Oleum and Sulfuric Acid as Reaction Media: Structural Features and Thermal Behavior of RE2[W2O3(SO4)6] (RE = Sm-Gd, Ho), RE2Nb2O2(SO4)3[H(SO4)2]2 (RE = Y, Ce-Nd, Sm-Er), Sm2Nb2O2(SO4)5(S2O7), and M2Nb4O5(SO4)8 (M = Bi, Eu)

2011 ◽  
Vol 2011 (28) ◽  
pp. 4400-4413 ◽  
Author(s):  
Ulf Betke ◽  
Mathias S. Wickleder
Keyword(s):  
Sulfuric Acid ◽  
Thermal Behavior ◽  
Structural Features ◽  
Reaction Media

The Gold Sulfates MAu(S04)2 (M = Na, K, Rb)

2001 ◽  
Vol 56 (12) ◽  
pp. 1340-1343 ◽  
Author(s):  
Mathias S. Wickleder ◽  
Oliver Büchner
Keyword(s):  
Sulfuric Acid ◽  
Single Crystals ◽  
Crystal Structures ◽  
Structural Features ◽  
Monovalent Cations ◽  
Coordination Numbers ◽  
Square Planar ◽  
Oxygen Atoms

AbstractThe evaporation of a solution of Au(OH)3 and Na2So4 in conc. sulfuric acid led to yellow single crystals of NaAu(SO4)2 (monoclinic, P21/n, Z = 2, a = 469.1, b = 845.9, c = 831.2 pm, β = 95.7°). Analogous procedures with K2SO4 or Rb2SO4 instead of Na2SO4 yielded single crystals of KAu(SO4)2 (monoclinic, C2/c, Z = 4, a = 1109.8, b = 724.2, c = 941.1 pm, β = 118.4°) and RbAu(S04)2, respectively, (triclinic, P1̄, Z = 1, a = 423.6, b = 497.5, c = 889.0 pm, a = 76.4°, β = 88.4°, γ = 73.5°). Although the crystal structures of the three sulfates are not isotypic they show similar structural features: The gold atoms are coordinated by four oxygen atoms in a square planar manner. These oxygen atoms belong to four SO42- ions which link the [AUO4] units to infinite chains according to 1∞[Au(SO4)4/ 2]- . These chains are connected via the monovalent cations which show coordination numbers of 6 (Na+), 10 (K+) and 12 (Rb+), respectively.

scholarly journals Highly Porous Carbon Materials from Biomass by Chemical and Carbonization Method: A Comparison Study

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Wan Nor Roslam Wan Isahak ◽  
Mohamed Wahab Mahamed Hisham ◽  
Mohd Ambar Yarmo
Keyword(s):  
Sulfuric Acid ◽  
Thermal Behavior ◽  
Surface Area ◽  
Porous Carbon ◽  
High Surface ◽  
High Surface Area ◽  
Empty Fruit Bunches ◽  
Heating Treatment ◽  
Concentrated Sulfuric Acid ◽  
Highly Porous

Porous carbon obtained by dehydrating agent, concentrated sulfuric acid (H2SO4), from biomass containing high cellulose (filter paper (FP), bamboo waste, and empty fruit bunches (EFB)) shows very high surface area and better thermal behavior. At room temperature (without heating), treatment of H2SO4removed all the water molecules in the biomass and left the porous carbon without emitting any gaseous byproducts. Brunauer-Emmett-Teller (BET) surface analysis has shown that bamboo-based carbon has good properties with higher surface area (507.8 m2/g), micropore area (393.3 m2/g), and better thermal behavior (compared to FP and EFB) without any activation or treatment process. By acid treatment of biomass, it was shown that higher carbon composition obtained from FP (85.30%), bamboo (77.72%), and EFB (76.55%) is compared to carbon from carbonization process. Under optimal sulfuric acid (20 wt.%) uses, high carbon yield has been achieved for FP (47.85 wt.%), bamboo (62.4 wt.%), and EFB (55.4 wt.%).

A comparison of the mechanisms of hydrolysis of benzimidates, esters, and amides in sulfuric acid media

2005 ◽  
Vol 83 (9) ◽  
pp. 1391-1399 ◽  
Author(s):  
Robin A Cox
Keyword(s):  
Sulfuric Acid ◽  
Isotope Effects ◽  
Ester Hydrolysis ◽  
Water Molecules ◽  
Acid Media ◽  
Tetrahedral Intermediate ◽  
Amide Hydrolysis ◽  
Solvent Isotope ◽  
Reaction Media ◽  
Hydrolysis Of

The mechanisms given in textbooks for both ester and amide hydrolysis in acid media are in need of revision. To illustrate this, benzimidates were chosen as model compounds for oxygen protonated benzamides. In aqueous sulfuric acid media they hydrolyze either by a mechanism involving attack of two water molecules at the carbonyl carbon to give a neutral tetrahedral intermediate directly, as in ester hydrolysis, or by an SN2 attack of two water molecules at the alkyl group of the alkoxy oxygen to form the corresponding amide, or by both mechanisms, depending on the structure of the benzimidate. The major line of evidence leading to these conclusions is the behavior of the excess acidity plots resulting from the rate constants obtained for the hydrolyses as functions of acid concentration and temperature. The first of these mechanisms is in fact very similar to one found for the hydrolysis of benzamides, as inferred from: (1) similar excess acidity plot behaviour; and (2) the observed solvent isotope effects for amide hydrolysis, which are fully consistent with the involvement of two water molecules, but not with one or with three (or more). This mechanism starts out as essentially the same one as that found for ester hydrolysis under the same conditions. Differences arise because the neutral tetrahedral intermediate, formed directly as a result of the protonated substrate being attacked by two water molecules (not one), possesses an easily protonated nitrogen in the amide and benzimidate cases, explaining both the lack of 18O exchange observed for amide hydrolysis and the irreversibility of the reaction. Protonated tetrahedral intermediates are too unstable to exist in the reaction media; in fact, protonation of an sp3 hybridized oxygen to put a full positive charge on it is extremely difficult. (This means that individual protonated alcohol or ether species are unlikely to exist in these media either.) Thus, the reaction of the intermediate going to product or exchanged reactant is a general-acid-catalyzed process for esters. For amide hydrolysis, the situation is complicated by the fact that another, different, mechanism takes over in more strongly acidic media, according to the excess acidity plots. Some possibilities for this are given.Key words: esters, amides, benzimidates, hydrolysis, excess acidity, mechanism, acid media.

OBTAINING MICROCRYSTALLINE CELLULOSE FROM MELON CROPS AND STUDYING ITS STRUCTURE

2020 ◽  
pp. 38-41
Keyword(s):  
Heat Treatment ◽  
Hydrogen Peroxide ◽  
Sulfuric Acid ◽  
Microcrystalline Cellulose ◽  
Moisture Sorption ◽  
Structural Features ◽  
Ash Content ◽  
Optical Parameters ◽  
Cellulose Sample ◽  
Water Swelling

The aim of the study was to obtain microcrystalline cellulose from gourds. Cellulose was isolated from the stems of watermelon and pumpkin by acid and alkaline heat treatment. Microcrystalline cellulose was obtained from cellulose by hydrolysis. Cellulose was hydrolyzed in a mixture of sulfuric acid and hydrogen peroxide. The optical parameters of the microcrystalline cellulose sample, ash content, bulk density, water swelling, and moisture sorption were determined. The structural features of the obtained microcrystalline cellulose were studied by IR spectroscopy. The functional groups present under various conditions for the production of microcrystalline cellulose were determined. The influence of the duration of cellulose treatment on the degree of ordering of microcrystalline cellulose was established.

scholarly journals The Thermal Behavior of Lyocell Fibers Containing Bis(trimethylsilyl)acetylene

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 537
Author(s):  
Igor Makarov ◽  
Markel Vinogradov ◽  
Maria Mironova ◽  
Georgy Shandryuk ◽  
Yaroslav Golubev ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Thermal Behavior ◽  
Carbon Fibers ◽  
Coefficient Of Thermal Expansion ◽  
Structural Features ◽  
Amorphous Structure ◽  
Processing Temperature ◽  
Composite Fibers ◽  
Scanning Calorimetry ◽  
Lyocell Fibers

This study focuses on the preparation of carbon fiber precursors from solutions of cellulose in N-methylmorpholine-N-oxide with the addition of bis(trimethylsilyl)acetylene, studying their structural features and evaluating thermal behavior. The introduction of a silicon-containing additive into cellulose leads to an increase in the carbon yield during carbonization of composite precursors. The type of the observed peaks on the differential scanning calorimetry (DSC) curves cardinally changes from endo peaks intrinsic for cellulose fibers to the combination of endo and exo peaks for composite fibers. For the first time, coefficient of thermal expansion (CTE) values were obtained for Lyocell fibers and composite fibers with bis(trimethylsilyl)acetylene (BTMSA). The study of the dependence of linear dimensions of the heat treatment fibers on temperature made it possible to determine the relation between thermal expansion coefficients of carbonized fibers and thermogravimetric curves, as well as to reveal the relationship between fiber shrinkage and BTMSA bis(trimethylsilyl)acetylene content. Carbon fibers from composite precursors are obtained at a processing temperature of 1200 °C. A study of the structure of carbon fibers by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy made it possible to determine the amorphous structure of the fibers obtained.

Structure and thermal behavior studies of ZrO2 treated by different concentrations of sulfuric acid

1991 ◽  
Vol 26 (12) ◽  
pp. 1379-1383 ◽  
Author(s):  
Shian-Jy Wang ◽  
Shu-Hua Chan ◽  
Weir-Mirn Hurng
Keyword(s):  
Sulfuric Acid ◽  
Thermal Behavior

Synthesis of Conducting Polyaniline Using Compound Oxidant

2009 ◽  
Vol 87-88 ◽  
pp. 300-305 ◽  
Author(s):  
Hui Huang ◽  
Jin Quan Xu ◽  
Zhong Cheng Guo
Keyword(s):  
Ascorbic Acid ◽  
Sulfuric Acid ◽  
Room Temperature ◽  
Structural Changes ◽  
Ammonium Persulfate ◽  
Red Shift ◽  
Conducting Polyaniline ◽  
Polymerization Condition ◽  
Conductive Polyaniline ◽  
Reaction Media

Conductive polyaniline (PANI) was synthesized by the oxidation of aniline with complex oxidant composed of ammonium persulfate ((NH4)2S2O8) and ascorbic acid (C6H8O6) in a reaction media containing sulfuric acid (H2SO4). The effects of concentration of H2SO4, (NH4)2S2O8 and (NH4)2S2O8/C6H8O6 mol ratio on the polymerization of aniline were studied. The optimal polymerization condition was aniline 1mol/L, H2SO4 1mol/L, and compound oxidant (mole ratio of (NH4)2S2O8 to C6H8O6 as to 10:1) 1mol/L at room temperature without the protection of N2. The conductivity and yield of PANI reach 13.3S/cm and 96.7%, respectively. The structural changes of PANI were measured by FTIR, Raman and XRD. The results indicated that PANI was some crystal and its groups took place red shift.

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