Residual reaction exotherm

These results confirmed that the experimental procedure followed worked satisfactory. Figure 1.20 shows a typicaL result. The reaction exotherm of the epoxy/benzoic acid system is measured during the first scan. This effect is characterised by a Tmax.-value of 139°C and a dH-value of 87 kJ/mol. No sign of a residual reaction exotherm is measured during the second scan. The Tg-value increased from -109°C for the liquid epoxy as such to -48°C after the reaction with benzoic acid. A Tg-value of -48°C was also measured during the third scan, indicating that no (detectable) further progress of the reaction occurred after the first scan. The results of the measurements performed in this way are listed in Table 1.8. 

In the batch process low-water-solubility monomers are emulsified in water by water-soluble surfactants, purged and heated at the initiation temperature (for energy saving this is usually lower than the reaction temperature to benefit from the reaction exotherm) and the initiator added. Temperature is then maintained for the reaction period, which can range from 1 to 24 h. Reactions are driven to the maximum conversion compatible with the system and the residual monomer and other volatile compounds are removed either by stripping or by chemical treatment. 

The circles show measurements of a determined by the disappearance of the acetylene IR band at 941 cm ( ). The squares show the DSC residual heat measurements. It should be noted that a problem occurs in the analysis of the DSC data since another exotherm is observed in acetylene terminated sulfones at higher temperatures than the reaction exotherm but sufficiently low so as to overlap with the end of the reaction exotherm. The residual heat data were determined by estimating the contribution of the second exotherm and graphically subtracting it from the total heat evolved. While this approximate method produces considerable scatter in the data, it appears to agree quite well with the infrared data. 

The reaction exotherms were used to indicate the degree of cure for the polymer samples. The areas under the DSC curves (see Fig 1), between 20 and 350 C, were measured and taken to be the total heats of reaction. Additional specimens were prepared and placed in an air oven at 177 C (350°F). Periodically, specimens were withdrawn frgm the oven, placed in the DSC and scanned from 20 to 350°C at 20°C/min and the residual exotherms were measured. These tests were repeated in a nitrogen environment. 

Tetrolic acid (11) A solution of sodium hydroxide (48 g) in water (40 ml) is dropped during 20 min into a solution of the iodide (10) (76.2 g) in water (40 ml) at —10°. The exothermic reaction is complete in about 1 h. The trimethylamine evolved may be collected by passage through a wash-bottle containing hydrochloric acid. The residual reaction mixture is washed with ether, and the aqueous layer is then acidified cautiously with hydrochloric acid and extracted several times with ether. The ethereal extracts are united and dried over sodium sulfate. The residue obtained on removal of the ether crystallizes completely (yield 11.8 g, 70.2%) and after recrystallization from light petroleum melts at 78-78.5°. 

Fit a 1500 ml. bolt-head flask with a reflux condenser and a thermometer. Place a solution of 125 g. of chloral hydrate in 225 ml. of warm water (50-60°) in the flask, add successively 77 g. of precipitated calcium carbonate, 1 ml. of amyl alcohol (to decrease the amount of frothing), and a solution of 5 g. of commercial sodium cyanide in 12 ml. of water. An exothermic reaction occurs. Heat the warm reaction mixture with a small flame so that it reaches 75° in about 10 minutes and then remove the flame. The temperature will continue to rise to 80-85° during 5-10 minutes and then falls at this point heat the mixture to boiling and reflux for 20 minutes. Cool the mixture in ice to 0-5°, acidify with 107-5 ml. of concentrated hydrochloric acid. Extract the acid with five 50 ml. portions of ether. Dry the combined ethereal extracts with 10 g. of anhydrous sodium or magnesium sulphate, remove the ether on a water bath, and distil the residue under reduced pressure using a Claiseii flask with fractionating side arm. Collect the dichloroacetic acid at 105-107°/26 mm. The yield is 85 g. 

To a mixture of 65 ml of dry benzene and 0.10 mol of freshly distilled NN-di-ethylamino-l-propyne were added 3 drops of BFa.ether and 0.12 mol of dry propargyl alcohol was added to the reddish solution in 5 min. The temperature rose in 5-10 min to about 45°C, remained at this level for about 10 min and then began to drop. The mixture was warmed to 60°C, whereupon the exothermic reaction made the temperature rise in a few minutes to B5 c. This level was maintained by occasional cooling. After the exothermic reaction (3,3-sigmatropic rearrangement) had subsided, the mixture was heated for an additional 10 min at 80°C and the benzene was then removed in a water-pump vacuum. The red residue was practically pure acid amide... 

The extracts were kept below 0°C (note 5). The combined extracts were washed with 5i acetic acid and subsequently dried over magnesium sulfate (note 6). The extract was concentrated in a water-pump vacuum to about 60 ml by means of the rotary evaporator, care being taken that the bath temperature remained below 25°C. The remaining pale yellow solution was warmed to about 35°C (internal temperature). The temperature rose gradually but was kept at about 45°C by occasional cooling. When after about 45 min the exothermic reaction had subsided, the flask was placed in a water-bath at 55°C. After 30 min the remaining pentane was removed in a water--pump vacuum. The orange residue, n 1.5878, yield aa. 92% was almost pure allenic dithioester. 

Some unsaturated ketones derived from acetone can undergo base- or acid-catalyzed exothermic thermal decomposition at temperatures under 200°C. Experiments conducted under adiabatic conditions (2) indicate that mesityl oxide decomposes at 96°C in the presence of 5 wt % of aqueous sodium hydroxide (20%), and that phorone undergoes decomposition at 180°C in the presence of 1000 ppm iron. The decomposition products from these reactions are endothermic hydrolysis and cleavage back to acetone, and exothermic aldol reactions to heavy residues. 

Concentrated sulfuric acid (97 wt %) at 300—400°C has been used to solubili2e niobium from columbite and pyrochlore (18,19). The exothermic reaction is performed in iron or siUcon-iron cmcibles to yield a stable sulfato complex. The complex is filtered free of residue and is hydroly2ed by dilution with water and boiling to yield niobic acid which is removed by filtration as a white coUoidal precipitate. 

EDTA (ethylenediaminetetraacetic acid, [60-00-4]) chelates any trace metals that would otherwise decompose the hydrogen peroxide [7722-84-1]. The amine is preheated to 55—65°C and the hydrogen peroxide is added over one hour with agitation the temperature is maintained between 60 —70°C. The reaction is exothermic and cooling must be appHed to maintain the temperature below 70°C. After all the peroxide has been added, the temperature of the reaction mixture is raised to 75°C and held there from three to four hours until the unreacted amine is less than 2.0%. The solution is cooled and the unreacted hydrogen peroxide can be destroyed by addition of a stoichiometric amount of sodium bisulfite. This may not be desirable if a low colored product is desired, ia which case residual amounts of hydrogen peroxide enhance long-term color stabiUty. 

A pressure safe glass bottle containing 7.4 g (0.05 mol) of potassium thio-phenoxide and 50 mL of dimethylformamide is placed under vacuum The bottle IS charged with 2 7 bars of bromotnfluoromethane and shaken for 3 h. The reaction is slightly exothermic. The mixture is poured in 100 inLof 17% hydrochloric acid The aqueous phase is extracted with hexane. The organic layer is washed with water and dried over potassium carbonate The solvent is evaporated, and the residue is distilled to give 5 5 g (62%) of trifluoromethylthiobenzene (bp, 77-78 C at 754 mm of Hg). 

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