Pyrolysis of Propyne/2-Methylbut-l-ene-3-yne Mixtures

between 350 and 450°C

CHARLES HARPER and JULIAN HEICKLEN Department of Chemistry, The Pennsylvania State University, University Park,

Pennsylvania 16802

Abstract

2-Methylbut-1-ene-3-yne and Propyne mixtures were pyrolyzed at 350-450°C in the absence and presence of O2 and NO. The major product of the reaction is a polymer, but rn-xylene andp-xylene are also produced and were studied as the species of interest. The CsHIo formation rate is first-order in C3H4 and C5H,. The rate coefficient is best fitted by

lOg[k(CBHIo),M~'s~'] = (11.2 2 1.0) - (166 ? 13)/2.3RT

though i t is not inconsistent with

log[k(CgH,,), W'S-'] = (8.17) - (125.9)/2.3RT

where R is the ideal gas constant in kJ/mol-K. Experiments in the presence of NO show that m-xylene and p-xylene formation occur by two processes: a concerted molecular mechanism (= 41%) and a singlet diradical mechanism (= 59%).

Introduction

Pyrolysis, or thermally activated hydrocarbon reactions not due to combustion, has been shown to be a factor in soot formation. The re- action paths leading to soot formation have been studied over several temperature ranges by various researchers. At temperatures below 1200°C hydrocarbons are cracked to C,H,. The acetylene can then go on to form soot, by polymerization and dehydrogenation, processes that at lower temperatures involve aromatic compounds as intermediates [ 1-51.

The aromatic compounds formed as intermediates include polynuclear aromatic compounds. Many of these are carcinogenic compounds, and as such are. undesirable in the environment. These compounds are also reactive to the HO. radical so their emission into the atmosphere is of concern in photochemical smog formation [61. The mechanisms of formation for these aromatic compounds are therefore of interest so that they might be minimized.

Cullis and Franklin [71 investigated the pyrolysis of acetylene at temperatures from 500-1000°C and reported vinylacetylene as the

International Journal of Chemical Kinetics, Vol. 21, 175-191 (1989) 0 1989 John Wiley & Sons, Inc. CCC 0538-80661891030175-17$04.00

176 HARPER AND HEICKLEN

sole initial product. Secondary products included diacetylene, methyl- acetylene, and benzene. Stehling et al. [81 also studied acetylene pyroly- sis reporting benzene as a major product at 600°C with vinylacetylene and styrene also formed.

The pyrolysis of vinylacetylene has been studied by many researchers over temperatures ranging from 300-950°C [9-131. Cullis and Read [la1 were the only researchers to study vinylacetylene pyrolysis both above and below 500°C. They reported the formation of large amounts of H, and C,H, above this temperature, while below this temperature the main product is a polymeric material. Lundgard and Heicklen [13] did a more detailed study of the pyrolysis of vinylacetylene between 300-450°C. They reported the major product as being a polymer with C,H, (four isomers) also being formed. The formation of some aro- matic compounds such as benzene, toluene, xylene, naphthalene, and indene were also identified.

The pyrolysis of acetylene and vinylacetylene mixtures has been studied [8,9,121 with a brown solid being the main product. Due to ex- perimental limitations these studies were limited to low molecular weight products. Yampol’skii et al. [ l l l found benzene to be produced in mixtures of C2H2 and C4H4 at 800-950°C.

Chanmugathas and Heicklen [141 did more detailed research into the pyrolysis of acetylene-vinylacetylene mixtures between 400-500°C. They also found the major product to be a polymeric material, but fo- cused attention to the [2 + 41 cycloaddition formation of benzene. They found the C6H6 formation rate t o be first-order in C,H, and C4H4. They also found benzene formation to occur by two processes: a concerted molecular mechanism (= 50%) and a singlet diradical mechanism (= 50%).

Harper and Heicklen [15] examined the analogous pyrolytic [2 + 41 cycloaddition of 2-butyne and vinylacetylene to form o-xylene. They found the C,H,, formation to be first order in C4H, and C,H4. It was also concluded that o-xylene formation occurred by two processes: a concerted molecular mechanism (= 67%) and a singlet diradical mechanism (= 33%).

This work has been undertaken to further obtain detailed kinetic in- formation of the low-temperature reactions of acetylene-vinylacetylene mixtures by using homologous compounds. In this particular work, propyne is reacted with 2-methylbut-l-ene-3-yne and the formation of C,H,, is monitored during the initial stages of the reaction to see what effect substitution of the H atom on acetylene has on the rate and mechanisms of reactions. Also, since the two major [2 + 41 cycloaddi- tion mechanisms lead to two different xylene isomers, gas chromato- graphic data can be used examine the validity of these mechanisms.

PYROLYSIS OF PROPYNE/2-METHYLBUT-l-ENE-3-YNE 177

Experimental

The experimental apparatus and procedure were similar to that described earlier [13-161. Pyrolysis was carried out in a 1306.2 cm3 spherical quartz vessel surrounded by a cylindrical resistively-heated oven. A proportional temperature controller (Omega model #E924K31F20) was used t o maintain a constant temperature t o within +-3”C. The reaction vessel was connected to a conventional grease-free vacuum line fitted with Teflon stopcocks with Viton A or FETFE “0” rings. Each reaction was started by expanding a reaction mixture into the preheated reaction vessel.

Kinetic data were obtained by mass spectrometry. The mass spec- trometric sampling system consisted of a quartz pinhole (30 pm di- ameter) through which the reaction vessel contents continuously bled through a differentially-pumped intermediate region to a second pin- hole which was mounted on the mass filter of an Extranuclear Type 11 Quadrupole mass spectrometer. Total pressure in the reaction vessel was between 5 and 100 torr while the differentially-pumped interme- diate region between the two pinholes was kept at -20 mtorr.

For quantitative analysis, a small measured amount of krypton gas was added to the reaction mixture as an internal standard to mini- mize the effect of instrumental and sampling fluctuations. Mass spec- tral calibrations were made for the product using the krypton m/e = 84 peak. For C,H,, the calibration factor (the factor used, the ratio of CBH,,-to-Kr ion currents when present at the same concentrations, to obtain the C,H,, concentration) was approximately 0.71. The detector was found to respond the same to both m-xylene and p-xylene, so m-xylene was used for all calibrations (i.e., the ratio of m-xylene to p-xylene ion currents equals 1 for the same concentrations.

2-Methylbut-l-ene-3-yne was found to form xylene in a reaction with itself under experimental conditions. Therefore experiments were run with 2-methylbut-l-ene-3-yne alone to calculate the rate for forma- tion of xylene (or any other m/e = 106 source) to be used as a correc- tion factor. Gas chromatographic data on a Bentone 34 column suggest the source of this correction factor to be mainly due to m-xylene and p-xylene. The correction factor was then subtracted from the experi- mental data from 2-methylbut-l-ene-3-ynejpropyne mixtures.

For qualitative analysis, an Aerograph (model 1520) gas chro- matograph with a flame ionization detector was used as described be- fore [151 except that the column used was 5% SP-1200/5% Bentone 34 rather than 5% SP-1200/1.75% Bentone 34. Meta-xylene and para- xylene were qualitatively identified as products in the 2-methylbut-l- ene-3-yne/propyne experiments.

178 HARPER AND HEICKLEN

Materials

2-Methylbut-l-ene-3-yne (Wiley Organics) 98% was purchased with impurities of methylbutanol and acetone. Also present was phenyl-a- napthylamine (0.1%) to inhibit polymerization or peroxide formation. The 2-methylbut-l-ene-3-yne was purified by degassing at - 107°C. Before use the purity was found to be greater than 99.9% by gas chro- matographic analysis on columns of Porapak Q and 10% Silar 1OC and 5% Bentone 34.

Propyne (Matheson) 98% was used directly from the lecture bottle. Manufacturer list typical impurities as acetylene (O.l%), 2-butyne (<0.1%), dimethyl ether (1.2%), and allene (0.5%). Before use the purity was found to be greater than 99.9% by gas chromatographic analysis on a column of 5% Bentone 34.

Meta-xylene (Aldrich) 99% and para-xylene (Aldrich) 99%, were degassed several times at - 198°C and used without further purifica- tion. Before use the purity was found to be greater than 99% by gas chromatographic analysis on a column of 5% Bentone 34.

Krypton (Matheson) research purity was analyzed by the manufac- turer and reported to be 99.995% pure and was used directly from the lecture bottle.

Oxygen (Matheson) research purity was analyzed by the manufac- turer and reported to be 99.997% pure and was used directly from the lecture bottle.

Nitric oxide (Matheson) C.P. grade was analyzed by the manufacturer and reported to be greater than 99.0% pure. The nitric oxide was dis- tilled from - 186°C to - 196°C before use.

Results

The pyrolysis of 2-methylbut-l-ene-3-yne at 375-450°C gives several types of products [161. The major product is polymer, with C,H, dimers accounting for about 3% of the reactant consumed. Among the minor products produced are CH4, CzH4, C2H6, and C3H,. Chanmu- gathas and Heicklen [161 also report that p-xylene is formed in that reaction. In our study C,H, and C,H, mixtures were pyrolyzed. The production of m-xylene and p-xylene were monitored as products of this reaction mixture. A pyrolysis experiment using 2-methylbut-l- ene-3-yne alone found via gas chromatography that both m-xylene and p-xylene were formed. Corrections for the formation of these xylenes were made, so that xylenes formed only by the [2 + 41 cycloaddition of propyne and 2-methylbut-l-ene-3-yne could be monitored. Pyroly- sis of propyne alone showed no xylenes to be formed.

Figure 1 is a sample plot of the time history of C,H,, formation. Initial rates of C,H,, (m-xylene + p-xylene) formation are given in

10

9

8

S!

'n 0 6 x

z 0 F 5 a a

E 4 I-

0 z 0 V

3

2

I

C

PYROLYSIS OF PROPYNE/Z-METHYLBUT-l-ENE-3-YNE

I I 1 I 1 , I ! 100 200 300 400 500 600 700 800

REACTION T I M E , s e c

179

)

Figure 1. [C,H,lo = 9.53 x 10-4M, [C,H,lo = 9.51 x 10-4M, and [Kr] = 7.19 x W 5 M .

Plot of C8HI0 pressure vs. reaction time for a run a t 400°C with

Table I as a function of reaction concentrations at temperatures from 350-450°C. The initial rates of C,H,, formation increase with both the C,H, and C3H4 concentrations.

The log of the initial rates of C,H,, formation are plotted vs. the log of the product of the reactant concentrations in Figures 2(a)-2(b). The data are plotted in log form because we expect them to have the fol- lowing functional form:

+R, (C,Hio) = k([C&ciI [C3H41)" where Ri stands for the initial rate of reaction. Least squares regres- sion analyses of the plots yield the straight lines plotted in Figures 2(a)- 2(b) and give values for the parameters listed in Table 11. It can be seen that within the experimental uncertainty, n is equal to 1.00 at 4 of the 5 temperatures. At 425"C, where we have few data points, the

180 HARPER AND HEICKLEN

TABLE I. Initial rates of formation of C8HI0 (n-xylenelp-xylene).

Temperature = 350 OC

0.823 2.86 1.06 1.89 2.14 7.92 2.70 5.17 2.76 3.04 8.10 15.4 8.28 5.27 10.2 10.1

Temperature = 375 OC

0.205 0.829 0.825 1.66 2.23 2.73 3.63 10.5 1.47 5.01 9.57 17.1

11.2 10.6

Temperature = 400 OC

0.163 0.228 0.427 0.602 0.809

1.28 0.503 3.55 2.45 0.948

1.71 7.10 3.59 6.03 3.63 6.03 3.66 6.05 6.02 13.3 9.06 9.53

Temperature = 425 OC

0.426 1.19 1.65 6.96 1.69 2.37 2.19 4.64 6.32 4.57 7.07 14.4

Temperature = 450 OC

0.0909 0.954 0.389 1.15 0.553 2.35 1.52 2.26 2.13 4.61 5.90 4.46

2.88 5.63 2.70 5.22 9.08 5.25

15.7 10.2

2.47 4.96 8.19 3.45

5.61 14.9

10.5

1.28 4.53 1.20 2.45 8.53 2.41 5.96 6.03 6.05 4.53 9.51

3.58 2.37 7.12 4.71

4.89 13.8

0.954 3.39 2.35 6.70 4.61 13.2

0 .lo6 0.108 0.631 0.458 1.08 0.763 2.18 2.66

0.185 0.568 1.26 4.29 3.83 8.81 7.35

0.309 0.584 0.445 0.985 1.46 2.22 7.38 6.33 5.56 34.9 10.4

3.34 6.09

7.87 11.6

15.6 26.0

2.46

9.70 11.8

45.0 28.4 132.

PYROLYSIS OF PROPYNE/2-METHYLBUT-I-ENE-3-YNE 18 1

- 6

- 7

h 0 0 v)

\

Zl

0 I

V 0 -8 1

CY U

0 W 0 -I

-9

- I C - 8 - 7 -6

LOG,, (CC, H,lCC,H,l , M' )

Figure 2(a). A, 350°C, 0, 4OO0C, 0, 450°C.

Plot of Log (initial rate of CsHlo formation) vs. Log ([C,Hs][C3H4]):

slope is lower. However we assume that the physically meaningful slope is 1.00 at all temperatures, i.e., the reaction is first-order in each reactant. On this basis, least squares regression is again done yielding values for the second-order rate constants which are listed in Table 111. An Arrhenius plot using these constants is found in Figure 3. This plot yields the Arrhenius parameters found in Table 111.

In order to determine the extent of free radical vs. molecular reaction, experiments were done at 400°C with added 0, or NO. The results are plotted in Figures 4 and 5 respectively. The addition of 0, has no effect on the rate of xylene formation. However, addition of NO decreased the initial rate of xylene formation by about 59%.

Gas chromatographic data were also taken giving the relative percentages of m-xylene and p-xylene formed in experiments with 2-methylbut-l-ene-3-yne alone, propyne with 2-rnethylbut-l-eneS-yne,

182 HARPER AND HEICKLEN

-8 -7 -6

LOG,, { C C , H , l C C , H , l , M 2 ]

Figure 2(b). 0 , 375"C, 0,425"C.

Plot of Log (initial rate of C8Hlo formation) vs. Log ([C,H,][ I:

and with reaction mixtures containing added NO and 0,. These data are summarized in Table IV. In the absence of added NO about 2/3

-1.74 +/- 1 . 4 2 1 .15 +/- 0 . 2 2 3 5 0 375 -2 .39 +/- 0 . 5 9 0.96 +/- 0 .09

-1 .48 +I- 0.77 1 . 0 4 +/- 0 .11 4 0 0 -3.66 +/- 0 .83 0.66 +/- 0 . 1 3 4 2 5 -1 .22 +/- 0.74 0.92 +/- 0 . 1 0 4 5 0

a +cZIC,8iolldt = M[C&I "3U." buni ts of M-' and s-', uncertainties are lu.

PYROLYSIS OF PROPYNE/Z-METHYLBUT-l-ENE-3-YNE 183

TABLE 111. Second-order rate coefficients."

350 2.13 +/- 1.06

400 20.5 +/- 13.2 425 46.9 +/- 21.3 450 234. +/- 69.

375 7-15 +I- 2.38

log[k(C8H10), M-ls-'] = (11.2 +/- 1.0) - (166 +/- 13)/2.3RT

a Uncertainties are lv.

of the xylene formed is rn-xylene, and 1/3 is p-xylene. Added NO lowers the relative amount of rn-xylene formed to about 1/2. Added 0, does not effect the ratio of m-xylene to p-xylene product formed.

Discussion

The products of the reaction are the same as in the pyrolysis of C5H6 alone [16] but with the addition of m-xylene and p-xylene as products of the [2 + 41 cycloaddition. Again, the major products were a yellow polymeric material and black carbonaceous material.

The addition of O2 showed no noticeable effect on the production rate of xylenes. Therefore intermediates involving triplet radicals are not seen. However, the addition of NO reduced the initial rate of C,H,, formation by about 59%. The intermediates are therefore about 41% molecular in nature and 59% free radical in nature. The free radical mechanism is presumed to be of a singlet diradical form. These find- ings are analogous to those found in the C,H,-C,H, system [141 and the C4H6-C4H, system [151.

Chanmugathas and Heicklen [161 pyrolyzed a vinylacetylene homo- l o p e (2-methylbut-l-ene-3-yne) and showed that head-to-head addi- tions (triple bond to triple bond) are free radical in nature, whereas head-to-tail additions (triple bond to double bond) are a concerted molecular process, i.e., ring closure is so fast that the intermediate cannot be intercepted by free radical scavengers. We presume that the same mechanisms apply to the [2 + 41 cycloaddition reactions between C5H, and C,H, in the present study. The structure of the propyne molecule allows for two orientations with respect t o the 2-methylbut-l-ene-3-yne molecule, thus the following reaction com- binations are possible:

184 HARPER AND HEICKLEN

-) ----- - - I I +

singlet diradical intermediate

very short-lived intermediate

singlet diradical intermediate

very short-lived intermediate

Harper and Heicklen [ E l found that methyl substitution of the hydro- gens on the acetylene sterically inhibit the rate of the reaction by a factor of 5.8. Therefore, in the above reactions, mechanisms 1 and 4 will be sterically unfavorable due to the steric hindrance of the methyl group. Mechanisms 2 and 3 are not sterically hindered and are pre- sumed to be the primary routes to xylene formation.

If comparisons are made to the pyrolysis of acetylene and vinyl- acetylene mixtures to form benzene [141, the rate coefficients and Arrhenius parameters are higher in the present study. Chanmugathas and Heicklen found the log of the preexponential factor to be 8.65 (M-'s ' ) and the activation energy to be 125.9 kJ/mol for benzene formation. The only major differences between their study and the present work is the addition of a methyl group to the acetylene mole- cule. Comparisons to the acetylene/vinylacetylene system and the 2-butyne/vinylacetylene system are summarized in Table V. In the present system the preexponential factor and activation energy are higher than expected. Most likely this effect is not real and only re- flects experimental uncertainty in the present study where formation rates are small due to steric hindrance on one end of the acetylenic molecule and a correction factor was used due to xylene formation from other sources.

PYROLYSIS OF PROPYNE/Z-METHYLBUT-l-ENE-3-YNE 185

13 14 15 16

lo3/ T , K - '

Figure 3. Arrhenius plot for the rate coefficients for CBHIO formation.

A recalculation of the Arrhenius parameters with the activation energy forced to 125.9 kJ/mol gives the log of the preexpotential factor (M-ls- ' ) of 8.17. These Arrhenius parameters predict the rate coeffi- cient for xylene formation exactly a t 400°C and to within a factor of two at 350 and 450°C.

Table V also shows the calculated rate for formation of the [2 + 41 cycloaddition product for the three systems at 400°C assuming 25.0 torr of each reactant. This best shows the effect of steric hindrance caused by methyl groupb) on the acetylenic hydrocarbon. Compared

I I

I I

0

0

O n

0

C 0

05

I0

1

5

20

10*

x to

, 1,

M

Figu

re 4

. [C

3H4I

0 = (

5.96

rfi 0.

09)

x 10

-4M

. In

itial

C,H

,, fo

rmat

ion

rate

s as

a f

unct

ion

of a

dded

O2

at 4

00°C

for

[C,H

,],

= (

5.98

& 0

.09)

x l

O-*

M an

d

0

0

I I

I I

05

10

I5

2

0

1O'x

"

01

, M

5

Figu

re 5

. [C

3H4I

0 = (

6.00

t 0

.06)

x 1

0-4M

. In

itia

l CsH

lo fo

rmat

ion

rate

s as

a fu

nctio

n of

add

ed N

O a

t 400

°C fo

r [C5

H&

, = (

6.00

t 0

.06)

x 1

0-4M

and

188 HARPER AND HEICKLEN

TABLE IV. Relative percentages of m-Xylene and p-Xylene formed."

!!!:XYlSL?!? EzXYl_ens + L : - k - -

2-Methylbut-1-ene-3-yne 71.3 % 28.7 % +/- 4.3 % ( 2 5 Torr)

67.4 % 32.6 % +/- 8.1 % b Mixture

2-methylbut-l-ene-3-yne, propyne ( 2 5 Torr each)

Mixtureb' 52.9 % 47.1 % +/- 5.1 % with NO (10.4 Torr)

Mixtureb' 13.2 % 26.8 % +/- 4.0 % with O2 (11.0 Torr)

"Reactions occurred a t 400"C, for 10 min. Products were separated by gas chroma- tography on a column of 5% SP-1200/5% Bentone 34.

bAt 400"C, 25 torr 2-methylbut-1-ene-3-yne forms 33.5% of the total xylene formed by the pyrolysis of 25 torr 2-methylbut-1-ene-3-yne with 25 tor r propyne (a correction amounting to 55 mtorr out of the 163 mtorr of xylenes produced in the re- action mixtures). The results were corrected for this fact.

2-Methylbut-1-ene-3-yne and propyne, 25 ton- each.

to the acetylene/vinylacetylene data, one methyl group causes a fac- tor of 3.7 drop in product formation rate, and two methyl groups cause a factor of 5.8 drop.

Finally, Table IV shows chromatographic data collected for exper- iments with reaction mixtures alone or with NO or 0,. The data show that in the absence of added NO or 0, about 2/3 of the xylene product is m-xylene and 1/3 is p-xylene. These two products are formed by mechanisms 2 and 3 above (because mechanisms 1 and 4 are steri- cally hindered). Added 0, does not effect the ratio of rn-xylene to p-xylene, which is expected because 0, does not effect the rate of xylene production. I t was predicted tha t added NO would inhibit mechanism 3 since it is the major mechanism proceeding via a radical intermediate. Therefore a drop in the percentage of m-xylene formed was expected. The data shows that this is true. In the presence of added NO the proportion of m-xylene formed drops to about 1/2. It does not drop to 0 because mechanisms 1 and 4 do actually occur to some extent.

The above argument can be placed on a more quantitative basis if we assume that mechanisms 1 and 4 have the same rate coefficients as the C,H,/C,H, system and that mechanisms 2 and 3 have the same rate coefficients as the C,H,/C,H, system. This assumption requires that methyl substitution for H atoms at carbons not directly involved

C2H,/C4H4b

12

6 +

/-

5 8.

65

+/-

0.35

50 %

si

ngle

t 2.61

E-8

di

radi

cal

C4H6/C4HqC

80.1

+/-

7 4

.33

+/-

0.58

33 %

si

ngle

t 4

.53

E

-9

dira

di ca 1

C3H4/C5H6d

166

+/-

13

11.2

+/-

1.0

59

% si

ngle

t 7.10

E-9

dira

dica

l - "R

ate

of [

2 +

41 pr

oduc

t fo

rmat

ion

wit

h 25

tor

r of

eac

h re

acta

nt a

t 400

°C.

'Har

per

and

Hei

ckle

n [1

51.

dThi

s wor

k.

Cha

nmug

atha

s an

d H

eick

len

1141

.

190 HARPER AND HEICKLEN

in the reaction does not change the rate, and is probably valid to within a factor of two. We can then calculate the rate coefficients for each of the 4 mechanisms from the C,H,/C,H, and C,H,/C,H, systems and compare them with the observed rates obtained in the C,H,/C,H, system.

This is done in Table VI assuming that any differences in rate coef- ficients are entirely in the Arrhenius preexponential factor. l b o dif- ferent sets of calculations are made, one in which it is assumed that mechanisms 1 and 3 are diradical and mechanisms 2 and 4 have the very short-lived intermediate, and one in which the reverse is as- sumed. The ratio of calculated-to-observed rate coefficients is 1.0 to within a factor of 2 for three of the mechanisms if mechanisms 1 and 3 are considered to have the diradical route, but only in one of the mechanisms if mechanisms 2 and 4 are considered to have the diradi- cal route. Furthermore for mechanism 2, in which the ratio exceeds 2 for either assumption, it is smaller if mechanisms 1 and 3 are the diradical mechanisms. Thus this calculation supports the argument that mechanisms 1 and 3 are diradical and that mechanisms 2 and 4 have the very short-lived intermediates.

In conclusion we find that the replacement of CH, groups for H atoms in acetylene reduces the rate of [2 + 41 cycloaddition product formation, but does not change the mechanism. The triple bond to triple bond addition proceeds via a singlet diradical, whereas the

TABLE VI. A comparison of calculated and observed rate coefficients.

lo-’ A , M-ls-l(calc)a‘b 0.141 1.12 1.12 0.286

0.197 0.286 0.68 0.32

Ratio 0.72 3.92 1.65 0 . 8 9

-1 -1 b A , M s (obs)

10” A , M-ls-l(calc)a‘c 0.286 1.12 1 .12 0.141

A , M-ls-l(obs)c 0.286 0.197 0.32 0.68

Ratio 1 .00 5.69 3.5 0.21

“Calculated from C,H, + C4H4 data [141 and the C4Hs + C4H4 data [ E l . bAssuming mechanisms 1 and 3 are singlet diradical (intercepted by NO) and mech-

anisms 2 and 4 have a very short-lived intermediate (not intercepted by NO). ‘Assuming mechanisms 2 and 4 are singlet diradical (intercepted by NO) and mecha-

nisms 1 and 3 have a very short-lived intermediate (not intercepted by NO).

PYROLYSIS OF PROPYNE/Z-METHYLBUT-I-ENE-3-YNE 191

triple bond to double bond addition has a very short-lived intermedi- ate which is not intercepted by NO.

Bibliography

[ l ] B. S. Haynes and H. G. Wagner, Prog. Energy Combust. Sci., 7,229 (1981). [2] J. B. Edwards, Combustion, the Formation and Emission of Trace Species, Ann

131 M. S. B. Munson and R. C. Anderson, Carbon, 1, 51 (1963). 141 H. B. Palmer and C. F. Cullis, in The Chemistry and Physics of Carbon, Vol. 1, P. L.

151 0. I. Smith, Prog. Energy Combust. Sci., 7, 275 (1981). I61 K. R. Darnall, A. C. Lloyd, A.M. Winer, and J . N. Pitts, Jr., Environmental Science

[71 C. F. Cullis and N. H. Franklin, Proc. Roy. SOC. (London), A280, 139 (1964). I81 F. C. Stehling, J. D. Frazee, and R. C. Anderson, Eighth Symposium (International)

[9l T. Ikegami, Reu. Phys. Chem. Jpn., 33, 15 (1963).

Arbor Science, Ann Arbor, 1974, Chap. 2.

Walker, Ed., Dekker, New York, 1965, Chap. 5.

and Technology, 10, 692 (1976).

on Combustion, Williams & Wilkins Co., Baltimore, 1962, p. 774.

[lo] K.C. Hou and R.C. Anderson, J . Phys. Chem., 67, 1579 (1963). L111 Yu. P. Yampol ‘skii, Yu. V. Maksimov, and K. P. Lavrovskii, J . Phys. Chem. USSR

(English transl.), 182, 940 (1968); Dokl. Akad. Nauk SSSR, 182, 1344 (1968). [121 C. F. Cullis and I. A. Read, Trans. Faruday SOC., 66, 920 (1970). [131 R. Lundgard and J. Heicklen, Intern. J . Chem. Kinetics, 16, 125 (1984). 1141 C. Chanmugathas and J. Heicklen, Intern. J . Chem. Kinetics, 18, 701 (1986). 1151 C. Harper and J. Heicklen, Intern. J . Chem. Kinetics, 20, 9 (1988). F161 C. Chanmugathas and J . Heicklen, Intern. J . Chem. Kinetics, 17, 871 (1985).

Received March 29, 1988 Accepted September 6, 1988