THE REACTION OF 2,2,5,5-TETRAMETHYL-3,4-DIPHENYLHEXAME WITH D-2 - STEREOCHEMICAL EFFECTS IN A HIGH-TEMPERATURE

The thermolysis of 2,2,5,5-tetramethyl-3,4-diphenylhexane was carried out at temperatures above 300 degrees C in the absence and presence of D-2(14 MPa). The presence of D-2 results in a greatly increased yield of the major product, neopentylbenzene. However, at higher concentrat ions of starting material, up to 50% of the neopentylbenzene formed av oids deuterium incorporation, an outcome believed to result partly fro m participation of the phenylneopentyl radical in radical disproportio nation reactions. The meso-isomer of starting material produces a subs tantial yield of stilbene in both the absence and presence of D-2. Und er D-2, 1,2-diphenylethane is produced, and it is believed that stilbe ne and other alkenes present serve as D atom traps producing radicals which then participate in termination by disproportionation. Remarkabl y, the d,l-diastereomer gives a different product distribution than th e meso-isomer, giving very little stilbene or other products of tert-b utyl group loss. However, both systems produce 1-phenyl-2-methyl-2-pro pene by methyl radical loss from the phenylneopentyl radical. The form ation of such alkenes and the path to termination they provide is blam ed for the absence of efficient kinetic chains involving D atoms.