Hendry, D . G., Russell, G . A., J . A m . Chem. Soc. 86, 2368 (1964). Hiatt R., Traylor, T. G., J . A m . Chem. SOC.87, 3766 (1965). Howard, J. A., Ingold, K. U., Can. J . Chem. 43, 1044, 1250 (1964). Mayo, F. R., J . A m . Chem. Soc. 80, 2465 (1958). Mayo, F. R., Preprints, Division of Polymer Chemistry, 153rd Meeting, ACS, Miami Beach, Fla., 1967, p. 11. Mayo, F. R., Miller, A. A., J . A m . Chem. SOC. 80, 2480, 2493, 6701 (1958). Mayo, F. R., Miller, A. A., Russell, G. A., J . A m . Chem. SOC.80, 2500, 6701 (1958). Miller, A. A . , Mayo, F. R., J . A m . Chem. Soc. 78, 1017 (1956). Morton, M., Salatiello, P. P., Landfield, H. J., J . Polymer Sei. 8, 215, 279 (1952).
Russell, G. A., J . A m . Chem. SOC.78, 1035, 1041 (1956). Sanderson, R. T., “Vacuum Manipulation of Volatile Compounds,” Wiley, New York, 1948. Silverstein, R. M., Bassler, G. C., “Spectrometric Identification of Organic Compounds,” pp. 71-89, Wiley, Xew York, 1963. Van Hook, J. P., Tobolsky, A. V., J . A m . Chem. Soc. 80, 779 (1958). Van Sickle, D. E., Mayo, F. R., Gould, E. S., Arluck, R . M., J . A m . Chem. Soc. 88,977 (1967). Walling, C., “Free Radicals in Solution,” p. 230, Wiley, New York, 1957.
RECEIVED for review August 9, 1967 ACCEPTED January 31, 1968
STABILITY OF BUTADIENE POLYPEROXIDE DALE
G . HENDRY,
FRANK
R.
MAYO,
DAVID
A.
JONES,
AND
DENNIS SCHUETZLE
Department o f Physical Organic Chemistry, Stanford Research Institute, Menlo Park, Calif.
940%5
The effects of temperature, solvent, and additives on the stability of butadiene polyperoxide, (C4H602)I, were investigated. Small samples of undiluted polyperoxide have half lives at 1OO’C. of about 3 hours. Dilution to 0.03 mole per liter in benzene extends the half life to about 80 hours. The critical radius for thermal explosion is estimated to be 9.0 cm. at 27’C. and 0.2 cm. at 127’C. Impact sensitivity of the polyperoxide is comparable to that of nitroglycerin. Catalytic amounts of amine accelerate the decomposition of the polyperoxide at 25’C., although some of the primary and secondary amines are consumed. In the absence of any solvent, high pressures of gaseous trimethylamine decompose the polyperoxide explosively. Toluene solutions of the polyperoxide react rapidly and smoothly with 1% aqueous solutions of trimethylamine at room temperature. An iodometric method for the quantitative determination of butadiene polyperoxide is described.
THOUGH butadiene polyperoxide, the alternating copolymer of butadiene and oxygen, has been the cause of a number of industrial accidents, no quantitative study has been made of its thermal and chemical properties. Robey et al. (1944) first reported a dangerously unstable polymeric material formed from the reaction of butadiene and oxygen. Handy and Rothrock (1958) reported this material to be butadiene polyperoxide, a copolymer of oxygen and butadiene. They noted that although dilute solutions were relatively stable (13-hour half life a t 100”C.),ignition or severe shock would explode the pure polyperoxide. Alexander (1959) studied the oxidation of butadiene and ascribed a $500,000 industrial explosion to 10 to 15 pounds of the polyperoxide. Through the support of a number of butadiene producers and users, we have investigated, and report here, the
thermal stability of butadiene polyperoxide and its chemical reactivity toward amines. We have also obtained information on the critical radius for thermal explosion, the sensitivity to heat and impact, and the chemical analysis of the polyperoxide. T h e ultimate objective of our investigation has been to promote safe handling of the polyperoxide. The facile formation of the butadiene polyperoxide is the subject of another paper (Hendry et al., 1968). Thermal Stability
Effect of Temperature and Solvent on Thermal Stability. Thermal decompositions of butadiene polyperoxide were carried out on pure samples or solutions degassed and sealed in evacuated reaction tubes. T h e neat samples were always kept small (-10 mg.) to limit self-heating. After VOL. 7 N O . 2 JUNE 1 9 6 8
145
Table I. Decomposition of Butadiene Peroxide
Temp., ' C.
Solvent and Additiue
8
tert-Butylbenzene, exposed to air Benzene
50
Cumene 60
None
80
Benzene
100
Benzene, 0.01M ABCb Benzene, 0.04M tert-butylcatechol None Benzene
Cumene Benzene, 0.01M ABiT' Benzene, 0.01M ABNd Benzene, 0.01M ABN' Benzene
Time, Hr
Concentrationa Initial Final
Decomwosition II C
rc
hr
1900 71.6 124.2 262.6 100.3 361.2 20.5 42.5 16.5 91 136.2
0.0392 0.706 0.706 0.706 0.740 0.740 0.0116' 0.0116" 0.0352 0.0352 0.0352
0.0296 0.664 0.583 0.578 0.753 0.704 0.0094* 0.0088. 0.0309 0.0236 0.0189
24.5 5.95 17.5 18.1 0.8 4.87 19 24 12.2 32.9 46.3
0.013 0.083 0.141 0.069 0.008 0.013 0.93 0.57 0.74 0.36 0.34
16.5
0.0352
0.0168
52.3
3.27
19.0 1.01 3.08 16.5 91.0 115.6 12.5 21.1 7.72 16.7
0.0352 0.0116* 0.0116' 0.0352 0.0352 0.0352 0.706 0.706 0.740 0.740
0.0328 0.0078' 0.0043' 0.0294 0.0100 0.0110 0.381 0.262 0.464 0.362
6.8 33 63 16.5 71.6 68.8 46.0 62.9 37.1 51.0
0.36 32.6 20.4 1.o 0.79 0.60 3.68 2.98 4.82 3.05
1.0
0.0296
0,0277
6.5
6.5
1.0
0.0296
0.0277
6.5
6.5
Apparent First-Order Rate Constant 0.000147 0.00085 0.00155 0.00076 0.00007 0.00014 0.0103 0.0065 0.00802 0.00440 0.00457
0.39 0.32 0.0110 0.0138 0.0100 0.0476 0.0853 0.0602 0.0405
2.26 38.5 17.0 0.0182 0.0296 3.5 234 58.2 0.294 0.25 0.706 2.9 152 76.0 0.169 0.706 0.50 186 2.25 31.7 0.505 0.17 0.740 Cumene 2.08 182 60.0 0.296 0.33 0.740 2.01 117 70.0 0.222 0.60 0.740 0.127 10 37 0.019 3.63 0.030 160 tert-Butylbenzene 0.206 12 70 5.63 0.0072 0.023 "Concentrations in moleslliter in tert-butylbenzene or benzene, except where an asterisk indicates moleslgram for neat peroxides. Concentrations determined by analytical procedure described in Appendix. *Half life of l,l'-azobis(l-cyanocyclohexane) ( A B C ) at 80" C., 22 hours. ' H a l f life of azobis(2-methylpropionitrile) ( A B N ) at 100" C., 0.12 hour dSampleswere degassed except as marked. 150
reaction, the tubes were opened and the contents were titrated by a modification of an iodometric procedure of Mair and Graupner (1964) described in the Appendix. Table I summarizes the rate data for the decomposition of pure polyperoxide and its solutions. The polyperoxide samples used throughout were prepared by oxidizing neat butadiene a t 50°C. in the presence of 1 atm. of oxygen and -0.01M azobis(2-methylpropionitrile)(ABN) . The polyperoxide was purified by reprecipitation from either benzene or chloroform with methanol, then placed under vacuum of torr a t room temperature until constant weight was reached. At each temperature and concentration the calculated first-order rate constant shows little change with conversions up to 60 or 70:b. However, the estimated first-order rate constants vary with the initial peroxide concentration. The variation in rate of initial decomposition is actually about 1.5 order in peroxide, which is consistent with a chain decomposition reaction initiated by unimolecular decomposition. Simple dialkyl peroxides have half lives of 100 to 400 hours a t 100°C. (Batt and Benson, 1962), and a similar half life would be expected for butadiene polyperoxide if decomposition of the peroxide groups occurs only by unimolecular thermal cleavage. However, the neat perox146
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
ide (10-mg. samples) has a half life of only about 3 hours a t 100°C., while a 0.7M solution in benzene has a half life of about 20 hours. [Half lives for styrene polyperoxide solutions under the same conditions are about one half these values (Mayo and Miller, 1956).] The decrease in apparent first-order rate constant with dilution suggests that more chain decomposition occurs at higher concentrations. Support for this idea comes from the increased rate of decomposition with 1,l'-azobis(1cyanocyclohexane) (ABC) as chain initiator and from retardation of the decomposition by substitution of cumene for benzene as solvent or by addition of tert-butylcatechol. I n the ABC experiment the rate of formation of radicals from the initiator (Wu et al., 1960) was 3.6 x 10 ' mole per hour and the rate of disappearance of peroxide was about 10 x 10 ' mole per hour, so that 3 units of peroxide were decomposed for each radical generated. Chains would be longer a t lower initiator (and radical) concentrations. Thus, in this system thermal cleavage of the 0-0 bond probably produces radicals at about the same rate as in other dialkyl peroxides, but most of the peroxide linkages then react by a chain mechanism. A reasonable mechanism for this chain decomposition is Reactions 1 to 5:
This mechanism differs from the induced decomposition of tert-butyl peroxide, in which a methyl or tert-butoxy (RO .) radical abstracts a hydrogen atom from tert-butyl peroxide to give .CHJ- -CMe2-OJ-tert-Bu, which decomposes to 2-methylpropene (isobutylene) oxide and tertbutoxy radicals (Batt and Benson, 1962; Bell et al., 1950). The carbon-hydrogen bond being attacked in Reaction 3 is activated by both the adjacent peroxide and vinyl groups. Reaction 3 is exothermic by about 22 kcal. per mole: The bond dissociation energies are about 80 kcal. per mole for the carbon-hydrogen bond being broken and 102 kcal. per mole for the oxygen-hydrogen bond being formed. Reactions 2, 4,and 5 are also exothermic. Critical Radii Necessary for Thermal Explosions. Any sample of material which generates heat from exothermic decomposition faster than the heat can be transferred to its environment will self-heat and may eventually reach an explosive rate of decomposition. Whether or not an explosion occurs depends mostly on the nature of the decomposition. The critical radii for pure polyperoxide have been estimated by the method described in the Appendix. The estimated values for 27" and 127°C. (81" and 261°F.) are reported in Table 11; included are corresponding values calculated for styrene polyperoxide (Mayo and Miller, 19561, tert-butyl hydroperoxide (Morse, 19571, and, for comparison, trinitrotoluene (Cross and Amster, 1962). The calculated critical radius for an infinite cylinder is 0.775 times that for the sphere, and the critical half-thickness for a slab is 0.514 times the sphere radius.
Consistent with the small critical radius a t the higher temperature is the observation that small amounts (3 to 4 cu. mm.) of butadiene polyperoxide decompose rapidly and with an easily detected explosion when a test tube containing the sample is placed in an oil bath a t 125°C. A similar observation has been made with somewhat larger amounts of styrene polyperoxide a t about 130°C. These experiments serve as crude verification of the critical radii for these materials a t the higher temperature. The larger values for tert-butyl hydroperoxide are in agreement with the fact that it can be distilled without apparent difficulty a t reduced pressures near room temperature, although any hot spot formation or failure in the vacuum system might cause trouble. In view of their calculated critical radii, butadiene and styrene polyperoxides should be considered equally dangerous. However, the practical problems with butadiene polyperoxide are more serious because it has low solubility in butadiene and concentrates by settling. Sensitivity of Butadiene Polyperoxide to Impact and Heat. Sensitivity of polyperoxide to impact was measured using the standard drop-weight test (Liquid Propellant Test Method. Test 4). In this test the sensitivity value is the potential energy value (height x weight) of the weight dropped on a 0.03-ml. sample where the probability of explosion is 50LC. Impact sensitivities for butadiene polyperoxides of various oxygen content prepared by oxidizing butadiene a t controlled oxygen pressures are given in Table 111. Two types of decomposition were observed: Low energy impacts produce deflagration, but high energy impacts produce explosion. Data for some other common explosives (Wenograd, 1961) are included in the table for comparison. Direct comparison of the experimental values for the polyperoxide with these literature values is difficult because results may vary somewhat from apparatus to apparatus. The ease with which butadiene polyperoxide deflagrates in our studies is consistent with the small critical radius and with practical experience with this material
~~
Table Ill. Impact and Heat Sensitivity of Butadiene-Oxygen Copolymers
Tested Material
Defhgration Explosion 50% Point, 50% Point, M i n . Temp? for Kg. Cm. Kg. Cm. Explosion of at 2;J0 at 250 -5 Mg., C.
Polyperoxide comp.,
CIHeIO?
Table II. Calculated Critical Radii for Spheres of Various Peroxides for Thermal Explosion
('o mpound Butadiene polyperoxide Styrene polyperoxide tert-Butvl hvdroperoxide ThT' I
Frequency Factor," Sec. '
Actication Energy,n Kcal. Mole
10-*
20
10"
31.4
10" 10 ' ( I
31.0 35
Critical Radius, Cm .
2P
e.
9.0 22
127" c.
0.2 0.06
"
1.5 X 10' 2.8 x 10
3.1 160
" Ecaluated assuming first-order decomposition. ' FrequencJI factor times heat o f reaction reported to be 6 x IO" cal. see. gram.
1.0, No. l o 1.0, No. 2* 1.3 2.0 5.0 1.0 plus equal wt. tertBuPh Nitroglycerin' Trinitrobenzene" Trinitrotoluene"
d
2
89 110
85
187
125 None None None
183 4-8 100 160
115-118 145-150 180-186 > 188
I I
I
' S e e text for significance. ' Both 1.0 samples prepared similarly, but N o . 1 stored seueral months prior to analysis. ' N o measurement. Below 110 kg. em., deflagration occurred but there was not suficient material for actual 5 0 r r point determination. ' From Wenograd (1961). Literature iialues are unsuitable for comparison with our peroxide data, since actual temperatures measured depend on the apparatus,
VOL. 7 N O . 2 JUNE 1 9 6 8
147
(Alexander, 1959). However, polymer formed a t 50" C. and a t oxygen pressures below 10 torr is less sensitive to impact because it has less than one 0 2 unit per C 4 H h unit. The lower the oxygen content, the greater is the energy of impact required to produce deflagration or explosion. Dilution of the 1-to-1 copolymer with an equal weight of inert solvent also significantly reduces the sensitivity. The temperature a t which a 5-mg. sample of peroxide spontaneously explodes also increases as the oxygen content of the polyperoxide decreases. For our heat sensitivity experiments, also summarized in Table 111, 5 mg. of reprecipitated polyperoxide were placed in the bottom of a melting point tube (1.0-mm. i.d., 1.4-mm. 0.d.) by means of a syringe and subsequent centrifuging. A polytetrafluoroethylene plug was placed on top of the sample, and the tube was then dropped into an oil bath of the desired temperature behind a safety shield. Explosive decomposition occurred within 10 seconds or not a t all. Several experiments a t different temperatures were required to obtain the minimum temperature for explosion in the system. Slow decomposition was usually observed in those experiments where explosion did not occur. A different procedure might have given different absolute results, but the sequence would have remained the same. I n earlier
studies on heat sensitivity of explosives (Henkin and McGill, 19521, the values obtained provided only a rough idea of sensitivity. Our results are subject to the same limitation. Reaction of Butadiene Polyperoxide with Amines
Decomposition in Solution. The decomposition of styrene polyperoxide by various agents has been studied in some detail (Mayo and Miller, 1956). Besides being sensitive to heat and light, this peroxide is easily decomposed by amines, alkoxides, and reducing agents to give tractable products such as benzaldehyde, formaldehyde, phenylglyoxal, and phenylglycol. Table IV summarizes data on the reaction of butadiene polyperoxide with various amines in the presence of water or toluene. These experiments employed 14 t o 16 mg. of polyperoxide (0.32 to 0.37 base mmole) and (usually) 1.0 ml. of 1 to 3% of weight solutions of amines in water or toluene. The mixtures stood in air at room temperature for the indicated times. The volatile material was then removed a t reduced pressure and the residue was titrated for peroxide by the method in the final section. Since the reactions in toluene were homogeneous, they were faster than those in water. Reaction of polyperoxide with aqueous amine was facilitated by adding toluene
~~
Table IV. Decomposition of Butadiene Polyperoxide by Amines
Expt. No. 30-H 31-0 313 30-c 30-D 31-G 32-B 32-Pa 31-11' 31-JJ' 32-Qd 32-R 30-F' 31-P 31-R 31-Q 31-T 31-N 31-Y 31-FF 31." 31-2 32-C 32-G 32-S' 32-D 32-Jc'8 32-E 32-H 32-F 32-10," 33-K"'." 32-M 31-V 31-w 31-X 32-N I
Amine None Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine Methylamine n-Propylamine n-Propy lamine n-Propylamine n-Propylamine n-Propylamine n-Propylamine tert-Butylamine D imethylamine D imethylamine Trimethylamine Trimethylamine Trimethylamine Trimethylamine Trimethylamine Trimethylamine Trimethylamine Trimethylamine EtdNOH EtdNOH EtdNOH EtiNOH
Moles of Amine per CIH602Unit
... 1.60 1.83 1.82 0.17 1.95 0.68 1.68 1.68 1.70 2.60 2.47 0.18 1.6 1.53 1.43 0.94 0.92 0.94 2.78 2.60 3.03 1.67 2.00 2.20 2.04 2.07 0.50 0.46 1.oo 1.91 2.07 1.66 1.61 1.61 1.59 2.41
Soluent, MI. None 1 H2O 1 H10 1 HrO 1 HYO 1 HJO 0.3 H J 0 0.3 H?O 1 HXO 1 HA0 1 HyO 1 HZO 1 HrO 1 PhMe 1 PhMe 1 PhMe 1 PhMe 1 PhMe 1 PhMe 1 PhMe 1 PhMe 1 PhMe 1Hi0 1 H20 1 HJO 1 HA0 1 HZO 0.25 HJO 0.25 HJO 0.5 H2O 1 H>O 1 HY0 1 PhMe 1 HA0 1Hi0 1 H?O 1 HyO
Time, Hr. 60.0 1.0 5.0 19.5 19.5 40.0 39.0 15.0 13.3 13.3 50.0 5.0 14.7 1.0 5.0 16.2 1.0 5.0 15.2 1.0 5.0 15.0 16.0 10.0 2.1 2.0 2.1 2.1 4.8 2.1 0.7 1.1 0.4 1.0 5.0 16.0 72.0
Peroxide Remaining, cC 98.5 97.5 86.9 45.8 94.5 0.0 12.0 On 4.7 32.8 jb
5O 43.2 88.7 39.0 14.4 96.2 69.0 33.5 75.0 25.0 0.8 20.0 0.0 Ob 1.5 Ob 38.0 3.0 28.5 OD Ob 40.0 92.5 91.0 90.5 0.0
Dec., Ac. i; H r . 0.025 2.5 2.6 2.8 0.28 > 2.3 2.26 > 6.6 7.18 5.06 2.0 20.0 3.86 11.3 12.2 5.3 3.6 6.2 4.4 25.0 15.0
6.6 1.67 > 10.0 > 48.0 49.0 > 48.0 29.5 19.5 34.5 > 140.0 89.0 150.0
- .aI
1.8 0.53 > 1.4
" A i r absent. b B y inspection on disappearance or near disappearance of peroxide. 'Peroxide dissolved in 25 p l , toluene; expt. 31-11 shaken continuously but expt. 31-55 not. d,"Ternperature held at 20" C.: 30" C.: or 50" C!. 'Aqueous phase concentrated and titrated for peroxide: 64.45;in 32-5 (with air), 32-K ixithout air) 17.4('; m. No noncondensablegas formed.
148
18EC PRODUCT RESEARCH A N D DEVELOPMENT
turned orange and a white cloud appeared in the gas phase. Products included 0.0515 mole of CO (other reactions formed no noncondensable gas) and unidentified products from reacted trimethylamine. This experiment emphasizes the hazard of bringing undiluted peroxide together with high concentrations of reactive reagents. With larger amounts of peroxide, thermal explosion might occur at lower pressures of amine. Reactions of Polyperoxide with Other Reagents. The reactions of some other reagents with butadiene polyperoxide have had limited study. A 0.035M solution of butadiene polyperoxide in tert-butylbenzene a t 80" C. in the presence of an equal molar amount of sodium diethyldithiocarbamate, boron trifluoride etherate, or aniline gave approximately 80, 40, or 25'; decomposition of peroxide: respectively, in 19 hours. I n a 1-hour experiment with sodium diethyldithiocarbamate a t 50" C., although there was only about 1 0 5 decrease in total peroxide content, about half the methanol-insoluble peroxide had reacted or become soluble in methanol. These reactions appear slow compared t o the reactions with amines.
to dissolve the peroxide and then shaking the two-phase system (Experiments 31-0, 31-11, and 31-JJ). I n heterogeneous systems, results may not be reproducible. Whether the peroxide was in contact with aqueous solution or dissolved in toluene, the amines had the following order of reactivity in decomposing peroxide: M e S > Me?l\jH > Me"?, n-PrNH?,and tert-BuSHL.This order does not correspond with the basicity of the amines in aqueous solution ("Handbook of Chemistry and Physics," 1964) (MeNHa i Me.$N > N H J nor with their complexing ability with trimethylboron (Brown and Taylor, 1947). The decomposition by aqueous amines must depend on the partition coefficient of the amine between the peroxide and water, presumably larger for more alkyl substitution. The small effects of tetraethylammonium hydroxide and n-diethylhydroxyamine may be due to small partition coefficients. Reaction rates are proportional to the concentration of amine in the aqueous phase (compare 31-0 and 30-D), the actual amount of amine in the aqueous phase being less critical than the concentration (compare 32-D, 32-F, and 3%-E).The decomposition with aqueous amines is faster a t higher temperatures (compare 32-P and Q, 30-D and F, 32-G and S). The disappearance of titratable peroxide is significantly faster in the absence of air (32-P and 3042, 32-1 and D ) ; oxygen may retard chain decomposition or form new peroxide. The following discussion shows that the action of the amines is more catalytic than stoichiometric. Decompositions by Gaseous Amines. I n these experiments, gaseous amine was measured into a 13.3-ml. reaction tube containing 15 mg. (0.174 mmole) of degassed peroxide without solvent. The air-free tube was then closed by a stopcock. Amine pressures were about 600 mm. at amine-C4H60?mole ratios of 2 and about 60 mm. a t ratios of 0.25. After reaction, the contents were separated into noncondensable, condensable, and nonvolatile fractions. The first two fractions were analyzed by GLC, and the nonvolatile fraction was titrated. These experiments permitted us to determine the consumption of amines. Results are summarized in Table V. At 0.25 mole of amine per CIHhO? unit, the order of activity of gaseous amines in decomposing peroxide is about the same as with solvents, Me& > M e S H L > N H ; . Solubility of amine in peroxide may be important. I n these experiments, very little trimethylamine was consumed; its action appears t o be truly catalytic. With methylamine and ammonia, about 1 mole of amine is consumed per 3 peroxide units. The disappearance of these amines is probably the result of reaction with the aldehydes generated from decomposing peroxide. I n the experiment with 2.27 MeiN per C 4 H 6 0 aunit, a rapid decomposition occurred; the peroxide
Volumetric Determination of Butadiene Polyperoxide
The determination of polyperoxides formed from conjugated olefins has long been recognized as difficult (Wagner et al., 1947); with styrene polyperoxide, only 8 0 5 of the expected active oxygen could be found by the best of several methods tried (Mayo and Miller, 1956). T h e difficulty is that the dialkyl peroxide groups are much less susceptible to reduction than the hydroperoxide groups. As conditions to bring the dialkyl peroxide group into reaction become more strenuous, side reactions occur that may make the results high or low, depending on the conditions. Butadiene dimer may interfere with some analyses. Of the analytical methods which have been investigated, the best are iodometric. Mair and Graupner (1964) macie a systematic investigation of various iodometric procedures and found one variation which was satisfactory for titrating 89 to 93% of rnost diaralkyl peroxides (MairGraupner Method 11). We found that this method also titrated 9 0 5 of butadiene polyperoxide. The titers were constant over 0.67 to 1.0 hour, indicating that the reaction product did not react further, and a control showed that 4-vinylcyclohexene does not interfere. Thus with a 10' correction, Method I1 can be used for quantitative determination of the polyperoxide even in the presence of vinylcyclohexene. During our study of the Mair-Graupner methods, we found that addition of HC1 in Method I1 increased the reducing power of the medium; the details of the procedure are given in the Appendix. Table VI summarizes the
Table V. Reaction of Gaseous Amines with Butadiene Polyperoxide at 25' C.
Amine I"
Me"? M e9
' Explosioe
Moles of Amine per CIHt,OL Cnit
Time, Hr.
2.13 0.24 0.25 2.27 0.25 0.25
1.25 14.6 1.32 125 1.25 3.42
Pero x ide Remaining,
A Peroxide
f
Amine Consumed, Mmole
AAmine
Peroxide , 1f Hr.
66.0 33.6 39.6 1.7 17.0 4.7
0.0211 0.0314 0.043 0.044" 0.004 None
2.79 3.67 2.44 3.80 36 >3ti
27.0 4.6 30.0 78.2 66.4 27.8
-
-A
decompositiun: set' text
VOL. 7 NO. 2 JUNE 1968
149
Table VI. Determination of Butadiene Polyperoxide by Modified Mair-Graupner Procedures
Added Reagents, M1.
Reflux
HClconcn. H d l 0’ 3.0
Min.
Time,
Peroxide, Meq.
Peroxide Found,
6. Added Foundn /c 40 0.157 0.141 89.8 60 0.141 0.157 89.8 2.0‘ 0 40 0.297 165.0 0.487 2.0 2.0 20 0.211 0.207 102.0 40 0.215 0.188 114.0 2.0 3.0 10 0.254 0.332 76.5 20 0.354 0.352 99.5 20 0.323 100.3 0.325 40 0.442 0.440 100.5 2.0 4.0 20 95.6 0.363 0.383 40 0.178 0.188 94.8 “Correctedfor blank ”air-Graupner Method I 1 ‘Mair-Graupner Method I I I
effect of water and hydrochloric acid on the reaction. As Table VI shows, 2.0 ml. of hydrochloric acid with 3.0 ml. of water gave quantitative results with samples refluxed for 20 to 60 minutes. Addition of less water gave peroxide titers greater than 1008, which continued to increase with refhxing. Addition of more water gave low values which remained constant with refluxing. Although the modified method is excellent for determining pure polyperoxide, 4-vinylcyclohexene (butadiene dimer) interferes. This interference, presumably due to reduction of the terminal double bond by H I , makes the method unsatisfactory whenever the dimer is present to an estimated extent of more than 50 p.p.m. Under such circumstances Mair-Graupner Method I1 (with correction) is preferred. Handy and Rothrock have reported an iodometric method for quantitatively determining butadiene polyperoxide. However, we have found the results with their method t o be subject to small variations in experimental conditions and do not consider it completely reliable. Braithwaite and Penketh (1967) have developed a procedure using lithium iodide, with which we have had limited success. Appendix
Estimation of Parameters for Thermal Explosion. The theory of thermal explosions has been discussed by several authors (Bowden, 1958; Bowden and Yoffe, 1952; Cook, 1958; Frank-Kamenetskii, 1955). An approximate solution of steady-state equations (Chambre, 1952; FrankKamenetskii, 1955), where the heat loss is equated with the heat gain of the sample, leads to the relationship for the critical radius
where a = dimensionless parameter which is a function of the shape of the sample: 3.32 for a sphere, 2.0 for an infinite cylinder, and 0.88 for a semi-infinite slab R = gas constant, 1.987 cal./mole K. ? ’ = surface temperature, K. E = energy of activation of the apparent unimolecular decomposition, cal./mole d = density of reactant, g./cc. H = heat of reaction, cal. /gram A = the Arrhenius factor for the apparent unimolecular decompositioii reaction, sec. ’ A = thermal conductivity, cal./sec. cm. K. 150
I & E C PRODUCT RESEARCH A N D D E V E L O P M E N T
The equation assumes that heat dissipation is only by conduction as in the case for solids. However, butadiene polyperoxide, being a viscous liquid, would not be expected to dissipate localized heat significantly by convection, especially under conditions of rapid heating. The terms A and E are determined from the temperature dependence of decomposition reaction, and because of their exponential role in this equation they must be reasonably well known. The other parameters can be estimated with satisfactory precision. Since the decomposition of peroxides is induced, neat peroxide decomposes faster than in solution. Therefore, for substitution in the critical radius equation, A and E must be evaluated for the neat liquid. From the data in Table 11, these terms can be evaluated for neat peroxide, and the critical radii can be calculated assuming d = 1 gram per cc., = 4 x 10 cal. per sec. cm. OK. H is assumed to be 40 kcal. per mole or 465 cal. per gram, an estimate based on bonds made and broken in the following reaction: 2 5 ncol 35 Kcat -CM20!OCn,
- -2 -
i t / CHO*+-
oc
licol
C = O + H iOCH,
-
H
Modification of Mair-Graupner Method 11. Glacial acetic acid (50 ml.) was placed in a 300-ml. round-bottomed flask fitted with a reflux condenser and side arm for a nitrogen inlet. Nitrogen was bubbled through the solution for 5 minutes; then 6 grams of NaI were added. After the NaI was partially dissolved, 3.0 ml. (or the desired amount) of water were added. Then the peroxide sample (up to 0.5 meq.) was added either as an undiluted sample in a small glass weighing tube or as an aliquot in butadiene, benzene, xylene, toluene, or tert-butylbenzene solution. If concentrated hydrochloric acid was to be used, 2.0 ml. were added a t this time. The mixture was swept with nitrogen and brought to reflux generally with a heating mantle. After refluxing 20 to 40 minutes (see Table VI for effect of conditions on the reflux time), the mixture was cooled with an ice bath while the nitrogen sweep was continued. Then 100 ml. of water were added through the condenser and the mixture was titrated under nitrogen with 0.10N N a 2 S 2 0 ito the end point, faint yellow to clear. Blank experiments usually gave 0.01 t o 0.02 meq., depending mostly on the NaI used. If the analysis was performed in the dark, the blanks were reduced to about 0.003 meq. Solvents used to transfer the peroxide were checked in blank reactions. For some reason butadiene increases the blanks t o 0.035 meq. and must be included in the blank if the sample is a butadiene solution. (To obtain peroxide-free butadiene for such blanks, butadiene from the same source should be transferred as vapor and condensed.) The weight parts per million of peroxide as -O?- was calculated by the formula
Wt. p.p.m. of -02- =
( S - B ) N x 16,000 ExW
where S and B are milliliters of thiosulfate solution for sample and blank, N is the normality of the thiosulfate, W is the weight of butadiene sample in grams, and E is the efficiency of the method in determining the peroxide, 0.90 for the unmodified Mair-Graupner Method I1 and 1.0 for the modification using 3.0 ml. of water and 2.0 ml. of HC1. Wt. p.p.m. of -02- can be converted to other concentration units by the relations: 1.00 wt. p.p.m.
of -OL= 1.06 wt. p.p.m. as H,O, = 2.69 wt. p.p.m. as (C4H602)= 0.65 mg. of -Oeper liter a t 0” = 0.58 per liter a t 50” = 1.7 mole p.p.m. of -02mg. of -OrH 2 0 2 or , -C,HeO2--. Literature Cited
Alexander, D . S., Znd. Eng. Chem. 51, 733 (1959). B a t t , L., Benson, S.W., J . Chem Phys. 36, 895 (1962). Bell, E. R., Rust, F. F., Vaughn, W. E., J . Chem. Phys. 72, 337 (1950). Bowden, F. P., “Fast Reactions in Solids,” Academic Press, New York, 1958. Bowden, F. P., Yoffe, A. D . , “Initiation and Growth of Explosions in Liquids and Solids,” Cambridge University Press, London, 1952. Braithwaite, B., Penketh, G. E., Anal. Chem. 39, 1471 (1967). 69, 1332 Brown, H. C., Taylor, M. D., J . Am. Chem. SOC. (1947). Chambre, P. L., J . Chem. Phys. 20, 1795 (1952). Cook, M. A., “The Science of High Explosives,” Reinhold, New York, 1958. Cross,D., Amster, A. B., 8th Symposium on Combustion, Pasadena, Calif., 1960, p. 728; CA 57, 10093g (1962). Frank-Kamenetskii, D. A., “Diffusion and Heat Exchange in Chemical Kinetics,” Princeton University Press,
Princeton, N. J., 1955; Acta Phys. Chem. USSR 10, 365 (1939). “Handbook of Chemistry and Physics,” 45th ed., p. D-76, Chemical Rubber Publishing Co., 1964. Handy, C. T., Rothrock, H . S., J . Am. Chem. Soc. 80, 5306 (1958); (to E. I. du Pont de Nemours and Co.) U. S. Patent 2,898,377 (Aug. 4,1959). Hendry, D . G., Mayo, F. R., Schuetzle, D., IND. CHEM. ENG.,PROD. RES.DEVELOP. 7,136 (1968). Henkin, H., McGill, R., Ind. Eng. Chem. 44, 391 (1952). Liquid Propellant Information Agency, The Johns Hopkins University, Baltimore, Md., “Liquid Propellant Test Methods, Test No. 4 Drop-Weight Test.” Mair, R. D., Graupner, A. J., Anal. Chem. 36, 194 (1964). Mayo, F. R., Miller, A. A., J . A m . Chem. SOC.78, 1023 (1956). Morse, B. K., J . A m . Chem. SOC.79, 3375 (1957). Robey, R . F., Wiese, H. K., Morrell, C. E., Znd. Chem Eng. 36, 3 (1944). Wagner, C . D., Smith, R . H., Peters, E. D . , Znd. Eng. Chem., Anal. Ed 19, 976 (1947). Wenograd, J., Trans. Faradaq SOC57, 1612 (1961). Wu, C.-H., Hammond, G. S., Wright, J. M., J . A m . Chem. SOC.82, 5386 (1960). RECEIVED for review August 9,1967 ACCEPTED April 8,1968
REACTION OF RESORCINOL AND FORMALDEHYDE IN LATEX ADHESIVES FOR TIRE CORDS G
,
E
.
V A N G I L S , The General Tire & Rubber Co., Akron, Ohio
44309
The thin-layer chromatography (TLC) technique w a s used to study the reaction of resorcinol and formaldehyde. Two different consecutive reactions occur. Under the reported experimental conditions, methylol resorcinols are formed in the first hour. These reactions are then gradually overtaken by a second process, the formation of high molecular weight condensation products. The reaction w a s also studied by viscometry, calorimetry, and cryoscopy. The results are consistent with the TLC findings.
condensates in cord dip adhesives were used back as far as 1935 (Baumann, 1936; Charch and Maney, 1938; du Pont Rayon Co., 1937; Mighton, 1951). Since that time, many other patents have been issued and many publications have appeared, but basically the process has not changed. I n this process, resorcinol and formaldehyde are prereacted in aqueous solution in the presence of NaOH catalyst, and after a certain degree of condensation has been reached, the product is added to the vinylpyridine copolymer latex. Many authors have stressed the importance of controlling the resorcinol formaldehyde ( R F ) reaction, specifically the determination of the right time before mixing with the latex. For this reason, we have t o look more closely into the kinetics of this reaction. Resorcinol reacts with formaldehyde essentially in the same way as phenol. However, whereas the phenol reaction has been studied very extensively, comparatively little work has been done on the resorcinol reaction, not only because phenol resins are economically and technically more important, bLt also because the reaction between resorcinol and formaldehyde is so fast that isolation and identification of intermediate products are very difficult. Sen and Sarkar (1925) were able to prepare one of the many possible condensation products, monomethylolRESORCINOL-FORMALDEHYDE
resorcinol, which they found discolored rapidly to a brick red-brown color even in a vacuum desiccator and became insoluble in alcohol. Similar results were obtained by the author as reported later. Stedry (1951) recommended ultraviolet absorption measurement as a tool for studying the R F reaction kinetics. He used the 365-mp wavelength which is less susceptible to colored oxidation products. A conceivable way to study the kinetics of the phenolformaldehyde reaction is to follow the disappearance of the formaldehyde during the reaction and also t o measure the reactive sites of the phenolic compound. This method, which consists of measuring the amount of bromine taken up by phenol, has been applied to resorcinol by Doyle (1960). In the first hours of reaction, methylol resorcinols are formed, hut the number of reactive sites as determined by the bromine method remained the same, since the methylol group is just as replaceable to Br atoms as an active H atom of the resorcinol. On further reaction, di-, tri-, and polynucleic compounds result through formation of methylene bridges, so that the number of reactive sites drops. Doyle found that, in conjunction herewith, the adhesive properties of the dip diminish. Levitin et al. (1962a) followed the R F reaction polarographically and correlated the gradual disappearance of VOL. 7 N O . 2 JUNE 1 9 6 8
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