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Product Design

Reaction Mechanism in the Burning Cigarette

Date: 1976 (est.)
Length: 32 pages
1000145220-5251
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Abstract

Summarizes the chemical reactions of a burning cigarette. Identifies the high temperature, pyrolysis-distillation and low temperature zones of burning cigarettes as areas of complex chemical reactions. Describes pyrolysis and the formation of end products, indicates that condensation and filtration occurs in the low temperature zone and states the reactions taking place in a burning cigarette are very complicated.

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Appears to be a publication in prep. and resembles Bates # 1000145162-5219 expect for font size.

Author
Osdene, Thomas Stefan, Ph.D. (Director of Science and Technology, Philip Morris [1986])
Ph.D. in Organic Chemistry. Ten years of research when he started with PM in 1965. Worked in Chemical Research Division of PM 1965-66; Chemical and Biological Research Division 1966-69; Director of Research 1969-1984, also assumed independent position as Director of Research and Extramural Studies during these years; became Director of Science and Technology in 1984, reporting directly to Philip Morris USA Executive VP Mark Serrano. Involved with Center for Indoor Air Research (CIAR) 1988. Attended PM's Operation Downunder Conference in June, 1987. Retired 1993.
Hypothesis
Mainstream constituent yields
Modification of selected mainstream smoke constituents in response to health concerns.
Sidestream constituent yields
Modification of selected sidestream smoke constituents in response to health concerns.
Smoke constituent testing
Development of methods for measurement of gas and particulate yields in mainstream and sidestream smoke.
Keyword
Burn rate control
Burn rate is controlled through use of burn additives, density, paper, etc.
Butt length (smoked)
Environmental Tobacco Smoke ETS
Heat flux
Initial puffs (First puffs)
Passive Smoking
Puff parameters
Pyrolysis
Reaction products
Secondhand Smoke (Sidestream smoke, SS)
Total particulate matter (TPM or Tar)
Additive
Menthol
Smoke Constituent
acetaldehyde
Acetamide
Acetic acid
Acetone
Acetonitrile
Acrylonitrile
ammonia
Benzo(a)pyrene
Butanedione (2,3-Butanedione)
Butanone (2-Butanone)
Carbon dioxide
Carbon monoxide
Dimethylpyrazine (2,5 and 2,6-Dimethylpyrazine)
Formamide
Hydrogen cyanide (HCN)
Methanol
Methylpyrazine
Methylpyrrole
Nicotine
Nitric oxides
Phenol
Propionamide
Propionic acid
Pyridine
Pyrrole
Design Component
Air dilution
Ash formation
Ash temperature
Burn rate
Coal temperature
Combustion temperature
Cone temperature
Dynamic mass burn rate
Free burn rate
Humectant
Mass burn rate (MBR)
Static burn rate
Named Organization
Tobacco and Health Research Institute
University of Kentucky
Brand
KENTUCKY REFERENCE
Subject
aerosol (technology)
Ammoniation (Technology)
Burn Rate (Design)
Metabolites (Measures)
Puff Parameters (Measures)
Reaction Processes (Technology)
secondhand smoke
Secondhand Smoke/Constituents
Smoke Constituents
Tar (Measures)
Test/Smoke Condensate (Testing)
Test/Smoke Constituents (Testing)
Test/Smoke Machine (Testing)
Transfer to Smoke (Measures)

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Page 1: blf08e00
OSDENE, page 1 .> r . , A REACTION MECHANISMS IN THE BURNING CIGARETTE By Thomas S. Osdene~ . 0 Director of Research, Philip Morris U.S.A.
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OSDENE, page 2 In any discussion of chemical reactions, in the burning cigarette it is essential that we first describe the present state of the art of what is known about the basic energy relationships that govern the burning process. Using temperature =- profiles and major reaction zones, I will develop in some detail " a model of the burning cigarette that will show the major sources and sinks of energy that determine the generation and fate of the various classes of smoke products. I will describe the use of some' of the modern techniques that have been used to confirm.the existence and location of the reaction zones and to elucidate the reactions known at the present time. . x c It is in our own laboratories,.here at the Philip Morris Research Center, that many of the techniques using isotopes--both radioactive ones such as carbon-14 and heavy isotopes such as nitrogen-15 and oxygen-18--have been pioneered. I will.therefore draw heavily on the work done by my colleagues over the last decade or so.. Perhaps Z should say at the very outset that I am really here to represent them and to describe their outstanding contributions to our understanding of the reactions within the burning cigarette.. It should be noted that some 2,000 chemical components have .been identified in cigarette smoke at the present time and that perhaps tens of thousands are as yet undiscovered. Obviously, ~ it would be an impossible task to determine the mechanisms by ~ . © which each individual component is formed. However, there is a N ~ great de r al to be learned from a.discussion of certain aspects ~ of the reactions where mechanisms have been elucidated. .
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OSDENE, page 3 ( Before discussing temperature profiles and reaction zones, some basic definitions are in order. When a smoker puffs on a ~ cigarette, the smoke that issues from the butt end of the cigarette is called mainstream smoke. During the interval between puffs the smoke that rises from the lit end of the cigarette is sidestream smoke. Mainstream smoke is formed during dynamic puffing and is quite different chemically from sidestream smoke generated during static burning between puffs. Both sidestream and mainstream smoke can be divided into a particulate phase and a gas phase. The particulate phase has been arbitrarily defined as that portion of the smoke collected on a conventional Cambridge ( filter pad (99 .9°!o efficient for particles > 0.1` µ); the portion • that passes through the Oamb ridge filter is gas phase. These terms are illustrated in Fig. 1. ---------------------------------------------------------------------- [insert Fig. 1] ----------------------------------------------------------------------- In order to compare results between laboratories, a set of standard smoking conditions has been established. These conditions ~ are: puff volume, 35 ml; puff duration, 2 sec; interval between :;the completion of one puff and~ initiation of the next puff, 58 , sec. Also, the Tobacco and Health Research Institute of the ~_ University of Kentucky has estab lished a series of standard ~ O experimental b lended cigarettes called the Kentucky Reference I~ Series. One of these cigarettes, designated 1RI, has as a tiP been used C4 standard by tobacco research scientists throughout the `r ~ worl.d.N N ,
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and thus becomes a source of heat for solids behind the comhastion zone. The major source of combustion during the puff is not located at the periphery but rather in the center of the ciWette. Previous deductions that the periphery was the major sourcecif _ combustion were probably due.-to the ease of measuring the sutface hot spots. Baker's flow rate was quite low (120 ml/min)-whzds .0 Y w would result in more heat transfer than at the standard flov rate Fig. 3 shows the classical solid temperature profiles of the burning cigarette obtained by Egerton, Gugan, and Weinbex&2 . •• ------------ ---.--.---------•• --------------------------w w-- __- _ [insert Fig. 3a and 3b] ( . ------------------------- ------------------------------------- Fig. 3a is for the second or third puff, while Fig. 3b is the profile for the last puff. These temperatures were obtained v3.th flow rates between,600 and 1200 ml/min--rates which reflect more realistically the conditions in most machine-smoking espwiments. Note again the hot spot in the vicinity of the char line and the high surface temperature over the entire coal that serves to preheat the incoming air. On the last puff (Fig. 3b) the heat gradient from the 'pyrolysis region.of 400°C +-back toward the butt is very sharp. This demonstrates dramatically the heat-abso6ing quality of previously condensed material on the tobacco. Becais e .& .these materials are lost to the sidestream between puffs, the temperature gradient forward of the pyrolysis region is not appreciably altered by the puff position. 0
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OSDENE, page 6 . Based on these temperature profiles, the model of the burning In the high-temperature zone (900-600°C) the exothermic oxidation of carbon heats the oxygen-depleted gas stream which serves as an energy.source for.the complex reactions that take place in , . . The occurrence and location of these reaction zones have been the pyrolysis-distillation zone (600-100°C). Overall, the reactions in this region are endothermic and the gas stream cools quite rapidly, merging into a low-temperature zone (100°C-ambient). burning cigarette.3 The carbon monoxide concentration measured ----------------------------------------------------------------- [insert Fig. 4] cigarette can be visualized as consisting of 3 major reaction zones. : verified recently in our lab oratories, where probing experiments have been conducted on the concentrations of several gases.ia.the . --------------------------.------------------------------ ------.-- through the longitudinal axis of the rod on the second puff of a.. cigarette is shown in Fig. 4. Superimposed on this plot is the- . . . '' longitudinal gas-temperature profile of the cigarette: Starting from the left we see that the gas temperature, represented by ~ ., the dotted line, precedes the exothermic combustion, represented by the first solid-line peak. The carbon monoxide concentration is now quite high, but drops very rapidly as carbon monoxide is lost from the coal. (Note that we are still in.front of the char line at this point.) The second carbon monoxide'peak represents .not a geaneraT reaction zone but a reaction specific to carbon . monoxide, namelyJ reduction of carbon dioxide under the influence , of the hot char. The last carbon monoxide peak occurs in the
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OSDENE, page 7 general pyrolysis region. Due to sampling conditions, the pyrolysis peak actually occurs at approximately 5 mm from the char line instead of 10 mm as indicated in Fig. 4. The negative slopes on the carbon monoxide peaks represent areas of rapid diffusion out of the cigarette. There*is a rapid loss of gas temperature behind the pyrolysis region. A steady decline in the carbon monoxide concentration continues as near-isothermal diffusion occurs down the rod. On the other hand, oxygen concentration, as illustrated in Fig. 5, drastically decreases in the area of carbon oxidation, as . . . ----------------------------------------------------------------- jinsert Fig. 5] ------------------------------------------------------------------ one would expect, and is still quite low in the pyrolysis region. The oxygen concentration then increases due to diffusion of oxygen through the paper into the cigarette. HIGH-TEMPERATURE ZONE I will now discuss the reaction zones in more detail. As a p O puff is taken on the cigarette, air enters the periphery of the O coal at the char line. In the -high- temperature zone there is an ~ exothermic oxidation of carbon~and heat is transferred to the ~ rA gas stream. The hot gas stream serves as an energy source for the subsequent decomposition of the tobacco in the pyroJ.ysis-distillatior .region, fThe products generated in the high-ternperature zone are mainly gaseous, including carbon dioxide, carbon monoxide, hydrogen,
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OSDENE, page 8 methane, some free radicals, and small amounts of water and organic compounds. A portion of the products diffuses through the coal to the sidestream. The remainder stays in the hot gas stream. These observations have been verified in our laboratories by a series.of oxygen-18 experiments.4 Kentucky Reference 1R1 cigarettes were smoked in an atmosphere containing oxygen-18 and the incorporation of the isotope in various smoke components was determined. Table I gives the results.that were obtained. ------------------------------------------------------------------ [insert Table I] ----------------------------------------------------------------- a by these pyrolytically derived compounds delivered to the sidestream reduced atmospheric oxygen incorporation in water, acetone, and acetaldehyde--compounds which are derived principally from pyrolytic processes. Further, the uptake of atmospheric oxygen SS/MS ratios of near unity. Contrast this.with the greatly Combustion products such as carbon monoxide and carbon dioxide derive more than 50% of their oxygen from the atmosphere. The oxides of carbon incorporate atmospheric oxygen to the same extent in both mainstream (MS) and sidestream (SS) smoke as indicated by is much greater than the uptake by the same components delivered to the mainstream. Water is an important combustion product which rivals the oxides of carbon on the basis of mass. The overwhelming O preference p of "combustion" water for the sidestream leads us to propose that ~11 water rgsults mainly from the reaction of pyrolytically formed 0 Cn hydrogen with oxygen. An alternate mechanism involving the interaction of oxygen with hydrogen bound to a char-like solid
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.- OSDENE, page 9 structure can be rejected, since the SS/MS ratio of water by this mechanism should parallel that of the oxides of carbon. YYROLYSIS-DISTILLATION ZONE The energy provided by the oxygen-depleted hot gas stream from • the combustion zone leads to a host of complex reactions which occur in the pyrolysis-distillation zone. The tobacco decomposes to yield high-b:oiling compounds which are the main source of .particulates; "char" that serves as fuel for combustion; carbon monoxide; organic gases such as acrolein, acetaldehyde, and hydrogen cyanide; and intact distillation products such as nicotine and the humectants. In this zone the aerosol, which is not in thermal equil ibrium with the,gas, is rapidly forming, with the higher-boiling compounds condensing first. The gases such as carbon monoxide, carbon dioxide, and hydrogen diffu e out through the paper while oxygen diffuses into the rod. The overall sum of the reactions is endothermic, so that the gas stream cools rapidly. All these reactions are temperature- and residence-time-dependent; • so pyrolysis and distillation reactions are subject to change by alteration of the cigarette parameters, and/or the smoking conditions. r 4 have led us to conclude Our oxygen-18 incorporation studies that gas-phase components in the sidestream smoke incorporate higher percentages of'atmospheric oxygen than do those of the particulate phase. (See Table II.) Certain organic compounds contain appreciable OO amounts of atmospherically derived oxygen. These are principally A r aliphatic aldehydes, ketones, and carboxylic acids. Some oxygern in phenol is also derived from the atmosphere.
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OSDENE, page 11 C The composition of products in the smoke from cigarettes containing, these additives is dependent on the decomposition temperature of the additive. For example, we have found that the reduction of benzo(a)pyrene in smoke from nitrate-treated cigarettes varies - ~ with the decomposition temperature of the added salt. It has been . ,shown previously that the addition of..nitrate salts to cigarettes o . ~ can significantly modify other chemical components in the smoke.6 These results suggest that significant modifications of smoke chemistry may be obtained by the proper selection of additives which decompose at temperatures coinciding with the formation o-f- c r,n " particular z$nes. salts have also been useful for studying the various classes of compounds formed when nitrogenous compounds are converted into smoke products. With [15N]-glycine as an ammonia source, various amides, nitriles, and N-heterocyclics were formed. Percent The cigarettes with added [15N]-glycine and various [15N]-nitrate. ( . f incorporations for these compounds are shown in Tables IV and V. ----------------------------------------------------------------- . [insert Tab les IV and Vj ------------------------------------------------------------------ Note that K15N03 and Oa(15N03)2 give results similar to Nai5N03. The enrichment of amides is very similar to that of ammonia, suggesting an ammonia route to the amides. While all the compounds O O show efficient enrichment of the nitrogen-15 label, note particularlyR the nitrile enrichment, which is greater than that observed for ~ ~ ammonia, amides, and the N-heterocyclics. Two possible mechanisms ~ 47~ may account for nitrile formation:
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OSDENE, page 12 .1. Ammonia may be generated at a temperature that enables nitriles or suitable nitrile precursors to be formed. 2. Highly enriched nitric oxide may react with free radicals to give oximes, which on dehydration yield nitxiles. Our study could not distinguish between these 2 mechanisms. ~Note (Table V) that the heterocyclics are enriched to a much lesser extent than the amides or ammonia (Table IV). This is to be expected if one considers,other nitrogen sources such as - alkaloids which would yield similar substances with no nitrogen-15 enrichment whatsoever. Some reactions which yield N-heterocyclics .via ammonia are shown in Fig. 6. Thus, hydroxymethyltetrahydrofuran a ----------------------------------------------------------------- [insert Fig. 6] --- ----------------------------------------------- ---------- can yield pyridine, while acrolein can yield methylpyridine and dimethylpyrazine on reaction with ammonia. Two additional nitrogenous compounds that should be mentioned are nitrous oxide and nitric oxide.' With the oxygen-18 label, we found (as indicated above) that nitrous oxide incorporates 38-65% of atmospheric oxygen and that it is delivered almost exclusively to the-sidestream smoke. Nitric oxide has been studied using the K 15N03 precursor and an enrichment of 85 1SN atom-% was found,5a This is identical to the nitrate enrichment of the unburned tobacco, .- indicating that nitrate is the major precursor of nitric oxide in .smoke. I would now like to turn to the use materials and present some data that can of carb on-14- l.ab e led contribute further to t our understanding of the reactions in the pyrolysis-distillation zone of the burning cigarette.

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