This idea is speculative. As far as I know, there is no experimental evidence to support it. For example, it is not known for any particular reaction mixture how much of that mixture could be mixed with how much of the hexane-methanol azeotrope and still actually get separation into the two phases at the conclusion of the reaction. Also, even if liquid layer separation is achieved, we cannot know in advance what the difference in partition coefficients between mixture constituents will be even though this will determine how practical the separation will be and how many times the procedure would need to be repeated to get a useful concentration of even one species.
The azeotropic mixture of hexane and methanol split into two phases when cooled below 35℃. At temperatures below the UCST, there exist two phases containing different proportions of hexane and methanol. The azeotrope between hexane and methanol has bp 50℃; its composition is 73.1% hexane and 23.9% methanol by weight. The relative volumes of the upper and lower phases are 67.8: 32.2, about two parts to one part. When the hexane-methanol separates on cooling the composition of the upper layer will be 85% hexane and 15% methanol with specific gravity of 0.675. The composition of the lower layer will be 42% hexane and 58% methanol with specific gravity of 0.724. The difference in densities should accelerate layer separation.
The inputs for a reaction mixture would be combined in the warm single phase above 35℃, with precautions to avoid any runaway exothermicity. Then after the reaction’s completion, it is cooled to split the reactor’s contents into two phases between which the reaction mixture’s substrates would partition. In most cases, the desired product will not be conveniently distributed in only one of these phases. The advantage of the azeotropic mixture is that the reactor contents can be concentrated by distilling the azeotropic composition and then by adding either methanol of hexane as desired azeotrope distillation can be continued to provide the reaction mixture in either hexane or in methanol as subsequent treatments require. It should be noted that it is essential for this processing that the reaction mixture not be degraded during the distillation that is required for the solvent change.
The process is ‘green’ in the respect that distillation should recover a significant portion of the azeotrope solvent mixture since most preferably the azeotrope solution will be concentrated down to the minimum storable volume of the reactor before more methanol of hexane is added to chase the residual azeotrope volume.
Performing chemical reactions in a homogeneous mixture of hexane and methanol have further advantages when one no longer insists upon using the actual azeotropic composition as the composition of the liquid medium. Hexane/methanol mixtures of different relative ratios will span a wider range of solvent environments and this choice can be very beneficial in optimizing reaction conditions. A variable parameter such as a ratio of solvents is much easier to work with than an invariant parameter.
A mixture of solvents provides the opportunity to dissolve some reactant first in one of the pure solvent components and then dilute with the second pure solvent component to reach the optimized ratio before commencing a reaction.
These substrate concentrates could then each separately again be dissolved in a new portion of the single phase azeotropic above the 35 C UCST and again cooled and the phases separated and evaporated. These oily residues are treated just the way solutions are treated in a liquid-liquid extraction to improve the degree of separation of the substrates.
The disadvantage of the methodology will be that each time the extracts need to be evaporated essentially to dryness because otherwise the proportions of liquids hexane and methanol will change so that the two phases will not continue to separate.
The advantage is that because both phases contain the same two solvents-just in different proportions, the partitioning of substrates between the phases might be expected to be closer to 1:1 and so the selectivity in the partitioning of two similar substrates might be more sensitive. That is to say, one substrate might be slightly more soluble in the methanol-rich phase while the other might be more soluble in the hexane-rich one.
If no separation of liquid phases occurs at any stage it is possible that a larger proportion of the hot azeotropic hexane/methanol mixture is required. This is easily rectified. Simply add more of the hot azeotrope composition and rewarm the total solution until above the UCST and recool.
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