INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
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TABLE 111. COMPARISON OF REACTIVITY INDICES Volatile Matter (d.a.f.),
' C. 2b 30 289 274 10.8 292 242 232 18 2 238 220 228 228 22 0 228 227 221 25.6 227 226 26.0 226 226 220 28.9 225 226 31.8 225 218 214 217 218 35.0 217 229 227 37.1 204 212 212 38.2 212 216 217 39.0 Calculated on the basis of the first-order law. Calculated on the basis of Equation 1. Directly observed in the adiabatic test. Tis,
%
la
.
a b c
1
374 286 264 267 264 258 250 206 283 251 258
Tis, O C. 2 384 293 276 279 277 269 272 269 296 265 274
3 371 294 281 277 286 281 273 268 270 253 272
original objective of measuring self-heating rates, with no heat exchange between the sample and its surroundings, has been a p proximately achieved. A choice between the two types of apparatus cannot be easily made. The adiabatic equipment (a) is more difficult to fabricate and involves complex control equipment, .(b) requires more skill in operation, as errors in adiabatic control cannot be detected later except by poor reproducibility of reactivity indices, but (c) provides data on the self-heating rate over an extended temperature range in a single gas, and (d) does so with approximately the same time per run but is ready for the next run within less than a half hour. The older equipment (a) is comparatively simple and requires only that the desired input voltage be held reasonably constant, ( b ) requires little skill beyond that needed to operate a potentiometer on a time schedule, (c) gives only one rate at one temperature for each of two gases, and ( d ) requires several hours cooling time between runs unless special means are provided for cooling the massive furnace. The amount of calculational work is roughly the same for either test. The particular advantage of the adiabatic procedure is that it yields additional information without any appreciable change in the time requirement and, if assistance is available for calculations, can be conveniently used for another determination within a few minutes. Duplicate determinations in one gas, sufficient to obtain checks on both TUand Tn, requires 4 to 5 hours of work. Whatever choice of equipment and procedures might be made, there remains a question as to the practical significance of the test. The reactivity indices are of importance to high temperature processes, where mass transport by diffusion and
Vol. 40, No. 3
convection become rate-controlling factors, only in so far as they indicate the temperature levels at which mass transport assumes control. For study of such systems as well as low temperature processes, ahere the reactivity indices are generally applicable, Equations 2 and 3 may be sufficiently precise, although some deviations from these equations exceed the precision of measurement. The Coal Research Laboratory reactivity test, in either form, is quite useful as a research tool for studying the reactions between fuels and oxidizing gases; but it cannot be recommended as a commercial test unless it can be shown that more precise estimates of the reactivity indices are needed than can be obtained by means of Equations 2 and 3. Until such a need is demonstrated, rather than refine the test further, it would appear more profitable to search for other properties of the fuels which are more easily determined and from which the reactivity indices might be calculated. The volatile matter content is correlated with many other properties of fuels which might show more precise relations. SUMMARY
1. A modified apparatus and procedure for the determination of the reactivity indices of solid fuels has been described which La based on the measurement of self-heating rates while adiabatic conditions are maintained over an extended temperature range. 2. It was found that the reaction between coals and oxidizing gases was not first order with respect to the partial pressure of oxygen. The order varied with temperature. Since the limited temperature range within which observations could be made was found a t lower temperatures for fuels of decreasing rank, the order varied from approximately one for cokes and anthracites to nearly zero for lignites. 3. The approximate correspondence of data obtained in two distinctly different types of equipment lends confidence in the reactivity indices as measures of intrinsic properties of the fuel independent of the apparatus. 4. The reactivity test is recommended as a research tool for studying the reaction between fuels and oxidizing gases, but not as a commercial test until the value of the reactivity indices in r e lation to commercial application can be demonstrated. LITERATURE CITED (1) Elder. J . L.. Schmidt. L. D.. Steiner. W. A,. and Davis. J. D..
Am. Gas Assoc. M o n t h l ~27, , 411-5 (1945); U.S.Bur. Mines, Tech. Paper 681 (1945). (2) Oming, A. A., ISD.EKG.CHEAL, 36, 814-6 (1944). (3) Rees, 0.W., and Wagner, W.F., Ibid, 35,346-8 (1943). (4) Sebastian, J. J. S.. and Navers. hl. A.. Ibid.,29, 1118-24 (1937). (5) Sherman, R. A,, Pilcher, J. M., and Ostborg, H. N., Am. SOC. Testing Materials, Bull. 112,23-34 (1941). RECEIVED September 30, 1946.
ROBERT F. TAYLOR ASD G. H. MOREYl Commercial Solvents Corporation, Terre Haute, Ind. LTHOUGH the polymerization and copolymerization of butadiene have been studied extensively, relatively little attention has been given to its potentialities as a chemical raw material. Early in 1941 an investigation of the reactions of butadiene rras begun in this laboratory, and during the course of this work a simple method was developed for the production of 3,4-dichloro-l-butene and 1,4-dichloro-2-butene by the vaporphase chlorination of butadiene. Three methods for carrying out this reaction are described in the literature. Muskat and 1
Present address, Glae-Col Apparatus Company, Terre Haute, Ind.
Northrup ( 4 ) obtained aImost quantitative yields of the isomeric 'dichlorobutenes by chlorinating butadiene at low temperatures in dilute chloroform solutions. Rearne and LaFrance ( 8 ) carried out the reaction at temperatures above 150" C. in the absence of a liquid phase. They found it necessary t o use not less than 2 moles of olefin per mole of chlorine in order to obtain good yields. Other workers (3)used an inert gaseous diluent and maintained the temperature of the reaction zone between -20" and C20"C. I n the work which was done in this laboratory, the chlorination was carried out between 60' and 140" C. with various ratios !o
March 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
In the vapor-phase chlorination of butadiene at 65" to 75" C., the highest conversions and yields of 1,4-dichloro-%butene and 3,4-dichloro-1butene are obtained with a chlorinebutadiene mole ratio of 1.1 to 1.2. The principal side reaction is substitution Qf chlorine into butadiene, and this reaction is not inhibited by oxygen. The use of carbon dioxide as a diluent does not increase the yield of dichlorobutenes. A surface-volume ratio of 0.16 sq. mm. per cu. mm. is necessary for complete reaction in the vapor phase. The other products of the reaction are high boiling materials including two trichlorobutenes.
Figure 1. Side View reactants and in the presence and absence of Chloriof diluent gases. The results obtained led t o nation Apthe conclusion that the highest yield of the paratus isomeric dichlorobutenes may be obtained by chlorinating butadiene at 65" to 75" C. in the absence of diluents with a chlorine-butadiene mole ratio of approximately 1.2. APPARATUS AND PROCEDURE
433
diene w&s begun first, the chlorine was turned on within 30 seconds, and consequently there was little excess butadiene present. The total flow of reactants varied between 1.05 and 1.25 moles per hour, with the proportion of chlorine to butadiene adjusted according to the ratid desired in any particular run. The initial temperature reading was taken as soon as the flow of reactants was started, and readings were continued at 15minute intervals throughout the run. Each time, the temperature was read at the point a t which the flow of gases converged and a t three evenly spaced intervals between this point and the side wall of the reactor. Between readings the thermocouple well was withdrawn from the reaction zone to eliminate any wall effect it might have. Runs were continued for 31/2 to 4 hours to give approximately 250 grams of reaction product. At the end of the run, air was hour to sweep out the repassed through the apparatus for sidual hydrogen chloride and butadiene. The butadiene trap was disconnected and weighed, and the product receiver was detached from the condenser. A stopper holding a capillary tube was inserted in the neck of the receiver. and a slow stream of air was drawn through the reaction product and into the caustic wash bottles for hour to remove traces of hydrogen chloride dissolved in the product. The scrubber solution was then titrated, and hydrogen chloride was determined by difference. The liquid reaction product was distilled under reduced pressure to give 3,4-dichloro-l-butene and 1,4dichloro2-butene. Since early experiments had shown that the higher boiling products decomposed when distillation was attempted, the distillation was stopped when the dichlorobutenes had been removed and the residue was weighed and analyzed for chlorine. The dichlorobutenes were identified by physical constants and chlorine analyses, Essentially the same procedure was followed in the experiments summarized in Tables 11, 111, and IV, except that straight-walled, water-jacketed tubes were. used in place of the bulb reactor shown in Figure 1. The reactor used in the experiments reported in Tables I1 and I11 was 62.5 em. in 'Figure 2. Delength and 2.5 em. in inside diameter, tail of Mixing and those used for determining the opHead
-
Figure 1 shows the essential parts of the apparatus used for the experiments on the chlorination of butadiene which are summarized in Table I. The reactor consisted of a 2-liter flask to which had been sealed a condenser and a ground-glass connection for the gas mixing head. A thermocouple well was inserted through a short glass tube on the side of the flask. It was held in place by a section of rubber tubing which permitted it to be moved to various points within the reactor or withdrawn from the reaction zone during the period between temperature readjngs. The gas-mixing head (Figure 2) was constructed in such a way that the gases met a t a right angle 1 em. from the tips of the jets and slightly above the, center of the reaction bulb. The flows of chlorine and butadiene were measured by flowmeters attached to the top of the head by ground-glass joints. Raw materials of commercial grade were used in all experiments since preliminary tests had shown that purification of the chlorine and butadiene did not affect the results obtained. At the beginning of each run the flowmeters were adjusted and the apparatus was purged with air. A receiver of convenient &e was then attached to the . TABLE I. EFFECT OF C11/C4HaRATIO ON YIELD OF DICHLOROBUTENES AT 65' TO 75" c. bottom of the product condenser, and the outlet from this receiver was connected with an iona, Yield4 of total Chlorine, absorption train designed to Mole C4H6 % of Input Reacted % % 7roduot % recover excess reactants and 54.3 62.4 15.4 0.22 1 0.55 0.60 0.92 55.93, 12.9 62.3 71.8 18.8 0.21 2 0.58 13.2 0.60 0.97 gaseous products. The absorp64.0 70.3 18.8 0.19 .. 3 0.60 0.60 1.00 9.0 tion train consisted of two 65.1 70.2 21.5 0.21 .. 4 0.63 0.60 1.05 7.3 6 7 . 7 0 . 1 8 5 0 . 6 5 4 . 5 0 . 6 0 1 . 0 8 wash-bottles containing stand7 50 . 9 6 21 08 . 58 62:3 73.3 0.20 6 0.55 3.0 0.50 1.10 76.5 78.9 19.0 0.21 62.9 7 0.56 0.50 1.12 3.0 ard sodium hydroxide solution 7 4 . 9 7 6 . 8 2 1 . 2 0 . 2 2 63.8 8 0.58 0.50 1.16 2.5 to remove hydrogen chloride, 75.7 0.20 64.1 77.3 21.8 0.62 0.53 1.17 9 2.1 7 4 . 2 7 5 . 4 2 4 . 0 0 . 2 2 64.9 0 . 6 0 10 0.50 1.20 1.6 a drying tube, and a trap cooled 76.7 77.5 24.4 0.21 66.3 11 0.61 0.50 1.22 1.1 7 1 . 4 66.4 7 2 . 4 2 8 . 2 0 . 2 2 12 0 . 6 3 0 . 5 0 1 . 2 6 1.4 in a n acetone-solid carbon 65.0 38.3 0.24 63.7 65.0 13 0.65 0.49 1.33 2.0 dioxide bath to condense un5 Based on butsdiene. reacted butadiene. b A small amount of hydrogen chloride was released before the distillation was stopped. Although the flow of buta-
..
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
434
timuni surface-volume ratio (Table IV) were of the same length, but t,he inside diameter varied as indicated. Cooling water was used in t,he jackets of the reactors in all runs reported in Tables 11, 111, and IV, except those in Table I1 vihich were made at, 135" to 140' C. The cooling had little effect on the reaction temperature in the 2.5-cm. reactor since an unjacketed tube of the same diameter gave nearly the same results, but cooling condensed the reaction products and removed them from t,he reaction zone. The higher temperature was reached when the reactor was insulated from the surrounding atmosphere by draining t'he jacket and allowing it to serve as a dead air space. Temperatures n w e measured in these runs by means of a thermocouple in a well which extended from the top of t,he mixing head (Figure 2 ) to a point betn-een the jet,s where the gases mixed. It \vas recognized that this arrangement introduced surface into the reaction zone, and consequently the mixing head v a s only used in experiments made to determine the temperature of reaction. The runs reported in the tables were made with the mixing head a5 shown. When air, oxygen, or carbon dioxide was used (Tables I1 and 111),the gas was measured by a floivmeter and introduced into the gas stream through a three-way stopcock in the chlorine line. The products and unreacted butadiene were recovered a3 indicated previously. The hydrogen chloride in the efflueiit gases from the receiver was removed by scrubbing with caustic solution, but no attempt was made to determine the quantity evolved in these runs except in three runs reported in Table 11. CHLORIXE-BUTADIEYE MOLE RATIO
A11 of the earlier studies of the chlorination of but,adiene (2, 3,4)indicated t,hat an escess of butadiene \vas necessary if good yields of dichlorobutenes uere to be obtained. For t'his reason several preliminary experiments were run with a mole ratio of chlorine to butadiene as low as 0.5. Increasing this ratio did not reduce the yield of dichlorobutenes, and it' \vas soon observed that when the reaction was carried out at 60' to 75' C., the highest conversions and yields were obtained when an excess of chlorine was present. The results of a series of experiments in which the chlorine-butadiene mole ratio was varied from 0.92 to 1.33 are summarized in Table I. Since the two isomeric dichlorobutenes, 3,4-dichloro-l-butene and 1,Cdichloro2-butene, were formed in almost equal proportions, only the total yields and conversions are report,ed. It may seem surprising that the maximum conversions t o dichlorobutenes were obtained in runs 6 to 12 where excess
TABLE11. EFFECTOF AIR L. Air/ L. C I H ~ Temp., C. 0 70- 75 0.15 70- 75 0.37 70- 75 0.370 70- 75 135-140 0 0.01 135-140 135-140 0.10 a Oxygen used instead of air.
ON
Vol. 40, No. 3
chlorine was present, but this observation is easier to understand lvhen it is noted t,hat approximately 0.2 nnok of hydrogen chloride was evolved per mole of but#adiene reacting, regardless of the mole ratio of chlorine to butadiene. The hydrogen chloride might have been formed by substitution of chlorine in either butadiene or the dichlorobutenes. In the case of butadiene, monochlorobut,adienes would be formed as primary substitution products, and these compounds could add chlorine t,o form trichlorobutenes. If t,he substitution reactions involved the dichlorobutenes, tiichlorobutencs would be formed directly, Seither of the isomeric monochlorobutadienes was ever identified among the reaction products even Tvhen hydroquinone was added to the product receiver to inhibit polymerization during distillation, but the fact that the proportion of hydrogen chloride formed did not vary with the yields of dichlorobutenes suggest's strongly that the substitution reaction involved butadiene. The chlorine analyses of the distillation residue aft,er the dichlorobutenes had been removed also shored that compounds having less chlorine than trichlorobutenes (Cl = 66.7T0) were present. Thus, the substitution reaction could not have involved the dichlorobutenes exclusively if it involved t,hcm at allz. Since significant quantities of butadiene mere rwovered in several runs vihile no monochlorobutadiene was ever found among t'he reaction products, it is apparent that monochlorobutadiene adds chlorine more rapidly than does but,adiene itself. If this be the case, an additional mole of chlorine ehould be required for each mole reacting by substitution, and maximum conversion to dichlorobutenes should be obtained when the excess of chlorine equals the amount of hydrogen chloride evolved on a molar basis. The data in Table I show this supposition t o be correct. Test,ing the effluent gases with moist starch-potassium iodide paper showed that all of the chlorine was reacting. EFFECT OF OXYGEX AND DILUENTS
Rust and Vaughan (6) pointed out that two types of substitution may take place in the vapor-phase reaction of chlorine with unsaturated hydrocarbons. One type involves a chain reaction and is inhibited by oxygen, whereas the other goes through a bimolecular association and is not inhibited. The data in Table I1 indicate that, in the chlorination of butadiene at 70' to 75" C., the substitution is of the latter type since the evolution of hydrogen chloride was not decreased by the presence of air or oxygen. If it be assumed that substitution is also the principal side reaction at 135" to 140" C., the fact that in this temperature range the yield of dichlorobutenes was increased by the use of air as an inhibitor suggests that part of the substitution at least took place by a chain mechanism. Previous workers (3) stated that, a t temperatures below 20 C., the yield of dichlorobutenes was increased by using an YIELDOF DICHLOROBUTENES inert diluent with the reactants and that as the temperature Yield CIHRC~Z, Mole HC1/ was raised the proportion of the diluent should be increased. Mole CaHe % The present authors have found that, in the temperature range 70.0 in which they operated, the use of carbon dioxide in the reaction 70.5 71.5 mixture not only did not increase the yields of the dichloro70.5 15.6 butenes, but actually caused a decrease (Table 111). 36.2 ... ...
50.8
SURFACE-VOLUME RATIO
It has been shown (6) that the presence of a liquid phase proOF COz o s CHLORIXATION OF BUTADIENE motes addition reactions, and the formation of tetrachloroTABLE 111. EFFECT AT 65" TO 75" C. butanes in some early experiments suggested that the reactor (C~Z/CIHB mole ratio = 0.80) was not large enough to permit complete reaction in the vapor Yield phase, Several runs were made in straight-walled, waterC~Hsclz, 70
50.3 53.8 57.3 66.0 70.8
2 One of the reviewers of this paper has suggested that chlorine may have catalyzed the polymeriration of butadiene or i t s chlorinated derivative@. Undoubtedly polymerization did occur, particularly in those runs in which relatively less butadiene wan used, since the distillation residues contained materials boiling higher than would be expected for trichlorobutenes but which contained less chlorine than the trichlorobutenes.
.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
435
OTHER PRODUCTS
In addition to the dichlorobutenes the reaction product obtained by the chlorination of butadiene contained from 20 to 85% Yield of Dichlorobutenes of higher boiling materials. It has been pointed out that t,he Surface-Volume Reactor walls Reactor wall8 chlorine analyses of the residues from which the dichlorobutenes Diam. of Ratio, Sq. Mm./Cu. not washed, washed, Reactor, Mm. Mm. % % had been distilled approached the theoretical for trichlorobutene 7 0.57 30.2 54.9 In the runs made with a low chlorine-butadiene mole ratio, the 11 0.36 43.6 69.7 residues were dark in color and decomposed, releasing hydrogen 25 0.16 76.9 76.9 11 Packed 41.0 .. chloride when distillation was attempted even a t very low pressures. As the chlorine-butadiene r h o TABLE V. PROPERTIES OF TRICHLOROBUTENES FROM DISTILLATION RESIDUES was increased, the became lighter in and more stable, and it was found possible to fracMolecular at Chlorine Refraction tionate a part of the combined residues from runs 1B.P. 0 Mm., 20 Compound C. dzo %D Obsvd. Calcd. Obsvd. Calcd. 6 t o 13 (Table I) after a preliminary distillation I 57 1.3480 1.5042 66.4 66.7 35.03 34.81 had removed unstable compounds. Two products I1 ' 68 1.3442 1.5079 66.8 . . . 35.35 .,, were isolated having the properties shown in Table V. 2,3,4-Trichloro-l-butene (I) 40-41 1.3430 1.4944 ,,, . . . 34.72 ,,, 1,2,4-Trichloro-2-butene (1) 64-65 1.3843 1.5175 . . . ' ., . 34.89 ,.. The properties of two trichlorobutenes reported by 1,2,4-Trichloro-2-butene (6) 67-9 1.3575a 1,5121b , , , ... .. . ... Carothers and Berchet ( I ) and by Petrov (6) are a At d i 5 . included for comparison. b At nk'. The properties of the trichlorobutenes which were isolated do not correspond t o those given by Carothers and Berchet ( I ) for 2,3,4-trichloro-ljacketed reactors to determine the optimum size, and the results butene or 1,2,4-trichloro-2-butene,although the properties of of these experiments are shown in Table IV. Although other product I1 are similar to those reported by Petrov ( 5 ) for 1,2,4workers (3) had described the use of a packed reactor, the present trichloro-2-butene. Several attempts were made to characterize authors found that packing the reactor with glass wool reduced these compounds by the permanganate oxidation method dethe yield of dichlorobutenes, and further investigation showed scribed by Carothers and by Petrov, but no oxidation products that a surface: volume ratio approaching 0.16 sq. mm. per cu. could be isolated. I n addition to the two trichlorobutenes, mm. was necessary to allow complete reaction in the vapor phase. the residue also .contained other high boiling materials which This conclusion was verified by the use of reactors in which the could not be purified by distillation or crystallization. walls were continuously washed with carbon tetrachloride or chloroform to remove the products from the reaction zone. LITERATURE CITED In the reactor having a surface-volume ratio of 0.16, washing (1) Carothers, W. H., and Berchet, G. J., J. Am. Chem. Soc., 55, 1628 (1933). the walls had no effect on the yield of dichlorobutenes, whereas (2) Hearne and LaFrance, U. S. Patent 2,299,477 (Oot. 20, 1942). in reactors having a higher ratio, the increase in yield was pro(3) I. G. Farbenindustrie A.-G., Brit. Patent 518,697 (Aug. 28, nounced; this indicated that a portion of the chlorine had been 1939). reaching the walls and reacting with the liquid reaction products. (4) Muskat and Northrup, J. Am. Chem. Soc., 52,4046 (1930). (5) Petrov, A. A,, J. Gen. Chem. (U.S.S.R.), 13, 102 (1943). Further evidence that the reaction occurred in the vapor phase (6) Rust, F. E., and Vaughan, W. E., J. Org. Chem., 5 , 4 7 2 (1940). was obtained during the runs reported in Table I by inserting a RECEIVED October 12,1946. piece of moist starch-potassium iodide paper in the bulb reactor a t . a distance of 2 inches from the point where the reactants were mixed. The paper did not show the characteristic blue color of the starch-iodine complex, which indicated that there Composition of Vapors from Boiling was no free chlorine at this point. When the bulb was viewed Binary Systems-Correction against a white background during the course of a run, it was impossible to detect the greenish color typical of free chlorine, In the article on "Composition of Vapors from Boiling Binary although the color could be seen clearly when no butadiene was Solutions'' [Othmer, D. F., and Savitt, S. A,, IND.ENG.CHEW, being admitted to the reaction chamber. 40, 168 (1948)l the data for the boiling temperatures of the It was impossible to take temperature readings during the pure components under the several pressures were not included series of experiments summarized in Table IV without introin the tables as experimental data. These particular results ducing more surface into the reaction zone and changing the show up in the printed paper only in the tables of smoothed surface-volume ratio. From duplicate experiments in the same data, even though they were experimentally determined. reactors in which a thermocouple was used, it seems probable These experimental vapor pressure data follow (as printed in that the temperatures were in the 65' to 70" C. range. Since the 0% and 1 0 0 ~ lines o in the smoothed data), along with values of the latent heat determined from them by the use of the logathe reactors were cooled by water in the cooling jackets, it is rithmic plots and method already described [IND.ENG.CHEM., logical to expect that the reactions in the smaller reactors were 32,841 (1940)]. carried out a t lower temperatures. The bulb reactor shown in Figure 1 was designed with a thermocouple well which could be BOILINQ TEMPERATURES AND LATENT HEATBOF PUREMATERIALS UNDER GIVENPRESSURES moved to various points within the reactor. During the first 2,6Y few minutes of each run the temperature rose rapidly in the P-Picoline Lutidine Picoline Phenol reaction bulb, but a t the end of 15 minutes it leveled out and BoilBoilBoilBoilPresing ing Ing ing remained constant a t 72' to 75' C. Readings were taken at four sure t;mg, L, temp., L, temp., L , temp., L , Mm: cal./g. C. cal./g. C. cal./g. C. cal./g points within the bulb each 15 minutes, and there was never a 760 143.0 107.2 143.3 100.0 144.8 107.2 181.5 ,109.7 variation of more than 1 " C. in these readings. The relatively 600 135.3 108.7 134.5 101.0 136.0 108.5 170.5 111.6 constant temperature was maintained in part by the dissipation 400 121.0 110.5 121.0 103.0 122.6 110.5 157.3 114.2 200 99.9 113.2 100.8 101.5 105.5 113.4 137.1 123.4 of heat to the surrounding atmosphere, and in part by the preDONALD F. OTHMER heating of the reactants which passed through 6-inch sections of POLYTECHNIC INSTITUTE OF BROOKLYN glass tubing in the reaction zone before they were mixed. N. Y. BROOKLYN, TABLE
IV.
EFFECT OF SURFACE-VoLUME
DICHLORQBUTENES
ON
OF
.
O
O
