Ethyl formate, pyrolysis

Another important application of bond surfaces is to the description of the bonding in transition states. An example is the pyrolysis of ethyl formate, leading to formic acid and ethylene. 

Additional animations show the positive nature of the hydrogen being transferred during pyrolysis of ethyl formate and the fact that the two new carbon-carbon bonds are formed at dilferent rates during Diels-Alder cycloaddition of cyclopentadiene and acrylonitrile. 

Figures 15-1 and 15-2 provide evidence for the extent to which transition states for closely-related reactions are very similar. Figure 15-1 compares the transition state for pyrolysis of ethyl formate (leading to formic acid and ethylene) with that for pyrolysis of cyclohexyl formate (leading to formic acid and cyclohexene). Figure 15-2 compares the transition state for Diels-Alder cycloaddition of cyclopentadiene and acrylonitrile with both syn and anti transition states for cycloaddition of...

Besides formic acid and acetaldehyde, the oxidative pyrolysis also generates ethanol, ethyl formate, ethane, CO2, CO, etc. 

This conclusion was supported by the observation that pyrolysis of 3-butenol has a AS of —8.8 eu, which is similar to the activation entropy values reported for pyrolysis of ethyl formate and for 3-butenoic acid, and the activation energies for all three pyrolyses are also similar (about 40 kcal/mol). Another well-known concerted syn elimination is the Cope elimination, which involves the thermal elimination of an alkene from an amine oxide (Figure 10.53). Unlike the reactions discussed above, all of which have... 

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

The present procedure uses sodium methoxide in methanol for generation of the tosylhydrazone salt. This procedure gives the highest reported yield and, unlike other procedures, also gives pure diazo compounds free from solvents. This vacuum pyrolysis method appears applicable to the formation of relatively volatile aryldiazomethanes from aromatic aldehydes. Table I gives yields of diazo compounds produced by this vacuum pyrolysis method. The yields have not been optimized. The relatively volatile diazo esters, ethyl a-... 

The reaction of ketocarbenoids with pyrroles leads to either substitution or cyclopropanation products, depending on the functionality on nitrogen. With N-acylated pyrrole (209) reaction of ethyl diazoacetate in the presence of copper(I) bromide generated the 2-azabicyclo[3.1.0]hex-3-ene system (210) and some of the diadduct (211 Scheme 44).162163 On attempted distillation of (210) in the presence of copper(I) bromide rearrangement to the 2-pyrrolylacetate (212) occurred, which was considered to proceed through the dipolar intermediate (213). In contrast, on flash vacuum pyrolysis (210) was transformed to the dihydropyridine (214). A plausible mechanism for the formation of (214) involved rearrangement of (210) to the acyclic imine (215), which then underwent a 6ir-electrocyclization. 

By analogy with ethyl 4-bromobutyrate thermolysis, the kinetics of the pyrolysis and the product formed from ethyl 4-chlorobutyrate were examined172. At the same time, the pyrolysis of the expected stable product 4-chlorobutyric acid product (equation 78), which results in butyrolactone formation, was also carried out. 

In connection with the methoxy participation, the gas-phase pyrolytic elimination of 4-chloro-1 -butanol was investigated177. The products are tetrahydrofuran, propene, formaldehyde and HCl. It is implied that the OH group provides anchimeric assistance from the fact that, besides formation of the normal unstable dehydrochlorinated intermediate 3-buten-l-ol, a ring-closed product, tetrahydrofuran, was also obtained. The higher rate of chlorobutanol pyrolysis with respect to chlorethanol and ethyl chloride (Table 27) confirmed the participation of the OH group through a five-membered ring in the transition state. 

The formation of the dimeric product (227) in the furo[3,2-6]pyrrole series was observed under conditions of flash vacuum pyrolysis of the acid (215) and its ethyl ester <82CC360>. 

A 1-methoxy-l-silacyclopropane intermediate 70 has been suggested in order to explain the formation of l-methoxy-3,4-dimethyl-l-silacyclopent-3-ene. Vacuum pyrolysis of l,2-diethyl-l,l,2,2-tetramethoxydisilane in the presence of 2,3-dimethyl-l,3-butadiene, at 400-500°C and 10 torr, in a vertical quartz tube, produces 1-ethyl-l-methoxy-, 1-ethyl-, and l-methoxy-3,4-dimethyl-l-silacyclopent-3-ene. The 1-methoxy-l-silacyclopro-pane intermediate has been suggested in order to explain the formation of l-methoxy-3,4-dimethyl-l-silacyclo-pent-3-ene along with ethyltrimethoxysilane. Product 71 was obtained via the proposed silacyclopropane intermediate 70 (Scheme 18), while the other products proceed via an oxasilacyclopropane intermediate <1997JOM219>. 

The first step in the pyrolysis of the alkyl nitrates has been supposed to be O N bond fission to give NO2 and an alkoxy radical. The activation energy is 39-5 kcal for methyl nitrate and 39-9 or 34-6 kcaP <> for ethyl nitrate. If the latter value for ethyl nitrate is taken, and assumed to be i)(EtO -NO2) a value for the heat of formation of the ethoxy radical in good agreement with that given by Rebbert and Laidler is obtained, so apparently we may put D(MeO -NO2) =40 kcal, and i)(EtO -NO2) =34 kcal. In the opinion of the present author, however, the mechanism of the reaction is not sufficiently well established to allow this to be done. The discrepancy between the result of Adams and Bawn and that of Phillips 390 is large and may well be because of the different pressure ranges in which these authors worked. A further examination of the effect of pressure on rate constant is necessary before it can be taken as established that the reaction is of the first order. 

In the ethane pyrolysis the H atoms react with ethane with the abstraction of a hydrogen atom and the formation of an ethyl radical, viz. 

The proposed transition states have been supported by deuterium isotope studies Evidence such as the decomposition behaviour in solution and the nature of the increases in the rates of decomposition along the series of chloro-formates methyl, ethyl, isopropyl, 2-butyl, /-butyl suggests that the transition states are somewhat polar °> . Lewis and Herndon found 2-methylbut-1-ene and 2-methylbut-2-ene as the olefinic products of the elimination reaction of neopentyl chloroformate, and the kinetic evidence supports a Wagner-Meerwein rearrangement in the gas-phase as in the case of neopentyl chloride pyrolysis (refs. 407, 408, 566). 

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