Competing Fragmentation, Substitution and Elimination in the Solvolysis of Alkylated 3-Chloropropanols and their Ethers. Fragmentation reactions no. 28
✍ Scribed by Walter Fischer; Cyril A. Grob
- Publisher
- John Wiley and Sons
- Year
- 1978
- Tongue
- German
- Weight
- 763 KB
- Volume
- 61
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
The unstrained 3‐chloroalcohols 1a, 2a and 3a do not undergo solvolytic fragmentation in neutral and weakly acidic 80% ethanol, only substitution and elimination products being formed by the limiting S~N~1‐E1 mechanisms. This also applies to the corresponding ethers 1b and 3b. Addition of sodium hydroxide causes the observed rate constants for the 3‐chloroalcohols to rise steeply by factors of at least 10^3^ to 10^5^. These level off at higher base concentrations due to an opposing ionic strength effect. Whereas 3a fragments quantitatively in the presence of base, 1a and 2a fragment in competition with elimination to the Δ^3^‐olefins 9a and 10, respectively. 2a also yields 2% of the oxetane 6b.
These results support a concerted base‐induced fragmentation mechanism which competes with intramolecular base‐induced elimination (E~i~) in the case of the acyclic chloroalcohols 1a and 2a. The formation of small amounts of the oxetane 6b from 2a is attributed to intramolecular nucleophilic substitution at the tertiary carbon atom.