Jan. 20, 1957
SOLVOLYSIS O F Q - D E U T E R O A L K Y L
benzhydrol, m .p. 44.0-44.5 (uncor .),reported1243" ; p-isopropylbenzhydrol, m.p. 59.5-60.6 (uncor.), reported'2 60"; p-tbutylbenzhydrol, m.p. 81.5-82 (uncor.), reported'2 82'; mmethylbenzhydrol, m.p. 54-55 (uncor.), reportedI2 53-54'. p-n-Propylbenzhydrol gave m.p. 41-42", Anal. Calcd. for Cj6HI80: C, 84.91; H, 8.02. Found: C , 84.80; H , 8.12. p-Isobutylbenzhydrol formed gels on attempts a t recrystallization from petroleum ether and could not be satisfactorily recrystallized. T h e chloride prepared in the manner described below gave good first-order rate constants and was therefore presumably pure enough. p-Neopentylbenzhydrol gave m.p. 83.5-84.0' and mixed m.p. with p-t-butylbenzhydrol 70-72'. Anal. Calcd. for C18H~20:C, 84.99; H, 8.72. Found: C, 84.61; H , 9 . 1 . m-t-Butylbenzhydrol gave m.p. 67.5-68'. Anal. Calcd. for C I ~ H Z O OC, : 81.95; H, 8.39. Found: C, 84.85; H , 8.48. Benzhydryl Chlorides.--A portion of the alkylbenzhydrol was placed in a vial and anhydrous hydrogen chloride was passed through until the solid hydro1 dissolved. T h e mixture was taken up in ether, washed rapidly with ice-cold mater, and the ether layer after separation was dried with potassium carbonate. T h e ether was removed on the steambath and the last traces were removed under reduced pressure. T h e chlorides obtained in this way were used without further purification and in all cases gave good first-order solvolysis rate constants when followed to more than 75'30 reaction. Further, p-methylbenzhydryl chloride prepared in separate batches gave essentially the same solvolysis rate constants. Preparation of Solvents.-The reaction solvents were prepared by mixing the appropriate volumes, measured a t 25', of acetone and water or of ethanol and water. T h e percentage designations refer to volume per cent., i.e., "8070'' aqueous ethanol was made by mixing four volumes of ethanol and one of water. T h e ethanol was dried by distilling added benzene from commercial absolute alcohol through a packed column. After removing the water benzene-alcohol azeotrope (b.p. 64.9"), the ethanol-benzene azeotrope (b.p. 68.2') and a generous foreshot of ethyl alcohol (b.p. 78.5"), the material to be used was collected. Eastman Kodak Co. spectro grade acetone was used without additional purification. Infrared analysis based on the water absorption band a t about 2.8 p showed that the acetone contained 0.3% by weight of water. T h e solvent compositions given are not corrected for this small water content of the acetone. T h e water used was distilled and subsequently passed through an ion-exchange column. T h e conductances of the solutions used were always less than 1 X ohm-' at the start of each kinetic experiment. Kinetic Apparatus.-The solvolysis rate constants could be measured very simply and accurately by a conductance method because the reactions produce hydrogen chloride in
[CONTRIBUTION NO. 742
FROM THE
BENZHYDRYL CHLORIDES
373
initially non-ionic solutions. T h e constant temperature bath containing ethylene glycol and water was kept a t 0' by continuous refrigeration and intermittent heating. T h e temperature regulation was f 0 . 0 1 ' set with an accuracy of f 0 . 0 1 ' by a Beckman thermometer calibrated in a n icewater-bath. T h e conductivity apparatus consisted of a Leeds and Northrup variable frequency oscillator operated a t 2,000 c.P.s., an amplifier and a Jones-Josephs bridge.24 An oscilloscope was used to determine the balance point. A number of conductance cells were made using 10 X 14 mm. platinum electrodes fixed 5 mm. apart. T h e electrodes were platinized in a 370platinum chloride solution. Through the use of standard hydrogen chloride solutions in the respective solvents it was determined that the conductivity was proportional to hydrogen chloride concentration in the range ohm-' for 80% aqueous acetone and from 5 to 100 X from 5 to 75 X 10-4 ohm-' for 90y0 aqueous ethanol. Absolute alcohol showed marked deviations from linearity and was not used as a reaction solvent. It was deemed unnecessary to check the linearity relationship in 70 and 66.7% aqueous acetone. T h e conductivity of these solutions was stable a t least for several days. Kinetic Procedure.-Fifteen to twenty milliliters of the solvent was poured into a n 8-inch test-tube a n d the conductance cell with stopper inserted into the tube. After allowing a t least one-half hour for the cell and contents to come t o temperature the cell was raised in the tube and one drop of the organic chloride was added from a capillary pipet. T h e tube and cell was closed and shaken vigorously in the bath for 30 seconds. Since the reactions were all first order, was taken a t a n y convenient time the zero resistance (Ro) (to). T h e reaction was followed for a t least two half-lives during which period the resistance of the cell was measured 40 to 80 times. T h e rate constants for the individual points were calculated from the integrated first-order rate law in the form
where Rt is the cell resistance a t time t and Rm is the resistance after 10 to 20 half-lives. T h e rate constants and standard deviations recorded in Table I were obtained from a least squares treatment of the plot of log ( l / R m - 1/Ro/ l / R m - l / R t ) us. time. Fourteen t o twenty points chosen a t random were used in the least squares calculations. I n a trial calculation on one run the use of 40 instead of 20 points had no appreciable effect on the results. Standard deviations in the rate constants were all of the order of O.lyo. Duplicate runs never differed by more than 0.5%. (21) P. H. Dike, Reg. Sci. I n s f r u m m t s , 2 , 379 (1931)
BLOOMINGTON, INDIANA
DEPARTMENT O F CHEMISTRY, INDIANA UNIVERSITY]
The Effects of Deuterium Substitution on the Rates of Organic Reactions. 1V.I Solvolysis of p-Deuteroalkyl Benzhydryl Chlorides2 BY V. J. SHINER, JR.,
AND
C. J. VERBANIC
RECEIVED JULY23, 1956 p-CD,-, p:CHBCD2-,p-( C H S ) ~ C H C D and Z - p-( CH$)sCD-benzhydrylchlorides were synthesized and their solvolysis rates compared with those of the corresponding protium analogs in several different solvents. T h e isotope rate effects (1) are positive and of the order of 6% or less, (2) become progressively smaller in the order listed above and ( 3 ) apparently show a marked solvent dependence.
The rather large secondary deuterium isotope rate effects that have been observed in certain organic (1) Part 111, THISJOURNAL, 76, 1603 (1954). ( 2 ) (a) Abstracted from the thesis submitted by C. J. Verbanic t o the Graduate School of Indiana University in partial fulfillment of the requirements for the Ph.D. degree. (b) Presented in part before the Division of Organic Chemistry a t the 129th National Meeting of the American Chemical Society, Dallas, Texas, April 12, 1956. (c) Supported in part by the National Science Foundation.
reactions in recent years1z3give promise of providing a very powerful tool for the investigation of mechanisms of organic reactions with particular reference to the nature of the bonding of certain hydrogen atoms (which can be isotopically substituted) in transition states. However, before these secondary (3) E. S. Lewis and C. E. Boozer, THISJOURNAL, 76, 791, 794 (1954).
v. J. SHINER,JR.,
374
AND
c. J. 'I'ERFL4NIC
Vol. 79
isotope rate effects can be interpreted unambiguously in terms of conventionally recogni~edmodes of intramolecular electronic transmission, more systeniatic data from presumably well characterized reactions must be obtained and interpreted. Such p-Alkyl group ethaniil :Icetone results, besides serving to clarify our understanding M e t h y l (i, 3 2 3 0 ,80 17 of secondary isotope rate effects, may also cause A .341 862.5 some revision or refinement of current ideas conA x I .i" cerning the reactions studied. (j, li;S ,81413 With these aims in mind the authors decided to Met 11yl-d~ ri. 195 . 8l.W measure secondary isotope rate effects in the solvolR I .Xi' ysis of p-alkylbenzhydryl chlorides. This class of 5.632 .6 1 2 reactions provides some of the best data for the Ethyl .i . (i 13 . (i320 Baker-Nathan effect that exist in the literature.' In addition, since the solvent has come to be recog- Ethyl-a-d? 5,sc,7 ,6333 nized as an important factor in the Baker-Sathan 5 . 385 .G33i ~ f f e c tit, ~ was hoped that a study of solvent ef- Isopropyl 1.796 ,4973 fects on the isotope rate effect would prove fruit4.789 ,4979 ful. At the start of this work it was not known Isopropyl-a-d 4 x00 '1911 whether a measurable secondary isotope rate ef4.801 ,447 fect could be transmitted across a molecule through . ,501 1 unsaturated linkages. After this program was well 1sObutJ-l 5029 underway a cominunication by Lewis and Coppin4029 ISOfJUtJ-l-cu-d, ger6 confirmed that they had been able to observe 4915 such an effect in the solvolysis of methyl-p-tolyl17,273 Methyl ( 2 6 ' ) carbinyl chloride. 17 377 p-Methyl-&-benzhydryl chloride was obtained via the corresponding benzhydrol from toluene-a-d? Methpl-d:%( 2 5 ' ) 17 00 made by the deuteriumolysis of benzyl-a-d2 alcohol 17,1-3 over palladium-on-charcoal. The benzyl- a d " alUnits arc 10-4 see.-'. Scp:ir:ite preparation of tlic cohol was made by lithium aluminum deuteride h d i d e from the hydrol. reduction of ethyl benzoate. The other deuteroalkylbenzhydryl chlorides were made from the cor- These constants agreed with the others within the responding deuteroalkylbenzenes. The other deu- usual limits of error. The d a t a of Table I1 are furteroalkylbenzenes were made by deuteriumolysis ther suinmarized in Table 111. of the corresponding a-hydroxy or a-keto benzene T A B L E 111 derivatives. Combustion deuterium analyses were carried out on all of the deuterated benzhydrols RATE RATIOSFOR THE S O L V O L Y S I S O F . I L K T L - A S D D E U T E R O AI.KYLIJENZIIYDRTL C H L O R I D E S and on several of the other cornpounds as well. Thesc results arc given in Table I ,
,
,
(L
TADLF I r ) F U ? FRIKJM i U A L \ SFS
C o m p ~ u i11 i
Toluene-a-di p-Mcthyl-d?-benzophenone p-Methyl-dl-benzhl.dro1 p-Methyl-dd-benzhydryl chloride p-Ethj 1-a-ds-benzhydrol p-Isopropyl-a-d-benzhydrol p-Isohutql-a-d2- benzhydrol
I\ dtljms 11 moiecule
2 2 2 2 1 0 1
71 GA
54 46 82 92 72
A v . atoms I3 per deuterated bond
0.90
,886 ,846 .82 .9l .92 .86
The solvolysis rate constants were measured conduetimetrically as described in a preceding paper.$ The results are given in Table 11. The duplicate values of the rate constants given show that they could be reproduced generally to within 0.;i70 or better. One run each on the p methyl and @-methyl-dacompounds was done using a different preparation of the alkylbenzhydryl chloride made from a sample of the alkylbenzhydrol which had been recrystallized one additional time. (4) C . I(.Inxold, E. D . Hughes and N Taher, J . C h e w . S O L . ,040 ( I 940). ( , 5 ) V J Shinrr, J r , and C . J Verhanic. l'rirs J O U R N A L , 79, 3GO
(IXIi), ( 6 ) 17. S. I,ewi.:
tiiid
C> hT. Coppinger. ibi
