August 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY ACKNOWLEDGMENT
Special acknowledgment is made to .kiton Gabriel, assistant chief, Metallurgical Division, Bureau of Mines, and Wilbert J. Huff, chairman, Department of Chemical Engineering, University of Maryland, for assistance and criticism. Experimental work on titanium by the junior author will be offered as a part of a thesis in partial satisfaction of the requirements €or the degree of Doctor of Philosophy in chemical engineering a t the University of Maryland.
1673
(3) Dean, E. S.,Long, J. R , W a r t m a n , F. S., a n d Anderson, E. L., Metals Technol., 13, 12-13 (1946) (Tech. Pub. 1961). (4) Dean, R. S., a n d Silkes, B., U . S. Bur. Mines, Inform. Circ. 7381 (November 1946). ( 5 ) F o n t a n a , M . G., IND. ENG.CHEIM., 40, No. 10, 99A (1948). (6) Gee, E. A., Long, J. R., a n d W'aggaman, W. H., MateriaZs & Methods, 27,75-8 (1948). (7) Gillett, H. W., Foote Prints, 13,No. 1, 5-7 (1940). (8) K r o l l , W . J., Mttallwirtschaft, 18,77-80 (1939). (9) Kroll, W . J., Trans. Electrochem. Soc., 78, 35-47 (1940). (10) W a g g a m a n , W. H., a n d Gee, E. A., Chem. Eng. .\'ews, 26, 37781 (1948).
LITERATURE CITED (1) Am. SOC. Testing
Materials, Standards, pp. 793-802 (1946), A.S.T.M. Designation B185-43T. (2) B r a d f o r d , C.I., U. S. Navy Dept., Office of Naval Research, Tit a n i u m Symposium, p a p e r 6 (December 1948).
RECEIVED September 30, 1948. This study is part of a joint research project on the corrosion resistance of metals by the Metallurgical Division of t h e Bureau of Mines and the Department of Chemical Engineering of the University of AVaryland.
Di-tert-butyl Peroxide and 2,2-Bis(tert-buty1peroxy)butane J
PREPARATION, ANALYSIS, AND PROPERTIES F. H. DICKEY, J. H. RALEY, F. F. RUST, R. S. TRESEDER, AND W. E. VAUGHAN Shell Development Company, Emeryuille, Calif.
Di-tert-bu tyl peroxide and 2,2-bis(tert-butylperoxy)butane are two new liquid compounds, the properties of which have been studied extensively. They possess predictable decomposition characteristics and other properties which render them of value.
T
HE rapid growth of the held of synthetic resins and elas-
tomers in the past decade has been paralleled by a stimulus in the development of chain reaction initiators or catalysts, principally in the domain of the organic peroxides. A considerable number of such compounds has been added to the formula indexes, and some of these new materials have demonstrated promise in industrial applications as polymerization catalysts, as Diesel fuel ignition accelerators, and as tools in organic syntheses. Two of these compounds, di-tert-butyl peroxide (DTBP) and 2,2-bis(tert-butylperoxy) butane (2,2-PB), both of which are presently available, have been rather extensively investigated in these laboratories in regard to their syntheses, fundamental chemical reactivity, and industrial applications. This work revealed that certain characteristics of these chemicals render them highly advantageous for commercial use. This paper presents data relating to the compounds, and their stabilities and controlled decomposition rates are compared with those of other commercial peroxides;. The following paper (29) describes application data, particularly In polymerizations. PREPARATION
Di-tert-butyl Peroxide (8'4). The earliest mentions of this compound in the literature appear to be l ? and 8%'. It may he obtained by the hydrogen bromide catalyzed oxidation of isobutane (23,25); this reaction is discussed elsewhere ( 4 , 20, 21) in some detail regarding the mechanism. Di-terthutyl peroxide may be synthesized in high yield also by the interaction of tert-
butyl hydroperoxide and lert-butyl alcohol in the presence of sulfuric acid ( I S , 18,24). CH3
1 1
CH3-C-OOH CH3
+ HO-
XH3 I
-CH3
+
CH3
AH3
I
+ H20
(1)
CHI
,4third method of preparation is reaction of an alkali or alkaline earth metal salt of tert-butyl hydroperoxide with a tert-butyl halide (IO),for example: CHa C~3-L-OONa bH8
CH3
+ CI-d-cH, I
-+
CH3 CHI
CH3
CH3-(&--00-&-CHa CHI I AH3
+ NaCl
(2)
This peroxide is not an oxidizing agent in the ordinary sense of the term nor is it especially reactive chemically in other ways. It is virtually insoluble in water and is stable thermally a t temperatures below approximately 80" C. A ternary azeotrope of composition-44.0% di-tert-butyl peroxide, 49.3% tert-butyl alcohol, 6.7% water, boiling point 77" C.-has been used for separating the peroxide from certain mixtures ( 17 ) .
INDUSTRIAL AND ENGINEERING CHEMISTRY
1674
PHYSICAL PROPERTIES
2,2-Bis(tert-buty1peroxy)butane. This compound may be prepared (8, 9, 1 1 ) by reacting tert-butyl hydroperoxide with methyl ethyl ketone in the presence of an acid catalyst,:
CH3 2CH3-C-OOH
I
0
The important physical properties of di-tert-butyl peroxide and of both pure and technical 2,2-bis(tert-FJutylperosy)butane are given in Table I.
a+
li
H
+ CHa-C-C-CH, H
TOXICITY
I_
Toxicit'y tests have indicated t h a t di-tert-butyl peroxide and 2,2-bis( tert-buty1peroxy)butane do not present' any paiticularly serious toxicological hazards in normal handling. Precautions should be taken to prevent accumulat~ionof high concentrations of t'he vapors as eventually they may cause some lung irritation. If the liquids accidentally contact the skin or eyes, the areas should be irrigated with copious quantities of water.
CH, CH,
CH,
I I
HCH
I C~I,-c-oo-c-oo-
dH3
C'H,
iH3+ I
-CH,
TI20 (3)
CH3
ASALYSIS
Compared t o di-tert-butyl peroxide, it is more reactive and is less stable thermally. It can be partially hydrolyzed by acids and this must be guarded against during its isolation. Furthermore, in concentrated state it can be decomposed explosively at elevated temperatures (above about 85' C.) and caution should be exercised in this regard. The stability is discussed i r i detail later in this paper. At present pure 2,2-bis(tert-butylperoxy)butaneis not, available. The technical grade contains approximately 25 to 30% di-tertbutyl peroxide which, because of the higher temperatures required for its decomposition, does not enter into the reaction wherein 2,2-bis(tert-butjylperoxy)butaneis the catalyst, but instead acts as an inert diluent and does not interfere with the desired process.
It is a well essablished fact that organic peroxides differ widely in their response to peroxide-detect,ing reagents and to analytical procedures-for example, (26-28). A usual method is that involving the liberation of iodine from alkali iodide in the presence of acet,ic acid. Hydroperoxides, such as te/.t-butyl, and diacyl peroxides, such as benzoyl, are determined easily by this technique. IIowever, 2,2-bis( tert-but'ylperoxy )butane reacts only slowly with this reducing agent and di-tert-butyl peroxide is complet,ely unaff'ected by it. Further, di-lert-butyl peroxide docs not react with ferrous ion and hence the titanous sulfatethiocyanate procedure fails. The response of 2,2-bis(lertbuty1perosy)butane to this reagent is too slow for utility. The two peroxides may be det,ermined by the following methods:
TABLE I. PHYSICAL PROPERTIES Di-ted-butyl Peroxide Empirical formula
C12H2~01
Molecular weight 146.22 Physical s t a t e Specific gravity, dza 0.7940 Refractive index, n%O 1.3890 Melting point,, O C. -40.0 Boiling pointa, O C. 111 a t 760 mm.b Flash point (Tag Open C u p ) , O F. 65 Solubility ( a t 20' C.) I n water Insoluble I n acetone bIiscible I n toluene Miscible I n octane Aliscible hIild ethereal Odor Available oxygenc (t,heoretical), % I O . 93 Optical d e n s I t yd (ultraviolet absorption), g./1. 10 3400 A . 3000
CIHP
h
..
234.44
Colorless, mobile liquid
0,865 1.400 - 2 6 t o -10
-0.8
...
26 a t 0.2 m m . ; 50 a t 2 mm.
AboT-e 150
84
Insoluble AIiscible lIiscible AIiscible F a i n t ethereal
Insoluble hliscible F a i n t ethereal
13.66
1 3 . 1 (approx.)
..
11.9
... ...
0 . 012
0.185 0.475 0.900 1.60
2600 2400 Heat of combustion (liquid at 25' C.), kg.-cal./mole 1273.0*1 2 a
CHS
0,8886 1.4145
.0,0l7 0.137 0,285 n ,460 0,603
2800
Technical 2,Z-Bi(tert-butylperoxg)burane
2,2-Bis (tert-burylperoxy) butane
CsHisOr
...
...
1869.3 * 1 . .5
..
1233.2
C.) Correlated values are as follows: 1.
C.
p , mm.
0 5.82
t("
10 10.78
+ 204
20 19.51
30 33.54
40 5Ll4
60 87.20
60 133.2
70 197.2
80 284.0
111 i60
Heat of raporization (calculated): AH* a t b.p. = 9.6 kg.-cal./mole. See section on methods of analysis. d Obtained from iso-octane solutions in I-om. cell in Beckman spectrophotometer; optical density (transmission) -1. c
Di-lerf-butyl Peroxide. The sample dissolved in glacial acetic acid is mixed in an inert atmosphere with an equal volume of constant boiling. aqueous hydrogen iodide (c.P., 56%,). The container is closed, the mixture heated a t B O O (1. for 45 minutes, arid t h e liberated iodine titrated with standard thiosulfat,e solution after dilution n-ith oxygenfree water. By this method all ot,her types of peroxides are determined and corrections must be made for their presence. Other organic substances reactive with concentrated hydrogen iodidP will interfere. It should be mentioned also that di-tert-butyl pcroxide, as well as its ultimate products of decomposition, ketones and tert-butyl alcohol, can be accurately determined by infrared spectrometry (16). This method is obviously subject to interference by copresent molecules. 2,2 Bis(lert butylperoxylbutane. The sample is added t o isopropyl alcohol containing a small amount of acetic acid and sodium iodide. The mixt,ure is boiled under a reflux condenser in an inert at,mosphere for a few minutes, a small amount of concentratcd hydrochloric acid added, and the boiling continued for a short t,ime. The liberated iodine is titrated with standard thiosulfate solution after dilution with water (11). This method will determine all compounds as reactive or more
-
..
These liquids should not be distilled a t atmospheric, pressure (see section on stabilit,y). Vapor pressure of D T B P is given by the equation: log,op(mni.) = 6.7960 -
Vol. 41, No. 8
log10
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1949
1675
The methyl and R radicals produced in 5 and 6 may abCurnene, 0.80 Mole/Kg. Solution tert-Butylbensene, 0.78 Mole/Kg. Solution stract hydrogen, add to unt l / 2 = 3.0(10--20)ea7,600/RT t i l 2 X 1.7(10-20)e'S,U00/RT-Half Stoichioinetryb ; Half Stoichiometry saturated bonds, or associate life, t-Butyl kn, life, t-Butyl Temp., ka, with another radical. These alcohol Acetone hr. - 1 hr. alcohol Acetone t0.1' C. hr.-1 hr. are, of course, the commonly 1 2 . 8 0 . 7 5 1 . 2 5 0 . 3 9 0.054==0.007 1 61 125 0.058a0.004 12.0 0.49 3.9 0.56 1.44 3.7 1.51 0.18 10.01 135 0 . 1 9 *0 .01 accepted steps in polymeriza0.77 1.2 1.23 0.54 =t0.08 1.3 0.46 1.54 145 0.56 10.05 tion processes: chain transfer, chain initiation, and chain Half Stoichiometry Half _ _Stoichiometry _ _ _ ~ termination (19). life, t -_ Rn t v"l _ . -_ Temp. ka, life, t-Butyl lid hr. alcohol Acetone hr. - 1 hr. alcohol Ketonese t0.1O hr.-1 2,2 - Bis(terf buty1peroxy)ca. 1 . 9 ca. 0 . 1 0.040 17.5 0 2.0 11 3 125 0.061+0.011 butane. Kinetic studies of 5.3 0 2.0 ea. 0 . 1 0.13 4.6 ca. 1 . 9 135 0 . 1 5 A0.02 1.7 0 2.0 ca. 0 . 1 0.41 1.2 ca. 1 . 9 the decomposition of 2,2145 0.58 k0.07 Calculated from d a t a for first 50% decomposition. bis( tert-buty1peroxy)butane are b Products from 1 molecule of ROOR (R = t-butyl): Equations 4 , 5 , a n d 6. not as complete as those of C Interpolated a n d extrapolated from reference ( 1 6 ) ; temp. range, 139.8-159.8' C. d Calculated from d a t a for f i r s t 33% decomposition. di-tert-butyl perouide. Howe Principally acetone with a b o u t 570 methyl ethyl a n d higher ketones. ever, the data thus far obtained for the reaction in cumene or dibutyl phthalate reactive than 2,2-bis(tert-butylperoxy)butallc. Di-tert-alkyl persolution show that the rate of total peroxide disappearance [as oxides are not affected. determined by the analytical procedure for 2,2-bis(tert-butylperoxy)butane given above] is adequately described b y t h e DECOMPO SITION S first order expression (Table 111). As also shown in Table IV, the decomposition velocities and effects of temperature thereon Both di-tert-butyl peroxide and 2,2-bis(tert-butylperoxy)in these two solvents are nearly identical. It seems likely, butane undergo controllable thermal dissociation with highly therefore, t h a t the rates of free radical production by this perefficient production of free radicals. This fundamental property oxide in a hydrocarbon- or ester-type monomer would be closely is the basis of their application as ignition accelerators, polymeri- , approximated by the data of Table IV. A comparison of the zation catalysts, and intermediates in organic synthesis. Di-tert-butyl Peroxide. Extensive studies (15, 17, 19) of the activation energy (36 kg.-cal. per mole) with t h a t for di-tertbutyl peroxide suggests that the rate-determining step is likedecomposition of di-tert-butyl peroxide have shown that the wise the dissociation of an oxygen-oxygen bond, but definite reaction is unimolecular under the conditions of the experimentst h a t is, it is independent of the concentration and the environassignment is not possible a t the present time. ment. This may be seen from the data in Table 11, which compares the rates and effects of temperature thereon in vapor phase and in three diverse solvents, cumene, tert-butyl benzene, and TABLE111. DECOMPOSITION O F 2,2-BIs(tert-BuTYLPEROXY)BUTAh7E tri-n-butylamine. The uniformity implies that the same simple Initial process-namely, scission of the nxygen-oxygen linkage-is Concentration, % rate-determining in all cases. This is further supported by the li, Hr.-l Decomposed Mole/Ka. fact that the activation energy of t h e decomposition, 37.9 =t Cuinene Solution, 110' C. 0.6 kg.-cal. per mole, is closely the energy of dissociation of the 0.0927 GO 0.15 * 0.01 57 0 . 1 3 * 0.01 0,354 peroxide oxygen-oxygen bond, 39 kg.-oal. per mole. 92 0.13 0.01 0,681 71 0.15 1 0 . 0 2 0.699 This finding is of importance in the industrial application of Dibutyl Phthalate Solution, 110' C. di-tert-butyl peroxide as a resin polymerization catalyst as only 82 0.134 A= 0.001 0.0443 the temperature of operation, and not the kind of monomer or 83 0,0991 0.137 0.001 prepolymer, appreciably affects the rate of chain initiation. This 0.138 * 0.001 84 0.653 behavior differs from that of certain commonly used peroxides whose specific decomposition rates vary markedly with the TABLE IV. DECONPOSITION O F 2,2-BIS(k?Tt-BUTYLPEROXY)solvent and concentration. For example, benzoyl peroxide BUTANE ( 1 , 2, 3, 7 , 1 4 ) decomposes in a more complex manner, and an Cumene, Dibutyl Phthalate, 0.1-0.7 Mole/Kg. Solution 0.1-0.5 Mole/Kg. Solution important fract'ion of the free radicals potentially available for = 1 . 4 (10-?Q),aE,UOQIRT,-t~,~ = 1.5 (10-2U)e36,00QlRTchain initiation may be wasted. I n amines i t shows violent Half life, k, Half life, Temp. k, hr. - 1 hr. i.0.1' 'c. hr.-1 hr. decomposition (3,1 4 ) whereas di-tert-butyl peroxide decomposes 0.001 17.3 0.0384 i0.0004 18.0 100 0.040 smoothly and a t a predictable rate (Table 11). 0 . 1 3 8 + 0.001 5.0 110 0.14 + 0.01 4.9 120 0 004 1.5 0 . 4 6 =t 0 . 0 4 1.5 0.466 Scission of the oxygen-oxygen bond leads to two tert-butoxy Half Life ( h i ? ) Hours , radicals:
TABLE11. DECOMPOSITION OF Dr-terl-BvTYL PEROXIDE 7 -
IN
VARIOUS ENVIRONMENTS
7 -
e.
-
I
'
(1
;t
;f
;f
(CHa),CO-OC(CHa)a
* 2(CH3)3CO-
(4)
These in certain environments are capable of abstracting hydrogen atoms, forming tertbutyl alcohol and another free radical :
(CH8)aCO-
+ RH +(CHa)aCOH + R
into acetone and a reactive free methyl radical: (CH,),CO
+ CHI
115
%-Butyl alcohol, 0.5 mole/kg. solution
0.5 Tri-n-butylamine, rnole/kn. solution
10.1 6.0 2.0 1.2
10.5 6.6 1.9
1.1
(5)
If the solvent is resistant, the tert-but,oxy radical can dissociate (C&)$CO-
Temp., ~ 0 . C. 1 ~ 95 I00 110
(6)
The dat>ain Table I1 show that,, despite large variations in the reactivities of the solvents toward the tert-butoxy radicals, the rat,e of decomposition of the peroxide is affected but little.
In n-butyl alcohol or tri-n-butylamine solution the decomposition proceeds more rapidly and, in the latter solvent, slight deviations from fist order behavior are noticeable, particularly a t the lower temperatures. The reaction velocity, therefore, is expressed in Table IV only in terms of the measured half lives for a 0.5 mole per kg. of solution. With other initial concentrations these values would be altered slightly. It is noteworthy
1676
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
that, like di-tert-butyl peroyide, 2,2-bis(teit-butylperoxy)butane decomposes in a regular and predictable manner when dissolved in a n amine. As might be expected, the stoichiometrv of the 2,2-bis(feitbuty1perosy)butane deconiposition is more complicated than that of di-tert-butyl peroxide. However, in cuniene or tri-nbutylamine solution at least 90% of the tert-butoxy groups appear as terf-butyl alcohol which probably originates in the same manner as that from di-tert-butyl peroxide. A small amount of ketone is also formed. The butane chain in the peroxide appears as carbon dioxide, methane, and rthane. As is the case with acetyl peroxide (12),the cumene appears largely as dicuniyl. The amounts of the various products indicate that approximately four free radicals are produced from each molecule of 2.2-bis( fertbuty1perouy)butane
TABLE5'.
THERlIAL
Peroxide Di-tert-butyl (DTAP)
Z,Z-Bis(tert-butylneroxy)butane (2,Z-PB)
RATES O F
nECohIPoSITIOX
(Solvent, benzene) Conceotration, Temperature, Mole g,
c.
6 1
PEROXIDES Half lifea, Ilr. 239 21.8
138
4.4
84
90.0 29.0 8.0 0.8
95
33 .i 10 2 3.1 1 .0
Benzoyl
Lauroyl
r
fert-Butyl perbenzoate
{E;
1
(125 4.2 105 7.6 For purposes of comparison, the d~compositionsof these perosiides a i c all regarded as first order reactions. ~
~~
~~~~~~~~
Comparison with Other Peroxides. The decomposition rates, as measured in these laborat.ories, of several commercially available peroxides are given in Table .'1 (For purposes of intercomparison. these values xvere all obtained in a single solvent, henzene; its low lmiling point made it necessary t o carry out the dccompoRitions i n sealed glass t,ubes.) Ahhough only the decomposition of di-teit-butyl peroxide has been shown to b(. unimolecular, the deviat.ions from first order behavior shown by the other perosides are not so large as to vitiate entirely a treatment, of the processes as Erst order. This has been done in Table V in the column giving the half lives. These data for di-tertbutyl peroxide in benzene agree suhstantially vith those for thc other media (Table, IJ). Di-tert-but,yl peroxide a i 136" C. decompose,. with n half life of 4.4 hours, whereas 2,2-bis(tertbuty1perosy)hutane has a comparable rate at about 110" C., tert-butyl perbenzoate at 115" C., benzoyl at 80" C., and laurovl peroxide at 70" C. This sequence permits a rough estimate of the temperatures at which the several compounds would give the same rate of chain initiation. However, the table does not convey any information regarding subsequent steps of propagation, transfer, or terniination; these are almost entirely governed by the environment,. STABILITY
Di-teit-butyl peroxide, even in the pure state, decomposes nonviolently in an open system and is insensitive to impact' according to the present tests. I t proves to be a surprisingly stable substance. 2,2-Bis(tert-butylperoxy)butane, either pure or as the technical preparation (containing approximately 30y0 di-tert-butyl peroxide) presente a greater hazard as it, can be exploded m?-ithviolence if subjected to elevated temperatures. is
Vol. 41, No. 8
sensitive to impact', arid burns rapidly when ignited. However, pure 2,2-bis( tert-butylperox.i-)butane possesscs a high flash point. Further, if diluted with certain inert, solvent,s, the ha,zard of explosion and conibust>ionis greatly reduced. Bot,h compounds are compared in the follo~~ing text with some commercial peroxides and from these results it can be stated that di-tert-butyl peroxide is generally less dangerous than the common commercial materials and that the over-all hazards of solutions of 2,2-bis(tert-buty1peroxy)butane are no greater a,xid frequently less than the hazards associated with the more usual compounds. In addition to tests conducted by t,he Bureau of Explosives of the Association of American Railroads ( 6 ) , other test,s performed at these laboratories serve t,o define the stability liinitations of t,he two compounds. Storage Tests. A %gallon sample of di-tert-butyl peroxide in a steel drum for 10 days at 115' to 140" F. shon-ed no pressure increase detectable by a mercury manometer. At higher teniperatures, 194" t o 230' F. di-tert-butyl peroxide will evaporate from open containers without violence (see thermal tests). A 50-ml. sample of t,echriical 2,2-bis( ?ert-butg1peroxy)butane in glass at 122" F. for 6 days remained unchanged and showed no gas evolution. A 50-ml. sample vas held at 194' F. for 48 hours without apparent incident; at the end of that time the sample was reduced 50% in volume. Corrosion Tests. Closely allied with storage stability are corrosion d a h . It' has boon conclusively demonstrated that di-tert-butyl peroside is noncorrosive toward st,eel and aluminum, an important factor in the storage and shipping of this niaterial. In these test,s 0.75 X 1 inch specimens of drum steel were placed at various positions in a glass jar containing 300 mi. of pla.nt run di-tert-butyl peroxide. The tests were conducted a.t, atmospheric temperature. For comparison the same t,ests were made using 9hell rubber solvent A in place of di-ler2-buty-I peroxide. At the end of 6 months results were as given in Table VI. Of considerable importance is t,he fact that in these tesk the concentration of the peroxide showed a decrease of less than 1%. This is comparable to the decomposition that occurs when glass containers are emplopti under the same conditions and shows that steel does not, affect tli-terf-butyl peroxide.
VI.
S I X - 1 1 O S T H
