[foxfourfive]

So in a set of instructions I have the following section:

There was a slight exothermic reaction (the temperature went up to 32°C) and after ten minutes the reaction mixture was quenched by pouring it into 2 L of water. This basic solution was extracted with 4x100 mL of ether, and the pooled ether extracts back- extracted with 3x100 mL dilute sulfuric acid. These bright yellow extracts were made basic with saturated aqueous sodium carbonate, extracted with 3x100 mL methylene chloride which, after pooling and removal solvent under vacuum, yielded 4.11 g of a pale yellow oil.

My question is, how basic is necessary for a process like this? Is there a pH I'm looking for before extracting with DCM?

[AWK]

Sodium carbonate is just base and indicator. It reacts with acid with bubbling.
Using pH papers in mainly organic solvents makes no sense.

[orthoformate]

saturated aqueous sodium carbonate

As AWK said, it is difficult to get an accurate pH reading of an organic phase. As long as you are using saturated aqueous sodium carbonate you will be ok.

Are you wondering how basic sat. NaCO₃ is? Because that is something you can answer.

[foxfourfive]

saturated aqueous sodium carbonate

As AWK said, it is difficult to get an accurate pH reading of an organic phase. As long as you are using saturated aqueous sodium carbonate you will be ok.

Are you wondering how basic sat. NaCO₃ is? Because that is something you can answer.

Perfect, thank you both. Yes I understand how basic sat NaCO₃ is, just wondering how much would be needed to achieve a basic solution.

[orgopete]

As I'm reading this, the poster has an amine or possibly an aniline. It was first extracted with ether, the amine taken into dilute sulfuric acid, neutralized and extracted again.

I don't think it should be too difficult to check the pH of the dilute sulfuric acid as it is being neutralized. How much carbonate? You have to neutralize all of the sulfuric acid. You should be able to calculate it. I used to have an approximate molarity written on my bottle of sat'd Na2CO3. I think it was about 1.1M, but you can calculate it. What is the concentration of the sulfuric acid?

Also, caution, add the carbonate slowly as it will foam.

[foxfourfive]

As I'm reading this, the poster has an amine or possibly an aniline. It was first extracted with ether, the amine taken into dilute sulfuric acid, neutralized and extracted again.

I don't think it should be too difficult to check the pH of the dilute sulfuric acid as it is being neutralized. How much carbonate? You have to neutralize all of the sulfuric acid. You should be able to calculate it. I used to have an approximate molarity written on my bottle of sat'd Na2CO3. I think it was about 1.1M, but you can calculate it. What is the concentration of the sulfuric acid?

Also, caution, add the carbonate slowly as it will foam.

This is exactly what I needed, A+.

I have prepared a 10% dilute solution of sulfuric acid from 18M or 98% reagent grade stuff I had. Thanks again for a very informative answer.