Rearrangement studies with 14 C. XLIV. Ion-pairs and dissociated ions in the solvolysis of triphenyl[2- 14 C]vinyl and trianisyl[2- 14 C]vinyl bromides in 70% acetic acid – 30% water

• Published in: Canadian journal of chemistry 1980-11, Vol.58 (22), p.2369-2376
• Main Authors: Lee, Choi Chuck, Ko, Eric C. F., Rappoport, Zvi
• Format: Article
• Language: fre
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v80-381

In the solvolysis of triphenyl[2- 14 C]vinyl bromide (1-Br-2- 14 C) in 70% HOAc – 30% H 2 O, the presence of up to 30 equiv. of added NaOAc or 25 equiv. of added Et 4 NBr did not significantly change the extent of scrambling of the label from C-2 to C-1 in the reaction product. The mean scrambling value observed for 1-Br-2- 14 C under a variety of conditions was 14.7 ± 0.7%. On the other hand, in the similar solvolysis of trianisyl[2- 14 C]vinyl bromide (2-Br-2- 14 C), the extent of scrambling in the product was found to decrease with increasing amounts of added NaOAc. The observed scramblings varied from a mean of 27.7% to 5.7%, respectively, for reactions without and with 10 M added NaOAc. With 1-Br-2- 14 C, the possibility is considered that ionization proceeds only to an ion-pair in which the scrambling via 1,2-phenyl shift is not affected by the presence of added OAc − . In the case of 2-Br-2- 14 C, further dissociation to the free trianisylvinyl cation took place and in the dissociated ion, competition between the scrambling process and capture reactions with all the nucleophiles present resulted in a decrease in the extent of scrambling with the presence of the more nucleophilic OAc − . Using the extents of scrambling as well as product data, various ratios including k SOH /k r , k OAc /k r , [Formula: see text], and k OAc /k HOAc , are evaluated.