Ammonium chromates

This catalyst is prepared by the decomposition of basic copper ammonium chromate the main reactions may be written as ... 

Ammonium chromates and some other solids exhibit aging effects. Material that has been stored for months or years follows a cubic law with respect to time, but fresh materials are about fifth-order. At I99°C (390°F), the Front-Tompkins law was followed. 

Aluminum chlorate Ammonium chromate Benzoyl peroxide, dry... 

The ammonium chromates, which have been studied more extensively than any other salts of these anions, are considered in the next section. 

The first step in the decomposition of ammonium chromate is conversion to the dichromate [981] ( 375 K), the rate of this process being reduced by oxygen [982] (1—100 Torr). Thermoanalytical measurements have identified four stages in the decomposition [983], At 508 K... 

Ammonium chromate Potassium chromate Chromium potassium sulphate Lithium chromate (yitomium trinitrate Sodium chromate Clsomium fV )oxide Lead chromate Strontium chromate 2nc ctvomate... 

Five beakers are placed in a row on a countertop. Each beaker is half fdled with a 0.20 M aqueous solution. The solutes, in order, are (1) potassium sulfate, (2) methyl alcohol, (3) sodium carbonate, (4) ammonium chromate, and (5) barium chloride. The solutions are all at 25 °C. 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

Copper(ll) chromite is obtained by heating copper chromate, CuCr04 at 400°C. The Adkin catalyst, a mixture of copper oxide and copper chromite, is prepared by mixing aqueous solutions of copper nitrate, sodium dichromate and ammonium hydroxide the orange precipitate of copper ammonium chromate formed is dried and then heated below 400°C. 

Guanidine nitrate 28.0% Ammonium chromate 8.0% Dimethyl diphenyl urea 4.0% Beech charcoal 4.0%... 

Ammonium chromate [7788-98-9] M 152.1. Crystd from weak aqueous ammonia (ca 2.5ml/g) by cooling from room temperature. 

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