Hexadienes from pyrolysis

Ethylene has been separated from ethane by a silver nitrate solution passing countercurrent in a hollow fiber poly-sulfone.165 This separation has also been performed with the silver nitrate solution between two sheets of a polysilox-ane.166 A hydrated silver ion-exchanged Nafion film separated 1,5-hexadiene from 1-hexene with separation factors of 50-80.167 Polyethylene, graft-polymerized with acrylic acid, then converted to its silver salt, favored isobutylene over isobutane by a factor of 10. Olefins, such as ethylene, can be separated from paraffins by electroinduced facilitated transport using a Nafion membrane containing copper ions and platinum.168 A carbon molecular sieve made by pyrolysis of a polyimide, followed by enlargement of the pores with water at 400 C selected propylene over propane with an a-valve greater than 100 at 35°C.169... 

Allyl(allyloxy)dimethylsilane (18) was also proposed by Barton and coworkers as being the source of 10 in gas-phase pyrolysis24. It has been suggested that the generation of 10 by pyrolysis of 18 results from consecutive loss of two allyl radicals. 1,5-Hexadiene and cyclosiloxanes 19 (D3) and 20 (D4) were the final pyrolysis products of 18 (Scheme 6). 

Davidson and Wiggins (1956) isolated it from ammoniated molasses a few years before its discovery in coffee. It was identified in the pyrolysis products of amino acids by Kato et al. (1973a,b), in the pyrolysis products of trigonelline by Viani and Horman (1974), and in model reactions involving serine and/or threonine with or without sucrose under coffee-roasting conditions by Baltes and Bochmann (1987d). Mottram (1991) explained the possible formation of 2-methylpyridine by reaction of ammonia with 2,4-hexadienal. 

Doering and Roth provided stereochemical evidence that is consistent with a chair-like transition state.Thus, upon heating /zr o-3,4-dimethyl-1,5-hexadiene gave a 9 1 mixture of E,E- and Z,Z-2,6-octadiene, respectively, with less than 1% of the , Z-diene being formed kinetically, presumably via a boat-like transition state. To confirm the hypothesis, pyrolysis of o f/ir6>-3,4-dimethyl-1,5-hexadiene gave 99.7% , Z-2,6-octadiene as is expected from a chair-like transition state and only... 

---