Etydhv

I am forming 2,2-dimethoxyacetic acid from its methyl ester, and below is the experimental protocol I am following (from Tetrahedron 2016, 72 (3), 420–430):

2,2-Dimethoxy Acetic Acid Formation

1. Add lithium hydroxide monohydrate ($pu89.5 mmol$, $pu3.75 g$, $pu1.2 equiv$) to a solution of methyl dimethoxyacetate ($pu74.6 mmol$, $pu10 g$, $pu1 equiv$) in dioxane ($pu45 mL$) and water ($pu45 mL$) at $pu0 ^circC$.


2. Stir the mixture for $pu1 h$ at $pu0 ^circC$ and one additional hour at room temperature.


3. Add sodium hydroxide ($pu1M$ aq soln, $pu75 mL$) to the mixture.


4. Extract the mixture with diethyl ether ($pu375 mL$).


5. Acidify the recovered aqueous layer with hydrogen chloride ($pu6N$ aq soln) until a pH of 1-2.


6. Extract the organics with diethyl ether ($pu375 mL$).


7. Dry the combined organic layers with magnesium sulfate and filter.


8. Evaporate the solvent slowly under reduced pressure to obtain 2,2-dimethoxyacetic acid.

I repeated this reaction many times but every time I check the $mathrm^13C$-NMR, I only see a single peak at $delta : pu67.12 ppm$. I believe this corresponds to C-OMe. By theory (and by literature) I should see 3 peaks.
$mathrm^1H$-NMR does show 6:1 ratio of singlets at $delta : pu3.704 ppm$ (6H) and $delta : pu3.458 ppm$ (1H) but it is not well aligned with literature; By theory, a single hydrogen atom adjacent to $ceC=O$ group should be more deshielded than $delta : pu3.458 ppm$ (i.e. be placed at higher ppm). I thought through what I have done and I still can't figure out which step has gone wrong. Any thoughts and ideas? Would appreciate any advice.

If your reaction has worked and you get the expected product, you should see following NMR data as the sought literature reported:

$mathrm^1H$-NMR: $delta$ 3.44 (s, $ce6H$), 4.85 (s, $ce1H$), and 10.32 (broad s, $ce1H$).

$mathrm^13C$-NMR: $delta$ 54.1 ($ce2CH3$), 98.6 ($ceCH$), and 170.7 ($ceC_q$).

Instead, you got two peaks, $delta$ 3.704 (s, $ce6H$) and $delta$ 3.458 (s, $ce1H$), in your $mathrm^1H$-NMR. And, you got only one peak at $delta$ 67.12 in your $mathrm^13C$-NMR. All this data telling me is your reaction has not worked as expected. What you have is 1,4-dioxane during the ether extract, $mathrm^1H$-NMR of which gives only a singlet at $delta$ 3.71 when $ceCDCl3$ is the solvent. It also gives one peak at $delta$ 67.14 in $mathrm^13C$-NMR under same solvent (Ref.1).

I believe your compound may still be in the aqueous phase. You may need to saturate the aqueous phase with salt ($ceNaCl$) before extract the product to organic phase. Note that acetic acid is very soluble in water. Therefore, I expect 2,2-dimethoxyacetic acid to be highly soluble in water as well (a $ceC4(H2O)4$ compound like a monosaccharide).

References:

1. H. E. Gottlieb, V. Kotlyar, A. Nudelman, “NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities,” J. Org. Chem. 1997, 62(21), 7512–7515 (DOI: 10.1021/jo971176v).

The answer from @Mathew Mahindaratne in my opinion correctly identifies what the OP has isolated. It remains to suggest how to get the required product. It may be a matter of salting out the aq phase, but there are other possibilities. Some observers may feel that given a literature prep from a respected group there is no need to alter it, however the OP has not been able to replicate it. Accordingly I offer this procedure.

Dissolve the methyl dimethoxy acetate in a mixture of 9:1 THF/water at rt. Add 1.1eq of LiOH monohydrate. Leave to stir at rt overnight. Concentrate under reduced pressure. Dissolve the residue in a minimum amount of water, cool in ice bath. Wash with Et2O. Acidify using a slight excess of 2N HCl (pH really doesn't need to go below 3.0 as pKa of product is probably around 3.7). Extract x3 with Et2O. Dry the combined organic extract, filter and concentrate. This should minimise any change of hydrolysing the acetal.