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Doubling reaction recipe while maintaining concentration

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Hyo X
Nov16-13, 01:23 AM
P: 37
Say we are running a chemical reaction of some kind, in liquid, in a round bottom flask.

We have a solvent, two reactants, a product, and the reaction is under stirring, reflux (volume maintained) and constant temperature.

In my mind, if we simply double the volume of all the reactants and the solvent, and maintain the same reaction conditions, really it is only the concentrations of the reactants that matter. So ideally the product should be the same.

Is this true? What other variables would make a double-batch reaction different than a standard batch? Why or how?

Do nucleation sites, or interaction of the solvent with the vessel walls or air surface matter? I can be more specific about our reaction if necessary. Thanks.
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Nov16-13, 03:37 AM
Borek's Avatar
P: 23,393
Scaling is not always that easy. Especially when the reaction is exo- or endothermic heat transfer can become a problem.
Nov16-13, 10:05 AM
P: 1,405
As Borek mentioned, scaling isn't easy. It's why chemical engineers are needed when pharmaceuticals need to be made on the hundreds of kg scale. Even things like stirring speed can drastically affect your % yield on a different scale. Stirring can become tricky when you are working with kilos worth of material. I'll never forget the time our process chemist was scaling up a reaction I did on the multiple kg scale and dropped her glove inside the reaction vessel. The reaction worked beautifully. After that though she could never get it to repeat again.

I used to also manufacture the silica gel packings that go into hplc columns and size of scale was critically important. It took the companies years to optimize the reaction conditions between different size batches of silica in order to make reproducible lots of hplc columns. A reaction with 50g starting material had a different stirring speed and reaction time as a 500 g reaction.

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