May, 1944
REACTIONOF MONO-SUBSTITUTED ETHYLENIC DIBROMIDES WITH POTASSIUM IODIDE705
behave differently, the unbracketed "complex" is probably unstable, while the liberated Cu+ ion is likely to undergo rapid oxidation to Cu++.
the rate increase becomes proportional to the increase in the copper concentration. 5. The dependence of the rate on p H in the presence of copper has the appearance of being SummgfV complex. However, analysis shows that neither 1. The autoxidation rate of 1-ascorbic acid in the neutral acid nor the divalent ion, but o d y the presence of copper (2 X 10" mole/liter) is the monovalent ion of I-ascorbic acid is the substrate of the copper catalysis, and that the apparent irinvestigated from p H 2.59 to 9.31. 2. The results agree with the assumption that regularity in the dependence of the rate on p H in the primary reaction, one mole of dehydroas- is caused by complex formation of some of the corbic acid and of hydrogen peroxide is formed bufTem with the co per catalyst. A concentration of 2 X rnole)ker of copper, about 4 mg. of from one mole of ascorbic acid and oxygen. 3. The rate is independent of the ascorbic Cu(NO& per liter, increases the reaction rate of acid concentration, and, as shown in the pre- the monovalent ascorbate ion by a factor of 104. 6. No corresponding effect of silver was found ceding paper of the series, proportional to the at pH 5.12. oxygen concentration. 7. The mechanism of the catalysis is discussed 4. At very low copper concentrations, the rate increases faster than the concentration of the briefly. metal. At higher concentrations of the latter, ROCHESTER,NEW YORK RECEIVED FEBRUARY 1, 1944
[CONTIUBUTXON FROM THE
DEPARTMENT OF CHEMISTRY OF THE UNIVERSITY OF
CALIFORNIA AT h S ANGELES]
The Reaction of Dibromides of Mono-substituted Ethylenes with Potassium Iodide BY DAVIDPRESSMAN AND WILLIAM G. YOUNG Iodide ion reacts with the dibromide of an olefinic compound to yield the originalunsaturated compound, bromide ion and triiodide ion according to equatbn 1. HCHBrCHSBr 4-31- + 2Br-
+ L- + RHC = CHs
(1)
Experimental Rate6 of Reaction.-The
rate constants were obtained graphically by the use of equation 2
where a and b are the initial iodide and dibromide concen-
The reaction proceeds h s t order with respect to trations respectively, rp is the fraction of dibromide reacted the dibromide concentration and also with respect and f is the time in hours. The following corrections were to the iodide ion concentration in 99% methanol made as discussed previously': (a) correction to standard temperature of 46.00, 60.00, 75.00, 80.00 or 85.00',.(b) solution and is practically independent of the correction for activity of solvent (methanol preparations triiodide ion concentration. I, 11, I11 are the same as those used previously*), (c) We have shown that in the reactions of di- correction for salt &e&, and (d) correction for solvent bromides of cis and trans olefins with potassium expansion.' iodide the reaction is slower for the dibromide Reparation of Material8 from the cis olefin2and that the olefin produced is 1-Pentene dibromide was prepared by mixing slowly a t in its original stereofom in the case of the 2- 0" bromine with the 1-pentene obtained from ethylmagbutene &bromides.* The reaction takes place nesium bromide and allyl bromide. The product was fractionated through a Weston column and the fraction boiling presumably through the attack by an iodide ion 'at 84.5-85.5' at 15 mm. was used. to remove a positive bromine atom as iodine Acrylic Acid Dfbromide.-The Eastman Kodak Co. bromide while, simultaneously, the electron pair product melting at 59-61' was used. Styrene dibromide was prepared from styrene and which is left unshared by this removal attacks bromine in carbon disulfide. The solvent was evaporated the carbon face opposite the remaining bromine and the product recrystallized from alcohol; m. p. 74.0atom forming a double bond and liberating a 7 4 . 5 O . negative bromide ion.s Allylbenzene dibromide was prepared by brominating, Our purpose in this research was to determine in carbon tetrachloride, allylbenzene obtained from allyl and phenylmagnesium bromide. The product the reactivity of various mono-substituted ethyl- bromide was fractionated and the fraction boiling at 126' at 2 mm. ene dibromides with iodide ion. The reactions was used. were studied in 99% methanol a t two or more Allyl Alcohol Di-da-The Eutmsn Kodrk Co. product was refracbonated and the fraction boiling 113temperatures. (1) R . T. Dillon, Tlus JOURNAL, 64, 952 (1932). (2) W. G . Young, D.Pressman and C. D. Coryell, ibid., 61, 1640 (1000). (s) S. Winstein.
(maw.
D.Preasman and W. 0.Young,
ibid., 61, 1645
114' a t 13 mm. was used.
(4) C ~ O of m8.0, 4& e,$, 7 6 u d 8.1% u.f. made at temW ,-*; (e ref. 2) h n d o l t perature# 45, 80, 75, 80 a Bdmstein, "Tabellen," V& von Julius Springer, Berlin, 1928, Vol. I, p. 278.
DAW PRESSMAN AND WILLIAM G.YOUNG
706 REACTION ~ Parent compound
Ethylene
T
Vol. 66
TABLE I CONSTANTS E AND HEATSOF ACTIVATION FOR THB REACTION OF RCHBrCHnBr k, obr.
Temp., OC.
1-34" 0.299" .0582" 0113" .0794" .0148" 3.9ab 3.98Sb l.665* 1.66d 0.417b .41@ ,1021' .lo* .097$ .0979 .01905" .01955c .0918
KI
Dibromide
moiesh., motesb., b a
k c0r.d
-
k cor. KI 0:25
WITH
Av. k l./mol* hr.
POTASSIUM IODIDE
-
DeviaAH*, tion, % KI 0.95
74.93 0.22 0.022 1.54 23.2 (1.54). .22 .027 0.344 59.72 ( .344)* Propylene 74.93 .024 .0669 .22 25.2 ( .0669)' .0130 .22 59.72 .022 ( .0130)' I-Butene 74.93 .23 .0913 ( .0913)' ,034 25.8 59.72 .22 .0171 ( .0171)* 4.28 4.27 85.38 .243 ,023 4.26 Acrylic acid 20.9' 0.2 4.26 85.38 ,248 ,023 4.26 1.822 1.825 .2 74.91 .252 ,021 1.825 1.828 .251 .022 1.830 74.90 0.466 0.467 .256 .025 0.468 .1 79.46 .252 79.46 .467 .467 ,021 .1100 .I108 .1109 44.75 .023 .1 .238 .1109 ,241 .025 44.75 I1103 .lo75 .lo90 .lo79 Allyl alcohol ,027 25.2 74.90 * 245 1.0 ,1068 .lo70 .027 .254 74.91 .02079 ,02081 ,02107 1.2 .!248 ,028 59 * 64 .OB .02131 .02133 59.64 249 .278 Allylbenzene 74.95 .022 .09B .0967 1.0 24.6 ,0978 .021 .242 .0983 * 0988 .0915c 74.95 ,251 ,020 .01834" 59.64 .02000 .OM8 ,01987 0.6 .252 ,022 .01978 ,01976 .0181lc 59.64 .0591 ,0571 .0581 25.0 1.7 Bromoethylene .055? 85.37 ,310 .026 .251 .0591 .0592 ,028 .055$ 85.37 ,02121 + 02115 .255 .oa9 .02134 0.9 .0193d 74.90 .02141 .02152 .028 .01945b 74.90 .242 .lo07 .lo12 .loo6 ,023 .6 24.8 .09m 74.58 1-Peatene * 242 ,0999 .022 .loo0 .248 ,0896 74.60 .02o00 .02012 ,02015 .020 ,240 .2 .0183T 59.64 .02016 .OB18 ,248 .020 ,01850" 59.64 4.37 4.34 21.7/ .239 .023 4.34 .7 4 . 05b 85.36 Styrene 4.31 .023 4.30 4. 03b 85.36 .a46 2.868 2.868 2.657 80.12 .2"8 .025 2.880 1.802 1.811 .021 1.796 1.612 74.55 .244 .5 .025 1.831 ,261 1.820 1.648 74.59 .024 0.429 0.429 0.436 1.6 .249 0.389 59.48 ,211 .3925a 59.48 .028 ,433 .442 ,251 .021 ,0925 ,0924 .0931 0.8 .OM@ 44.75 .021 ,0926 .0937 .OM9 44.75 .231 0 These data were reported by Dillon using methanol which gave rate constants 7% lower than those obtained with the synthetic product (I) used gs a standard in this work. * Synthetic methanol 11, rates 2% lower than in methanol I. The constants have been corrected for reactivity of solvent, c Synthetic methanol 111, rates same as in methanol I. solvent expansion and to the temperatures 45.00,60.00, 75.00,80.00 or 85.00°. * These calculations were made from data reported by Dillon. Correction has not been made for the potassium iodide effect. This value was obtained from slope of the curve in Fig. 2.
.
I
Bromoethylenc Dibromide.-The Eastman Kodak Co. product was refractionated and the fraction boiling at 86.0-87.0' a t 18 mm. was used.
Experimental Results The pertinent date for the compounds studied are in Table I. There are also listed the values of the heats of activation calculated by the Arrhenius equation AH+ = R P d In k , b . / d t
(3)
In Table I1 are given the observed relative
Am
values of the heats of activation and the entropies of activation 4 9 (equation 4).6 AS*
- As$
=
:!
- (RT in
i)
- A€@ - @ (4)
A€@ and AS? are, respectively, the heat and entropy of activation of the reference compound, ethylene dibromide. (5) See L. P. Hammett, "Physical Organic Chemistry," McGrer.
Hill Book Co., New York. N. Y.,1940,Chapter IV.
May, 1944 REACTION OF MONO-SUBSTITUTED ETHYLENE DIBROMIDES WITH POTASSIUM IODIDE707 TABLE I1 RELATIVE ENTROPIES AND HEATSOF ACTIVATION FOR THE REACTION OF RCHgrCHZBr WITH POTASSIUM IODIDE Aiio
Parent compound
I./mole hr.
R
Ethylene Propylene 1-Butene 1-Pentene Allylbenzene Styrene Bromoethylene Allyl alcohol Acrylic acid
H
1.54 0.0669 CHI GHK .0913 .lo06 CsHi .0978 CHzGHs 1.811 GHi 0.02134 Br CHiOH .lo79 COOH 1.825
-
AS* AS?
cal./deg
0 -0.5 1.8 -0.8 1.5 -4.0 -3.3 0.4 -6.3
-
AH*
AH?
Substituting for k1 and kl, their values as given in equations 7 and g7
-
ka =
kcal.
0 2.0 2.6 1.6 1.4 -1.5 1,8 2.0 -2.3
kT e ~ ~ ? / ~ e - ~ ~ $ / ~ T
equation 9 is obtained. kT A S ? / R ~ - AH?/RT d l n T (e
+e
AS?/ R ~ A- H ? / R T
)dT
&/RP (9) Carrying out the indicated differentiation and neglecting the small term, 1/T, gives equation 10.
The observed effect of various substituents, R, on the reaction of RCHBrCH2Br with iodide ion is to increase the heat of activation in the order COOH < C6H6 < H < CeH6CH2 < CaH7 < Br < CHaOH, CHa < GH6 and to increase the entropy of activation in the order: COOH < CsH6 < Br < CiHaCHz < CsH7 < CHa < H < CHZOH < CZHK.
(10)
As the temperature increases the apparent value AH* approaches the value ( A E @ ~ ( ~ = - A S ? ) / R AHF)/(e(ASF-AS?)/R + I). This reduces to the average e ) / 2 if the entropy of activation is the same for the two reactions, i. e., A* = A$. As the temperature decreases, the apparent Discussion value of A m approaches the smaller of the two The functions AH* and AS* are in general values A B or A H f . We have adopted the conrelatively independent of temperature and are vention that A@ is the smaller.s more reliable standards of comparison of reactivity A more useful equation for discussion is obtained than is the rate constant, since a sequence of order by subtracting from both sides of equation of reactivity as determined by the rate constant 10 to give equation 11. a t any one temperature may be different at some other temperature. Empirically this occurs in the case of acrylic acid dibromide and styrene dibromide.6 The rate constant of acrylic acid dibromide is larger than that of styrene dibromide This equation shows that the difference between a t 45' but smaller at 85'. the observed value AH* and the heat of activaHowever, in the reaction of potassium iodide tion for the reaction of either of the bromine with unsymmetrical dibromide such as styrene atoms is a function of the relative values ( dibromide, even the observed heats of activation A@) and (A$ AS?) and of T and is and the observed entropies of activation are not independent of the absolute magnitude of AH*. reliable bases of comparison of reactivity since In Table I11 are given for several different they would be expected to be functions of temperature, aside from their general variation with assumed values of AH? - AHf and, of A$ temperature due to changes in the vibrational and AS?, the values at 75' of (a) A H f rotational energy states with temperature. This (b) the rate of change of AH* with temperatures; arises from the fact that either bromine atom in an and (c) the fraction of the total reaction which olefin dibromide molecule may be attacked by is due to the bromine atom with the lower heat of iodide ion and in the case of an unsymmetrical activation,'O kl/(kl K2). The assumed values of dibromide the two bromine atoms would be at(7) H. Eyring, J . Chcm. Phyr.. 8, 107 (1936). tacked a t different rates. The rate of liberation of (8) Similar to AH*, aS* is a function of T , AS?, AS:, AH? iodine is thus given by the equation and AH?.
+
(m+
m;
+
d (Ia-)/dt = e
(kl
+ kr)(Dibromide)(I-) (Dibromide)(I-)
kob.
(5)
where kl and K2 are the rate constants for the attack of the individual bromine atoms by iodide ion and kobs. is the observed rate constant which is equal to the s u m of kl and Kz. The obswed heat of activation AH* is given then by equation 6 . d In
(kl
+ kg)/dT = A H * / R P
(6)
(6) Similar cases have been pointed out by T. L. Davis and R. Heggie, J . Utp. Chcm., 4, 470 (1937).
(9) The rate of change of the observed heat of activation with temperature is given by equation 12.
d AHS dT (AH,+ =
-
AH?)I , ( A s ~ - A S ~ ) / R e ( A H ~ - A H ~ ) / R T
R T ' ( e ( ~ ~ ? - ~ ~ ~+) l)a/ ~ e ( ~ ~ ~ - ~ ( 12)
(10) This fraction is given by equation 13.
DAW PRESSMAN AND WILLIAMG. YOUNG
708
Vol. 66
-
TABLEI11 AH? - A@ and ASf A@ used are of the APPARENT HEATOF ACTIVATION, ITS RATE OF INCREASE Same magnitude as was observed in changing WITH TEMPERATURE AND THE FRACTION OF THE REACTIONsubstituents in symmetrically sbbstituted ethylene WHICH IS DUE TO THE BROMINEATOMWITH THE LOWBR dibromides. HEAT OF ACTIVATIONAS FUNCTIONS OF AH? - AH: Figure 1 shows plots of the apparent heat of activation relative to the lower of the individual AND A s ? - A S T AT 75" values, A@, as a function of temperature as Value of AS? - AS? (cal./deg.) (assumed) calculated from equation 11 for several Werent mf - AH?, cal. (assumed)
-4.6
25 19 10.4 5.4 2.3
700 1400
2100 2800 3500
550 800
260 189 100
53
700 450
23
220
d aH*/dP' (cal./deg.) 0.069 0.75 .I04 1.08 0.81 .094 .60 .062 32 ,032
700 1400
2100 2800
3600
k,/(k, 0.96 .99 1.00 1.00 1,m
700 1400 2100 2 m
3500 100 I
15001
4.6
0
-- AH? (cal.)
AH*
200
0 .33 1.93 4.00 4.30 2 95
+ kz! 0.21
0.73 ,8'7 .95 .98 .99
400
300
.43 .67
.84 .94 ,500
600 -
I
1 ;$
I1
Absolute temperature. Fig. 1.-Plot of values of & Hi* against absolute temperature for various assumed values of AH^+ - AH,* and AS,* - AS1*:
-
AH&A B C D
E P
G H
AH,*:. cal. 700 700 700 2100 2100
2100 3600 3500 3 5rm
.
1
__
-
I
'
0
Curve
assumed values of AH? - @ and of A* AS?. The temperature region in which our experiments were carried out is marked by dotted lines. The calculated values in Table I11 and the plots of Fig. 1show that the observed value, AH*, may be quite different from either of the values hH;+ and A@ which must be known before any quantitative theoretical consideration can be given to a discussion of the effect of structure on the reaction. The calculated values of the rate of change of AH* with temperature indicate that such a change would probably not be observed within the accuracy of our experiments. Experimentally, the heats of activation of the reactions of styrene dibromide and of acrylic acid dibromide appear to be constant over a range of 40' as is shown by the straight line character of the plots of the logarithms of the reaction rate constants against the reciprocals of the absolute temperatures (Fig. 2).
AS*
- ASi*, Ed.
4.6
0
-4.6 4 6 0 -4.6 4 6 0 I f
2.90 3.00 3.10 3.20 lOOO/T. Fig. 2.-Plot of log,& against reciprocal abselute temperature for acrylic acid dibromide 0 , and for styrene dibromide 0. 8.70
2.80
The authors are indebted to Dr. C. D. Coryell for assistance in the calculation of the reaction rate constants. summary The reaction rate constants and the heats and entropies of activation were determined for the
THEA m m OF TYROSINASE TOWARD PHENOL
May, 1944
reaction in 99% methanol of potassium iodide with monosubstituted ethylene dibromides, RCHBrCH2Br where R was CsH,, CaH6, CaH&!H2, CH20H,COOH and Br. It is shown that, since each of the bromine atoms can react and at a different rate and with a
[CONTRIBUTION FROM THE
709
different heat of activation, no theoretical significance can be given to the effect of various substituents, R, on the observed values of the heats of activation and entropies of activation of the reaction of RCHBrCHzBr with potassium iodide. LOS ANGELES,
DEPARTMENT OF CHEMISTRY,
CALIFORNIARECEIVED JANUARY 18, 1944
COLUMBIA ~JNIVERSITY
1
The Activity of Tyrosinase toward Phenol BY RALPHC. BEHMAND J. M. NELSON As shown by several investigators1s2Dathe phenol oxidase, tyrosinase, possesses two essentially different enzymatic activities. It not only catalyzes tbe aerobic oxidation of many odihydric phenols to their corresponding oquinones, but also catalyzes the introduction of a second hydroxyl group into several monohydric phenols, o r t h to the hydroxyl group already present. These oxidation reactions are not simple, but involve several consecutive and concurrent reactions, especially when monohydric phenols constitute the substrate. Taking phenol and catechol as representing the two types of phenols, the final oxidation product in both instances is p-hydroxyq~inone.~In the enzymatic oxidation of phew1 at PH 6, 3 atoms of oxygens are consumed per molecule of phenol oxidized. OH OH
uptake by means of a Warburg or Barcroft respirometer.6 It is apparent, however, from what has been stated above, that only the first atom of oxygen is concerned with the enzyme’s action on the monohydric phenol. The remaining two atoms of oxygen are consumed in the enzyme’s action on the o-dihydric phenol. The question therefore arises: Can the rate of oxygen uptake serve as a true measure of the enzyme’s activity toward a monohydric phenol? To answer the latter question, it was decided to determine, instead of the rate of oxygen uptake, the rate of disappearance of the monohydric phenol from the reaction mixture. Such a method would be independent of all the accompanying reactions encountered in the oxygen uptake method. For the purpose a reaction mixture, consisting of the enzyme, phenol, b d e r and water, was placed in a reaction vessel and air bubbled through the mixture. Samples were removed at regular time intervals and their phenol +of oxygen 1st atom-+ (JOH contents determined. The results obtained are shown as Curve I. Curve I1 represents the rate OH 0 of oxygen uptake for a reaction mixture, identical I in composition with the one used in following the rate of phenol disappearance. It will be observed of oxygen 2nd atom + H%O(l) (2) that the two curves coincide within experimental error, showing that, at least when phenol is the monohydric phenol being oxidized by means of the enzyme, the concurrent reactions, equations (2), (3) and (4) must proceed at rates at least as great as the rate of the initial oxidation of the phenol (equation 1) and that, therefore, the rate of oxygen uptake can serve as a true measure of OH the enzyme’s activity toward phenol. 0 OH Tyrosine preparations, depending on the I method of preparation, often vary widely with respect to their relative activities toward mono+ 3rd atom of oxygen + hydric and o-dihydric phenols. Therefore, it has become customary, in these Laboratories, to The method usually used for estimating the designate a preparation low in activity toward pactivity of tyrosinase toward a monohydric cresol compared to its activity toward catechol phenol is based on determining the rate of oxygen as a high catecholase preparation and a preparation high in p-cresolase activity as a high cresolase (1) Pugh and Roper, Biochsm. J . , 01, 1370 (1927). preparation.’ Since in the present study phenol (2) Dalton and Nelson, T m s JOURNAL, 61,2946 (1939). was used instead of p-cresol, it should be men(3) Bordner and Nelson, ibid.. 61, 1507 (1939).
8 (yoH +
@+
(4) Wagreich and Nelson, ibid., 60, 1645 (1988). ( 5 ) Vnnubliahed results obtained in these 1,aboratories.
(6) A d a m and Nelson, THISJOVRNAL, 60, 2472 (1938) (7) Parkinson and Nelson, ibid , 6¶, 1693 (1940)
