Cannizzaro Carbon dioxide

Formaldehyde is readily reduced to methanol by hydrogen over many metal and metal oxide catalysts. It is oxidized to formic acid or carbon dioxide and water. The Cannizzaro reaction gives formic acid and methanol. Similarly, a vapor-phase Tischenko reaction is catalyzed by copper (34) and boric acid (38) to produce methyl formate ... 

Since by Avogadro s hypothesis both samples of gas contain the same number of molecules, the mass of an oxygen molecule (which he assumed to be O2) must be 32 relative to a mass of 2 for the H2 molecule. Since each molecule contains two atoms, the relative atomic masses for oxygen and hydrogen are then 16 and 1, respectively. Using this same method, Cannizzaro found the relative molecular mass of carbon dioxide to be 44 (relative to 2 for H2). Chemical analysis of carbon dioxide had shown it to contain 27% carbon (by mass). This percentage corresponds to (0.27)(44 g), or 12 g, of carbon in 44 g of carbon dioxide, and 44 g — 12 g = 32 g... 

Cannizzaro addressed this problem by obtaining the relative molecular masses of many other compounds containing carbon. For example, consider the data shown in Table 2.1. Notice from these data that the relative mass of carbon present in the compounds is always a multiple of 12. This observation strongly suggests that the relative mass of carbon is 12, which in turn would mean that the formula for carbon dioxide is CO2. 

By contrast, formaldehyde is unstable in SCW, with its decomposition rate being strongly temperature-dependent. At temperatures above the critical, formaldehyde completely decomposes to methanol, formic acid, carbon oxide, and carbon dioxide. The main decomposition product at low temperatures is methanol, which gives way to carbon monoxide at high temperatures. At 300 atm, 300—500 °C, and a residence time of 2 min, formaldehyde decomposes almost completely. The rapid decomposition of formaldehyde seems to be the main reason for its absence in the reaction products in a number of works. The Cannizzaro reaction, leading to the formation of methanol and CO, makes it possible to purify dilute formaldehyde wastewater to form easily separable methanol [233]. 

Caduceus, 43, 48 Cagliosiro, 74 Calcination, 33, 114, 140 Caine, 134 Calx, 114, 120 Cambridge, 162 Canches, 51 Cannizzaro, 152 Canons, 72, 76 Canon s Ttoman s Talt 76 CatUttbury Tales, 76 Carbon, t66 dioxide, 124, 127, 141 monoxide, 153 Carbureued hydrogen, 15O CaHnthia, 96 Catalyst, 16... 

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