gmol −1 , crystallizes in the orthorhombic space group Pnma with a=14.544(2) A , b=6.859(3) A , c=6.131(1) A , V=611.7(3) A 3 , Z=4, D x =1.27 Mgm −3 , λ (MoK α )=0.71073 A , μ =0.091 mm −1 . The structure was resolved by direct methods and refined by least-square calculations to R=0.038 for 531 reflections. Observed changes in bond angles imply that there is a repulsion between nitrogen and oxygen. The melting point (measured at onset) is 570 K. FTIR spectra of anhydrous betaine and monohydrate were recorded. Clear differences were found between the two compounds based on infrared (i.r…
Thermal behaviour of anhydrous, dihydrate and (2/1) ethanol forms of 1-O-α-d-glucopyranosyl-d-mannitol
1998
Abstract The melting points of anhydrous 1-O-α- d -glucopyranosyl- d -mannitol, 1-O-α- d -glucopyranosyl- d -mannitol dihydrate and a new compound, 1-O-α- d -glucopyranosyl- d -mannitol-ethanol (2/1) were determined using differential scanning calorimetry. The melting onset values were 169.2 (3), 104.3 (18) and 158.7 (9), respectively, and the melting peak values were 171.4 (5), 107.9 (15) and 160.1 (6), respectively. 1-O-α- d -glucopyranosyl- d -mannitol dihydrate and 1-O-α- d -glucopyranosyl- d -mannitol-ethanol (2/1) decompose to anhydrous form when heated at slow heating rates. According to TG-FTIR measurements, 1-O-α- d -glucopyranosyl- d -mannitol-ethanol (2/1) lost its ethanol in the…
Hydrolytically stable chemically bonded silica supports with metal complexating ligands: Synthesis, characterization and use in high-performance liga…
1982
A silica of 14 nm pore size was reacted according to two procedures with the following silanes: γ-aminopropyltriethoxysilane (1), N-aminoethyl-N′-aminopropyltrimethoxysilane (2), N-aminoethyl-N′-aminoethyl-N″-aminopropyltrimethoxysilane (3), N-(3-triethoxysilanepropyl)-N, N-diacetic dimethylester (4), N-(3-trisodiumsilanolatepropyl)-N, N-diacetic acid disodium salt (5) and N-(3-trisodiumsilanolatepropyl)-ethylenediamine-N, N′, N′-triacetic acid trisodium salt (6). The reaction of silanes 1–4 with the silica was carried out under anhydrous conditions (procedure A). Silanes 1–6 were subjected to surface modification under essentially hydrous conditions applying a two-step procedure (procedure…
Spontaneous cocrystal hydrate formation in the solid state: crystal structure aspects and kinetics
2013
Kinetics of anhydrous cocrystal hydration and that of cocrystal monohydrate formation from starting compounds in the solid state are studied as a function of RH and time. The propensity of the anhydrate to hydration is related to the crystal structures of anhydrous and hydrated forms.
Three anhydrous forms and a dihydrate form of quifenadine hydrochloride: a structural study of the thermodynamic stability and dehydration mechanism
2015
Crystal structures of dihydrate (DH) and three anhydrous forms (A, B and C) of quifenadine (1-azabicyclo[2.2.2]oct-8-yl-diphenyl-methanol) hydrochloride are presented, and crystal structure information is used to explain and rationalize the relative stability of polymorphs and observed phase transformations. The dehydration mechanism of the hydrate is provided by interpreting the results obtained in studies of crystal structures, dehydration kinetics and thermal analysis. Structural analysis is used to explain the observed relative stability of the anhydrous phases and the hydrate. The crystal structures have been determined either from single crystal (form DH) or from powder diffraction da…
Why betaine crystallizes in high local C s symmetry. An ab initio MO and DFT study of anhydrous betaine and betaine monohydrate
1999
A theoretical study of the structure, charge distribution, rotational barrier and fundamental vibrations of anhydrous betaine (CH3)3NCH2COO (trimethylglycine) was carried out and compared with available experimental data. Calculations were carried out at HF, MP2 and B3LYP levels using a 6-31+G(d,p) basis set. The calculated rotational barrier of the betaine carboxylic group is 40.5 kJ/mol at the MP4(SDQ)/6-311G(d,p)//HF/6-31+G(d,p) level of theory. The rotation of the carboxylic group changes the molecule from a highly symmetric (C s ) conformation into a twisted conformation resulting in shortening of the molecule by about 50 pm. Natural population analysis (NPA) indicates intramolecular i…
Novel Phases in the V-P-O Catalytic System from Oxovanadium Hydrogenphosphate Precursors
1994
ABSTRACTSeveral biphasic VOP04/(VO)2P2O7 redox partners seem to be active in the catalytic cycles involved in the mild oxidation of simple hydrocarbons to maleic anhydride. The present X-ray time resolved thermal-diffractometric study reveals the existence of a new anhydrous variety of the oxidized form, ω-VOPO4, which may appear as an intermediate in the formation of the well known β-VOPO4. This new phase only remains well crystallized at relatively high temperatures, and when it is allowed to cool down in wet air VOPO4·2H2O results. In turn, another well defined phase, VOPO4·1.58H2O, can be recognized in the course of the hydration process.
Hydrated Layer Formation on Tricalcium and Dicalcium Silicate Surfaces: Experimental Study and Numerical Simulations
2001
In this paper, an original approach is used to study the calcium silicate hydrate (C−S−H) layer formation on the surface of grains of anhydrous silicate during tricalcium and dicalcium silicate hydration from the variation of the rate of hydration with lime concentration. The effects of C−S−H nucleation and growth on the curves for the degree of reaction against time have been separated in both experimental study of the rate of hydration in controlled conditions and numerical simulation of the growth of C−S−H on a surface from a particle aggregation model. The influence of the number of nuclei and of the different growth modes has been quantified.