2.1 Materials
All Chemicals and solvents were purchased from Sigma-Aldrich and Merck Chemical Companies and used without further purification.
2.2 Catalyst synthesis
A 10% solution of PVA (Mw = 70000) was prepared by dissolving of PVA in deionized hot water (95 °C). The pH value was adjusted about pH=3, by adding HCl. To prevent thermal decomposition and monitor the temperature of the PVA solution, a water bath was used. 50 ml of a 1 M solution of ZrOCl2.8H2O added dropwise to precursor solution and heated at the 60 °C for 2 h with constant stirring using a magnetic stirrer that leads to a better dispersion of Zr4+ ions into the polymer chains. To the resulted homogeneous solution, under ultrasonication, 50 ml of 2 M H3PO4 added dropwise at 50-60 °C for 2 h. On addition of phosphoric acid, Zr4+ ions reacted with PO43− ions almost immediately to form in situ ZP. The resulted mixture was allowed to age for 6 h, then the precipitate was filtered and washed with distilled water several times and dried in an oven at 80 °C overnight. The obtained white colored fluffy precursor was ground and calcined at the 550 °C for 4 h to decompose the organic matrix. The final product, the desired pure ZP nanocrystals, was identified as ZPA. A 10% solution of PVP (Mw = 40000) was prepared by dissolving PVP in deionized water. After this, the same procedure, as described in the above, was performed to produce ZP anoparticles. The final product was identified as ZPP. The summarized procedure is presented in Scheme 1.
Scheme 1. Summarized process of α-zirconium phosphate nanoparticles (ZPA and ZPP) preparation.
The detailed procedure for the preparation of the α-ZrP can be found in the literature [28]. P2O5/Al2O3 [54], P2O5/SiO2 [55], 1-H-3-methyl-im...
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... solid catalysts is known to occur either by the adsorption of both the aromatic and the alkylating agent molecules on the surface i.e., by a Langmuir–Hinshelwood (LH) mechanism or by the reaction of the adsorbed alkylating agent with aromatic molecules in gas phase, i.e., by an Eley–Rideal (ER) mechanism [59-62].
Scheme 3. H-bonds interactions between polymers and the P-OH groups of ZP.
It seems TBA and phenol adsorbed on the ZPA (or ZPP) surface due to hydrogen bondings. In the presence of ZPA (or ZPP) as solid acid catalyst, TBA turns to tert-butyloxonium which is so reactive toward nucleophiles, such as phenol, which produces 2-TBP, 4-TBP and 2,4-DTBP, Scheme 3. The main advantage of ZPA (or ZPP) as an alkylating catalyst, in comparison with other catalysts, is that it can significantly influence the product selectivity due to its uniform structure (scheme 4).
Alcohol, which is the nucleophile, attacks the acid, H2SO4, which is the catalyst, forming oxonium. However, the oxonium leaves due to the positive charge on oxygen, which makes it unstable. A stable secondary carbocation is formed. The electrons from the conjugate base attack the proton, henceforth, forming an alkene. Through this attack, the regeneration of the catalyst is formed with the product, 4-methylcyclohexene, before it oxidizes with KMnO4. In simpler terms, protonation of oxygen and the elimination of H+ with formation of alkene occurs.
A condenser and heat reflux was used to prevent reagents from escaping. Then the solid product was vacuum filtered. The product was recrystallized to purify it and the unknown
The good symmetry in para-xylene, makes all of the hydrogen atoms equivalent. As such, if any hydrogen atom is substituted with an alkyl group, it leads to a similar alkylated product. The reaction is electrophilic substitution in which
The diazonium ion is reasonably stable in aqueous solution at 0°C; on warming up it will form the phenol. A versatile functional group, it will undergo all the reactions depicted there as well as couple to aromatic rings activated with substituents such as amino and hydroxyl groups to form the huge class of azo dyes.
As tetragonal phase has high toughness and high strength, additional stabiliser such as Yttria can maintain the tetragonal phase of zirconia at low temperature. However, degradation gradually happens in Y-TZP after a certain years, especially under hydrothermal condition.
Rasmussen, T.; Jensen, J. F.; Ostergaard, N.; Tanner, D.; Ziegler, T.; Norrby, P. Chem. Eur. J., 2002, 8, 177.
The dehydration of 2-butanol, a secondary alcohol, progresses readily in the presence of a strong acid like concentrated sulfuric acid (H2SO4). The reaction is completed via the E1 mechanism. Initially, the hydroxyl group is a poor leaving group, but that is remedied by its protonation by the acid catalyst (H2SO4) converting it to a better leaving group, H2O. The loss of this water molecule results in a secondary carbocation intermediate that continues to form an alkene in an E1 elimination. If the elimination happens with either protons on the terminal methyl group, the resultant product is 1-butene, a Hoffman product (monosubstituted alkene). In contrast, elimination of either β-hydrogens by the conjugate base of sulfuric acid (HSO4---) on the methylene group leads to an alkene that is disubstituted. Either the cis- or trans-2-butene can form depending which hydrogen is deprotonated. These are the Saytzeff products since they are the most substituted ones. In this case, the trans-alke...
In the second part of phase 1 which was steps 5-8 4 different pieces of clean zinc were placed in 4 different acids. The acids were Hydrochloric ...
Silvery white and soft enough to be cut with a knife, gallium takes on a
In chemistry, out of all the elements on the periodic table, there are a few that stand out because of certain characteristics, Gallium is one of these elements. On the periodic table, Gallium has the symbol Ga and atomic number 31. Gallium is a metal that has uses in such things as, medical, industrial, and everyday life.
The most common form of polyethylene is petroleum based or olefins based; as before mentioned polyethylene compounds have a wide commercial applicability and are made from non-renewable resources (Harding, Dennis, von Blottnitz, Harrison, & S.T.L., 2007). Its manufacturing processes are regarded as energy intensive and release significant amount of CO2 and heat into the atmosphere (Broderick, 2008). Next a little more detailed description of polyethylene’s production processes will be presented, with a focus on the way the material inputs are extracted and synthesized.
This takes place by addition of the alcohol oxygen to chromium, forming a zwitterion. Water removes a proton which is transferred to the chromate ester. After hydrolysis, the carbonyl compound is formed (fig.5). By limiting the amount of water and oxidant present in the reaction , the second oxidation can be stopped and an aldehyde forms (see fig 1 where R1 = H).3 Tertiary alcohols are resistant to oxidation because you need at least one alpha hydrogen attached to the carbinol
Plontke, R. (2003, March 13). Chemnitz UT. TU Chemnitz: - Technische Universität Chemnitz. Retrieved April 1, 2014, from http://www.tu-chemnitz.de/en/
Predictions may be made about the suitability of possible catalysts by assuming that the mechanism of catalysis consists of two stages, either of which can be first:
Toluene hydrodealkylation or hydrodealkylation of toluene (HDA) is a process that used to produce benzene. The reaction occurs as: