NOTES
2361
IO00
800 GO
400
200 0
/ 0
0.02
0.04 0.06 0.08
0.10
0.12
0.14
p 6 ~S 5S C ~ H mole/. ~ . Figure 1. Dependence of t h e G value for isomerization of cis-polybutadiene (17,solution i n benzene) o n t h e sensitizer concentration.
mole), we may consider that C6H6SSC6H5*in (1) will dissociate with an efficiency which is a t least as great as, and possibly even greater than, that obtained experimentally by Seely’ for the diphenyl disulfide photolysis, vix., 0.13. Accordingly, the limiting G(C&S.) is of the (order of a t least 4.4 X 0.13 X 2 or 1.14, and may be closer to 1.40.’ An alternative route to this estimate stems from the work of Ando, Sugirnoto, and Oae on the radiolysis of thiophenol in benzene in which they indicated ,a G value of 0.7 for the production of excited benzene molecules. Since this value was based on a kinetic approach where it was assumed that practically all of the benzene excitation energy is transferred to thiophenol, which then dissociates with an efficiency approaching unity, it would follow from their work that G(-C&SH) = G(C6H6S.) = 0.7. Although these workers also studied the radiolysis of diphenyl disulfide in benzene, they did not provide suficient data to permit a direct estimate of G(C6H6S.)for this reaction. However, by virtue of the close similarity of C6H6Sl[ and C,&SSC6&, it is reasonable to consider that these compounds will radio lyze in benzene with comparable yields. Hence, G(C6H.8.) from C6H6SSC6H6can be taken to be twice that from C&6fgH, or 1.4, which agrees very well with the value obtained from Cundall and Griffiths’ work. For a saturation G(C,H&) of -1.1-1.4, then, the limiting Go of around 1400 given above signifies that
-1000-1300 cis double bonds isomerize per thiyl radical (neglecting the minor contribution from direct radiolysis of the sensitizer). This chain length is of the same order of magnitude as that indicated by Seely, thus emphasizing the parallelism between the photo- and radiation-sensitized isomerization of polybutadiene in benzene; a t the same time it represents a major revision of the previous crude estimate of lo4. If the chain length is largely independent of the sensitizer concentration a t the dilutions considered, Fig. 1 provides a measure of the efficiency of energy transfer from C6H6*to CaHjSSC6H6, varying from about 5% a t 0.001 M sensitizer to 90% at 0.1 M , and on up to 100% beyond 0.14 M . Finally, it may be suggested that the number of double bonds isomerized per thiyl radical in Seely’s work should be 750 instead of 370, which would bring the photo- and radiation-chemical values into even better agreement. The value of 750, corresponding to the ratio of rate constants for the isomerization and termination processes, and not one-half of it, should represent the chain length: although two C6H& radicals are formed in the initiation step, they both take part in isomerization and termination.
Acknowledgments. The author wishes to acknowledge helpful discussions with Drs. Theodore Mill and A. H. Samuel. This m7ol.k was supported by Stanford Research Instihte. (7) I t should be noted that Seely showed with the aid of a relation developed by R. M . Noyes, 2. Elektrochem., 64, 153 (1960), t h a t the above dissociation efficiency of photoexcited diphenyl disulfide was quite reasonable, obtaining a theoretical estimate of 0.10-0.15. An analogous calculation by the present author for the sensitized radiolysis of t h e disulfide yielded a value of 0.17.
The Effect of Pressure on the Benzylation of 1-Methyl-2-naphthoxide Ion
by W. J. le Noble Department of Chemistry, State University of New York, Stony Brook, New York (Received February 86, 1964)
The effect of pressure on the product distribution in the reaction of phenoxide ion with allyl chloride was described in an earlier paper.’ It was found that in protic solvents ring alkylation, particularly in the para position, was favored a t high pressure. This (1) W. J. le Noble, J . Am. Chem. Soc., 8 5 , 1470 (1963).
Volume 6 8 , Number 8 August, 1.964
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fact was shown to be consistent with a suggestion made earlier2 to the effect that the solvation sphere of an ambident anion might in certain cases have a decisive influence on its alkylation. In that system the hypothesis also suggests that the volumes of activation of these simultaneous reactions would not be so different in a solvent not particularly suited to solvate anions. On that score the evidence was inconclusive since allyl phenyl ether was the only detectable product in such solvents a t any pressure. Clearly needed was information on the effect of pressure in an alkylation reaction in such a solvent in which both products are formed in easily measurable amounts. Kornblum and Derby3 had found that the reaction of benzyl bromide with lithium 1-methyl-2-naphthoxide in 1,2dimethoxyethane gives substantial amounts of both benzyl-2-(l-methyl)naphthylether (I) and l-benzyl1-methyl-2-naphthalenone (11) ; this reaction is therefore well suited to illuminate that point.
Experimental The preparation of 1-methyl-2-naphthol has been d e ~ c r i b e d . ~The 1,2-dimethoxyethane was dried by distillation from lithium aluminum hydride; a 0.1 M solution of the salt in this solvent was prepared from a solution of 2-methyl-1-naphthol and the equivalent amount of freshly pressed lithium ribbon. It was found that the salt was alkylated by benzyl bromide a t 50.0" t o the extent of 95% in 48 hr.; the benzylatioiis of the salt in methanol (also 0.1 ill) a t 25.0' required about 24 hr. After neutralization of the residual base and removal of the solvent by flash evaporation, the residue could be chroniatographed by elution of hexane-benzene and benzene-ether mixtures on alumina to give I, m.p. 65-70' (lit3 m.p. 70-71') and 11, m.p. 57-61' (litS3m.p. 62-63). Infrared spectra were measured for the routine analysis of mixtures of these compounds; synthetic mixtures were prepared for comparison, In about half of the experiments the mixtures were also analyzed by the chromatographic f,echnique described above. Both methods were found to be reliable to about 1%. The high pressure technique was described earlier.
Results The difference in product distribution between the methanol and 1,Bdimethoxyethane reactions a t 1 atm. is best explained as the result of more intense solvation in the former solvent and thus greater The Journal of Physical Chemistry
shielding of the oxygen atom against the approach of the alkylating agent.* Since pressure facilitates the process of solvation, the carbon to oxygen (II/I) ratio in the alkylation reaction is expected to increase with pressure; this is indeed observed in methanol. On the other hand, 1,Zdimethoxyethane is not well suited for the solvation of anions, so that pressure should not affect the C/O ratio of the alkylation reaction very much in that solvent. The data in Table I bear out these expectations. Table I : Product Distribution in the Reaction of B e n ~ y l Bromide with Lithium 1-Methyl-2-naphthoxide Solvent
Temp., "C.
P, kbar
% 0,I
?4 C, I1
1,2-Dimethoxyethane 1,2-Dimethoxyethane 1,2-Dimethoxyethane 1,2-Dimethoxyethane 1,2-Dimethoxyethane 1,2-Dimethoxyethane lj2-Dimethoxyethane Methanol Methanol Methanol Methanol Methanol
50 50 50 50 50 50 50 25 25 25 25 25
0.00 1.24 2.47 3.79 4.84 6.72 8.41 0.00 1.41 2.93 4.17 5.65
79 80 80 78 78 78 80 57 52 50 49 48
21 20 20 22 22 22 20 43 48 50 51 52
From the expression ( b in k / b ~ = ) ~ -AV*/RT, one can readily show that at 1 atm. V,* - V,* = 2-3 ml./mole in methanol. In l,Bdimethoxyethane, V,* = Vo*; it had been anticipated, in fact, that the C/O ratio might show a small decrease in that solvent. Kornblum has shown that such ratios tend to decrease when various solvents of increasing dielectric constants are compared.6 Since the dielectric constants of liquids are pressure dependent, changes in the product distribution due to this effect are likely. However, the increase in D over the pressure range used in this work is so small (from 7 to 9, as estimated from the Owen-Brinkley equation6) that its effect is probably within the range of analytical uncertainty.
Acknowledgment. Support from the National Science Foundation for this work is gratefully acknowledged. ( 2 ) X . Kornblum, P. J. Berrigan, and W. J. le Noble, J . Am. Chem. SOC.,8 5 , 1141 (1963). (3) N. Kornblum and R. Derby, unpublished results. The author IS grateful to Professor Kornblum for making a numher of experimental details available prior t o publication. (4) J. Cornforth, 0. Kauder, J. E. Pike, and R. Robinson, b. Chem. SOC..3354 (1955). ( 5 ) N. Kornblum, R. Seltzer, and P. Haherfield, J . Am. Chem. SOC., 8 5 , 1148 (1963). (6) B. B. Owen and S.R. Brinkley, Jr., Phys. Rea., 64, 32 (1943).
