Oct., 1960
I < I N E T I C S O F T H E RC.4CTION O F
AROMATICI I Y n R O C A R R O N S I N SULFURIC I!CIT)
Z1 = ZZ,we find P2/P1 = 0.26. If we accept the previously' suggested valuesof EZ= 4.1 kcal. mole-' and Pz = 0.09, me find E1 = 4.6 kcal. and PI = 0.34. For the reaction of D with DzS, the previously' derived values were E = 5.0 kcal. mole-' and
1433
P = 0.73. The slightly lower activation energy and P factor for reaction 1 is not unexpected since substitution of H by CHs usually results in a lower dissociation energy of the remaining bond and also halves the intrinsic probability of the reaction.
TIIF, KIK'ETICS OF THE REACTIOSS OF AROMATIC HYDROCARHONS I N SULFURIC AC1D.l I. BESZESE BY MARTINKILPATRICK, MAXW. MEYERAND MARYL. KILPATRICK The Department of Chemistry, Illinois Institute of Technology, Chicago,Ill. Received March 18. 1900
The rate of sulfonation of benzene in sulfuric acid solution has heen measured spectrophotometrically; the results ohtained are in fair agreement with those of Gold and Satchell, obtained by an isotope-dilution technique. An empirical equation has been found which fits the experimental results and which can be interpreted in terms of the concentration of the molecular sulfuric axid present in mixtures of sulfuric acid and water, as determined by Young and co-workers using Raman spectra, and the activity of water in these mixtures, as determined by Giauque and co-workers.
In an attempt to unravel the kinetics of the Jacobsen reactic1nl2it became necessary to understand the kinetics of sulfonation of the four- and five-methylsubstituted benzenes. The range of concentration of sulfuric acid for pure sulfonation is limited for durene (1,2,4,5-methylbenzene), isodurene (1,2,3,5-methylbenzene) and pentamethylbenzene by desulfonation, isomerization and disproportionation reactions. To avoid complications, the first series of experiments was carried out with benzene. The rate of reaction was determined by following the appearance with time of benzenesulfonic acid spectrophotometrically in the ultraviolet. A Cary Spectrophotometer Model 11 equipped with a program attachment was used. The reaction vessel was the absorption cell, and the general procedure was as follows. Sulfuric acid of known concentration was cooled in a refrigerator below the temperature planned for the experiment, a drop of hydrocarbon added from a syringe 1.0 give a concentration of 1 X 10-4 mole per liter, and a.fter shaking for five minut'es the absorption cell was filled and placed in the thermostated compartment of the spectrophotometer. After allowing a suitable time for the establishment of thermal equilibrium, the recording spectrophotometer was started and the rate of formation of sulfonate determined a t the absorption peak 272 mp. The molar extinction coefficient for the benzenesulfonic acid is so much greater than that for benzene that no appreciable error is introduced by the presence of unreact,ed hydrocarbon. Experiments were carried out at 25 and 12.3"with t,emperature control of =k0.05" in most cases. As the r e a d o n proved to be strictly first order in hydrocarbon, as shown by a typical run in Fig. 1, in most later experiments the Guggenheim3 method of evaluating the velocity constant was used. The quc'ted rate constants have limits of (1) Presented in part a t the 134th Meeting of the American Chemical Society, Chicago. #jePtemher1958, before the Division of Physical Chemistry. (2) 0. Jacobsen. Bet., 19, 1209 (1886); 20, 896 (1887). (:;) E. A . Ciimzetilicim, Z'hil. M a g . , 1 , 5.38 (19%).
error of &5% (as compared with +20% in the work of Gold and Satchell). The equation d[ArS03H1 = ko~,s
