Nucleophilic Reactivity of the Carbon-Carbon Double Bond. 111. A Comparison of the Solvolytic Behavior of 5-Hexenyl and Cyclopentylcarbinyl p-Nitrobenzenesulfonates' Paul D. Bartlett, William D. Closson, and Thomas J. Cogdell
Contribution f r o m the Converse Memorial Laboratory of Harvard Universitj., Cambridge 38, Massachusetts. Received July 24, 1964 The acetolysis of 5-hexenyl p-nitrobenzenesulfonate proceeds 1.7 times as f a s t as that of n-hexyl p-nitrobenzenesulfonate, in contrast to 4-pentenyl p-nitrobenzenesulfonate, which is only 0.72 times as f a s t as the saturated analog. The acetolysis of 5-hexenyl p-nitrobenzenesulfonate at 80.8" in the presence of 1.6 equiv. of sodium acetate yielded 83.7% 5-hexenyl acetate, 4.7% cyclohexene, and 11.6 % cyclohexyl acetate, none of these products undergoing any further reaction when subjected separately to the reaction conditions. Without the sodium acetate, acetic acid added to the double bond at this temperature and the chief product was a high-boiling material, presumably 1,5-diacetoxyhexane, along with 2 % cyclohexene, 42 % cyclohexyl acetate, and 8 % 5-hexenyl acetate. Cyclopentylcarbinyl p-nitrobenzenesulfonate, which undergoes acetolysis 3.5 times as f a s t as n-hexyl, gives cyclohexene and cyclohexyl acetate as the principal products. Since the acetolyses of these two sulfonates might proceed to cyclohexane derivatives bj' way of the same intermediate ion X I , formed by the r-route in the one case and the u-route in the other, the product compositions f r o m the two have been quantitativelj> compared. The ratio of cyclohexene to cyclohexyl acetate in the product, under the same conditions, is 0.40 f r o m 5hexenyl, 3.4 f r o m cyclopentylcarbinyl, and 6.7 f r o m cyclohexyl p-nitrobenzenesulfonate. Possible reasons f o r these large differences are discussed. Introduction As indicated in the previous discussion^,^- the activity of the carbon-carbon double bond as an internal nucleophilic reagent varies enormously with its geometry, substitution, and position in the molecule. The two preceding papers have dealt with double bonds in the 5,6-position which have the advantage of symmetrical location relative t o the ionizable center, and of being a t least disubstituted. As part of a survey of double bonds located in an ordinary carbon chain, we have investigated the solvolytic behavior of 4-pentenyl a n d 5-hexenyl p-nitrobenzenesulfonates. Finding a minor amount of acceleration and ring closure attending the acetolysis of the latter compound, we have compared it as t o rate and products with two other compounds which also solvolyze t o cyclohexane derivatives, namely the p-nitrobenzenesulfonates of cyclohexanol and of cyclopentylcarbinol. ( I ) Presented at the 100th Annual Meeting of the National Academq of Sciences, Washington, D. C., April 1963. (2) P. D. Bartlett, Ann., 653, 45 (1962). (3) Part I of this series: P. D. Bartlett, S . Bank, R. J. Crawford, and G . H. Schmid, J . Am. Chem. SOC.,87, 1288 (1965). (4) Part 11: P. D. Bartlett, and G. D. Sargent, ibid., 87, 1297 (1965).
1308
Results All the alcohols involved in this work are well known, and attention was centered on careful purification of materials and accurate quantitative accounting of products. The characterization and analysis of these compounds is summarized in Tables 111 and I V , and the calibration of the columns under the conditions of the vapor phase chromatographic separations is summarized in Table V. Preliminary solvolysis of 4-pentenyl ( I ) and 5 hexenyl (11) p-nitrobenzenesulfonates in pure acetic acid showed addition of acetic acid to the double bond, ONs
I
9 ONs
I1 ONs = O a S O N O z
apparently catalyzed by the accumulating sulfonic acid, competing with or following solvolysis. When 1 was heated under reflux in acetic acid for 5 hr. (about 6 half-lives), the product consisted of nearly equal amounts of 4-pentenyl acetate and an ill-defined mixture of materials having about twice the retention time of 4-pentenyl acetate. Solvolysis of 1 in the presence of excess sodium acetate, however, yielded only 4-pentenyl acetate. Compound I1 likewise yielded a high-boiling fraction on acetolysis in the absence of sodium acetate. In one experiment an acetic acid solution 0.175 M in TI and 0.01 M in perchloric acid was allowed to react at 79.4" for 34 hr., about 4 solvolytic half-lives, and then analyzed both on an LAC-446 column a n d on one of diisodecyl phthalate. There were nine peaks on the vapor chromatogram; 35 % of the material had the long retention times characteristic of the diacetates, 42% was cyclohexyl acetate, 2% was cyclohexene, and 8 % was 5-hexenyl acetate. Control experiments showed that these solvolysis products were not themselves stable in acetic acid containing 0.01 M perchloric acid, and therefore detailed product studies were made in acetic acid containing enough sodium acetate to neutralize the sulfonic acid produced. All the identified products were separately shown to suffer n o change under these experimental conditions. Bicyclo[3.1 .O]hexane was not formed in the acetolysis of 5-hexenyl p-nitrobenzenesulfonate. The products of acetolysis of 5-hexenyl p-nitrobenzenesulfonate are shown in Table 1. In three runs in the presence of excess sodium acetate the cyclization amounted t o 16.3, 18, and 18.7%. With 0.3 M
Journal of the American Chemical Society 1 87:6 1 March 20, 1965
Summary of Product Runs, Acetolysis
Table I.
Analysis
7% Temp., "C
Time, hr.
(RX)
(NaOAc)
80.8 80.8 80.8 80.8
86 86 86 34
0.17 0.17 0.17 0.17
80.8 80.8 80.8 80.8 80.8
52.3 52.3 52.3 64.5 64.5
0.18 0.18 0.18 0.18 0.18
0.271 0.271 0.271 None (b) 0.271 0.271 0.271 0.271 None
80.8
0.7
0.17
0.271
Re(LiCIOa) covery
A, B, cyclo- Cyclohexyl hexane acetate
5-Hexenyl acetate
A/B
(a) From hexenyl p-nitrobenzenesulfonate 11.6 0.40 94 4.7 0 13.2 0.42 98 5.5 0.03 0.82 17.9 0.30 98 14.7 0 55 2 42 0.05 From cyclopentylcarbinyl p-nitrobenzenesulfonate 18.0 3.4 0 83 61.9 18.8 3.3 0.03 80 62.3 4.4 0.30 90 68.5 15.4 20 3 83 60 None 88 0.045 78 4 None (c) From cyclohexyl p-nitrobenzenesulfonate 0 82 87 13 6.7
Cyclo1-Methyl- pentylcyclocarbinyl pentenem acetate
83.7 81.3 67.4 8
0 0 0 0
0 0 0 0 0
15.1 14.1 13.8 12 8
5.1 4.9 2.3 0
0
0
0
0
In two V.P.C.analyses with direct injection of solvolysis product, I-methylcyclopentene and methylenecyclopentane were found in amounts of 9 and 4 %, respectively, in the first, and 10 and 3 % in the second. After extraction the methylenecyclopentane appeared to be converted (as in the other analyses) into 1-methylcyclopentene. Q
Table 11. Summary of Kinetic Runs, 79.5", HOAc
p-Nitr obenzenesulfonate
Concn., M
n-Hexyl
(NaOAc)
0.02
5-Hexenyl
0.02
4-Pentenyl
0.02
Cyclopentylcarbinyl
0.02
Cyclohexyl
0.02
0 0 0 0.0355 0.0355 (0.0309 M LiClO,) 0 0 0.0355 0 0 0.0355 0.0355 0 0 0.0355 0.0355 0-
0 0.0355 0.0355
lithium perchlorate present in addition, the cyclization rose to 3 2 . 6 z ; , and the ratio of cyclohexene to cyclohexyl acetate doubled. Table I also shows the products when cyclopentylcarbinyl p-nitrobenzenesulfonate (HI) is subjected to acetolysis under the same conditions. The products found are the unrearranged acetate (IV), l-methylcyclopentene (V), cyclohexyl acetate (VI), and cyclohexene (VII). The products IV and V, as well as VI and VII, were unchanged in control experiments in
111
IV
o O A c
VI
k X 105, set.-'
V
0 VI1
which they were held under the conditions of reaction. The contrary was true of methylenecyclopentane (VIII), Bartlett, Clossen, Cogdell
b
k/khexyi
1.02 1.01 0.99 1.58 1.29 1.71 1.75 2.25 0.72 0.72 1.03 3.50 3.45 3.68 3.54) 103 102 108 1 108
@H* VI11
13.8 8.9 1.72 8.4
13
1.49 0.72 0.70 3.47
1.4
2.40 102
1.6
0
