On market you can find commercial reagents as HCl•MeOH, just add 2 or 3 equivalents and should be work in a few seconds, usually if you run your reaction in a organic solvent as MeOH the hydrochloride should be precipitated immediately.

Dry hydrogen chloride bubbled through a methanol solution of the amino acid will work.... success depending on the amino acid in question. Not a nice reaction procedure either but better than thionyl chloride.

Just a suggestion you can generate HCl adding slowly drops of H2SO4 to NaCl and then you can bubble the gas using a tube and pipette to your flask.

You could also generate methanolic HCl by carefully adding Acetylchlorid to MeOH. This generates HCl and MeOAc as "sideproduct". You could than add your aminoacid and as Amador stated, your hydrochloride of the ester could precipitate.

I agree with Daniel, I used the same method and it workes perfectly. Just be careful when you add acetyl chloride to MeOH (do it while cooling on ice bath). I used acetyl chloride 10% V/V. The product is then obtained by evaporation on which side product MeOAc is removed.

Both the above methods are widely used based on the scale of reaction and manufacturability. Thionyl chloride reactions could be carried out at lower temperatures first adding 1.5 mole equivalents of thionyl chloride into methanol at 0 -5°C controlling the exotherm. after that put your amino acid in one lot and stir till completion of your reaction at ambient temperature. whereas methanolic HCl (~20%) can be used at reflux temperature till completion of reaction. But my personal experience about this method is that it proceeds with difficulty at the end and unconverted amino acid remained as contaminant.

Note: if you are using chirally pure amino acid please check for any racemisation in either methods due to application of heat and strong acidic environment.

Efficient syntheses of acid methyl ester hydrochlorides were performed with two equivalents of TMSCl. However, for substrates having two carboxyl groups, so four equivalents of TMSCl were used in the esterifications of these substrates. This including natural amino acids, aromatic amino acids and aliphatic amino acids was transformed to corresponding amino acid methyl ester hydrochlorides in good to excellent yields. Compared with other methods, the yields obtained with the TMSCl/MeOH system were in most cases comparable to or even higher than those obtained with the thionyl chloride/MeOH and HCl/MeOH systems.

The best results obtained with the other methods, were the temperature of the thionyl chloride/MeOH system should be strictly maintained between –5~0 °C and with HCl/MeOH gas must be continuously passed through the refluxing mixture in the MeOH/HCl method.

General procedure for the preparation of amino acid methyl ester hydrochlorides

Amino acid (0.1mol) was taken in a round bottom flask. Freshly distilled chlorotrimethylsilane (0.2mol) was added slowly and stirred with a magnetic stirrer. Then methanol (100 mL) was added and the resulting solution or suspension was stirred at room temperature. After the completion of reaction (as monitored by TLC), the reaction mixture was concentrated on a rotary evaporator to give the product amino acid ester hydrochloride.

I belive that you will have problems with thionyl chloride, as the resulting aminoacid chloride will collapse into the diketopiperazine product (i.e. aminoacid cyclic dimer). Dissolving the aminoacid in MeOH and stiring it under a stream of dry HCl would be the best choice. If the reaction does not go to completion, you could add some 2,2-dimethoxypropane to the mixture (acetone dimethy ketal). The MeOH-dry HCl reagent should also work. Good luck!

Efficient syntheses of acid methyl ester hydrochlorides were performed with two equivalents of TMSCl.

The best results obtained with the other methods, were the temperature of the thionyl chloride/MeOH system should be strictly maintained between –5~0 °C and with HCl/MeOH gas must be continuously passed through the refluxing mixture in the MeOH/HCl method.

General procedure for the preparation of amino acid methyl ester hydrochlorides

Amino acid (0.1mol) was taken in a round bottom flask. Freshly distilled chlorotrimethylsilane (0.2mol) was added slowly and stirred with a magnetic stirrer. Then methanol (100 mL) was added and the resulting solution or suspension was stirred at room temperature. After the completion of reaction (as monitored by TLC), the reaction mixture was concentrated on a rotary evaporator to give the product amino acid ester hydrochloride.

we generally prepare EA.HCl by dissolving HCl gas in EA and then treat our compounds with that, if you want to prepare EA.HCl then add sulfuric acid drop wise to the NaCl powder, there are some solvent commercially available also like dioxane.HCl, MeOH.HCl

hi

you can read these articles

https://www.researchgate.net/publication/47644372_Synthesis_of_ethyl_ferulate_in_organic_medium_using_Celite-immobilized_lipase

https://www.researchgate.net/publication/298208671_Immobilization_of_a_novel_cold_active_esterase_onto_Fe3O4cellulose_nano-composite_enhances_catalytic_properties

https://www.researchgate.net/publication/257908646_Effective_immobilisation_of_lipase_to_enhance_esterification_potential_and_reusability

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