[Tom_Boomer]

Hey everyone,
I am currently conducting a research on the amidation (through acid chloride intermediate) of 4-hydroxyphenylacetic acid. For this I added 4-hydroxyphenylacetic acid into dichloromethane (solvent) together with dimethylformamide (catalyst) before adding thionyl chloride. The attachment contains the TLC (2:1, methanol:n-hexane and alluminium-backed silica plates, visualised with 254nm UV light, acid chloride was first reacted with methanol to form the stable ester) results of the reaction progression as monitored over 30 minutes after the addition of the thionyl chloride. I was wondering what the structures at the 'dot-spot' are as they are quite intense and seem to be extremely polar. I was thinking it would be thionyl chloride or one of its products but was unable to find any literature on it. The same goes for the upper spot, would this be the ester?
Thank you so much for your help in advance!

[Babcock_Hall]

What is the R_f of the starting carboxylic acid in your solvent?  Do I understand correctly that you are using 2:1 methanol/hexane as the TLC solvent?  I was under the impression that methanol and hexane are immiscible. 

[wildfyr]

Thionyl chloride would not visualize on tlc and probably degrades immediately.

You should co-spot your starting material to see how it runs. I think this is straightforward enough though, the product on the baseline is the starting material, the one that runs is the ester.

Honestly though, using an excess of thionyl chloride most acid chlorides quantitatively convert to acid chlorides in a couple hours, I personally do not even track such a reaction by TLC. The act of taking some out and forming the ester with it will cause some hydrolysis due to wet solvents so I just trust the chemistry.

[Tom_Boomer]

Thank you for your response wildfyr! In regards to:

the product on the baseline is the starting material, the one that runs is the ester.

I assumed the same at first, however, I started to wonder as to why at the sample at T0 there would be no dot in that case, even though the starting product dissolves in the DMF. Hence, me wondering what it could be.