The thermal reactions of 2,5-dimethylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1070−1370 K and overall densities of ∼3 × 10-5 mol/cm3. A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. A methyl group migration from C(2) to C(3) in the ring with the elimination of CO produces four isomers of C5H8 in unimolecular processes. An additional unimolecular process is the decomposition of 2,5-dimethylfuran to CH3CO and C4H5 which is an important initiator of free radical reactions. Ejection of a hydrogen atom from the methyl group in the molecule is another channel for initiation of free radical reactions in the system. The 2,5-dimethylfuryl radical, which is obtained in the process of H-atom ejection, decomposes in channels similar to those of 2,5-dimethylfuran to produce, among other products, C5H7, which is the precursor of cyclopentadiene. The major decomposition product found in the post shock mixtures is carbon monoxide. The rate constant of its overall formation is estimated as k CO = 1015.81exp(−75.1 × 103/RT) s-1 where R is expressed in units of cal/(K mol). Other products that were found in the postshock samples in decreasing order of abundance were C4H4, C2H2, and CH4 in roughly the same abundance, C2H4, C2H6, CH2CH−CHCH2, cyclopentadiene p-C3H4, and a-C3H4 and 2-methylfuran. Other isomers of C4H6, C5H6 and C5H8, and some additional products were found in very small quantities. The total decomposition of 2,5-dimethylfuran in terms of a first-order rate constant is given by:  k total = 1016.22exp(−77.5 × 103/RT) s-1. An oxygen−carbon mass balance among the decomposition products is obtained. A reaction scheme composed of 50 species and some 180 elementary reactions accounts for the product distribution over the temperature range covered in this study. First-order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested, and results of computer simulation and sensitivity analysis are shown. Differences and similarities among the reactions of furan, 2-methylfuran, and 2,5-dimethylfuran are discussed.

The thermal decomposition of furan was studied behind reflected shocks in a single shock tube, over the temperature range 1050-1460 K, at total gas densities of approximately 3 X mol/cm3. Methylacetylene and carbon monoxide are the major reaction products and are formed by the reaction furan -CH3C*H + CO (l), with a rate constant kl = 1015.25*0.5 exp(-(77.5 f 2.5) X 103/Rq s-l. A second initiation reaction produces acetylene and ketene according to the reaction furan -CH*H + CH2=€0 (2), with a rate constant k2 = 1014.7M.5 exp(-(77.5 * 2.5) X 103/Rq 8. The rate constant obtained for the overall decomposition of furan in the temperature range 106C-1260 K is = 10'5.43M.45 exp(-(78.3 i 2.0) X 103/Rg s-'. The overall pyrolysis rate measured in this investigation is about 8 times lower than the rate extrapolated from an estimated value suggested for the low-pressure pyrolysis. Additional reaction products which appear in the pyrolysis are CH,=C=CH,, C4H6, C2H4, CH4, C4H4, C4H2, and C&6. They appear in noticable quantities at high temperatures and are probably secondary products. IntroductionWe have recently published an investigation describing the thermal decomposition of tetrahydrofuran behind reflected shocks, in a single-pulse shock tube.' A wide spectrum of products was analyzed in this pyrolysis and a mechanism for their formation was suggested.In an effort to elucidate the pyrolysis pattern of other fivemember ring ethers, we have carried out a detailed investigation of the pyrolysis of furan behind reflected shocks.As in the case of tetrahydrofuran, very little effort has been devoted in the past to the study of the thermal reactions of furan. The only investigation that we are aware of is a recent study by Grela, Amorebieta, and Colussiz who studied the very low pressure pyrolysis (VLPP) of furan, 2-methylfuran, and 2,5-dimethylfuran over the temperature range 1050-1270 K. The reactant molecules were heated in a steady flow reactor and the product analysis was done by an on-line mass spectrometry. The overall pyrolysis was determined by the decay of the parent ion intensity at m l z 68 (F), 82 (MF), and 96 (DMF).

The thermal reactions of 2-methylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1100−1400 K and with overall densities of ∼3 × 10-5 mol/cm3. A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. The unimolecular decomposition is initiated by two parallel channels:  (1) 1,2-hydrogen atom migration from C(5) to C(4) and (2) a methyl group migration from C(2) to C(3) in the ring. Each channel is followed by two parallel modes of ring cleavage. In the first channel, breaking the OC(2) and the C(4)C(5) bonds in the ring yields CO and different isomers of C4H6, whereas breaking of the OC(2) and the C(3)C(4) bonds yields CH2CO and two isomers C3H4. In the second channel, breaking the OC(5), and C(2)C(3) bonds in the ring yields again CO and isomers of C4H6, whereas in the second mode OC(5), C(2)C(3), and C(3)C(4) are broken to yield CO, C2H2, and C2H4. The four C4H6 isomers in decreasing order of abundance were 1,3-butadiene, 1-butyne, 1,2-butadiene, and 2-butyne. The major decomposition product is carbon monoxide. The rate constant for its overall formation is estimated to be k CO = 1015.88 exp(−78.3 × 103/RT) s-1, where R is expressed in units of cal/(K mol). Other products that were found in the postshock samples in decreasing order of abundance were C4H4, C2H2, CH4, p-C3H4, C2H6, C2H4, a-C3H4, C6H6, C4H4O, C3H6, and C4H2. The total decomposition of 2-methylfuran in terms of a first order rate constant is given by k total = 1014.78 exp(−71.8 × 103/RT) s-1. This rate and the production rate of carbon monoxide are slightly higher than the ones found in the decomposition of furan. An oxygen−carbon mass balance among the decomposition products was obtained. A reaction scheme composed of 36 species and some 100 elementary reactions accounts for the product distribution over the temperature range covered in this study. First order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested, and results of computer simulation and sensitivity analysis are shown. Differences and similarities in the reactions of furan and 2-methylfuran are discussed.

compatible microcomputer. Thus, this procedure is applicable to real time, on-line kinetic analysis and model testing.Precision in the rate constants of the two more slowly decomposing anion radicals was excellent. However, a visible trend seen in Tables 111 and IV is the deterioration of precision in k at higher rates. While work is being done to fully explain the cause of such behavior, we feel that it is mainly a limitation of electrode size and data acquisition rate of 1 point/ms. Analysis of data for faster reactions is more heavily influenced by instrumental errors in the measured charge. Also, deviation from the model due to the time dependence of charging of the electrode double layer (Qdl) is most pronounced in the first few milliseconds after the potential step. This also contributes to degraded precision for larger rate constants where most of the kinetic information is contained at short times.* This limitation may possibly be removed by using ultramicroelectrodes, decreasing the time window into the submillisecond range and increasing the rate at which data are collected. Such an approach may also require incorporation of the time dependence of Q d ] in the model.Orthogonalization necessitates deriving an orthogonal form of the model. After the values of regression parameters are obtained by use of such a model, deconvolution to recoup the original set of parameters is required. Fortunately, the nature of GramSchmidt orthogonalization should eventually enable fully automated transitions between the original basis set and the orthogonal one. It is not necessary or practical to use an orthogonalized model for every problem to be solved by nonlinear regression analysis. However, our results demonstrate the usefullness of orthogonalization when serious correlation between parameters creates problems in convergence of nonlinear regression analyses. Since the transformation is made on the model, the method is compatible with currently used general programs for nonlinear regression.The thermal decomposition of pyrrole was studied behind reflected shocks in a pressurized driver single-pulse shock tube over the temperature range 1050-1450 K and overall densities of -3 X mol/cm3. Under these conditions the nitrogen-containing products found in the postshock mixtures were cis-CH,CH=CHCN, HCN, CH2=CH-CH2CN, trans-CH,CH=CHCN, CH,CN, CH2=CHCN, C2H5CN, CHcC-CN, and small quantities of C6HSCN, C6HSCH2CN, CH2=C=CHCN and CH,C=C-CN which began to appear at the high end of the temperature range. Products without nitrogen were CH,C=CH, CH=CH, CH2=C=CH2, CH4, C2H4, and small quantities of C4H6, C4H4, C4H2, C6H6, C6H5C=CH, and C6H5CH3 which appeared only at high temperatures. The main reaction of pyrrole under these conditions is a simultaneous unimolecular bond cleavage in the 1-5 (1-2)-position and a hydrogen atom transfer, followed by electronic rearrangement and (1) isomerization to cis-crotonitrile, (2) dissociation to HCN + C3H4 (mainly propyne) and (3) isomerization to allyl cyanide, with a branching ratio of approx...

No abstract