Hi,

Benzaldehyde is easily oxidized to benzoic acid which can impede its desired reaction and hence it is always recommended to use freshly distilled benzaldehyde.

Simple bicarbonate treatment of benzaldehyde should remove all/any benzoic acid present to the feed Benzaldehyde.

Keeping Benzaldehyde feed in inert atmosphere (oxygen free) will definitely diminish the formation of benzoic acid. 

Addition of oxygen scavenger to the feed Benzaldehyde will also help to diminish the formation of benzoic acid.

Thanks,

Ravindra

To my opinion, the most obvious choices for following the conversion are 1H NMR and GC. If you use GC you would need to chose a special column like Nukol-TM (or check the website of Agilent), otherwise the carboxy group will stick on the column giving you problem in detectection of the acid. However, very conveniently, you can derivatize the acid with methylating or silylating agents. I'd suggest the latter like MSTFA, BSTFA etc. in the presence of pyridine, because it will give you full conversion to the trifluoro ester and your aldehyde function is not disturbed. The (silyl) ester can be readily quantified (calibrated) on the most common columns like the CP-Sil family. (Prerequisite for the derivatization that your solvent is non-protic, otherwise you need an extra extraction step). For the recovery of benzaldehyde, distillation (70 C boiling point difference at atmospheric pressure) or extraction seems to be the most feasible option (for example with ether and sodium hydrocarbonate solution).

Hi,

Benzaldehyde is easily oxidized to benzoic acid which can impede its desired reaction and hence it is always recommended to use freshly distilled benzaldehyde.

Simple bicarbonate treatment of benzaldehyde should remove all/any benzoic acid present to the feed Benzaldehyde.

Keeping Benzaldehyde feed in inert atmosphere (oxygen free) will definitely diminish the formation of benzoic acid. 

Addition of oxygen scavenger to the feed Benzaldehyde will also help to diminish the formation of benzoic acid.

Thanks,

Ravindra

Add a small quantity of a antioxidant such as 2,6-ditert-butyl phenol to distilled benzaldehyde.Oxidation to benzoic acid can be avoided.

Paknikar, presently at VerGo pharma, Verna, Goa

Of course, both Dr. Singh and Dr. Paknikar are right. Obviously I have completely misunderstood your main question given in bold letters (you don't want to control but to avoid conversion). Indeed, if you want to keep your benzaldehyde intact, it is best to add a little oxygen or radical scavenger and keep your bottle tight or under an inert gas. Recovery of benzaldehyde from the formed benzoic acid is more expensive than avoiding it as you need to use hydride reagents for this in the laboratory.

hydroquinone, 0.1%

Use an antioxidant. Phenolicws are a good choice