## 3 Results and Discussion
### Screening of Reaction Conditions  
We tested different bases to carry out the selective formation of benzylic lactates, without involving the hydroxyl fraction. The racemic lactate reacted with three benzyl halides (benzyl bromide **1a**, 2-nitrobenzyl chloride **2a** and 2,4-dinitrobenzyl chloride **3a**) to obtain a pair of enantiomers of the benzyl lactate esters.  
Below, we report the synthesis of two new LA derivatives (2-nitrobenzyl 2-hydroxypro panoate and 2,4-dinitrobenzyl 2-hydroxypropanoate) and benzyl 2-hydroxypropanoate (**1b**-**3b**) (Figure 2 and Table 1).  
In the first instance, racemic lactic acid was reacted with DBU (1,8-diazabiciclo[5.4.0]undec-7-ene) as the organic base in toluene (Table 1, entry 1) [22]. After 12 h of reaction at 90 \({}^{\circ}\)C using benzyl bromide **1a** as the benzyl halide, we obtained a 50% yield of the isolated  
Figure 2: Synthesis of benzyl lactate esters **1b**, **2b** and **3b**.  
product (\(\pm\))-**1b**. Later, we tested some inorganic bases (potassium carbonate, potassium hydroxide, sodium hydroxide, sodium methylate), in polar protic and aprotic solvents, at room temperature or at reflux. Except for potassium carbonate in the polar aprotic solvent at reflux (Table 1, entry 2), the remaining inorganic bases did not yield useful results (Table 1, entries 3-6). Then, we tested triethylamine in acetonitrile under reflux (Table 1, entry 7). After 4 h, the reactions yielded lactates **1b**, **2b** and **3b** in good yields (56-89%, entries 7-10, Table 1). At this stage, we considered these reaction conditions to be satisfactory, and then we tested them with a sample of enantiopure lactic acid (Table 1, entry 10). L-lactic acid and **2a** were reacted in the best reaction conditions to yield (\(-\))-**2b** (82%, entry 10, Table 1). The obtained lactate, (\(-\))-**2b**, was found to be enantiopure (HPLC, Figure 3b,d), thus giving us the confidence that the optimized reaction conditions do not cause racemization of these compounds. Lactates **1b**, **2b** and **3b** were isolated and purified to provide a complete characterization. We checked the possibility of extending the validity of the method even to mixtures with a higher water content. The reaction was repeated at 60 \({}^{\circ}\)C in solvent-free conditions by simply mixing L-lactic acid (85% in water), triethylamine and **2a**. The desired product (\(\pm\))-**2b** was obtained after 1 h in 50% yield (Table 1, entry 11). The reaction was, finally, repeated using water as a solvent to simulate the biological environment or a dilute solution of the analyte. In this case, after a 1 h reaction time, product **2b** was obtained in 38% yield (Table 1, entry 12). These crude reaction mixtures were analyzed with HPLC without any purification to set up a method for the fast indirect determination of the enantiopurity of lactic acid.  
Figure 3: Mono-dimensional chromatogram plot of the chiral separation of 2-nitrobenzyl lactate **2b** in DAD mode with Chiralpak IA column and hexane/2-propanol/80/20 as the mobile phase: (**a**) racemic 2-nitrobenzyl lactate; (**b**) chiral 2-nitrobenzyl lactate. Three-dimensional chromatogram plot of the chiral separation of 2-nitrobenzyl lactate **2b** (the different wavelengths are represented by different colors): (**c**) racemic 2-nitrobenzyl lactate; (**d**) chiral 2-nitrobenzyl lactate (also see Figure S13).