Effect of Droplet-Wake Phenomena on Mixing-Sensitive Pharmaceutical Reactions - Pharmaceutical Technology

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Effect of Droplet-Wake Phenomena on Mixing-Sensitive Pharmaceutical Reactions

Pharmaceutical Technology

The continuous phase was charged to the column and allowed to settle to remove all visible air droplets. The iodine solution was injected subsurface using a 20-gauge PTFE needle. Droplets were released at least 4 s apart, thus guaranteeing that a local steady-state had been reached. The iodine charge times for the reported experiments varied between 0.25 and 3.0 h. For analysis purposes, only a 300-mL sample was collected from the middle section of the column with a set of valves. All of the remaining continuous phase was drained to waste, and the sample was analyzed using HPLC.

Table III: Experimental properties.
The viscosity of the solution was controlled by adding glycerin, which lowers the droplet Reynolds number and changes the wake dynamics of a droplet. The glycerin, however, does not affect the reaction nor the HPLC analysis. The glycerin concentration was fixed at either 10% or 30% (and 50%) for the set of experiments. Table III contains information about the experimental properties of the two phases as well as the droplets' parameters.


Although the amount of iodine that phase transfers is not known ahead of time, the initial molar ratio of l-tyrosine to iodine can be determined a posteriori by using the measured concentration of reaction products. Although the absolute amounts cannot be known, the "molar charge ratio"—that is, the initial moles of l-tyrosine to the total moles of iodine that transferred phases—can be calculated as:

in which A o are the moles of l-tyrosine available for reaction; B o are the moles of iodine that transfer phases and are available for reaction; P is the concentration of 3-iodo-l-tyrosine in moles per liter, and BP stands for the byproduct concentration of 3,5-diiodo-l-tyrosine in moles per liter. A is the concentration of l-tyrosine at the end of the reaction in moles per liter. The selectivity Y P of the reaction was determined by dividing the total amount of desired product formed by the total amount of products formed:

The experiments focused on identifying how the selectivity varies with the initial molar charge ratio for experiments run with 10% and 30% glycerin.


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