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The study of the thermal decomposition of Tetracyclo[3.3.1.1[sup 3,7].0[sup 1,3]]decane in octane and cumene at 1950 McIntyre, Brian William

Abstract

Tetracyclo[3.3.1.1[sup 3,7].0[sup 1,3]]decane, also called 1,3-dehydroadamantane or DHA, was heated at 195° C in n-octane and cumene solutions, with and without added 2,6-di-t-butyl-p-cresol, hereafter referred to as cresol. The kinetic order of the decomposition of DHA at 0.015 to 0.15 M solutions varied from 1.7 in octane to 1.5 in cumene and was 1.0 in solutions containing cresol. The overall rate of reaction increased on changing solvent systems in the order octane, cumene, octane with cresol and cumene with cresol. The first order rate constants for the reactions in the octane and cumene solutions containing cresol wereu7.9 x 10⁻³ min ⁻¹ and 14.3 x 10"3 min-1 respectively. By comparison, the rate constants from a first order calculation using the data for the reactions in octane and cumene were 2.2 x 10⁻³ min ⁻¹ and 4.6 x 10⁻³ min ⁻¹ respectively. The products of reaction in octane solution were l,l'-biadamantane, ca. 70%, adamantane, ca. 3%, polyadamantanes, ca_. 15%, and three unidentified liquids, ca. 10% total. With the addition of the cresol, the products were l,l'-biadamantane, ca. 70%, adamantane, ca. 17%, and the three unidentified products, ca. .10% total, with no polyadamantanes observed. In cumene solution, the products of reaction were 1,1'-biadamantane, 29%, 2-(1-adamantyl)~2-phenylpropane, 20%, 2,3-dimethyl-2,3-di phenyl butane, 37%, adamantane, 8%„ and an unidentified product, 5%. The presence of dimeric and polymeric products and the change in rate on addition of cresol suggest a radical chain mechanism. The initiation step was considered to be most likely the attack of the vibrationally excited DHA molecule on the solvent, the dissolved cresol if present, or another DHA molecule. Some brief, unsuccessful attempts were made to prepare DHA from 1-bromoadamantane using n-butyllithium and using KOH in methanol and from 1,3-dibromoadamantane using n-butyl Grignard reagent. No DHA was observed. The unusual bonding present in DHA results in a UV spectrum having four local maxima at 282-285 nm., 274 nm., 265 nm., and 254-257 nm., with the maximum at 274 nm., e = 13.

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