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Chemical Structure| 544-76-3 Chemical Structure| 544-76-3
Chemical Structure| 544-76-3

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Product Details of Hexadecane

CAS No. :544-76-3
Formula : C16H34
M.W : 226.44
SMILES Code : CCCCCCCCCCCCCCCC
English Name :Hexadecane
MDL No. :MFCD00008998
InChI Key :DCAYPVUWAIABOU-UHFFFAOYSA-N
Pubchem ID :11006

Safety of Hexadecane

Application In Synthesis of Hexadecane

* All experimental methods are cited from the reference, please refer to the original source for details. We do not guarantee the accuracy of the content in the reference.

  • Downstream synthetic route of [ 544-76-3 ]

[ 544-76-3 ] Synthesis Path-Downstream   1~14

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YieldReaction ConditionsOperation in experiment
analog verlaeuft die Elektolyse von Gemischen mit den Kaliumsalzen der Chloressigsaeure,der Propionsaeure und der Buttersaeure.Electrolysis;
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YieldReaction ConditionsOperation in experiment
With oxygen; ozone Multistep reaction;
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YieldReaction ConditionsOperation in experiment
With oxygen; ozone 1.) methanol; 2.) methanol; Multistep reaction;
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YieldReaction ConditionsOperation in experiment
91% With sodium tetrahydroborate In water; toluene at 80℃; for 6h;
81% With sodium tetrahydroborate; 1-{6-[dibutyl(chloro)stannyl]hexyl}-3-methyl-1H-imidazolium iodide In methanol; acetonitrile at 80℃; for 36h; Inert atmosphere;
68 % Chromat. With 2,2'-azobis(isobutyronitrile); tris-(trimethylsilyl)silane In toluene Heating;
With hydrogen In n-heptane at 199.84℃; Autoclave;

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YieldReaction ConditionsOperation in experiment
at 70 - 75℃; Electrolysis;
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YieldReaction ConditionsOperation in experiment
und Destillation des Reaktionsprodukts;
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YieldReaction ConditionsOperation in experiment
With Dimethyldisulphide; hydrogen at 363℃; for 120h; 1 Experiment 1; A liquid feed mixture of 69.74 wt% decalin (C10H18), 0.26wt% dimethyl disulphide (DMDS) and 30wt% tallow oil was prepared. The tallow oil comprised fatty acid chains with 12 to 20 carbon atoms (including the carboxyl carbon), the bulk of the molecules having 16 or 18 carbon atoms in the fatty acid chain (including the carboxyl carbon). The liquid mixture was fed to a reactor as illustrated in Figure 4, operating at 363°C and 30 barg (3.1 MPa) pressure, at a feed-rate of 60mL/hour. A cobalt-molybdenum on alumina catalyst was used. The liquid hourly space velocity (LHSV) of the liquid feed over the catalyst was 4 h-1. A flow of hydrogen was also fed to the reactor, such that the ratio of H2 gas volume to liquid feedstock volume was maintained at a value of 200 Nm3/m3 (gas volume at 15.6°C and 1 atm). Reaction was maintained over a period of 5 days. Liquid samples were collected daily and analysed according to a chromatographic method described in ASTM D2887, and also by GCMS. Gaseous off-gas samples were analysed using gas chromatography. The quantity of liquid product was determined gravimetrically. Off-gas volume was measured using a wet-test flow meter. The mass balance calculated from the quantities of the identified components of the obtained liquid and gaseous products was 99% with 1% standard deviation. The carbon balance was 100% with 1% standard deviation.
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YieldReaction ConditionsOperation in experiment
1: 8.59% 2: 11.49% 3: 8.97% 4: 4.71% 5: 1.86% 6: 0.6% 7: 0.17% 8: 1.31% 9: 6.85% 10: 11.49% 11: 10.27% 12: 6.01% 13: 2.59% Stage #1: tri(octadecyl)aluminium; ethene; trioctylaluminum In toluene at 20 - 116℃; for 2.33333h; Stage #2: With sulfuric acid; water at 40℃;
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YieldReaction ConditionsOperation in experiment
2.a Preparation of 2,4-dimethyl-6-sec-hexadecylphenol EXAMPLE 2a Preparation of 2,4-dimethyl-6-sec-hexadecylphenol The preparation is carried out analogously to Example 1.672 g of α-hexadecene (purity: 92%) and 366.5 g of 2,4-xylenol are employed as the reactants. The resulting product is a colourless liquid and is in the form of a mixture of 2,4-dimethyl-6-(1-methylpentadecyl)-phenol and 2,4-dimethyl-6-(2-ethyltetradecyl)-phenol in a ratio of 81/7.
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YieldReaction ConditionsOperation in experiment
With oxygen; ozone In water B Example B; Degradation of benzo[a]pyrene; This example focuses on an integrated treatment of benzo[a]pyrene involving sequential chemical oxidation and biological degradation. The objectives are to: 1) provide mechanistic details in the ozone-mediated degradation of benzo[a]pyrene in the aqueous phase, 2) test the biodegradability of resultant intermediates, and 3) test the feasibility for the coupled chemical-biological treatment of the 5-ring PAH. Batch and packed column reactors were used to examine the degradation pathways of benzo[a]pyrene subject to ozonation in the aqueous phase. After different ozonation times, samples containing reaction intermediates and byproducts from both reactors were collected, identified for organic contents, and further biologically inoculated to determine their biodegradability. The O3-pretreated samples were incubated for 5, 10, 15, and 20 days; afterward biochemical oxygen demand (BOD), chemical oxygen demand (COD), and E-Coli toxicity tests were conducted along with qualitative and quantitative determinations of benzo[a]pyrene, intermediates, and reaction products by GC/FID and GC/MS methods. Prevalent intermediates identified at different stages included ring-opened aldehydes, phthalic derivatives, and aliphatics. The degradation of benzo[a]pyrene is primarily initiated via O3-mediated ring-opening, followed by O3 and hydroxyl radical fragmentation, and ultimately brought to complete mineralization primarily via hydroxyl radicals. Intermediates formed during chemical oxidation were biodegradable with a measured first-order rate constant (k0) of 0.18 day-1. The integrated chemical-biological system seems feasible for treating recalcitrant compounds, while pretreatment by chemical oxidation appears useful in promoting soluble intermediates from otherwise highly insoluble, biologically inaccessible benzo[a]pyrene.Materials and MethodsDescriptions of sections on Chemicals, Analytical Methods and Equipment, and Reactors and Procedures were identical to Example A. Only deviations from Example A are highlighted here. Benzo[a]pyrene (BaP) (98%, Aldrich Chemical Co.) in place of pyrene was used and purified as described. A typical sample size for analysis is 150 ml and the storage temperature awaiting analysis -12° C. With the same GC/MS system, a split ratio of 5:1, solvent delay at 6 min, and scan range from m/z 15 to m/z 500 at 1.4 scan/s were used. Comparison of parent compound structure and interpretation of mass spectra of the intermediates from ion fragmentation information were performed particularly for the identification of key intermediates 7-propanal-8-methylpyrene, 7-ethyl-8-ethanalpyrene, and 4-methyl-5-hydroxylchrysene. Reactor systems (FIG. 1) were identical to ones previously used except that 0.15 g benzo[a]pyrene was prepared and loaded into the packed column reactor. Samples during batch reaction were taken at 2, 10, 20, 30, and 50 min. Sample BOD and toxicity were determined in triplicates and duplicates, respectively. Previous analytical efforts for pyrene were redirected toward benzo[a]pyrene.; Results and DiscussionThe degradation pathway, biodegradability of intermediates, and oxidant balance during ozonation of BaP will be addressed in turn.Degradation Pathways of Ozonated Benzo[a]pyreneCOD measurements were made for three solutions: 1) a saturated aqueous solution of BaP, 2) the solution after ozonation of a batch of excess BaP suspension (0.150 g/10.7 L), and 3) the effluent of a column packed with excess BaP solid (0.149 g) and glass beads (7.5 in. in bed-length). The saturated BaP solution was prepared by allowing excess BaP solid to reach dissolution equilibrium in water overnight followed by removal of the excess solid using a 0.45-μm filter. The ozonated batch solution was obtained after 50 min of ozonation and filtered, while the column effluent was collected from the packed column fed with an ozonated water over a 4-hr period and filtered. Table B-I shows the results COD measurements of all solutions and one BOD5 measurement for the column effluent. The saturated solution of BaP, due to its very limited aqueous solubility, registered a negligible COD value compared to that of the ozonated batch solution or the ozonated column effluent. In both the batch and column solutions, much higher COD values were measured after ozonation, which indicated dissolution of daughter compounds of BaP into the aqueous phase as a result of ozonation. A relativbiochemical oxygen demand ely high BOD5-to-COD ratio of 0.43 was observed for the column effluent, which suggested the intermediates were susceptible to biodegradation, a point of further discussion later.The COD values in the batch solution were relatively stable at about 15 mg/L during the 50-min ozonation period, as shown in FIG. 11. This seemingly steady-state level of COD could be indicative of the relatively constant quantity of intermediates that were continually added to the aqueous phase via oxidation of the parent BaP solid, as well as continually being removed via further mineralization by ozone.The aqueous intermediates after ozonation were identified and quantified by GC/MS techniques. Over sixty compounds were identified as intermediates and products in this example. Table B-II lists the identified compounds in the order of increasing retention time in the GC column, and labels them numerically in the like order. Among the myriad of those identified are five intermediates including ring-opened aldehyde (28), phthalic derivatives (29 and 38), and alkane/alkene (34, 12). These products would likely abound at different stages of ozonation, i.e., with the aldehyde and acid more prevalent in the initial stage of ozonation and the alkene and alkane the later stage.FIG. 12 shows the identified, quantified species during 50-min ozonation of a BaP batch suspension. Salient of this figure is the largely absence, particularly beyond initial minutes, of compounds with longer column retention time (e.g., >20 min; or compound 27 or higher) that are typical of intermediates found in the early stages of ozonation or shortly after ring-opening of BaP. The absence is indicative of further oxidation of early intermediates such as phthalic acids into other products. Furthermore, that those compounds with shorter column retention times (e.g., compound 26 and lower) remained relatively constant over the ozonation period was consistent with the relatively stable COD measurements of FIG. 11 shown for the same period. Long-chain aliphatic alkanes such as compounds 58 to 61 eventually disappeared with ozonation treatment longer than 2 minutes, as they were likely fragmented by secondary free-radical oxidants such as the OH.. Therefore, FIG. 12 indicates a steady-state conversion of the excess BaP solid into more water-soluble intermediates such as aldehydes and acids that are rapidly converted to various alkane and alkene mainly by radical reactions discussed below. That, the reaction rates of oxidants (both O3 and secondary oxidant OH.) with the earlier intermediates such as oxygenated compounds being relatively faster than those with later intermediates such as alkenes and alkanes, would explain the absence of the former intermediates but an abundance of the latter during the seemingly steady-state mineralization.FIGS. 13a and 13b outline (with the top of 13b starting at the bottom of 13a) a general degradation pathway of BaP subject to ozonation in the aqueous phase based on actual identified compounds. In general, the earlier reaction stage is populated with aromatic, oxygenated intermediates, while the latter stage with alkenes and alkanes. In more details, FIGS. 13b and 13c proposed mechanistic steps leading to the formation of various oxygenated intermediates (Sequences I to IV) and aliphatic compounds (Sequences V and VI), respectively. The underlined, numerated species were identified whereas the curly-bracketed ones were proposed intermediates. As shown in FIGS. 13a and 13b, the degradation was initiated by electrophilic attack of O3 on one of the electron-rich conjugate rings of the BaP molecule resulting in the formation ring-opening products 27 and aldehydes 28 and 30. Subsequent reactions of intermediates with O3 or its concomitant oxygenated radicals (e.g., OH., O2.-, O3.-) resulted in additional oxygenated intermediates such as 36, 35, 29, 22, 32, 33. The production of alkenes (e.g., compounds 2, 3, 4, 5, 6, 7, 9, 11, 14, 16, 17, 19, and 21) and long-chain aliphatic alkanes (e.g., compounds 60, 61, 31, 58) was attributed to oxidation reactions prompted by O3, OH., and other free radicals. It should be noted that the formation of secondary radical oxidants including O2.-, O3.-, OH. as well as H2O2 resulting from hydrolysis of O3 has been extensively documented.FIGS. 13b and c explain the formation of observed products (species numbers underlined) via proposed intermediates (shown in curly brackets), many of which have been reported as plausible elsewhere and their reaction steps are cited with italicized numerals. Sequence I of FIG. 13c shows upon ozonation of BaP the formation of 7-methyl-8-prypanal-pyrene (28) via epoxidation at 7,8-bond, followed by bond breakage resulting the aldehyde, followed by further epoxidation at the 9,10-position resulting in the dihydrodiol that further reacts with O3 and with loss of H2O2 ultimately leads to compound 28. The 4,5- and 7,8-bond cleavage products (30 and 28, respectively) were found in this example. These bonds have lowest localization energy and thus are sites most susceptible to epoxide formation.Sequence II produces phthalic anhydride (29) via 1,6-quinione of benzeno[a]pyrene and 1,2-anthraquinonedicarboxylic acid intermediates. Further ozonation of intermediates results in the primary ozonide structure and secondary peroxidic intermediates, phthaladehydic acid, then ultimately phthalic anhydride 29.Sequence III suggests that continued ozonation of phthalic anhydride 29 leads to identified intermediates 35 and 36 via phthalic acid and its radical that subsequently recombines with other alkyl radicals. The breakage of fragile R-O bonds in 35 and 36 further leads to 32 and 33. Ozonation of phthalic anhydride 29 can also cleave the molecule at the 1,2-position, resulting in a primary ozonide structure. Alternatively, Sequence IV suggested continued ozonation of phthalic anhydride leads to a primary ozonide and peroxidic intermediates (as in Sequence III), followed by loss of -CO2 and -CO groups resulting in the formation of 1,3-diene intermediate, which upon renewed O3 attacks as shown leads to the formation of ester 22.Sequence V of FIG. 13d shows ring-opening products as phthalic acid derivatives, which upon OH. attack form alkene radicals. These radicals undergo additional free-radical reactions with other alkene fragments, and their eventual radical recombinations lead to alkene products such as 7 and 19. Appearing prima facie puzzling was an abundance of alkenes and alkanes observed amid the panoply of oxidized products in the ozonated, highly oxidizing environment, which might have suggested them products of reduction reactions. Similar products were observed in Examples A for the ozonation of pyrene. Other alkanes, alkenes, and related compounds were previously observed as products from ozonation of hydrocarbons as well. Nonanal and nonanoic containing straight chain carbons were reported as oxidation products from ozonation of PAHs (20, 21). Decane, decene, and epicosane were obtained from ozonation of 1-dodecene (38). These aliphatic compounds were attributed to free radical mechanisms at work. It is well accepted that as O3 undergoes hydrolysis during ozonation, both O3 and OH. are available for reactions with species in the reaction medium. Sequence VI proposes a polymerization pathway for the formation of long-chain alkanes by the actions of O3 and OH. radical. As shown, it is initiated by ring opening of intermediates such as 29, followed by fragmentation into ethene and diene that undergo ionic and/or radical polymerization in the presence of OH., resulting in identified alkanes such as tridecane (34) and henicosane (61).An observation supporting the involvement of free radicals was the disappearance of these long-chain alkanes if the effluent was subject to prolonged ozone hydrolysis. Long-chain alkanes are characteristically resistant to electrophilic attack by O3 yet susceptive to degradation by OH. produced via O3 hydrolysis. Simpler short-chain polar aliphatic compounds were expected but not found in the reaction mixture; their absence was attributed to analytical extraction and preparation procedures that failed to retain compounds with less than six carbons.As already mentioned, the presence of organic co-solvent and the concentration of O3 play an important role in determining product formation and distribution.In summary, this example demonstrates that the degradation mechanism of BaP is, as reconstructed based on about 60 observed intermediates and products, initiated primarily via ring-opening by O3 at the onset, continued in fragmentation by both O3 and OH., and ultimately brought to complete mineralization primarily via OH. radicals.
YieldReaction ConditionsOperation in experiment
for 120 - 480h; A Biodegradation of Ozonated Column Effluent; The biodegradability of the ozonated column effluent was tested by incubating the effluent over a 20-day period throughout which the COD and BOD of the flasks were monitored. FIG. 8 shows the measurements taken after 0, 5, 10, 15, and 20 days. The results indicated an increase of BOD from 0 to 4.2 mg/L during the first 10 days and leveling off over the remaining. The measured COD exhibited a complimentary curve showing a decrease in COD from 7.0 mg/L to 3.1 mg/L over the first 10 days and a constant level afterward. These results suggested that biodegradable organic compounds in the effluent were biodegraded over the first 10 days. The BOD curve was fitted with first-order kinetics using the least-square method with a first-order rate constant k0=0.243 day-1 and an ultimate BOD L0=4.25 mg/L. The obtained value of k0 approximates closely that of domestic wastewater routinely treated by biological unit processes.The acute aqueous toxicity during the 20-day incubation period was also monitored using a standard effluent toxicity test (HACH, 1988-1995b). FIG. 9 shows the percentage inhibition value (% inhibition) of the incubated samples over the same intervals. The measurements registered inhibition values within +/-10% that was within the nontoxic range of the method. This means that the effluent was nontoxic to the receiving E-Coli bacteria, and that the effluent contained biodegradable intermediates and byproducts, including biodegradation products, which possessed no acute toxic effects to the bacteria.Concurrent to measurements of COD, BOD, and toxicity was the GC/FID/MS identification of various intermediates and byproducts present in the flask over the same incubation period. FIG. 10 shows compounds found after 0, 5, 10, 15, and 20 days of incubation. The changes of speciation in the incubated effluent are more clearly tracked by Table A-III. The disappearance of 11 intermediates, including species 1, 3, 7, 8, 10, 13, 15, 16, 19, 21, and 22, during the first 5 days of incubation was most notable. Dissolved parent compound pyrene (1) and intermediates dialdehyde (2), tetraaldehyde (3), and other benzenedicarboxylic acids either disappeared or decreased in concentrations over the incubation period. The significant disappearance of many intermediates in the first 5 days is consistent with the much more rapid changes in BOD and COD during the initial period. After 5 days, virtually all other compounds remained detectable throughout the incubation, which signaled that these compounds could not be further biodegraded, consistent with relatively mild changes in BOD and COD. Also detected after 15 and 20 days was the phosphoric acid tributyl ester with a structure similar to high-energy phosphoanhydride bonds, which indicated that biosynthesis of ATP might have occurred along with the biodegradation processes.
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YieldReaction ConditionsOperation in experiment
With oxygen; ozone In water for 0.25 - 2h; A Example A; Degradation of pyrene; This example focuses on an integrated approach for the degradation of pyrene involving chemical oxidation followed by biological treatment. The objectives were to: 1) provide mechanistic details in the degradation of pyrene subject to ozone treatment, 2) test the combined technique of ozone pretreatment followed by biological degradation, and 3) test a pretreatment column to promote efficient use of chemical oxidants and biodegradability. Batch and packed column reactors were used to examine the degradation pathways of pyrene subject to ozonation in the aqueous phase. After different ozonation times, samples containing reaction intermediates and byproducts from both reactors were collected, identified for organic contents, and further biologically inoculated to determine biodegradability. The O3-pretreated samples were incubated for 5, 10, 15, and 20 days, after which biochemical oxygen demand (BOD), chemical oxygen demand (COD), and toxicity tests along with qualitative and quantitative GC/FID and GC/MS analyses of pyrene, intermediates, and products were performed. Intermediates identified at different stages included 4,5-phenanthrenedialdehyde, 2,2',6,6'-biphenyltetraaldehyde, and long-chain aliphatic hydrocarbons, which suggested that the degradation of pyrene was initiated by O3 via ring cleavage at the 4,5- and 9,10-bonds and that further oxidation ensued via reactions with both O3 and OH. until complete mineralization. Intermediates formed during chemical oxidation were biodegradable with a measured first-order rate constant (k0) of 0.243 day-. The integrated chemical-biological system appeared to be feasible for treating recalcitrant compounds, and a chemical pretreatment column was particularly useful in promoting soluble intermediates from otherwise highly insoluble, inaccessible pyrene.Materials and MethodsChemicalsOzone (1% w/w ozone in air) was generated from filtered, dry air by an ozonator (Model T-816, Polymetrics Corp.). Pyrene (99%, Aldrich Chemical Co.) was washed with distilled-deionized (DD) water three times, extracted by dichloromethane (DCM), and the solvent evaporated by a gentle stream of nitrogen gas. Stock and working indigo blue solutions were prepared from potassium indigo trisulfonate (C16H7N2O11S3K3, Aldrich Co.) per Standard Methods (APHA et al., 1992a). Polyseed (Hach Co.) was used in dilution water for biochemical oxygen demand (BOD) measurements per Standard Methods (APHA et al., 1992b). Inoculum for toxicity test was prepared according to a Hach method (HACH, 1988-1995b). COD digestion solutions (0-15,000 mg/L, 0-40 mg/L range, Hach Co.), ToxTrak reagent powder pillows, and ToxTrak accelerator solution (Hach Co.) were purchased and used according to the manufacturer's methods without further processing. Low-organic (<15 ppb as TOC), low-ion (resistivity>18 MΩ-cm), and non-pyrogenic (up to 4-log reduction with reverse osmosis pretreatment) DD water was used in all procedures (4-stage Mill-Q Plus system, Millipore Co.). Dichloromethane (Fisher Scientific) of HPLC grade was used in liquid-liquid extraction procedures. Other chemicals used in this research were of reagent grade.; Results and Discussion; Ozonation of pyrene was carried out in batch and column reactors to study: 1) the effect of reactor on intermediates and products formation, 2) the degradation pathway of pyrene under ozonation, 3) the biodegradability of intermediates, and 4) the feasibility of a combined chemical-biological treatment system for pyrene. Reaction solutions during ozonation and biodegradation processes at different stages were collected and the intermediates and byproducts identified by GC/MS techniques.1. Effects of the Reactor Type on Intermediates and Products FormationTo delineate the influence of reactor configurations on the formation of intermediates and products, ozonation experiments using aqueous and excess pyrene were carried out in batch and packed column reactors. BOD5 and COD were measured for three ozonated, filtered solutions: 1) a saturated aqueous solution of pyrene (0.13 ppm), 2) the solution after ozonation of an excess pyrene suspension (1 g/1.7 L), and 3) the effluent of a column packed with excess pyrene solid (1 g) and glass beads (7.5 in. in bed-length). The saturated pyrene solution was prepared by allowing excess pyrene solid to reach dissolution equilibrium in water overnight followed by removal of the excess solid using a 0.45-μm filter. The ozonated batch solution was obtained after 10 min of ozonation and filtered, while the effluent was collected from the packed column fed with ozonated water over a 4-hr period. Table A-I shows the results of BOD5 and COD measurements. The BOD5 for the saturated pyrene solution approximates over 80% of the COD value, suggesting that pyrene in its dissolved form is amenable to biodegradation, albeit in small quantity. The aqueous phase COD from the ozonated batch reactor increased after ozonation possibly due to occurrence of intermediates or pyrene-derivatives that are more soluble in water as a result of ozonation. The new, lower BOD5/COD ratio of 66% appeared to suggest either that a larger amount of degradable substrates was available after ozonation that resulted in lower BOD5, or more likely that the biodegradability of the ozonated solution decreased as a result of ozonation possibly due to formation of slightly more recalcitrant intermediates. Following the reasoning of increased aqueous COD due to abundance of more soluble intermediates, the measured COD for column effluent would imply that it contained much more intermediates and byproducts. The new BOD5/COD ratio registered a slightly smaller value of 0.53. These ratios are well within those commonly observed for domestic wastewater and do not seem to signify toxicity.Parallel to BOD5 and COD measurements of the ozonated reaction media, the effects of reactors on intermediates formation were further probed using GC/FID and GC/MS identification techniques. FIG. 2 shows the gas chromatograms of parent and identified intermediate compounds in 1) the aqueous pyrene solution without ozonation, 2) ozonated column effluent, and 3) ozonated batch solution. Despite its low solubility, the parent pyrene (peak 1 as labeled) was found in all solutions. As listed in Table A-II, twenty-five other compounds were found in the column effluent, and except for two of them were identifiable by MS library comparison. Two important intermediates 4,5-phenanthrenedialdehyde (species 2) and 2,2',6,6'-biphenyltetraaldehyde (species 2) were found in the ozonated column effluent but not in the ozonated batch solution. The mass spectra of these two intermediates, species 2 (m/z 234) and 3 (m/z 266), are shown in FIGS. 3(a) and (b), respectively.In the ozonated batch solution, found in place of the di- and tetra-aldehydes was a variety of benzenediacarboxylic acids, which apparently are subsequent byproducts in the oxidative chain of events. Comparison of gas chromatograms (b) and (c) of FIG. 2 shows that the column effluent contained an abundance of intermediates (such as species 2 and 3) whereas the ozonated batch solution contained less intermediates but more fragments that were products further down the degradation process. These identifications are consistent with the higher COD measurement in the column effluent than that in the batch solution.These results indicated that ozone was capable of degrading pyrene via ring opening, as evidenced by intermediates dialdehyde and tetraaldehyde (species 2 and 3 in the column effluent), and further oxidation by ozone (and other oxygenated radicals to be discussed) to other fragments and byproducts (such as 1,2-benzenedicarboxylic acid, diisooctyl 4, benzylbutyl phthalate 5, hexacosane 23, henicosane 20, and nonyl phenol 13 in the batch solution) if the intermediates were to remain exposed to ozone. These results underscored the importance of the role that the reactor configuration played in determining the kinds and amounts of intermediates and byproducts to be found after ozonation. The influence of a column reactor on the types and amounts of intermediates and byproducts formed are illustrated in FIG. 4. A batch reactor readily subjects the intermediates from pyrene to continual O3 attack and further degradation, whereas the column reactor allows the intermediates to be eluted from the O3-rich area, i.e., the reactive zone. Thus, to promote the formation of intermediates that could be subsequently biodegraded rather than relying upon ozone as the sole oxidant in the complete degradation of pyrene, a column reactor was used to collect effluent that was rich in partially treated intermediates for further mechanistic and biodegradability studies.Degradation Pathway of Pyrene in Ozonated WaterThe effluent from a pyrene-packed column fed with ozonated water was collected and identified for intermediates and byproducts via GC/FID and GC/MS. The up-flow influent water contained 5 mg/L O3 while the effluent none, indicating that complete consumption of O3 occurred in the column. The filtered (through 0.45 μm) effluents exhibited yellowish intermediate compounds that were not apparent in previous samples from ozonated batch solutions. The absence of colored compounds in the batch reaction was attributed, as explained previously, to continual degradation of the colored intermediates by O3. FIG. 5 identified species found in the effluents collected at different time intervals. These identified species, including the dialdehyde (2) and tetraaldehyde (3) intermediates, resembled those identified in FIG. 2. In addition to the molecular ion peaks, other fragments including m/z 205, 176 and 29 corresponding to the loss of -CHO groups were noticeable in the mass spectra in the case of 4,5-phenanthrenedialdehyde, and m/z 237, 29 of 2,2',6,6'-biphenyltetraaldehyde. A biphenyl fragment was found at m/z 152 in FIG. 3(b), which suggested the presence of a biphenyl structure as 2,2',6,6'-biphenyltetraaldehyde.FIG. 2a showed a substantial variety of (unozonated) compounds eluted from the column even prior to the start of ozonation. These compounds were in many cases similar to that after ozonation as shown in FIG. 5a. This was attributed to the occurrence of autooxidation (reaction with molecular oxygen), which is also an oxidation process albeit at a much slower rate than of oxidation by ozone, resulting in similar intermediates and products. Autooxidation of pyrene could have occurred during storage on the shelf or by dissolved oxygen after being dispersed and thinly packed in the column. The latter was more likely as calibration runs prior to column loading did not reveal the intermediates. However, clearly discernable was that these intermediate and product peaks intensified pronouncedly after the ozone oxidant was introduced, as evident in comparison of FIG. 5a with FIG. 2a. Data estimation suggested that oxygenated compounds such as 5, 8, 9, 11, 12, 13, and 16 increased by 1290%, 1160%, 690%, 1130%, 60%, 20%, and 200%, respectively, while aliphatic compounds such as 17, 18, 20, 22, 23, and 24 increased by 410%, 1410%, 3530%, 3530%, 2670%, 4140%, respectively.FIG. 6 identified intermediates found in ozonated column effluents collected by more frequent samplings. The gas chromatograms as shown focused on species with retention times of 40-50 min, which consisted mainly of pyrene, 2,2',6,6'-biphenyltetraaldehyde (2), 4,5-phenanthrenedialdehyde (3), and 1,2-benzenedicarboxylic acid, diisooctyl (4). In addition to these major species, spectrum (b) of FIG. 6 also identified long-chain aliphatic carbon compounds, including C21, C22, C23, C24, C25, and C26, shown as species 5 to 10, respectively. These long-chain hydrocarbons disappeared as the column effluent established steady-state levels of intermediates; henceforth only four major intermediates (1 to 4) remained after 45 min., as shown by chromatogram of FIG. 6(c). The presence of long-chain aliphatic hydrocarbons that have more carbons than the 16-C pyrene parent is suggestive of, during ozonation, the involvement of free-radical pathways in which radical recombinations are prevalent. The decomposing of O3 in water is known to occur through a series of free radical chain reactions that involve reactive radicals including OH./O.-, HO3./O3.-, and HO2./O2.. These reactive radicals are potent oxidants that can react with organic molecules leading to their mineralization.With identified intermediates and byproducts, in FIGS. 7a and 7b (the top of 7b continues from the bottom of 7a) is shown a proposed mechanism depicting the degradation pathway of pyrene under ozonation. As shown, the degradation was initiated by electrophilic attack of O3 on one of the electron-rich conjugate rings of the pyrene molecule resulting in the formation of dialdehyde (2) and, upon another ring-opening attack, tetraaldehyde (3). Pyrene has an asymmetrical fused-ring structure. The bonds between fused angular rings, as in 4,5- and 9,10-bonds (referred to as the K-regions), have the highest bond order (0.833) and shortest bond length (1.367) in the pyrene molecule (Harvey, 1997). These bonds show considerable double-bond character and are more reactive than other bonds, consistent with K-regions being the first activated reaction sites in metabolic oxidation. The preferential attack of O3 on the 4,5-bond of the pyrene molecule is also explained in terms of localization energy that marks the site as being most reactive (Bailey, 1982). Subsequent reactions of intermediates with O3 or oxygenated radicals (e.g., OH., O2.-, O3.-) resulted in additional intermediates (4)-(16). The production of long-chain aliphatic hydrocarbons, compounds (13) through (25), was attributed to oxidation reactions prompted by O3, OH., and other free radicals. With proposed intermediates and identified ones, FIGS. 7c and 7d details the formation and destruction of some of these compounds based on known reaction pathways reported in the literature. As shown, these reactions produced alkyl radicals that further propagated chain reactions and eventually led to polymerization via recombination of the organic radicals. Thus, the formation of many oxygenated intermediates (4, 7, 9, 12, 14, 16) as well as n-alkanes (19, 22) could be accounted for by FIGS. 7c and 7d. Another observation supporting the involvement of free radicals was the disappearance of these long-chain alkanes if the effluent was subject to prolonged ozone hydrolysis. Long-chain alkanes are characteristically resistant to electrophilic attack by O3 yet susceptive to OH. oxidation. Simpler short-chain polar aliphatic compounds were expected but not found in the reaction mixture; their absence was attributed to analytical extraction and preparation procedures that failed to retain compounds with less than six carbons. As O3 undergoes hydrolysis during ozonation, both O3 and OH. are available for the degradation of pyrene. It is plausible that the degradation pathway is initiated mainly via ring opening by O3, continued in fragmentation by both O3 and OH., and ultimately brought to complete mineralization primarily via OH. radicals.
 

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