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287
thylbenzenes), could be entirely avoided, and thus substantially the same product profile as that of the MTG process was obtained.
converted to gasoline in the second reactor containing ZSM-5 in the presence of unchanged syngas. This system has several advantages as follows: (1)DME synthesis reaction is much more favored than methanol synthesis reaction in terms of thermodynamics, and high CO conversion (77.2%) can be attained at low pressure (2.1 MPa). (2) The high conversion level was proved to be attainable experimentally by utilizing a hybrid catalyst composed of methanol synthesis catalysts and yA1203. (3) By the separate use of methanol synthesis catalyst and ZSM-5, unfavoriible side reactions in the one-step process, such as the hydrogenation of lower olefins or the secondary methylation of methylbenzenes to poly(me-
Literature Cited Argauer, R. J.; Landoh, G. R. US. Patent 3702886, 1972. Chang, C. D.; Sihrestri, A. J. J. Catal. 1977, 4 7 , 249. Chang, C. D.; Lang, W. H.; Smith, R. L. J . Cafe/. 1979, 56, 169. Chang. C. D.; Lang, W. H.; Silvestri, A. J. J. Catal. 1979, 56, 268. Fujimoto, K.; Kudo, Y.; Tominaga, H. J. Catal. 1084, 6 7 , 136. Meisel, S. L.; McCullough, J. P.; Lechthaier, C. H.; Weisz, P. E. CHEMECH 1976, 6, 86. Shimomura, K.; Ogawa, K.; Oba, M.; Kotera. Y. J . Cafal. 1978, 52, 191. Topsoe Top. 1982 (December).
Received for review October 28, 1985 Accepted January 19, 1986
GENERAL ARTICLES Continuous Wave Carbon Dioxide Laser-Induced Chemistry of the Allyl Halides Joseph K. McDonald' and James A. Merrltt Research Directorate, Research, Development 8 Engineerlng Center, U.S. Army Missile Command, Redstone Arsenal, Alabama 35898
James R. Durlgt Department of Chemlstry, Unlverslty of South Carollna, Columbia, South Carollna 29208
Vlctor F. Kalaslnskyt Department of Chemlstry, Mlsslsslppl State Unlverslty, Mlsslsslppi State, Mlssisslppl 39762
Samuel P. McManust Department of Chemlstry, The Unlverslty of Alabama in Huntsville, Huntsville, Alabama 35899
The gas-phase CW C02 laser-induced reactions (LIRs) of allyl chloride, allyl bromide, and allyl fluoride have been studied. I n the case of the chloride, where several other studies have appeared, the results of the LIR have been compared with pyrolytic studies, the SF,-sensitized CW-C02 LIR, and a gas-phase temperature photolysis study at 200 nm. Allyl chloride and allyl bromide appear to follow essentially the same mechanistic pathway for their LIR. There are, however, differences that can be attributed to the weaker C-Br bond and the relative reactivity difference of the halogen radicals. The principal products that both give are benzene, ethylene, propene, acetylene, methane, and the respective hydrogen halide. Allene and propyne were formed In modest yields from the chloride but were trace products from the bromide. Along with HF, allyl fluoride gives principally allene and propyne.
Introduction The development of new chemical processes that are highly selective, efficient, and inexpensive are permanent
goals in our profession. Thus the use of lasers to drive chemical reactions has attracted considerable attention in recent years (Moore, 1975-79; Grunwald et al., 1978; Bloembergen and Yablonovitch, 1978; Zewail, 1980; Letokhov, 1980; h e and Shen, 1980; Zare and Bernstein, 1980; Steinfeld, 1981). The widespread availability of tunable lasers has enhanced the interest in photochemical processes. However, because the output of a carbon di-
* To whom inquiries should be addressed (ATTN: AMSMIRD-RE-QP). 'Research supported by U.S.Army Contract DAAG29-81-D0100 through the Battelle Research Triangle Park office. O196-4321/86/ 1225-0267.$O1.5O/O
0
1986 American Chemical Society
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oxide infrared laser is resonant with the vibrational frequencies of a wide variety of organic molecular types, this type of gas laser has become the most popular for studies of laser-induced chemical reactions (LIRs). The absorption of the laser radiation by the molecules promotes molecules into excited vibrational states, thus making the molecules highly reactive. In principle, the laser energy can be deposited into a single vibrational mode, causing vibrational excitation to the point of dissociation. The resulting reactive species would be expected to react further. However, energy relaxation within a given vibrational mode generally occurs on a time scale of picoseconds. For complex molecules there is also a redistribution of energy among different vibrational modes as well as translational and rotational levels. Furthermore, at pressures of a few torr and higher, intermolecular redistribution accompanies collisions. Consequently, after irradiation by an infrared laser, only a few microseconds are required for the sample to reach thermal equilibrium. Once the laser energy has been distributed throughout a molecule, normal thermolytic reactions are observed. However, since wall reactions are not thought to be important in the LIRs, they may differ from typical pyrolysis processes. Comparison of the two types of reaction processes has verified this in many cases (Steinfeld, 1981). Alkyl halides are generally known to undergo hydrogen halide loss in both pyrolytic reactions (Maccoll, 1969) and LIRs (Steinfeld, 1981). Allyl chloride (AC), however, would have to eliminate HCl to form allene (1,2-propadiene) if this route were followed. Previous studies of the pyrolytic reaction have revealed that instead of allene the major products are propene and benzene, eq 1 (Hughes and
- /-,+ 0+
HCI
+
other products (1)
Yates, 1960; Porter and Rust, 1956; Goodall and Howlett, 1954; Kunichika et al., 1969; Ruzicka and Bryce, 1960). It is interesting to note that the gas-phase photochemical reaction of AC at 229 nm and 27-108 *C gives some of the pyrolytic or LIR products (propene, allene, and 1,Bhexadiene, vide supra), but no benzene is formed and several chlorinated derivatives are obtained (Sears and Volman, 1984). The process by which benzene is produced in the thermolysis of AC is of significant theoretical as well as practical interest. One interest of ours in this process is its resemblance with the pathway proposed for the undesirable thermal degradation of poly(viny1 chloride), PVC, eq 2 (McManus et al., 1983; Raghavachari et al., 1982;
CI
CI
I
CI
l
CI
l
CI
/
/
several steps
CI
“G.,
Starnes, 1981; Braun, 1981). Because of the widespread use of PVC as a wire molding, understanding and controlling this reaction has been important to PVC producers and users. In this article we discuss the laser-induced chemistry of AC using a C02 laser to initiate the gas-phase reactions.
So that we could learn more about the conversion of AC to benzene, we have also looked at the LIRs of some other molecules which were useful in discerning the mechanistic pathway followed by AC. Thus, in this article we discuss the mechanism of AC thermolysis and compare the laser-induced and pyrolytic processes. The LIRs of allyl bromide (AB) and fluoride (AF) were also run for comparison, and those processes are described. Experimental Methods Materials. Except for AF, samples used were reagent grade commercial materials. The sample for AF was prepared by the reaction of AB with potassium fluoride in ethylene glycol (Hoffman, 1949). Purification was accomplished by using low-temperature vacuum distillation through a fractionating column. The structure and purity were verified by comparison of the mid-IR spectrum of the vapor with that which was previously reported (Durig et al., 1985). Each sample was transferred by using vacuum techniques, and structures were verified by infrared analysis before each irradiation. Reactions were carried out in cylindrical stainless steel cells (5 X 10 cm) equipped with O-ring seals for securing the ZnSe windows (5-cm diameter) through which the laser beam passed (10-cm path length). Infrared spectra of the cell contents were obtained through either KC1 or ZnSe windows mounted perpendicular to the laser path. Laser Photochemical Experiments. Infrared laser excitation in the range 9.4-10.4 pm was provided by a Coherent Radiation Laboratories Model 41 continuouswave (CW) C02laser. The exact frequencies were verified by using an Optical Engineering C02 spectrum analyzer. In single-line operation, output powers up to 150 W could be obtained by varying the current and the (C02-N2-He) gas mixture in the laser tube. AC has a strong infrared absorption between 940 and 920 cm-l. The P(26) line of the C 0 2 laser (938.69 cm-l) was strongly absorbed by the sample and hence was used for the AC experiments. AB also has a strong infrared absorption in this region. The P(36) laser line (929.02 cm-’) was used for most runs with this substrate. It was determined that other laser lines in this same region gave essentially identical product mixtures. Product Analysis. Infrared spectra were collected on either a Digilab FTS-20 or Mattson Sirius 100 spectrometer, each equipped with KBr/Ge beamsplitters and triglycine sulfate detectors. Interferogramswere transformed after applying a triangular apodization function with an effective spectral resolution of 1 cm-’. This resolution was sufficient to allow unequivocal identification of major peaks of hydrocarbon products expected on the basis of reported pyrolysis experiments and our studies of the LIR of 1J-hexadiene (1,5-H, diallyl) (McDonald et al., 1985). Gas chromatographic (GC) analyses were performed on the gas samples by using either Hewlett-Packard Model 5840A or Varian Model 4600 chromatographs equipped with OV 101 coated capillary columns and flame ionization detectors. Areas were electronically integrated. Reaction mixtures from some of the reactions were analyzed by GC and FTIR in order to confirm the products identified by FTIR analysis. Reaction mixtures containing either HBr or HC1 were found to undergo significant changes in product composition upon standing. Hence analyses reported here are those of product mixtures determined less than 1 h after reaction. Results Allyl Chloride, AC. Irradiation of 10-100-torr samples
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269
30
20 K
0 v
w r w
‘1
N
2
m Y
, 3
10
10
1;
TIt‘E (SEC)
Figure 3. Benzene yield as a function of laser power at 100 W/cm2 laser power: (0)80-torr allyl chloride; (A)40-torr allyl chloride.
15 I
I
20
40
I
I
60
-
120
100
80
ALLYL CHLORIDE (TORR)
Figure 1. Benzene yields as a function of allyl chloride at a constant 1500-5laser irradiation: (0)100 W/cm2; (A)50 W/cm2.
I 20
40
60
80
100
120
140
160
LASER POYER (UATT/cm21
Figure 2. Benzene yield as a function of laser power at constant 1500-5irradiation: (0) 80-torr allyl chloride; (A)40-torr allyl chloride.
of AC with laser powers between 25 and 150 W for times of 0.2-60 s was accomplished. During a normal irradiation of ca. 10 s, a pressure-dependent luminescence, lasting about 3-4 s, was visible. Polymeric materials were observed on the windows and cell walls after reaction. By FTIR analysis, the products of the laser-induced reaction of AC are found to be benzene, methane, acetylene, ethylene, propene, allene, propyne, 1,3-cyclopentadiene (trace), 1,3-~yclohexadiene(1,3-CH, trace), 1,3-butadiene (1,3-B), and HCI. GC analysis confirms these organic products and shows that several other trace products are present along with some products with longer retention times (probably chlorinated compounds). Chloroethylene and chloroethane were found not to be products. Also, it was found that product mixtures were unstable, probably owing to the addition of HC1 to reactive alkenes and dienes. Figure 1 is a plot of AC pressures vs. benzene absor-
1 .o
2.0
TIVE (SEC)
Figure 4. Product yields as a function of irradiation time: (0) benzene; (A)ethene; (0) propene; (V)allene.
bances at 50 and 100 W for 30 and 15 s, respectively. A laser fluence of 1500 J was arbitrarily chosen. The plot indicates that a threshold pressure of AC is needed for benzene production. A laser-power dependence is evident from Figure 2, where laser power is plotted against benzene production. Figure 3 shows that the reactions reach optimum production of benzene after 5-10 s when a laser power of 100 W/cm2 is used. A graphite shutter, adjustable to 0.1 s, was used between the laser and the sample cell, and a series of runs was conducted with sample irradiation times of 0.1-1.9 s at laser powers of 75 and 100 W/cm2. From standard plots of concentration vs. pressure determined by FTIR, concentrations of AC, benzene, allene, HC1, ethylene, and propene were calculated. The results of one of these are
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986
270 5J
Allyl Fluoride, AF. The LIR of this substrate produced mainly propyne, allene, and HF. Smaller amounts of acetylene and ethylene were formed, and traces of benzene, propene, methyl fluoride, and vinyl fluoride were identified by characteristic bands in the FTIR of the products.
1
4 30-l
-I
\
\ \
-0, P P % t .
*fi--
7
Figure 5. Dependence of decomposition of allyl bromide to laser power at constant 1000-5 laser energy: (0) allyl bromide; (0) propene; (A)benzene.
plotted in Figure 4. Various treatments of AC concentration vs. time suggested a three-halves overall reaction order. This result was confirmed by measuring initial rates at two different concentrations. Allyl Bromide, AB. Laser irradiation of AB produces essentially the same products as the AC reaction. The most important products are benzene, propene, ethylene, acetylene, methane, and HBr. Allene and propyne are trace components, and 1,3-B and 1,3-CH are not observed. A pressure-dependent weak glow was observed along the laser path during irradiation, and a carbon-like deposit was observed on the cell walls and windows after the reaction. A plot of the concentration of the reactant and major organic products against laser power was determined at an arbitrarily chosen laser fluence of 1000 J (Figure 5). A laser-power threshold was not indicated from this plot. The higher laser powers gave more side products and carbon-like deposits. A reaction order for AB was determined by following the reaction at two initial reactant concentrations (25 and 50 torr). To keep the temperature approximately constant, different laser lines were used: P(36), 929.02 cm-', and P(22), 942.38 cm-', respectively. The ratio of the initial rates indicated that AB followed an overall first-order reaction. However, in the 25-torr reaction, as the concentration decreased, the overall reaction order tended toward second order. For the first-order reaction, by the use of the Arrhenius equation determined by Maccoll and our experimental rate constant, an effective temperature of 515 "C can be calculated.
Discussion Reaction Mechanisms. From a cursory evaluation based on the products, AB and AC apparently follow the same general mechanism of reaction when irradiated with the CW COz laser. They give products that implicate involvement of the allyl radical, eq 3. However, AF appears to follow a different, nonradical, path. In the gas phase a t the pressures evaluated, the reaction of the chloride proceeds smoothly in ca. 10 s with a laser power of 50-75 W/cm2. Because the C-Br bond is weaker than the C-Cl bond, AB reacts with a lower energy input than AC. Also, with AC, but apparently not with the bromide, benzene production only occurred above a threshold power level (ca. 25 W/cm2). Also, again only with the chloride, an induction period was observed. We believe the induction period results from the production of the benzene precursors and the need for the production of a sufficient concentration of radicals for conversion of these precursors to benzene. This view is supported by other work which shows that benzene is a secondary product (McDonald et al., 1985; Nohara and Sakai, 1973). Various investigators have shown that the products of AC thermolysis are greatly dependent on reaction conditions. Reported products are benzene, propyne, allene, 1,5-H, 1,3-CH, ethylene, acetylene, methane, 1,3-B, HC1, and tars. Shilov (1954) and Goodall and Howlett (1954) proposed that the primary reaction in AC pyrolysis is HC1 loss to give allene, which undergoes further reaction. Porter and Rust (1956) indicated that their results were more consistent with a radical process with C-C1 bond cleavage the primary initial reaction. More recent accounts (Hughes and Yates, 1960; Kunichika et al., 1969) have supported this view. There is evidence that one mechanism may not suffice. For example, ethylene, acetylene, methane, and 1,3-B are reported only from reactions a t high temperature (>BOO "C); therefore, they must be products of alternate reaction pathways. Ignoring these latter products gives a grand reaction scheme, as put forth in the literature and shown in eq 3-12. CHZ=CHCH2Cl-+ CHz=CHCHz* + C1. (3) CH2=CHCHzCl + C1. -+ CH2=CHCHC1 + HCl (4) CH2=CHCH2Cl+ CHZ=CHCHy CH2=CHCHC1 + CH2=CHCH3 ( 5 ) 2CH,=CHCHy CH2=CHCHZCHzCH=CH2 (6) CH2=CHCH2* + CH,=CHCHCl-+ CH,=CHCH2CHClCH=CHz (7) CH2=CHCH,CHClCH=CH, C6H6 + HC1 + Hz (8) 2CHz=CHCHC1 C6H6+ 2HC1 (9) CHZ=CHCHz* CHZ=C=CHZ + H. (10) CHZ=CHCHy + HC1 H- + CH2=CHCH&l(11) H. + CHz=CHCH*. ---* CHZ=CHCH3 (12) First, we will discuss formation of the noncyclic products. It is somewhat surprising that addition reactions to the C=C bond have been ignored by previous workers in this area. Bryce and Ruzicka (1960) established convincing precedents for this process in their earlier studies of the allyl radical in the presence of simple alkenes. At 500 "C, they found that addition to the C=C bond and hydrogen -+
+
--
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986
abstraction are competitive processes. An a chlorine substituent is known to retard hydrogen abstraction by C1(Lowry and Richardson, 1981). Therefore, radical addition to AC (eq 13) may be more important than hydrogen abstraction (eq 4). Also, fragmentation of radicals by expulsion of a group /3 to the carbon radical, such as the process shown in eq 14, is an increasingly facile process as the temperature is increased (Huyser, 1973). Given these considerations, the reactions shown in eq 13 and 14 CH2=CHCH2. + CH2=CHCH2C1CH2=CHCH2CH2CHCHzC1(13) CH2=CHCH2CH2CHCH2C1 CH2=CHCH2CH2CH=CH2 C1. (14)
-
+
should be the important ones leading to 1,5-H. Although hydrogen abstraction from AC will occur to some degree, the chloroallyl radical could add to AC, giving, after chlorine atom loss, 3-chloro-1,5-hexadiene (eq 15 and 16), which is also a known precursor for 1,3-CH CH2=CHCHCl+ CH2=CHCH2C1 C H ~ = C H C H C ~ C H ~ C H C H(15) ~C~ CHz=CHCHC1CH2CHCH2C1 CH2=CHCHClCH2CH=CH2 + C1. (16)
-
-
(McDonald et al., 1985). Except in the laser beam path, it is unlikely that the allyl radical concentration is high; thus, the radical combination reactions, e.g., eq 6 and 7, may not account for the major part of the six-carbon products. In our studies of the LIR of 1,5-H (McDonald et al., 1985), the pathways by which benzene is formed from 1,5-H were discussed. The reactions that probably occur are shown in eq 17-26.
+c-c+
CH2=CHCH2'
CHz=CHCHs
or
or
Ck
C
'
C
-
(17)
HCI
+
(18)
CI*
(19)
(23) CHZ=CHCH,*
CH2=CHCH,
or
or
CI*
HCI
(24)
(25)
(26)
The above reaction schemes do not account for ethylene and acetylene, both of which are significant products in
271
the AC and AB reactions. These products are also formed from pyrolysis and the LIR of 1,5-H. The most economical route to their production is by initial breaking of the C2-C, bond in 1,5-H. While this may occur, there is experimental evidence that the 1,5-hexadienylradical, CH2=CHCH2CH=CHCH2-, fragments to give two- and four-carbon radicals (James and Troughton, 1966; McDonald et al., 1985). Either pathway would account for the 1,3-B, ethylene, and acetylene. Alternatively, in a very hot zone, one may anticipate low selectivity; thus, other routes to the low molecular weight materials are apparent, e.g., eq 27 and 28. CH2=CHCHZCl+ CH2=CH. + CH&1 (27) CH2=CH2
R.
CH2=CH.
R. HCECH -RH (or -H.)
(28)
Propyne has been shown to be thermally produced from allene (Sakakibara, 1964). The propyne formed in the LIR of AC is best accounted for by this mechanism since, in control experiments, we found that allene was converted to propyne upon laser irradiation. It has been the general view of those who have reported the pyrolysis work with AC that 1,5-H is the logical intermediate which leads to 1,3-CH and that 1,3-CH is the precursor of benzene. We recently confirmed that 1,3-CH is a product of the LIC reaction of 1,5-H (McDonald et al., 1985) and presented experimental evidence which agreed with literature precedents (Isagulyants et al., 1981; Nohara and Sakai, 1973) suggesting that 1,3-CH could have come from 1,3,5-hexatriene (1,3,5-H). However, we were unable to conclude that benzene comes solely from 1,3-CH. Benzene forms from 1,4-cyclohexadiene by a concerted thermal mechanism, while radicals are needed to convert l,&cyclohexadieneto benzene. Since control experiments showed that 1,6cyclohexadiene, as the minor product in eq 20, may be a product in these reactions (McDonald et al., 1985), we must consider that both dienes may be benzene precursors here. The general mechanistic scheme for AC seems to be applicable to AB, yet the yields of products suggest differences. Two factors seem to contribute to this. First, because the C-Br bond is weaker than the C-C1 bond, reaction of AB occurs at a lower energy input and the LIR probably occurs at a lower temperature than that of AC. Second, the bromine radical is more selective than the chlorine radical in its reactions. This probably provides some differences in pathways followed by the two halogen radicals, thus leading to different product compositions. A cursory examination of the products suggests that AF is following a different mechanism than the other halides. The principal products are propyne, allene, and HF. Smaller amounts of acetylene and ethylene were formed along with traces of benzene, propene, methyl fluoride, and vinyl fluoride. Since the C-F bond is as strong or stronger than C-C bonds, allyl radicals are not expected to be prominent in the reaction mechanism. From the amounts of propyne and allene formed, a concerted or near-concerted loss of HF is suggested. An alternate view of the overall mechanistic scheme for the allylic halides (AX) is possible. Two competing mechanisms are conceivable. The more selective pathway, occurring at lower temperatures and to a greater extent with the weaker C-X bonds, is C-X bond cleavage to give the halogen radical and the allyl radical. The alternate pathway occurring at higher temperatures and with stronger C-X bonds is concerted (or nearly concerted) loss of HX. The first process occurs predominately with AB, while the alternate pathway is followed by AF. The mechanism followed by AC, if competing processes are
272
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1986
occurring, is a function of temperature. Thus AC seems to primarily follow the first mechanism a t lower energy inputs (lower temperatures), but at high temperatures the second mechanism becomes more important. If there are not two competing mechanisms for AC, the allyl radical must have a short lifetime a t very high temperatures with eq 10 becoming very facile. Comparison with Pyrolysis Experiments. From the products obtained, we conclude that basically the same processes are involved in the LIR and the pyrolysis processes. Indeed the pyrolysis processes vary depending on the manner in which the experiments are conducted and, especially, the temperature. There have been no reported pyrolytic studies of AF for comparison. The 3 / 2 reaction order found for the LIR of AC differs from the first-order process reported in the pyrolysis studies (Goodall and Howlett, 1954; Kunichika et al., 1969), but our AB LIR order (first order) agrees with the reported pyrolysis reaction order. Since these measured reaction orders are for the overall complex processes, we cannot directly relate them to mechanism. Finally, we must comment on the ease of carrying out processes using a laser source vs. typical pyrolytic processes in a tube furnace. While pyrolysis with a tube furnace presently is best for throughput of larger quantities of materials, the LIR process is much more convenient for studying the products of reactions and carrying out small-scale reactions. The LIR process requires no lengthy warm-up time; a complete experiment can be conducted in a few minutes, including the time for sample transfer. Related Studies. One other LIR of AC appeared during the course of this work. Pola (1983) studied AC using SF6as a laser-absorbing energy transfer substrate and observed a LIR process dissimilar in several respects to the one described here. Most significantly, there is no mention of ethylene and propene even as trace products. Also, much higher yields of propyne and allene than obtained in our LIRs or in pyrolysis were reported. Surprisingly, the yields of these substances both decrease with percent conversion. Pola attributes the differences between his results and pyrolysis experiments to the absence of wall reactions. However, it must be more complex than this since wall reactions are not significant in our LIRs. SF6is considered to be an unreactive, infrared absorber which only acts to transfer, by collision, vibrational energy to a molecule which does directly absorb the infrared energy. While this may be the case, we have observed that some H F forms under conditions similar to those used by Pola. Also, the temperatures in the SF,-sensitized LIRs are expected to be substantially higher than those in our system. With these differences, it is not surprising that there are substantial differences in the two studies. If SF6 is acting only to transfer vibrational energy to AC, then it appears that under Pola's conditions the high-energy mechanism discussed above occurs. In another study appearing after this work was essentially complete, Sears and Volman (1984) reported studies
on the photolysis at 229 nm of gaseous AC a t 27-108 "C. Their results were also considerably different from our LIR, although 1,5-H, allene, and propene were products common to our study. They also obtained and isolated several monochlorinated and dichlorinated products, which may not be stable under our reaction conditions. They proposed that chlorine radical addition to AC was an important product-producing reaction. The reverse reaction, P fission of the 1,3-dichloro-2-propylradical, is apparently not as important at low temperatures as it is at high temperatures, e.g., eq 14 and 16.
Conclusions AB, AC and AF absorb irradiation from a CW COPlaser, allowing the study of their LIRs. Where comparisons are possible, the LIRs appear to be similar to pyrolysis reactions with these substrates. However, significant differences are evident between the results of these studies and the LIR of AC where a SF, sensitizer is included. If allene and propyne are the products sought, the sensitized process is the better. The present process, especially when AB is the substrate, is the better one for benzene production. Registry No. AC, 107-05-1; AB, 106-95-6; AF, 818-92-8.
Literature Cited Bloembergen, N.; Yablonovitch, E. Phys. Today 1978, 37(5), 23. Braun, D. Dev. Polym. Degradetion 1981, 3 , 101. Bryce, W. A.; Ruzicka, D. J. Can. J . Chem. 1880, 38, 835. Durig, J. R.; Zhen, M.; Little, T. S. J . Phys. Chem. W85, 81, 4259. Goodall, A. M.; Howlett, K. E. J . Chem. SOC. 1954, 2596. Grunwald, E.; Dever, D. F.; Keehn, P. M. Megawatt Infrared Laser Chemistry; Wiley: New York, 1978. Hoffman, F. W. J . Org. Chem. 1949, 1 4 , 105. Hughes, L. J.; Yates, N. F. J . Phys. Chem. W80, 6 4 , 1789. Huyser, E. S.I n Organic Reactive Intermediates; McManus, S . P., Ed.: Academic: New York, 1973; Chapter 1. Isagulyants, G. V.; Dubinskii, Y. G.; Rozengart, M. I.Izv. Akad. Nauk SSSR, Ser. Khim. lS81, 462. James, D. G. L.; Troughton, G. E. Trans. Faraday SOC. 1988, 6 2 , 145. Kunichika, S.; Sakakibara, Y.; Taniuchi, M. Buii. Chem. SOC.Jpn. 1989, 42, 1082. Lee, Y. T.; Shen. Y. R. Phys. Today 1980, 33(11), 52. Letokhov, V. S.Phys. Today 1980, 33(11), 34. Lowry, T. H.; Richardson, K. S. Mechanism and Theory in Organic Chemistry, 2nd ed.; Harper and Row: New York, 1981; pp 717-721. Maccoii, A. Chem. Rev. 1969, 6 9 , 33. McDonald, J. K.; Merritt, J. A.; Alley, B. J.; McManus, S. P. J . Am. Chem. SOC. 1985, 107, 3008. McManus, S . P.; Smith, M. R.; Smith, M. 6.: Worley, S. D. Tetrahedron Lett 1983, 24, 557. Moore, C . B. Chemical and Biochemical Applications of Lasers ; Academic: New York, 1975-79; Vol. I-IV. Nohara, D.; Sakai. T. Ind. Eng. Chem. Prod. Res. Dev. 1973, 12, 322. Pola, J. J . Chem. SOC.,Perkins Trans. 2 1983, 231. Porter, L. M.; Rust, F. F. J . Am. Chem. SOC.1958, 78, 5571. Raghavachari, K.; Haddon, R. C.; Starnes, W. H. J . Am. Cttem. SOC.1983, 104, 5054. Ruzicka, D. J.; Bryce, W. A. Can. J . Chem. 1080, 3 8 , 827. Sakakibara, Y. Bull. Chem. SOC.Jpn. 1984, 3 7 , 1268. Sears, T. S.;Volman, D. H. J . Phofochem. 1984. 2 6 , 85. Shiiov, A. E. Dokl. Akad. Nauk SSSR 1954, 9 8 , 601. Starnes, W. H. Dev. Polym. Degrad. 1981, 3, 135. Steinfeld, J. I . Laser-Induced Chemical Processes ; Plenum: New York, 1981. Zare, R . N.; Bernstein, R. B. Phys. Today 1980, 33(11), 43. Zewail, A. H. Phys. Today 1980, 33(11).27.
Received for review September 4, 1985 Accepted December 16, 1985
