cooled t o -40" while 18.1 g. (0.1 mole) of ethyl /3-bromopropionate wis added dropwisc r i t h stirring. A thin slurry of phenylbiguanide, 17.7 g. (0.1 mole), in 40 nil. of methanol was added slowly while the temperature was maintained a t -40". On standing overnight, white crystals separated, 7.2 g. (33.6%), m.p. 241-24Z0, identical with a known sample of phenylbiguanide hydrobromide, m.p.241 -243", mixed m.p. 241-243". The filtrate was allowved t o stand for three to fi\-e day.: and poured into 350 i d . of 1070 trichloroacetic acid. A xhite precipitate ieparated, 11 .O g. (26.6%), m.p. 188 13!lo,1* the trichloroacetic acid salt of I , R = -CH2CHn-C-
! CPYI'RIHUTIOS
CH3. The free base, 5.9 g. (90.5y0), mas liberated by the acidition of dilute aqueous methanolic alkali, 11i.p. 116118O, mixed m.p. 114-118°.11bJ2
Achowiedgment.-Li:e are grateful to D ~~~~i~ . H. FrWdman of the u.s. Vitamin Corporation) Yonkers, N. Y . , for his generosity in allowing one of us to use the facilities of their laboratories. We would also like to thank the ~~~~i~~~ cynamid Company for a generous supply of phenvlhiguanide. RROOKI,YX,SEK YORK
F R O M 'I'IIE D R P A R l M E N T O F CHEMISTRY, C A R N E G I E I N S T I I'TTrE O F TECIlYOT.OGJ'
1
The Benzidine Rearrangement. IV. Kinetics of the Rearrangement of o-Hydrazotoluene 131, ROBERTB. CARLINAND RAYMOND C. ODIOSO RECEIVED AEGUST 10,195X The spectrophotometric analytical method was used to study the rate of rearrangement of o-hydrazotoluene by hydrogen chloride in %55; ethanol. a-Tolidine was shown to be the sole rearrangement product under the imposed conditions. The rate is first order with respect t o o-hydrazotoluene concentration, but. in contrast with the rearrangements of hydrazohrnzene which are second order in acid concentration, the order of participation of acid concentration in the rate expression for the rearrangement of o-hydrazotoluene is 1.6. Chloride ion concentration is not involved in the rate expression. Activation energies for the process (18.7, 19.1 and 20.2 kcal./mole) were computed from measurements carried out under three sets of conditions, and an entropy of activation ( -0.62 kcal./deg./mole) was calculated; but little significance is attributed to these quantities. There is a positive salt effect on the rate which is similar in magnitude with that observed in investigations of the rearrangements of hydrazobenzene. Increasing the proportion of water in the solvent causes a rate increase, but replacement of part of the ethanol by dioxane effects little change. Arguments are advanced t o show that the observations resulting from this investigation can be reconciled with Hammond'i proposed reaction sequence for the benzidine rearrangement
Recent kinetic studies of the acid-catalyzed re- not investigated. In the study reported here the arrangements of hydrazobenzene have demon- spectrophotometric analytical method first used in strated t h a t the reaction rate is first order with re- kinetic measurements of the rearrangements of was again employed, so that both spect to hydrazobenzene c ~ n c e n t r a t i o n ~and - ~ sec- hydra~obenzene~ ond order with respect to acid concentration,3--j the concentration of o-hydrazotoluene and that of its that there is a positive salt effect upon the rate3%$o-tolidine (3,3'-dimethyl-4,4'-diaminobiphenyl), which satisfies the Br@nsted-Bjerrum e q ~ a t i o n , ~sole transformation product, could be followed sithat the rate increases steadily with increasing di- multaneously. The order in which acid concenelectric constant in ethanol-water solution^,^ that tration appears in the rate expression was deterthe reactions are subject to general acid catalysis6 mined, and the salt effect and some observations reand that the simultaneous rearrangements to benzi- lated to medium effects were recorded. The solvent chosen for most of the rate runs on dine and diphenyline are identical kinetically and substantially free, under the chosen conditions, of o-hydrazotoluene was 9570 ethanol, in order that side reactions such as disproportionation.4 I n an the results could be compared justifiably with effort to observe the effects of substituents on the those from the preceding study of hydrazobenzene,4 kinetics, a series of investigations of the rates of in which the same solvent was used. The ultrarearrangements of some substituted hydrazoben- violet extinction curves for o-hydrazotoluene and zenes has been undertaken. This paper reports the o-tolidine were determined in 95% ethanol solution results of a study of the kinetics of the hydrogen (Fig. 1). Then o-hydrazotoluene was subjected to chloride-catalyzed rearrangement of o-hydrazotol- the action of hydrogen chloride in 9570 ethanol under the same conditions which were to be used in uene (3,2'-dimethylhydrazobenzene). Using the analytical technique first described by the rate runs, and the extinction curve for the prodDewar,? Croce and Gettler5 measured the rates, uct solution was identical, within experimental eractivation energy, P Z factor and related quantities ror, with that of o-tolidine solutions. Therefore, for the transformation of o-hydrazotoluene by hy- o-tolidine was the sole product under the imposed drogen chloride in 90% ethanol ; however, the prod- conditions, and the absence of rearrangements to uct or products of the transformation were not dis- other isomers and of disproportionation was demclosed, and the salt and solvent effects and the order onstrated. This observation contrasts with those of the effect of acid concentration on the rate were of previous investigators,' who have reported that diphenyline formation and disproportionation ac(1) From t h e D.Sc. Thesis b y Raymond C. Odioso. company the main reaction when o-hydrazotoluene (2) hl. J. S. Dewar, J . Chem. Sac., 777 (1946). 13) C. S. Hammond and H. J. Shine, THISJ O U R ~ A L ,73,220 (1950). is boiled with concentrated hydrochloric acid. The ( 4 ) R. 13. Carlin, R . G . S e l b and R. C . Odioso, i b i d . , 73, 1002 apparent discrepancy undoubtedly can be attrib(1951). uted to the well known effect of change in reaction ( 5 ) 1,. 7 . Croce :inti J D. Gettler, i b i v l . . 7 5 , 8 i I (1953) ( 6 ' 11 1) ('i1lirii: ~ n , lC.
S TTammond, zhi,i , 75, 830
(10.3)
( 7 ) F: SciPlttng and P Wernpr Bn , 23, 3 2 i 2 (1890).
101 22
18 n
2
14
X w
10
230 240 250 260 270 280 290 300 310 Fig. 1.-The
Wave length. ultraviolet absorption spectra of: drazotoluene; - - - - - , o-tolidine.
-,
o-hy-
conditions upon the nature and proportions of the transformation products. The o-tolidine structure for the rearrangement product of o-hydrazotoluene appears to have been proved adequately,8 and the close similarity between its extinction curve and that for benzidine4 can be considered confirmatory evidence. T h e spectrophotometric analytical method was prepared and used in the same way which had proved successful in the study of the rearrangements of hydra~obenzene.~T h e two wave lengths 245 and 285 mp were selected for measurement of optical densities leading to the analysis of mixtures of o-hydrazotoluene and o-tolidine. These wave lengths, which correspond to the absorption maxima for the two compounds (Fig. l), satisfy all three fundamental requirements for satisfactory analytical wave lengths4 Optical density vs, concentration plots for each component in 95y0 ethanol a t each wave length showed that Beer’s law was being obeyed in all cases; Fig. 2 shows the two plots for o-hydrazotoluene. The slopes of these plots yielded the extinction coefficients (Table I) which were TABLE I SPECIFIC EXTINCTION COEFFICIENTS Compound
246 mfi
285 mfi
o Hydrazotoluene o-Tolidine
95 0 18.6
19.0 103.0
used in the two equations from which the analytical results were computed for each mixture. The development and use of the equations based on these data followed the procedures reported in the preTen analyses by this method of ceding a r t i ~ l e . ~ known mixtures of o-hydrazotoluene and o-tolidine in which the composition varied between 20 and SOYo in one component gave results having the average deviation 0.82% from the known. The method is thus substantially more accurate with these mixtures containing but two components than it was with mixtures formed by the rearrangements of hydrazobenzene, in which three components were present. Experimental o-Hydrazoto1uene.-A vigorously stirred mixture of 120 g. of zinc dust, 68 g. of o-nitrotoluene and 300 ml. of methanol was treated dropwise with 250 ml. of 30% aqueous ( 8 ) G. Schultz, G. Rhode and F. Vicari. A n n . , 362, 111 (1907)
0.004 0.008 0.012 0.016 0.020 Concentration, g./l. Fig. 2.-Verification of validity of Beer’s law and determination of extinction coefficients for o-hydrazotoluene a t (1)245 mp, and (2) 285 mp. sodium hydroxide, and the mixture was boiled for several hours. Most of the methanol was removed by distillation, and the solids were collected by filtration and extracted with hot ethanol. The ethanol extracts were concentrated and treated first with 50 ml. of concentrated aqueous ammonia and then with hydrogen sulfide until the red color of the solution disappeared. The pale yellow crude o-hydrazotoluene (26 g., 50%), m.p. 158-162”, which crystallized from solution throughout the hydrogen sulfide treatment, was removed from time to time. Recrystallization of the crude material from petroleum ether yielded white flakes, m.p. 165’, in agreement with the reported value.9 For spectral measurements the white material was recrystallized from petroleum ether until the extinction curve became constant. o-Tolidine (Eastman Kodak Co.) was purified by allowing its benzene solution to trickle through a 12 X 1 cm. column of activated alumina and then crystallizing from benzene-petroleum ether. This process was repeated, and the white crystals, m.p. 131-132°,10 were recrystallized until the extinction curve was constant. The N,N’-diacetyl and N,N’-bis-salicylal derivatives had the m.p’s. 318-319”11 and 202’,12 respectively. Dioxane was purified by the method given by Fieser.’3 Other solvents, reagents and solutions and the apparatus and experimental procedures were the same as those used in the work on hydrazobenzene.4 Pseudo first-order rate constants were computed from the good linear plots of log (loo/% unchanged o-hydrazotoluene) as. time in minutes; 10 t o 18 points determined the slope of each line. A plot of the data from a typical run (no. 11) is shown in Fig. 3.
Results In Table I1 the data from 26 rate runs are listed. At least two independent runs were carried out under each of the majority of sets of experimental conditions. A comparison of runs 1-3 and 6-10 shows the effect of varying the acid concentration a t constant temperature and ionic strength. A plot of log k~ US. log [HCl] using the data from (9) H. Petriew, Ber., 6 , 557 (1873). (10) A. L. Guitermann. ibid., 20, 2016 (1887), reported t h e m.p. 129O. (11) G. Schultz, { b i d . , 17, 463 (1884), reported t h e m.p. 315O. (12) H. Schiff and A. Vani, A n n . , 218, 377 (18901, reported the m.p. 2020. (13) I,. F. Pieser, “Experiments in Organic Chemistry,” Second Ed.. Part 11, D. C . Heath and Co., N e w York, N. Y , 1941, p . .?GO.
ROBERT B. CARLINAND RAYMOND C. ODIOSO
102
VOl. 76
0.9
2.00
& 0.7
x&
0.5 0
1.80
2 2 0.3
i
M
M
I
0.1
1.fin
60
80 100 120 140 Time in minutes. of pseudo fist-order rate constant Fig. 3.-Determination for rate run no. 11. 20
40
these runs is shown in Fig. 4 ; the experimentally determined points correspond to a linear relationship having the slope 1.60. It is therefore clear t h a t the rearrangement rate is not second order with respect to hydrogen chloride concentration, as is the rate of rearrangements of hydrazobenzene under identical conditions; rather, the order of involvement of acid concentration in the rate expression is 1.6 in this case. Therefore, kexp = kl [HCI]'.'.
110 320 130 140 150 -log (HC1) X 10'. Fig. 4.--o-Tolidine: effect on pseudo first-order rate colistant of varying acid concentration a t constant ionic strength and temperature. Since slope of line = 1.60, it follows that Rex,. = kl[HCI]l.s. 100
ionic strength were held constant, t h a t the observed rate increase is solely a function of acid conM I centration. The implication thus derived that REARRANGEMENT OF O-HYDRAZOTOLUENE (1.18 X BY HYDROGEN CHLORIDE chloride ion concentration is not involved in the Run [HCI Total ionic Temp., kr X I?', rate expression receives substantial support from mole)l. strengtha min. no. OC. the data from runs 4-7 and 11 and 12, in which the 1 0 . iozn 0.1020 14.60 4.61 acid concentration and temperatures were held 14.60 4.74 2 ,1020 . 1020 constant while the ionic strength was varied by the 3 .lo20 ,1020 14.60 4.97 addition of lithium chloride. Although the rate 4 1.15 .051 n .0510 14.60 increased with increasing lithium chloride concen.cjin .0510 1.11 14.60 5 tration, the relationship was not linear with respect 1.61 ,0510 , 1020 6 14.60 to chloride ion concentration, and a twofold in7 .05m .in20 1.59 14.60 crease in chloride ion concentration caused a rate 2.99 .0765 .I020 8 14.60 increase of only about 50%. ,0892 ,1020 3.85 9 14.60 Plots of log kl vs. 1/T afforded activation energies 0.875 .0340 .I020 10 14. 60 (Ea) under three sets of conditions, so t h a t a quali1.54 .051n . n850 11 14.60 tative evaluation of the effects on E" of changes in 12 1.41 .05m . noso 14.60 acid strength and in ionic strength was possible. A 13 4.42 ,0510 . osio 25.00 plot of the data from runs 1-3 and 15-18 is shown in 14 4.44 .0510 .0510 25.00 Fig. 5; the slope of the straight line, determined by ,1020 ,1021) 16.1 15 25.00 the method of least squares, corresponds to an ac.lo20 ,1020 15.8 16 25.00 tivation energy of 19.1 kcal./mole. Since the rate 0.822 . inzn ,1020 17 0.00 measurements from which this figure was derived ,821 , 1020 . 1020 .00 18 were made in solutions 0.1020 M in hydrogen chlo,192 ,0.510 ,0511) 19 .00 ride which contained no other electrolyte, the value ,0510 .0510 .I96 20 .00 may be compared with 20.6 kcal./mole, which was 21* 25.00 ,0510 ,0510 13.7b the Ea value for the rearrangements of hydrazoben4.72" 22' 25.00 .0510 .0510 zene derived from rate measurements carried out in .0510 .lo20 5.06 23 25.00 solutions of the same electrolyte and solvent com5.26 24 25.00 ,0510 ,1020 p ~ s i t i o n . ~Data from runs 4, 5 , 13, 14, 19 and 20 25 ,0510 .lo20 0.276 0.00 yielded in a similar way Ea = 18.7 kcal./mole for 0.292 26 0.00 .os10 ,1020 solutions 0.0510 M in hydrogen chloride which conLithium chloride was used to increase the ionic strength tained no other electrolyte. Data from runs 6, 7 of those solutions whose total ionic strength exceeds that and 23-26 led to Ea = 20.2 kcal./mole for solutions owing to hydrogen chloride. Solvent 75:25 ethanol0.0510 M in hydrogen chloride in which the total mater. e Solvent 75: 25 ethanol-dioxane. ionic strength was made 0.1020 by addition of It is also clear from the results of runs 1-3 and lithium chloride. When the value 19.1 kcal./mole 6-10, in which chloride ion concentration as well as for Ea and the rate constant kexp ( = kl/[HCI]1.6) TABLE I1
Jan. 5, 1954
KINETICSOF REARRANGEMENT OF 0-HYDRAZOTOLUENE
103
from run 15 were substituted into the equation“ 2.35
kexp = (ekT’/h)e-Ea/RTeASt/R
AS* was calculated to be -0.62 cal./mole deg. This value was obtained from runs carried out in solutions of the same electrolyte and solvent composition as those from which AS* = 2.9 cal./mole deg. was computed for the rearrangements of hydraz~benzene.~ T h e Ea values calculated from the work reported here agree well with the figure 19 kcal./mole reported by Croce and Gettler.5 Their value of 1.3 cal./mole deg. for AS* may a t first glance seem significantly different from ours; however, when consideration is given to the fact t h a t their ks ( = kl/ [HC1I2) from which presumably they computed their AS* value is of a different nature from the kexp( = kl/[HC1]1.6) from which our value was derived, the discrepancy has no meaning. A comparison of the rate constants from runs 4-7 and 11 and 12, wherein the acid concentration was held constant while the ionic strength of the solutions was varied, shows t h a t the rate of rearrangement of o-hydrazotoluene, like t h a t of hydrazobenzene, is subject to a positive salt effect. When hydrazobenzene and o-hydrazotoluene rates derived from runs carried out in solutions of identical electrolyte and solvent composition are compared, the magnitudes of the salt effects on the two rates are found to be very similar. A plot of log k1 vs. d p , where p is the ionic strength, using the data from runs 4-7 and 11 and 12, is not linear, in conformity with the Brgnsted-Bjerrum equation (log k = log ko Z d ~ A ’ f i )but is a curve of decreasing slope. T h e slope of the curve in the region of the experimental points corresponding to the smallest ionic strengths (runs 4 and 5) was about 3.4. When this figure is divided by the value 1.6 calculated for A’ (=2A/2.303) from the defining equation for AlS and dielectric constant data for %yoethanol, the quotient, which is the ion charge product ZAZB, is found to be about 2. Because there is no assurance t h a t the slope 3.4 used in these calculations approximates the limiting slope, and because the application of expressions derived from the DebyeHuckel limiting law to solutions of such comparatively high ionic strength in a medium of such lowdielectric constant is of doubtful validity, the significance of the value 2 for ZAZBis questionable. Likewise, the apparent contradiction between the value 2 obtained in this work and the value 1 from the work of Croce and Gettlers may have little meaning. It does seem safe to conclude from studies of the salt effect on the rate of the rearrangements of hydrazobenzene and of o-hydrazotoluene t h a t the reaction in the sequence which is most responsive to changes in ionic strength involves two ions of like sign. The solvent in run 21 was 75:25 ethanol-water and in run 22 i t was 75 :25 ethanol-dioxane. When the rate constant from run 21 is compared with those from runs 13 and 14, which were carried out under the same conditions of temperature, ionic
+
(14) S. Glasstone, IC. J. Laidler and H. Eyring, “The Theory of Rate Processes,” McGraw-Hill Book Co., Inc., New York, N. Y., 1941, p. 197. (15) E. S. Amis. “Kinetics of Chemical Change in Solution,’’ The Macmillan Co.. New York, N. Y., 1949, p. 25.
2.05
J
7 1.45 1.15 0.00355 0.00345 0.00335 1/T. Fig. B.--o-Tolidine : plot from which activation energy (E‘) of 19.1 kcal./mole was computed from rate measurements made in solutions 0.1020 M in hydrogen chloride, 0.00365
the only electrolyte.
strength and acid concentration, it is apparent t h a t an increase in the proportion of water in the solvent (and consequently in the dielectric constant) causes a marked increase in the reaction rate. This observation parallels those of Croce and Gettler,6 who studied in more detail the relationship between the rate constant and the dielectric constant in the rearrangements of hydrazobenzene in ethanolwater solutions. T h e rate constant from run 22 is greater than those from runs 13 and 14 by a small but significant margin. If the only effect of medium on reaction rate were t h a t caused by changes in the macroscopic dielectric constant, then, as long as the rate increases when the solvent is changed from 95y0 ethanol to 75 :25 ethanol-water, the rate should decrease when the change is to 75:25 ethanol-dioxane. T h a t no such rate decrease is observed constitutes evidence t h a t medium effects are involved other than those owing to the macroscopic dielectric constant. In this work, as in the rearrangements of hydra~ o b e n z e n e ,the ~ reproducibility of the individual rate constants was considered to be the measure of precision. For nine rate constants, each of which was measured in two or more independent runs, the average deviation from the mean was 1.3y0, and the greatest deviation from the mean was 2.8%. The errors thus introduced into the Ea and A S + values are of the order 125 cal./mole and 0.70 cal./ mole-deg., respectively16; consequently, the differences among the three Ea values derived from measurements made under varying solution conditions probably are indicative of real differences, rather than of statistical variation in observations. Discussion The fact t h a t acid concentration is present to the 1.6 power, rather than to the second power, in the rate expression for the rearrangement of o-hydrazotoluene under the conditions imposed in this work certainly makes i t unjustifiable to assume secondorder dependence on acid concentration of the rates of rearrangement of all substituted hydrazobenzenes. Until enough substituted hydrazobenzenes have been examined to permit the deduction of generalizations concerning the relationships be(16) F. P Price, Jr , and L. P. Hammett, TEISJOURNAL, 68, 2387 (1941).
tween structure and acid concentration order, the order will have to bc detcrmincd for cuch hydrazo compound which is newly subjected to kinetic measurement, The mixed order of acid concentration involvement in the rate expression for the rearrangenicnt of o-hydrazotoluene may be interpreted in terms of the reaction sequence proposed by Hammnnd and Shine.3
that for hydrazobenzene and that K l [ H + ] M 1 for o-hydrazotoluene, while Kl [H+] < 1 for hytlrazobenzene Since Kl = &/ICs, where Kb is the base dissociation constant and K,the ionic dissociation constant for the solvent, the first requirement is that o-hydrazotoluene must be a stronger base than hydrazobenzene. Consideration of the polar effects of methyl groups does not make this condition appear altogether unreasonable, despite the fact that aniline is very slightly more basic in water C G H ~ S H S H C G+HH ~ C&€~SFT?NIHCI;H; 1 solution (pKb = 9-42) than is o-toluidine ( ~ K I=, + + + C ~ H ; K H ? S H C G+ H ~H + C G H ~ N T J ? X H ~ C (G2H ) ~ 9.48). The second requirement of this interpretn+ + tion, that K,[H+] ts: 1 for o-hydrazotoluene or, CsHjSHySH?CsHj--+ H ~ S C ~ H ~ C G F I ~ S 211’ H ? (3) in other words, that Kb be within about an order In the preceding publication of this series4 the ex- of magnitude of K,, also appears reasonable in view pression 4 was indicated to be derivable from the of Dewar’s estimate t h a t p K b for hydrazobenzene reaction sequence 1-3 and the assumptions (a) should be about 14 (presumably in water).* Unthat reaction 3 is slow and 1 and 2 rapidly reversible fortunately, no quantitative information about Kb and (b) that acid concentration is effectively con- for any aromatic hydrazo compound appears to stant. In equation 4, [Hy]Ebsand [Hylobsare the have been published. Thus, the occurrence of acid observed concentrations of unchanged hydrazoben- concentration to the 1.6 power in the rate expression for the rearrangement of o-hydrazotoluene can be l n [ H p ] ~ b a / [ H y ]= o bIn s lOO/%Hy = reconciled with Hammond’s reaction sequence, within the limits of the information now available. If the postulate is correct t h a t the 1.6 order of zene a t zero time and at time t , respectively, %Hy rate dependency on acid concentration is associis the per cent. observed unchanged hydrazoben- ated with the proximity to unity of Kl[H+], then zene after time t , and K1, I(? and kJ are the equilib- i t follows that a change of acid concentration in the rium and rate constants for the corresponding solutions by a factor of ten should produce a subnumbered steps in the reaction sequence. A similar stantial change in the observed order. An atexpression 3 can be derived from the same reaction tempt will be made to put this possibility to experisequence, the constancy of acid concentration, and mental test. the assumption, based on Hammond’s recent obAttention has already been drawn to the fact s e r v a t i o n ~that , ~ ~ ~step 2 is slow in the forward di- that E‘ and A S i for the rearrangement of hydrazorection and step R rapid. benzene cannot a t present be related to the activeK k [ +* tion energy and entropy for the rearrangement step I n [Hy]:ba/[HyIobs= In lOO/%Hy = - --la t (5) 1 Ki[H+I in the reaction sequence.4 The same uncertainty ( k z is the rate constant for the second step). Be- concerning the meaning of these quantities also cause the third term in the denominator of the is obtained in the o-hydrazotoluene rearrangement. right-hand member of equation 1 is almost cer- Xoreover, in the latter case another complication tainly negligibly small compared to the second term, arises from the mixed order of acid concentration equations 4 and 3 have the same essential form. in the rate expression. If the interpretation of this Still another equation of the same form can be mixed order given in the preceding paragraph is derived on the assumption that both steps 2 and 3 correct, then, for the rearrangement of hydrazoare slow but that the reverse of step 2 is rapid. benzene kl = C[H+]?,where Cis derived from equa811 of these equations reduce to the form ti. I t is tion 0 while, for the rearrangement of o-hydrazotoluene, kl = C[H+J2,’(1 K,[H+]). In the former clear from ii case the observed activation energy and entropy C[H+IZ I n lOO/%Hy = (6) may be related to the rate and equilibrium con1 + Kl[H+Tt stants which compose C, but in the latter case no where C is a constant, composed of equilibrium such simple relationship exists. It follows, then, and rate constants, that if K1\H+] > 1, then k1 = C’[H+],so that the two rearrangements, there is little known basis for a rate will be dependent upon the square of the acid comparison of the two sets of E“ and A S * value. concentration in one instance and on its first power Finally, the observed positive salt effect on the in the other. However, should K l [ H + ] be of the rate of rearrangement of o-hydrazotoluene and the order of unity, then an order of dependence on acid rate increase which occurs when the proportion of concentration between 1 and 2 might be observed. water in the ethanol-water solvent is increased are Inasmuch as the rate of rearrangement of hydrazo- consistent with Hammond’s postulate that the slow benzene has been shown to be second order in acid step in the reaction sequence involves the interacconcentration in the same short range of acid con- tion of two ions of like sign. centration and under the same solution conditions Acknowledgment.-The authors are grateful to which obtain when the rate of rearrangement of o-hydrazotoluene shows a 1.6order of dependency the Research Corporation for a Frederick Gnrdner on this quantity, the foregoing interpretation re- Cottrell Grant in support of this work. quires that K 1 for o-hydrazotoluene be greater than PIT~ S B U R G H13, PENNSYLVASIA 4
+
1
+
+
+
