Zinc hydroxide, dehydration

The hrst step in the preparation of the antidepressant maprotiline (33-5) takes advantage of the acidity of anthrone protons for incorporation of the side chain. Thus treatment of (30-1) with ethyl acrylate and a relatively mild base leads to the Michael adduct saponihcation of the ester group gives the corresponding acid (33-1). The ketone group is then reduced by means of zinc and ammonium hydroxide. Dehydration of the hrst-formed alcohol under acidic conditions leads to the formation of fully aromatic anthracene (33-2). Diels-Alder addition of ethylene under high pressure leads to the addition across the 9,10 positions and the formation of the central 2,2,2-bicyclooctyl moiety (33-3). The hnal steps involve the construction of the typical antidepressant side chain. The acid in (33-3) is thus converted to an acid chloride and that function reacted with methylamine to form the amide (33-4). Reduction to a secondary amine completes the synthesis of (33-5) [33]. 

Overall, [([12]aneN3)Zn(0H2)](C104)2 exhibits pH-dependent catalytic behavior for the hydration of C02 and dehydration of HCO. The rate-determining step of the C02 hydration reaction is the uptake of C02 by the zinc hydroxide complex. The rate-determining step in bicarbonate dehydration is substitution of the labile zinc-bound water molecule by the bicarbonate anion. The overall catalytic mechanism for both reactions is shown in Scheme 4. In considering this mechanism, it is... 

A comparison, however, of zinc oxide catalysts prepared in different ways, i.e. (A) precipitation of zinc hydroxide from zinc sulfate, (B) dry process commercial zinc oxide, and (C) hydrolysis of zinc isopropoxide in moist air, showed that the mode of preparation had a marked effect on the catalyst action. The percentage of olefin formed at a given temperature varied from 5 to 88 for isopropanol, 10 to 20 for ethanol, 1 to 31.5 for isobutanol, and 2 to 15 for n-propanol and butanol. In general, catalyst A was best for dehydration, and catalyst B for dehydrogenation, except in the case of ethanol where they were about the equal. Catalyst C behaved about the same as B, except in the case of ethanol, in which case it was a better dehydration material. 

Dehydration of zinc hydroxide can then lead to formation of the thermodynamically more stable zinc oxide. 

At a point depending on the initial composition of the anode and the rate and depth of discharge, however, the electrolyte becomes saturated with zincate, causing the product of the reaction to change to Zn(OH)2. In the water-starved environment of the alkaline anode, zinc hydroxide then slowly dehydrates to ZnO in the following sequence ... 

In 2012, Chen et al. reported a solution-processed nanocrystalline ZnO ETL in an inverted OSC which exhibited a PCE of 3.7% with a device structure of ITO/nanocrystalline ZnO/PSHTrPCBM/MoOj/Ag. The crystalline ZnO NPs were synthesized using zinc acetate dehydrate (ZnAc), ethanol, and potassium hydroxide (KOH). The ZnO NP solution was spincoated over the pre-cleaned ITO substrate and annealed at 120 °C for 10 minutes. The crystalline ZnO NPs provided ideal energy level alignment to PCBM, and high eonductivity. 

Preparation of ZnO for DSSC Applications Nanostructured ZnO electrodes can either be synthesised from ZnO nanoparticles that are prepared in a separate procedure, or produced in a single synthetic step. Crystalline ZnO nanoparticles can be prepared at room temperature in non-aqueous solutions.In a typical preparation, a solution of zinc acetate in alcohol is mixed with an equimolar amount of hydroxide. The dehydrating properties of the solvent prevent the formation of zinc hydroxide and promote formation of crystalline ZnO. Transparent ZnO colloidal solutions are easily prepared. The particles tend to be approximately spherical and their size depends strongly on the preparation... 

Reaction XXIV. Condensation of certain Carbonyl Compounds with one another under the influence of Dehydrating Agents. (A., 223, 139.)— Aldehydes and ketones readily condense with one another under the influence of such reagents as zinc chloride, hydrochloric acid, sulphuric acid, alkali hydroxides, sodium acetate solution, etc., to give a/J-olefinic aldehydes and ketones ... 

Carbonic anhydrase is a zinc(II) metalloenzyme which catalyzes the hydration and dehydration of carbon dioxide, C02+H20 H+ + HC03. 25 As a result there has been considerable interest in the metal ion-promoted hydration of carbonyl substrates as potential model systems for the enzyme. For example, Pocker and Meany519 studied the reversible hydration of 2- and 4-pyridinecarbaldehyde by carbonic anhydrase, zinc(II), cobalt(II), H20 and OH. The catalytic efficiency of bovine carbonic anhydrase is ca. 108 times greater than that of water for hydration of both 2- and 4-pyridinecarbaldehydes. Zinc(II) and cobalt(II) are ca. 107 times more effective than water for the hydration of 2-pyridinecarbaldehyde, but are much less effective with 4-pyridinecarbaldehyde. Presumably in the case of 2-pyridinecarbaldehyde complexes of type (166) are formed in solution. Polarization of the carbonyl group by the metal ion assists nucleophilic attack by water or hydroxide ion. Further studies of this reaction have been made,520,521 but the mechanistic details of the catalysis are unclear. Metal-bound nucleophiles (M—OH or M—OH2) could, for example, be involved in the catalysis. 

The high catalytic activity of [([12]aneN4)Zn(0Hw)](C104)w (n = 1 or 2) derivatives in C02 hydration and dehydration, relative to other reported model systems, has been attributed, in part, to high stability constants for zinc binding to the supporting chelate ligand. Enhanced stability imposed by the chelate structure should make the coordinated water molecule more labile for displacement by HCOJ, and the zinc-bound hydroxide more nucleophilic toward C02. 

A second synthesis for the preparation of 2H5V (29) starts by condensation of o-nitrobenzenediazonium chloride withT-hydroxyaceto-phenone. The azo compound was reduced with zinc and sodium hydroxide without reduction of the carbonyl group of the acetyl group. After acetylation, 2(2-acetoxy-5-acetylphenyl)2H-benzotriazole (2A5A) was reduced with sodium borohydride and the secondary alcohol was dehydrated with potassium hydrogen sulfate after hydrolysis, 2H5V was... 

In the presence of catalysts such as are used for the synthesis of methanol from mixtures of hydrogen and carbon monoxide and which have been promoted by the addition of an alkali oxide, ethanol may be dehydrated to form butanol in a high pressure process. Catalyst mixtures composed of chromium and zinc oxides to which either barium hydroxide or potassium oxide has been added have been specified.6 ... 

When higher-temperature heat is available, other systems are possible. A school in Munich, Germany, dehydrated 7 metric tons of zeolites using 130°C steam in the district heating system during off-peak hours, then passed moist air over them in the day to recover the heat.201 Pellets of calcium hydroxide containing zinc, aluminum, and copper additives were dehydrated to calcium oxide using solar heat from a solar concentrator then the reaction was reversed to recover the heat.202 Zeolite 13X has been used to store carbon dioxide obtained from the decomposition of calcium carbonate at 825°C (15.2).203 Such temperatures are available with solar furnaces (where a whole field of mirrors focus on the reaction vessel). 

Reactions of Acetic Acid.—Acetic acid shows the properties which are characteristic of acids. It decomposes carbonates, forms salts with metallic hydroxides, and reacts v/ith iron, zinc, and other metals. Acetic acid forms esters with alcohols. In order to increase the yield of the ester and the rate of the reaction, a dehydrating agent is usually added to the mixture of alcohol and acid. Ethyl acetate is prepared by warming a mixture of glacial acetic acid, alcohol, and sulphuric acid —... 

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