Monobromination of α,ω‐Diols: Highly Efficient Preparation of Synthetic Intermediates

• Published in: ChemistrySelect (Weinheim) Vol. 4; no. 36; pp. 10843 - 10845
• Main Authors: Oliveira, Adeildo Junior, Souza, Isis Torres, Bernardo, Vanderson Barbosa, Santos, Larissa C., Lima, Maria Raquel Ferreira, Goulart, Henrique Fonseca, Goulart Santana, Antônio Euzébio
• Format: Journal Article
• Language: English
• Published: 30-09-2019
• Subjects: Monobromination; Substitution Reactions; Synthetic Intermediates; α,ω-Diols; ω-Bromoalcohols
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.201901879

The present work aimed to evaluate different conditions to perform monobromination reactions of α,ω‐diols using HBr. Three solvents were tested, toluene, isooctane, 1,2‐dichloroethane, in two distinct molar proportions between 1,8‐octanediol and HBr (1:1 and 1:2 equivalents). All reactions occurred under reflux. After stablishing the best reactional conditions, assays with four symmetric α,ω‐diols, 1,6‐hexanediol; 1,7‐heptanediol; 1,8‐octanediol; and 1,10‐decanediol, with 2 eq. HBr in 1,2‐dichloroethane, were conducted. Using toluene as solvent lead to the best reaction yields (81‐95%), producing the least amount of unwanted dibrominated product. Reactions in 1,2‐dichloroethane gave similar results to the ones with toluene when 2 eq. HBr were used. The lowest reactional efficiency registered in these assays occurred in isooctane, forming the highest amount of dibromide. Diols 1,7‐heptanediol and 1,8‐octanediol showed the best results under the conditions studied, in 1,2‐dichloroethane.
The present work reports a highly efficient method for monobromination of α,ω‐diols with HBr, using toluene, isooctane and 1,2‐dichloroethane as solvents. Two molar proportions (ndiol/nHBr) (1/1 and 1/2 eq.) were tested. Toluene gave excellent results under both conditions, followed by 1,2‐dichloroethane, with 2 eq. HBr. This reaction is a viable and cost‐effective alternative to prepare ω‐bromo alcohols.