Methyl combustion

Glanzer K, Quack M and Troe J 1977 High temperature UV absorption and recombination of methyl radicals in shock waves Proc. 16th int. Symp. on Combustion (Pittsburg, PA The Combustion Institute) pp 949-60... 

Table 2 3 lists the heats of combustion of several alkanes Unbranched alkanes have slightly higher heats of combustion than their 2 methyl branched isomers but the most important factor is the number of carbons The unbranched alkanes and the 2 methyl branched alkanes constitute two separate homologous senes (see Section 2 9) m which there is a regular increase of about 653 kJ/mol (156 kcal/mol) m the heat of combustion for each additional CH2 group... 

FIGURE 3 20 The enthalpy difference between as- and trans 1 2 dimethylcyclopropane can be determined from their heats of combustion Van der Waals strain between methyl groups on the same side of the ring make the cis isomer less stable than the trans... 

Their heats of combustion (Table 3 2) reveal that trans 1 4 dimethylcyclohexane is 7 kJ/mol (17 kcal/mol) more stable than the cis stereoisomer It is unrealistic to believe that van der Waals strain between cis substituents is responsible because the methyl groups are too far away from each other To understand why trans 1 4 dimethylcyclo hexane is more stable than cis 1 4 dimethylcyclohexane we need to examine each stereoisomer m its most stable conformation... 

Orientation of methyl groups m most stable conformation Heat of combustion heat of combustion More stable stereoisomer... 

In poly(ethylene terephthalate) (14—16) and poly(methyl methacrylate) (17—19), the mechanism of action of phosphoms flame retardants is at least partly attributable to a decrease in the amount of combustible volatiles and a corresponding increase in nonvolatile residue (char). In poly(methyl methacrylate), the phosphoms flame retardant appears to cause an initial cross-linking through anhydride linkages (19). 

Foam Inhibitors. Methyl sihcone polymers of 300-1000 mm /s(= cSt)) at 40°C are effective additives at only 3—150 ppm for defoaming oils in internal combustion engines, turbines, gears, and aircraft appHcations. Without these additives, severe churning and mixing of oil with air may sometimes cause foam to overflow from the lubrication system or interfere with normal oil circulation. Because sihcone oil is not completely soluble in oil, it forms a dispersion of minute droplets of low surface tension that aid in breaking foam bubbles. 

Fire Hazards - Flash Point (deg. F) 203 OC Flammable limits in Air (%) 3 - 6.3 Fire Extinguishing Agents Water, foam, dry chemical, or carbon dioxide Fire Extinguishing Agems Not to be Used Not pertinent Special Hazards of Combustion Products Sulfur dioxide, formaldehyde, and methyl mercaptan may form Behavior in Fire Not pertinent Ignition Temperature (deg. F) 572 Electrical Hazard Not pertinent Burning Rate 2.0 mm/min. 

Like the 1,4-dimethyl derivatives, trani-1,2-dimethylcyclohexane has a lower heat of combustion (see Table 3.2) and is more stable than d5-l,2-dimethylcyclohexane. The cis ster eoisomer has two chair conformations of equal energy, each containing one axial and one equatorial methyl group. 

Uses. (See also under Perchlorate Explosives) Combustible Cartridge Cases. Cotton cloth is impregnated with a siurry of AP and a monomer in methyl ethyl ketone, the solv evapd, and the monomer cured on a meld to give a combustible cartridge case (Ref 35)... 

A number of thermoplastics undergo depolymerisation on heating. These include poly(styrene), poly(methyl methacrylate), and poly(oxymethylene). Such depolymerisation will occur regardless of the prevailing oxygen concentration and under well aerated conditions will provide a ready source of fuel for sustained combustion. 

The fact that many 4 systems are paratropic even though they may be nonplanar and have unequal bond distances indicates that if planarity were enforced, the ring currents might be even greater. That this is true is dramatically illustrated by the NMR spectrum of the dianion of 83 (and its diethyl and dipropyl homologs). We may recall that in 83, the outer protons were found at 8.14-8.67 8 with the methyl protons at —4.25 8. For the dianion, however, which is forced to have approximately the same planar geometry but now has 16 electrons, the outer protons are shifted to about -3 8 while the methyl protons are found at 21 8, a shift of 258 We have already seen where the converse shift was made, when [16]annulenes that were antiaromatic were converted to 18-electron dianions that were aromatic. In these cases, the changes in NMR chemical shifts were almost as dramatic. Heat of combustion measurements also show that [16]annulene is much less stable than its dianion. 

Ofiwald, P. et al.. Isomer-specific fuel destruction pathways in rich flames of methyl acetate and ethyl formate and consequences for the combustion chemistry of esters, /. Phys. Chem. A, 111, 4093,2007. 

In Table IV we report the available enthalpies of formation, sublimation, and combustion of methyl-adamantanes, dimethyl-adamantane, trimethyl-adamantane, and tetramethyl-adamantane and compare them with the same properties of adamantane as measured by various investigators [29, 30]. Also reported in Table IV are the same properties for 1-methyI-diamantane, 3-methyI-diamantane, and 4-methyI-diamantane as compared with the diamantane data. 

Methyl nitrate is prepared by the effect of nitric acid on methanol in the presence of sulphuric acid. Operating conditions are critical, given the exothermicity of the reaction and the compound thermal instability (see previous table). Moreover, methyl nitrate is very sensitive to impact. It combusts spontaneously at 250-316°C when it is in the vapour state and even when the vapour is diluted by an inert gas. The flame temperature reaches 2600°C. 

Methyl and ethyl nitrates are promoters of the combustion of hydrocarbons. Nitrobenzene and aromatic nitrated explosives are mostly insensitive to impact. They become sensitive when potassium or Na-K alloy is present. 4-Nitrotoluene with sodium in diethyl ether medium forms a black residue that combusts spontaneously in air. 

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