Butyl Triethyl Ammonium bromide is an interesting phase-transfer catalyst. It has a q-value of 1.75 which makes it excellent for T-Reactions, like methyl tributyl ammonium chloride that also has a q-value of 1.75. With a C# of only 10, it is more hydrophilic than methyl tributyl ammonium (C# = 13), so it is much easier to wash out into water which means less aqueous waste to achieve lower residual catalyst in the product.
One might be concerned that butyl triethyl ammonium chloride might not be organophilic enough to be an effective phase-transfer catalyst, but since most T-Reactions use concentrated NaOH, the salting out effect combined with the organophilic nature of the organic nucleophiles (carbanions, N-anions, enolates, etc.) renders the quat-anion pair organophilic enough to perform many PTC strong base reactions.
In addition, the bromide of butyl triethyl ammonium bromide can co-catalyze alkylations using alkyl chlorides to form the alkyl bromides in-situ that react faster than the alkyl chloride starting material.
On the negative side, the ethyl group is the most sensitive to Hofmann degradation in the presence of concentrated NaOH due to reduced steric hindrance around the terminal methyl groups and the fact that there are three beta protons to the nitrogen versus 2 beta hydrogens for other higher alkyl groups. Moreover, butyl triethyl ammonium has three ethyl groups (9 beta protons) which makes it very susceptible to Hofmann Elimination.
In the end, the only way to know if butyl triethyl ammonium bromide will outperform methyl tributyl ammonium chloride is to screen the two catalysts against each other.
In Halpern’s early work using butyl triethyl ammonium bromide for the methylation of deoxybenzoin, it performed at the highest level together with methyl tributyl ammonium chloride (see graph).
If your company can benefit from unmatched highly specialized expertise in PTC strong base reactions to achieve low-cost high-performance green chemistry, now contact Marc Halpern of PTC Organics to explore a path forward to integrate that expertise with your process R&D program.
