Propane, decomposition thermal

The reaction of diiodomethane with a variety of bases (sodium hexamethyldisilazanide, lithium diisopropylamide, potassium triphenylmethanide, potassium iert-butoxide, potassium hydroxide under phase-transfer conditions, methyllithium) and alkenes does not afford iodocyclo-propanes. The thermal decomposition of diiodomethyl(phenyl)mercury in an alkene also does not result in the formation of iodocyclopropanes." ... 

Thermal decomposition of propane in the fuel supply has to be avoided for a stable ejector operation because solid depositions will immediately plug the nozzle and thus cut fuel supply. Tests with propane fed through the ejector nozzle at different ejector temperatures are conducted to determine the stability limit for the propane fuel. Propane decomposition can be detected by measuring the concentration of the decomposition products hydrogen and methane in the exhaust gas. Results of these measurements are shown in Figure 11, the concentrations were measured by gas chromatography. 

Recently, the thermal decomposition of diaryl alkanes such as dibenzyl and 1,3-diphenyl propane has been studied by Sato and coworkers (13), Collins and coworkers (14). These compounds were confirmed to be decomposed to alkyl benzenes gradually as a function of carbon chain length. 

One of the problems associated with thermal cyclodimerization of alkenes is the elevated temperatures required which often cause the strained cyclobutane derivatives formed to undergo ring opening, resulting in the formation of secondary thermolysis products. This deficiency can be overcome by the use of catalysts (metals Lewis or Bronsted acids) which convert less reactive alkenes to reactive intermediates (metalated alkenes, cations, radical cations) which undergo cycloaddilion more efficiently. Nevertheless, a number of these catalysts can also cause the decomposition of the cyclobutanes formed in the initial reaction. Such catalyzed alkene cycloadditions are limited specifically to allyl cations, strained alkenes such as methylenccyclo-propane and donor-acceptor-substituted alkenes. The milder reaction conditions of the catalyzed process permit the extension of the scope of [2 + 2] cycloadditions to include alkene combinations which would not otherwise react. 

Pyrazolines, in general, undergo a photochemically induced ring contraction in solution to form a cyclopropane derivative and nitrogen. This process, unlike some equivalent thermal decompositions, is stereospecific, and methyI-as-3,4-dimethyl-l-pyrazoline-3-carboxyl-ate (88) is converted in high yield into methyl-as-1,2-dimethylcyclo-propane carboxylate (89).69 This route is of considerable preparative... 

In the interpretation based on reactions (13)-(22) the observed increase in C2H6/C4Hio is due to combination of (thermalized) ethyl radicals with H atoms. The concentration of H atoms increases at lower pressures as a result of increased decomposition of the hot ethyl radicals and as a result the ratio C2H6/C4Hi0 also increases. It is of interest that Bradley et al. had indications that some propane was formed, which, if true, would suggest that C2H6 and H did interact to some extent at least. With improved analytical techniques Heller and Gordon (56) have been able to measure the small amounts of propane formed under their experimental conditions. 

Primary alcohols in particular give an M — 18 peak due to loss of water from the molecular ion although this peak may partly arise from thermal decomposition of the alcohol in the ion source. Initial migration of a hydrogen on the alkyl chain is followed by cleavage of the carbon-oxygen bond, see, for example, the spectrum of propan-l-ol, Fig. 3.81, which shows strong peaks at m/z 59, 42, 31... 

In the case of highly cross-linked material, water is not released until above 400°C, and decomposition starts above 500°C as confirmed using differential thermal analysis (DTA).55 The amount of char depends on the structure of phenol, initial cross-links, and tendency to cross-link during decomposition. The main decomposition products may include methane, acetone, CO, propanol, and propane. 

Experimental data on these primary processes are very limited. Reliable data do not appear to exist for the thermally activated decomposition of propane, or for the pressure dependence of the activated system that arises on association of methyl and ethyl radicals. The most consistent data are for the activation reaction, iso-CjH7 + H — CjHg, which is summarized in Table XV. At 25°C., the calculated value of 2 X 10T sec.-1 shows a discrepancy of about 7 compared to the observed average value of 3 X 10s sec.-1. Reliable data for the primary rate of decomposition of butane are absent. 

The thermal decomposition of ammonium dichromate is an impressive reaction. When heated with a Bunsen burner or propane torch, the orange crystals of ammonium dichromate slowly decompose to green chromium(III) oxide in a volcano-like display. Colourless nitrogen gas and water vapour are also given off. 

Flame processes have been widely used to synthesize nanosize powders of oxide materials. Chemical precursors are vaporized and then oxidized in a combustion process using a fuel/oxidant mixture such as propane/oxygen or methane/air [190]. They combine the rapid thermal decomposition of a precursor/carrier gas stream in a reduced pressure environment with thermophoretically driven deposi-... 

Slobodin et al. [39] confirmed that thermal decomposition of EPR (equimolar ratio) began at 170 °C and ceased at 360 C. A total 93.66% condensate products, 5.2% gas and 1.14% carbonaceous residue were obtained, mainly at 235 °C. The composition of the gaseous portion, determined by GLC was ethane-ethylene 1.25%, propane 0.81%, propylene 0.98%, butane-butylene 0.99% and butadiene 0.99% by wt. of EPR. The liquid products were separated into five fractions with boiling ranges of 100 C, 100-150 C, 150-200 °C, 200-250 °C, and >250 °C. The fractionation yielded pentane, 1-pentene, 2-methylbutane, 2-methyl-l-butene, 2-methyl-2-butene, isoprene and piperylene of C5 hydrocarbon and hexane, 1-hexane, 2-methylpentane of Cg hydrocarbons. Based on these data, the thermal degradation was proposed to proceed via a free-radical mechanism. A free radical CH3... 

The thermal decomposition of the polymer seems to generate between 10% and 25% propane in addition to other fragments typically with 3n number of carbons (1 < n < 6). However, the cleavage of the molecular backbone can take place randomly, and other fragments are generated with 3n+1 or with 3n-1 numbers of carbon atoms. The first reaction under the influence of heat is the random scission shown below ... 

Formation of 5-methyltricyclo[3.3.0.0 ]oct-6-en-3-one (1) by thermal decomposition of l-diazo-3-(l-methylcyclopenta-2,4-dienyl)propan-2-one succeeded remarkably well. It is worth noting that the Wolff rearrangement leading to [(l-methylcyclopenta 2,4-dienyl)methyl]ketene is of no importance, in contrast to the direct, unsensitized irradiation of the diazo compound (see Section 1.2.1.2.4.2.6.2.). 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

A mixture of 1-aryl-l-chlorodiazirine and an alkene in hexane sonicated with ultrasound (Fisher Scientific Solid State Ultrasound FS-9) at 40 °C for two hours afforded 1-aryl-l-chlorocyclo-propanes with yields similar to those obtained by photolysis. Electrophilic as well as nucleophilic alkenes were used. Photolytic, thermal or ultrasonic decomposition of 3-chloro-3-phenyl-3//-diazirine in 2-vinylpyridine did not give the corresponding 1-chloro-l-phenylcyclopropane derivative (see Section 1.2.1.3.1.2.2.1). 

Tribromomethyl anion is not involved in the thermal decomposition of tribromo-methyl(phenyl)mercury, therefore this method allows the preparation of 1,1-dibromocyclo-propanes even from electrophilic alkenes. As a rule, this method is very efficient, yet the high cost and toxicity of dibromocarbene precursor, restrict its wide (particularly large scale) application. For the preparation of tribromomethyl(phenyl)mercury, see ref 5 and Houben-Weyl, Vol. E19b, p 1532). 

The thermal decomposition (140 C, 8d) of [dichloro(phenylsulfonyl)methyl]phenylmercury with an excess of alkene in benzene (sealed glass tube), gave 1-chloro-l-phenylsulfonylcyclo-propanes (Houben-Weyl, Vol.E19b, pp 1729-1730). 

---