Org. Synth. 1964, 44, 12
DOI: 10.15227/orgsyn.044.0012
7-t-BUTOXYNORBORNADIENE
[2,5-Norbornadiene, 7-tert-butoxy-]
Submitted by Paul R. Story and Susan R. Fahrenholtz
1.
Checked by Eric Block and E. J. Corey.
1. Procedure
A 2-l. three-necked flask, fitted with stirrer, condenser, dropping funnel, and an arrangement for maintenance of an inert atmosphere, is charged with a mixture of 300 g. (3.26 moles) of norbornadiene (Note 1) and 0.650 g. (4.53 mmoles) of cuprous bromide (Note 2) in 500 ml. of benzene (Note 3). Dry nitrogen is introduced continuously, and, after the flask contents are brought to reflux, 245 g. (1.26 mole) of t-butyl perbenzoate (Note 4), dissolved in 100 ml. of benzene, is added over approximately 1 hour to the stirred mixture. The solution immediately becomes blue or blue-green. The modest heat of reaction requires the application of some heat throughout the reaction period in order to maintain reflux. After the addition is completed, the solution is heated at the reflux temperature for an additional 30 minutes (Caution! (Note 5)).
The mixture is cooled to room temperature, transferred to a 4-l. separatory funnel, and washed with three 300-ml. portions of saturated brine, to remove copper salts, and three 300-ml. portions of 10% aqueous sodium hydroxide, to remove benzoic acid (Note 6). The benzene solution is then washed with 150 ml. of brine and is dried over anhydrous sodium sulfate.
The dried solution is transferred to a 2-l. flask fitted with a Claisen head attached to a 30-cm. Vigreux column. Benzene is removed fairly rapidly at about 200 mm. so that the benzene boils at 45–50° (Note 7). After removal of most of the benzene, the pressure is slowly lowered to 10–15 mm.; a negligible amount of fore-run is obtained before the product begins to distil at about 65° at 15 mm. The product is collected until the temperature reaches 80–85° at the same pressure (Note 8). The yield of 7-t-butyoxynorbornadiene is 42–51 g. (20–25%,, based on t-butyl perbenzoate) (Note 9). Gas-phase chromatographic analysis of the product shows it to be about 95% pure. Greater purity can be obtained, if required, by fractionation through a spinning band column; the pure product is collected at 70–72° (14 mm.) (Note 10).
2. Notes
1.
Norbornadiene as supplied by Shell Chemical Co. is used without further purification. Distillation of the
norbornadiene immediately before use gives no change in yield of
7-t-butoxynorbornadiene.
2.
The
cuprous bromide was used as obtained from E. H. Sargent Co. One instance of an ineffective batch of
cuprous bromide from another source has been reported to the submitters.
Cuprous bromide is only slightly soluble in the
benzene solution. Greater amounts of catalyst have no effect on the yield of product.
3.
Baker and Adamson or
Merck reagent grade benzene was used.
4.
t-Butyl perbenzoate was used as received from Lucidol Division of Wallace and Tiernan Co., Buffalo, New York.
5.
Normally, after this time, the
t-butyl perbenzoate is completely reacted. It is advisable, however, to check for its presence because distillation of a crude product containing some perester can lead to an explosion.
t-Butyl perbenzoate absorbs strongly in the infrared at 5.65–5.70 μ, and examination of the infrared spectrum of the
benzene solution is a sufficiently sensitive test. No difficulty has ever been encountered during reactions with
norbornadiene. However, unreacted
t-butyl perbenzoate has caused a minor explosion with another, less reactive olefin.
6.
Unless the copper salts are removed first, the basic wash frequently produces a thick emulsion which requires considerable time to settle.
7.
The
benzene is removed at reduced pressure to minimize heating of the product which consists chiefly of high-boiling esters. The last trace of
benzene and
norbornadiene is removed at a lower pressure.
8.
7-t-Butoxynorbornadiene is collected over this wide temperature range since the last portion of the distillate is super-heated because of the large quantity of high-boiling materials remaining in the pot. No other reaction products boil in the same range, and GPC analysis has shown the last fraction of distillate to be nearly as pure as the middle cut.
9.
This reaction has been conducted under a variety of conditions, but the yield of
7-t-butoxynorbornadiene has never been less than
20% or greater than
26%.
10.
Infrared (μ, CCl
4): 6.48 (w), 7.20 (m), 7.35 (s), 7.61 (m), 9.05 (s), 13.7 (s). The absorptions at 6.48 (double-bond stretch) and 13.7 (
cis double bond C-H out-of-plane deformation) are very characteristic of the
norbornadiene nucleus. N.m.r. spectrum (CCl
4): τ = 3.56 (m), 3.70 (m), 6.77 (m), 6.38 (m), 8.94 (s).
3. Discussion
The only method reported
2 for the preparation of
7-t-butoxynorbornadiene is that described here. The general reaction of
t-butyl perbenzoate with various olefins has been described by many investigators.
3 When
benzoyl peroxide is used in place of
t-butyl perbenzoate under similar conditions,
7-benzoxynorbornadiene is obtained in
38% yield; it is said to be more easily hydrolyzed to the alcohol than
7-t-butoxynorbornadiene.
44. Merits of the Preparation
7-t-Butoxynorbornadiene provides a convenient route to 7-substituted norbornenes and norbornadienes including
anti-7-norbornenol,
2 7-norbornadienyl acetate,
2 7-norbornadienol,
2 7-chloronorbornadiene,
5 7-methylnorbornadiene,
6 and
7-phenylnorbornadiene.
6 These compounds are useful in studies of the nature of chemical bonding.
5,7
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
brine
t-butyl perbenzoate
Benzene (71-43-2)
sodium hydroxide (1310-73-2)
sodium sulfate (7757-82-6)
nitrogen (7727-37-9)
Benzoic acid (65-85-0)
cuprous bromide (7787-70-4)
benzoyl peroxide (94-36-0)
norbornadiene
7-benzoxynorbornadiene
7-norbornadienyl acetate
7-norbornadienol
7-chloronorbornadiene
7-methylnorbornadiene
7-phenylnorbornadiene
7-t-BUTOXYNORBORNADIENE,
2,5-Norbornadiene, 7-tert-butoxy- (877-06-5)
anti-7-norbornenol
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved