Exothermic, generally

Because of the medium or relatively large sample quantities used and the instrumental sensitivity, isoperibolic calorimetry is a useful tool in determining the onset temperature of an exotherm. In fact, in its simplest construction, this is really the only measurement. Digital data acquisition does allow computer analysis of the peak or area under the curve, which indicates the order of magnitude of the exotherm. Generally, the detected onset temperatures are similar to those found in the ARC (see later in Section 2.3.23) and are significantly lower than in the DSC (Section 2.3.1.1) [79]. 

Combustion reaction of ketones are exothermic. General combustion reaction of ketones occur according to the following equation. 

The above estimates illustrate that the M—C and M—H bond energies can be large enough to overcome the strength of the C—bond, so that the oxidative addition of hydrocarbons can be exothermic. General aspects of the bond energies in organometallic species have been reviewed by Simoes and Beachamp and by Hoff. More recent developments, especially for early transition metals, have been discussed by Marks and co-woricers. ... 

Generally speaking, temperature control in fixed beds is difficult because heat loads vary through the bed. Also, in exothermic reactors, the temperature in the catalyst can become locally excessive. Such hot spots can cause the onset of undesired reactions or catalyst degradation. In tubular devices such as shown in Fig. 2.6a and b, the smaller the diameter of tube, the better is the temperature control. Temperature-control problems also can be overcome by using a mixture of catalyst and inert solid to effectively dilute the catalyst. Varying this mixture allows the rate of reaction in different parts of the bed to be controlled more easily. 

The reactivity of the halogens decreases m the order F2 > CI2 > Br2 > I2 Fluo rme is an extremely aggressive oxidizing agent and its reaction with alkanes is strongly exothermic and difficult to control Direct fluonnation of alkanes requires special equip ment and techniques is not a reaction of general applicability and will not be discussed further... 

Ma.nufa.cture. In general, manufacture is carried out in batch reactors at close to atmospheric pressure. A moderate excess of finely divided potassium hydroxide is suspended in a solvent such as 1,2-dimethoxyethane. The carbonyl compound is added, followed by acetylene. The reaction is rapid and exothermic. At temperatures below 5°C the product is almost exclusively the alcohol. At 25—30°C the glycol predominates. Such synthesis also... 

Acrolein a.s Dienophile. The participation of acrolein as the dienophile in Diels-Alder reactions is, in general, an exothermic process. Dienes such as cyclopentadiene and l-dieth5laniino-l,3-butadiene react rapidly with acrolein at room temperature. 

Acrylate and methacrylate polymerizations are accompanied by the Hberation of a considerable amount of heat and a substantial decrease in volume. Both of these factors strongly influence most manufacturing processes. Excess heat must be dissipated to avoid uncontrolled exothermic polymerizations. In general, the percentage of shrinkage decreases as the size of the alcohol substituent increases on a molar basis, the shrinkage is relatively constant (77). 

Quahtative insight can, however, be obtained by focusing on the reactions with water, the extent and vigor of which can vary widely. In general, however, hydrides react exothermically with water, resulting in the generation of hydrogen. 

Nitrations are highly exothermic, ie, ca 126 kj/mol (30 kcal/mol). However, the heat of reaction varies with the hydrocarbon that is nitrated. The mechanism of a nitration depends on the reactants and the operating conditions. The reactions usually are either ionic or free-radical. Ionic nitrations are commonly used for aromatics many heterocycHcs hydroxyl compounds, eg, simple alcohols, glycols, glycerol, and cellulose and amines. Nitration of paraffins, cycloparaffins, and olefins frequentiy involves a free-radical reaction. Aromatic compounds and other hydrocarbons sometimes can be nitrated by free-radical reactions, but generally such reactions are less successful. 

Spent Acid or Burning. Burners for spent acid or hydrogen sulfide are generally similar to those used for elemental sulfur. There are, however, a few critical differences. Special types of nozzles are required both for H2S, a gaseous fuel, and for the corrosive and viscous spent acids. In a few cases, spent acids maybe so viscous that only a spinning cup can satisfactorily atomize them. Because combustion of H2S is highly exothermic, carehil design is necessary to avoid excessive temperatures. 

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