Adogen 464 is a registered trademark of Evonik and is essentially the same material as Aliquat 336 (registered trademark of BASF) which represents methyl tricaprylylammonium chloride. This material has an effective molecular weight of 432 g/mole since the “caprylyl” alkyl groups are a 2:1 molar mixture of octyl to decyl groups. As we teach in our 2-day PTC course, Adogen 464 has an effective C# of 27 and an effective q-value of 1.34.
The patent shown in the figure that issued this month used Adogen 464 for an etherification. Since Adogen 464 has an average of 27 carbon atoms, it distributes nearly exclusively into the toluene phase. This is important for workup. More hydrophilic quaternary ammonium phase-transfer catalysts, such as tetrabutylammonium, would distribute significantly into both the organic and aqueous phases. That affects aqueous waste treatment.
In this patent, tosylate was the leaving group. Tosylate is sometimes a catalyst poison in PTC systems. As we teach in our 2-day PTC course, in cases such as this one, tosylate does not bind irreversibly to the organophilic quat since it is competing for association with the anion of 7-hydroxy-4-(4-bromo-2-fluoroanilino)-6-methoxyquinazoline that contains many carbon atoms, more than tosylate.
If you want to learn how to choose a phase-transfer catalyst like an expert, now register for the public PTC course to be conducted in Prague in October 2019 or bring our highly valuable 2-day PTC course in-house to your company.
Tetrabutylphosphonium bromide (TBPB) was used as an ionic liquid solvent and bromide source in dozens examples at 150 C for 48 hours to produce acrylic acid from lactide, a natural source instead of producing acrylic acid from non-renewal petroleum. Some of the examples were performed in 47% HBr at 100 C for 72 hours. This patent demonstrates the thermal stability and chemical resilience to acid of TBPB.
Be aware that TBPB does NOT have similar stability in the presence of base. In our 2-day course “Industrial Phase-Transfer Catalysis” we show data about the stability of TBPB in the presence of NaOH.
Rayner, C.; Barnes, D.; Jakab, G.; Schoolderman, C.;
(C-Capture Ltd) US Patent 10,279,307, 07-May-2019
Carbon dioxide capture is a major environmental goal in this century. The background section of this patent gives an excellent perspective on this crucial issue.
The inventors found that tetrabutylammonium carboxylates capture carbon dioxide faster and more effectively than the corresponding potassium salts. The basis for the capture and release of carbon dioxide is based on the pKa’s in the equilibrium between carbonic acid, hydrogen carbonate and carbonate.
The pKa of acetic acid in water is 4.76 and is too low to capture carbon dioxide. Phenol has a pKa of about 10 and phenolate salts capture CO2 well. The inventors wanted a practical system that not only captures carbon dioxide well but also can release the carbon dioxide on demand, all with low energy requirements and be reversible.
This table from the patent shows the dramatic difference in pKa of acetic acid of nearly 20 orders of magnitude when changing solvents. These differences are being leveraged to capture carbon dioxide in a low energy process then release the carbon dioxide at will in another low energy process by simply changing solvent which in turn changes the pKa and ability to react with tetrabutylammonium acetate.
Although this is not a phase-transfer catalysis system, it is a phase-transfer system and due to it’s high level of interest, we chose to highlight this patent using a tetrabutylammonium salt that just issued this month.
This patent describes the chlorination of sucrose-6-acetate with chlorodimethylformiminium chloride to form sucralose using a 2-phase system with DMF and perfluorooctane. The inventors used Aliquat 336 and observed 3 phases in the initial stages of the reaction at low temperature. The inventors state “Aliquat 336 helps to mix the co-solvent and chlorination mixture forming a third intermediate phase.” As we teach in the 2-day course “Industrial Phase-Transfer Catalysis,” PTC systems enjoy enhanced reactivity when a third intermediate phase can be created. This may be the case in this system. If so, then the three phases are DMF, perfluorooctane and a small phase rich in Aliquat 336. Upon heating to higher temperature for an extended period of time, two phases are formed from the 3-phase system. The perfluorooctane is recovered and recycled without purification.
In most 3-liquid phase PTC systems, the phases are an aqueous phase, a non-polar organic solvent such as heptane and the third intermediate phase is rich in a phase-transfer catalyst such as tetrabutylammonium. In such systems, Aliquat 336 would distribute into the non-polar organic phase, but in this patent the inventors used DMF and perfluorooctane. This is quite different than most 3-liquid phase PTC systems.
The use of the expensive hexafluorophosphate counteranion is surprising for the PTC carbene addition described in this month’s PTC Reaction of the Month (US Patent 10,219,516). We do not know the rationale of the inventors for choosing tetrabutylammonium hexafluorophosphate, which is usually used as an electrolyte in nonaqueous electrochemistry since it is highly soluble and stable in polar organic solvents used in such electrochemistry.
If the inventors really wanted to use a tetrabutylammonium salt for some reason, they could probably have used the more common and less expensive tetrabutylammonium hydrogen sulfate. The excess base (25 equiv) was more than enough to neutralize the hydrogen of the hydrogen sulfate, so that would not have been a concern, especially since the resulting sulfate anion is not nucleophilic and has low affinity for pairing with the quat.
Tetrabutylammonium bromide, which is the least expensive and most common tetrabutylammonium salt, would have been less desirable since it could have resulted in some Cl/Br exchange (in chloroform or the CCl3- anion) which would contaminate the product.
The more classical triethyl benzyl ammonium (TEBA) chloride may have been a better choice for this PTC carbene addition, or possibly methyl tributyl ammonium chloride, which would probably likely be more stable than TEBA under these conditions.
To benefit from PTC Organics’ highly specialized expertise in choosing the best phase-transfer catalyst, now contact Marc Halpern of PTC Organics to explore collaboration to achieve low-cost high-performance green chemistry using PTC.
An invention is described in Cooks, R.; Jjunju, F.; Li, A.; Roqan, I.; (Purdue Research Foundation) US Patent 10,197,547, 05-Feb-2019, that is stated to “relate to methods of analyzing crude oil.” For the PTC community, it’s much more than that. This patent addresses a long standing issue in industrial PTC research which is how to quantify the presence of quaternary ammonium salts in an organic phase, including in non-polar solvents, especially at very low concentration.
Paper-spray mass spectrometry was used to identify a variety of quat salts including tetraoctylammonium bromide, tetradodecylammonium bromide, tetrahexylammonium bromide, tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium bromide, benzylhexadecyldimethylammonium chloride, hexadecyltrimethylammonium bromide, and a mixture of alkyldimethylbenzyl ammonium chloride where the alkyl group is predominantly n-dodecyl. In some cases, the analytical method is performed without any sample pre-purification steps.
Figure 2 in this patent shows a 5-point calibration curve for the quantitative analysis of ammonium salts in oil matrix using a commercial ion trap mass spectrometer. The R-squared value of the line was 0.997 and the highest concentration of quat was 500 parts per billion.
This patent may be of great interest to those who need to detect quat salts at low concentrations such as residual quat in product.
The background for this quat salt and similar salts that are used in synthesis (not as phase-transfer catalysts) is best described in US Patent 10,179,795 that was issued this month.
“Isotopically enriched boron-10 compounds, such as salts of polyhedral boranes can be used in research laboratories for the preparation of therapeutic agents for the boron neutron capture therapy of cancer (BNCT). However, these compounds are not commercially accessible. As a result, there is a need to provide a straightforward and easily scalable method for the synthesis, isolation, and purification of boron-10 isotopically-enriched compounds. “
“The present invention is directed to a process for the synthesis of mixtures of salts of polyhedral boranes and includes the steps of first, combining a methyltriethylammonium halide with an alkali metal tetrahydroborate in a reaction mixture; second, reacting the methyltriethylammonium halide and the alkali metal tetrahydroborate to form a methyltriethylammonium tetrahydroborate intermediate and an alkali metal halide; and third, pyrolizing the methyltriethylammonium tetrahydroborate intermediate to produce a product mixture comprising methyltriethylammonium decahydrodecaborate and methyltriethylammonium dodecahydrododecaborate. “
Examples 2 and 3 of this patent describe the synthesis and isolation of the salt shown in the figure.
Tetrabutylammonium borohydride was used in the ethylene addition reaction shown in the diagram.
PTC is used in conjunction with transition metal catalysts for a wide variety of applications, but I have not seen before the use of tetrabutylammonium borohydride which maybe suggests that one of the other catalysts needs to be reduced from time to time to remain active. I’ll be curious to learn of any explanations from our readers for why is the borohydride needed in this case.
The 15 mole% tetrabutylammonium borohydride describes the amount of quat. There is 60 mole% hydride. The total of the other three catalysts is 45 mole%, so there is enough hydride to cover the other catalysts if they somehow get deactivated and if borohydride can reactivate them.
In a patent describing “Processes for producing diazabicyclooctane compounds” there was a need to purify an organic sulfate intermediate together with a deprotection step. The inventors leveraged the ability of quat salts to be moved at will between phases to isolate and purify an organic sulfate.
Since sulfates usually have low affinity for quats, the inventors likely chose to use tetrabutylammonium hydrogen sulfate for the ion exchange since the anions in commercial tetrabutylammonium salts other than hydrogen sulfate (such as bromide in TBAB) are typically so much more organophilic that they would preferentially pair with the TBA cation, not allowing the sulfate to pair with the quat.
We explain the practical ramifications of the affinity of various anions to quaternary ammonium cations in our 2-day course “Industrial Phase-Transfer Catalysis.” Now inquire about conducting this valuable course in-house at your company.
Usually when we see quat fluorides they are deprotecting a silyl ether. In this patent, tetraethylammonium fluoride was used to radiolabel a compound with fluorine-18.
The fluorine isotope was formed in a cyclotron by bombardment of water with O-18. Then, it was still not trivial to pair the quat with the fluoride to form tetraethylammonium fluoride. The inventors strategically used tetraethylammonium bicarbonate that has an extremely hydrophilic anion that has a similar low affinity for the quat as the very hydrophilic fluoride anion. Indeed, the quat fluoride was in a mixture with tetraethylammonium bicarbonate.
